Regulation And Significant Of UCH-L1 Expression In Podocytes

To our knowledge, the degradation of ubiquitin-conjugated cellular proteins by the proteasome system plays a key role in many cellular processes, including cell cycle control, DNA repair, regulation of transcription, growth differentiation, receptor function, immune and inflammatory responses, and oncoprotein degradation. This system is also regulated by a reversible process involving many deubiquitination factors. Among these deubiquitination enzyme families, the best characterized are the ubiquitin COOH-terminal hydrolases (UCHs) and the ubiquitin-specific processing proteins(UBPs). UCH-L1 is an important member of UCH family, whose expression normally exhibits a prominent specificity of tissues including the brain, the testis and the kidney.Besides regulating targeted proteins through ubiquitin-proteasome pathway, a large amount of researches indicate that UCH-L1 also associates with some diseases, such as neurodegenerative diseases and cancers.In recent years, the UCH-L1 abnormal expression relate to podocytes injury has also been demonstrated.our team discovered the expression level of UCH-L1 was markedly higher in in APGN, LN, MGN and IgA nephropathy with massive immune complex deposition than that in FSGS, MCD, minor abnormalities and normal kidney tissue. In vitro experiment, we further confirmed that the immune injury was one main factor which induced up-expression of UCH-L1 in podocytes. But the mechanism of up-regulation of UCH-L1 by immune complex is still not elucidated. Work from Hyamman lab demonstrated that the so-called neonatal Fc receptor (FcRn) was presanted on human renal podocytes. FcRn was first discovered as the intestinal epithelial receptor responsible for transporting maternal IgG into the bloodstream of the baby. It was later found to be important for the long serum half-life of IgG.While FcRn-mediated halflife extension is beneficial for IgG antibody responses against pathogens, it also prolongs the serum half-life of IgG autoantibodies and thus promotes tissue damage in autoimmune diseases. However, it is unclear that the significance of expression of FcRn in podocytes during the immune mediating inflammation. We speculated that FcRn may be an immune susceptor of podocytes to transfer the stimulation by immune complex to intracellular signaling pathways. But there is no report about the study on it. Therefore, ongoing studies should clarify the role of the FcRn as a potential target for immune complexes on podocytes and should assess its relevance in physiology and pathology.In the present study, to evaulate this hypothesis, we used western blot, immunofluorescence in cultured mouse podocytes and immunohistochemistry in kidney biopsy tissues to investigated the FcRn expression in normal and immune stimulating circumtance. Our work revealed the positive association of expression of FcRn and immune stimulation in cultured podocytes, which was accompnaied with the time-dependent pattern.The blocked FcRn by RNAi interference decreased expression of UCH-L1 induced by ATS. It clear indicate FcRn is a kay factor for the mechanism of up-regulation of UCH-L1 expression in podocytes injury.Further investigation discovered that p38 MAPK was involved in regulating the expression of UCH-L1. We found a marked increase of phosphorylated p38 MAPK in the presente of immune complex in cultered podocytes. Special inhibitor of p38 may partially down-regulated UCH-L1 expression of podocytes upon challenge with ATS. Moreover, the podocyte FcRn blocked by RNAi interference can markdly decreased the phosphorylation of p38 and expression of UCH-L1, while the useless effect of inhibition of p38 phosphorylation on FcRn in turn.In order to clarify the role of UCH-L1 expression in podocytes,we transfected pIRES2-EGFP-UCHLl-myc plasmid into podocytes.Using western blot analysis, we found that over-expression of UCH-L1 in podocytes was related to decreased level of CDK5, Synaptopodin and p27.These information suggests the up-regulation of UCH-L1 in podocytes of may be associated with podocyte injury as well as de-dediffentiation.In summary, our experiment discovered that FcRn could up-regulate the expression of UCH-L1 via the activation of p38 induced by immune complex stimulation. The UCH-L1 expression up-regulation may be a symble for the cell injury and de-deffirenciation of podocytes during the glomerulonephritides. Our study opens up a possibility that FcRn and, possibly, p38 MAPK could become potential targets for therapeutic intervention in proteinuric glomerulopathies.