Abstract Body: HFpEF is an unmet medical need. Aging, obesity and hypertension are risk factors of HFpEF. We showed that aging exacerbates metabolic and hypertensive stresses (2-hit stress) induced HFpEF. HFpEF and aging are associated with immune remodeling and declined NAD levels. We hypothesized that immunometabolic signaling contributes to HFpEF progression.
We utilized a 2-hit diet protocol to induce HFpEF in young and old wild-type (WT) mice. To determine the effects of aging and longitudinal 2-hit stress in HFpEF, we harvested left ventricles of 7-month old (young:control), 23-month old (old:control), 23-month old with 5-week (old:5-week) and 23-month old with 15-week 2-hit diet stress (old:15-week) for sn-RNA-seq. We identified myocyte, vascular, fibroblast and immune cell types in all hearts. More lymphoid cells, particularly T cell marker-expressing cells, were observed in old control hearts and this trend maintained with hearts from old:5-week or old:15-week mice. Myeloid cells, particularly inflammatory and antigen presenting macrophages, were reduced in old:control hearts but recovered in old:5-week or old:15-week hearts. To test the role of SARM1 NAD hydrolase in HFpEF, we subjected WT and knock out (KO) mice to 2-hit diet for 15-week. Despite declined NAD levels as reported in 2-hit hearts, there were no changes in expression of NAD synthesis genes. RNA-seq identified upregulated immune-related genes in WT:2-hit hearts. Using flow cytometry, we observed increased T and macrophage cell populations in WT:2-hit hearts. KO:2-hit hearts had improved diastolic function and reduced hypertrophy compared to WT:2-hit hearts. RNA-seq analysis of KO:2-hit hearts showed the downregulations of transcripts in immune activation pathways, associated with less macrophage count. In sn-RNA-seq analysis, Lyve1 expression was lowered in WT:2-hit macrophages, and was recovered in KO:2-hit macrophages. Induced cytotoxic gene expressions in WT:2-hit T cells were suppressed in KO:2-hit T cells. In summary, our findings suggest a working model that aging and 2-hit stress may remodel activations of different immune cells in a temporal dependent manner during HFpEF progression. SARM1 may play a key role in regulation of immunometabolic mechanisms in HFpEF.