title: Antagonistic Regulation of Parvalbumin Expression and Mitochondrial Calcium Handling Capacity in Renal Epithelial Cells.
abstract: Parvalbumin (PV) is a cytosolic Ca2+-binding protein acting as a slow-onset Ca2+ buffer modulating the shape of Ca2+ transients in fast-twitch muscles and a subpopulation of neurons. PV is also expressed in non-excitable cells including distal convoluted tubule (DCT) cells of the kidney, where it might act as an intracellular Ca2+ shuttle facilitating transcellular Ca2+ resorption. In excitable cells, upregulation of mitochondria in "PV-ergic" cells in PV-/- mice appears to be a general hallmark, evidenced in fast-twitch muscles and cerebellar Purkinje cells. Using Gene Chip Arrays and qRT-PCR, we identified differentially expressed genes in the DCT of PV-/- mice. With a focus on genes implicated in mitochondrial Ca2+ transport and membrane potential, uncoupling protein 2 (Ucp2), mitocalcin (Efhd1), mitochondrial calcium uptake 1 (Micu1), mitochondrial calcium uniporter (Mcu), mitochondrial calcium uniporter regulator 1 (Mcur1), cytochrome c oxidase subunit 1 (COX1), and ATP synthase subunit β (Atp5b) were found to be up-upregulated. At the protein level, COX1 was increased by 31 ± 7%, while ATP-synthase subunit β was unchanged. This suggested that these mitochondria were better suited to uphold the electrochemical potential across the mitochondrial membrane, necessary for mitochondrial Ca2+ uptake. Ectopic expression of PV in PV-negative Madin-Darby canine kidney (MDCK) cells decreased COX1 and concomitantly mitochondrial volume, while ATP synthase subunit β levels remained unaffected. Suppression of PV by shRNA in PV-expressing MDCK cells led subsequently to an increase in COX1 expression. The collapsing of the mitochondrial membrane potential by the uncoupler CCCP occurred at lower concentrations in PV-expressing MDCK cells than in control cells. In support, a reduction of the relative mitochondrial mass was observed in PV-expressing MDCK cells. Deregulation of the cytoplasmic Ca2+ buffer PV in kidney cells was counterbalanced in vivo and in vitro by adjusting the relative mitochondrial volume and modifying the mitochondrial protein composition conceivably to increase their Ca2+-buffering/sequestration capacity.
authors.affiliation: Anatomy, Department of Medicine, University of Fribourg, Fribourg, Switzerland.
authors.forename: Thomas
authors.initials: T
authors.lastname: Henzi
authors.affiliation: Anatomy, Department of Medicine, University of Fribourg, Fribourg, Switzerland.
authors.forename: Beat
authors.initials: B
authors.lastname: Schwaller
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000378:metabolism; D002135:Calcium-Binding Proteins / Q000378:metabolism; D002460:Cell Line; D003600:Cytosol / Q000378:metabolism; D004285:Dogs; D003576:Electron Transport Complex IV / Q000378:metabolism; D004847:Epithelial Cells / Q000378:metabolism*; D007473:Ion Channels / Q000378:metabolism; D007668:Kidney / Q000378:metabolism*; D061985:Madin Darby Canine Kidney Cells; D053078:Membrane Potential, Mitochondrial / Q000502:physiology; D051379:Mice; D018345:Mice, Knockout; D008822:Mice, Transgenic; D008928:Mitochondria / Q000378:metabolism*; D024101:Mitochondrial Proteins / Q000378:metabolism; D053142:Mitochondrial Size / Q000502:physiology; D010320:Parvalbumins / Q000378:metabolism*; D011689:Purkinje Cells / Q000378:metabolism; D000071246:Uncoupling Protein 2
chemical_list: D015220:Calcium Channels; D002135:Calcium-Binding Proteins; D007473:Ion Channels; D024101:Mitochondrial Proteins; D010320:Parvalbumins; C000604390:Ucp2 protein, mouse; D000071246:Uncoupling Protein 2; C034703:mitochondrial calcium uniporter; D003576:Electron Transport Complex IV; C085577:Ca2+-binding protein-1; D002118:Calcium