Remodeling of Purinergic Receptor 2 Signaling in Podocytes In Response to Diabetic Kidney Disease

Abstract

Growing evidence suggests that purinergic signaling undergoes significant changes in the kidney during pathophysiological conditions such as diabetes. The aim of this study was to determine the functional effect of both type 1 diabetes (T1D) and type 2 diabetes (T2D) with diabetic nephropathy (DN) on P2 receptor profile remodeling and purinergic calcium signaling in podocytes. To do this, we used a well-characterized T2DN model, which was compared to non-diabetic control rats (Wistar) and Goto-Kakizaki (GK) rats, which are diabetic but do not develop DN. As a T1D kidney model, we utilized streptozotocin (STZ)-injected Dahl Salt-Sensitive (SS) rats. The ATP-mediated calcium release in podocytes from intact glomeruli with diabetic kidney disease was measured using live confocal calcium imaging in combination with pharmacological inhibitors of P2 receptors. Both type 1 and type 2 diabetes resulted in a significant increase in the ATP-mediated [Ca2+]i flux in podocytes. Pharmacological inhibition of the ATP-mediated response indicated that ionotropic P2X4 and P2X7 are the major receptors contributing to the augmented ATP-mediated intracellular calcium signaling in diabetic podocytes, rather than metabotropic P2Y1, which was the predominant P2 signaling receptor observed in healthy adult Sprague Dawley rats (reported in an earlier study). The mRNA and protein expression profiles of several P2 receptors in the kidney cortex were also measured at different stages of disease. Ionotropic P2X4 and P2X7 receptor expression was elevated in the kidney cortex during early and late stages of T2D, compared to healthy kidneys. A decrease in metabotropic P2Y1 receptor abundance in the diabetic kidneys was also observed. Lastly, podocytes from T2DN rat glomeruli exhibited substantially elevated basal [Ca2+]i levels compared to controls (Wistar and GK). The observed changes in purinergic receptors’ expression and downstream effects may be a major contributor to podocyte loss and kidney injury in diabetes. This purinergic remodeling results in increased basal and ATP-stimulated [Ca2+]i, thereby exacerbating podocyte damage and further aggravating diabetic kidney disease progression.