TRPM7 channels mediate spontaneous Ca ²⁺ fluctuations in growth plate chondrocytes that promote bone development

Abstract

During endochondral ossification of long bones, the proliferation and differentiation of chondrocytes cause them to be arranged into layered structures constituting the epiphyseal growth plate, where they secrete the cartilage matrix that is subsequently converted into trabecular bone. Ca2+ signaling has been implicated in chondrogenesis in vitro. Through fluorometric imaging of bone slices from embryonic mice, we demonstrated that live growth plate chondrocytes generated small, cell-autonomous Ca2+ fluctuations that were associated with weak and intermittent Ca2+ influx. Several genes encoding Ca2+-permeable channels were expressed in growth plate chondrocytes, but only pharmacological inhibitors of transient receptor potential cation channel subfamily M member 7 (TRPM7) reduced the spontaneous Ca2+ fluctuations. The TRPM7-mediated Ca2+ influx was likely activated downstream of basal phospholipase C activity and was potentiated upon cell hyperpolarization induced by big-conductance Ca2+-dependent K+ channels. Bones from embryos in which Trpm7 was conditionally knocked out during ex vivo culture exhibited reduced outgrowth and displayed histological abnormalities accompanied by insufficient autophosphorylation of Ca2+/calmodulin-dependent protein kinase II (CaMKII) in the growth plate. The link between TRPM7-mediated Ca2+ fluctuations and CaMKII-dependent chondrogenesis was further supported by experiments with chondrocyte-specific Trpm7 knockout mice. Thus, growth plate chondrocytes generate spontaneous, TRPM7-mediated Ca2+ fluctuations that promote self-maturation and bone development.

High-Level Expression of Alkaline Phosphatase by Adeno-Associated Virus Vector Ameliorates Pathological Bone Structure in a Hypophosphatasia Mouse Model

“…In contrast, mice treated with 4.5 × 10 12 v.g./body exhibited the same morphology and ALP distribution as those seen in the control group. This result lends further support to the hypothesis that TNALP-D replacement at a dose sufficient to achieve normal levels of ALP in local bone brings about normal calcareous degeneration of the hypertrophic chondrocyte layer, leading to normal endochondral ossification [37], and ameliorates insufficient elongation, morphological irregularity, and hypomineralization of the femur. In the present study, we applied the frozen sections (10 µm thick) obtained from unfixed and undecalcified bone tissues to detect more accurate ALP activity.…”

L-type voltage-gated Ca2+channel CaV1.2 regulates chondrogenesis during limb development

“…One candidate channel is Ca V 3.2 because it is also expressed in limb chondrocytes and micromass-cultured limb mesenchyme from the Ca V 3.2 −/− mice exhibited attenuated cartilage formation (22). Another ion channel that potentially regulates late chondrogenesis is TRPM7 (transient receptor potential cation channel subfamily M member 7), because TRPM7-mediated Ca 2+ fluctuations in growth plate chondrocytes were found to be critical for chondrocyte maturation (44).…”

Functional expression of TRPM7 as a Ca2+influx pathway in adipocytes

“…It is well established that TRPM7 channel activity is tonically regulated by intracellular free Mg 2+ as well as Mg-nucleotides (Penner and Fleig 2007); however, little is known about the physiological stimuli that change the TRPM7 channel activity. Several reports indicate that activation of phospholipase C (PLC) induces Ca 2+ influx via TRPM7 in intact cells (Langeslag et al 2007;Qian et al 2019). There are contradicting reports showing that TRPM7 is inactivated by G aq -coupled receptor stimulation via the PLC-mediating depletion of phosphatidylinositol 4,5-bisphosphates (PIP 2 ) which is necessary for TRPM7 channel activity (Runnels et al 2002;Kozak et al 2005;Gwanyanya et al 2006;Bates-Withers et al 2011;Zhelay et al 2018).…”