Abstract:

Objective To investigate the effects of emodin on the proliferation，cell cycle，apoptosis， sebum synthesis and secretion of human HaCaT keratinocytes. Methods HaCaT cells were cultured and treated with emodin（0，25，50，100 μmol/L）. The cellular viability was detected by CCK ⁃ 8 assay. The colony formation was observed by crystal violet staining. Flow cytometry was used to determine cell cycle and apoptosis. Lipid content levels were visualized and analyzed by Oil Red O staining. Western blot was applied for detection of protein expression. Moreover，we used insulin⁃like growth factor⁃1（IGF⁃1）to stimulate lipid synthesis，and then the protein levels Akt/FoxO1 pathway molecules were quantified by western blot analysis. Results Compared to the control group，the cell confluence，numbers of colony formation as well as the viability of HaCaT cells in emodin⁃treated groups were significantly decreased in a dose⁃dependent manner（P < 0.001），while the expression of PCNA was downregulating（P < 0.05）. Flow cytometry analysis revealed that emodin induced G1/S arrest and cell apoptosis in HaCaT cells. The proportion of cell population in early and late apoptosis was markedly increased after emodin treatment，along with upregulation of pro⁃apoptotic protein Bax，downregulation of anti⁃apoptotic protein Bcl⁃2. Our results also showed that emodin reduced the accumulation of intracellular lipid droplets in HaCaT cells（P < 0.05）， and the expression levels of lipid factors（PPARγ，SREBP⁃1 and LXR）were decreased，as well（P < 0.05）. IGF⁃1 enhanced the lipid production（P < 0.001）and the phosphorylation of Akt and FoxO1（P < 0.001）when compared to the untreated group. However，emodin could reverse IGF⁃1⁃induced lipid overproduction and elevated phosphory⁃ lated levels of Akt and FoxO1（P < 0.001）. Conclusion Emodin could reduce sebum secretion in HaCaT cells，possibly due to its inhibitory effects on growth and lipogenesis on HaCaT cells，including suppressing proliferation， arresting cell cycle，inducing apoptosis，and inhibiting IGF⁃1⁃mediated activation of Akt/FoxO1 pathway. 

Key words: Emodin, human HaCaT keratinocytes, sebum synthesis, insulin?like growth factor?1, acne vulgaris