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Association of hypercholesterolemia and atherosclerotic cardiovascular disease (ASCVD) is well established. Reducing low-density lipoprotein-cholesterol (LDL-C) and raising high-density lipoprotein-cholesterol (HDL-C) have been the therapeutic targets to reduce the risk of ASCVD. Cholesterol-lowering medications have been used to provide both primary and secondary prevention of ASCVD for many years by reducing the absorption and reabsorption, promoting excretion, or decreasing the synthesis of cholesterol. Within the past five years, several new classes of cholesterol-lowering drugs have been tested and approved for patients with hypercholesterolemia that are not well controlled by conventional therapy (ezetimibe, bile-acid sequestrants, and statins). These drugs include proprotein convertase subtilisin/kexin type 9 (PCSK9) antibodies, apolipoprotein A-100 (Apo B-100) antisense, and microsomal triglyceride transfer protein (MTP) inhibitor. Clinical trials revealed that adding PCSK9 antibodies to the preexisting statin therapy can further reduce LDL-C by 60%. ApoB antisense and MTP inhibitor are currently approved for patients with homozygous familial hypercholesterolemia. Several HDL-raising drugs have also been tested, but the results are not promising. Studies suggest that specifically raising reverse cholesterol transport rather than HDL-C level could be a novel therapeutic approach to reduce cardiovascular risk. [ABSTRACT FROM AUTHOR]

Inguinal white adipose tissue (iWAT) is essential for the beneficial effects of exercise training on metabolic health. The underlying mechanisms for these effects are not fully understood, and here, we test the hypothesis that exercise training results in a more favorable iWAT structural phenotype. Using biochemical, imaging, and multi-omics analyses, we find that 11 days of wheel running in male mice causes profound iWAT remodeling including decreased extracellular matrix (ECM) deposition and increased vascularization and innervation. We identify adipose stem cells as one of the main contributors to training-induced ECM remodeling, show that the PRDM16 transcriptional complex is necessary for iWAT remodeling and beiging, and discover neuronal growth regulator 1 (NEGR1) as a link between PRDM16 and neuritogenesis. Moreover, we find that training causes a shift from hypertrophic to insulin-sensitive adipocyte subpopulations. Exercise training leads to remarkable adaptations to iWAT structure and cell-type composition that can confer beneficial changes in tissue metabolism. [Display omitted] • Exercise training decreases ECM and increases vascularization and innervation in iWAT • Adipose stem cells (ASCs) are major contributors of exercise-induced ECM remodeling • PRDM16 transcriptional complex is necessary for exercise-induced iWAT remodeling • NEGR1 functions as a link between PRDM16 and exercise-induced iWAT innervation Using multi-omics approaches in conjunction with detailed imaging, Nigro et al. find that exercise training promotes iWAT remodeling through changes in ECM, vascularization, and innervation. Moreover, they identify robust cell-type-specific adaptations in response to exercise that, in combination with structural changes, result in a healthier adipose tissue phenotype. [ABSTRACT FROM AUTHOR]

Catecholamine stimulation of β-adrenergic receptors (βAR) in adipocytes activates the cAMP-dependent protein kinase to promote liberation of fatty acids as a fuel source. The adipocyte β3AR also activates extracellular signal-regulated kinases (ERK)-1 and -2 through direct recruitment and activation of Src kinase. This pathway together with cAMP-dependent protein kinase contributes to maximal β3AR-stimulated lipolysis. In a search for other molecules that might associate with β3AR upon agonist stimulation, we identified vimentin using a proteomics approach. Immunoprecipitation of β3AR from adipocytes in the absence or presence of the β3AR agonist CL316,243, followed by Western blotting for vimentin confirmed this specific interaction. Since vimentin has also been identified on lipid droplets, the functional consequences of blocking the expression or structural integrity of vimentin intermediate filaments on β3AR regulation of ERK activation and lipolysis was assessed. Following disruption of intermediate filaments with β,β′-iminodipropionitrile, as confirmed by confocal microscopy, β3AR-stimulated ERK activation was blocked, and lipolysis was reduced by more than 40%. Independently, depletion of vimentin by small hairpin RNA (shRNA) completely inhibited β3AR-mediated ERK activation and significantly reduced lipolysis. By contrast, disruption of actin-containing microfilaments by cytochalasin D or microtubules by nocodazole had no effect on either lipolysis or ERK activation. These results indicate that vimentin plays an essential role in the signal transduction pathway from β3AR to the activation ERK and its contribution to lipolysis. [ABSTRACT FROM AUTHOR]

Catecholamine-stimulated lipolysis is primarily a β-adrenergic and cAMP-dependent event. In previous studies we established that the β3-adrenergic receptor (β3AR) in adipocytes utilizes a unique mechanism to stimulate extracellular signal-regulated kinases 1 and 2 (ERK) by direct recruitment and activation of Src kinase. Therefore, we investigated the role of the ERK pathway in adipocyte metabolism and found that the β3AR agonist CL316,243 regulates lipolysis through both cAMP-dependent protein kinase (PKA) and ERK. Inhibition of PKA activity completely eliminated lipolysis at low (subnanomolar) CL316,243 concentrations and by 75-80% at higher nanomolar concentrations. The remaining 20-25% of PKA-independent lipolysis, as well as ERK activation, was abolished by inhibiting the activity of either Src (PP2 or small interfering RNA), epidermal growth factor receptor (EGFR with AG 1478 or small interfering RNA), or mitogen-activated protein kinase kinase 1 or 2 (MKK1/2 with PD098059). PD098059 inhibited lipolysis by 53% in mice as well. Finally, the effect of estradiol, a reported acute activator of ERK and lipolysis, was also totally prevented by PP2, AG1478, and PD098059. These results suggest that ERK activation by β3AR depends upon Src and epidermal growth factor receptor kinase activities and is responsible for the PKA-independent portion of the lipolytic response. Together these results illustrate the distinct and complementary roles for PKA and ERK in catecholamine-stimulated lipolysis. [ABSTRACT FROM AUTHOR]

Abstract: Preadipocytes are periodically subjected to fatty acid (FA) concentrations that are potentially cytotoxic. We tested the hypothesis that prolonged exposure of preadipocytes of human origin to a physiologically relevant mix of FAs leads to mitochondrial inner membrane (MIM) permeabilization and ultimately to mitochondrial crisis. We found that exposure of preadipocytes to FAs led to progressive cyclosporin A-sensitive MIM permeabilization, which in turn caused a reduction in MIM potential, oxygen consumption, and ATP synthetic capacity and, ultimately, death. Additionally, we showed that FAs induce a transient increase in intramitochondrial reactive oxygen species (ROS) and lipid peroxide production, lasting roughly 30 and 120min for the ROS and lipid peroxides, respectively. MIM permeabilization and its deleterious consequences including mitochondrial crisis and cell death were prevented by treating the cells with the mitochondrial FA uptake inhibitor etomoxir, the mitochondrion-selective superoxide and lipid peroxide antioxidants MitoTempo and MitoQ, or the lipid peroxide and reactive carbonyl scavenger l-carnosine. FAs also promoted a delayed oxidative stress phase. However, the beneficial effects of etomoxir, MitoTempo, and l-carnosine were lost by delaying the treatment by 2h, suggesting that the initial phase was sufficient to prime the cells for the delayed MIM permeabilization and mitochondrial crisis. It also suggested that the second ROS production phase is a consequence of this loss in mitochondrial health. Altogether, our data suggest that approaches designed to diminish intramitochondrial ROS or lipid peroxide accumulation, as well as MIM permeabilization, are valid mechanism-based therapeutic avenues to prevent the loss in preadipocyte metabolic fitness associated with prolonged exposure to elevated FA levels. [Copyright &y& Elsevier]

Hepatic lipogenesis is the principal route to convert excess carbohydrates into fatty acids and is mainly regulated by two opposing hormones, insulin and glucagon. Although insulin stimulates hepatic lipogenesis, glucagon inhibits it. However, the mechanism by which glucagon suppresses lipogenesis remains poorly understood. In this study, we have observed that p38 mitogen-activated protein kinase plays an inhibitory role in hepatic lipogenesis. Levels of plasma triglyceride and triglyceride accumulation in the liver were both elevated when p38 activation was blocked. Expression levels of central lipogenic genes, including sterol regulatory element-binding protein-1 (SREBP-1), fatty acid synthase, hydroxy-3-methylglutaryl coenzyme A reductase, farnesyl pyrophosphate synthase, and cytochrome P-450-51, were decreased in liver by fasting and in primary hepatocytes by glucagon but increased by the inhibition of p38. In addition, we have shown that p38 can inhibit insulin-induced expression of key lipogenic genes in isolated hepatocytes. Our results in hepatoma cells demonstrate that p38 plays an inhibitory role in the activation of the SREBP-1c promoter. Finally, we have shown that transcription of the PGC-1β gene, a key coactivator of SREBP-1c, was reduced in liver by fasting and in isolated hepatocytes by glucagon. This reduction was significantly reversed by the blockade of p38. Insulin-induced expression of the PGC-1β gene was enhanced by the inhibition of p38 but suppressed by the activation of p38. Together, we have identified an inhibitory role for p38 in the transcription of central lipogenic genes, SREBPs, and PGC-1β and hepatic lipogenesis. [ABSTRACT FROM AUTHOR]

Hepatic gluconeogenesis is essential for maintaining blood glucose levels during fasting and is the major contributor to postprandial and fasting hyperglycemia in diabetes. Gluconeogenesis is a classic cAMP/protein kinase A-dependent process initiated by glucagon, which is elevated in the blood during fasting and in diabetes. In this study, we have shown that p38 mitogen-activated protein kinase (p38) was activated in liver by fasting and in primary hepatocytes by glucagon or forskolin. Fasting plasma glucose levels were reduced upon blockade of p38 with either a chemical inhibitor or small interference RNA in mice. In examining the mechanism, inhibition of p38 suppressed glueoneoganesis in liver, along with expression of key gluconeogenic genes, including phosphoenolpyruvate carboxykinase and glucose-6-phosphatase. Peroxisome proliferator-activated receptor γ, coactivator 1α and cAMP-response element-binding protein have been shown to be important mediators of hepatic gluconeogenesis. We have shown that inhibition of p38 prevented transcription of the PPARγ coactivator 1α gene as well as phosphorylation of cAMP-response element-binding protein. Together, our results from in vitro and in vivo studies define a model in which cAMP-dependent activation of genes involved in gluconeogenesis is dependent upon the p38 pathway, thus adding a new player to our evolving understanding of this physiology. [ABSTRACT FROM AUTHOR]

One of the phenotypes of mice with targeted disruption of the uncoupling protein-2 gene (Ucp2-/-) is greater macrophage phagocytic activity and free radical production, resulting in a striking resistance to infectious microorganisms. In this study, the molecular mechanisms of this enhanced immune response were investigated. We found that levels of nitric oxide measured in either plasma or isolated macrophages from Ucp2-/- mice are significantly elevated in response to bacterial lipopolysaccharide challenge compared with similarly treated Ucp2+/+ mice. Likewise, expression of inducible nitric-oxide synthase and inflammatory cytokines is higher in Ucp2-/- mice in vivo and in vitro. Key steps in the activation cascade of nuclear factor (NF)-κB, including IκB kinase and nuclear translocation of NF-κB subunits, are all remarkably enhanced in Ucp2-/- mice, most notably even under basal conditions. The elevated basal activity of IκB kinase in macrophages from Ucp2-/- mice can be blocked by cell-permeable inhibitors of superoxide and hydrogen peroxide generation, but not by a specific inhibitor for inducible nitric-oxide synthase. Isolated mitochondria from Ucp2-/- cells produced more superoxide/hydrogen peroxide. We conclude that mitochrondrially derived reactive oxygen from Ucp2-/- cells constitutively activates NF-κB, resulting in a ‘primed’ state to both potentiate and amplify the inflammatory response upon subsequent stimulation. [ABSTRACT FROM AUTHOR]

The development of the metabolic syndrome in an increasing percentage of the populations of Western societies, particularly in the United States, requires valid models for establishing basic biochemical changes and performing preclinical studies on potential drug targets. The C57BL/6J mouse has become an important model for understanidng the interplay between genetic background and environmental challenges such as high-fat/high-calorie diets that predispose to the development of the metabolic syndrome. This review highlights metabolic and signal transduction features that are altered during the course of disease progression, many of which mirror the human situation. [Copyright &y& Elsevier]