92: A novel epigenetic mechanism underlying maternal diabetes-suppressed mitochondrial fusion in congenital heart disease

Abstract

Maternal diabetes, induces congenital heart defects (CHDs), the most common structural birth defects in human. microRNAs (miRNA) are non-coding RNAs, which represses gene expression by degrading mRNA and/or inhibiting translation. Previous studies indicate that miRNAs are potentially involved in the pathogenesis of heart defects in diabetic pregnancy. The present study investigates the role of miR-140 in maternal diabetics-induced CHDs by examining its impact on mitochondrial dynamics. Type 1 diabetes in mir140 heterozygous (miR-140+/-) female mice was induced by streptozotocin (STZ) injections. Nondiabetic miR-140+/- males mated with nondiabetic and diabetic miR-140+/-to generate hearts from embryonic day 12.5 (E12.5) and E17.5 embryos for biochemical assessment and morphological examination of CHDs, respectively. Cardiomyocytes isolated from E12.5 hearts were treated with normal (5 mM glucose) and high glucose (25 mM glucose). miR-140 expression was significantly upregulated by maternal diabetes in vivo and high glucose in vitro. miR-140 homozygous deletion significantly reduced the CHD rate from 29.1% in Wild-type (WT) embryos to 4.4% in diabetic pregnancy. miR-140 heterozygous deletion slightly reduced the CHD incidence. Maternal diabetes suppressed mitofusin 1 (Mfn1) gene expression leading to impaired mitochondrial fusion. miR-140 targeted the Mfn1 mRNA resulting in its degradation. miR-140 homozygous deletion rescued Mfn1 expression in cardiomyocytes of E12.5 hearts exposed to maternal diabetes. Mitochondrial marker Tom20 immunofluorescence staining and mitochondrial time-lapse high resolution confocal microscopy revealed that maternal diabetes induced mitochondrial fragmentation due to mitochondrial fusion impairment in embryonic cardiomyocytes. Our study demonstrates that miR-140 is critically involved in the pathogenesis of maternal diabetes-induced CHDs. miR-140 suppresses Mfn1 expression leading to impaired mitochondrial fusion. The miR-140-Mfn1-impaired mitochondrial fusion axis mediates the teratogenic effect of maternal diabetes.