MicroRNA-mediated iPS cells

Abstract

The standard protocol for reverting somatic cells into induced pluripotent stem cells with viral vectors that introduce a quartet of transcription factors has low reprogramming efficiency. 1 Moreover, some human cell types are refractory to reprogramming with transcription factors. Now, researchers at the University of Pennsylvania report that microRNAs could address both problems, taking exogenous transcription factors out of the picture while increasing reprogramming efficiency. 2 The UPenn protocol still uses viral vectors, which could pose safety issues in the clinic. Thus, the group now needs to replicate the findings using nonviral delivery of the miRNAs.In 2006, Japanese researchers published the first protocol for reprogramming somatic cells into induced pluripotent stem (iPS) cells using retroviral vectormediated expression of the transcription factors Oct4, Sox2, Klf4 and c-Myc. Reprogramming efficiencies using the method range from 0.2%-0.8%. 3 The exogenous delivery of transcription factor proteins plus cocktails of small molecules could supplant viral vectors, but such protocols have even lower reprogramming efficiency. Also, the need for a steady supply of a transcription factor protein would not be cost effective."I think high reprogramming efficiencies would be necessary for developing a reliable high throughput platform for generating iPS cells," said Edward Morrisey, a professor of medicine at UPenn and scientific director of the Penn Institute for Regenerative Medicine.According to Morrisey, many types of human cells are refractory to reprogramming by using the transcription factors. Thus, his group at UPenn looked to miRNAs to address both efficiency and cell type issues.Recent studies showed that miRNAs can increase the efficiency of reprogramming with transcription factors. [4][5][6][7] The UPenn researchers went a step further and showed that lentiviral-mediated expression of the miRNA-302/367 cluster of miRNAs reprogrammed mouse embryonic fibroblasts into iPS cells with higher efficiency than the standard four transcription factor reprogramming protocol. At 8 and 10 days following viral transduction, cell counting showed that the miRNA reprogramming protocol generated about two orders of magnitude more iPS cells than the standard protocol. Similar results were seen in human fibroblasts.