Serum and glucocorticoid-regulated kinase 1 regulates transforming growth factor β1-connective tissue growth factor pathway in chronic rhinosinusitis.

Purpose: Serum/glucocorticoid-regulated kinase 1 (SGK1) has been identified as a crucial regulator in fibrotic disorders. Herein, we explored SGK1 role in tissue remodeling of chronic rhinosinusitis (CRS).
Methods: Lentivirus was employed to generate an SGK1-overexpressing human bronchial epithelial cell (16HBE) line. To screen SGK1 downstream genes, RNA sequencing was performed on SGK1-overexpressing and control cell lines. To determine protein and gene expression levels, immunohistochemistry, western blotting, and quantitative real-time polymerase chain reaction were employed. Correlation analysis was performed using mRNA expression levels of SGK1, transforming growth factor β1 (TGF-β1), and connective tissue growth factor (CTGF) derived from CRS mucosal tissue and GEO database. Gene set enrichment analysis was conducted using gene sets from Molecular Signatures Database. The severity of symptoms in CRS patients was assessed using the 22-Item Sinonasal Outcome Test.
Results: SGK1 overexpression significantly increased the expression of connective tissue growth factor (CTGF) in 16HBE cells (P < 0.01). Consistently, CTGF protein level was considerably greater in mucosal tissue of CRS without nasal polyps (CRSsNP) than in CRS with nasal polyps (CRSwNP) (P < 0.05) or in control subjects (P < 0.01). TGF-β1 protein level was higher in mucosal tissue of CRSsNP patients than in CRSwNP patients (P < 0.001) or in the control group (P < 0.01). mRNA levels of SGK1 and CTGF (P < 0.05, r = 0.668; P = 0.001, r = 0.630), TGF-β1 and CTGF (P < 0.05, r = 0.560; P < 0.05, r = 0.420), as well as SGK1 and TGF-β1(P < 0.05, r = 0.612; P < 0.05, r = 0.524) were significantly correlated in CRS mucosal tissue and GSE36830 dataset, respectively. TGF-β1-induced upregulated genes were significantly enriched in SGK1 overexpression group. In vitro assays, TGF-β1 promoted SGK1 and CTGF expression in a concentration- and time-dependent manner. Administrating an SGK1 inhibitor, GSK650394, significantly inhibited TGF-β1-induced CTGF expression in 16HBE and dispersed primary nasal polyp cells.
Conclusions: TGF-β1 stimulation significantly increases SGK1 and CTGF expression. By regulating TGF-β1-CTGF pathway, SGK1 may participate in tissue remodeling in the pathological mechanism of CRS.
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