Fig. 6

Age-dependent reduction of myofibroblast differentiation was restored by a sialidase inhibitor. a, b Western blot analysis of phosphorylated extracellular signal-related kinase (pERK) was performed in early passage (EP), late passage (LP), and zanamivir (2 mM)-treated LP fibroblasts. The histogram (b) shows mean densitometric readings ± SD for the phosphorylated proteins normalized to the loading controls. Values were obtained from three independent experiments. *P < 0.05, **P < 0.02. c, d Western blot analysis for α-smooth muscle actin (α-SMA) was performed 3 days after myofibroblast differentiation in EP, LP, and zanamivir-treated LP fibroblasts. The histogram (d) shows mean densitometric readings ± SD of α-SMA normalized to the loading control (β-actin). The values were obtained from three independent experiments. **P < 0.02. e Schematic representation of myofibroblast differentiation regulated by CD44 sialylation. Hyaluronic acid (HA) synthesized via HAS2 after transforming growth factor (TGF)-β1 stimulation contributes to the relocalization of CD44 to lipid rafts; the association between epidermal growth factor receptor (EGFR) and CD44 then activates MAPK/ERK signaling required for myofibroblast differentiation [23]. In aged fibroblasts, increased expression of the sialidase NEU1 contributes to the desialylation of CD44, which is unable to relocalize to lipid rafts even after TGF-β1 stimulation. Therefore, CD44 cannot bind anymore to the EGFR, leading to the inhibition of myofibroblast differentiation