Heart failure with preserved ejection fraction (HFpEF) is a common, morbid, and mortal syndrome for which there are no evidence-based therapies. Here, we report that concomitant metabolic and hypertensive stress in mice elicited by a combination of high fat diet (HFD) and constitutive nitric oxide (NO) synthase inhibition by N[w]-nitro-l-arginine methyl ester (L-NAME) recapitulates the numerous systemic and cardiovascular features of human HFpEF. One of the unfolded protein response (UPR) effectors, the spliced form of X-box binding protein 1 (Xbp1s), was reduced in the myocardium of both experimental and human HFpEF. Mechanistically, the decrease in Xbp1s resulted from increased inducible NO synthase (iNOS) activity and S-nitrosylation of endonuclease inositol-requiring protein 1α (IRE1α), culminating in defective Xbp1 splicing. Pharmacological or genetic suppression of iNOS, or cardiomyocyte-restricted overexpression of Xbp1s, each ameliorated the HFpEF phenotype. We have unveiled iNOS-driven dysregulation of IRE1α-Xbp1s as a crucial mechanism of cardiomyocyte dysfunction in HFpEF.

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Significance Cardiac hypertrophy and dysfunction in response to sustained hormonal and mechanical stress are sentinel features of most forms of heart disease. Activation of non–voltage-gated transient receptor potential canonical channels TRPC3 and TRPC6 may contribute to this pathophysiology and provide a therapeutic target. Effects from combined selective inhibition have not been tested previously. Here we report the capability of highly selective TRPC3/6 inhibitors to block pathological hypertrophic signaling in several cell types, including adult cardiac myocytes. We show in vivo redundancy of each channel; individual gene deletion was not protective against sustained pressure overload, whereas combined deletion ameliorated the response. These data strongly support a role for both channels in cardiac disease and the utility of selective combined inhibition.

Background: Heart failure with preserved ejection fraction (HFpEF) constitutes half of all HF yet lacks effective therapy. Understanding its myocardial biology remains limited due to a paucity of heart tissue molecular analysis. Methods: We performed RNA sequencing on right ventricular septal endomyocardial biopsies prospectively obtained from patients with consensus criteria for HFpEF (n=41) and contrasted to RV-septal tissue from HF with reduced EF (HFrEF, n=30) and donor controls (CON, n=24). Principal component analysis (PCA) and hierarchical clustering tested for transcriptomic distinctiveness between groups and impact of co-morbidities, and differential gene expression with pathway enrichment contrasted HF groups to CON. Within HFpEF, non-negative matrix factorization (NMF) and weighted gene co-expression analysis (WGCNA) identified molecular subgroups and the resulting clusters were correlated with hemodynamic and clinical data. Results: HFpEF patients were more often women (59%), African American (68%), obese (median BMI 41), and hypertensive (98%), with clinical HF characterized by 65% NYHA III-IV, nearly all on a loop diuretic, and 70% with a HF hospitalization in the prior year. PCA separated HFpEF from HFrEF and CON with minimal overlap and this persisted after adjusting for primary co-morbidities: BMI, sex, age, diabetes, and renal function. Hierarchical clustering confirmed group separation. Nearly half the significantly altered genes in HFpEF versus CON (1882 up, 2593 down) changed in the same direction in HFrEF; however, 5745 genes were uniquely altered between HF groups. Compared to CON, uniquely upregulated genes in HFpEF were enriched in mitochondrial ATP synthesis/electron transport, pathways downregulated in HFrEF. HFpEF-specific down-regulated genes engaged endoplasmic reticulum stress, autophagy, and angiogenesis. BMI differences largely accounted for HFpEF upregulated genes whereas neither this nor broader co-morbidity adjustment altered pathways enriched in downregulated genes. NMF identified three HFpEF transcriptomic subgroups with distinctive pathways and clinical correlates, including a group closest to HFrEF with higher mortality, and a mostly female group with smaller hearts and pro-inflammatory signaling. These groupings remained after sex adjustment. WGCNA analysis yielded analogous gene-clusters and clinical groupings. Conclusions: HFpEF exhibits distinctive broad transcriptomic signatures and molecular subgroupings with particular clinical features and outcomes. The data reveal new signaling targets to consider for precision therapeutics.