Background PPAR-gamma is an essential transcription factor that participates in the regulation of lipogenesis, whereas it also exerts significant anti-inflammatory actions. Reduced expression of PPAR-g has been described in human autoimmune diseases that are characterized by inflammatory damage of epithelial cells (e.g. ulcerative colitis, primary biliary cirrhosis). Primary Sjogren’s syndrome (SS) is characterized by chronic inflammatory lesions of epithelial tissues and experimental evidence has indicated the occurrence of chronic intrinsic activation of salivary gland epithelial cells (SGEC). Thus, SGEC are probably both the target and the inducer of inflammatory responses.
Objectives To investigate the constitutive expression of PPAR-g in cultured non-neoplastic SGEC lines from SS patients and non-SS controls, as well as to define potential cellular activators that affect PPAR-g expression.
Methods Total RNA was isolated from long-term cultured non-neoplastic SGEC and from peripheral blood mononuclear cells (PBMC) of 19 SS patients and 11 non-SS disease controls. The expression of PPAR-g was studied by Real-time PCR with primers specific for PPAR-g and the reporter gene HPRT1 and analyzed by the ddCt method. The PPAR-g protein expression was examined by immunoblotting of cellular extracts. To evaluate the effect of epithelial activation in the mRNA expression of PPAR-g, SGEC from non-SS controls were stimulated with specific ligands of TLR-3 (Polyinosinic-polycytidylic acid, PolyI:C, 5μg/ml), TLR-4 (lipopolysaccharide, LPS, 1μg/ml) receptor and the cytokines IFN-gamma (500U/ml) and IL-1β (10ng/ml).
Results The constitutive PPAR-g mRNA and protein expression was significantly reduced in the SGEC from SS patients, compared to controls (p=0.0002). In contrast, no difference was found in PPAR-g expression in PBMC between patients and controls. The activation of cultured SGEC by stimulation with PolyI:C, LPS, IFN-g and IL-1β resulted in significant down-regulation of PPAR-g mRNA expression (in all cases; by≈80-85% at 12 hours, p<0.05).
Conclusions Our results indicate that PPAR-g expression in human SGEC is significantly reduced following activation via TLRs and the pro-inflammatory cytokines INF-g and IL-1β. Furthermore, the present study demonstrates for the first time the significantly reduced expression of PPAR-g in the SGEC of SS patients. This finding likely owes to the chronic intrinsic activation, which characterizes the epithelia of SS patients.
References Manoussakis MN, Kapsogeorgou EK. The role of intrinsic epithelial activation in the pathogenesis of Sjögren’s syndrome. J Autoimmun. 35:219-24, 2010
Dubuquoy L. et al, Impaired expression of peroxisome proliferator-activated receptor gamma in ulcerative colitis. Gastroenterology 124:1265–1276, 2003.
Harada K. et al, Th1 cytokine-induced downregulation of PPARgamma in human biliary cells relates to cholangitis in primary biliary cirrhosis. Hepatology 41:1329-38, 2005.
Disclosure of Interest None Declared