The Role Of Sodium-dependent Phosphate Cotransporter Pit-1in Cardiac Hypertrophy And Fibrosis In Uremic Rats Fed A High Phosphate Diet

Objective:Hyperphosphatemia is a common complication in chronic kidney disease.It is closely related to cardiac hypertrophy, fibrosis,and vascular calcification,which is an independent risk factor for cardiovascular mortality rate. However, the mechanism of high phosphate on cardiac damage in the state of chroic kiney disease has not been clear. Sodium phosphate cotransporter is necessary for phosphorus transporting across the cell membrane, and PiT-1is widely expressed in the cardiac tissue. In our study, we assume that phosphorus can cause myocardial damage through PiT-1. This study use the adenine diet to induce chronic kidney failure rats model, in order to observe the adverse effect of hyperphosphatemia on myocardial tissue, signal transduction mechanism of PiT-1in myocardial damage and the ameliorative effect of PiT-1inhibtor on myocardial damage.Methods::24Male S-D rats weight280g, received a adenine and high phosphorus diet (n=18,CRF rats) or just high phosphorus diet (NHP group, n=6). After making uremic model, eighteen rats were randomly divided into three groups as follows:(1)CRF rats received high phosphorous diet only(UHP group, n=6).(2) CRF rats received high phosphorus diet and intraperitoneal phosphonoformic acid PFA0.15g/kg/every other day(UHP-PFA group, n=6).(3) CRF rats received high phosphorus diet and intraperitoneal normal saline infection0.15g/kg/every other day (UHP-NS group, n=6).At the4th(baseline) week and8th week(end point),serum creatimine(Scr),serum Ca,serum P,urine Ca,urine P and24hours urine protein were examined. At the end of the8th week,the rats were sacrificed and the hearts were excised. We calculate the left ventricle/100g body quality and the heart tissue was used to routine patholog. Masson staining was employed to detected the cardic tissue fibrosis. Immunohistochemical was used to detected the expression of PiT-1and Cbfa-1. Western-blot was used to explore the expression of PiT-1,TGF-β1,Cbfa-1and signaling molecules as follows:sphosphorylation p38mitogen-activated protein kinase(P-p38MAPK),and phosphorylation of ERK (pERK)Results:1.At the4th week, the Scr was higher and the Creatinine clearance(Ccr) was lower in the CRF rats than in the NHP rats.There were no significant difference of serum Ca,serum P,24hours urine protein,24hours urinary phosphate clearance and urinary calcium clearance among4groups (p>0.05).At the8th week, the serum P was higher and the serum Ca was lower in CRF groups than in NHP group and there was a significant difference (p<0.05).There was no significant difference of Scr,Ccr,serumCa,serumP,24hours urine protein,24hours urinary phosphate clearance and urinary calcium clearance among groups UHP-PFA,UHP-NS and UHP (p>0.05).2. Compared with NHP, the left ventricle/100g body quality, myocardial cell diameter,and the collagen volume fraction(%) increased in CRF rats(all p<0.05). However,the indicators above show a significant amelioration in PFA group(all p<0.05).3. The espression of PiT-1was rich in myocardial tissue especially in CRF rats.Immunohistochemical proved that PiT-1mainly expressed in myocardial cell membrane and sarcoplasmic reticulum and Cbfa-1mainly expressed in cytoplasm.Western-blot showed that the expression of PiT-1,TGF-β1,Cbfa-1were higher in CRF models than in NHP rats. Serum P level had a liner positive correlation with the expression of PiT-1(r=0.845, p<0.01). Equally, The expressions of p38MAPK and pERK were higher in CRF rats (all p<0.05). However, the indicators mentioned above show a much more significant amelioration in UHP-PFA than the other two CRF groups.Conclusion:There were significant cardiac hypertrophy and fibrosis in chronic renal failure(CRF) rats received high phosphate diet. The expression of PiT-1and its downstream targets of p38MAPK,ERK Signaling pathways were activated. The adverse effece of hyperphosphatemia on cardiac hypertrophy and fibrosis can be ameliorated by blocking PiT-1, indicating that PiT-1and the activation of its downstream signaling pathways play an important role in cardiac hypertrophy and fibrosis.