Mechanistic studies on the repression of cellular reaction to hypoxia as cause for chronic complications in diabetes

Abstract: Diabetes Mellitus is an ongoing epidemic, causing individual suffering as well as constituting an enormous burden to society and healthcare systems globally. Much of diabetes-associated morbidity and mortality are caused by chronic diabetes complications, for which there today is no specific treatment due to an incomplete understanding of the underlying disease mechanisms. In the last two decades, the dysregulated cellular response to hypoxia has emerged as a pathogenic mechanism driving the development of diabetes complications. This work has therefore aimed to investigate the dysregulated hypoxic response further in the setting of diabetes microvascular complications. In paper I, we have investigated the influence of the HIF-1A Pro582Ser polymorphism on the risk of developing diabetic retinopathy. We found that the HIF-1A Pro582Ser polymorphism confers a 95% risk reduction of developing severe diabetic retinopathy even when adjusting for traditional risk factors such as diabetes duration, hyperglycemia and hypertension. Moreover, we have further characterized the biological effects of this polymorphism and found that it increased HIF-1α transcriptional activity over a large spectrum of glucose concentrations despite being sensitive to hyperglycemia-induced degradation. Paper II explores the role played by a dysregulated HIF-1α in diabetic nephropathy and its interplay with oxidative stress, which is known to be an important pathogenic factor in the development of kidney injury in diabetes. We found that the repressed HIF-1α signaling in diabetic kidney contributes to excess ROS production through increased mitochondrial respiration. Pharmacologic or genetic approaches to restore HIF-1α function attenuated ROS overproduction despite persistent hyperglycemia which prevented kidney injury and improved renal function. In paper III, we have explored the regulation and function of the hypoxamiR-210 in diabetic wound healing. We found that diabetes repressed miR-210 in vitro and in vivo (human and mice wounds), which is pathogenic since local reconstitution of miR-210 improved wound healing in diabetic mice. Reconstitution of miR-210 resulted in restored cellular metabolism secondary to a decrease in mitochondrial respiration and ROS production and increased glycolysis, which improved cellular migration. In paper IV, we investigated miR-34a in the setting of diabetic wound healing. We found that it was hypoxia-responsive in macrophages and keratinocytes, and overall repressed by high glucose levels both in vitro and in vivo (diabetic wounds). This repression was p53-independent and mediated on the transcriptional level. Local reconstitution of miR-34a in the wound resulted in improved wound healing in a diabetic mice model.