Reduction in glomerular heparan sulfate correlates with complement deposition and albuminuria in active Heymann nephritis

Abstract

In a time-study of active Heymann nephritis, the expression of agrin, the main heparan sulfate proteoglycan in the glomerular basement membrane, was analyzed in relation to deposition of IgG and complement in the glomerular capillary wall and the development of albuminuria. Binding of IgG autoantibodies to the glomerular capillary wall could be detected from 2 wk onward, followed by activation of complement after 6 wk. Progressive albuminuria developed from 6 wk onward to a level of 274 ± 68 mg/18 h at week 12. The staining intensity for the agrin core protein decreased slightly, and the staining intensity for the heparan sulfate stubs that were still attached to the core protein after heparitinase digestion remained normal. From week 6 onward, however, a progressive decrease was seen in the staining of two monoclonal antibodies (mAb) directed against different epitopes on the heparan sulfate polysaccharide side chain of agrin (to 35 and 30% of the control level, respectively, at week 12, both mAb P = 0.016). Moreover, albuminuria was inversely correlated with heparan sulfate staining as revealed by these antibodies (r(s) = -0.82 and r(s) = -0.75, respectively, both mAb P < 0.0001). This decrease in heparan sulfate staining was due to a progressive reduction of glomerular heparan sulfate content to 46 and 32% of control level at week 10 and week 12 of the disease, respectively, as measured biochemically. It is speculated that the observed decrease in glomerular heparan sulfate in active Heymann nephritis is due to complement- mediated cleavage of heparan sulfate, resulting in an increased permeability of the glomerular basement membrane to macromolecules.