Figure 7.

Therapeutic targeting of MyoD in the lungs of aged mice with established fibrosis leads to fibrosis resolution. (A) Isolated lung fibroblasts from uninjured young mice were transfected with MyoD-targeting or -nontargeting siRNA. Transfected cells were serum starved overnight and treated with/without TGF-β (2 ng/ml) for 48 hours. MyoD was assessed by Western blotting. (B and C) Aged (18 mo old) C57BL/6 mice were subjected to lung injury by airway instillation of intratracheal bleomycin (1.25 U/kg). The mice were then treated with intranasal instillation of MyoD or vehicle siRNA every other day from Week 3 to Week 6. Lung tissue was harvested at 0 week (uninjured), 3 weeks, and 6 weeks after injury/treatment. Fibrosis was assessed by Masson’s trichrome blue staining for collagen (top panels) and MyoD was assessed by immunohistochemical staining for MyoD (bottom panels) (B), and whole-lung homogenates were analyzed by quantitative hydroxyproline assay (C). Scale bars: 100 μm. Data are expressed as total micrograms of hydroxyproline per whole lung. Differences among groups were assessed with one-way ANOVA multiple comparisons with Tukey’s post test. Values represent means ± SEM; n = 6–11 biological replicates; *P < 0.05 as compared with NT-siRNA using one-way ANOVA multiple comparisons with Tukey’s post test.