Spleen tyrosine kinase promotes acute neutrophil-mediated glomerular injury via activation of JNK and p38 MAPK in rat nephrotoxic serum nephritis.

Glomerular antibody deposition induces acute neutrophil-mediated glomerular injury via activation of c-Jun amino terminal kinase (JNK) and p38 mitogen-activated protein kinase (MAPK). However, the link between antibody deposition and activation of JNK/p38 MAPK signalling is unclear. This study tested the postulate that spleen tyrosine kinase (Syk), which is activated via Fcγ-receptor ligation, is required for activation of JNK and p38 signalling and acute neutrophil-mediated glomerular injury. We used a Syk inhibitor (SYKi) in rat nephrotoxic serum nephritis (NTN) in which neutrophil-mediated glomerular injury is dependent upon JNK and p38 signalling. SYKi or vehicle treatment of Sprague-Dawley rats began 30 min before administration of anti-GBM serum with rats killed 3 or 24 h later. Immunostaining identified de novo glomerular Syk activation (p-Tyr 525/526) in untreated NTN, being most prominent in neutrophils. Vehicle and untreated NTN exhibited heavy proteinuria and glomerular thrombosis at 24 h with P-selectin and fibrin immunostaining within capillaries, glomerular macrophage and T cell infiltration, activation of JNK and p38 MAPK signalling, and upregulation of glomerular mRNA levels of pro-inflammatory molecules (TNF-α, NOS2, MMP-12 and CCL2). In contrast, SYKi treatment provided complete protection from proteinuria, with a profound reduction in glomerular thrombosis and immunostaining for P-selectin and fibrin, and a substantial reduction in glomerular mRNA levels of pro-inflammatory molecules. SYKi treatment also reduced the acute glomerular neutrophil influx and pro-inflammatory response at 3 h in NTN. These protective effects were associated with a significant reduction in glomerular JNK and p38 MAPK activation. In addition, activation of Syk, JNK and p38 was identified in human biopsy samples of acute crescentic glomerulonephritis. In conclusion, this study demonstrates that Syk signalling is required for JNK and p38 MAPK signalling and acute neutrophil-dependent glomerular injury in rat NTN. These findings identify Syk as a potential therapeutic target in antibody-dependent kidney disease.