TRPV1 Potentiates TGFβ-Induction of Corneal Myofibroblast Development through an Oxidative Stress-Mediated p38-SMAD2 Signaling Loop

Abstract

Injuring mouse corneas with alkali causes myofibroblast expression leading to tissue opacification. However, in transient receptor potential vanilloid 1 channel (TRPV1-/-) knockout mice healing results in transparency restoration. Since TGFβ is the primary inducer of the myofibroblast phenotype, we examined the mechanism by which TRPV1 affects TGFβ-induced myofibroblast development. Experiments were performed in pig corneas and human corneal fibroblasts (HCFs). Immunohistochemical staining of α-smooth muscle actin (α-SMA) stress fibers was used to visualize myofibroblasts. Protein and phosphoprotein were determined by Western blotting. siRNA transfection silenced TRPV1 gene expression. Flow cytometry with a reactive oxygen species (ROS) reporting dye analyzed intracellular ROS. [Ca2+]I was measured by loading HCF with fura2. In organ cultured corneas, the TRPV1 antagonist capsazepine drastically reduced by 75% wound-induced myofibroblast development. In HCF cell culture, TGF-β1 elicited rapid increases in Ca2+ influx, phosphorylation of SMAD2 and MAPKs (ERK1/2, JNK1/2 and p38), ROS generation and, after 72 hrs myofibroblast development. SMAD2 and p38 activation continued for more than 16 h, whereas p-ERK1/2 and p-JNK1/2 waned within 90 min. The long-lived SMAD2 activation was dependent on activated p38 and vice versa, and it was essential to generate a > 13-fold increase in α-SMA protein and a fully developed myofibroblast phenotype. These later changes were markedly reduced by inhibition of TRPV1 or reduction of the ROS generation rate. Taken together our results indicate that in corneal derived fibroblasts, TGFβ- induced myofibroblast development is highly dependent on a positive feedback loop where p-SMAD2-induced ROS activates TRPV1, TRPV1 causes activation of p38, the latter in turn further enhances the activation of SMAD2 to establish a recurrent loop that greatly extends the residency of the activated state of SMAD2 that drives myofibroblast development.

TGF-β regulates phosphorylation and stabilization of Sox9 protein in chondrocytes through p38 and Smad dependent mechanisms

“…Specifically, it was shown that loss of p38 activity results in a decrease in phosphorylation of Smad2/3 after treatment with TGF-β39. This raises the possibility of cross-talk between p38 and Smad2/3 in post-translational regulation of Sox9.…”

Myofibroblasts

“…Fibroblasts derived from TRPV1 knockout mice show impaired myofibroblast activation in culture (Okada et al, 2011). TRPV1 is also expressed in human stromal fibroblasts of the cornea where it enhances pro-fibrotic effects of TGF-β1 and promotes activation of Smad2 and mitogen-activated kinases (Yang et al, 2013a;Yang et al, 2013b). TRPV4 is a mechanosensitive channel and as such mediates substrate-stiffness induced myofibroblasts in liver and lung, and in M A N U S C R I P T…”

Transient receptor potential vanilloid 1 is expressed in human cytotrophoblasts: Induction of cell apoptosis and impairment of syncytialization

“…On the other hand, the inhibition of TRPV1 by CPZ impaired osteoblasts and osteoclasts differentiation (Idris et al, 2010), suggesting that TRPV1 signalling is important for the differentiation of these bone cell types. Moreover, TRPV1 activation is important for the TGF-␤1-induced formation of myofibroblasts from corneal fibroblasts (Yang et al, 2013). For a normal course of pregnancy, it is required a controlled hCTs differentiation and deregulations in this process are associated with gestational complications (Langbein et al, 2008;Lim et al, 1997;Ruebner et al, 2010).…”