Interaction of complement and clusterin in renal injury.

Clusterin is a heterodimeric glycoprotein that has been associated with such diverse biologic functions as reproduction, cell regression, cell aggregation, and regulation of the cytolytic activity of the membrane attack complex of complement. Clusterin is a component of glomerular immune deposits in the kidney, and increased clusterin expression occurs in a number of renal injury states. To further explore the interaction between clusterin and complement, the requirement for an intact complement system for renal clusterin induction in an acute (folic acid nephropathy) and a chronic (subtotal renal ablation) model of renal injury was examined. After it was first demonstrated that folic acid increased renal clusterin mRNA in the rat, a species in which renal clusterin was highly inducible by other stimuli, the effects of folic acid (250 mg/kg ip) on clusterin mRNA and immunoreactivity were examined in mice sufficient and deficient for the fifth component of complement. Similar increases in clusterin mRNA and immunoreactivity were seen in both the C5-sufficient and C5-deficient mice compared with their respective vehicle-injected control groups. Renal clusterin mRNA was also increased to a similar extent in the remaining kidney of both C5-sufficient and C5-deficient mice 10 days after subtotal nephrectomy. In conclusion, the induction of clusterin after folic acid administration or subtotal nephrectomy was independent of the presence of an intact complement system, because similar increases in clusterin expression were observed in C5-sufficient and C5-deficient mice.