Transient Receptor Potential Vanilloid channel regulates fibroblast differentiation and airway remodeling by modulating redox signals through NADPH Oxidase 4

Abstract

Asthma is characterized by pathological airway remodeling resulting from persistent myofibroblast activation. Although transforming growth factor beta 1 (TGFβ1), mechanical signals, and reactive oxygen species (ROS) are implicated in fibroblast differentiation, their integration is still elusive. We identified that Transient Receptor Potential Vanilloid 4 (TRPV4), a mechanosensitive ion channel mediates lung fibroblast (LF) differentiation and D. farinae-induced airway remodeling via a novel TRPV4-NADPH Oxidase 4 (NOX4) interaction. NOX4-mediated ROS production is essential for TGFβ1-induced LF differentiation via myocardin-related transcription factor-A (MRTF-A) and plasminogen activator inhibitor 1 (PAI-1). Importantly, TRPV4 inhibition prevented TGFβ1-induced NOX4 expression and ROS production. Both TRPV4 and NOX4 are activated by phosphatidylinositol 3-kinase (PI3K) downstream of TGFβ1, and signals from both TRPV4 and Rac are necessary for NOX4 upregulation. Notably, NOX4 expression is higher in fibroblasts derived from asthmatic patients (disease human LF; DHLF) in comparison to non-asthmatics (normal human LF; NHLF). Further, NOX4 expression is up-regulated in the lungs of D.farinae-treated wild type mice (WT) relative to saline-treated WT, which was attenuated in TRPV4 knockout (KO) mice. Our findings suggest that TRPV4 integrates TGFβ1 and ROS signaling through NOX4 and, TRPV4-NOX4 interaction is amenable to target lung remodeling during asthma.

Advances in TRP channel drug discovery: from target validation to clinical studies

“…In IPF models, Trpv4 –/– mice are protected from fibrosis 187 . TRPV4 modulates transforming growth factor (TGF)-β1-dependent actions in a SMAD -independent manner with enhanced actomyosin remodelling and increased nuclear translocation of the α-smooth muscle actin-transcription co-activator, myocardin-related transcription factor (MRTF)-A 188 , 189 . These data point to TRPV4 inhibition as a potential therapeutic approach in pulmonary fibrosis 189 .…”

TRPV4 Mechanotransduction in Fibrosis

“…Although the exact reason for the requirement of different PI3K isoforms in these studies is not clear, it could be due to different fibroblast cells used. Furthermore, recent studies from Paruchuri and colleagues demonstrated a critical role for NOX4 and reactive oxygen species (ROS) in TRPV4-mediated TGF-β1 induced lung fibroblast differentiation and D. farina-induced airway remodeling [83]. Specifically, NOX4 was shown to regulate TGF-β1-induced fibroblast differentiation via the activation of MRTF-A and increased PAI-1 expression, suggesting that NOX4 regulates fibrotic gene expression and matrix remodeling.…”

“…Specifically, NOX4 was shown to regulate TGF-β1-induced fibroblast differentiation via the activation of MRTF-A and increased PAI-1 expression, suggesting that NOX4 regulates fibrotic gene expression and matrix remodeling. Interestingly, the inhibition of NOX4 activity did not change TRPV4 activity, suggesting that NOX4 is downstream of TRPV4 [83]. Fibroblast differentiation can also be modulated by nitric oxide (NO) [84,85].…”

TRPV4 integrates matrix mechanosensing with Ca2+ signaling to regulate extracellular matrix remodeling

“…Mechanistically, TRPV4 regulates the pro-fibrotic functions of TGFb by modulating signaling pathways downstream of this cytokine, including activation of Phosphoinositide 3 kinase (PI3K)/Protein kinase B (AKT), MAPK/ERK, Rho/Rho kinase, NADPH oxidase 4 (NOX4), Myocardin-related transcription factor A (MRTF-A), and YAP/TAZ (Fig. 2) [136,144,146]. Importantly, pharmacological activation of TRPV4 can upregulate the expression of a-SMA and matrix molecules, formation of aligned collagen, phosphorylation of AKT, and activation of MRTF-A independently from TGFb [2,4,147].…”