TLR4-dependent fibroblast activation drives persistent organ fibrosis in skin and lung

Area of Science:

• Immunology
• Fibrosis Research
• Dermatology

Background:

• Persistent organ fibrosis characterizes systemic sclerosis (SSc).
• Toll-like receptors (TLRs) and their endogenous ligands (DAMPs) are implicated in fibrosis.
• The specific role of TLR4 and its coreceptor MD2 in fibrosis persistence requires elucidation.

Purpose of the Study:

• To investigate the role of myeloid differentiation 2 (MD2) and Toll-like receptor 4 (TLR4) in driving persistent fibrosis in systemic sclerosis (SSc).
• To evaluate the therapeutic potential of a novel small molecule inhibitor targeting the MD2/TLR4 complex.

Main Methods:

• Quantification of MD2/TLR4 levels and TLR4-responsive gene signatures in SSc patient biopsies.
• Development and application of a selective MD2-blocking small molecule.
• Assessment of MD2/TLR4 targeting effects on fibroblast activation, matrix remodeling, and organ fibrosis in vitro, ex vivo, and in vivo preclinical models.
• Analysis of fibroblast-specific TLR4 deletion in mice.
• Comparison of experimental TLR4 gene signatures with SSc patient gene expression data.

Main Results:

• Elevated MD2, TLR4, and a TLR4-responsive gene signature were observed in SSc skin biopsies.
• Targeting MD2/TLR4 abrogated myofibroblast transformation and matrix remodeling in various experimental systems.
• A selective TLR4 inhibitor prevented and reversed organ fibrosis in multiple preclinical models.
• Fibroblast-specific TLR4 deletion in mice conferred significant protection against fibrosis.
• A subset of SSc patients exhibited an activated TLR4 signature.

Conclusions:

• MD2/TLR4-dependent fibroblast activation is a critical driver of persistent organ fibrosis in SSc.
• Selective inhibitors of the MD2/TLR4 complex represent a promising therapeutic strategy for SSc.
• SSc patients with high TLR4 activity may benefit most from MD2/TLR4 complex inhibitors.