Knockout of TRPV6 Causes Osteopenia in Mice by Increasing Osteoclastic Differentiation and Activity

Abstract

Background: Calcium ion (Ca²⁺) signals are required for osteoclast differentiation. Previous study showed that transient receptor potential vanilloid 5 (TRPV5) is an essential Ca²⁺ transporter in osteoclastogenesis and bone resorption. TRPV5 and TRPV6 represent two highly homologous members within the transient receptor potential (TRP) superfamily. However, the role of TRPV6 in bone metabolism is still controversial and little is known about the involvement of TRPV6 in receptor activator of nuclear factor κ-B ligand (RANKL)-induced osteoclastogenesis. Methods: In our study, gene knockout mice, RNA interference, western blot, quantitative real-time PCR, tartrate-resistant acid phosphatase (TRAP) staining, pit formation assay, histomorphometry and measurement of serum parameters were employed to investigate the role of TRPV6 in bone homeostasis, osteoclastogenesis and bone resorption. Results: We found that TRPV6 depletion results in noticeable destruction of bone microarchitecture in TRPV6 knockout mice (TRPV6^-/-), suggesting that TRPV6 is a critical regulator in bone homeostasis. Inactivation of Trpv6 had no effect on osteoblastic bone formation. However, quantification of the TRAP staining showed a significantly increased osteoclast number and surface area in the metaphyseal area of femurs bone sections derived from TRPV6^-/- mice. In agreement with our observations from TRPV6^-/- mice, TRPV6 depletion in vitro significantly increased osteoclasts differentiation and bone resorption activity. Conclusion: Based on these results above, we can draw conclusions that TRPV6 plays an essential role in bone metabolism and is a critical regulator in osteoclasts differentiation and bone resorption.

Mechanisms of otoconia and otolith development

“…The low endolymphatic pH in Pendrin-deficient mice appears to inhibit acid-sensitive TRPV5/6 calcium channels, increasing endolymphatic calcium that likely contributes to the formation of abnormal otoconia crystals (Nakaya et al, 2007). TRPV4 knockout mice have hearing defects, and both TRPV5 and TRPV6 mouse knockouts as well as a trpv6 mutant zebrafish have defective bone formation (Chen et al, 2014; Hoenderop et al, 2003; Tabuchi et al, 2005; Vanoevelen et al, 2011). However, TRPV-deficient mice and zebrafish have not been associated with significant otoconia/otolith abnormalities.…”

Picrasidine I from Picrasma Quassioides Suppresses Osteoclastogenesis via Inhibition of RANKL Induced Signaling Pathways and Attenuation of ROS Production

“…Although many systemic hormones and local cytokines participate in regulating osteoclast differentiation (osteoclastogenesis), the receptor activator of NF-κB (RANK) ligand (RANKL) is the most critical molecular for osteoclastogenesis in cooperation with macrophage colony-stimulating factor (M-CSF) in the interaction between stromal cells and cells of the OCs lineage [2, 3]. Binding of RANKL to cell surface receptor RANK sequentially activate downstream signaling molecules including: the nuclear factor-κB (NF-κB) and mitogen activated protein kinases (MAPKs) [4].…”

Knockdown of Bone Morphogenetic Proteins Type 1a Receptor (BMPR1a) in Breast Cancer Cells Protects Bone from Breast Cancer-Induced Osteolysis by Suppressing RANKL Expression

“…These results suggested that differentiation and activation of osteoclasts at the [2,32]. Among cytokines that demonstrate multi-effect in spurring excessive osteoclast activity and promoting osteolytic metastasis, RANKL is the most prominent cytokine inducer of osteoclastogenesis [1,33,34]. RANKL binding to its receptor (RANK) expressed on the osteoclast precursors and metastatic cells activates NF-κB signaling, resulting in both the transcription of crucial osteoclastogenic cytokines and elevated breast cancer cell migration selectively to bone [2].…”