Hypertonicity-induced mitochondrial membrane permeability in renal medullary interstitial cells: protective role of osmolytes.

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 (Delta Psi) 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 Delta Psi and increased permeability of the PTP. We further show that organic osmolytes stabilize the Delta Psi and decrease the concentration of cytochrome c and AIF in the cytoplasm.

Conclusion: Our study shows that organic osmolytes prevent hypertonicity-induced apoptosis by preventing dissipation of Delta Psi 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.