Accumulating evidence suggests that the generation of complement activation products from filtered
complement components in urine with nonselective
proteinuria leads to tubulointerstitial disease, resulting in progressive loss of renal function. To elucidate the role of
C5b-9 in
complement-mediated effects on renal tubular cells exposed to proteinuric urine, equivalent levels of
proteinuria were induced (using the
aminonucleoside of
puromycin) in normocomplementemic and genetically C6-deficient piebald viral glaxo (PVG) rats. Semiquantitative histologic analysis revealed that
complement-sufficient animals developed more severe tubulointerstitial disease than did C6-deficient rats. Amelioration of tubulointerstitial damage in C6-deficient animals was confirmed by studies with three independent markers of tubular damage, i.e.,
vimentin,
osteopontin, and
proliferating cell nuclear antigen. More tubular epithelial cells expressed
osteopontin (an early marker of tubular injury) in normocomplementemic rats, compared with C6-deficient rats, at both days 7 and 12. Staining of
vimentin in the tubules, near areas of tubular damage, was increased in normocomplementemic rats at day 12, and more
proliferating cell nuclear antigen-positive tubular cells were observed at day 12 in
complement-sufficient animals. The tubulointerstitial damage in
complement-sufficient rats was also associated with greater accumulation of extracellular matrix (
fibronectin) at day 12. These studies document for the first time an important role for C6, and therefore
C5b-9, in the pathogenesis of nonimmunologic tubulointerstitial injury induced by
proteinuria. These findings suggest that
C5b-9 formation resulting from
proteinuria contributes to the loss of nephron function by damaging the tubulointerstitium and that prevention of
C5b-9 formation in tubules could slow the deterioration of renal function.