Type 2 diabetes mellitus (T2D) increases the risk for heart failure. Whether mechanisms proposed to underlie cardiac alterations in the rodent diabetic heart are recapitulated in humans remains poorly investigated. We studied human LV samples of 8 subjects with T2D, preserved ejection fraction (EF) (63±5%) and no history of ischemic heart disease (Db-pEF), 7 subjects with T2D, reduced EF (26±9%) and ischemic heart disease (Db-ICM), and 15 non-diabetic individuals with normal EF. Label-free proteomics identified 1168 proteins with 146 differentially expressed in Db-ICM, and 66 in Db-pEF. Bulk RNA sequencing revealed 1795 differentially expressed genes (DEG) in Db-ICM and 527 in Db-pEF, with only 128 commonly regulated. Pathway analysis found enrichment of inflammation and extracellular matrix remodelling in Db-ICM or Db-pEF. Single nucleus RNAseq showed no differences in cell frequencies between the groups. However, the different cardiac cell types showed distinct regulation of pathways and key metabolic enzymes. Cardiomyocytes of diabetic hearts showed enrichments in pathways like insulin resistance, fatty acid oxidation, oxidative phosphorylation and oxidative stress. In cardiomyocytes key enzymes of fatty acid metabolism, glucose metabolism, and key metabolic regulators were regulated in both Db-pEf and Db-ICM while they were not in endothelial cells or fibroblasts. Endothelial cells showed alterations in pathways related with barrier dysfunction and inflammation. Thus, we present the first comprehensive atlas of molecular and cellular alterations in the human diabetic heart, confirming many pathomechanisms previously proposed in animal studies.
