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Ubiquitin related modifier 1 (Urm1) is a unique eukaryotic member of the ubiquitin-fold (UbF) protein family and conserved from yeast to humans. Urm1 is dual-functional, acting both as a sulfur carrier for thiolation of tRNA anticodons and as a protein modifier in a lysine-directed Ub-like conjugation also known as urmylation. Although Urm1 conjugation coincides with oxidative stress and targets proteins like 2-Cys peroxiredoxins from yeast (Ahp1) and fly (Prx5), it was unclear how urmylation proceeds molecularly and whether it is affected by the activity of these antioxidant enzymes. An in-depth study of Ahp1 urmylation in yeast from our laboratory (Brachmann et al., 2020) uncovered that promiscuous lysine target sites and specific redox requirements determine the Urm1 acceptor activity of the peroxiredoxin. The results clearly show that the dimer interface and the 2-Cys based redox-active centers of Ahp1 are affecting the Urm1 conjugation reaction. Together with in vivo assays demonstrating that high organic peroxide concentrations can prevent Ahp1 from being urmylated, Brachmann et al. provide insights into a potential link between Urm1 utilization and oxidant defense of cells. Here, we highlight these major findings and discuss wider implications with regards to an emerging link between Urm1 conjugation and redox biology. Moreover, from these studies we propose to redefine our perspective on Urm1 and the molecular nature of urmylation, a post-translational conjugation that may not be that ubiquitin-like after all.

Abstract Pulmonary arterial hypertension (PAH) is a fatal vasculopathy that ultimately leads to elevated pulmonary pressure and death by right ventricular (RV) failure, which occurs in part due to decreased fatty acid oxidation and cytotoxic lipid accumulation. In this study, we tested the hypothesis that decreased fatty acid oxidation and increased lipid accumulation in the failing RV is driven, in part, by a relative carnitine deficiency. We then tested whether supplementation of l‐carnitine can reverse lipotoxic RV failure through augmentation of fatty acid oxidation. In vivo in transgenic mice harboring a human BMPR2 mutation, l‐carnitine supplementation reversed RV failure by increasing RV cardiac output, improving RV ejection fraction, and decreasing RV lipid accumulation through increased PPARγ expression and augmented fatty acid oxidation of long chain fatty acids. These findings were confirmed in a second model of pulmonary artery banding‐induced RV dysfunction. In vitro, l‐carnitine supplementation selectively increased fatty acid oxidation in mitochondria and decreased lipid accumulation through a Cpt1‐dependent pathway. l‐Carnitine supplementation improves right ventricular contractility in the stressed RV through augmentation of fatty acid oxidation and decreases lipid accumulation. Correction of carnitine deficiency through l‐carnitine supplementation in PAH may reverse RV failure.

Background: In 2012, mutations in Cav1 were found to be the driving mutation in several cases of heritable pulmonary arterial hypertension (PAH). These mutations replaced the last 21 amino acids of Cav1 with a novel 22-amino-acid sequence. Because previously only Cav1 knockouts had been studied in the context of PAH, examining the in vivo effects of this novel mutation holds promise for new understanding of the role of Cav1 in disease etiology.Methods: The new 22 amino acids created by the human mutation were knocked into the native mouse Cav1 locus. The mice underwent hemodynamic, energy balance, and inflammatory measurements, both at baseline and after being stressed with either a metabolic or an inflammatory challenge [low-dose lipopolysaccharide (LPS)]. To metabolically challenge the mice, they were injected with streptozotocin (STZ) and fed a high-fat diet for 12 weeks.Results: Very little mutant protein was found in vivo (roughly 2% of wild-type by mass spectrometry), probably because of degradation after failure to traffic from the endoplasmic reticulum. The homozygous mutants developed a mild, low-penetrance PAH similar to that described previously in knockouts, and neither baseline nor metabolic nor inflammatory stress resulted in pressures above normal in heterozygous animals. The homozygous mutants had increased lean mass and worsened oral glucose tolerance, as previously described in knockouts. Novel findings include the preservation of Cav2 and accessory proteins in the liver and the kidney, while they are lost with homozygous Cav1 mutation in the lungs. We also found that the homozygous mutants had a significantly lower tolerance to voluntary spontaneous exercise than the wild-type mice, with the heterozygous mice at an intermediate level. The mutants also had higher circulating monocytes, with both heterozygous and homozygous animals having higher pulmonary MCP1 and MCP5 proteins. The heterozygous animals also lost weight at an LPS challenge level at which the wild-type mice continued to gain weight.Conclusions: The Cav1 mutation identified in human patients in 2012 is molecularly similar to a knockout of Cav1. It results in not only metabolic deficiencies and mild pulmonary hypertension, as expected, but also an inflammatory phenotype and reduced spontaneous exercise.

The yeast peroxiredoxin Ahp1, like related anti-oxidant enzymes in other species, undergoes urmylation, a lysine-directed conjugation to ubiquitin-like modifier Urm1. Ahp1 assembles into a homodimer that detoxifies peroxides via forming intersubunit disulfides between peroxidatic and resolving cysteines that are subsequently reduced by the thioredoxin system. Although urmylation coincides with oxidative stress, it is unclear how this modification happens on a molecular level and whether it affects peroxiredoxin activity. Here, we report that thioredoxin mutants decrease Ahp1 urmylation in yeast and each subunit of the oxidized Ahp1 dimer is modified by Urm1 suggesting coupling of urmylation to dimerization. Consistently, Ahp1 mutants unable to form dimers, fail to be urmylated as do mutants that lack the peroxidatic cysteine. Moreover, Ahp1 urmylation involves at least two lysine residues close to the catalytic cysteines and can be prevented in yeast cells exposed to high organic peroxide concentrations. Our results elucidate redox requirements and molecular determinants critical for Ahp1 urmylation, thus providing insights into a potential link between oxidant defense and Urm1 utilization in cells. Keywords: Saccharomyces cerevisiae, 2-Cys peroxiredoxin, Ahp1, Redox-active thiols, Dimer interface, Thioredoxin system, Ubiquitin-related modifier Urm1, Protein urmylation

Heart failure with preserved ejection fraction (HFpEF) currently has no therapies that improve mortality. Right ventricular dysfunction and pulmonary hypertension are common in HFpEF, and thought to be driven by obesity and metabolic syndrome. Thus, we hypothesized that an animal model of obesity-induced HFpEF with pulmonary hypertension would provide insight into the pathogenesis of right ventricular failure in HFpEF. Two strains of mice, one susceptible (AKR) and one resistant (C3H) to obesity-induced HFpEF, were fed high fat (60% fat) or control diet for 0, 2, or 20 weeks and evaluated by cardiac catheterization and echocardiography for development of right ventricular dysfunction, pulmonary hypertension, and HFpEF. AKR, but not C3H, mice developed right ventricular dysfunction, pulmonary hypertension, and HFpEF. NPRC , which antagonizes beneficial natriuretic peptide signaling, was found in RNA sequencing to be the most differentially upregulated gene in the right ventricle, but not left ventricle or lung, of AKR mice that developed pulmonary hypertension and HFpEF. Overexpression of NPRC in H9C2 cells increased basal cell size and increased expression of hypertrophic genes, MYH7 and NPPA . In conclusion, we have shown that NPRC contributes to right ventricular modeling in obesity-induced pulmonary hypertension-HFpEF by increasing cardiomyocyte hypertrophy. NPRC may represent a promising therapeutic target for right ventricular dysfunction in pulmonary hypertension-HFpEF.

Background Muscular dystrophy (MD) causes a progressive cardiomyopathy characterized by diffuse fibrosis, arrhythmia, heart failure, and early death. Activation of the thromboxane‐prostanoid receptor (TPr) increases calcium transients in cardiomyocytes and is proarrhythmic and profibrotic. We hypothesized that TPr activation contributes to the cardiac phenotype of MD, and that TPr antagonism would improve cardiac fibrosis and function in preclinical models of MD. Methods and Results Three different mouse models of MD (mdx/utrn double knockout, second generation mdx/mTR double knockout, and delta‐sarcoglycan knockout) were given normal drinking water or water containing 25 mg/kg per day of the TPr antagonist ifetroban, beginning at weaning. After 6 months (10 weeks for mdx/utrn double knockout), mice were evaluated for cardiac and skeletal muscle function before euthanization. There was a 100% survival rate of ifetroban‐treated mice to the predetermined end point, compared with 60%, 43%, and 90% for mdx/utrn double knockout, mdx/mTR double knockout, and delta‐sarcoglycan knockout mice, respectively. TPr antagonism improved cardiac output in mdx/utrn double knockout and mdx/mTR mice, and normalized fractional shortening, ejection fraction, and other parameters in delta‐sarcoglycan knockout mice. Cardiac fibrosis in delta‐sarcoglycan knockout was reduced with TPr antagonism, which also normalized cardiac expression of claudin‐5 and neuronal nitric oxide synthase proteins and multiple signature genes of Duchenne MD. Conclusions TPr antagonism reduced cardiomyopathy and spontaneous death in mouse models of Duchenne and limb‐girdle MD. Based on these studies, ifetroban and other TPr antagonists could be novel therapeutics for treatment of the cardiac phenotype in patients with MD.

Low-grade albuminuria, determined by the urinary albumin to creatinine ratio, has been linked to systemic vascular dysfunction and is associated with cardiovascular mortality. Pulmonary arterial hypertension is related to mutations in the bone morphogenetic protein receptor type 2, pulmonary vascular dysfunction and is increasingly recognized as a systemic disease. In a total of 283 patients (two independent cohorts) diagnosed with pulmonary arterial hypertension, 18 unaffected BMPR2 mutation carriers and 68 healthy controls, spot urinary albumin to creatinine ratio and its relationship to demographic, functional, hemodynamic and outcome data were analyzed. Pulmonary arterial hypertension patients and unaffected BMPR2 mutation carriers had significantly elevated urinary albumin to creatinine ratios compared with healthy controls ( P

Parenteral prostacyclin therapy is the most efficacious pharmacologic treatment for pulmonary arterial hypertension (PAH), but clinical response is variable. We sought to identify clinical, hemodynamic, and genetic associations with response to prostacyclin therapy. We performed a retrospective analysis of patients within a de-identified electronic health record and associated DNA biobank. Patients with PAH and a right heart catheterization (RHC) in the six months before initiation of a parenteral prostacyclin were included. Responders were defined a priori by attainment of World Health Organization (WHO) functional class (FC) 2 or better at the time of repeat RHC within two years. We performed exploratory analyses to identify genomic associations with prostacyclin response. Of 129 patients identified, 54 met our criteria for “responders.” These patients were younger, more likely to be male, and were less likely to have connective tissue disease-related PAH. At follow-up, responders had improved hemodynamics, 6-min walk distance, and long-term survival. Baseline PA oxygen saturation (hazard ratio [HR] 0.568 [0.34–0.95]) and follow-up FC (HR = 2.57 [1.22–5.43]) were associated with survival. Prostacyclin responders were enriched in alleles related to cell development and circulatory system development and pathways related to aldosterone metabolism, cAMP signaling, and vascular smooth muscle contraction ( P

Background: Pulmonary hypertension (PH) is a progressive cardiovascular disease, characterized by endothelial and smooth muscle dysfunction and vascular remodeling, followed by right heart failure. Group III PH develops secondarily to chronic lung disease such as idiopathic pulmonary fibrosis (IPF), and both hastens and predicts mortality despite of all known pharmacological interventions. Thus, there is urgent need for development of newer treatment strategies.Objective: Angiotensin converting enzyme 2 (ACE2), a member of the renin angiotensin family, is therapeutically beneficial in animal models of pulmonary vascular diseases and is currently in human clinical trials for primary PH. Although previous studies suggest that administration of ACE2 prevents PH secondary to bleomycin-induced murine IPF, it is unknown whether ACE2 can reverse or treat existing disease. Therefore, in the present study, we tested the efficacy of ACE2 in arresting the progression of group 3 PH.Methods: To establish pulmonary fibrosis, we administered 0.018 U/g bleomycin 2x/week for 4 weeks in adult FVB/N mice, and sacrificed 5 weeks following the first injection. ACE2 or vehicle was administered via osmotic pump for the final 2 weeks, beginning 3 weeks after bleomycin. Echocardiography and hemodynamic assessment was performed prior to sacrifice and tissue collection.Results: Administration of bleomycin significantly increased lung collagen expression, pulmonary vascular remodeling, and pulmonary arterial pressure, and led to mild right ventricular hypertrophy. Acute treatment with ACE2 significantly attenuated vascular remodeling and increased pulmonary SOD2 expression without measurable effects on pulmonary fibrosis. This was associated with nonsignificant positive effects on pulmonary arterial pressure and cardiac function.Conclusion: Collectively, our findings enumerate that ACE2 treatment improved pulmonary vascular muscularization following bleomycin exposure, concomitant with increased SOD2 expression. Although it may not alter the pulmonary disease course of IPF, ACE2 could be an effective therapeutic strategy for the treatment of group 3 PH.

Bone morphogenetic protein receptor type 2 (BMPR2) mutations are present in patients with heritable and idiopathic pulmonary arterial hypertension (PAH). Circulating levels of interleukin-1 (IL-1) are raised in patients and animal models. Whether interplay between BMP and IL-1 signaling can explain the local manifestation of PAH in the lung remains unclear. Cell culture, siRNA, and mRNA microarray analysis of RNA isolated from human pulmonary artery (PASMC) and aortic (AoSMC) smooth muscle cells were used. R899X +/– BMPR2 transgenic mice fed a Western diet for six weeks were given daily injections of IL-1ß prior to assessment for PAH and tissue collection. PASMC have reduced inflammatory activation in response to IL-1ß compared with AoSMCs; however, PASMC with reduced BMPR2 demonstrated an exaggerated response. Mice treated with IL-1ß had higher white blood cell counts and significantly raised serum protein levels of IL-6 and osteoprotegerin (OPG) plasma levels recapitulating in vitro data. Phenotypically, IL-1ß treated mice demonstrated increased pulmonary vascular remodeling. IL-1ß induces an exaggerated pulmonary artery specific transcriptomic inflammatory response when BMPR2 signaling is reduced.

Peroxiredoxins, a highly conserved family of thiol oxidoreductases, play a key role in oxidant detoxification by partnering with the thioredoxin system to protect against oxidative stress. In addition to their peroxidase activity, certain types of peroxiredoxins possess other biochemical activities, including assistance in preventing protein aggregation upon exposure to high levels of oxidants (molecular chaperone activity), and the transduction of redox signals to downstream proteins (redox switch activity). Mice lacking the peroxiredoxin Prdx1 exhibit an increased incidence of tumor formation, whereas baker’s yeast (Saccharomyces cerevisiae) lacking the orthologous peroxiredoxin Tsa1 exhibit a mutator phenotype. Collectively, these findings suggest a potential link between peroxiredoxins, control of genomic stability, and cancer etiology. Here, we examine the potential mechanisms through which Tsa1 lowers mutation rates, taking into account its diverse biochemical roles in oxidant defense, protein homeostasis, and redox signaling as well as its interplay with thioredoxin and thioredoxin substrates, including ribonucleotide reductase. More work is needed to clarify the nuanced mechanism(s) through which this highly conserved peroxidase influences genome stability, and to determine if this mechanism is similar across a range of species.

Serotonergic anorexigens are the primary pharmacologic risk factor associated with pulmonary arterial hypertension (PAH), and the resulting PAH is clinically indistinguishable from the heritable form of disease, associated with BMPR2 mutations. Both BMPR2 mutation and agonists to the serotonin receptor HTR2B have been shown to cause activation of SRC tyrosine kinase; conversely, antagonists to HTR2B inhibit SRC trafficking and downstream function. To test the hypothesis that a HTR2B antagonist can prevent BMRP2 mutation induced PAH by restricting aberrant SRC trafficking and downstream activity, we exposed BMPR2 mutant mice, which spontaneously develop PAH, to a HTR2B antagonist, SB204741, to block the SRC activation caused by BMPR2 mutation. SB204741 prevented the development of PAH in BMPR2 mutant mice, reduced recruitment of inflammatory cells to their lungs, and reduced muscularization of their blood vessels. By atomic force microscopy, we determined that BMPR2 mutant mice normally had a doubling of vessel stiffness, which was substantially normalized by HTR2B inhibition. SB204741 reduced SRC phosphorylation and downstream activity in BMPR2 mutant mice. Gene expression arrays indicate that the primary changes were in cytoskeletal and muscle contractility genes. These results were confirmed by gel contraction assays showing that HTR2B inhibition nearly normalizes the 400% increase in gel contraction normally seen in BMPR2 mutant smooth muscle cells. Heritable PAH results from increased SRC activation, cellular contraction, and vascular resistance, but antagonism of HTR2B prevents SRC phosphorylation, downstream activity, and PAH in BMPR2 mutant mice.

Many α,β-unsaturated carbonyl compounds are used in biochemical and medical research. Their biological effects are due in large part to their electrophilic properties, whereby they undergo reaction with nucleophilic sites in proteins and nucleic acids. Here, we describe a structure−activity comparison of the cytotoxic properties of diethyl maleate (DEM) and closely related chemical analogs. All molecules that contained an α,β-unsaturated carbonyl group were cytotoxic to human colorectal carcinoma cells, causing apoptotic cell death. However, related molecules lacking this chemical moiety were not cytotoxic. One of the molecules screened, diethyl acetylenedicarboxylate (DAD), was considerably more cytotoxic than DEM and other analogues. Induction of cell death by DAD was significantly decreased following preincubation of cells with N-acetylcysteine, suggesting that its reactivity with thiols in cells might account for its cytotoxicity. By use of a model thiol compound, it was found that DAD can undergo addition reactions with two equivalents of thiol. When the reactivity of DAD with proteins was explored, it was determined that DAD induces oligomerization of Gpx3p, a yeast glutathione peroxidase with highly reactive cysteine residues in its active site. Our results suggest that DAD functions as a protein−thiol cross-linker, providing a potential chemical explanation for its cytotoxic potency. [ABSTRACT FROM AUTHOR]