Trendy drinks come and go, but it looks like there are a couple of new cocktails that will have some staying power within the stem cell community. In last week’s issue of Cell Stem Cell, two independent groups report in back-to-back papers the development of small molecule chemical cocktails, which enable neurons to be directly derived from skin fibroblasts by “just” soaking them in the drug cocktail and without going through an intermediate pluripotent step.
While you won’t find these cocktails in your average hotel bar anytime soon, these small molecule cocktails could represent a significant step forward in the induction and use of reprogrammed cells in vivo and their possible therapeutic applications.
In the first paper, a group led by Dr. Hongkui Deng from the Peking University used a chemical screen for small molecules promoting Ascl1-based reprogramming of mouse fibroblasts to neurons.
Here’s what they found:
- A combination of four molecules (Forskolin; ISX9; CHIR99021, a GSK3 beta inhibitor, and I-BET151), which they called FICB, induced the reprogramming of a whooping 90% of fibroblasts into neurons.
- FICB-induced cells, termed chemically induced neurons (CiNs), showed electrophysiological properties characteristic of functional neurons.
- As 80% of the induced immature neurons failed to incorporate the DNA replication marker BrdU, the authors concluded that cell fate reprogramming bypassed an intermediate proliferative stage.
In the second paper, scientists led by Dr. Gang Pei from The Chinese Academy of Sciences in Shanghai, used their previously described small molecule cocktail VCR (valproic acid; CHIR99021 and Repsox) to manipulate the cell fate of adult human foreskin fibroblasts and convert them into neurons.
Here’s what they found:
- By itself, VCR had no effect on neuronal differentiation, but the addition of forskolin and other compounds known to induce neuronal differentiation such as SP600125 (JNK inhibitor), GO6983 (PKC inhibitor) and Y-27632 (ROCK inhibitor), made a potent seven-component cocktail, VCRFSGY, which induced neuronal conversion 7 days after incubation.
- Hallmark genes of neuroprogenitor cell fate, such as Sox2, Pax6, FoxG1 or nestin were never expressed in the chemically-induced cells, suggesting that the VCRFSGY cocktail induces the direct conversion of fibroblasts into neurons.
- The physiological properties of the human CiNs resembled those previously seen in neurons derived from iPSCs and neurons directly induced from fibroblasts by the expression of exogenous transcription factors (TF-iNs).
- Human CiNs from familial Alzheimer’s patients displayed similar neuronal characteristics but exhibit abnormal amyloid beta protein production, suggesting CiNS can be used to model neurological disorders.
There are interesting similarities between the two papers. Both cocktail recipes use forskolin to increase cyclic AMP levels and CHIR99021 to inhibit GSK3 beta activity, suggesting these cocktails work via common mechanisms. In both studies, fibroblast genes were downregulated and neuronal genes were upregulated during reprogramming, although the exact genes differ between the two studies.
So, next time you need some neurons for your disease model, remember to ask for your favorite cocktail…but shaken, not stirred.