Introduction: Differential display-polymerase chain reaction (DD-PCR) was used to screen for over-expressed genes during scarless fetal wound healing in the rat model. One gene identified was murine adherent macrophage (mama). The mama product has been identified in murine macrophages as a secreted protein, but its function and regulation is unknown. Mama expression in skin, and during wound healing, has not been reported. Methods: Sixteen day gestation fetal rat skin wound tissue was collected at 1d and 3d post-wounding. Up-regulated genes found by DD-PCR were cloned and sequenced, and their expression change confirmed by reverse Northern dot blot analysis. In situ hybridization was done on neonatal rat skin. To study the regulation of mama expression, confluent primary rat fetal and adult dermal fibroblasts were fasted overnight, and then treated with TGF-beta1, FGF-2, TNF-alpha, IFN-gamma and insulin, respectively for 30 min to 24 hours. Mama expression was analyzed by Northern blot analysis and quantitated by densitometry. Results: The expression of mama was increased in fetal skin scarless wounds by DD-PCR (3.8±0.72 fold at 1d and 3.8±0.66 fold at 3d post-wounding) and reverse Northern dot blot (5.3±0.69 fold at 1d and 3.3±0.59 fold at 3d post-wounding). Mama expression was localized to both dermal fibroblasts and keratinocytes by in situ hybridization. Mama gene expression in fetal dermal fibroblasts was higher than adult dermal fibroblasts (~1.8 fold). Of the cytokine tested, IFN-gamma increased mama expression in rat dermal fibroblasts: 4.9±1.34 fold after 24 hours treatment (P<0.05). Conclusion: This is the first observation of mama expression in skin and during scarless wound repair. Because the expression of mama was up-regulated, and it is a secreted protein, mama may have autocrine/paracrine effects on keratinocytes and fibroblasts during scarless repair. Additionally, IFN-gamma can induce mama expression in dermal fibroblasts, suggesting that increased mama expression may be one mechanism by which IFN-gamma reduces myofibroblast number and collagen fibrosis in adult wounds.
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