Regulation of mineralocorticoid receptor expression during neuronal differentiation of murine embryonic stem cells.

Mineralocorticoid receptor (MR) plays a critical role in brain function. However, the regulatory mechanisms controlling neuronal MR expression that constitutes a key element of the hormonal response are currently unknown. Two alternative P1 and P2 promoters drive human MR gene transcription. To examine promoter activities and their regulation during neuronal differentiation and in mature neurons, we generated stably transfected recombinant murine embryonic stem cell (ES) lines, namely P1-GFP and P2-GFP, in which each promoter drove the expression of the reporter gene green fluorescent protein (GFP). An optimized protocol, using embryoid bodies and retinoic acid, permitted us to obtain a reproducible neuronal differentiation as revealed by the decrease in phosphatase alkaline activity, the concomitant appearance of morphological changes (neurites), and the increase in the expression of neuronal markers (nestin, beta-tubulin III, and microtubule-associated protein-2) as demonstrated by immunocytochemistry and quantitative PCR. Using these cell-based models, we showed that MR expression increased by 5-fold during neuronal differentiation, MR being preferentially if not exclusively expressed in mature neurons. Although the P2 promoter was always weaker than the P1 promoter during neuronal differentiation, their activities increased by 7- and 5-fold, respectively, and correlated with MR expression. Finally, although progesterone and dexamethasone were ineffective, aldosterone stimulated both P1 and P2 activity and MR expression, an effect that was abrogated by knockdown of MR by small interfering RNA. In conclusion, we provide evidence for a tight transcriptional control of MR expression during neuronal differentiation. Given the neuroprotective and antiapoptotic role proposed for MR, the neuronal differentiation of ES cell lines opens potential therapeutic perspectives in neurological and psychiatric diseases.