Heart failure is a leading cause of morbidity and mortality worldwide. Emerging evidence points to vascular dysfunction as a major contributor to the development and progression of this grievous syndrome functional interplay between the myocardium and vasculature involves endothelial cells, vascular smooth muscle cells, and pericytes, governing tissue perfusion, vascular tone, inflammation, and metabolism. Vascular cells play a central role in maintaining cardiovascular homeostasis by sensing hemodynamic and inflammatory stimuli and releasing vasoactive and paracrine factors. Dysregulation of endothelium-derived mediators such as NO, endothelin-1, and endothelium-derived hyperpolarizing factors, along with vascular oxidative stress, inflammation, and vascular remodeling (eg, disturbances in angiogenesis and microvascular rarefaction) impair myocardial perfusion and can accelerate heart failure progression. Here, we summarize key molecular mechanisms linking vascular dysfunction to heart failure, emphasizing endothelial signaling, oxidative stress, inflammation, and angiogenic remodeling.

AIMS:Although growing evidence suggests that obesity/central adiposity predisposes to the development and exacerbation of heart failure with preserved ejection fraction (HFpEF), it remains to be clarified whether there is a causal relationship between adiposity and HFpEF pathogenesis. METHODS AND RESULTS:HFpEF was induced in male C57BL/6N mice using a high-fat diet + Nω-nitro-l-arginine methyl ester. Resection or transplantation of visceral adipose tissue (VAT) blunted or exacerbated HFpEF phenotypes, respectively, in mice. VAT from HFpEF mice displayed greater weight and secreted more small extracellular vesicles (sEVs) than those from chow-fed mice. Either systemic inhibition of sEV secretion or VAT-specific knockdown of Rab27b (an indispensable GTPase for sEV secretion) protected against HFpEF. Discovery-driven experiments identified miR-295-3p within sEVs as a possible mediator of the VAT-heart axis, which impaired cardiac autophagy by binding to Ulk1 mRNA. MiR-295-3p antagomir treatment mitigated HFpEF phenotypes. Additionally, neonatal mouse cardiomyocytes (NMCMs) manifested blunted autophagic flux after treatment with plasma sEVs from HFpEF mice. Notably, HFpEF patients displayed downregulated cardiac Ulk1 and autophagy compared with healthy individuals. Restoration of cardiac autophagy with rapamycin or ULK1 overexpression via AAV-9 attenuated the HFpEF phenotype in mice. CONCLUSION:The present work unveils a mechanism whereby obesity promotes HFpEF progression, emphasizing the role of VAT-heart crosstalk. Specifically, VAT-derived sEVs, miR-295-3p, and the resultant disruption of cardiac autophagy contribute significantly to the pathogenesis of HFpEF.

PC1 (polycystin-1), traditionally viewed through the lens of renal pathophysiology in autosomal dominant polycystic kidney disease, has emerged as a central regulator of cardiovascular mechanobiology. Recent structural elucidation of the PC1/PC2 (polycystin-2) complex provides a molecular framework emphasizing its mechanically sensitive ectodomain, regulated proteolytic cleavage, and functional coupling with PC2, framing PC1 as a versatile integrator of biomechanical cues, extracellular matrix interactions, and Ca2+ signaling across cardiovascular cell types. This review synthesizes evidence demonstrating that PC1 plays a direct and primary role in the cardiovascular system, independent of renal decline, regulating vascular homeostasis, endothelial shear stress responsiveness, smooth muscle phenotype, and myocardial mechanotransduction. We describe the molecular mechanisms whereby PC1 dysfunction perturbs nitric oxide signaling, cytoskeletal remodeling, excitation-contraction coupling, and hypertrophic transcriptional programs, and highlight tissue-specific roles in cardiac morphogenesis and adult myocardial integrity. By integrating structural biology with cardiovascular physiology, this review provides a unified framework for understanding PC1 as a master mechanosensor linking biomechanical forces to pathological remodeling. Critical knowledge gaps, emerging therapeutic opportunities, and the potential role of artificial intelligence in PC1-targeted drug discovery are also discussed.

BACKGROUND:Pathological cardiac remodeling and afterload-induced increases in energy demand contribute to heart failure (HF). Lysosome-assisted processes, such as autophagy, coupled with alterations in mitochondrial oxidative capacity, are critical regulators of this response. Furthermore, the lysosome is a hub for multiple signaling pathways governing hypertrophic growth. TFEB (transcription factor EB) has emerged as a key regulator of lysosomal genes and mitochondrial function in multiple tissues, especially in response to external stress. METHODS:Leveraging a cardiomyocyte-specific TFEB knockout mouse (CTKO), pressure overload was induced by transverse aortic constriction (TAC) to elucidate the role of TFEB under hypertrophic stress conditions. Echocardiography was employed to assess cardiac function, and hearts were subsequently harvested for transcriptomic, proteomic, and metabolomic analyses. To glean further insight into the molecular mechanisms involved, we studied neonatal rat ventricular myocytes exposed to phenylephrine, an in vitro model of cardiomyocyte hypertrophy. RESULTS:We report that TFEB is rapidly activated and translocates to the nucleus in cardiomyocytes exposed to hypertrophic stress conditions, triggering a lysosomal gene program independent of autophagy gene changes. At baseline, contractile function measured by echocardiography appeared normal in these mice compared with their Cre-negative littermates. However, in pressure-overload stress induced by TAC, CTKO mice manifested an amplified hypertrophic response, leading rapidly to HF. Unlike WT hearts, CTKO hearts failed to increase lysosomal capacity after TAC. They manifested an increase in the steady-state levels of autophagosome-associated proteins, such as LC3II and p62, as well as accumulation of ubiquitinated proteins, suggesting a defect in protein turnover. Interestingly, CTKO mice harbored altered mitochondrial structure, reduced oxidative capacity, and reduced abundance of peroxisome PGC-1α-b (proliferator-activated receptor-1 alpha-b). Furthermore, CTKO hearts manifested reduced expression of key enzymes within metabolic pathways essential for normal myocardial metabolism, including fatty acid metabolism, carbon metabolism, and branched-chain amino acid metabolism. Surprisingly, AMPK (AMP-activated protein kinase) signaling, while normal at baseline, was significantly decreased in CTKO hearts after TAC. This reliance on TFEB for growth trigger-induced AMPK signaling was also observed in vitro in cells exposed to phenylephrine, as were the antihypertrophic effects of TFEB activation, supporting a direct role of TFEB in this process. Finally, we report that exogenous activation of AMPK in the absence of TFEB can completely rescue the exacerbated hypertrophic response both in vitro and in vivo, independent of lysosomal function. Notably, blunting of the hypertrophic response did not impact the decreased contractile function observed in TAC-treated CTKO mice, highlighting the importance of TFEB in regulating mitochondrial function in response to stress. CONCLUSIONS:Our findings demonstrate that TFEB antagonizes pathological hypertrophic cardiac remodeling through upregulation of lysosomal capacity, maintaining mitochondrial energetic function, and promoting AMPK signaling.

Cardiomyocyte growth is tightly controlled by multiple signaling pathways. Identification of master kinases in this process is essential in exploring potential targets for the treatment of pathological cardiac hypertrophy and heart failure. Here we identified the mTORindependent activation of ribosomal protein S6 kinase b1 (Rps6kb1) during cardiomyocyte growth. By utilizing phosphoproteomics in primary neonatal rat ventricular myocytes, we revealed Rps6kb1 as one of most activated kinases under growth stimulation. We further demonstrated the role of Rps6kb1 phosphorylation in pathological cardiac hypertrophy and heart failure. We showed that the phosphorylation of multiple sites in Rps6kb1, including T367 in the kinase domain and S418/T421/S424 in the C-terminal domain, is not directly regulated by the activity of mTOR but coupled with the activation of the MEK1/ERK axis. In mice, cardiomyocyte-specific deletion of Rps6kb1 significantly inhibited both constitutively active ERK-and pressure overload-induced cardiac hypertrophy. In contrast, cardiomyocytespecific overexpression of wild-type Rps6kb1, rather than the phosphorylation-defective mutant, elevated cardiac hypertrophy and augmented pressure overload-induced heart failure. In conclusion, our findings reveal that the MEK/ERK axis primes Rps6kb1 activation through phosphorylation of 2 separate domains of Rps6kb1, which may play an essential role in cardiac hypertrophy and heart failure under hemodynamic stress.

Cardiometabolic heart failure with preserved ejection fraction (HFpEF) has emerged as a distinct and dominant endotype of HFpEF. Driven by prevalent comorbidities, its incidence and prevalence are projected to continue to rise amid the current global pandemic of obesity and metabolic disease. Recognizing the characteristic clinical and molecular features of cardiometabolic HFpEF is paramount for developing an efficacious therapeutic arsenal and improving clinical outcomes, challenges in which success to date has been modest. Studying relevant and clinically informative animal models of cardiometabolic HFpEF can afford valuable insights into the molecular underpinnings of this syndrome, allowing the possibility of novel advances with clinical relevance. Here, we outline the clinical and molecular features that define cardiometabolic HFpEF as a distinct endotype. We also discuss the bona fide animal models of cardiometabolic HFpEF currently available, as well as methods for developing new models.

Vascular cell adhesion molecule 1 (VCAM-1), a known downstream target of the Forkhead box O (FoxO) family of transcription factors, has well-established roles in development, cell-cell interactions, and cell survival. However, the specific role and mechanisms whereby VCAM-1 governs cardiomyocyte homeostasis in ischemic heart disease are incompletely understood. Here, we report that ischemia/reperfusion (I/R)-induced myocardial damage resulted in marked attenuation of FoxO1 and Vcam1 mRNA levels in wild-type (WT) mice, suggesting a protective role of the FoxO1/VCAM-1 axis in I/R injury. Indeed, compared with WT littermates, cardiomyocyte-specific loss of Vcam1 significantly exacerbated I/R-induced myocardial damage, apoptotic cardiomyocyte death, contractile dysfunction, and maladaptive cardiac remodeling. We go on to show that after exposure to ischemia, Vcam1-deficient cardiomyocytes (both in vivo and in vitro) manifested marked attenuation of essential pro-survival cues. These include a decrease in the cardiomyocyte-leukocyte interaction-mediated induction of Ezrin and its downstream Akt and ERK1/2 phosphorylation, as well as decreased expression of tumor necrosis factor α (TNFα) and manganese superoxide dismutase 2 (Sod2) genes. Collectively, our findings uncover a VCAM-1/Ezrin axis as an essential and previously unrecognized protective mediator of cardiomyocyte homeostasis in ischemic myocardium.

The physiological importance of cardiac myosin regulatory light chain (RLC) phosphorylation by its dedicated cardiac myosin light chain kinase has been established in both humans and mice. Constitutive RLC-phosphorylation, regulated by the balanced activities of cardiac myosin light chain kinase and myosin light chain phosphatase (MLCP), is fundamental to the biochemical and physiological properties of myofilaments. However, limited information is available on cardiac MLCP. In this study, we hypothesized that the striated muscle-specific MLCP regulatory subunit, MYPT2, targets the phosphatase catalytic subunit to cardiac myosin, contributing to the maintenance of cardiac function in vivo through the regulation of RLC-phosphorylation. To test this hypothesis, we generated a fl oxed-PPP1R12B mouse model crossed with a cardiac-specific Mer-Cre-Mer to conditionally ablate MYPT2 in adult cardiomyocytes. Immunofluorescence microscopy using the gene-ablated tissue as a control confirmed the localization of MYPT2 to regions where it overlaps with a subset of RLC. Biochemical analysis revealed an increase in RLC-phosphorylation in vivo. The loss of MYPT2 demonstrated significant protection against pressure overload- induced hypertrophy, as evidenced by heart weight, qPCR of hypertrophy-associated genes, measurements of myocyte diameters, and expression of beta-MHC protein. Furthermore, mantATP chase assays revealed an increased ratio of myosin heads distributed to the interfilament space in MYPT2-ablated heart muscle fi bers, confirming that RLC-phosphorylation regulated by MLCP, enhances cardiac performance in vivo. Our fi ndings establish MYPT2 as the regulatory subunit of cardiac MLCP, distinct from the ubiquitously expressed canonical smooth muscle MLCP. Targeting MYPT2 to increase cardiac RLC-phosphorylation in vivo may improve baseline cardiac performance, thereby attenuating pathological hypertrophy.

The myosin light chain phosphatase (MLCP), along with its regulatory subunit (MYPT2), plays a pivotal role in regulating cardiac myosin phosphorylation at its regulatory light chain (RLC) in vivo. Contrary to the hypertrophy observed in animal models and humans with hypertrophic cardiomyopathy mutations that increase the Ca2+-sensitivity of force, recent studies have shown that elevated baseline levels of RLC phosphorylation, ranging from 0.4 to 0.6 mol phosphate/mol RLC, can also increase the Ca2+-sensitivity of force while attenuating maladaptive hypertrophic responses in two distinct transgenic mouse models.

BACKGROUND:Cardiomyocyte growth is coupled with active protein synthesis, which is one of the basic biological processes in living cells. However, it is unclear whether the unfolded protein response transducers and effectors directly take part in the control of protein synthesis. The connection between critical functions of the unfolded protein response in cellular physiology and requirements of multiple processes for cell growth prompted us to investigate the role of the unfolded protein response in cell growth and underlying molecular mechanisms. METHODS:Cardiomyocyte-specific inositol-requiring enzyme 1α (IRE1α) knockout and overexpression mouse models were generated to explore its function in vivo. Neonatal rat ventricular myocytes were isolated and cultured to evaluate the role of IRE1α in cardiomyocyte growth in vitro. Mass spectrometry was conducted to identify novel interacting proteins of IRE1α. Ribosome sequencing and polysome profiling were performed to determine the molecular basis for the function of IRE1α in translational control. RESULTS:We show that IRE1α is required for cell growth in neonatal rat ventricular myocytes under prohypertrophy treatment and in HEK293 cells in response to serum stimulation. At the molecular level, IRE1α directly interacts with eIF4G and eIF3, 2 critical components of the translation initiation complex. We demonstrate that IRE1α facilitates the formation of the translation initiation complex around the endoplasmic reticulum and preferentially initiates the translation of transcripts with 5' terminal oligopyrimidine motifs. We then reveal that IRE1α plays an important role in determining the selectivity and translation of these transcripts. We next show that IRE1α stimulates the translation of epidermal growth factor receptor through an unannotated terminal oligopyrimidine motif in its 5' untranslated region. We further demonstrate a physiological role of IRE1α-governed protein translation by showing that IRE1α is essential for cardiomyocyte growth and cardiac functional maintenance under hemodynamic stress in vivo. CONCLUSIONS:These studies suggest a noncanonical, essential role of IRE1α in orchestrating protein synthesis, which may have important implications in cardiac hypertrophy in response to pressure overload and general cell growth under other physiological and pathological conditions.

Background:Metabolic substrate utilization in HFpEF (heart failure with preserved ejection fraction), the leading cause of heart failure worldwide, is pivotal to syndrome pathogenesis and yet remains ill defined. Under resting conditions, oxidation of free fatty acids (FFA) is the predominant energy source of the heart, supporting its unremitting contractile activity. In the context of disease-related stress, however, a shift toward greater reliance on glucose occurs. In the setting of obesity or diabetes, major contributors to HFpEF pathophysiology, the shift in metabolic substrate use toward glucose is impaired, sometimes attributed to the lower oxygen requirement of glucose oxidation versus fat metabolism. This notion, however, has never been tested conclusively. Furthermore, whereas oxygen demand increases in the setting of increased afterload, myocardial oxygen availability remains adequate for fatty acid oxidation (FAO). Therefore, a "preference" for glucose has been proposed. Methods and Results:Pyruvate dehydrogenase complex (PDC) is the rate-limiting enzyme linking glycolysis to the TCA cycle. As PDK4 (PDC kinase 4) is up-regulated in HFpEF, we over-expressed PDK4 in cardiomyocytes, ensuring that PDC is phosphorylated and thereby inhibited. This leads to diminished use of pyruvate as energy substrate, mimicking the decline in glucose oxidation in HFpEF. Importantly, distinct from HFpEF-associated obesity, this model positioned us to abrogate the load-induced shift to glucose utilization in the absence of systemic high fat conditions. As expected, PDK4 transgenic mice manifested normal cardiac performance at baseline. However, they manifested a rapid and severe decline in contractile performance when challenged with modest increases in afterload triggered either by L-NAME or surgical transverse aortic constriction (TAC). This decline in function was not accompanied by an exacerbation of the myocardial hypertrophic growth response. Surprisingly, metabolic flux analysis revealed that, after TAC, fractional FAO decreased, even when glucose/pyruvate utilization was clamped at very low levels. Additionally, proteins involved in the transport and oxidation of FFA were paradoxically downregulated after TAC regardless of genotype. Conclusions:These data demonstrate that cardiomyocytes in a setting in which glucose utilization is robustly diminished and prevented from increasing do not compensate for the deficit in glucose utilization by up-regulating FFA use.

Introduction: Pathological cardiac remodeling in response to elevated afterload can eventually progress to heart failure. Lysosome-assisted processes such as autophagy play an important role in this remodeling. The lysosome is also a nexus for some of the same signaling pathways that are involved in hypertrophic growth. The transcription factor EB (TFEB) has emerged as a key regulator of lysosomal genes in multiple tissues, especially in response to external stress. Methods and Results: Here, we report that TFEB is rapidly activated and translocates to the nucleus in cardiomyocytes under hypertrophic stress conditions, activating a lysosomal gene program independent of autophagy gene changes. We engineered a cardiomyocyte-specific TFEB knockout mouse (CTKO). At baseline, contractile function measured by echocardiography appears normal in these mice compared with their Cre-negative littermates. However, in the setting of pressure-overload stress induced by TAC (thoracic aortic constriction), the CTKO mice manifest an exacerbated hypertrophic response leading quickly to heart failure. Unlike the WT hearts, CTKO hearts fail to increase lysosomal capacity after TAC and manifest an increase in steady-state levels of autophagosome-associated proteins such as LC3II and p62, as well as accumulation of ubiquitinated proteins, suggesting a decrease in protein turnover. Surprisingly, AMPK signaling, while normal at baseline is significantly decreased in the CTKO hearts after TAC. This reliance on TFEB for PE-induced AMPK signaling is also observed in vitro , as are the anti-hypertrophic effects of TFEB activation, supporting a direct role of TFEB in this process. Finally, we show that exogenous activation of AMPK in the absence of TFEB can completely rescue the exacerbated hypertrophic response both in vitro and in vivo , independent of lysosomal function. Surprisingly, blunting of the hypertrophic response had no impact on the decreased cardiac function observed in the TAC-treated CTKO mice. Conclusion: Overall, our findings suggest that TFEB antagonizes pathological hypertrophic cardiac remodeling through up-regulation of lysosomal capacity and AMPK signaling.

Background: To support the unremitting contractile function of the heart, free fatty acids (FFA) are the substrate of choice, with a shift toward greater reliance on glucose when increased cardiac output is required. However, in the setting of obesity or diabetes, this metabolic flexibility is impaired. The putative necessity of a shift in substrate utilization has been hypothesized to occur due to the lower oxygen requirement of glucose versus fat metabolism, but this has never been tested conclusively. Furthermore, in the case of increased afterload, whereas oxygen demand increases, myocardial oxygen availability remains adequate for fatty acid oxidation (FAO). Therefore, a “preference” for glucose has been proposed. Methods and Results: Pyruvate dehydrogenase complex (PDC) is the rate-limiting enzyme linking glycolysis to the TCA cycle. By over-expressing PDC kinase 4 (PDK4) in cardiomyocytes, we ensured that PDC was phosphorylated and thereby inhibited. This leads to diminished use of pyruvate, limiting energy production primarily to FAO. Unlike high fat diet feeding, which also increases PDK4 and inhibits PDH, this model positioned us to query the impact of PDH inhibition under elevated workload demand in the absence of systemic high fat conditions. As expected, PDK4 transgenic mice manifested normal cardiac output at baseline. However, they manifested a rapid and severe decline in contractile function when challenged with increased afterload triggered by either L-NAME or surgical transverse aortic constriction (TAC). Metabolic flux analysis revealed that, after TAC, fractional FAO decreased - surprisingly - independent of an increase in glucose/pyruvate utilization. Additionally, proteins involved in the transport and oxidation of FFA were paradoxically down-regulated after TAC regardless of genotype. Conclusions: These data demonstrate that cardiomyocytes in a setting in which glucose utilization is clamped and prevented from increasing do not compensate for the deficit in glucose utilization by up-regulating FFA use. In aggregate, our findings suggest that reliance on glucose in the setting of pathological cardiac stress is largely a necessity rather than a simple preference.

Background: Nearly half of all patients receive radiation therapy as a component of their cancer care. Despite the efficacy of radiation therapy as a cancer treatment, cardiotoxicity is a major concern in patients receiving chest radiotherapy. There are currently no standardized approaches for early detection of radiation-induced cardiotoxicity as a stage that offers potential for early intervention. In this study, we employ hyperpolarized 13C- pyruvate magnetic resonance spectroscopy to non-invasively characterize early metabolic changes in the heart in response to radiation. Methods: We established a pre-clinical model of radiation induced heart disease (RIHD) by performing whole heart irradiation (8Gy x 5) in rats. Echocardiography was used characterize mechanical changes in the heart following radiation. To non-invasively detect myocardial mitochondrial dysfunction following cardiac irradiation in vivo, we employed hyperpolarized 13C- pyruvate magnetic resonance spectroscopy (MRS) to track the fate of pyruvate, an intermediate of glucose metabolism, as it is metabolized in the heart. Hyperpolarized 13C- pyruvate MRS was also employed in a patient who received thoracic radiation for treatment of thymoma to non-invasively study changes in glucose metabolism in response to radiation. Results: We identified evidence of early cardiac mitochondrial dysfunction prior to onset of mechanical changes in the heart. Following cardiac irradiation, due to mitochondrial dysfunction, pyruvate was preferentially metabolized to lactate in the cytoplasm (as opposed to bicarbonate in the mitochondria in non-irradiated hearts). The ratio of products of 13C- pyruvate metabolism in the mitochondria and cytoplasm as ascertained by hyperpolarized 13C- pyruvate MRS served as a biomarker for metabolic dysfunction in the heart both in a pre-clinical rat model and in a patient who received thoracic radiation. Conclusions: We have developed a non-invasive approach for detection of cardiac mitochondrial dysfunction, which may serve as a biomarker for early detection of radiation-induced cardiotoxicity, and shown feasibility in a human patient. Clinical adoption of this approach may enable early identification of patients who are at high risk for future cardiac complications and may benefit from mitigation strategies. Citation Format: Taylor-Jade Higgins, Jayesh Sharma, Elizabeth R. Zhang-Velten, Sarah Elliott, Junjie Ma, Jun Chen, Gabriele Schiattarella, Chantal Vidal, Nan Jiang, Daniel Daou, Joseph Hill, Thomas Gillette, Craig Malloy, Vlad Zaha, Jae Mo Park, Prasanna Alluri. Early and non-invasive detection of radiation-induced cardiotoxicity in pre-clinical and clinical models. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3584.

Heart failure with preserved ejection fraction (HFpEF) is now the most common form of heart failure and a significant public health concern for which limited effective therapies exist. Inflammation triggered by comorbidity burden is a critical element of HFpEF pathophysiology. Here, we discuss evidence for comorbidity-driven systemic and myocardial inflammation and the mechanistic role of inflammation in pathological myocardial remodeling in HFpEF.

Long non-coding RNAs (lncRNAs) comprise the most representative transcriptional units of the mammalian genome. They are associated with organ development linked with the emergence of cardiovascular diseases. We used bioinformatic approaches, machine learning algorithms, systems biology analyses, and statistical techniques to define co-expression modules linked to heart development and cardiovascular diseases. We also uncovered differentially expressed transcripts in subpopulations of cardiomyocytes. Finally, from this work, we were able to identify eight cardiac cell-types; several new coding, lncRNA, and pcRNA markers; two cardiomyocyte subpopulations at four different time points (ventricle E9.5, left ventricle E11.5, right ventricle E14.5 and left atrium P0) that harbored co-expressed gene modules enriched in mitochondrial, heart development and cardiovascular diseases. Our results evidence the role of particular lncRNAs in heart development and highlight the usage of co-expression modular approaches in the cell-type functional definition.

Heart failure with preserved ejection fraction (HFpEF) has few effective therapies yet exacts substantial mortality. Its multi-system nature has made animal modeling difficult, but recent efforts combining diet-induced obesity and hemodynamic stress are popular: mouse - L-NAME/high-fat diet (HFD) and ovariectomized (OVX) females with HFD-induced obesity/cardiac pressure overload (PO) (HFD+OVX+PO), ZSF1 rat, and obese/hypertensive Göttingen minipigs. We reported human HFpEF myocyte defects including reduced Ca 2+ -activated maximum tension (T max ) negatively correlate with body mass index, reduced Hill coefficient (n H, e.g., cooperativity) and Ca 2+ at 50% T max (EC 50 ), and higher resting tension. Here we tested whether such deficits are found in HFpEF animal models. The L-NAME/HFD mouse had no differences in Ca 2+ -activated (p=0.20) or resting (p=0.75) tension. In obese ZSF-1 rats, while T max (p=0.23) and resting tension (p=0.39) were not different, n H was reduced (2±1 vs. 4±2 p=0.01). In HFD+OVX+PO mice, T max (15±2 vs. 20±2 mN/mm 2 , p=0.006) and EC 50 (1.9±0.6 vs. 2.4±0.7 μM, p=0.008) were reduced, but resting tension (p=0.70) was not different. In the Göttingen minipig HFpEF model, EC 50 (p=0.93) and n H (p=0.35) were not different, whereas T max was reduced (17±3 vs. 27±3 mN/mm 2 , p=2x10 -6 ) and tension less at physiologic Ca 2+ . Resting tension was lower (not greater) in this model (p=0.001). The HFD+OVX+PO and minipig HFpEF models recapitulate depressed Ca 2+ -activated tension as in obese human HFpEF, whereas none manifested increased resting tension ( Table 1 ). Studies investigating HFpEF sarcomere dysfunction should consider these findings in model selection.

Radiation-induced heart disease is a major source of morbidity and mortality in patients receiving thoracic radiation. In this study, radiation-induced changes in cardiac metabolism is investigated using hyperpolarized [1- 13 C]pyruvate MRI in animals and patients. Myocardial bicarbonate-to-lactate ratios decreased following radiation treatments while no change was observed in the global strain, suggesting radiation-induced mitochondrial dysfunction in the heart. This translational study demonstrates clinical potential of hyperpolarized 13 C pyruvate for early and noninvasive detection of radiation-induced cardiac injury.