Evidence that androgens regulate early developmental events, prior to sexual differentiation.

Androgen signaling is critical for normal fetal development but is not thought to regulate events in early embryogenesis. Given the interest in factors controlling the differentiation of embryonic stem (ES) cells, we have explored the possibility that androgens may play a role. This study demonstrates expression of androgen receptor (AR) RNA and protein in four independent mouse ES (mES) cell lines, and shows that the AR is functional and can interact with transfected androgen response elements to promote green fluorescent protein expression. AR mRNA was detected throughout 10-d differentiation in embryoid bodies (EBs). Exposure of EBs to testosterone (T) or dihydrotestosterone, at doses of 1 and 0.1 mum, respectively, promoted formation of beating cardiomyocytes. Flow cytometric analyses demonstrated a significant increase in the number of alpha-actinin and tropomyosin (cardiac markers) positive cells after these treatments. Addition of flutamide (1 microM) to T-treated EBs inhibited the T-induced proliferation of cardiomyocytes, confirming that, in this instance, androgens act via the classical AR-mediated genomic pathway. We also report that mES cells express key steroidogenic enzymes, as detected by RT-PCR, and during 24-h incubations secrete T at concentrations of 1.38 +/- 0.22 nM, levels comparable to those secreted by cultured Leydig cells. These novel data demonstrate the capacity of androgens to stimulate increased differentiation of mouse ES cells to cardiomyocytes, and are in keeping with recent observations that AR-deficient mice exhibit cardiac impairment in adulthood.