Blockage of MyD88 in cardiomyocytes alleviates cardiac inflammation and cardiomyopathy in experimental diabetic mice

Hyperglycemia-associated inflammation contributes to diabetic cardiomyopathy. Myeloid differentiation primary-response protein 88 (MyD88) is an adapter protein of many Toll-like receptors (TLRs) and is recruited to TLRs to initiate inflammatory response in endotoxin-activated innate immunity. However, the role of MyD88 in diabetic cardiomyopathy is unknown. We examined the role and mechanism of MyD88 in inflammatory heart injuries in diabetes and identified MyD88 as a potential target for the treatment of diabetic cardiomyopathy. In this study, we first found that MyD88 expression was increased in cardiomyocytes of diabetic mouse hearts. In cultured cardiomyocytes, MyD88 inhibition either by siRNA or by small-molecular inhibitor LM8 markedly blocked TLR4-MyD88 complex formation, reduced pro-inflammatory mitogen-activated protein kinases/nuclear factor-κB (MAPKs/NF-κB) cascade activation and decreased pro-inflammatory cytokine expression under high glucose condition. Moreover, pharmacologic inhibition of MyD88 by LM8 showed significantly anti-inflammatory, anti-hypertrophic and anti-fibrotic effects in the hearts of both type 1 and type 2 diabetic mice. These beneficial effects of MyD88 inhibition were correlated to the reduced activation of TLR4-MyD88-MAPKs/NF-κB signaling pathways in the hearts. Taken together, MyD88 in cardiomyocytes mediates diabetes-induced cardiac inflammatory injuries and pharmacological inhibition of MyD88 shows significantly cardioprotective effects, indicating MyD88 as a potential therapeutic target for diabetic cardiomyopathy.