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Obesity-induced lipid overload in cardiomyocytes contributes to profound oxidative stress and cardiomyopathy, culminating in heart failure. In this study, we investigate a novel mechanism whereby lipids accumulate in cardiomyocytes and seek the relevant treatment strategies. P21-activated kinase 3 (PAK3) was elevated in obese human myocardium, and the murine hearts and cardiomyocytes upon diet- or fatty acid-induced stress, respectively. Mice with cardiac-specific overexpression of PAK3 were more susceptible to the development of cardiac dysfunction upon diet stress, at least partially, due to increased deposition of toxic lipids within the myocardium. Mechanistically, PAK3 promoted the nuclear expression of sterol regulatory element binding protein 1c (SREBP1c) through activation of mammalian target of rapamycin (mTOR) and ribosomal protein S6 kinase beta-1 (S6K1) pathway in cardiomyocytes, resulting in abnormal lipid genes profile, accumulation of excessive lipids, and oxidative stress. More importantly, PAK3 knockdown attenuated fatty acid-induced lipotoxicity and cell death in rat and human cardiomyocytes. More importantly, the S6K1 or SREBP1c inhibitor alleviated PAK3-triggered intracellular lipid overload and cardiac dysfunction under obese stress. Collectively, we have demonstrated that PAK3 impairs myocardial lipid homeostasis, while inhibition of cardiac lipotoxicity mitigates cardiac dysfunction. Our study provides a promising therapeutic strategy for ameliorating obesity cardiomyopathy., (© 2024 by the American Diabetes Association.)

Aims: Despite massive efforts, we remain far behind in our attempts to identify effective therapies to treat heart failure with preserved ejection fraction (HFpEF). Diastolic function is critically regulated by sarcoplasmic/endoplasmic reticulum (SR) calcium ATPase 2a (SERCA2a), which forms a functional cardiomyocyte (CM) microdomain where 3',5'-cyclic adenosine monophosphate (cAMP) produced upon β-adrenergic receptor (β-AR) stimulation leads to phospholamban (PLN) phosphorylation and facilitated Ca2+ re-uptake., Methods and Results: To visualize real-time cAMP dynamics in the direct vicinity of SERCA2a in healthy and diseased myocytes, we generated a novel mouse model on the leprdb background that stably expresses the Epac1-PLN Förster resonance energy transfer biosensor. Mice homozygous for the leprdb mutation (db/db) developed obesity and type 2 diabetes and presented with a HFpEF phenotype, evident by mild left ventricular hypertrophy and elevated left atria filling pressures. Live cell imaging uncovered a substantial β2-AR subtype stimulated cAMP response within the PLN/SERCA2a microdomain of db/db but not healthy control (db/+) CMs, which was accompanied by increased PLN phosphorylation and accelerated calcium re-uptake. Importantly, db/db CMs also exhibited a desensitization of β1-AR stimulated cAMP pools within the PLN/SERCA2a microdomain, which was accompanied by a blunted lusitropic effect, suggesting that the increased β2-AR control is an intrinsic compensatory mechanism to maintain PLN/SERCA2a-mediated calcium dynamics and cardiac relaxation. Mechanistically, this was due to a local loss of cAMP-degrading phosphodiesterase 4 associated specifically with the PLN/SERCA2a complex., Conclusion: These newly identified alterations of cAMP dynamics at the subcellular level in HFpEF should provide mechanistic understanding of microdomain remodelling and pave the way towards new therapies., Competing Interests: Conflict of interest: none declared., (© The Author(s) 2023. Published by Oxford University Press on behalf of the European Society of Cardiology.)

Background Prolonged activation of angiotensin II is the main mediator that contributes to the development of heart diseases, so converting angiotensin II into angiotensin 1-7 has emerged as a new strategy to attenuate detrimental effects of angiotensin II. Prolylcarboxypeptidase is a lysosomal pro-X carboxypeptidase that is able to cleave angiotensin II at a preferential acidic pH optimum. However, insufficient attention has been given to the cardioprotective functions of prolylcarboxylpeptidase. Methods and Results We established a CRISPR/CRISPR-associated protein 9-mediated global prolylcarboxylpeptidase-knockout and adeno-associated virus serotype 9-mediated cardiac prolylcarboxylpeptidase overexpression mouse models, which were challenged with the angiotensin II infusion (2 mg/kg per day) for 4 weeks, aiming to investigate the cardioprotective effect of prolylcarboxylpeptidase against hypertensive cardiac hypertrophy. Prolylcarboxylpeptidase expression was upregulated after 2 weeks of angiotensin II infusion and then became downregulated afterward in wild-type mouse myocardium, suggesting its compensatory function against angiotensin II stress. Moreover, angiotensin II-treated prolylcarboxylpeptidase-knockout mice showed aggravated cardiac remodeling and dampened cardiac contractility independent of hypertension. We also found that prolylcarboxylpeptidase localizes in cardiomyocyte lysosomes, and loss of prolylcarboxylpeptidase led to excessive angiotensin II levels in myocardial tissue. Further screening demonstrated that hypertrophic prolylcarboxylpeptidase-knockout hearts showed upregulated extracellular signal-regulated kinases 1/2 and downregulated protein kinase B activities. Importantly, adeno-associated virus serotype 9-mediated restoration of prolylcarboxylpeptidase expression in prolylcarboxylpeptidase-knockout hearts alleviated angiotensin II-induced hypertrophy, fibrosis, and cell death. Interestingly, the combination of adeno-associated virus serotype 9-mediated prolylcarboxylpeptidase overexpression and an antihypertensive drug, losartan, likely conferred more effective protection than a single treatment protocol to mitigate angiotensin II-induced cardiac dysfunction. Conclusions Our data demonstrate that prolylcarboxylpeptidase protects the heart from angiotensin II-induced hypertrophic remodeling by controlling myocardial angiotensin II levels.

Despite the development of clinical treatments, heart failure remains the leading cause of mortality. We observed that p21-activated kinase 3 (PAK3) was augmented in failing human and mouse hearts. Furthermore, mice with cardiac-specific PAK3 overexpression exhibited exacerbated pathological remodeling and deteriorated cardiac function. Myocardium with PAK3 overexpression displayed hypertrophic growth, excessive fibrosis, and aggravated apoptosis following isoprenaline stimulation as early as two days. Mechanistically, using cultured cardiomyocytes and human-relevant samples under distinct stimulations, we, for the first time, demonstrated that PAK3 acts as a suppressor of autophagy through hyper-activation of the mechanistic target of rapamycin complex 1 (mTORC1). Defective autophagy in the myocardium contributes to the progression of heart failure. More importantly, PAK3-provoked cardiac dysfunction was mitigated by administering an autophagic inducer. Our study illustrates a unique role of PAK3 in autophagy regulation and the therapeutic potential of targeting this axis for heart failure., Competing Interests: T.M.A.M. holds equities at Tenaya Therapeutics. The other authors have declared that no conflict of interest exists., (© 2023 The Authors.)

Endoplasmic Reticulum (ER) stress and oxidative stress have been highly implicated in the pathogenesis of cardiac hypertrophy and heart failure (HF). However, the mechanisms involved in the interplay between these processes in the heart are not fully understood. The present study sought to determine a causative link between Pak2-dependent UPR activation and oxidative stress via Nrf2 regulation under pathological ER stress. We report that sustained ER stress and Pak2 deletion in cardiomyocytes enhance Nrf2 expression. Conversely, AAV9 mediated Pak2 delivery in the heart leads to a significant decrease in Nrf2 levels. Pak2 overexpression enhances the XBP1-Hrd1 UPR axis and ameliorates tunicamycin induced cardiac apoptosis and dysfunction in mice. We found that Pak2 deletion and altered proteostasis render Nrf2 detrimental by switching from its antioxidant role to renin-angiotensin aldosterone system (RAAS) gene regulator. Mechanistically, Pak2 mediated Hrd1 expression targets Nrf2 for ubiquitination and degradation thus preventing its aberrant activation. Moreover, we find a significant increase in Nrf2 with a decrease in Pak2 in human myocardium of dilated heart disease. Using human-induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs), we find that Pak2 is able to ameliorate Nrf2 induced RAAS activation under ER stress. These findings demonstrate that Pak2 is a novel Nrf2 regulator in the stressed heart. Activation of XBP1-Hrd1 is attributed to prevent ER stress-induced Nrf2 RAAS component upregulation. This mechanism explains the functional dichotomy of Nrf2 in the stressed heart. Thus, Pak2 regulation of Nrf2 homeostasis may present as a potential therapeutic route to alleviate detrimental ER stress and heart failure., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Binder, Nguyen, Collins, Zi, Liu, Christou, Luo, Hille, Frey, Cartwright, Chernoff, Müller, Guan and Wang.)

Myocardial inflammation contributes to cardiomyopathy in diabetic patients through incompletely defined underlying mechanisms. In both human and time-course experimental samples, diabetic hearts exhibited abnormal ER, with a maladaptive shift over time in rodents. Furthermore, as a cardiac ER dysfunction model, mice with cardiac-specific p21-activated kinase 2 (PAK2) deletion exhibited heightened myocardial inflammatory response in diabetes. Mechanistically, maladaptive ER stress-induced CCAAT/enhancer-binding protein homologous protein (CHOP) is a novel transcriptional regulator of cardiac high-mobility group box-1 (HMGB1). Cardiac stress-induced release of HMGB1 facilitates M1 macrophage polarization, aggravating myocardial inflammation. Therapeutically, sequestering the extracellular HMGB1 using glycyrrhizin conferred cardioprotection through its anti-inflammatory action. Our findings also indicated that an intact cardiac ER function and protective effects of the antidiabetic drug interdependently attenuated the cardiac inflammation-induced dysfunction. Collectively, we introduce an ER stress-mediated cardiomyocyte-macrophage link, altering the macrophage response, thereby providing insight into therapeutic prospects for diabetes-associated cardiac dysfunction., Competing Interests: TMAM holds equities at Tenaya Therapeutics. The other authors have declared that no conflict of interest exists., (© 2022 The Authors.)

Pathological cardiac hypertrophy is a leading cause of heart failure, but knowledge of the full repertoire of cardiac cells and their gene expression profiles in the human hypertrophic heart is missing. Here, by using large-scale single-nucleus transcriptomics, we present the transcriptional response of human cardiomyocytes to pressure overload caused by aortic valve stenosis and describe major alterations in cardiac cellular crosstalk. Hypertrophied cardiomyocytes had reduced input from endothelial cells and fibroblasts. Genes encoding Eph receptor tyrosine kinases, particularly EPHB1, were significantly downregulated in cardiomyocytes of the hypertrophied heart. Consequently, EPHB1 activation by its ligand ephrin (EFN)B2, which is mainly expressed by endothelial cells, was reduced. EFNB2 inhibited cardiomyocyte hypertrophy in vitro, while silencing its expression in endothelial cells induced hypertrophy in co-cultured cardiomyocytes. Our human cell atlas of the hypertrophied heart highlights the importance of intercellular crosstalk in disease pathogenesis and provides a valuable resource., (© 2022. The Author(s).)

Fibroblast growth factor (FGF) 23 is elevated in chronic kidney disease (CKD) to maintain phosphate homeostasis. FGF23 is associated with left ventricular hypertrophy (LVH) in CKD and induces LVH via klotho-independent FGFR4-mediated activation of calcineurin/nuclear factor of activated T cells (NFAT) signaling in animal models, displaying systemic alterations possibly contributing to heart injury. Whether elevated FGF23 per se causes LVH in healthy animals is unknown. By generating a mouse model with high intra-cardiac Fgf23 synthesis using an adeno-associated virus (AAV) expressing murine Fgf23 (AAV-Fgf23) under the control of the cardiac troponin T promoter, we investigated how cardiac Fgf23 affects cardiac remodeling and function in C57BL/6 wild-type mice. We report that AAV-Fgf23 mice showed increased cardiac-specific Fgf23 mRNA expression and synthesis of full-length intact Fgf23 (iFgf23) protein. Circulating total and iFgf23 levels were significantly elevated in AAV-Fgf23 mice compared to controls with no difference in bone Fgf23 expression, suggesting a cardiac origin. Serum of AAV-Fgf23 mice stimulated hypertrophic growth of neonatal rat ventricular myocytes (NRVM) and induced pro-hypertrophic NFAT target genes in klotho-free culture conditions in vitro . Further analysis revealed that renal Fgfr1/klotho/extracellular signal-regulated kinases 1/2 signaling was activated in AAV-Fgf23 mice, resulting in downregulation of sodium-phosphate cotransporter NaPi2a and NaPi2c and suppression of Cyp27b1 , further supporting the bioactivity of cardiac-derived iFgf23. Of interest, no LVH, LV fibrosis, or impaired cardiac function was observed in klotho sufficient AAV-Fgf23 mice. Verified in NRVM, we show that co-stimulation with soluble klotho prevented Fgf23-induced cellular hypertrophy, supporting the hypothesis that high cardiac Fgf23 does not act cardiotoxic in the presence of its physiological cofactor klotho. In conclusion, chronic exposure to elevated cardiac iFgf23 does not induce LVH in healthy mice, suggesting that Fgf23 excess per se does not tackle the heart., Competing Interests: TT filed and licensed patents in the field of non-coding RNAs and is the founder and shareholder of Cardior Pharmaceuticals GmbH. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2021 Leifheit-Nestler, Wagner, Richter, Piepert, Eitner, Böckmann, Vogt, Grund, Hille, Foinquinos, Zimmer, Thum, Müller and Haffner.)

Myocardial insulin resistance contributes to heart failure in response to pathological stresses, therefore, a therapeutic strategy to maintain cardiac insulin pathways requires further investigation. We demonstrated that insulin receptor substrate 1 (IRS1) was reduced in failing mouse hearts post-myocardial infarction (MI) and failing human hearts. The mice manifesting severe cardiac dysfunction post-MI displayed elevated mir128-3p in the myocardium. Ischemia-upregulated mir128-3p promoted Irs1 degradation. Using rat cardiomyocytes and human-induced pluripotent stem cell-derived cardiomyocytes, we elucidated that mitogen-activated protein kinase 7 (MAPK7, also known as ERK5)-mediated CCAAT/enhancer-binding protein beta (CEBPβ) transcriptionally represses mir128-3p under hypoxia. Therapeutically, functional studies demonstrated gene therapy-delivered cardiac-specific MAPK7 restoration or overexpression of CEBPβ impeded cardiac injury after MI, at least partly due to normalization of mir128-3p . Furthermore, inhibition of mir128-3p preserved Irs1 and ameliorated cardiac dysfunction post-MI. In conclusion, we reveal that targeting mir128-3p mitigates myocardial insulin resistance, thereafter slowing down the progression of heart failure post-ischemia., Competing Interests: AR, MZ, SH, TA, NK, JJ, BN, KS, PB, LC, FP, HX, KG, NF, EC, OM, XW, WL No competing interests declared, (© 2020, Ruiz-Velasco et al.)

Rationale: Secreted and membrane-bound proteins, which account for 1/3 of all proteins, play critical roles in heart health and disease. The endoplasmic reticulum (ER) is the site for synthesis, folding, and quality control of these proteins. Loss of ER homeostasis and function underlies the pathogenesis of many forms of heart disease., Objective: To investigate mechanisms responsible for regulating cardiac ER function, and to explore therapeutic potentials of strengthening ER function to treat heart disease., Methods and Results: Screening a range of signaling molecules led to the discovery that Pak (p21-activated kinase)2 is a stress-responsive kinase localized in close proximity to the ER membrane in cardiomyocytes. We found that Pak2 cardiac deleted mice (Pak2-CKO) under tunicamycin stress or pressure overload manifested a defective ER response, cardiac dysfunction, and profound cell death. Small chemical chaperone tauroursodeoxycholic acid treatment of Pak2-CKO mice substantiated that Pak2 loss-induced cardiac damage is an ER-dependent pathology. Gene array analysis prompted a detailed mechanistic study, which revealed that Pak2 regulation of protective ER function was via the IRE (inositol-requiring enzyme)-1/XBP (X-box-binding protein)-1-dependent pathway. We further discovered that this regulation was conferred by Pak2 inhibition of PP2A (protein phosphatase 2A) activity. Moreover, IRE-1 activator, Quercetin, and adeno-associated virus serotype-9-delivered XBP-1s were able to relieve ER dysfunction in Pak2-CKO hearts. This provides functional evidence, which supports the mechanism underlying Pak2 regulation of IRE-1/XBP-1s signaling. Therapeutically, inducing Pak2 activation by genetic overexpression or adeno-associated virus serotype-9-based gene delivery was capable of strengthening ER function, improving cardiac performance, and diminishing apoptosis, thus protecting the heart from failure., Conclusions: Our findings uncover a new cardioprotective mechanism, which promotes a protective ER stress response via the modulation of Pak2. This novel therapeutic strategy may present as a promising option for treating cardiac disease and heart failure.