TRPV4 Protects the Lung from Bacterial Pneumonia via MAPK Molecular Pathway Switching

Abstract

Mechanical cell–matrix interactions can drive the innate immune responses to infection; however, the molecular underpinnings of these responses remain elusive. This study was undertaken to understand the molecular mechanism by which the mechanosensitive cation channel, transient receptor potential vanilloid 4 (TRPV4), alters the in vivo response to lung infection. For the first time, to our knowledge, we show that TRPV4 protects the lung from injury upon intratracheal Pseudomonas aeruginosa in mice. TRPV4 functions to enhance macrophage bacterial clearance and downregulate proinflammatory cytokine secretion. TRPV4 mediates these effects through a novel mechanism of molecular switching of LPS signaling from predominant activation of the MAPK, JNK, to that of p38. This is accomplished through the activation of the master regulator of inflammation, dual-specificity phosphatase 1. Further, TRPV4’s modulation of the LPS signal is mechanosensitive in that both upstream activation of p38 and its downstream biological consequences depend on pathophysiological range extracellular matrix stiffness. We further show the importance of TRPV4 on LPS-induced activation of macrophages from healthy human controls. These data are the first, to our knowledge, to demonstrate new roles for macrophage TRPV4 in regulating innate immunity in a mechanosensitive manner through the modulation of dual-specificity phosphatase 1 expression to mediate MAPK activation switching.

TRPV4—A Missing Link Between Mechanosensation and Immunity

“…This concept has already been well-established for epithelial and endothelial cells, where mechanical activation of TRPV4 has emerged a major regulator of barrier function and inflammatory responses. Yet, this notion has also been demonstrated for innate immune cells such as macrophages where Ca 2+ signaling as a function of TRPV4-mediated sensing of substrate stiffness has been shown to shift the immune response from pro-inflammatory to an anti-inflammatory and resolving phenotype (15,73) (Figure 2). Similar scenarios of mechanoregulation of immune cell function via TRPV4 may relate to a variety of scenarios where immune cells undergo changes in mechanical stress, such as during cell adhesion (shear stress) and transmigration (substrate stiffness, shape change), capillary transit (shape change) as well as tissue strain e.g., in mechanically ventilated lungs (stretch).…”

“…In gram-negative infections with bacteria such as Escherichia coli and Pseudomonas aeruginosa, TRPV4 activation by ECM stiffening during infection synergizes with LPS-stimulated TLR4 activation of p38 and thereby promotes host defense and resolution from lung injury (15,73). Conversely, activation of protease-activated receptor (PAR)-2 by thrombin suppresses TRPV4 activity in macrophages and resolves lung injury (74).…”

“…Conversely, activation of protease-activated receptor (PAR)-2 by thrombin suppresses TRPV4 activity in macrophages and resolves lung injury (74). Similarly, PARs are also activated by neutrophil elastase (NE), matrix metalloproteases (MMPs) or other microbial proteases (33,(75)(76)(77)(78)(79) which has been implicated to degrade ECM and thereby causing remodeling and matrix stiffening during infection (33,63,73,80).…”

“…In line with a critical role of substrate stiffness for immune cell function, the Ca 2+ response to LPS in of macrophages were shown to correlate with substrate stiffness. Notably, such substrate stiffness-dependent modulation of macrophage signaling can alter macrophage phenotype toward an antiinflammatory phenotype (M2) initiating bacteria clearance and resolution of lung injury (15,73).…”

Urgent reconsideration of lung edema as a preventable outcome in COVID-19: inhibition of TRPV4 represents a promising and feasible approach

“…Notably, phase I clinical trials using a selective TRPV4 inhibitor did not detect increased liver enzymes in healthy volunteers or patients with congestive heart failure (17). In regard to respiratory infections, recent studies report that TRPV4 inhibition may reduce bacterial clearance of Pseudomonas aeruginosa by macrophages (36). However, TRPV4 inhibition seems beneficial in lung infection with Streptococcus pneumoniae, the most frequent microbial cause of community-acquired pneumonia (29).…”