The contribution of podocytes to chronic allograft nephropathy

Progressive proteinuria and glomerulosclerosis characterize chronic allograft nephropathy. However, the causes are not fully elucidated. Podocytes function to prevent proteinuria; injury to this glomerular cell leads to glomerulosclerosis. The potential role of podocytes in the failing transplanted kidney is unknown. A rat model of kidney transplantation, characterized by proteinuria and glomerulosclerosis, was utilized to examine the potential role of podocytes.

Archival tissue was examined from allografts (Dark Agouti kidneys transplanted into operationally tolerant Albino Surgery rats), isografts (Dark Agouti) and controls (Dark Agouti: age-matched or after unilateral nephrectomy). The number of podocytes (by WT-1 staining) as well as the podocyte proteins podocin, nephrin and synaptopodin (by immunostaining) were measured at days 0, 2, 6 and at 6 months after transplantation. Changes in these parameters were compared between groups and correlated with urinary protein excretion.

At 6 months, podocyte number was reduced in allografted kidneys, accompanied by a decrease in nephrin and synaptopodin, but not podocin staining. Remnant kidneys in the uninephrectomized rats also showed a decreased podocyte number but no change in podocyte protein staining. Podocyte loss in allografts was established on day 6, whereas a decrease in nephrin and synaptopodin was not evident until 6 months. In contrast, podocyte number and protein staining was decreased but not significantly so in remnant and isografted kidneys.

A decrease in the slit diaphragm proteins, nephrin and synaptopodin, is a component of chronic allograft pathology.