The Damage Of Amylin On The Podocyte And The Mechanism

Background&ObjectiveApproaching epidemic levels, Diabetic nephropathy (DN) is now one of themost common microvascular disease in diabetic patients, and the key cause ofend-stage renal disease (ESRD). it is now widely recognized that proteinuria,specifically microalbuminuria, is one of the earliest clinically identifiable markers ofdiabetes-induced renal damage. Microalbuminuria results from the damage of theglomerular filtration barrier, podocytes are essential for glomerular filtration barrierintegrity, they are highly specialized, terminally differentiated cells, with cell bodies,major processes, and foot processes interlinked by30-40nm slit diaphragms.Podocyte injury leads to alterations of the foot process/slit diaphragm complex withloss of glomerular permselectivity, contributing to the pathogenesis of DN.Amylin is a37amino acid peptide that is co-released with insulin frompancreatic Islet β cells，As Amylin and Insulin share common promoter elements, itcoexpressed and cosecreted with insulin by pancreatic beta-cells. Much recent workhas focused on the physiology of pancreatic amylin, Amylin is believed to function asa hormone regulating glucose homeostasis, contribute to glycaemic control byslowing gastric emptying and inhibition of glucagon secretion.Actually, plasma amylin level is elevated in the type II diabetic and Insulin resistance patients,hyperinsulinemia inevitably accompanies by hyperamylinemia.In the present study,Amylin aggregation may also participates in activating the renin angiotensin system(RAS), and leading to injury of other organs. Islet amyloidosis is a major cause ofislet b-cell dysfunction and was found in70–90%of patients with type II Diabetesmellitus at autopsy.Moreover, There are functional expression of key components ofthe RAS in differentiated podocytes. Therefore, It hypothesized that Amylin mayresult in podocyte injury by the activation of local RAS, and participate in thedevelopment of DN. To study the damage of Amylin on podocyte and themechanism,the mouse podocytes were treated with super-physiologicalconcentrations of human amylin in the condition of hyperglycemia, and observed thechanges of podocyte-related proteins,RAS components and the apoptosis ofpodocytes.Materials&MethodsThe Podocytes of mouse cultured in high glucose (25mmol/L) medium with10%FBS were induced to differentiate at37℃. podocytes cultured in high glucosemedium (25mmol/L, group A) were served as control group (HG).the other groupstreated with Amylin,Captopril and Valsartan respectively, were divided into fivegroups: B1. group of HG+0.5μmol/l Amylin; B2. group of HG+1.0μmol/l Amylin;B3. group of HG+2.0μmol/l Amylin; C. group of HG+1.0μmol/l Amylin+Captoprilgroup; D. group of HG+1.0μmol/l Amylin+Valsartan; Each group was cultured for48h. Podocyte morphology was observed under Optical Microscope. The mRNAexpression levels of Nephrin, Podocin, Desmin were detected by RT-RCR. Theprotein expression of Nephrin, Podocin, Desmin were detected by Western blot.Results1. In the light microscopy, compared with podocytes which were not differentiatedat33℃,the podocytes differentiated at37℃presented with the polygoneal shape and the cell body broadened.2. Compared with group A, Amylin, significantly reduced the mRNA and proteinexpression of nephrin、podocin, but markedly enhanced the level of Desmin. Thedegree of damage of Podocytes were in a dose-dependent fashion.3. Compared with group B2, Captopril or Valsartan could restore the expression ofnephrin, podocin caused by Amylin.ConclusionsThe deposition of human amylin in the condition of hyperglycemia could inducethe apoptosis of Podocyte and decrease the protein of podocyte, such as Nephrin andPodocin, In contrast, it increased the expression of Desmin. The degree of damage ofPodocytes were in a dose-dependent fashion.When podocytes were preincubated withCaptopril or Valsartan,it can protect podocytes from the damage of Amylin. In aConclusion, The damage of Amylin on the podocytes may be, at least partly, by therenin-angiotensin system in podocyte. Treated with the inhibition of the RAS byangiotensin-converting enzyme inhibitors (ACEI) or angiotensin II–type receptorblocker (ATRB) can protect the podocyte from Amylin and slows the rate ofprogression to ESRD.