Diabetes induces differences in costameric proteins and increases cardiomyocyte stiffness

Several studies demonstrated that Diabetes mellitus can increase the risk of cardiovascular diseases, and remains the most common cause of death in these patients. Cardiomyocytes are subjected to continuous mechanical stress and some proteins like the costamere complex proposed as mechanosensors and mechanotransducers that directly sense and respond to mechanical loads. Costameres sense and transduce it both as lateral force and biochemical signals and are closely related to cardiac physiology because individual heart cells are connected by intercalated discs, which synchronise muscle contraction. Diabetes has an impact on the nano-mechanical properties of living cardiomyocytes, resulting in increased cellular stiffness, as evidenced in clinical studies of these patients and elevated diastolic stiffness. Whether costameric proteins are affected by diabetes in the heart has not currently been studied. In this work, we analyse the effect induced by diabetes in the heart on costameric proteins. The samples (tissue and isolated cardiomyocytes) were analysed by immunotechniques by laser confocal microscopy. Significant statistical differences have been found in the spatial arrangement of the costamere proteins. However, these differences are not due to their expression as evidenced by the Western blot analysis. Heart disease causes an alteration in myocardial relaxation and an increase in left ventricle stiffness, causing a decrease in ejection fraction. Atomic force microscopy was used to compare intrinsic cellular stiffness between diabetic and normal live cardiomyocytes and obtain the first elasticity map sections of diabetic living cardiomyocytes. The data obtained demonstrated that diabetic cardiomyocytes had higher stiffness than control. The present work shows experimental evidence that intracellular changes occur related to cell-cell and cell-extracellular matrix communication which could be related to cardiac pathogenic mechanisms. These changes could contribute to alterations in cardiomyocytes’ mechanical and electrical properties and consequently of the myocardium, producing several cardiac pathologies.

What Is Known?

• Costameres are closely related to cardiac physiology because cardiomyocytes are connected by intercalated discs, which synchronise muscle contraction.

• The structural organisation of the cardiomyocyte proteins is critical for its efficient functioning as a contractile unit in the heart.

• Changes in cellular stiffness are hallmark characteristics of several diseases.

What New Information Does This Article Contribute?

• Whether costameric proteins are affected by diabetes in the heart has not currently been studied. This work shows that T1DM induce significant changes in the spatial organisation of costamere proteins, T-tubules, and intercalated discs.

• The statistical differences in the spatial organisation of costamere proteins were not due to differential protein expression as evidenced by the Western blot analysis.

• Cardiomyocytes are subjected to continuous mechanical stress and some proteins as the costamere complex proposed as mechanosensors and mechanotransducers that directly sense and respond to mechanical loads. Several cardiomyopathies, such as myocardial infarction, are characterised by increased fibrosis and heart stiffness. We obtained the first elasticity map sections (10 μm ² ) of living diabetic cardiomyocytes to compare intrinsic cellular stiffness between diabetic and normal cardiomyocytes. The results show statistical differences in the map sections of T1DM and control cardiomyocytes. T1DM cardiomyocytes are stiffer than normal ones.