TRPV4-mediates oscillatory fluid shear mechanotransduction in mesenchymal stem cells in part via the primary cilium

Abstract

Skeletal homeostasis requires the continued replenishment of the bone forming osteoblast from a mesenchymal stem cell (MSC) population, a process that has been shown to be mechanically regulated. However, the mechanisms by which a biophysical stimulus can induce a change in biochemical signaling, mechanotransduction, is poorly understood. As a precursor to loading-induced bone formation, deciphering the molecular mechanisms of MSC osteogenesis is a critical step in developing novel anabolic therapies. Therefore, in this study we characterize the expression of the mechanosensitive calcium channel Transient Receptor Potential subfamily V member 4 (TRPV4) in MSCs and demonstrate that TRPV4 localizes to areas of high strain, specifically the primary cilium. We demonstrate that TRPV4 is required for MSC mechanotransduction, mediating oscillatory fluid shear induced calcium signaling and early osteogenic gene expression. Furthermore, we demonstrate that TRPV4 can be activated pharmacologically eliciting a response that mirrors that seen with mechanical stimulation. Lastly, we show that TRPV4 localization to the primary cilium is functionally significant, with MSCs with defective primary cilia exhibiting an inhibited osteogenic response to TRPV4 activation. Collectively, this data demonstrates a novel mechanism of stem cell mechanotransduction, which can be targeted therapeutically, and further highlights the critical role of the primary cilium in MSC biology.

Mechanotransduction and dynamic outflow regulation in trabecular meshwork requires Piezo1 channels

“…The sensitivity of flow-induced signals to GsMTx4 and Piezo1 knockdown identifies Piezo1 as the principal transducer of these responses. The fraction (~15%) of the flow-induced signal that was mediated by TRPV4 is in line with reports of TRPV4dependent shear transduction in SMCs and endothelia (67)(68)(69)(70). It is possible that the TRPV4 component might increase at shear stresses induced by larger pressure gradients (67-69).…”

Pressure‐induced mesenchymal stem cell osteogenesis is dependent on intermediate filament remodeling

“…Given the limited knowledge of the role of physiologic pressure on cell behavior, it is not surprising that the mechanisms of pressure mechanotransduction remain elusive. Many mechanotransduction mechanisms have been discovered within bone in response to fluid shear, and several of these represent an extension of the cytoskeleton, such as microtubule-based primary cilia or focal adhesion-integrin binding of the actin network (48)(49)(50)(51). Moreover, modulation of cytoskeletal architecture with bone lineage commitment has been indicated as a marker of mechanoadaptation, such as delayed actin remodeling and formation of dendritic processes in response to oscillatory fluid flow in osteocytes vs. osteoblasts (35,52).…”

Deficient primary cilia in obese adipose‐derived mesenchymal stem cells: obesity, a secondary ciliopathy?

“…Interestingly, MSCs with inhibited primary cilia showed a significant reduction in basal mRNA expression levels of all three lineages specific transcription factors, namely, RUNX2, the peroxisome proliferator-activated receptor γ (PPARγ) and SRY-box 9 (SOX9), for osteogenic, adipogenic and chondrogenic differentiation, respectively (52). The primary cilium of MSCs mediates mechanotransduction and affects the gene expression for osteogenic differentiation (53,54). The length of cilia was shown to be elongated after 2-d induction of adipogenic differentiation followed by increased nuclear PPARγ, an early marker of adipogenesis (55).…”