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Lipids are natural substances found in all living organisms and involved in many biological functions. Imbalances in the lipid metabolism are linked to various diseases such as obesity, diabetes, or cardiovascular disease. Lipids comprise thousands of chemically distinct species making them a challenge to analyze because of their great structural diversity.Thanks to the technological improvements in the fields of chromatography, high-resolution mass spectrometry, and bioinformatics over the last years, it is now possible to perform global lipidomics analyses, allowing the concomitant detection, identification, and relative quantification of hundreds of lipid species. This review shall provide an insight into a general lipidomics workflow and its application in metabolic biomarker research.

Background Heart failure with preserved ejection fraction (HFpEF) is highly prevalent in patients with cardiometabolic disorders and associates with a poor outcome. Pathological gene expression in heart failure is accompanied by changes in active histone marks without major alterations in DNA methylation. Histone 3 trimethylation at lysine 36 (H3k36me3) – an active chromatin mark induced by the methyltransferase SETD2 – was recently found among the top epigenetic signatures in failing human hearts. Yet, the role of SETD2/H3k36me3 in heart failure is poorly understood. Purpose To investigate whether SETD2 participates in the transcriptional regulation of cardiometabolic HFpEF. Methods Mice with cardiomyocyte-specific deletion of SETD2 (c-SETD2−/−) and control littermates (SETD2fl/fl) were generated and subjected to high fat diet feeding and L-NAME treatment for 15 weeks to induce cardiometabolic HFpEF. Histology, mouse echocardiography (Vevo3100) and Treadmill exhaustion test were performed. ChIP-Seq datasets were employed to determine the biological pathways regulated by H3k36me3, whereas chromatin immunoprecipitation assays (ChIP) were performed to investigate SETD2/H3k36me3 enrichment on gene promoters. SETD2 gain- and loss-of-function experiments were performed in cultured cardiomyocytes (CMs) exposed to palmitic acid. Lipotoxic injury was assessed by mass spectrometry (MS)-based quantification of lipid species, autophagic flux (by Western blot) and apoptosis (by Caspase-3 activity assay). SETD2/H3k36me3 were also investigated in left ventricular myocardial specimens from patients with HFpEF and were correlated to passive stiffness. Results ChIP-Seq in mouse CMs showed a strong enrichment of SETD2/H3k36me3 in pathways underpinning triglyceride synthesis. SETD2 and H3k36me3 were upregulated in HFpEF vs. control mouse hearts and were highly enriched on the promoter of sterol regulatory element-binding transcription factor 1 (SREBF1) gene. These changes were associated with SREBF1 upregulation, myocardial triglyceride accumulation and lipotoxic damage. In HFpEF mice, cardiomyocyte-specific deletion of SETD2 prevented hypertrophic remodeling, diastolic dysfunction and lung congestion while improving exercise tolerance. Moreover, SETD2 deletion blunted H3K36me3 enrichment on SREBF1 promoter thus preventing SREBF1-related lipid accumulation, impaired autophagic flux and apoptosis. In cultured CMs exposed to palmitic acid, SETD2 depletion prevented H3k36me3-driven SREBF1 upregulation, whereas SETD2 overexpression recapitulated lipotoxic damage. SREBF1 knockdown prevented lipotoxic injury in SETD2-overexpressing CMs, suggesting its direct role in SETD2 signalling. Finally, SETD2 was upregulated in myocardial samples from obese patients with HFpEF and positively correlated with cardiomyocyte stiffness, a major feature of HFpEF. Conclusions SETD2 may represent an attractive molecular target for the prevention of cardiometabolic HFpEF. Funding Acknowledgement Type of funding sources: Public Institution(s). Main funding source(s): University of Zürich

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