The Mechanism By Which GSK3? Enhances Renal Tubulointerstitial Fibrosis And The Potential Strategies Of Anti-kidney Fibrosis

Renal fibrosis,especially renal tubulointerstitial fibrosis(RTF)represents a pathological response to kidney inflammation,injury and drug toxicity.Renal fibrosis,especially renal tubulointerstitial fibrosis(RTF)is characterized by fibroblast activation;excessive production and deposition of extracellular matrix(ECM);tubular atrophy and microvascular rarefaction,which causes the destruction and collapse of renal parenchyma and progressive loss of kidney function and is a common outcome in chronic kidney diseases(CKD).Renal fibrosis can be promoted by a variety of pathogenic factors such as hypertension,inflammation,hyperglycemia,hyperlipidemia and drug toxicity.But,even though it is effective to control these factors,the process of renal fibrosis is sometimes difficult to suppress.Therefore,analyses of the molecular mechanism,therapeutic targets of the occurrence and development of fibrosis have become an important research direction in recent years.The formation and development of renal fibrosis is a dynamic process in which a variety of cellular and molecular pathways are involved.Lymphocytes and many inflammatory mediators can initiate renal fibrosis,resulting inflammatory cell infiltration,tubular epithelial EMT,etc..In the subsequent stages of fibrosis,multiple renal tissue cells can promote or differentiate into ECM production cells and TGF-?1,CTGF,FGF2,PDGF and angiotensin II,promote the deposition and modification of fibrinogen.Renal tubular injury,atrophy,microcirculation disturbance and chronic hypoxia are the ultimate manifestations of renal fibrosis in ending stage.Although there are lots of studies on the formation and development of renal fibrosis,but the exactly mechanisms are still not fully understood.In recent years,it is found that Glycogen syntheses kinase 3?(GSK3?)plays an important role in anti-fibrosis,but its mechanism is not clear.In the first part,we investigated a new mechanism of renal fibrogenisis.GSK3?was identified as a protein kinase inactivating glycogen synthase in 1980.Then activated GSK3? by insulin and many growth factors was revealed to play role in a number of cellular functions,including stem cell renewal,apoptosis,cell proliferation and development.It antici pated these events via insulin,Wnt/?-catenin and Hedgehog signaling pathways.It was found that GSK3? have a close relationship with nervous system disorders,diabetes and inflammation.Especially,GSK3? is involved in renal cell apoptosis and inflammation related pathways.In our study,we found that:1.High expression of GSK3? in fibrosis tissues;2.GSK3? antagonist,TDZD and Li Cl,can relieve renal cell fibrosis;overexpression of GSK3? results in an increasing expression of renal fibrosis markers;3.Furthermore,the functional inhibition of GSK3? leads to the down-regulation of Smad3 in TGF-Smad signaling.And we demonstrated that GSK3? may be involved in the process of renal fibrosis via a new Smad3 phosphorylation site at S204.According part 1,we are looking for new anti-kidney fibrosis approaches via suppressing GSK3? and Smad3.In part 2,we confirmed Farnesoid X receptor(FXR)is an important transcriptional factor of GSK3? and Smad3 and have a function of anti-fibrosis.1.The level of FXR is negatively correlated with that of GSK3?,Smad3 and FN in human fibrotic kidney.2.FXR represses fibrosis in HKC cells via downregulating GSK3? and Smad3 expression.In HKC fibrosis model,Smad3 expression levels were decreased in mRNA and protein level by activation of FXR.FXR represses GSK3? and Smad3 at transcriptional level using luciferase reporter assay.3.CDCA,a FXR agonist,protects against renal fibrosis and suppresses Smad3 expression in UUO mice.FXR is an important anti-inflammatory nuclear receptor and play a role in anti-fibrosis,but the exactly mechanism is still not understood.Based on these data,we can preliminarily determine that the activation of FXR could down regulated GSK3? and Smad3 at the transcriptional level and relieve renal fibrosis.It suggested that FXR can be used as a new way to control renal fibrosis.In addition,we explored other strategies that might inhibit renal fibrosis.Although the mechanism of renal fibrogenisis is still unclear,but the control and intervent ion of the disease process can reduce the degree of fibrosis and improve renal function.So,the strategies of anti-RTF were discussed.At present,the research on suppressing renal fibrosis is focused on the following aspects: improve microcirculation;anti-inflammation;developmental stimuli;cell-based therapies and epigenetic reprogramming.In these anti-RTF strategies,the study of epigenomic reprogramming is the newly emerging approach.Epigenetic regulations are identified as chromosome and histone modifications except other nuclear receptors regulatin such as FXR.These mechanisms mainly include histone acetylation/deacetylatin and DNA methylation/demethylation.Previous studies have demonstrated,it indicated that HDAC is involved in the process of inflammation,proliferation and differentiation.Furthermore,some data s showed that it may play an important role in occurrence of fibrosis.HDACi(HDAC inhibitor)are chemicals that inhibit HDAC enzymes,which lead to increased transcriptional activity a nd upregulation of specific genes.Published articles illustrated its potential anti-fibrosis role in liver.SAHA(Suberoylanilide hydroxamic acid;also known as vorinostat,),an FDA-approved HDACi,which was already in clinical use as a third-line drug for the treatment of cutaneous T-cell lymphoma.It may improve pulmonary fibrosis.However,it's still not fully understood which exactly signaling pathways were affected with SAHA in fibrogenesis.In the third part,the effect of SAHA on renal fibrosis and its possible mechanism were discussed.Our data indicated:1.SAHA decreases FN,Collagen IV and ?-SMA in mRNA and protein level;2.SAHA attenuates renal fibrosis and suppresses STAT3 phosphorylation.We speculate that one of the mechanisms may be that SAHA reduces STAT3 phosphorylation.3.SAHA-suppressed STAT3 phosphorylation is associated with the repression of ERK activation and increased PTP7Taken together,we investigated the mechanism of GSK3? in renal fibrogenisis and the potential treatment of RTF.These datas showed that GSK3? play an important role in RTF via TGF?-Smad3 pathway.FXR activation can relieve the renal cell fibrosis partly via suppressing GSK3? and Smad3.SAHA may downregulate fibrotic markers in TGF?1 induced HKC fibrosis model through STAT3 inactivation which is triggered by TGFRI-ERK pathway and activation of PTP7.In addition,fibrosis occurs not only in the kidney,but also in the intestine,liver,skin,heart and lungs,common fibrosis pathways are thought to exist.So it is not only for the disease itself to study the mechanism of RTF,but also to expand the treatment and reduce the renal fibrosis.These results provide a new understanding in the occurrence and development of RTF and provide a theoretical treatment basis for the study of renal fibrosis.