Effects Of Reduced β2-Glycoprotein Ⅰ On TGF-β1–p38 MAPK Pathway In Diabetic Nephropathy

Object Diabetic nephropathy(DN) is one of the major microvascular complications of diabetes mellitus(DM). Transforming growth factor-β1(TGF-β1) is a fibrogenic and inflammatory cytokine that plays a vital role in DN. The p38 MAPK signaling pathways have been reported to be activated, which mediates TGF-β1-induced collagen and fibronectin expression during the development of DN. Beta 2 glycoprotein I(β2-GPI) has been shown to have a positive effect on diabetic atherosclerosis and retinal neovascularization. β2-GPI can be reduced by thioredoxin-1, resulting in the reduced state of β2-GPI. In addition, reduced β2-GPI has been found to protect endothelial cells from oxidative stress–induced cell injury. However, the possible protective and beneficial effects of β2-GPI and reduced β2GPI on DN are not fully elucidated. The purpose of this study was to test a hypothesis that treatment with β2GPI and reduced β2GPI would improve diabetic nephropathy in streptozotocin(STZ) induced diabetic mice and high-glucose(HG) exposed rat mesangial cell(RMC).Method The study detected serum levels of β2-GPI and reduced β2-GPI by ELISA in inpatients with type 2 diabetes of Tianjin Medical University Metabolic Diseases Hospital. The relationship between β2-GPI and reduced β2-GPI levels and the degree of progress DN was observed. The STZ-induced BALB/c mice were administrated with β2-GPI and reduced β2-GPI at different time gradient. The changes of glomerular structure and expression of Collagen Ⅳin renal cortical were detected by immunohistochemical techniques, quantitative real-time PCR and Western blot. High glucose-induced rat mesangial cells were treated with β2-GPI and reduced β2-GPI at different concentrations gradient. The expression of Collagen Ⅳ in mesangial cells were detected by quantitative real-time PCR and Western blot.The expression of TGF-β1, p38 MAPK and phospho-p38 MAPK were observed in STZ induced diabetic mice and HG exposed RMC by quantitative real-time PCR and Western blot with or without the treatment of β2-GPI and reduced β2-GPI.Result β2-GPI and reduced β2-GPI attenuated albuminuria in diabetic mice, suggesting an improved kidney function. β2-GPI and reduced β2-GPI significantly decreased accumulation of collagenous components in cortical interstitium(kidney fibrosis) and expansion of mesangial matrix in glomeruli(glomerulosclerosis) in STZ-diabetic mice, suggesting an improved renal structural damage. The histological examination and molecular assays showed that treatment with β2-GPI and reduced β2-GPI in the STZ-diabetic mice and HG exposed RMC resulted in a decrease in expression levels of TGF-β1 and Collagen Ⅳ, with concomitant decrease in Phospho-p38 MAPK expression.Conclusion β2GPI and reduced β2GPI improved renal dysfunction and kidney fibrosis as well as decreased Collagen Ⅳ and TGF-β1 m RNA and protein expression in STZ-induced diabetic mice and high glucose-induced RMCs. Moreover, the present in vitro and in vivo studies demonstrated that the renoprotective and antifibrosis effects of β2GPI and reduced β2GPI in DN were closely associated with suppressing the activation of the TGF-β1-p38 MAPK pathway. However, the definitive molecular mechanism of β2GPI and reduced β2GPI inhibition of the TGF-β1-p38 MAPK pathway in DN needs to be investigated.