Figure 1: Noradrenergic signals and sympathetic nerves contribute to pulmonary fibrosis.
(A-E) Wild-type mice were administered 2.0 U/kg orotracheal bleomycin or control vehicle on Day 0 and sacrificed on Day 14. Bleomycin challenge resulted in increased collagen deposition, as evidenced by trichrome staining (A, B) and elevated right lung collagen content (C, P < 0.0001). BAL noradrenaline levels were significantly increased following bleomycin administration (D, P = 0.0138), while plasma levels remained unchanged (E). (F-K) Immunofluorescence and confocal imaging revealed α-SMA (red), PGP9.5 or TH (green), and DAPI nuclear staining (blue) in mouse lungs treated with vehicle or bleomycin. Normal lungs showed typical expression of PGP9.5 and TH in airways and blood vessels (F, I). Fibrotic lungs retained these markers and also displayed PGP9.5 or TH-positive nerves in alveolar regions (G, J). A significant positive correlation was established between both nerve types and these key effector cells (P = 0.0134 and P = 0.0203, respectively). (L-O) Mice with genetic deletion of TrkA in sympathetic nerves (genotype: Th-Cre; Ntrk1f/f) or intact TrkA (Th-Cre) were given orotracheal bleomycin on Day 0 and sacrificed on Day 14. In Th-Cre; Ntrk1f/f mice, BAL noradrenaline levels were reduced (L, P = 0.0267), along with decreased right lung collagen content (M, P = 0.0491) and improved trichrome staining (N, O). Images were captured at 20x magnification. Data are presented as mean ± SEM or median ± IQR. Statistical comparisons were conducted using Student’s t-test for normally distributed data and Mann-Whitney test for non-normally distributed data. Statistical correlations were conducted using Spearman’s Rank Correlation Coefficient. *P < 0.05, ****P < 0.0001. α-SMA, alpha-smooth muscle actin; BAL, bronchoalveolar lavage; DAPI, 4’,6-diamidino-2-phenylindole; HPF, high-power field; PGP9.5, ubiquitin carboxy-terminal hydrolase L1; TH, tyrosine hydroxylase.