Autophagy and its Regulation in Diabetic Embryopathy

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Pregestational diabetes induces neural tube defects (NTDs) in the offspring. Even under the best prenatal care, diabetic women are still three- to four-times more likely to have a child with birth defects than nondiabetic women. Diabetes-induced NTDs are significant public health problems for both the mother and her child. Yet, the molecular mechanism underlying the teratogenicity of maternal diabetes is still unclear. We recently discovered a microRNA-mediated stress pathway in maternal diabetes-induced autophagy impairment leading to NTDs. Prolonged unfolded protein response (UPR) and endoplasmic reticulum (ER) stress play critical roles in maternal diabetes-induced NTDs. The molecular link between prolonged UPR and autophagy impairment is elusive. We found that silencing the major UPR sensor, IRE1α, triggered de novo autophagosome formation, and deleting the Ire1a gene in the developing neuroepithelium rescued autophagy thereby preventing NTD in diabetic pregnancy. Therefore, we hypothesize that maternal diabetes triggers IRE1α activation through ASK1 and the ASK1-IRE1α signal inhibits autophagy in the developing neuroepithelium through IRE1α RNase activity by producing XBP1s and degrading miR-17, which targets Txnip. XBP1s, the miR-17-Txnip circuit, and their crosstalk mediate the teratogenicity of maternal diabetes leading to NTD formation. To test our hypothesis, we proposed three Specific Aims. Aim 1 will determine whether ASK1-activated IRE1α is responsible for autophagy impairment in diabetic embryopathy. We hypothesize that maternal diabetes-induced ASK1 activation triggers IRE1α activation via direct phosphorylation and suppresses ER-associated degradation (ERAD) of unfolded proteins. We further posit that the ASK1-IRE1α signal suppresses autophagy leading to NTD formation. Aim 2 will investigate the potential crosstalk between XBP1s and miR-17, and their roles in maternal diabetes-induced autophagy impairment and NTD formation. We hypothesize that IRE1α cleaves XBP1 mRNA to form XBP1s and represses miR-17 expression, collectively resulting in altered ATG expression, and that XBP1s and miR-17 are reciprocally regulated, leading to autophagy impairment in the developing neuroepithelium and NTDs in diabetic pregnancy. Aim 3 will determine whether Txnip is a target gene of the IRE1α-miR-17 pathway and participates in autophagy inhibition in diabetic embryopathy. Our hypothesis is that Txnip, a downstream effector of the IRE1α-miR-17 pathway, represses autophagy by binding to and thus disabling the ability of ATG4 in processing LC3-I in to LC3-II, an essential step for autophagosome formation, leading to cellular imbalance and NTDs in diabetic pregnancy.