In recent years, type 2 diabetes mellitus has evolved as a rapidly increasing epidemic that parallels the increased prevalence of obesity and which markedly increases the risk of cardiovascular disease across the globe. While ischemic heart disease represents the major cause of death in diabetic subjects, diabetic cardiomyopathy (DC) summarizes adverse effects of diabetes mellitus on the heart that are independent of coronary artery disease (CAD) and hypertension. DC increases the risk of heart failure (HF) and may lead to both heart failure with preserved ejection fraction (HFpEF) and reduced ejection fraction (HFrEF). Numerous molecular mechanisms have been proposed to underlie DC that partially overlap with mechanisms believed to contribute to heart failure. Nevertheless, the existence of DC remains a topic of controversy, although the clinical relevance of DC is increasingly recognized by scientists and clinicians. In addition, relatively little attention has been attributed to the fact that both underlying mechanisms and clinical features of DC may be partially distinct in type 1 versus type 2 diabetes. In the following review, we will discuss clinical and preclinical literature on the existence of human DC in the context of the two different types of diabetes mellitus.

Hypoadiponectinemia is an independent predictor of cardiovascular disease, impairs mitochondrial function in skeletal muscle, and has been linked to the pathogenesis of Type 2 diabetes. In models of Type 2 diabetes, myocardial mitochondrial function is impaired, which is improved by increasing serum adiponectin levels. We aimed to define the roles of adiponectin receptor 1 (AdipoR1) and 2 (AdipoR2) in adiponectin-evoked regulation of mitochondrial function in the heart. In isolated working hearts in mice lacking AdipoR1, myocardial oxygen consumption was increased without a concomitant increase in cardiac work, resulting in reduced cardiac efficiency. Activities of mitochondrial oxidative phosphorylation (OXPHOS) complexes were reduced, accompanied by reduced OXPHOS protein levels, phosphorylation of AMP-activated protein kinase, sirtuin 1 activity, and peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α) signaling. Decreased ATP/O ratios suggested myocardial mitochondrial uncoupling in AdipoR1-deficient mice, which was normalized by lowering increased mitochondrial 4-hydroxynonenal levels following treatment with the mitochondria-targeted antioxidant Mn (III) tetrakis (4-benzoic acid) porphyrin. Lack of AdipoR2 did not impair mitochondrial function and coupling in the heart. Thus, lack of AdipoR1 impairs myocardial mitochondrial function and coupling, suggesting that impaired AdipoR1 signaling may contribute to mitochondrial dysfunction and mitochondrial uncoupling in Type 2 diabetic hearts.