TRPV4-mediated calcium signaling in mesenchymal stem cells regulates aligned collagen matrix formation and vinculin tension

The development, repair, and regeneration of anisotropic connective tissues (e.g., tendon, ligament, meniscus) involve deposition of aligned fibrillar collagen by cells. However, the intracellular signaling mechanisms mediating this process are not fully understood. We show that the mechanosensitive cation channel transient receptor potential vanilloid 4 (TRPV4) plays a critical role in controlling aligned collagen assembly by mesenchymal stem cells. Specifically, inhibiting TRPV4 activity in mesenchymal stem cells disrupts aligned collagen matrix assembly, and conversely, activating TRPV4 accelerates collagen deposition. Additionally, TRVP4 activity modulates force transmitted across vinculin, a key mechanosensitive protein within cell–matrix adhesions, where cell-generated forces are critical in fibrillar collagen assembly. Understanding and controlling specific cell-signaling mechanisms underlying aligned matrix assembly could lead to improved tissue regeneration outcomes.Microarchitectural cues drive aligned fibrillar collagen deposition in vivo and in biomaterial scaffolds, but the cell-signaling events that underlie this process are not well understood. Utilizing a multicellular patterning model system that allows for observation of intracellular signaling events during collagen matrix assembly, we investigated the role of calcium (Ca2+) signaling in human mesenchymal stem cells (MSCs) during this process. We observed spontaneous Ca2+ oscillations in MSCs during fibrillar collagen assembly, and hypothesized that the transient receptor potential vanilloid 4 (TRPV4) ion channel, a mechanosensitive Ca2+-permeable channel, may regulate this signaling. Inhibition of TRPV4 nearly abolished Ca2+ signaling at initial stages of collagen matrix assembly, while at later times had reduced but significant effects. Importantly, blocking TRPV4 activity dramatically reduced aligned collagen fibril assembly; conversely, activating TRPV4 accelerated aligned collagen formation. TRPV4-dependent Ca2+ oscillations were found to be independent of pattern shape or subpattern cell location, suggesting this signaling mechanism is necessary for aligned collagen formation but not sufficient in the absence of physical (microarchitectural) cues that force multicellular alignment. As cell-generated mechanical forces are known to be critical to the matrix assembly process, we examined the role of TRPV4-mediated Ca2+ signaling in force generated across the load-bearing focal adhesion protein vinculin within MSCs using an FRET-based tension sensor. Inhibiting TRPV4 decreased tensile force across vinculin, whereas TRPV4 activation caused a dynamic unloading and reloading of vinculin. Together, these findings suggest TRPV4 activity regulates forces at cell-matrix adhesions and is critical to aligned collagen matrix assembly by MSCs.