The Pivotal Role of miRNA-21 in Myocardial Metabolic Flexibility in Response to Short- and Long-term High Glucose Treatment: Evidence in Human Cardiomyocyte Cell Line

Background miRNA-21 is a micro-RNA widely studied for its implications in several biological functions, including apoptosis, inflammation, fibrosis, and metabolism. Interestingly, miRNA-21 is a crucial regulator of developing cardiac diseases, but its role is controversial, and it is necessary to clarify its function in pathophysiological events of diabetic cardiomyopathy. In the present study we clarified the protective role of miRNA-21 at cardiac level and evaluated the involvement of miRNA-21 in high glucose induced-acute and chronic cardiac damage. Methods Human ventricular cardiac myoblasts AC16, treated and not with miR-21 inhibitor, were exposed to high glucose (33 mM) for 2 and 7 days, and the expression of fibrosis, inflammation, apoptosis, oxidative stress markers were assessed using western blotting. Further, cardiac energetic metabolism was evaluated by measuring both the expression of glucose transporters and regulators of lipids using western blotting analysis and key mitochondrial function parameters (oxygen consumption rate and proton production rate) using Seahorse technology. Results Short-term high glucose treatment induced a significant increase in miR-21 expression (p<0.05) that was associated with an increase in hydrogen ion flux and energy potential dissipation without any change in energy production or increase in the expression of genes involved in cellular damage. The reduction of miR-21 expression levels (p<0.05), observed after long-term (7 days) high glucose treatment, induced the activation of inflammation, apoptosis pathways and compromises mitochondrial function as demonstrated by the incapacity to answer energy demand and the impairment of physiological mitochondrial function (p<0.05). Conclusion In human cardiomyocytes, the abundance of miR-21 takes part in the first defense mechanism against cardiac insult and its cardioprotective effect depends on the time of exposure to the injury. Moreover, miRNA-21regulates mitochondrial respiration and the ability of cells to select the most appropriate substrate for ATP production in a given environment.