Modulation of Transient Receptor Potential Channels 3 and 6 Regulates Osteoclast Function with Impact on Trabecular Bone Loss

Sebastian Klein,Michael J Raschke,Otto Lindemann,Manfred Fobker,Thomas Pap,Melanie Timmen,Daniel Kronenberg,Richard Stange,Birgit Mentrup,Joanna Sherwood

doi:10.1007/s00223-020-00673-8

Abstract

Enhanced osteoclast formation and function is a fundamental cause of alterations to bone structure and plays an important role in several diseases impairing bone quality. Recent work revealed that TRP calcium channels 3 and 6 might play a special role in this context. By analyzing the bone phenotype of TRPC6-deficient mice we detected a regulatory effect of TRPC3 on osteoclast function. These mice exhibit a significant decrease in bone volume per tissue volume, trabecular thickness and -number together with an increased number of osteoclasts found on the surface of trabecular bone. Primary bone marrow mononuclear cells from TRPC6-deficient mice showed enhanced osteoclastic differentiation and resorptive activity. This was confirmed in vitro by using TRPC6-deficient RAW 264.7 cells. TRPC6 deficiency led to an increase of TRPC3 in osteoclasts, suggesting that TRPC3 overcompensates for the loss of TRPC6. Raised intracellular calcium levels led to enhanced NFAT-luciferase reporter gene activity in the absence of TRPC6. In line with these findings inhibition of TRPC3 using the specific inhibitor Pyr3 significantly reduced intracellular calcium concentrations and normalized osteoclastic differentiation and resorptive activity of TRPC6-deficient cells. Interestingly, an up-regulation of TRPC3 could be detected in a cohort of patients with low bone mineral density by comparing micro array data sets of circulating human osteoclast precursor cells to those from patients with high bone mineral density, suggesting a noticeable contribution of TRP calcium channels on bone quality. These observations demonstrate a novel regulatory function of TRPC channels in the process of osteoclastic differentiation and bone loss.

Highlights

Human diseases with an acquired loss of bone account for increased mortality especially among elderly men and women [1]
A significant increase in TRPC3 expression could be detected by comparing data set GSE7158, an Asian cohort of 12 females [age 25.3 (3.1) years] with an average hip bone mineral density (BMD) Z score of − 1.72 (0.60) and 14 females
Our transcriptome analysis revealed that women with low bone mineral density show an increased expression of TRPC3 in human osteoclast precursor cells

Summary

Introduction

Human diseases with an acquired loss of bone account for increased mortality especially among elderly men and women [1]. Monocyte/macrophage derived osteoclasts are considered to mediate the exceeding loss of bone Their differentiation depends on the availability of intracellular calcium ions, since calcium binding stimulates phosphatases including calcineurin [3], which subsequently facilitates the translocation of factors such as nuclear factor of activated T-cells NFATc1 into the nucleus and induces the transcription of osteoclastogenesis-promoting genes [4]. Many different membrane channels, including the transient receptor potential (TRP) ion channel family, control the entry of calcium ions into the cells [5] This family consists of six subgroups including the canonical (TRPC) and the vanilloid (TRPV) subtype, with TRPV channels previously demonstrated as modulators of calcium signaling in osteoclasts [6, 7]. TRPC channels belong to a group of seven cation channels divided into subgroups according to their amino acid sequence similarities and they can assemble as homo- and heterotetramers [8]

Objectives

Methods

Results

Conclusion