Role of Gq signaling in promoting podocyte injury in diabetes mellitus: Diabetic nephropathy (DN) is the most common cause of end stage renal disease (ESRD) in developed countries. Accumulating evidence indicates that a reduced number of podocytes are a characteristic feature of both animals and humans with diabetic kidney disease. Because podocytes are terminally differentiated cells with little potential for proliferation, podocytes that are lost cannot be effectively replaced. In turn, sufficient loss of podocytes leads to instability of the tuft and glomerulosclerosis. While the etiology of podocyte loss in DN is complex, a large body of evidence suggests that cell surface G protein coupled receptors (GPCRs) play an important, injury promoting role in DN including receptors for angiotensin II (ANGII), thromboxanes (TP), prostaglandins (EP1) and endothelins (ETA). Indeed, these GPCRs are expressed by glomerular podocytes and several of these receptor systems have been shown to promote podocyte injury both in vitro and in vivo. A common feature of these injury-promoting GPCRs is activation of Gq a-subunits (Gq). Activation of Gq and its downstream effectors might, therefore, be a final common signaling pathway that synergizes with other signaling cascades to promote podocyte injury in DN. In this regard, we found that Gq dependent CN activation promotes podocyte apoptosis, in part, by induction of the CN responsive gene COX2. Based on these observations, we hypothesized that Gq-coupled signaling cascades are important mediators of podocyte injury in DN by promoting podocyte apoptosis. To investigate this hypothesis, 3 specific aims are proposed.
In specific aim #1, we have created transgenic (TG) mice that express either a constitutively activate Gq a-subunit (GqQ>L) or a Gq inhibitor (Gqi) specifically in glomerular podocytes using an inducible promoter system. We will use GqQ>L or Gqi TG mice to determine if either activating or inhibiting Gq, respectively, specifically in glomerular podocytes modulates the severity of kidney disease in a genetic model of type 1 diabetes (Akita mice).
In specific aim #2, we will determine the signaling cascades activated by Gq that promote podocyte apoptosis in an immortalized podocyte cell line as well as in vivo. Lastly, in specific aim #3, we will create mice lacking COX2 specifically in podocytes and then determine the effects of podocyte specific COX2 deletion on podocyte apoptosis and glomerular damage in Akita mice. These studies will test the utility of inhibiting Gq signaling as a potential treatment strategy in DN and the role of podocyte COX2 expression in disease pathogenesis. If successful, the results may suggest novel therapeutic strategies for treating diabetic kidney disease.
Diabetic kidney disease is the most common cause of end-stage renal disease the United States of America. As a result, diabetic nephropathy (DN) is a significant clinical and economic burden to the health- care system. The goal of this grant application is to determine if multiple hormonal systems implicated in the pathogenesis of DN activate a final common signaling pathway that promotes kidney damage. If the studies are successful, this signaling pathway would be an important therapeutic target for the development of drugs to prevent diabetic kidney disease.
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