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It is well known that paraquat (PQ) poisoning can cause severe lung injury during the early stages of exposure, finally causing irreversible pulmonary fibrosis.Connective tissue growth factor (CTGF) is an essential growth factor that participates in tissue repair and pulmonary fibrogenesis.In the present study, we have explored the role of CTGF in a rat model of pulmonary fibrosis induced by PQ poisoning.Histological examination revealed interstitial edema and extensive cellular thickening of interalveolar septa at the early stages of poisoning.Two weeks after PQ administration, lung tissue sections displayed a marked thickening of the alveolar walls with an accumulation of interstitial cells with a fibroblastic appearance.Massons trichrome staining revealed a patchy distribution of collagen deposition, indicating pulmonary fibrogenesis.Western blot and immunohistochemical staining of tissue samples demonstrated that CTGF expression was significantly upregulated in the PQ treated group.Similarly, PQ treatment of MRC-5 human lung fibroblast cells caused an increase in CTGF in a dose-dependent manner.Furthermore, the addition of CTGF to MRC-5 cells triggered cellular proliferation and migration.In addition,CTGF induced the differentiation of fibroblasts to myofibroblasts, as was evident from increased expression of α-SMA and collagen.These findings demonstrate that PQ causes increased CTGF expression, which triggers proliferation, migration, and differentiation of lung fibroblasts.Therefore, CTGF may play an important role in PQ-induced pulmonary fibrogenesis, rendering this growth factor a potential pharmacologic target for reducing lung injury.