Hemopexin Modulates Expression of Complement Regulatory Proteins in Rat Glomeruli

In systemic hemolysis and in hematuric forms of kidney injury, the major heme scavenging protein, hemopexin (HPX), becomes depleted, and the glomerular microvasculature (glomeruli) is exposed to high concentrations of unbound heme, which, in addition to causing oxidative injury, can activate complement cascades; thus, compounding extent of injury. It is unknown whether unbound heme can also activate specific complement regulatory proteins that could defend against complement-dependent injury. Isolated rat glomeruli were incubated in media supplemented with HPX-deficient (HPX^-) or HPX-containing (HPX⁺) sera as a means of achieving different degrees of heme partitioning between incubation media and glomerular cells. Expression of heme oxygenase (HO)-1 and of the complement activation inhibitors, decay-accelerating factor (DAF), CD59, and complement receptor-related gene Y (Crry), was assessed by western blot analysis. Expression of HO-1 and of the GPI-anchored DAF and CD59 proteins increased in isolated glomeruli incubated with HPX^- sera with no effect on Crry expression. Exogenous heme (hemin) did not further induce DAF but increased Crry expression. HPX modulates heme-mediated induction of complement activation controllers in glomeruli. This effect could be of translational relevance in glomerular injury associated with hematuria.