Retinoid supplementation of differentiating human neural progenitors and embryonic stem cells leads to enhanced neurogenesis in vitro.

Retinoids are important molecules involved in the development and homeostasis of the nervous system. As such, various retinoid derivatives are often found in culture media and supplement formulations to support the growth and maintenance of neural cells. However, all-trans-retinoic acid (ATRA) and its associated derivatives are light sensitive and are highly susceptible to isomerisation. This can lead to variability in retinoid concentrations and the nature of the retinoid species present in culture solutions which in turn can influence biological activity and introduce inconsistency. We have previously described the development of the synthetic retinoid derivative, EC23, as a chemically and light stable alternative that does not degrade and has biological activity similar to ATRA. In this study we demonstrate that the addition of exogenous retinoid can significantly enhance neuronal differentiation of both human neuroprogenitor and human embryonic stem cells. In the former, both ATRA and EC23 induced increased maturation and stabilisation of the axonal cytoskeleton. However, EC23 was particularly potent at lower nanomolar concentrations resulting in significantly greater neurogenesis than ATRA. In ES cells enhanced motor neuron marker expression was also detected in response to both retinoids when incorporated into an established protocol for neuronal differentiation. We propose that synthetic retinoid EC23 represents a valuable addition to the formulation of new and existing culture supplements to enhance neuronal differentiation whilst enabling improved consistency.