Association between Lyn tyrosine kinase and renal injury in patients with systemic lupus erythematosus.

BACKGROUND: To investigate protein kinase Lyn expression in patients with systemic lupus erythematosus (SLE) or lupus nephritis (LN) and its association with clinical markers. METHODS: Sixty-one inpatients with SLE were categorized into low SLE Disease Activity Index (SLEDAI) group (SLEDAI < 6, n = 32) and high SLEDAI group (SLEDAI ≥ 6, n = 29). Thirty volunteers served as healthy controls (HC). SLE patients were further divided into non-LN (n = 31) and LN (n = 30) groups. Lyn mRNA and protein levels in peripheral blood mononuclear cells (PBMCs) were analyzed and correlations between Lyn expression and SLEDAI, clinical parameters were examined. Renal biopsies from LN (n = 24) were collected for immunohistochemical analysis of Lyn level. RESULTS: Compared to the HC group, SLE patients exhibited a decline in both Lyn mRNA and protein expression in PBMCs, with significant downregulation in the high SLEDAI group versus the low SLEDAI group and a notable reduction in the LN group relative to the non-LN group. Lyn levels negatively correlated with SLEDAI and 24-hour urine protein (24h-U-pro) while positively correlated with serum C3, C4, hemoglobin, and albumin. Multiple linear regression indicated an independent association between Lyn mRNA and SLEDAI. ROC curve analysis suggested Lyn as a reliable predictor for SLE, LN, and lupus activity, with histopathological examination revealing that decreased Lyn expression correlated negatively with the renal pathology index (r = -0.8016, p = 0.0016). CONCLUSIONS: The protein kinase Lyn was inversely associated with disease activity, albuminuria level and renal pathology activity in SLE and may be a promising biomarker for assessing LN disease activity.