This study discusses the critical role of the
metalloproteinase meprinbeta in the progression of
glomerulonephritis. Using a microarray technique, the gene expression profiles in glomeruli isolated from high serum
IgA (HIGA) mice with a purity of 97% or greater were examined. HIGA mice are a valid model of human
IgA nephropathy (IgAN), with the typical pathological features of this condition, including a consistently high serum
IgA level as well as dominant mesangial
IgA deposition and mesangial enlargement. Among the many upregulated/downregulated genes after the development of IgAN, the downregulation of meprinbeta was intriguing. The expression level of the meprinbeta gene at 40 weeks of age was 52% of that observed at 8 weeks of age (prior to the development of IgAN), although in the control BALB/c mice, a 2.19-fold elevation was seen. These results were also confirmed by semi-quantitative RT-PCR and immunostaining analyses. As meprinbeta is a subunit of
metalloproteinase meprins (
meprin A,
meprin B) and meprins are capable of proteolytically degrading extracellular matrix (ECM) components and proteolytically processing bioactive
peptides, the downregulation of meprinbeta may contribute to the progression of
glomerulonephritis and the eventual glomerular
scarring. This working hypothesis was examined using an in vivo meprinbeta inhibition study. The inhibition of meprins by
actinonin exacerbated some parameters of renal injury in mice afflicted with anti-glomerular basement membrane (
anti-GBM) antibody-associated
nephritis. These in vitro and in vivo results suggest that meprinbeta may play a protective role against the progression of renal injury through the degradation of ECM and bioactive
peptides.