Expression and function of the growth hormone receptor (GHR) is essential for the action of pituitary growth hormone (GH). The GH/IGF-1 axis plays a critical permissive role in the pathogenesis of chronic microvascular complications of DM. A direct role for GH/GHR in the pathogenesis of DM nephropathy is supported by studies using GH and GH-antagonist transgenic mice, total GHR knockout mice, and pharmacological blockade of GHR using pegvisomant. These studies demonstrate that absence of functional GHR confers a protective effect against DM nephropathy. Our laboratory is focused on understanding the molecular and cellular basis for GH's actions in the pathogenesis of DM nephropathy and the identification of novel therapeutic targets that will alter the outcome of diabetic kidney disease. Our recent studies have established the molecular mechanisms resulting in dysregulation of the GHR gene in DM. We have identified fatty acids (FA) as a specific metabolic signal that transduces the effect of DM on GHR gene expression and have identified the glomerular podocyte as potential target of GH action in the kidney. We propose to expand on these preliminary observations by the pursuing the following SPECIFIC AIMS:
Specific Aim 1 tests the hypothesis that FAs modulate the expression of the GHR gene expression in DM in a tissue-specific manner. The proposed experimental paradigm will identify and characterize a potentially novel trans-acting factor(s) that plays a role in the transduction of the effect of FA on GHR expression. We also propose to test the sub- hypothesis that FAs transduce their effects on GHR expression via Toll receptors and increase in oxidative stress.
Specific Aim 2 tests the hypothesis that tissue-specific dysregulation of GHR gene expression with abrogation of hepatic GHR expression and concomitant retention of expression of GHR in the kidney plays a crucial role in the pathogenesis of renal complications of DM. This hypothesis will be tested by analyzing the effect of podocyte- targeted deletion of the GHR gene on DM nephropathy.
