Abstract
We have reported previously that adipose tissue-derived stem cells (ADSC) could be induced by isobutylmethylxanthine (IBMX) to differentiate into neuron-like cells and such differentiation was mediated by insulin-like growth factor I (IGF-I) signaling. In the present study we show that both IBMX and IGF-I upregulated neural markers beta-III-tubulin and paired-like homeobox transcription factor (Pitx3) in ADSC. Because Pitx3 is important for the maturation and function of dopaminergic neurons and has been shown to be regulated by microRNA miR-133b, we also examined the effects of IBMX and IGF-I on miR-133b expression. The results show that both IBMX and IGF-I upregulated miR-133b expression. When miR-133b was overexpressed in ADSC through transfection of a synthetic microRNA mimic, it caused a downregulation of beta-III-tubulin as evidenced by immunofluorescence staining and western blot analysis. Overexpression of miR-133b also downregulated Pitx3 and IGF-1 receptor (IGF-IR), and all such downregulation occurred at the protein but not the RNA level. The apparent posttranscriptional regulation was subsequently found to be exerted through a potential miR-133b target in the 3'-untranslated region of IGF-IR, as evidenced by luciferase assay. Thus, IGF-I signaling and miR-133b co-regulate potential neural differentiation of ADSC through a feedback mechanism, in which IGF-I upregulates miR-133b while miR-133b in turn downregulates IGF-IR.