Fig. 8.

Hypothesized model for the molecular mechanism involved in high density lipoprotein promoting proliferation of adipose-derived stem cells. High density lipoprotein (HDL) binds to S1P1 receptor in the plasma membrane of adipose-derived stem cells, stimulates Akt and ERK1/2 phosphorylation, activates Akt and ERK1/2 signaling pathways in cytoplasm, increases expression of cell cyclins (cyclin D₁ and cyclin E), and reduces the expression of cyclin-dependent kinase inhibitors (p21 and p27) to promote cell cycle progression and to achieve cell proliferation