Expression of ion channels of the TRP family in articular chondrocytes from osteoarthritic patients: changes between native and in vitro propagated chondrocytes

Abstract

The maintenance of a differentiated chondrocyte phenotype is influenced by several factors of which signal transduction of extracellular stimuli through the cell membrane is of major interest. One important group of membrane-bound proteins which are involved in transmembrane signal transduction are ion channels. Human articular chondrocytes were obtained from osteoarthritic femoral condyles. Cells were released from the surrounding matrix and cultivated under standard conditions. We investigated gene expression of 12 members of the TRP ion channel family of freshly prepared (passage 0; P0) and in vitro propagated human articular chondrocytes (passage 2; P2) using conventional and real-time PCR (RT-PCR). In addition, the protein appearance of four TRP channels was demonstrated by immunofluorescence and western blotting. Chondrocyte differentiation was monitored by quantification of collagen type-II, type-I, and aggrecan gene expression. By conventional PCR, 8 channels could be detected, of which some displayed a heterogeneous PCR pattern. RT-PCR quantification revealed that TRPC1 was expressed on the same level in P0 and P2 chondrocytes while gene expression of TRPC3 and TRPC6 was elevated in passage 2 cells. TRPM5, TRPM7, and TRPV1 displayed an enhanced gene expression in freshly isolated chondrocytes. Immunofluorescence signal intensity of all four investigated TRP proteins was consistent with the corresponding gene expression data. In the present study, a correlation between the appearance of some members of the TRP ion channel family and the state of de-differentiation of osteoarthritic articular chondrocytes was shown. A possible direct involvement in the process of chondrocyte de-differentiation has to be investigated in further studies.

Accelerated Ca2+ entry by membrane hyperpolarization due to Ca2+-activated K+ channel activation in response to histamine in chondrocytes

“…The positive feedback mechanism including the activation of K Ca channels and further facilitation of Ca 2ϩ entry by membrane hyperpolarization appeared to play a role in SOCE in OUMS-27 treated with thapsigargin. Expressions of some TRP channels has been reported in chondrocytes (5). However, detailed identification of Ca 2ϩ entry pathway, including the functional expression of Orai and STIM as the SOCE channel (25), remains to be demonstrated in this cell line.…”

The ClC-7 Chloride Channel Is Downregulated by Hypoosmotic Stress in Human Chondrocytes

“…In nonexcitable cells such as chondrocytes, membrane hyperpolarization facilitates Ca 21 entry through nonselective cation channels (Gavenis et al, 2009;Funabashi et al, 2010b;Hdud et al, 2012). Blockage of Cl 2 channels by DIDS caused a significant hyperpolarization followed by an increase in [Ca 21 ] i .…”

Vascular Smooth Muscle Cell Differentiation to an Osteogenic Phenotype Involves TRPM7 Modulation by Magnesium

“…Such phenomena extend beyond the vasculature, as recently shown in patients with osteoarthritis, where TRPM7 expression was found to be altered in articular chondrocytes. 55 To examine the significance of our findings in an animal model of genetically low [Mg 2ϩ ] i , we investigated VSMCs from MgL mice, which we previously characterized in detail. 30 These mice are hypomagnesemic, have increased blood pressure, and display endothelial dysfunction and vascular remodeling.…”