Intrinsic nanomechanical changes in live diabetic cardiomyocytes

Patients with diabetes develop a cardiomyopathy that is independent of both coronary artery disease and hypertension and contributes to mortality and morbidity caused by diabetes. The mechanisms underlying the development of diabetic cardiomyopathy are poorly understood. Increased diastolic left ventricular (LV) stiffness is an early manifestation of diabetic myocardial dysfunction. This increase is usually attributed to myocardial fibrosis or to myocardial deposition of advanced glycation end products. Alteration of the stiffness (resting tension) of the diabetic cardiomyocyte was also proposed to be an important factor contributing to increased LV stiffness. Some of these data were obtained from isolated cardiomyocytes from human frozen biopsy samples that had been thawed, mechanically disrupted, and incubated with Triton X-100, disrupting sarcolemmal and sarcoplasmic membranes. We therefore determined the stiffness of live isolated cardiomyocytes from control and streptozotocin-treated mice using atomic force microscopy (AFM) nanoindentation. We show that 3 months of type 1 diabetes provoked fragmentation and disorder of myocardial fibers, interstitial collagen deposition, reduction in SERCA2a calcium pump expression and changes in F-actin organization. Moreover, we show that live isolated diabetic cardiomyocytes are stiffer than control cardiomyocytes when tested in Tyrode buffer with different ionic compositions. Hence, it is very likely that intrinsic mechanical changes of cardiomyocytes are an important factor in increasing myocardial stiffness in vivo .