B19-07 NGF-TrkA Signaling Drives Sympathetic Nerve-Dependent Pulmonary Fibrosis

Abstract Rationale Pulmonary fibrosis is characterized by relentless scar formation and accumulation of α-smooth muscle actin (αSMA)+ myofibroblasts. While fibroblast activation via TGF-β signaling drives extracellular matrix deposition, the role of neuro-fibrotic crosstalk remains poorly defined. We previously identified aberrant sympathetic innervation in fibrotic regions enriched with αSMA+ myofibroblasts, forming a distinct nerve-fibroblast niche. Nerve growth factor (NGF), a key mediator of sympathetic nerve growth, functions as a pleiotropic cytokine that influences multiple cell types. We tested the hypothesis that NGF promotes sympathetic nerve-dependent fibrogenesis through its high-affinity receptor, tropomyosin receptor kinase A (TrkA). Methods NGF expression was assessed in bleomycin-induced lung fibrosis in vivo and in normal human lung fibroblasts stimulated with TGF-β1 or co-cultured with sympathetic neurons derived from mouse superior cervical ganglia in vitro using RT-PCR, ELISA, and immunohistochemistry. Functional blockade of NGF was achieved by systemic administration of anti-NGF IgG in bleomycin-challenged wild-type mice and by generating mice with sympathetic nerve-specific deletion of TrkA (Th-Cre; Ntrk1f/f). Sympathetic innervation was analyzed using whole-lung tissue clearing and 3D light-sheet microscopy to identify TH+ nerves. Inflammation and fibrosis were quantified by bronchoalveolar lavage (BAL) white blood cell (WBC) counts, Sircol collagen assay, and Masson’s trichrome staining. Results In bleomycin-challenged lungs, αSMA+ myofibroblasts co-expressed NGF, while NGF concentrations were overall unchanged in BAL and tissue lysates. TGF-β1 stimulation increased NGF expression in human lung fibroblasts, which was further enhanced by neuronal co-culture. Neutralization of NGF with systemic anti-NGF IgG increased BAL WBC counts and exacerbated fibrosis, as evidenced by elevated collagen deposition and higher Modified Ashcroft scores. In contrast, sympathetic nerve-specific deletion of TrkA reversed bleomycin-induced aberrant sympathetic innervation, restored inflammatory homeostasis, and attenuated lung fibrosis, suggesting that TrkA signaling is a key driver of sympathetic nerve-dependent fibrogenesis. Conclusions Lung fibroblasts are a critical source of NGF within the profibrotic nerve-fibroblast niche. The deleterious effects of systemic NGF blockade exacerbate lung injury and fibrosis and underscore its context-dependent, pleiotropic regulatory role in tissue homeostasis. The finding that sympathetic nerve-specific TrkA deletion attenuates fibrosis positions NGF-TrkA signaling as a key mediator of the profibrotic nerve-fibroblast axis. Together, these findings reveal a previously unrecognized neuro-fibrotic signaling pathway with therapeutic potential in pulmonary fibrosis. This abstract is funded by: GI was supported by T32HL007778, a Scholar Award from the Pulmonary Fibrosis Foundation, Wit Family Distinguished Scholar in Inflammation Science, Yale Physician Scientist Development Award (UL1 TR001863), and Parkar B. Francis Fellowship Award. AG was supported by T32HL007778. ELH was supported by R01HL152677 and R01HL163984.