The ClC-7 Chloride Channel Is Downregulated by Hypoosmotic Stress in Human Chondrocytes.
Articular chondrocytes in osteoarthritis (OA) patients are exposed to hypoosmotic stress because the osmolality of this synovial fluid is significantly decreased. Hypoosmotic stress can cause an efflux of Cl(-) and an associated decrease of cell volume. We have previously reported that a Cl(-) conductance contributes to the regulation of resting membrane potential and thus can alter intracellular Ca(2+) concentration ([Ca(2+)]i) in human chondrocytes. The molecular identity and pathologic function of these Cl(-) channels, however, remained to be determined. Here, we show that the ClC-7 Cl(-) channel is strongly expressed in a human chondrocyte cell line (OUMS-27) and that it is responsible for Cl(-) currents that are activated by extracellular acidification (pH 5.0). These acid-sensitive currents are inhibited by 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS; IC50 = 13 μM) and are markedly reduced by small-interfering RNA-induced knockdown of ClC-7. DIDS hyperpolarized these chondrocytes, and this was followed by an increase in [Ca(2+)]i. ClC-7 knockdown caused a similar hyperpolarization of the membrane potential. Short-term culture (48 hours) in hypoosmotic medium (270 mOsm) reduced the expression of ClC-7 and decreased the acid-sensitive currents. Interestingly, these hypoosmotic culture conditions, or ClC-7 knockdown, resulted in enhanced cell death. Taken together, our results show that the significant hyperpolarization due to ClC-7 impairment in chondrocytes can significantly increase [Ca(2+)]i and cell death. Thus, downregulation of ClC-7 channels during the hypoosmotic stress that accompanies OA progression is one important concept of the complex etiology of OA. These findings suggest novel targets for therapeutic intervention(s) and drug development for OA.
Department of Molecular and Cellular Pharmacology, Graduate School of Pharmaceutical Sciences, Nagoya City University, Nagoya, Japan (T.K., H.Y., Y.S., Y.I.); and Faculty of Kinesiology, University of Calgary, Calgary, Alberta, Canada (W.R.G.).
Takashi
T
Kurita
Department of Molecular and Cellular Pharmacology, Graduate School of Pharmaceutical Sciences, Nagoya City University, Nagoya, Japan (T.K., H.Y., Y.S., Y.I.); and Faculty of Kinesiology, University of Calgary, Calgary, Alberta, Canada (W.R.G.).
Hisao
H
Yamamura
Department of Molecular and Cellular Pharmacology, Graduate School of Pharmaceutical Sciences, Nagoya City University, Nagoya, Japan (T.K., H.Y., Y.S., Y.I.); and Faculty of Kinesiology, University of Calgary, Calgary, Alberta, Canada (W.R.G.).
Yoshiaki
Y
Suzuki
Department of Molecular and Cellular Pharmacology, Graduate School of Pharmaceutical Sciences, Nagoya City University, Nagoya, Japan (T.K., H.Y., Y.S., Y.I.); and Faculty of Kinesiology, University of Calgary, Calgary, Alberta, Canada (W.R.G.).
Wayne R
WR
Giles
Department of Molecular and Cellular Pharmacology, Graduate School of Pharmaceutical Sciences, Nagoya City University, Nagoya, Japan (T.K., H.Y., Y.S., Y.I.); and Faculty of Kinesiology, University of Calgary, Calgary, Alberta, Canada (W.R.G.) yimaizum@phar.nagoya-cu.ac.jp.
Yuji
Y
Imaizumi
D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid / Q000494:pharmacology; D017209:Apoptosis; D002118:Calcium / Q000378:metabolism; D002460:Cell Line; D018118:Chloride Channels / Q000235:genetics* / Q000378:metabolism; D002712:Chlorides / Q000378:metabolism*; D019902:Chondrocytes / Q000378:metabolism* / Q000473:pathology; D003470:Culture Media / Q000737:chemistry / Q000494:pharmacology; D005786:Gene Expression Regulation; D055785:Gene Knockdown Techniques; D006801:Humans; D008564:Membrane Potentials / Q000187:drug effects; D009997:Osmotic Pressure / Q000187:drug effects; D010003:Osteoarthritis / Q000235:genetics / Q000378:metabolism* / Q000503:physiopathology*
C097540:CLCN7 protein, human; D018118:Chloride Channels; D002712:Chlorides; D003470:Culture Media; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; D002118:Calcium