Cardiovascular microRNAs: early modulators in the pathogenesis of diabetic heart disease

Diabetic heart disease (DHD) is often unrecognized in the subclinical stage due to absence of pathognomonic signs, thereby restricting timely diagnosis and management of disease. Identifying early modulators of disease will not only help in early detection of disease, but also allow sufficient time for optimization of treatment. Recently, microRNAs (miRs) are gaining popularity as diagnostics and key regulators in the pathophysiology of several diseases including cardiovascular diseases. However, the diagnostic potential and pathophysiological role of miRs in DHD is still unrecognized. In the initial phase of my PhD, I carried out three pilot studies: 1) performing miR microarray using Taqman miR array cards using human diabetic myocardium; 2) identifying the onset alteration in pro-survival and 3) apoptosis pathways in human and type-2 diabetic mice. The outcomes of these pilot studies were that there was dysregulated expression of cardiovascular miRs (miR-1, miR-133a, miR-208a, miR-499, miR-126 and miR-132) in human diabetic heart compared to non-diabetic heart, suggesting these miRs as key players in pathogenesis of DHD. In addition to above mentioned miRs, I also included miR-15a and miR-15b into my study based on their cardio-enrichment and a recently published report showing their involvement in cardiac fibrosis. To further answer whether dysregulation of cardiovascular miRs has a correlation with aetiology of DHD, I carried out an animal study using db/db mice. Remarkably, all investigated miRs and their target proteins were dysregulated in diabetic myocardium, from the early stages of diabetes (8-12 weeks of age) vs age-matched non-diabetic control (p<0.05). Importantly, echocardiography and immunohistochemical analyses did not reveal any noticeable changes in diabetic mice until 20-weeks of age (p<0.001). These findings confirmed my hypothesis that miRs are early modulators of DHD and can be explored as therapeutic interventions for prompt management of DHD. In line with these results, I elicited in vitro modulation of some of my cardiovascular miRs (miR-1, miR-208a, miR-15a, miR-15b, miR-126, and miR-132) to explore their therapeutic potential in diabetic state. Using curative approach, I demonstrated that modulation of miRs in HL-1 cardiomyocytes (miR-1, miR-208a, miR-15a and miR-15b) and human umbilical vein endothelial cells (miR-126, and miR-132) abrogated the deleterious effects of high-glucose-induced impairment in cardiac/endothelial cell phenotype. Further, in order investigate their role as early modulators of DHD; it was essential to study the expression of cardiovascular miR at an early stage of diabetes. To address this, I recruited diabetic individuals from Dunedin and Christchurch Hospitals without any known history of cardiovascular disease. Quantitative real time PCR analyses revealed marked dysregulation of some of the circulating cardiovascular miRs (miR-1, miR-133a, miR-499, miR-126 and miR-132) in diabetic plasma samples at different duration of diabetes. I demonstrated a significant upregulation of miR-1, miR-126, miR-132 and miR-133 from early stage of diabetes (all p<0.05) while a significant downregulation of miR-499 in early (p<0.001) and later stage of diabetes (p