TRPV4 differentially controls inflammatory cytokine networks during static and dynamic compression of the intervertebral disc

Abstract

BackgroundThe ion channel transient receptor potential vanilloid 4 (TRPV4) critically transduces mechanical forces in the IVD, and its inhibition can prevent IVD degeneration due to static overloading. However, it remains unknown whether different modes of loading signals through TRPV4 to regulate the expression of inflammatory cytokines. We hypothesized that TRPV4 signaling is essential during static and dynamic loading to mediate homeostasis and mechanotransduction.MethodsMouse functional spine units were isolated and either cyclically compressed for 5 days (1 Hz, 1 h, 10% strain) or statically compressed (24 h, 0.2 MPa). Conditioned media were monitored at 6 h, 24 h, 2 days, and 5 days, with and without TRPV4 inhibition. Effects of TRPV4 activation was also evaluated without loading. The media was analyzed for a panel of 44 cytokines using a microbead array and then a correlative network was constructed to explore the regulatory relationships during loading and TRPV4 inhibition. After the loading regimen, the IVDs were evaluated histologically for degeneration.ResultsActivation of TRPV4 led to an increase interleukin‐6 (IL‐6) family of cytokines (IL‐6, IL‐11, IL‐16, and leukemia inhibitory factor [LIF]) and decreased the T‐cell (CCL3, CCL4, CCL17, CCL20, CCL22, and CXCL10) and monocyte (CCL2 and CCL12) recruiting chemokines by the IVD. Dynamic and static loading each provoked unique chemokine correlation networks. The inhibition of TRPV4 during dynamic loading dysregulated the relationship between LIF and other cytokines, while the inhibition of TRPV4 during static loading disrupted the connectivity of IL‐16 and VEGFA.ConclusionsWe demonstrated that TRPV4 critically mediates the cytokine production following dynamic and static loading. The activation of TRPV4 upregulated a diverse set of cytokines that may suppress the chemotaxis of T‐cells and monocytes, implicating the role of TRPV4 in maintaining the immune privilege of healthy IVD.

Diverse and multifunctional roles for perlecan (HSPG2) in repair of the intervertebral disc

“… 163 Sustained compressive loading of the IVD resulted in elevated NF‐κB activity, IL‐6 and vascular endothelial growth factor A (VEGFA) production, and degenerative changes to the ECM, whereas TRPV4 inhibition during loading mitigated the changes in inflammatory cytokines and protected against IVD degeneration. 166 These results indicate that mechano‐osmotic signaling via TRPV4 plays an important role in both short‐ and long‐term adaptations of the IVD and could be targeted to prevent load‐induced IVD degeneration. A number of studies have demonstrated the responsiveness of AF and NP cells to short duration or long term dynamic compression which can result in a combination of anabolic and catabolic responses that may result in ECM remodeling or enhanced matrix synthesis.…”

“…While the TRPV4 ion channel can regulate secretion of inflammatory mediators contributing to IVD degenerative changes and pain, 166 , 173 a recent study demonstrated that activation of the innate immune response through toll‐like receptors (TLRs) can also contribute to deleterious IVD changes in IVDD. 174 Mechanically loaded rat IVDs displayed increased pro‐inflammatory mediators with static but not dynamic loading.…”

Analysis of Infiltrating Immune Cells Following Intervertebral Disc Injury Reveals Recruitment of Gamma-Delta (γδ) T cells in Female Mice

“…The mechanisms that promote immune cell infiltration into the IVD due to injury were not investigated. Previous work has demonstrated that applying damaging mechanical loads promotes production of neutrophil-recruiting chemokines and mechanosensitive ion channel activation temporally regulates immune cell-recruiting chemokines 51 . Endogenous production of immune-related chemokines from IVD cells could partially explain how immune cells home to injured IVDs.…”

Advancing basic and preclinical spine research: Highlights from the ORS PSRS 6th International Spine Research Symposium

“…Using a rabbit model, Fainor et al show that perturbations in disc biomechanics not only cause local pathological remodeling in structures such as the vertebral endplates, but also in adjacent structures such as the facet joints 2 . Easson et al identified the ion channel transient receptor potential vanilloid 4 (TRPV4) as performing a critical role in mediating the interplay between inflammation and loading in mouse intervertebral discs 3 …”