Asiaticoside induces human collagen I synthesis through TGFβ receptor I kinase (TβRI kinase)-independent Smad signaling

Skin aging appears to be principally related to a decrease in the levels of type 1 collagen, the primary component of the skin dermis. Asiaticoside, a saponin component isolated from Centella asiatica, has been shown to induce type 1 collagen synthesis in human dermal fibroblast cells. However, the mechanism underlying asiaticoside-induced type 1 collagen synthesis, especially at a molecular level, remains only partially understood. In this Study we have attempted to characterize the action mechanism Of asiaticoside in type 1 Collagen synthesis. Asiaticoside was determined to induce the phosphorylation of both Smad 2 and Smad 3. In addition, we detected the asiaticoside-induced binding of Smad 3 and Smad 4. In a consistent result, the nuclear translocation of the Smad 3 and Smad 4 complex was induced via treatment with asiaticoside, pointing to the involvement of asiaticoside in Smad signaling. In addition, SB431542, an inhibitor of the TGF beta receptor I (T beta RI) kinase, which is known to be an activator of the Smad pathway, was not found to inhibit both Smad 2 phosphorylation and Type 1 collagen synthesis induced by asiaticoside. Therefore, our results show that asiaticoside can induce type 1 collagen synthesis via the activation of the T beta RI kinase-independent Smad pathway.