Molecular mechanisms linking proteinuria and sodium retention

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The clinical association between protein loss in the urine and retention of salt, resulting in high blood pressure and progressive decline in kidney function, is well known. Under normal conditions, the kidneys filter 180 litres of water and reabsorb 1.7 kg of salt per day, a function which is principally performed by the kidney tubules in the kidney. Similarly the kidney tubule cells reabsorb and break down up to 3 grams of albumin per day. In the past, it has been considered that excessive protein loss in the urine is primarily due to problems in the filtering units of the kidneys, rather than due to abnormalities in the reabsorption of protein in the kidney tubules. However, we consider that common abnormalities in the processes within the kidney tubules that regulate both the reabsorption of salt and the excretion of acid may result in concomitant high blood pressure and increased protein loss in the kidney. Thus the overall aim of the project is to investigate the interrelationship between protein reabsorption and catabolism and Na+ reabsorption in the human kidney tubule. The project uses the combined methods of cultured human kidney tubules, biochemical and molecular biology techniques which are unavailable in other laboratories in Australia (and internationally). This project will comprehensively characterise the mechanisms of protein uptake and salt reabsorption in human kidney tubule cells when exposed to both normal and high concentrations of protein. The exact nature of the interaction of protein uptake with salt reabsorption and hence high blood pressure will be determined. As both hypertension and persistent proteinuria are the most important predictors of tubulointerstitial pathology and progressive decline in renal function in almost all renal disease, the understanding of the precise interaction between these two factors is essential in the design of renoprotective therapies.