The mechanism by which anti-DNA antibodies mediate lupus nephritis has yet to be conclusively determined. Previously, we found that treatment of mesangial cells with anti-DNA antibodies induced high expression of neutrophil gelatinase-associated lipocalin (NGAL), an iron-binding protein up-regulated in response to kidney injury. We undertook this study to determine whether NGAL is instrumental in the pathogenesis of nephritis, is induced as part of repair, or is irrelevant to damage/repair pathways.
To investigate the role of NGAL in antibody-mediated nephritis, we induced nephrotoxic nephritis by passive antibody transfer to 129/SyJ and C57BL/6 mice. To determine if NGAL up-regulation is instrumental, we compared the severity of renal damage in NGAL wild-type mice and NGAL-knockout mice following induction of nephrotoxic nephritis.
We found that kidney NGAL expression, as well as urine NGAL levels, were significantly increased in mice with nephrotoxic nephritis as compared to control-injected mice. Tight correlations were observed between NGAL expression, renal histopathology, and urine NGAL excretion. NGAL-knockout mice had attenuated proteinuria and improved renal histopathology compared to wild-type mice. Similarly, following nephritis induction, NGAL injection significantly exacerbated nephritis and decreased survival. NGAL induced apoptosis via caspase 3 activation and up-regulated inflammatory gene expression in kidney cells in vitro and when injected in vivo.
We conclude that kidney binding of pathogenic antibodies stimulates local expression of NGAL, which plays a crucial role in the pathogenesis of nephritis via promotion of inflammation and apoptosis. NGAL blockade may be a novel therapeutic approach for the treatment of nephritis mediated by pathogenic antibodies, including anti-glomerular basement membrane disease and lupus nephritis.