Sublytic C5b-9 induces S100A8/A9 expression via SMYD4-dependent SOX7-K159 methylation in the glomerular mesangial cells of Thy-1 nephritis rats

Rat Thy-1 nephritis (Thy-1 N) is a model for human mesangioproliferative glomerulonephritis (MsPGN). Although sublytic C5b-9 has been reported to affect pro-inflammatory cytokine expression in glomerular mesangial cells (GMCs), the induction of other pro-inflammatory mediators remains unclear. In this study, we demonstrated that SET and MYND domain-containing protein 4 (SMYD4), SRY-related HMG-box gene 7 (SOX7), S100 calcium-binding protein A8 (S100A8), and S100A9 were overexpressed in the renal tissues of Thy-1 N rats and in the GMCs stimulated by sublytic C5b-9. Mechanistically, SOX7 triggered S100A8/A9 gene transcription through binding to S100A8 promoter (+21 to + 31 nt) and S100A9 promoter (-1698 to -1688 nt), and SMYD4 mediated SOX7 methylation at K159, a new methylation site, enhancing SOX7 function and S100A8/A9 transcription. The animal experiments confirmed that silencing SMYD4, SOX7, or S100A8/A9 gene could inhibit GMC proliferation, extracellular matrix accumulation, and proteinuria in Thy-1 N rats. Moreover, silencing SMYD4 gene could inhibit renal SOX7-K159me2/3, and silencing SMYD4 or SOX7 gene could inhibit renal S100A8/A9 production. Meanwhile, the SOX7-K159 methylation inhibitory peptide exhibited the similar intervention effects as SMYD4 and SOX7 knockdown in Thy-1 N rats. In addition, the expression levels of SMYD4, SOX7, SOX7-K159me2/3, and S100A8/A9 all increased in the renal tissues of MsPGN patients. Collectively, our findings suggest that SMYD4-mediated SOX7-K159me2/3 partly contributes to sublytic C5b-9-induced S100A8/A9 expression in Thy-1 N rats, which provides a novel insight into human MsPGN pathogenesis.