No abstract

No abstract

Elevated plasma phosphate levels are signifcantly associated with progression of chronic kidneydisease (CKD). Interstitial fibrosis is an important factor in the progression of CKD. In this studywe investigate the role of inorganic phosphate in stimulating fibronectin (FN) synthesis in akidney fibroblast cell line (NRK-49F). We find that phosphate increases FN abundance andmessage in a dose–dependent fashion and that both ERK1/2 and AKT are important signalingpathways that mediate phosphate-dependent FN expression in NRK-49F cells. Moreoverphosphate srimulates the expression of the transcription factors osterix and NFATc1, whichform complexes and mediate FN synthesis. Another transcription factor involved in phosphatedependentFN synthesis is the AP1 family member c-Fos. In summary we show that evenmildly elevated serum phosphate levels can induce synthesis of the interstitial matrix proteinfibronectin through activation of ERK1/2 and AKT signaling pathways in kidney fibroblasts andthat the synthesis of fibronectin is mediated by a transcriptional complex consisting of NFATc1,osterix and c-Fos.

Background: Hyperosmotic stress causes cell death through activation of apoptotic pathways if the protective osmolyte response is impaired. In this study we attempt to elucidate the molecular mechanisms of hypertonicity-induced apoptosis and the effect of major organic osmolytes upon those. Methods: Hypertonicity-induced changes in Bcl2-family protein abundance and the presence of cytochrome c and apoptosis inducing factor (AIF) in the cytoplasm, were measured using western blot and immunofluorescence labeling. To determine dissipation of mitochondrial membrane potential ( ) though the permeability transition pore (PTP), the lipophilic cationic carbocyanine fluorescence probe JC-1 and TMRM fluorescence probes were used. Results: Hypertonic culture conditions increase the abundance of proapoptotic Bax and the concentration of cytochrome c and apoptosis inducing factor (AIF) in the cytoplasm. These changes are associated with a dissipation of and increased permeability of the PTP. We further show that organic osmolytes stabilize the and decrease the concentration of cytochrome c and AIF in the cytoplasm. Conclusion: Our study shows that organic osmolytes prevent hypertonicityinduced apoptosis by preventing dissipation of through stabilization of the PTP. These findings further support the important role of organic osmolytes in preventing hypertonicity-mediated cell death in medullary kidney cells.

No abstract