Coordinate expression of NGF and alpha-smooth muscle actin mRNA and protein in cutaneous wound tissue of developing and adult rats

Nerve growth factor (NGF) is synthesized in cutaneous wound tissue, and its higher levels in the neonate may contribute to more efficient wound healin g. We used in sim hybridization and immunohistochemistry to define NGF mRNA and protein expression in intact skin and following excision wounding in n eonatal and adult rats. To determine whether NGF is associated with wound c ontractile fibroblasts (myofibroblasts), we also examined expression of alp ha-smooth muscle actin (alpha-SMA) mRNA and protein, established markers fo r these cells. In intact skin, NGF mRNA and protein were present in vascula r and arrector pill smooth muscle, hair follicle sheath cells, keratinocyte s, and hypodermal fibroblasts. Neonatal adipocytes and Schwann cells also e xpressed NGF mRNA and protein, while adult adipocytes and Schwann cells dis played only NGF-ir. Following wounding, NGF mRNA expression was exuberant i n these cell types, and increased similarly at both ages and appeared de no vo in skeletal muscle cells. Additionally, both NGF mRNA and protein were p resent in macrophages and myofibroblasts, and expression in myofibroblasts was significantly greater in neonates. Wound myofibroblasts also expressed alpha-SMA. Surprisingly, after wounding alpha-SMA mRNA and protein were pre sent in essentially all cells in which NGF mRNA was detected. We conclude t hat NGF expression is enhanced in many cell types after wounding, but great er NGF synthesis in neonates appears to be due to a more robust myofibrobla st response. In addition, cell types which demonstrated NGF mRNA also expre ssed alpha-SMA, and staining for both markers increased following wounding, suggesting synthesis of both proteins is regulated in a coordinated fashio n.