TRPV4 Mechanosensitive Ion Channel Regulates Lipopolysaccharide-Stimulated Macrophage Phagocytosis

Abstract

Macrophage phagocytosis of particles and pathogens is an essential aspect of innate host defense. Phagocytic function requires cytoskeletal rearrangements that depend on the interaction between macrophage surface receptors, particulates/pathogens and the extracellular matrix. In the present report we determine the role of a mechanosensitive ion channel, transient receptor potential vanilloid 4 (TRPV4), in integrating the lipopolysaccharide (LPS) and matrix stiffness signals to control macrophage phenotypic change for host defense and resolution from lung injury. We demonstrate that active TRPV4 mediates LPS-stimulated murine macrophage phagocytosis of non-opsonized particles (E. coli) in vitro and opsonized particles (IgG-coated latex beads) in vitro and in vivo in intact mice. Intriguingly, matrix stiffness in the range seen in inflamed or fibrotic lung is required to sensitize the TRPV4 channel to mediate the LPS-induced increment in macrophage phagocytosis. Furthermore, TRPV4 is required for the LPS induction of anti-inflammatory/pro-resolution cytokines. These findings suggest that signaling through TRPV4, triggered by changes in extracellular matrix stiffness, cooperates with LPS-induced signals to mediate macrophage phagocytic function and lung injury resolution. These mechanisms are likely to be important in regulating macrophage function in the context of pulmonary infection and fibrosis.

TRPV4 mediates the Ca2+ influx required for the interaction between flightless-1 and non-muscle myosin, and collagen remodeling

“…As Ca 2+ plays a central role in controlling actomyosin contractile forces during cell motility (Wei et al, 2009), we used FliI WT and KND cells to examine the involvement of Ca 2+ in FliI-NMMIIA interactions. We found that in intact cells, localized Ca 2+ fluxes were concentrated at growing cell extensions, which were enriched with TRPV4 channels (Adapala et al, 2013;Scheraga et al, 2016;Thodeti et al, 2009). …”

“…Notably, TRPV4 activation requires application of mechanical strain at focal adhesions, which results in Ca 2+ influx (Matthews et al, 2010). In professional phagocytic cells such as macrophages, lipopolysaccharide-stimulated phagocytosis is also regulated by TRPV4 (Scheraga et al, 2016), indicating a broader role for this channel protein in determining the interactions of cells with external particles and matrix molecules.…”

Biophysical regulation of macrophages in health and disease

“…Macrophages express TRPV4, TRPV2, TRPC6, and TRPM7, which have roles in inflammatory activation and phagocytosis. TRPV4 appears to negatively regulate LPS‐induced inflammation, but enhances both LPS‐mediated phagocytosis and ox‐LDL uptake . In contrast, a recent study found that TRPM7 positively regulates LPS‐induced inflammatory activation by enhancing endocytosis of the LPS‐TLR4 complex, and its depletion has been shown to protect mice from LPS‐induced peritonitis .…”

“…Finally, manipulation of the expression and activity of TRPV2 and TRPC6 reveals that these channels are required for phagocytosis in macrophages . While all of these channels have been shown to be regulated by biophysical cues in other cell types, thus far, only TRPV4 activity is known to be influenced by the mechanical environment in macrophages . BMDMs seeded on stiffer substrates exhibited increased LPS‐mediated intracellular calcium influx and phagocytic capacity compared to cells on soft surfaces, and pharmacological inhibition or reduced expression of TRPV4 resulted in decreased phagocytosis in BMDMs cultured on stiff substrates.…”

A pathologic two‐way street: how innate immunity impacts lung fibrosis and fibrosis impacts lung immunity

“…Neutrophil chemotaxis is also regulated by DDR2 when cultured in 3D matrices . Additionally, transient receptor potential vanilloid 4 or TRPV4, an ion channel sensitive to changes in collagen stiffness, has been shown to regulate macrophage phagocytosis . Increasing levels of collagen can be found in the lungs as the development of fibrosis progresses, so it is plausible that collagen and matrix stiffness can mediate the function of immune cells through the actions of the aforementioned receptors to alter their responses to respiratory infections.…”