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Background: Latent TGFβ binding protein‐2 (LTBP2) is a fibrillin 1 binding component of the microfibril. LTBP2 is the only LTBP protein that does not bind any isoforms of TGFβ, although it may interfere with the function of other LTBPs or interact with other signaling pathways. Results: Here, we investigate mice lacking Ltbp2 (Ltbp2−/−) and identify multiple phenotypes that impact bodyweight and fat mass, and affect bone and skin development. The alterations in skin and bone development are particularly noteworthy since the strength of these tissues is differentially affected by loss of Ltbp2. Interestingly, some tissues that express high levels of Ltbp2, such as the aorta and lung, do not have a developmental or homeostatic phenotype. Conclusions: Analysis of these mice show that LTBP2 has complex effects on development through direct effects on the extracellular matrix (ECM) or on signaling pathways that are known to regulate the ECM. Key Findings: Ltbp2 deficiency results in trabecular bone overgrowthLtbp2 deficiency results in skin alterationsLtbp2 deficiency may impact metabolismLtbp2 deficiency does not result in obvious alterations of lung and aortal tissue [ABSTRACT FROM AUTHOR]

Hutchinson-Gilford progeria syndrome is a premature aging disease caused by LMNA gene mutation and the production of a truncated prelamin A protein "progerin" that elicits cellular and organismal toxicity. Progerin accumulates in the vasculature, being especially detrimental for vascular smooth muscle cells (VSMC). Vessel stiffening and aortic atherosclerosis in HGPS patients are accompanied by VSMC depletion in the medial layer, altered extracellular matrix (ECM), and thickening of the adventitial layer. Mechanisms whereby progerin causes massive VSMC loss and vessel alterations remain poorly understood. Mature VSMC retain phenotypic plasticity and can switch to a synthetic/proliferative phenotype. Here, we show that progerin expression in human and mouse VSMC causes a switch towards the synthetic phenotype. This switch elicits some level of replication stress in normal cells, which is exacerbated in the presence of progerin, leading to telomere fragility, genomic instability, and ultimately VSMC death. Calcitriol prevents replication stress, telomere fragility, and genomic instability, reducing VSMC death. In addition, RNA-seq analysis shows induction of a profibrotic and pro-inflammatory aging–associated secretory phenotype upon progerin expression in human primary VSMC. Our data suggest that phenotypic switch-induced replication stress might be an underlying cause of VSMC loss in progeria, which together with loss of contractile features and gain of profibrotic and pro-inflammatory signatures contribute to vascular stiffness in HGPS. [ABSTRACT FROM AUTHOR]

Sushi, von Willebrand factor type A, EGF and pentraxin domain containing 1 (SVEP1) is an extracellular matrix protein that causally promotes vascular disease and associates with platelet reactivity in humans. Here, using a human genomic and proteomic approach, we identify a high affinity, disease-relevant, and potentially targetable interaction between SVEP1 and the orphan receptor Platelet and Endothelial Aggregation Receptor 1 (PEAR1). This interaction promotes PEAR1 phosphorylation and disease associated AKT/mTOR signaling in vascular cells and platelets. Mice lacking SVEP1 have reduced platelet activation, and exogenous SVEP1 induces PEAR1-dependent activation of platelets. SVEP1 and PEAR1 causally and concordantly relate to platelet phenotypes and cardiovascular disease in humans, as determined by Mendelian Randomization. Targeting this receptor-ligand interaction may be a viable therapeutic strategy to treat or prevent cardiovascular and thrombotic disease. SVEP1 is linked to numerous human diseases, though its disease-promoting mechanism has remained unclear. Here, the authors identify SVEP1 as a ligand for the orphan receptor PEAR1 and provide insight into the role of this interaction in cardiovascular disease. [ABSTRACT FROM AUTHOR]

Sushi, von Willebrand factor type A, EGF and pentraxin domain containing 1 (SVEP1) is an extracellular matrix protein that causally promotes vascular disease and associates with platelet reactivity in humans. Here, using a human genomic and proteomic approach, we identify a high affinity, disease-relevant, and potentially targetable interaction between SVEP1 and the orphan receptor Platelet and Endothelial Aggregation Receptor 1 (PEAR1). This interaction promotes PEAR1 phosphorylation and disease associated AKT/mTOR signaling in vascular cells and platelets. Mice lacking SVEP1 have reduced platelet activation, and exogenous SVEP1 induces PEAR1-dependent activation of platelets. SVEP1 and PEAR1 causally and concordantly relate to platelet phenotypes and cardiovascular disease in humans, as determined by Mendelian Randomization. Targeting this receptor-ligand interaction may be a viable therapeutic strategy to treat or prevent cardiovascular and thrombotic disease. SVEP1 is linked to numerous human diseases, though its disease-promoting mechanism has remained unclear. Here, the authors identify SVEP1 as a ligand for the orphan receptor PEAR1 and provide insight into the role of this interaction in cardiovascular disease. [ABSTRACT FROM AUTHOR]

Elastin (ELN) insufficiency leads to the cardiovascular hallmarks of the contiguous gene deletion disorder, Williams--Beuren syndrome, including hypertension and vascular stiffness. Previous studies showed that Williams--Beuren syndrome deletions, which extended to include the NCF1 gene, were associated with lower blood pressure (BP) and reduced vascular stiffness. NCF1 encodes for p47phox, the regulatory component of the NOX1 NADPH oxidase complex that generates reactive oxygen species (ROS) in the vascular wall. Dihydroethidium and 8-hydroxyguanosine staining of mouse aortas confirmed that Eln heterozygotes (Eln+/-) had greater ROS levels than the wild-types (Eln+/+), a finding that was negated in vessels cultured without hemodynamic stressors. To analyze the Nox effect on ELN insufficiency, we used both genetic and chemical manipulations. Both Ncf1 haploinsufficiency (Ncf1+/-) and Nox1 insufficiency (Nox1-/y) decreased oxidative stress and systolic BP in Eln+/- without modifying vascular structure. Chronic treatment with apocynin, a p47phox inhibitor, lowered systolic BP in Eln+/-, but had no impact on Elnþ/þ controls. In vivo dosing with phenylephrine (PE) produced an augmented BP response in Eln+/- relative to Elnþ/þ, and genetic modifications or drug-based interventions that lower Nox1 expression reduced the hypercontractile response to PE in Eln+/- mice to Elnþ/þ levels. These results indicate that the mechanical and structural differences caused by ELN insufficiency leading to oscillatory flow can perpetuate oxidative stress conditions, which are linked to hypertension, and that by lowering the Nox1-mediated capacity for vascular ROS production, BP differences can be normalized. [ABSTRACT FROM AUTHOR]

Probing plaque pathogenesis: Genetic variants linked to cardiometabolic disease can help identify targets for therapies. An SVEP1 mutation had previously been associated with coronary artery disease, and here, Jung et al. studied the role of this extracellular matrix protein in atherosclerosis. SVEP1 was expressed by vascular smooth muscle cells in human tissue samples from patients with atherosclerosis and was up-regulated in a mouse model of atherosclerosis. SVEP1 induced proliferation and differentiation of smooth muscle cells and promoted inflammation in plaques. Results suggest that targeting SVEP1 could protect against atherosclerosis. A low-frequency variant of sushi, von Willebrand factor type A, EGF, and pentraxin domain-containing protein 1 (SVEP1), an extracellular matrix protein, is associated with risk of coronary disease in humans independent of plasma lipids. Despite a robust statistical association, if and how SVEP1 might contribute to atherosclerosis remained unclear. Here, using Mendelian randomization and complementary mouse models, we provide evidence that SVEP1 promotes atherosclerosis in humans and mice and is expressed by vascular smooth muscle cells (VSMCs) within the atherosclerotic plaque. VSMCs also interact with SVEP1, causing proliferation and dysregulation of key differentiation pathways, including integrin and Notch signaling. Fibroblast growth factor receptor transcription increases in VSMCs interacting with SVEP1 and is further increased by the coronary disease–associated SVEP1 variant p.D2702G. These effects ultimately drive inflammation and promote atherosclerosis. Together, our results suggest that VSMC-derived SVEP1 is a proatherogenic factor and support the concept that pharmacological inhibition of SVEP1 should protect against atherosclerosis in humans. [ABSTRACT FROM AUTHOR]

Elastin is a primary structural protein in the arterial wall that contributes to vascular mechanical properties and degrades with aging. Aging is associated with arterial stiffening and an increase in blood pressure. There is evidence that arterial aging follows different timelines with sex. Our objective was to investigate how elastin content affects arterial remodeling in male and female mice with aging. We used male and female wild-type (Eln+/+) and elastin heterozygous (Eln+/-) mice at 6, 12, and 24 mo of age and measured their blood pressure and arterial morphology, wall structure, protein content, circumferential stress, stretch ratio, and stiffness. Two arteries were used with varying contents of elastin: the left common carotid and ascending aorta. We show that Eln+/- arteries start at a different homeostatic set point for circumferential wall stress, stretch, and material stiffness but show similar increases with aging to Eln+/+ mice. With aging, structural stiffness is greatly increased, while material stiffness and circumferential stress are only slightly increased, highlighting the importance of maintaining these homeostatic values. Circumferential stretch shows the smallest change with age and may be important for controlling cellular phenotype. Independent sex differences are mostly associated with males being larger than females; however, many of the measured factors show age × sex and/or genotype × sex interactions, indicating that males and females follow different cardiovascular remodeling timelines with aging and are differentially affected by reduced elastin content. [ABSTRACT FROM AUTHOR]

Deposition of elastin and collagen in the aorta correlates with increases in blood pressure and flow during development, suggesting that the aorta adjusts its mechanical properties in response to hemodynamic stresses. Elastin knockout (Eln−/−) mice have high blood pressure and pathological remodeling of the aorta and die soon after birth. We hypothesized that decreasing blood pressure in Eln−/− mice during development may reduce hemodynamic stresses and alleviate pathological remodeling of the aorta. We treated Eln+/+ and Eln−/− mice with the anti-hypertensive medication captopril throughout embryonic development and then evaluated left ventricular (LV) pressure and aortic remodeling at birth. We found that captopril treatment decreased Eln−/− LV pressure to values near Eln+/+ mice and alleviated the wall thickening and changes in mechanical behavior observed in untreated Eln−/− aorta. The changes in thickness and mechanical behavior in captopril-treated Eln−/− aorta were not due to alterations in measured elastin or collagen amounts, but may have been caused by alterations in smooth muscle cell (SMC) properties. We used a constitutive model to understand how changes in stress contributions of each wall component could explain the observed changes in composite mechanical behavior. Our modeling results show that alterations in the collagen natural configuration and SMC properties in the absence of elastin may explain untreated Eln−/− aortic behavior and that partial rescue of the SMC properties may account for captopril-treated Eln−/− aortic behavior. [ABSTRACT FROM AUTHOR]

Key points: We report that a sodium‐activated potassium current, IKNa, has been inadvertently overlooked in both conduit and resistance arterial smooth muscle cells.IKNa is a major K+ resting conductance and is absent in cells of IKNa knockout (KO) mice.The phenotype of the IKNa KO is mild hypertension, although KO mice react more strongly than wild‐type with raised blood pressure when challenged with vasoconstrictive agents.IKNa is negatively regulated by angiotensin II acting through Gαq protein‐coupled receptors.In current clamp, KO arterial smooth muscle cells have easily evoked Ca2+‐dependent action potentials. Although several potassium currents have been reported to play a role in arterial smooth muscle (ASM), we find that one of the largest contributors to membrane conductance in both conduit and resistance ASMs has been inadvertently overlooked. In the present study, we show that IKNa, a sodium‐activated potassium current, contributes a major portion of macroscopic outward current in a critical physiological voltage range that determines intrinsic cell excitability; IKNa is the largest contributor to ASM cell resting conductance. A genetic knockout (KO) mouse strain lacking KNa channels (KCNT1 and KCNT2) shows only a modest hypertensive phenotype. However, acute administration of vasoconstrictive agents such as angiotensin II (Ang II) and phenylephrine results in an abnormally large increase in blood pressure in the KO animals. In wild‐type animals Ang II acting through Gαq protein‐coupled receptors down‐regulates IKNa, which increases the excitability of the ASMs. The complete genetic removal of IKNa in KO mice makes the mutant animal more vulnerable to vasoconstrictive agents, thus producing a paroxysmal‐hypertensive phenotype. This may result from the lowering of cell resting K+ conductance allowing the cells to depolarize more readily to a variety of excitable stimuli. Thus, the sodium‐activated potassium current may serve to moderate blood pressure in instances of heightened stress. IKNa may represent a new therapeutic target for hypertension and stroke. Key points: We report that a sodium‐activated potassium current, IKNa, has been inadvertently overlooked in both conduit and resistance arterial smooth muscle cells.IKNa is a major K+ resting conductance and is absent in cells of IKNa knockout (KO) mice.The phenotype of the IKNa KO is mild hypertension, although KO mice react more strongly than wild‐type with raised blood pressure when challenged with vasoconstrictive agents.IKNa is negatively regulated by angiotensin II acting through Gαq protein‐coupled receptors.In current clamp, KO arterial smooth muscle cells have easily evoked Ca2+‐dependent action potentials. [ABSTRACT FROM AUTHOR]

Alveologenesis, the final step of lung development, is characterized by the formation of millions of alveolar septa that constitute the vast gas-exchange surface area. The genetic network driving alveologenesis is poorly understood compared with earlier steps in lung development. FGF signaling through receptors Fgfr3 and Fgfr4 is crucial for alveologenesis, but the mechanisms through which they mediate this process remain unclear. Here we show that in Fgfr3; Fgfr4 (Fgfr3;4) global mutant mice, alveolar simplification is first observed at the onset of alveologenesis at postnatal day 3. This is preceded by disorganization of elastin, indicating defects in the extracellular matrix (ECM). Although Fgfr3 and Fgfr4 are expressed in the mesenchyme and epithelium, inactivation in the mesenchyme, but not the epithelium, recapitulated the defects. Expression analysis of components of the elastogenesis machinery revealed that Mfap5 (also known as Magp2), which encodes an elastin-microfibril bridging factor, is upregulated in Fgfr3;4 mutants. Mfap5 mutation in the Fgfr3;4 mutant background partially attenuated the alveologenesis defects. These data demonstrate that, during normal lung maturation, FGF signaling restricts expression of the elastogenic machinery in the lung mesenchyme to control orderly formation of the elastin ECM, thereby driving alveolar septa formation to increase the gasexchange surface. [ABSTRACT FROM AUTHOR]

Mutations in lysyl oxidase (LOX) are associated with thoracic aortic aneurysm and dissection (TAAD). Mice that do not express Lox (Lox-/-) die soon after birth and have 60% and 40% reductions in elastin- and collagen-specific cross-links, respectively. LOX inactivation could also change the expression of secreted factors, the structural matrix, and matrixassociated proteins that constitute the aortic matrisome. We hypothesized that absence of Lox will change the mechanical behavior of the aortic wall because of reduced elastin and collagen cross-linking and alter the expression levels of matrisome and smooth muscle cell (SMC) genes in a vascular location-specific manner. Using fluorescence microscopy, pressure myography, and gene set enrichment analysis, we visualized the microarchitecture, quantified the mechanical behavior, and examined matrisome and SMC gene expression from ascending aortas (AAs) and descending aortas (DAs) from newborn Lox-/-) and Lox-/-) mice. Even though Lox-/-) AAs and DAs have fragmented elastic laminae and disorganized SMCs, the unloaded outer diameter and wall thickness were similar to Lox-/-) AAs and DAs. Lox-/-) AAs and DAs have altered opening angles, circumferential stresses, and circumferential stretch ratios; however, only Lox-/-) AAs have increased pressurized diameters and tangent moduli. Gene set enrichment analysis showed upregulation of the extracellular matrix (ECM) regulator gene set in Lox-/-) AAs and DAs as well as differential expression of secreted factors, collagens, ECM-affiliated proteins, ECM glycoproteins, and SMC cell cycle gene sets that depend on the Lox genotype and vascular location. These results provide insights into the local chemomechanical changes induced by Lox inactivation that may be important for TAAD pathogenesis. NEW & NOTEWORTHY Absence of lysyl oxidase (Lox) causes thoracic aortic aneurysms. The aortic mechanical behavior of Lox-/-) mice is consistent with reduced elastin and collagen cross-linking but demonstrates vascular location-specific differences. Lox-/-) aortas show upregulation of matrix remodeling genes and location-specific differential expression of other matrix and smooth muscle cell gene sets. [ABSTRACT FROM AUTHOR]

Mutations in lysyl oxidase (LOX) are associated with thoracic aortic aneurysm and dissection (TAAD). Mice that do not express Lox (Lox-/-) die soon after birth and have 60% and 40% reductions in elastin- and collagen-specific cross-links, respectively. LOX inactivation could also change the expression of secreted factors, the structural matrix, and matrixassociated proteins that constitute the aortic matrisome. We hypothesized that absence of Lox will change the mechanical behavior of the aortic wall because of reduced elastin and collagen cross-linking and alter the expression levels of matrisome and smooth muscle cell (SMC) genes in a vascular location-specific manner. Using fluorescence microscopy, pressure myography, and gene set enrichment analysis, we visualized the microarchitecture, quantified the mechanical behavior, and examined matrisome and SMC gene expression from ascending aortas (AAs) and descending aortas (DAs) from newborn Lox+/+ and Lox-/- mice. Even though Lox-/- AAs and DAs have fragmented elastic laminae and disorganized SMCs, the unloaded outer diameter and wall thickness were similar to Lox+/+ AAs and DAs. Lox-/- AAs and DAs have altered opening angles, circumferential stresses, and circumferential stretch ratios; however, only Lox-/- AAs have increased pressurized diameters and tangent moduli. Gene set enrichment analysis showed upregulation of the extracellular matrix (ECM) regulator gene set in Lox-/- AAs and DAs as well as differential expression of secreted factors, collagens, ECM-affiliated proteins, ECM glycoproteins, and SMC cell cycle gene sets that depend on the Lox genotype and vascular location. These results provide insights into the local chemomechanical changes induced by Lox inactivation that may be important for TAAD pathogenesis. [ABSTRACT FROM AUTHOR]

Aortic valve disease (AVD) is a common condition with a progressive natural history, and presently, there are no pharmacologic treatment strategies. Elastic fiber fragmentation (EFF) is a hallmark of AVD, and increasing evidence implicates developmental elastic fiber assembly defects. Emilin1 is a glycoprotein necessary for elastic fiber assembly that is present in both developing and mature human and mouse aortic valves. The Emilin1-deficient mouse (Emilin1 -/- ) is a model of latent AVD, characterized by activated TGFb/MEK/p-Erk signaling and upregulated elastase activity. Emilin1 -/- aortic valves demonstrate early EFF and aberrant angiogenesis followed by late neovascularization and fibrosis. The objective of this study was to test the effectiveness of three different targeted therapies. Aged (12-14 months) Emilin1 -/- mice were treated with refametinib (RDEA-119, MEK1/2 inhibitor), doxycycline (elastase inhibitor), or G6-31 (anti-VEGF-A mouse antibody) for 4 weeks. Refametinib- and doxycycline-treated Emilin1 -/- mice markedly reduced MEK/p-Erk activation in valve tissue. Furthermore, both refametinib and doxycycline attenuated elastolytic cathepsin K, L, MMP-2, and MMP-9 activation, and abrogated macrophage and neutrophil infiltration in Emilin1 -/- aortic valves. RNAseq analysis was performed in aortic valve tissue from adult (4 months) and aged (14 months) Emilin1 -/- and age-matched wild-type control mice, and demonstrated upregulation of genes associated with MAPK/MEK/p-Erk signaling and elastases at the adult stage and inflammatory pathways at the aged stage controlling for age. These results suggest that Erk1/2 signaling is an important modulator of early elastase activation, and pharmacological inhibition using refametinib may be a promising treatment to halt AVD progression [ABSTRACT FROM AUTHOR]

Correction to: I Nature Communications i https://doi.org/10.1038/s41467-023-36486-0, published online 15 February 2023 In this article the author name Arturo Alisio was incorrectly written as Arturo Aliso. The original article can be found online at https://doi.org/10.1038/s41467-023-36486-0. [Extracted from the article]

Thoracic aortic aneurysms and dissections (TAAD) represent a substantial cause of morbidity and mortality worldwide. Many individuals presenting with an inherited form of TAAD do not have causal mutations in the set of genes known to underlie disease. Using whole-genome sequencing in two first cousins with TAAD, we identified a missense mutation in the lysyl oxidase (LOX) gene (c.893T > G encoding p.Met298Arg) that cosegregated with disease in the family. Using clustered regularly interspaced short palindromic repeats (CRISPR)/clustered regularly interspaced short palindromic repeats-associated protein-9 nuclease (Cas9) genome engineering tools, we introduced the human mutation into the homologous position in the mouse genome, creating mice that were heterozygous and homozygous for the human allele. Mutant mice that were heterozygous for the human allele displayed disorganized ultrastructural properties of the aortic wall characterized by fragmented elastic lamellae, whereas mice homozygous for the human allele died shortly after parturition from ascending aortic aneurysm and spontaneous hemorrhage. These data suggest that a missense mutation in LOX is associated with aortic disease in humans, likely through insufficient cross-linking of elastin and collagen in the aortic wall. Mutation carriers may be predisposed to vascular diseases because of weakened vessel walls under stress conditions. LOX sequencing for clinical TAAD may identify additional mutation carriers in the future. Additional studies using our mouse model of LOX-associated TAAD have the potential to clarify the mechanism of disease and identify novel therapeutics specific to this genetic cause. [ABSTRACT FROM AUTHOR]

Alport syndrome is a familial kidney disease caused by defects in the collagen type IV network of the glomerular basement membrane. Lack of collagen-α3α4α5(IV) changes the glomerular basement membrane morphologically and functionally, rendering it leaky to albumin and other plasma proteins. Filtered albumin has been suggested to be a cause of the glomerular and tubular injuries observed at advanced stages of Alport syndrome. To directly investigate the role that albumin plays in the progression of disease in Alport syndrome, we generated albumin knockout (Alb−/−) mice to use as a tool for removing albuminuria as a component of kidney disease. Mice lacking albumin were healthy and indistinguishable from control littermates, although they developed hypertriglyceridemia. Dyslipidemia was observed in Alb+/− mice, which displayed half the normal plasma albumin concentration. Alb mutant mice were bred to collagen-α3(IV) knockout (Col4a3−/−) mice, which are a model for human Alport syndrome. Lack of circulating and filtered albumin in Col4a3−/−;Alb−/− mice resulted in dramatically improved kidney disease outcomes, as these mice lived 64% longer than did Col4a3−/−;Alb+/+ and Col4a3−/−;Alb+/− mice, despite similar blood pressures and serum triglyceride levels. Further investigations showed that the absence of albumin correlated with reduced transforming growth factor-β1 signaling as well as reduced tubulointerstitial, glomerular, and podocyte pathology. We conclude that filtered albumin is injurious to kidney cells in Alport syndrome and perhaps in other proteinuric kidney diseases, including diabetic nephropathy. [ABSTRACT FROM AUTHOR]

Marrow adipose tissue (MAT) is an endocrine organ with the potential to influence skeletal remodeling and hematopoiesis. Pathologic MAT expansion has been studied in the context of severe metabolic challenge, including caloric restriction, high fat diet feeding, and leptin deficiency. However, the rapid change in peripheral fat and glucose metabolism associated with these models impedes our ability to examine which metabolic parameters precede or coincide with MAT expansion. Microfibril-associated glycoprotein- 1 (MAGP1) is a matricellular protein that influences cellular processes by tethering signaling molecules to extracellular matrix structures. MAGP1-deficient (Mfap2-/-) mice display a progressive excess adiposity phenotype, which precedes insulin resistance and occurs without changes in caloric intake or ambulation. Mfap2-/- mice were, therefore, used as a model to associate parameters of metabolic disease, bone remodeling, and hematopoiesis with MAT expansion. Marrow adiposity was normal in Mfap2-/- mice until 6 months of age; however, by 10 months, marrow fat volume had increased fivefold relative to wild-type control at the same age. Increased gonadal fat pad mass and hyperglycemia were detectable in Mfap2-/- mice by 2 months, but peaked by 6 months. The development of insulin resistance coincided with MAT expansion. Longitudinal characterization of bone mass demonstrated a disconnection in MAT volume and bone volume. Specifically, Mfap2-/- mice had reduced trabecular bone volume by 2 months, but this phenotype did not progress with age or MAT expansion. Interestingly, MAT expansion in the 10-month-old Mfap2-/- mice was associated with modest alterations in basal hematopoiesis, including a shift from granulopoiesis to B lymphopoiesis. Together, these findings indicate MAT expansion is coincident with insulin resistance, but not excess peripheral adiposity or hyperglycemia in Mfap2-/- mice; and substantial MAT accumulation does not necessitate a proportional decrease in either bone mass or bone marrow cellularity. [ABSTRACT FROM AUTHOR]

Increased arterial stiffness is a common characteristic of humans with Williams-Beuren syndrome and mouse models of elastin insufficiency. Arterial stiffness is associated with multiple negative cardiovascular outcomes, including myocardial infarction, stroke, and sudden death. Therefore, identifying therapeutic interventions that improve arterial stiffness in response to changes in elastin levels is of vital importance. The goal of this study was to determine the effect of chronic pharmacologic therapy with different classes of antihypertensive medications on arterial stiffness in elastin insufficiency. Elastin-insufficient mice 4-6 wk of age and wild-type littermates were subcutaneously implanted with osmotic micropumps delivering a continuous dose of one of the following: vehicle, losartan, nicardipine, or propranolol for 8 wk. At the end of treatment period, arterial blood pressure and large artery compliance and remodeling were assessed. Our results show that losartan and nicardipine treatment lowered blood pressure and pulse pressure in elastin-insufficient mice. Elastin and collagen content of abdominal aortas as well as ascending aorta and carotid artery biomechanics were not affected by any of the drug treatments in either genotype. By reducing pulse pressure and shifting the working pressure range of an artery to a more compliant region of the pressurediameter curve, antihypertensive medications may mitigate the consequences of arterial stiffness, an effect that is drug class independent. These data emphasize the importance of early recognition and longterm management of hypertension in Williams-Beuren syndrome and elastin insufficiency. [ABSTRACT FROM AUTHOR]

Key points Increased large artery stiffness is a hallmark of arterial dysfunction with advancing age and is also present in other disease conditions such as diabetes. Increased large artery stiffness is correlated with resistance artery dysfunction in humans., Using a mouse model of altered arterial elastin content, this is the first study to examine the cause-and-effect relationship between large artery stiffness and peripheral resistance artery function., Our results indicate that mice with genetically greater large artery stiffness have impaired cerebral artery endothelial function, but generally preserved skeletal muscle feed artery endothelial function. The mechanisms for impaired cerebral artery endothelial function are reduced nitric oxide bioavailability and increased oxidative stress., These findings suggest that interventions that target large artery stiffness may be important to reduce disease risk associated with cerebral artery dysfunction in conditions such as advancing age., Abstract Advancing age as well as diseases such as diabetes are characterized by both increased large artery stiffness and impaired peripheral artery function. It has been hypothesized that greater large artery stiffness causes peripheral artery dysfunction; however, a cause-and-effect relationship has not previously been established. We used elastin heterozygote mice ( Eln+/-) as a model of increased large artery stiffness without co-morbidities unrelated to the large artery properties. Aortic stiffness, measured by pulse wave velocity, was ∼35% greater in Eln+/- mice than in wild-type ( Eln+/+) mice ( P = 0.04). Endothelium-dependent dilatation (EDD), assessed by the maximal dilatation to acetylcholine, was ∼40% lower in Eln+/- than Eln+/+ mice in the middle cerebral artery (MCA, P < 0.001), but was similar between groups in the gastrocnemius feed arteries (GFA, P = 0.79). In the MCA, EDD did not differ between groups after incubation with the nitric oxide (NO) synthase inhibitor Nω-nitro- l-arginine methyl ester ( P > 0.05), indicating that lower NO bioavailability contributed to the impaired EDD in Eln+/- mice. Superoxide production and content of the oxidative stress marker nitrotyrosine was higher in MCAs from Eln+/− compared with Eln+/+ mice ( P < 0.05). In the MCA, after incubation with the superoxide scavenger TEMPOL, maximal EDD improved by ∼65% in Eln+/- ( P = 0.002), but was unchanged in Eln+/+ mice ( P = 0.17). These results indicate that greater large artery stiffness has a more profound effect on endothelial function in cerebral arteries compared with skeletal muscle feed arteries. Greater large artery stiffness can cause cerebral artery endothelial dysfunction by reducing NO bioavailability and increasing oxidative stress. [ABSTRACT FROM AUTHOR]

Microfibril-associated glycoprotein 1 (MAGP1) is a component of extracellular matrix microfibrils. Here we show that MAGP1 expression is significantly altered in obese humans, and inactivation of the MAGP1 gene (Mfap2-/-) in mice results in adipocyte hypertrophy and predisposition to metabolic dysfunction. Impaired thermoregulation was evident in Mfap2-/- mice prior to changes in adiposity, suggesting a causative role for MAGP1 in the increased adiposity and predisposition to diabetes. By 5 weeks of age, Mfap2-/- mice were maladaptive to cold challenge, uncoupling protein-1 expression was attenuated in the brown adipose tissue, and there was reduced browning of the subcutaneous white adipose tissue. Levels of transforming growth factor-b (TGF-β) activity were elevated in Mfap2-/- adipose tissue, and the treatment of Mfap2-/- mice with a TGF-β–neutralizing antibody improved their body temperature and prevented the increased adiposity phenotype. Together, these findings indicate that the regulation of TGF-β by MAGP1 is protective against the effects of metabolic stress, and its absence predisposes individuals to metabolic dysfunction. [ABSTRACT FROM AUTHOR]

Elastin (Eln) insufficiency in mice and humans is associated with hypertension and altered structure and mechanical properties of large arteries. However, it is not known to what extent functional or structural changes in resistance arteries contribute to the elevated blood pressure that is characteristic of Eln insufficiency. Here, we investigated how Eln insufficiency affects the structure and function of the resistance vasculature. A functional profile of resistance vasculature in Eln+/- mice was generated by assessing small mesenteric artery (MA) contractile and vasodilatory responses to vasoactive agents. We found that Eln haploinsufficiency had a modest effect on phenylephrine-induced vasoconstriction, whereas ANG II-evoked vasoconstriction was markedly increased. Blockade of ANG II type 2 receptors with PD-123319 or modulation of Rho kinase activity with the inhibitor Y-27632 attenuated the augmented vasoconstriction, whereas acute Y-27632 administration normalized blood pressure in Eln+/- mice. Sodium nitroprusside- and isoproterenol-induced vasodilatation were normal, whereas ACh-induced vasodilatation was severely impaired in Eln+/- MAs. Histologically, the number of smooth muscle layers did not change in Eln+/- MAs; however, an additional discontinuous layer of Eln appeared between the smooth muscle layers that was absent in wild-type arteries. We conclude that high blood pressure arising from Eln insufficiency is due partly to permanent changes in vascular tone as a result of increased sensitivity of the resistance vasculature to circulating ANG II and to impaired vasodilatory mechanisms arising from endothelial dysfunction characterized by impaired endotheliumdependent vasodilatation. Eln insufficiency causes augmented ANG II-induced vasoconstriction in part through a novel mechanism that facilitates contraction evoked by ANG II type 2 receptors and altered G protein signaling. [ABSTRACT FROM AUTHOR]

Osteoclastic bone resorption depends upon the cell's ability to organize its cytoskeleton via the αvβ3 integrin and osteoclastogenic cytokines. Because paxillin associates with αvβ3, we asked if it participates in skeletal degradation. Unlike deletion of other αvβ3-associated cytoskeleton-regulating molecules, which impairs the cell's ability to spread, paxillin-deficient (Pax−/−) osteoclasts, generated from embryonic stem cells, 'superspread' in response to receptor activator of NF-κB ligand (RANKL) and form large, albeit dynamically atypical, actin bands. Despite their increased size, Pax−/− osteoclasts resorb bone poorly, excavating pits approximately one-third normal depth. Ligand-occupied αvβ3 or RANKL promotes paxillin serine and tyrosine phosphorylation, the latter via cellular sarcoma (c-Src). The abnormal Pax−/− phenotype is rescued by wild-type (WT) paxillin but not that lacking its LD4 domain. In keeping with the appearance of mutant osteoclasts, WT paxillin, overexpressed in WT cells, contracts the cytoskeleton. Most importantly, the abnormal phenotype of Pax−/− osteoclasts likely represents failed RANKL-mediated delivery of myosin IIA to the actin cytoskeleton via the paxillin LD4 domain but is independent of tyrosine phosphorylation. Thus, in response to RANKL, paxillin associates with myosin IIA to contract the osteoclast cytoskeleton, thereby promoting its bone-degrading capacity. © 2012 American Society for Bone and Mineral Research. [ABSTRACT FROM AUTHOR]

Increased arterial stiffness and blood pressure are characteristic of humans and adult mice with reduced elastin levels caused by aging or genetic disease. Direct associations have been shown between increased arterial stiffness and hypertension in humans, but it is not known whether changes in mechanical properties or increased blood pressure occur first. Using genetically modified mice with elastin haploinsufficiency (Eln+/-), we investigated the temporal relationship between arterial mechanical properties and blood pressure throughout postnatal development. Our results show that some mechanical properties are maintained constant regardless of elastin amounts. The peak diameter compliance for both genotypes occurs near the physiologic pressure at each age, which acts to provide maximum pulse dampening. The stress-strain relationships are similar between genotypes and become nonlinear near the systolic pressure for each age, which serves to limit distension under high pressure. Our results also show that some mechanical properties are affected by reduced elastin levels and that these changes occur before measurable changes in blood pressure. Eln+/- mice have decreased aortic diameter and compliance in ex vivo tests that are significant by postnatal day 7 and increased blood pressure that is not significant until postnatal day 14. This temporal relationship suggests that targeting large arteries to increase diameter or compliance may be an effective treatment for human hypertension. [ABSTRACT FROM AUTHOR]

The article discusses a study on the pathogenesis of autosomal dominant cutis laxa (ADCL) with ELN gene mutations. Exons 28-34 of ELN in five probands showing ADCL characteristics were sequenced leading to the detection of five de novo heterozygous mutations. Some probands presented with progressive aortic root dilatation, bicuspid aortic valves and severe emphysema. All patients had stable mutant messenger RNA (mRNA) based on reverse transcription-polymerase chain reaction (RT-PCR) analysis.

Despite evidence that DAP12 regulates osteoclasts, mice lacking the ITAM-bearing protein exhibit only mild osteopetrosis. Alternatively, Dap12-/- mice, also lacking FcRγ, are severely osteopetrotic, suggesting that FcRγ compensates for DAP12 deficiency in the boneresorbing polykaryons. Controversy exists, however, as to whether these co-stimulatory molecules regulate differentiation of osteoclasts or the capacity of the mature cell to degrade bone. We find that Dap12-/- osteoclasts differentiate normally when generated on osteoblasts but have a dysfunctional cytoskeleton, impairing their ability to transmigrate through the osteoblast layer and resorb bone. To determine whether the FcRγ co-receptor, OSCAR mediates osteoclast function in the absence of DAP12, we overexpressed OSCAR fused to FLAG (OSCAR-FLAG), in Dap12-/- osteoclasts. OSCAR-FLAG partially rescues the abnormal cytoskeleton of Dap12-/- osteoclasts grown on bone, but not those grown on osteoblasts. Thus, cytoskeletal dysfunction, and not arrested differentiation, is the dominant consequence of DAP12 deficiency in osteoclasts. The failure of osteoblasts to normalize Dap12-/- osteoclasts indicates that functionally relevant quantities of OSCAR ligand do not reside in bone-forming cells. [ABSTRACT FROM AUTHOR]

Elastin is an essential component of vertebrate arteries that provides elasticity and stores energy during the cardiac cycle. Elastin production in the arterial wall begins midgestation but increases rapidly during the last third of human and mouse development, just as blood pressure and cardiac output increase sharply. The aim of this study is to characterize the structure, hemodynamics, and mechanics of developing arteries with reduced elastin levels and determine the critical time period where elastin is required in the vertebrate cardiovascular system. Mice that lack elastin (E1n-1-) or have approximately one-half the normal level (E1n-1-) show relatively normal cardiovascular development up to embryonic day (E) 18 as assessed by arterial morphology, left ventricular blood pressure, and cardiac function. Previous work showed that just a few days later, at birth, E1n-1- mice die with high blood pressure and tortuous, stenotic arteries. During this period from E18 to birth, E1n-1- mice add extra layers of smooth muscle cells to the vessel wall and have a mean blood pressure 25% higher than wild-type animals. These findings demonstrate that elastin is only necessary for normal cardiovascular structure and function in mice starting in the last few days of fetal development. The large increases in blood pressure during this period may push hemodynamic forces over a critical threshold where elastin becomes required for cardiovascular function. Understanding the interplay between elastin amounts and hemodynamic forces in developing vessels will help design treatments for human elastinopathies and optimize protocols for tissue engineering. [ABSTRACT FROM AUTHOR]

1. It is known that ATP-sensitive potassium (KATP) channels regulate the membrane potential of smooth muscle cells and vascular tone. Because their activity is altered during ageing, many pharmacological treatments aimed at improving KATP channel and cardiovascular functions have been evaluated. Nicorandil, a KATP channel opener, nitric oxide (NO) donor and anti-oxidant, induces vasodilation, decreases blood pressure and exhibits cardioprotection in ageing, as well as after ischaemia–reperfusion. 2. In the present study, using tension myography and biochemical and histological techniques, we investigated the effects of chronic (2 months) low-dose nicorandil (0.1 mg/kg per day) treatment on the function of rat aorta during ageing (in 4-, 12- and 24-month old rats). 3. The results showed that chronic nicorandil treatment significantly improves mechanical relaxation and noradrenaline-induced vasoconstriction in aged rats. At all ages, the nicorandil-induced vasodilation was primarily mediated by its NO donor group. Nicorandil treatment resulted in an additional 0.5–1 elastic lamella in the aorta and decreased total protein, collagen and elastin content in the aortic wall at all ages. However, in 4-month-old rats, nicorandil significantly increased the elastin : total protein ratio by 19%. 4. In contrast with results of previous studies that used high doses of nicorandil (i.e. 60 mg/kg per day), low-dose nicorandil treatment in the present study did not lead to a progressive desensitization to nicorandil and may be beneficial in improving arterial function in ageing or cardiovascular diseases. [ABSTRACT FROM AUTHOR]

The article focuses on the structural extracellular matrix (ECM) proteins in the vertebrate aortic wall, and the arterial mechanics associated with the vascular system. It examines cardiac and vascular development by correlating the mechanics of the vessel wall structure with physiological blood pressure among animal species. It also discusses mechanical models that can be utilized in designing tissue-engineered vessels with better quality, and in evaluating the efficacy of clinical treatments.

Elastin is a major structural component of large elastic arteries and a principal determinant of arterial biomechanical properties. Elastin loss-of-function mutations in humans have been linked to the autosomal-dominant disease supravalvular aortic stenosis, which is characterized by stenotic lesions in both the systemic and pulmonary circulations. To better understand how elastin insufficiency influences the pulmonary circulation, we evaluated pulmonary cardiovascular physiology in a unique set of transgenic and knockout mice with graded vascular elastin dosage (range 45-120% of wild type). The central pulmonary arteries of elastin-insufficient mice had smaller internal diameters (P < 0.0001), thinner walls (P = 0.002), and increased opening angles (P = 0.002) compared with wild-type controls. Pulmonary circulatory pressures, measured by right ventricular catheterization, were significantly elevated in elastin-insufficient mice (P < 0.000 1) and showed an inverse correlation with elastin level. Although elastin-insufficient animals exhibited mild to moderate right ventricular hypertrophy (P = 0.0001) and intrapulmonary vascular remodeling, the changes were less than expected, given the high right ventricular pressures, and were attenuated compared with those seen in hypoxia-induced models of pulmonary arterial hypertension. The absence of extensive pathological cardiac remodeling at the high pressures in these animals suggests a developmental adaptation designed to maintain right-sided cardiac output in a vascular system with altered elastin content. [ABSTRACT FROM AUTHOR]

Recent studies demonstrate that lysyl oxidase cuproenzymes are critical for zebrafish notochord formation, but the molecular mechanisms of copper-dependent notochord morphogenesis are incompletely understood. We, therefore, conducted a forward genetic screen for zebrafish mutants that exhibit notochord sensitivity to lysyl oxidase inhibition, yielding a mutant with defects in notochord and vascular morphogenesis, puff daddy gw1 ( pfd gw1). Meiotic mapping and cloning reveal that the pfd gw1 phenotype results from disruption of the gene encoding the extracellular matrix protein fibrillin-2, and the spatiotemporal expression of fibrillin-2 is consistent with the pfd gw1 phenotype. Furthermore, each aspect of the pfd gw1 phenotype is recapitulated by morpholino knockdown of fibrillin-2. Taken together, the data reveal a genetic interaction between fibrillin-2 and the lysyl oxidases in notochord formation and demonstrate the importance of fibrillin-2 in specific early developmental processes in zebrafish. Developmental Dynamics 237:2844-2861, 2008. © 2008 Wiley-Liss, Inc. [ABSTRACT FROM AUTHOR]