Parathyroid hormone-mitogen-activated protein kinase axis exerts fibrogenic effect of connective tissue growth factor on human renal proximal tubular cells.

BACKGROUND: Enhanced and prolonged expression of connective tissue growth factor (CTGF) is associated with kidney fibrosis. Parathyroid hormone (PTH) is involved in the genesis of disturbed calcium/phosphate metabolism and ostitis fibrosa in renal failure. PTH activated mitogen-activated protein kinase (MAPK) signaling pathway is present in renal tubular cells. The aim of this study was to identify the mechanism how the signal is transduced to result in extracellular signal-regulated protein kinase (ERK) activation, leading to upregulation of CTGF. METHODS: The levels of CTGF mRNA and protein in human kidney proximal tubular cells (HK-2) treated with PTH in the presence or absence of the MAPK inhibitor PD98059 were analyzed by quantitative real-time polymerase chain reaction (RT-PCR) and immunoblotting assay. The activation of the CTGF promoter in HK-2 cells was determined by the dual-luciferase assay. The effects of the protein kinase A (PKA) activator 8-Br-cAMP and protein kinase C (PKC) activator phorbol 12-myristate 13-acetate (PMA) on MAPK phosphorylation, and the effects of the PKA inhibitor H89 and PKC inhibitor calphostin C on MAPK phosphorylation and CTGF expression were detected by immunoblotting assay. RESULTS: PD98059 inhibited the PTH stimulated expression of CTGF, which strongly suggested that the MAPK signaling pathway plays an important role in the PTH-induced CTGF upregulation in renal tubular cells. A PKA activator as well as PKC activators induced MAPK phosphorylation, and both PKA and PKC inhibitors antagonized PTH-induced MAPK phosphorylation and CTGF expression. CONCLUSION: CTGF expression is upregulated by PTH through a PKC/PKA-ERK-dependent pathway.

[Oxidative stress status in patients with various degrees of chronic renal insufficiency].

OBJECTIVE: To observe the changes of lipid peroxidation and antioxidative enzyme activities of chronic renal insufficiency (CRI) and to explore their effects on the pathogenesis of CRI. METHODS: Serum levels of malondialdehyde (MDA), serum glutathione peroxidase (GSH-Px) and serum superoxide dismutase (SOD) in 36 non-dialyzed patients with various degrees and 12 hemodialyzed (HD) were determined with the method of chemistry colorimetry. RESULTS: Thirty-six CRI and 12 HD patients included in the study had higher SOD activities when compared with the controls [(110.30+/-18.60) kNU/L]. They also had lower serum GSH-Px activity than the controls [(120.63+/-27.57) x 10(4)U/L]. Serum MDA levels in the patients were higher than that in the controls [(4.06+/-0.67) micromol/L]. Serum SOD, GSH-Px and MDA concentrations in 36 non-dialyzed patients with various degrees were also correlated with creatinine clearance (r(G)=0.68, P<0.01; r(M)=-0.52, P<0.01; r(S)=-0.44, P<0.05). CONCLUSION: Free radicals, lipid peroxidation and the abnormality in antioxidative system may play an important role in the pathogenesis of CRI and correlated with impaired renal function, and that they can be regarded as important clinical indexes to infect the severity of chronic renal insufficiency.