Giovani B Peres and Yara M Michelacci
The present paper reviews the role of proximal tubular cells in the early stages of diabetic nephropathy. The chronic hyperglycemia that occurs in diabetes mellitus may have different effects on different cells, and some kidney cell types may be injured earlier than others. Recent findings point towards a relevant involvement of proximal tubular cells in the early stages of diabetic nephropathy. As normal urine contains very low amounts of proteins, while proteinuria occurs in kidney diseases, it was believed that the glomerular filtration barrier was capable of preventing the passage of proteins. Nevertheless, recent data indicate that the primary filtrate does contain albumin and other proteins, which possibly are reabsorbed by tubular cells. So, the increased albuminuria that occurs in diabetic nephropathy and other renal diseases could result, at least in their early stages, from defective tubular processing. The participation in this process of the receptors megalin, cubilin, and the newborn Fc receptor (FcRn) is discussed, regarding both protein transcytosis and lysosomal digestion. The processing and urinary excretions of sulfated polysaccharides are also briefly considered.