MOLECULAR MECHANISMS IN HEREDITARY NEPHRITIS

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Alport Syndrome is a hereditary disorder characterized by progressive nephropathy which is frequently associated with sensorineural deafness and ocular abnormalities. The nephropathy has been linked to a structural abnormality in the glomerular basement membrane (GBM) which is caused by mutations in the gene encoding the alpha3, alpha4 and alpha 5 chains of type IV collagen. The most common form is X-linked, in which over 200 mutations have been found in the COL4A5 gene encoding the alpha5 chain. These mutations interfere with the formation of the alpha3(IV)/alpha4(IV)/alpha5(IV) supramolecular network of type IV collagen. Most male patients have near normal kidney function at birth, which deteriorates over time leading to end-stage renal disease by mechanisms that are not understood. The central thrust of this proposal is to test the hypothesis that the progression to end-stage renal disease in X -linked hereditary nephritis evolves from a congenital malformation of the glomerular basement membrane (GBM) which involves COL4A5 mutations that arrest a developmental switch from the immature alpha1(IV)/alpha2(IV) network to the nature alpha3(IV)/alpha4(IV)/alpha5(IV) network, and the persistence of this immature network predisposes the GBM to proteolytic degradation. The cornerstone of the research plan is a use of the canine X-linked model of the human disease in which the COL4A5 gene mutation is a premature stop codon. The specific aims are: Aim 1: Determine the nature and timing of the switch from immature to mature GBM in normal dog kidney in comparison to affected male dogs. Aim 2: Determine which glomerular cells synthesize the alpha3(IV), alpha4(IV) chains. Aim 3: Examine the relationship between the expression of the alpha3(IV), alpha4(IV) and alpha5(IV) chains. Aim 4: Determine the temporal relationship at both the message nd protein levels of the expression of the alpha1(IV)-alpha6(IV) chains in normal dogs compared to affected male dogs during progression of their disease. Aim 5: Determine the susceptibility of type IV collage of GBM to proteolytic degradation in normal and affected male dogs. The achievement of these aims requires application of the techniques of molecular biology, biochemistry, immunochemistry and cell biology. It is anticipated that the achievement of the aims will yield new insights into the mechanisms underlying the pathogenesis of Alport Syndrome. An understanding of these mechanisms is fundamental to the development of therapeutic measures to correct the disorder by gene therapy or to delay progression to end stage renal disease.