The essential role of microRNAs in Diabetes Mellitus: regulators of β cell function and potential disease biomarkers

The PhD thesis entitled “The essential role of microRNAs in Diabetes mellitus: regulators of β cell function and potential disease biomarkers” is mainly divided into three parts: i) an introduction about Diabetes mellitus, β cell identity and function, microRNAs (miRNAs) in diabetes and circulating miRNAs in diabetes; ii) a main project about the upstream and downstream molecular mechanisms which confer a protective role to miR-184 in type 2 diabetes (T2D); iii) two side projects about circulating miRNAs as biomarkers of bone complications of type 1 diabetes (T1D) and gestational diabetes mellitus (GDM). The results of the main project revealed a downregulation of miR-184 in pancreatic islets of T2D respect to non diabetic multiorgan donors. Moreover, the synthetic inhibition of miR-184 in EndoC-βH1 human β cells stressed with palmitate resulted in a lower apoptosis rate, protecting these cells from lypotoxicity-induced apoptosis. Importantly, we reported that this protective mechanism was mainly mediated by CRTC1, that we validated as a direct target gene of miR-184. Furthermore, miR-184 promoter is directly bound by NKX6.1, a transcription factor essential for the maintenance of β cell identity. Therefore, we speculated that the regulatory axis NKX6.1-miR-184-CRTC1 could be potentially involved β cell dedifferentiation, previously reported as a failure mechanism, that, in this case, could result as a protective mechanism against β cell stress-induced apoptosis. Although a depth study is necessary, the understanding of this regulatory mechanism could be potentially used as therapeutic target for the treatment of T2D. In the side project “Serum levels of miR-148a and miR-21-5p are increased in type 1 diabetic patients and correlated with markers of bone strength and metabolism” we reported an upregulation of two miRNAs (miR-21-5p and miR-148a-3p) in the serum of T1D patients with an impaired bone metabolism. Importantly, circulating levels of miR-148a and miR-21-5p levels are associated with BMD (Bone Mineral Density)-Total Body (TB), PTH (Parathormone), and BMC (Bone Mineral Content)-FEM (Femur). Moreover, the bioinformatics analysis of the validated target genes of these altered miRNAs, revealed that miR-148a and miR-21-5p target several genes involved in bone metabolism and bone remodeling. Therefore, miR-21-5p and miR-148a-3p could potentially used as circulating biomarkers of altered bone metabolism in T1D patients. In the side project “Altered expression of circulating miR-330-3p in women with physiologic pregnancies and with gestational diabetes mellitus” we reported the results of a primary analysis, revealing an upregulation of miR-330-3p in plasma of a subpopulation of GDM patients with a worse clinical outcome, respect to both GDM patients with a better clinical outcome and to non diabetic patients. Interestingly, from a secondary analysis, we observed that the levels of miR-330-3p in non-pregnant subjects did not differ from those of GDM patients, and that miR-330-3p expression is reduced in physiologic pregnancies. Therefore, we speculate that miR-330-3p could be a potential biomarker of GDM-complicated pregnancies, in which a lack of suppression of its expression is observed.