Abstract
Abstract only Background: Non-ischemic diabetic heart disease (NiDHD) is characterised by diastolic dysfunction and decreased or preserved systolic function, eventually resulting in heart failure. The fundamental mechanisms leading to NiDHD are still not known. microRNAs (miRNAs) plays a significant role in the development of NiDHD. Objective: To investigate the pathological role of cardiomyocyte enriched pro-apoptotic miR-320 in the development of NiDHD and to determine if therapeutic knockdown of miR-320 can restore impaired cardiac function and angiogenesis in the diabetic heart. Methods and Results: Cardiac tissue were collected from type-2 diabetic individuals undergoing cardiac surgery showed marked upregulation of miR-320, which was associated with downregulation of its direct target pro-survival insulin growth factor-1 (IGF-1) and anti-apoptotic protein Bcl-2. Analysis of cardiac tissue samples collected from type 2 diabetic mice (BKS.Cg-m+/+Leprdb/J) every 4wks, from 8 to 32wks of age showed activation of miR-320 and downregulation of IGF-1 at the later stages of diabetes. To determine if therapeutic knockdown of miR-320 is beneficial, high glucose cultured adult cardiomyocytes were treated with either locked nucleic acid (LNA) anti-precursor (pre)-miR-320 or scrambled (Scr) sequence. Results showed that LNA-anti-pre-320 significantly restored IGF-1 expression and reduced apoptotic cells death (3.1±05 in Scr vs 1.3±0.6 in LNA-anti-pre-320, P<0.01). Finally, to confirm if the effect can be translated in vivo , 24 weeks old type 2 diabetic mice with established systolic dysfunction were injected with LNA-anti-pre-320 once a week for 4wks. Echocardiography confirmed significant restoration of diastolic function and partial restoration of systolic function. Molecular analysis showed marked reduction in miR-320 expression, which was associated with recovery of IGF-1 and Bcl-2. Further, histological analysis confirmed improved angiogenesis and reduced fibrosis in the LNA-anti-pre-320 treated group. Conclusion: miR-320 is a late responding miRNA that aggravates apoptosis and cardiac dysfunction in diabetic heart, and that therapeutic knockdown of miR-320 is beneficial in partially restoring the deteriorated cardiac function.