A Novel Mechanism For Renal Osmoregulation

Osmoregulation is one of the basic cellular physiological activities,but the regulatory mechanisms through which cells respond to hyperosmotic/hypertonic stresses remain to be completely elucidated.We utilized Oil Red O staining,chemical measurement and flow cytometry to find that hypertonic stress enhance triglyceride(TG) accumulation and lipid droplet formation in mouse inner medulla collecting duct cells(mIMCD3).ACC inhibitor TOFA and FASN inhibitor Cerulenin were able to attenuate the enhanced TG content in mIMCD3 cells under 550 mOsmol/kg hypertonic stress,to different extent.So it implicates that fatty acids contribute to TG content increase may partilally derive from de novo synthesis.900 mOsmol/kg hypertonic stress plus TOFA or Cerulenin treatment led to mIMCD3 cellular osmotic intolerance and significant cell death phenotype.So we had discovered a novel hyeprtonic osmoprotective behavior in mIMCD3 cells,and this metabolic change may exert an potential function in hypertonic adaptation of mIMCD3 cells.Further,we assayed the protein expression of two transcription factors, SREBP1 and PPARγ,both of which play important roles in lipid metabolism,under hypretonic stress,by Western Blot.We also determined the mRNA expression of several target genes mRNA of these two transcription factors with semi-quantitive RT-PCR.Unexpectedly,mRNA expression of SREBP1 targets,including ACC1, GPAT1 and ACL did not appear to be significantly affected by 700 mOsmol/kg hypertonic treatment for 24 h.PPARγtarget genes,such as ap2,CD36 and LPL showed an extreme low mRNA expression profile in mIMCD3 cells,even under 700 mOsmol/kg hypertonic stress.So we guess the enhanced TG accumulation and lipid droplets formation in mIMCD3 cells under hypertonic stress was possibily regulated by post-transcriptional,post-translational regulation or modification of the critical genes.