REGULATION OF SERUM PROTEIN COMPOSITION IN NEPHROSIS

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The nephrotic syndrome is characterized by altered glomerular permselectivity causing the urinary loss of proteins of intermediate molecular weight (MW). Although albumin synthesis is increased by over 3 fold, its serum concentration decreases to less than 25% of normal, causing a fall in serum oncotic pressure (pl). In contrast to albumin, the serum concentration of many high MW proteins is increased in nephrosis, helping to defend pl, as well as in rats with hereditary analbuminemia (HA), animals with no significant urinary protein loss. Proteins in intermediate NW (transferrin, gamma globulin and a globulins) are also increased in HA rats, suggesting that reduced serum pl rather than either urinary protein loss or increased albumin synthesis is the stimulus for increased production of both intermediate and high MW proteins. We hypothesize that serum pl regulates the synthesis of a specific array of acute phase reactant proteins , and further that this control mechanism acts at the level of gene transcription. To test the hypothesis we will determine the relationship between pl and the rate of synthesis and catabolism of a group of acute phase reactant proteins of a range of MW's (alpha1AG, alpha1 antitrypsin, transferrin, alpha2 macroglobulin), and determine the hepatic steady state levels and rate of transcription of each species of mRNA in two experimental animal models: 1) Sprague Dawley rats (SD) with the nephrotic syndrome: a model of reduced pl caused by urinary protein loss, and 2) HA rats: a model of reduced pl with no external protein loss. We will further determine whether increasing serum pl to normal in nephrotic rats and rats with HA by the infusion of hetastarch or polyvinylpyrrolodone, suppresses increased synthesis of these proteins and of their mRNA's. Using cultured hepatocytes isolated from normal SD and HA rats, we will determine the relationship between pl and the synthesis of albumin, transferrin, a1AG, a1 antitrypsin, a2 macroglobulin and steady state concentration and rate of transcription of their mRNA's in response to varying concentrations of albumin, PVP and hetastarch in the culture medium. Since we have shown that dietary protein restriction prevents enhanced expression of the albumin gene when serum pl is reduced, we will also determine whether protein restriction modulates the response of other proteins to reduced serum pl. If these studies indicate that serum pl regulates the synthesis of an array of proteins at the level of gene transcription, we will initiate molecular studies to define the factor(s) which control this response.