Abstract Body: Background. GLP1 agonism has recently emerged as a therapy for heart failure with preserved ejection fraction (HFpEF) in humans, but the cellular targets and subcellular mechanisms by which this drug elicits its effects in the heart are unknown.

Hypothesis. Semaglutide possesses direct cardiac mechanisms, distinct from the anti-obesity properties, that contribute to the amelioration of HFpEF.

Methods. Ten-week-old male ZSF1 obese rats (which exhibit HFpEF) were treated with low-dose semaglutide (30 nmol/kg subq twice weekly, n=6) or vehicle (n=6) for 16 weeks. Hearts were subjected to single nuclei RNA-seq. Gene expression changes greater than log2 fold +/- 0.5 and p value < 0.05 were chosen to examine transcriptome remodeling in myocytes, fibroblasts, endothelial, smooth muscle and myeloid and lymphoid lineages.

Results. This dose of semaglutide reduced blood glucose and ameliorated HFpEF symptoms: semaglutide improved cardiac relaxation (E/e’) and exercise tolerance, reducing cardiac fibrosis without reducing body weight. Despite a global down-regulation of gene expression after semaglutide (~10 down- for every 1 up-regulated gene across cell types), myocytes exhibited up-regulation of multiple steps in the branched chain amino acid (BCAA) metabolic pathway, including the first step in BCAA metabolism (Bcat2), the oxidative decarboxylation step in catabolism (Bckdha/b, Dbt) and the mitochondrial phosphatase required for activation of BCKDH (Pp2cm; BCKDK, the kinase that inhibits BCAA metabolism, was unchanged). KLF15, the transcription factor controlling expression of many BCAA enzymes, was also up-regulated by semaglutide. Fibroblasts from semaglutide treated hearts also exhibited up-regulation of BCAA catabolism and one carbon metabolism (e.g. Mthfd1l). Semaglutide induced down-regulation in multiple collagen isoforms (e.g. Col1a1, and Col8a2), periostin, Smad3/7, multiple ribosomal proteins (e.g. Rps19 and Rpl13) and members of the complement cascade (C4b) in fibroblasts which, together with decreased percentage of myeloid cells (7% in ZSF1 HFpEF vs 5% after semaglutide), suggest anti-fibrotic and anti-inflammatory effects.

Conclusion. These studies are the first single cell transcriptome analyses of semaglutide’s actions on the heart, revealing a strong effect to restrict gene expression, promote BCAA metabolism and decrease pathological fibrosis.