Pulmonary arterial hypertension (PAH) is a progressive vascular syndrome characterized by aberrant signaling, severe pulmonary artery remodeling, and right ventricular (RV) failure, a major driver of morbidity and mortality. Dysregulation of the apelinergic pathway has been implicated in pulmonary vascular remodeling in PAH. Using a sugen-hypoxia rat model of PAH, we assessed the ability of a potentially novel apelin analog, resistant to native peptidase degradation, to reverse the pathological hallmarks of PAH and RV dysfunction. Apelin analog therapy corrected the vascular lesions in the lungs and nearly normalized pulmonary arterial pressures. Early cardiorenal syndrome, RV dilation, and dysfunction, as well as RV cardiomyocyte and fibroblast activation induced by pressure overload, were also reversed by apelin analog treatment. Single-nucleus RNA-seq of the lungs and RV revealed apelin-analog treatment activated several protective pathways, including rebalancing protective bone morphogenetic protein receptor type 2 (BMPR2) signaling to counteract excessive pathogenic TGF-β receptor 2 (TGFBR2) activity in PAH. These findings highlight the therapeutic potential of exogenous apelin in reversing pulmonary vascular and cardiac pathologies in PAH and support further investigation to evaluate the clinical benefits of apelin analog treatment in patients with PAH and RV failure.

Myocardial infarction (MI) is a leading cause of morbidity and death worldwide. Endothelial cells (ECs) contribute to post-MI remodeling through angiogenesis, inflammation, and endothelial-to-mesenchymal transition (EndMT). ADAM17, a membrane-bound protease, is upregulated in ischemic heart disease, but its role in endothelial function post-MI is unknown. We investigated whether loss of endothelial ADAM17 could improve post-MI recovery using male and female mice with inducible endothelial-specific ADAM17 knockdown (Adam17f/f/Cdhr5-CreERT2; Adam17EC-KD). Surprisingly, male Adam17EC-KD mice exhibited compromised post-MI survival (42% death due to LV rupture vs. 13%), and progressive decline in cardiac function compared to controls (Adam17f/f-MI). Post-MI rupture was less drastic but detected in female Adam17EC-KD-MI mice. Adam17EC-KD hearts exhibited increased neutrophil infiltration, NETosis, and cytotoxic CD8+ T-cell accumulation post-MI; however, depletion of these immune cells did not improve post-MI survival. Single-nuclei RNA-seq analyses identified suppression of pro-angiogenic and EndMT markers, and emergence of an EC subpopulation enriched for necroptotic markers. Decreased vascularization was confirmed in the infarcted myocardium with reduced coronary density (CD31 staining; 3-D micro-CT) and pVEGFR2 signaling. Suppressed EndMT in Adam17EC-KD mice was linked to reduced collagen crosslinking, decreased activation of the SMAD pathway (pSMAD2/3), decreased expression of lysyl oxidase and Fibronectin in infarcted myocardium. In EC-fibroblast co-cultures in vitro, endothelial Adam17 knockdown suppressed tubular formation in hypoxic conditions and reduced EndMT. Conditioned media from hypoxic ECAd17-KD suppressed fibroblast activation. Increased necroptosis in vivo (Adam17EC-KD-MI), and in vitro (ECAd17-KD±hypoxia), was associated with increased TNFR1-RIPK3-RIPK1-MLKL signaling due to stabilization of TNFR1 in the absence of its ADAM17-mediated shedding. The critical role of necroptosis in impaired post-MI recovery was confirmed as inhibition of necroptosis (necrostatin-1) markedly improved post-MI survival and coronary vascularization in Adam17EC-KD-MI hearts. This study demonstrates that ADAM17 regulates post-MI endothelial functions, necroptosis, vascularization, and EndMT, with necroptosis as a critical factor in post-MI adverse myocardial remodeling and survival.

Aims Myocardial infarction (MI) triggers a complex remodeling that, if uncontrolled, leads to heart failure. Increased levels of ADAM17 (disintegrin and metalloproteinase-17) in ischemic injury has been reported, but its direct role in scar formation and subsequent recovery from MI has not been identified. We investigated the role of ADAM17 in the function of homeostatic fibroblasts (FBs) vs. activated myofibroblasts (myoFBs) in scar formation, and recovery following MI.Methods and Results Human myocardial specimens showed upregulated ADAM17 in the infarct tissue, colocalized to myofibroblasts. We generated two inducible genetic mouse models with Adam17 knockdown in FBs (Adam17FB-KD) or myoFB (Adam17myoFB-KD) and subjected them to MI. Loss of ADAM17 in FBs impaired infarct formation and increased mortality due to left ventricular (LV) rupture in males and females. In contrast, ADAM17 loss in myoFBs limited infarct expansion, LV dilation and dysfunction up to 4-wks post-MI. Macrophage infiltration was suppressed in both genotypes. Ex vivo and in vitro experiments revealed that loss of ADAM17 in myoFB resulted in scar tissue with reduced stiffness due to suppressed activation of epidermal growth factor receptor and the Yes-associated protein (YAP) pathway. This promoted VEGFR signaling, endothelial cell (EC) proliferation, and vascularization in the infarcted myocardium, limiting infarct expansion. RNAseq analyses showed drastic changes in extracellular matrix (ECM) genes in Adam17KD FB and myoFBs in hypoxia. In vitro co-culture of myoFB and ECs confirmed that the ECM deposited by Adam17-deficient myoFB promotes EC proliferation and sprouting. Pharmacological inhibition of ADAM17 before MI was ineffective, but short-term ADAM17 inhibition after MI (targeting the myoFBs), limited infarct expansion, LV dilation and dysfunction up to 4-weeks post-MI.Conclusion Short-term inhibition of ADAM17 after MI optimizes the compliance of the infarct tissue, promoting vascularization, limiting infarct expansion, preventing long-term adverse LV remodeling, dysfunction, and heart failure. Targeting the homeostatic FB vs. myoFB also highlights the critical timing of ADAM17 inhibition as its presence is essential for the initial healing of the infarcted heart, but inhibition of its persistent upregulation reduces scar stiffness and improves the outcome post-MI.

Introduction: Myocardial infarction (MI) is a leading cause of death worldwide, and endothelial cells (ECs) are central to the repair process by coordinating angiogenesis, immune cell recruitment, and endothelial-to-mesenchymal transition (EndMT). ADAM17, a membrane-bound protease elevated in cardiovascular disease, regulates multiple cellular processes through ectodomain shedding of different molecules. However, the causal role of endothelial ADAM17 in post-MI recovery remains poorly defined. Methods: Male and female mice with inducible endothelial-specific ADAM17 knockdown ( Adam17 f/f / Cdhr5 Cre ERT ; Adam17 EC-KD ) and control cohorts ( Adam17 f/f , Cdhr5 Cre ERT , WT) underwent left anterior descending coronary artery ligation to induce experimental MI. Cardiac structure and function were evaluated (echocardiography), histological analyses (Trichrome staining), molecular analyses (immunofluorescent staining (IF), western blotting, and single-nucleus RNA sequencing (snRNA-seq)) at various post-MI time points. Results: Adam17 EC-KD mice exhibited reduced post-MI survival (increased LV rupture), increased left ventricular rupture, and progressive decline in cardiac function with reduced ejection fraction. Adam17 EC-KD mice exhibited increased neutrophil infiltration, NETosis, and cytotoxic T cell accumulation at 1 day post-MI; however, depletion of any of these immune cells further exacerbated the post-MI mortality (due to LV rupture), highlighting their potential protective contribution. Loss of endothelial ADAM17 resulted in decreased coronary density in the infarct myocardium (CD31 IF; 3-D micro-CT imaging), with reduced pVEGFR2 signaling, suggesting impaired angiogenesis. In addition, SnRNA-seq confirmed the suppressed pro-angiogenic pathways, and identified an endothelial cell subpopulation enriched for necroptotic markers, displaying increased ligand-receptor interactions with inflammatory macrophages. Mechanistically, endothelial ADAM17 deficiency enhanced necroptotic cell death via activation of the TNFR1-RIP3K-RIP1K-MLKL axis. Adam17 EC-KD hearts also showed impaired collagen crosslinking and reduced activation of the SMAD pathway (pSMAD2/3), lysyl oxidase, and Fibronectin expression, indicating defective EndMT, supported by reduced EndMT gene signatures in snRNA-seq. Conclusion: Endothelial ADAM17 is essential for effective post-MI cardiac repair by regulating endothelial survival, angiogenesis, immune cell infiltration, and infarct formation.

AIMS:Although current clinical therapies following myocardial infarction (MI) have improved patient outcomes, morbidity, and mortality rates, secondary to ischaemic and ischaemia reperfusion (IR) injury remains high. Maintaining mitochondrial quality is essential to limit myocardial damage following cardiac ischaemia and IR injury. The mitochondrial deacetylase sirtuin 3 (SIRT3) plays a pivotal role in regulating mitochondrial function and cardiac energy metabolism. In the current study, we hypothesize that 19,20-epoxydocosapentaenoic acid (19,20-EDP) attenuates cardiac IR injury via stimulating mitochondrial SIRT3. METHODS AND RESULTS:Ex vivo models of isolated heart perfusions were performed in C57BL/6 mice to assess the effect of 19,20-EDP on cardiac function and energy metabolism following IR injury. In vivo permanent occlusion of the left anterior descending coronary artery was performed to induce MI; mice were administered 19,20-EDP with or without the SIRT3 selective inhibitor 3-TYP. Mitochondrial SIRT3 targets and respiration were assessed in human left ventricular tissues obtained from individuals with ischaemic heart disease (IHD) and compared to non-failing controls (NFCs). Binding affinity of 19,20-EDP to human SIRT3 was assessed using molecular modelling and fluorescence thermal shift assay. Results demonstrated that hearts treated with 19,20-EDP had improved post-ischaemic cardiac function, better glucose oxidation rates, and enhanced cardiac efficiency. The cardioprotective effects were associated with enhanced mitochondrial SIRT3 activity. Interestingly, treatment with 19,20-EDP markedly improved mitochondrial respiration and SIRT3 activity in human left ventricle (LV) fibres with IHD compared to NFC. Moreover, 19,20-EDP was found to bind to the human SIRT3 protein enhancing the NAD+-complex stabilization leading to improved SIRT3 activity. Importantly, the beneficial effects of 19,20-EDP were abolished by SIRT3 inhibition or using the S149A mutant SIRT3. CONCLUSION:These data demonstrate that 19,20-EDP-mediated cardioprotective mechanisms against ischaemia and IR injury involve mitochondrial SIRT3, resulting in improved cardiac efficiency.

Background: Myocardial infarction (MI) is a major cause of morbidity and mortality in elderly individuals, yet our understanding of age-related causes is limited. CYP450 epoxygenases metabolize polyunsaturated fatty acids into cardioprotective epoxylipids, which are readily degraded by soluble epoxide hydrolase (sEH). We have reported that sEH deletion is protective against MI-induced cardiac dysfunction in young mice, but its protective role in aged mice remains unclear. This study investigates if the cardioprotective effect of sEH deletion is also present in aged mice following MI injury. Methods: Male and female 15-month-old wild-type (WT) and sEH null mice were subjected to permanent LAD ligation to induce MI. Assessments of frailty index, a measure of health status, and cardiac function were performed prior to, and 7 days post-MI. Hearts were collected for histological, molecular and biochemical analyses. Results: Female sEH null mice, but not males, demonstrated significantly better frailty indices compared to WT female mice, suggesting better recovery from MI. Echocardiographic analyses revealed sEH null female mice had better post-MI cardiac function compared to WT counterparts (EF%: 26.9% vs. 37.6%). MI-induced cardiac and pulmonary hypertrophy were also attenuated in female sEH null mice but not males. Histological assessment of hearts using H&E and Masson’s Trichrome revealed better cardiac tissue architecture with denser tissue connection and less interstitial edema in the infarct border zone in sEH-null compared to WT female mice. Additionally, PSR staining analysis demonstrated thicker and more cross-linked collagen formations in the peri-infarct area, reflecting a better transition toward structured, stable extracellular matrix (ECM) remodeling. These findings were further supported by attenuated expression of ECM-related genes (Mmp2, Mmp14, Col1a1) in sEH null female hearts. Conclusion: Our data highlight sex-specific differences in markers of cardiac injury following MI in aged mice. Notably, preliminary findings indicate that sEH inhibition confers greater cardioprotection in female but not in males mice, providing potential insights into the mechanism of age-related cardiac repair.

Background: Myocardial infarction (MI) triggers a complex remodeling process. Disintegrin and metalloproteinase-17 (ADAM17) is a membrane-bound proteinase with a broad range of substrates. Increased ADAM17 in ischemic injury has been reported and linked to adverse outcomes, but its direct role in recovery from MI has not been identified. We aimed to determine the role of ADAM17 in the function of homeostatic (quiescent) fibroblasts (FBs) versus activated myofibroblasts (myoFBs) in scar formation, cardiac remodeling and recovery following MI. Methods and Results: We generated two inducible genetic mouse models with Adam17 knockdown in homeostatic FBs ( Adam17 f/f / Tcf21- Cre Esr1 ; Adam17 FB-KD ) or in myofibroblasts ( Adam17 f/f / Posn Cre ERT ; Adam17 myoFB-KD ), and subjected male and female to MI (by LAD ligation). Loss of ADAM17 in FBs increased left ventricle (LV) rupture due to suppressed collagen cross-linking and impaired scar formation. In contrast, ADAM17 loss in myoFBs limited infarct expansion and LV dilation up to 4 weeks post-MI. Further, ADAM17 loss in myoFBs increased coronary artery density (CD31 immunostaining, 3-D microCT scan), which was found to be due to reduced stiffness of the infarct tissue in these mice (indentation test using Mach-1 Biomomentum mechanical tester). Molecular analyses showed that ADAM17 loss in myoFBs suppresses the epidermal growth factor receptor (EGFR)-Yes-associated protein (YAP) pathway, reducing mechanical stiffness. FBs (passage 1) and myoFBs (activated with TGFβ) were isolated from adult mouse hearts and incubated in normoxia or hypoxia (1% O 2 ) to mimic the in vivo conditions. In vitro co-culture of myoFBs and endothelial cells (ECs) revealed that Adam17 -deficient myoFBs promote EC proliferation and vascular sprouting, consistent with the in vivo observation. Furthermore, pharmacological inhibition of ADAM17 before onset of MI was ineffective, but short-term ADAM17 inhibition after MI (days 1-4, targeting myoFBs) preserved cardiac structure&function up to 4 weeks. Conclusions: Short-term inhibition of ADAM17 after MI (targeting myoFBs) optimizes the compliance of the newly synthesized infarct tissue and promotes vascularization, limits infarct expansion, and prevents long-term adverse LV remodeling, dysfunction, and heart failure.

Heart failure is a prevalent disease worldwide. While it is well accepted that heart failure involves changes in myocardial energetics, what alterations that occur in fatty acid oxidation and glucose oxidation in the failing heart remains controversial. The goal of the study are to define the energy metabolic profile in heart failure induced by obesity and hypertension in aged female mice, and to attempt to lessen the severity of heart failure by stimulating myocardial glucose oxidation. 13-Month-old C57BL/6 female mice were subjected to 10 weeks of a 60

AIMS:Heart failure with preserved ejection fraction (HFpEF) is a prevalent disease worldwide. While it is well established that alterations of cardiac energy metabolism contribute to cardiovascular pathology, the precise source of fuel used by the heart in HFpEF remains unclear. The objective of this study was to define the energy metabolic profile of the heart in HFpEF. METHODS AND RESULTS:Eight-week-old C57BL/6 male mice were subjected to a '2-Hit' HFpEF protocol [60% high-fat diet (HFD) + 0.5 g/L of Nω-nitro-L-arginine methyl ester]. Echocardiography and pressure-volume loop analysis were used for assessing cardiac function and cardiac haemodynamics, respectively. Isolated working hearts were perfused with radiolabelled energy substrates to directly measure rates of fatty acid oxidation, glucose oxidation, ketone oxidation, and glycolysis. HFpEF mice exhibited increased body weight, glucose intolerance, elevated blood pressure, diastolic dysfunction, and cardiac hypertrophy. In HFpEF hearts, insulin stimulation of glucose oxidation was significantly suppressed. This was paralleled by an increase in fatty acid oxidation rates, while cardiac ketone oxidation and glycolysis rates were comparable with healthy control hearts. The balance between glucose and fatty acid oxidation contributing to overall adenosine triphosphate (ATP) production was disrupted, where HFpEF hearts were more reliant on fatty acid as the major source of fuel for ATP production, compensating for the decrease of ATP originating from glucose oxidation. Additionally, phosphorylated pyruvate dehydrogenase levels decreased in both HFpEF mice and human patient's heart samples. CONCLUSION:In HFpEF, fatty acid oxidation dominates as the major source of cardiac ATP production at the expense of insulin-stimulated glucose oxidation.

Aims Cardiac energy metabolism is perturbed in ischaemic heart failure and is characterized by a shift from mitochondrial oxidative metabolism to glycolysis. Notably, the failing heart relies more on ketones for energy than a healthy heart, an adaptive mechanism that improves the energy-starved status of the failing heart. However, whether this can be implemented therapeutically remains unknown. Therefore, our aim was to determine if increasing ketone delivery to the heart via a ketogenic diet can improve the outcomes of heart failure.Methods and results C57BL/6J male mice underwent either a sham surgery or permanent left anterior descending coronary artery ligation surgery to induce heart failure. After 2 weeks, mice were then treated with either a control diet or a ketogenic diet for 3 weeks. Transthoracic echocardiography was then carried out to assess in vivo cardiac function and structure. Finally, isolated working hearts from these mice were perfused with appropriately 3H or 14C labelled glucose (5 mM), palmitate (0.8 mM), and beta-hydroxybutyrate (beta-OHB) (0.6 mM) to assess mitochondrial oxidative metabolism and glycolysis. Mice with heart failure exhibited a 56% drop in ejection fraction, which was not improved with a ketogenic diet feeding. Interestingly, mice fed a ketogenic diet had marked decreases in cardiac glucose oxidation rates. Despite increasing blood ketone levels, cardiac ketone oxidation rates did not increase, probably due to a decreased expression of key ketone oxidation enzymes. Furthermore, in mice on the ketogenic diet, no increase in overall cardiac energy production was observed, and instead, there was a shift to an increased reliance on fatty acid oxidation as a source of cardiac energy production. This resulted in a decrease in cardiac efficiency in heart failure mice fed a ketogenic diet.Conclusion We conclude that the ketogenic diet does not improve heart function in failing hearts, due to ketogenic diet-induced excessive fatty acid oxidation in the ischaemic heart and a decrease in insulin-stimulated glucose oxidation. Graphical Abstract

BackgroundIron overload cardiomyopathy (IOC) is a major co-morbidity of genetic hemochromatosis and secondary iron overload with limited therapeutic options. We aim to investigate mechanisms of rescue action of amlodipine in the murine model of iron overload, characterize changes in human cardiac tissue due to IOC, and compare them to the changes in the animal model of IOC.Methods and resultsAs an animal model, we used male hemojuvelin knockout (HJVKO) mice, which lacked hemojuvelin (a co-receptor protein for hepcidin expression). The mice were fed a high-iron diet from 4 weeks to 1 year of age. As a rescue, iron-fed mice received the Ca2+ channel blocker, amlodipine, from 9 to 12 months. Iron overload resulted in systolic and diastolic dysfunctions and changes in the cardiac tissue similar to the changes in the explanted human heart with IOC. An IOC patient (β-thalassemia) with left-ventricular ejection fraction (LVEF) 25% underwent heart transplantation. The murine model and the explanted heart showed intra-myocyte iron deposition, fibrosis, hypertrophy, oxidative stress, remodeling of Ca2+ cycling proteins, and metabolic kinases typical of heart failure. Single-myocyte contractility and Ca2+ release were diminished in the murine model. The amlodipine-treated group exhibited normalization of cellular function and reversed fibrosis, hypertrophy, oxidative stress, and metabolic remodeling. We also report a clinical case of primary hemochromatosis successfully treated with amlodipine.ConclusionsThe aged HJVKO murine model on the iron-rich diet reproduced many features of the human case of IOC. The use of amlodipine in the murine model and clinical case reversed IOC remodeling, demonstrating that amlodipine is effective adjuvant therapy for IOC.

Introduction: COVID-19 disproportionately affects older, male obese patients leading to a high prevalence of adverse outcomes. SARS-CoV-2 mediated ACE2 loss may further increase the susceptibility of these patients to adverse outcomes. Loss of ACE2 may be a causative factor in cardiovascular (CV) injury independent of primary viral-mediated injury. Methods: Male, 6-month-old, diabetic, obese db/db Ace2 -/y (double mutant, DM) mice and respective WT, Ace2 -/y , and db/db controls (n=12) were assessed for injury across the gut-heart axis. Cardiovascular parameters were evaluated by echocardiography, pressure-volume loops, and histology. Alterations in gut permeability were determined by measuring plasma peptidoglycan (PGN) levels and immunological staining of microvilli structure. Metagenomics and metatranscriptomics determined the functional and phyla alterations of the gut microbiota. Results: Loss of ACE2 in diabetic obese mice led to increased left atrium diameter (P<0.001) and elevated left ventricular end-diastolic pressures (P<0.05) compared to db/db mice. Cardiac remodeling was prevalent in DM hearts with increased cardiomyocyte hypertrophy (P<0.001), cardiac fibrosis (P<0.05), lipid accumulation (P<0.01), and reactive oxygen species (ROS; P<0.01) compared to db/db mice. This was associated with elevated aortic ROS (P<0.001), and impaired femoral artery vasodilation (P<0.001). DM mice had increased gut-blood barrier permeability, with elevated plasmalemma vesicle-associated protein-1 staining (P<0.05) and plasma PGN levels (P<0.01). Principal coordinates analysis of gut microbial β diversity showed distinct populations across the experimental groups (P<0.05). Loss of ACE2 in db/db mice resulted in the divergence of metatranscriptomics profiles with increased expression of neutral amino acid metabolism, PGN and toxin production pathways. Conclusions: Loss of ACE2 in diabetic obese mice worsened cardiovascular dysfunction and adverse remodeling and was associated with an altered gut-cardiovascular axis characterized by elevated gut permeability and dysbiosis. Our results support worsening CV injury arising from the loss of ACE2 and may indicate a pathway of SARS-CoV-2 infection mediated CV injury.

Cardiac metabolism is perturbed in heart failure and is characterized by a shift from mitochondrial oxidative metabolism to glycolysis. Notably, the failing heart relies more on ketones for energy than a healthy heart, an adaptive mechanism that improves the energy-starved status of the failing heart. However, whether this can be implemented therapeutically remains unknown. Therefore, our aim was to determine if increasing ketone delivery to the heart via a ketogenic diet can improve the outcomes of heart failure.

Background Myocardial iron deficiency (MID) in heart failure (HF) remains largely unexplored. We aim to establish defining criterion for MID, evaluate its pathophysiological role, and evaluate the applicability of monitoring it non‐invasively in human explanted hearts. Methods and Results Biventricular tissue iron levels were measured in both failing (n=138) and non‐failing control (NFC, n=46) explanted human hearts. Clinical phenotyping was complemented with comprehensive assessment of myocardial remodeling and mitochondrial functional profiles, including metabolic and oxidative stress. Myocardial iron status was further investigated by cardiac magnetic resonance imaging. Myocardial iron content in the left ventricle was lower in HF versus NFC (121.4 [88.1–150.3] versus 137.4 [109.2–165.9] μg/g dry weight), which was absent in the right ventricle. With a priori cutoff of 86.1 μg/g d.w. in left ventricle, we identified 23% of HF patients with MID (HF‐MID) associated with higher NYHA class and worsened left ventricle function. Respiratory chain and Krebs cycle enzymatic activities were suppressed and strongly correlated with depleted iron stores in HF‐MID hearts. Defenses against oxidative stress were severely impaired in association with worsened adverse remodeling in iron‐deficient hearts. Mechanistically, iron uptake pathways were impeded in HF‐MID including decreased translocation to the sarcolemma, while transmembrane fraction of ferroportin positively correlated with MID. Cardiac magnetic resonance with T2* effectively captured myocardial iron levels in failing hearts. Conclusions MID is highly prevalent in advanced human HF and exacerbates pathological remodeling in HF driven primarily by dysfunctional mitochondria and increased oxidative stress in the left ventricle. Cardiac magnetic resonance demonstrates clinical potential to non‐invasively monitor MID.

CID is highly prevalent in advanced human HF and exacerbates pathological remodeling in HF driven primarily by dysfunctional mitochondria and increased oxidative stress in the LV. CMR demonstrates clinical potential to non-invasively monitor CID.

Plasma low-density lipoprotein (LDL) is primarily cleared by LDL receptor (LDLR). LDLR can be proteolytically cleaved to release its soluble ectodomain (sLDLR) into extracellular milieu. However, the proteinase responsible for LDLR cleavage is unknown. Here we report that membrane type 1-matrix metalloproteinase (MT1-MMP) co-immunoprecipitates and co-localizes with LDLR and promotes LDLR cleavage. Plasma sLDLR and cholesterol levels are reduced while hepatic LDLR is increased in mice lacking hepatic MT1-MMP. Opposite effects are observed when MT1-MMP is overexpressed. MT1-MMP overexpression significantly increases atherosclerotic lesions, while MT1-MMP knockdown significantly reduces cholesteryl ester accumulation in the aortas of apolipoprotein E (apoE) knockout mice. Furthermore, sLDLR is associated with apoB and apoE-containing lipoproteins in mouse and human plasma. Plasma levels of sLDLR are significantly increased in subjects with high plasma LDL cholesterol levels. Thus, we demonstrate that MT1-MMP promotes ectodomain shedding of hepatic LDLR, thereby regulating plasma cholesterol levels and the development of atherosclerosis.

Heart failure presents as the leading cause of infant mortality in individuals with Barth syndrome (BTHS), a rare genetic disorder due to mutations in the tafazzin (TAZ) gene affecting mitochondrial structure and function. Investigations into the perturbed bio-energetics in the BTHS heart remain limited. Hence, our objective was to identify the potential alterations in myocardial energy metabolism and molecular underpinnings that may contribute to the early cardiomyopathy and heart failure development in BTHS. Cardiac function and myocardial energy metabolism were assessed via ultrasound echocardiography and isolated working heart perfusions, respectively, in a mouse model of BTHS [doxycycline-inducible Taz knockdown (TazKD) mice]. In addition, we also performed mRNA/protein expression profiling for key regulators of energy metabolism in hearts from TazKD mice and their wild-type (WT) littermates. TazKD mice developed hypertrophic cardiomyopathy as evidenced by increased left ventricular anterior and posterior wall thickness, as well as increased cardiac myocyte cross-sectional area, though no functional impairments were observed. Glucose oxidation rates were markedly reduced in isolated working hearts from TazKD mice compared with their WT littermates in the presence of insulin, which was associated with decreased pyruvate dehydrogenase activity. Conversely, myocardial fatty acid oxidation rates were elevated in TazKD mice, whereas no differences in glycolytic flux or ketone body oxidation rates were observed. Our findings demonstrate that myocardial glucose oxidation is impaired before the development of overt cardiac dysfunction in TazKD mice, and may thus represent a pharmacological target for mitigating the development of cardiomyopathy in BTHS. NEW & NOTEWORTHY Barth syndrome (BTHS) is a rare genetic disorder due to mutations in tafazzin that is frequently associated with infantile-onset cardiomyopathy and subsequent heart failure. Although previous studies have provided evidence of perturbed myocardial energy metabolism in BTHS, actual measurements of flux are lacking. We now report a complete energy metabolism profile that quantifies flux in isolated working hearts from a murine model of BTHS, demonstrating that BTHS is associated with a reduction in glucose oxidation.

Objective: Atherosclerosis is accumulation of lipids and extracellular matrix in the arterial wall. TIMPs (tissue inhibitor of metalloproteinases) can impact plaque deposition by regulating ECM (extracellular matrix) turnover. TIMP4 also influences lipid metabolism and smooth muscle cell (SMC) proliferation. We investigated the role of TIMP4 in atherosclerosis. Approach and Results: Mice lacking low-density lipoprotein receptor ( Ldlr −/− ) and Timp4 ( Timp4 −/− / Ldlr −/− ) were fed high-fat diet (HFD) or regular laboratory diet. After 3 or 6 months, HFD-fed male and female Timp4 −/− / Ldlr −/− mice exhibited higher plaque density in the abdominal aorta (but not in aortic valves, arch, thoracic aorta) compared with Ldlr −/− mice. Although plasma lipid and cholesterol levels were lower in Timp4 −/− / Ldlr −/− -HFD, cholesterol content in the abdominal aorta was higher along with elevated inflammatory cytokines, MMP (matrix metalloproteinase) activities, CD68 + /calponin + macrophage-like SMCs in Timp4 −/− / Ldlr −/− -HFD compared with Ldlr −/− -HFD mice. In vitro, oxidized LDL (low-density lipoprotein) markedly increased CD68 expression, reduced SMC markers, increased lipid uptake, and reduced cholesterol efflux protein ABCA1 (ATP-binding cassette transporter A1) in Timp4 −/− / Ldlr −/− compared with Ldlr −/− primary SMCs from abdominal, but not thoracic aorta. TIMP4 expression in the abdominal aorta (in vivo) and its corresponding SMCs (in vitro) was ≈2-fold higher than in the thoracic aorta and SMCs; TIMP4 levels decreased following HFD. Timp4 -deficiency in bone marrow–derived macrophages did not alter their foam cell formation capacity. Conclusions: TIMP4 protects against plaque deposition in the abdominal aorta independent of plasma cholesterol levels. TIMP4 prevents proteolytic degradation of ABCA1 in SMCs, hindering cholesterol accumulation and transdifferentiation to macrophage-like foam cells, representing a novel negative regulator of atherosclerosis.

Dystrophin is a 427 kDa protein that stabilizes muscle cell membranes through interactions with the cytoskeleton and various membrane-associated proteins. Loss of dystrophin as in Duchenne muscular dystrophy (DMD) causes progressive skeletal muscle weakness and cardiac dysfunction. Multiple promoters along the dystrophin gene (DMD) give rise to a number of shorter isoforms. Of interest is Dp71, a 71 kDa isoform implicated in DMD pathology by various animal and patient studies. Strong evidence supporting such a role for Dp71, however, is lacking. Here, we use del52;WT mice to understand how Dp71 overexpression affects skeletal and cardiac muscle phenotypes. Apart from the mouse Dmd gene, del52;WT mice are heterozygous for a full-length, exon 52-deleted human DMD transgene expected to only permit Dp71 expression in muscle. Thus, del52;WT mice overexpress Dp71 through both the human and murine dystrophin genes. We observed elevated Dp71 protein in del52;WT mice, significantly higher than wild-type in the heart but not the tibialis anterior. Moreover, del52;WT mice had generally normal skeletal muscle but impaired cardiac function, exhibiting significant systolic dysfunction as early as 3 months. No histological abnormalities were found in the tibialis anterior and heart. Our results suggest that Dp71 overexpression may have more detrimental effects on the heart than on skeletal muscles, providing insight into the role of Dp71 in DMD pathogenesis.

Background Cancer therapies inhibiting PI 3Kα (phosphoinositide 3-kinase-α)-dependent growth factor signaling, including trastuzumab inhibition of HER 2 (Human Epidermal Growth Factor Receptor 2), can cause adverse effects on the heart. Direct inhibition of PI 3Kα is now in clinical trials, but the effects of PI 3Kα pathway inhibition on heart atrophy, remodeling, and function in the context of cancer therapy are not well understood. Method and Results Pharmacological PI 3Kα inhibition and heart-specific genetic deletion of p110α, the catalytic subunit of PI 3Kα, was characterized in conjunction with anthracycline (doxorubicin) treatment in female murine models. Biventricular changes in heart morphological characteristics and function were analyzed, with molecular characterization of signaling pathways. Both PI 3Kα inhibition and anthracycline therapy promoted heart atrophy and a combined effect of distinct right ventricular dilation, dysfunction, and cardiomyocyte remodeling in the absence of pulmonary arterial hypertension. Congruent findings of right ventricular dilation and dysfunction were seen with pharmacological and genetic suppression of PI 3Kα signaling when combined with doxorubicin treatment. Increased p38 mitogen-activated protein kinase activation was mechanistically linked to heart atrophy and correlated with right ventricular dysfunction in explanted failing human hearts. Conclusions PI 3Kα pathway inhibition promotes heart atrophy in mice. The right ventricle is specifically at risk for dilation and dysfunction in the setting of PI 3K inhibition in conjunction with chemotherapy. Inhibition of p38 mitogen-activated protein kinase is a proposed therapeutic target to minimize this mode of cardiotoxicity.