Although growth retardation is a serious complication in children with chronic renal failure (CRF), its pathogenesis is poorly understood. The long-term goal of this research is to develop therapeutic strategies for the prevention and treatment of growth retardation in children with CRF based on understanding of its molecular pathophysiology. Using a primary culture of tibial epiphyseal chondrocytes in a rat model of growth retardation in CRF, growth hormone (GH) and insulin-like growth factor(IGF)-I resistance in cellular growth responses have been demonstrated. Two specific molecular defects in the GH-IGF-I axis have been identified in CRF chondrocytes. Growth hormone receptor(GHR) mRNA (Northern blot) and protein (immunoblot) are both decreased in CRF chondrocytes and may account for GH resistance. Intracellular phosphatidyl-inositol(PI) 3 kinase protein (85 kDa subunit) is decreased in CRF chondrocytes and may account for IGF-I resistance. Mechanisms underlying these molecular abnormalities will be studied in CRF. Experiments will be designed to test the roles of elevated GH and adrenal glucorticoids as well as 1,25 vitamin D3 deficiency in the pathogenesis of the GH-IGF-I defects in CRF. The hypothesis, that these molecular defects in GH-IGF-I axis are important in the pathogenesis of GH, IGF-I resistance and growth retardation in CRF chondrocytes, will be tested. The role of the local GH-IGF-I axis in CRF chondrocytes will be examined by measuring IGF-I mRNA generation with GH stimulation as well as growth responses with GH and IGF-I antibody co-incubation in both CRF and control chondrocytes. The effects of specific inhibition of PI3 kinase (by wortmannin) on growth response and IGF-I sensitivity will be examined in normal chondrocytes. The local role of GH-IGF-I axis, in the face of these dual molecular defects in CRF, will be integrated at molecular and autocrine/paracrine levels. Finally in vitro gene transfer studies using fusion genes of GHR (and PI3 kinase) and a reporter gene with a lipofectin system will be performed to examine if normalization of these molecular abnormalities will lead to correction of GH, IGF-I resistance, and growth retardation in CRF chondrocytes.
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