TRP channels are both present and functional in human osteoblast-like cells [Abstract]

Transient receptor potential (TRP) cation channels are currently drawing a lot of interest in many tissues, but relatively little interest in bone. TRP channels are mostly non-selective and are generally widely expressed with increased expression in some malignancies1, and TRPV1 and TRPM8 ligands, for example, may have potential uses as anti-cancer agents2 in prostate malignancy. As prostate cancer cells metastasize to and cohabit with bone cells, this area of research is potentially important and deserves attention. The putative roles of TRP channels include growth, repair, metastasis, apoptosis and cell calcium entry — all of which are relevant to osteoblasts. We aim to show that TRP channels are present and active in osteoblast-like cells. RT-PCR was carried out using intron-spanning primer pairs for TRPV1, TRPV5, TRPV6, TRPM7 and TRPM8 subunits in MG63 and SaOS-2 osteoblast-like cells. Cell proliferation assays were performed over 72 hours to test the effects of known TRP ligands on cell number, using trypan blue exclusion testing and MTS-conversion assay. Patch-clamp analysis was performed on MG63 and SaOS-2 cells using calcium-free and/or sodium gluconate solutions to minimise the confounding influence of other channel subtypes. RT-PCR has revealed appropriate sized bands for TRPV1, TRPV5, TRPV6, TRPM7 and TRPM8 in MG63 and SaOS-2 cell lines. In cell proliferation assays, > 10 μM capsaicin or capsazepine significantly reduced MG63 cell number (P 10 μM capsaicin. In addition, resiniferatoxin (TRPV1 agonist), SB366791 (TRPV1 blocker) and anandamide (cannabinoid and TRPV1 modulator) all decreased MG63 cell numbers. Patch-clamp analysis has revealed small conductance channels of 18 — 30 pS in excised inside-out patches, and slightly larger conductance channels in cell-attached and inside-out patches at depolarised and hyperpolarised potentials in MG63 and LNCaP (prostate cancer) cells. Given our preliminary data, we propose that five members of the TRP channel family are expressed in osteoblast-like cell lines, and we show electrophysiological and pharmacological data which lead us to suggest that at least one TRP channel type is active and functional in bone. TRP channels could therefore be new targets in the battle against bone disorders, and some known TRP channel ligands could be included in that armoury