Altered signaling and regulatory mechanisms of apoptosis in focal and segmental glomerulosclerosis.

Abstract

The purpose of this study was to investigate signaling and regulatory mechanisms of apoptosis in a model of focal and segmental glomerulosclerosis. Sprague-Dawley rats received two doses of puromycin aminonucleoside (PAN) (day 0 and week 3) and a uninephrectomy (PAN model). Apoptosis was detected with the use of the terminal deoxynucleotidyl transferase mediated dUTP nick end labeling technique. Bax, Bcl-2, Fas, and Fas ligand expression was analyzed by competitive reverse transcription-PCR. Bax, Bcl-2, and Fas mRNA were localized by in situ hybridization. Renal function was transiently impaired after the first PAN dose. After the second PAN dose, further progressive renal impairment, tubular atrophy, interstitial fibrosis, and glomerulosclerosis were evident. Eighteen percent of PAN samples demonstrated up to 4 apoptotic cells/50 glomeruli, compared with 7% of sham controls (not significant). No consistent significant change in glomerular Bax, Bcl-2, Fas, and Fas ligand mRNA was evident by reverse transcription-PCR, although focal increases in glomerular Bcl-2 mRNA were demonstrated by in situ hybridization. In the tubulointerstitium, apoptosis was increased from weeks 1 to 12 (P < 0.01 PAN versus sham), correlated to renal function and tubulointerstitial injury (P < 0.01). Total renal Bax, Fas, and Fas ligand mRNA were upregulated in the PAN model, peaking at week 17 (P < 0.01 versus sham), whereas Bcl-2 mRNA was not significantly different in PAN versus sham controls. In situ hybridization in the PAN model demonstrated prominent Bax mRNA in dilated tubules and infiltrating leukocytes. Fas mRNA signal was localized to tubular epithelial cells and leukocytes. The results suggest that altered apoptotic signaling and regulatory mechanisms contribute to the tubulointerstitial injury in this model.