Murine embryonic stem cell line CGR8 expresses all subtypes of muscarinic receptors and multiple nicotinic receptor subunits: Down-regulation of α4- and ß4-subunits during early differentiation.

Non-neuronal acetylcholine mediates its cellular effects via stimulation of the G-protein-coupled muscarinic receptors and the ligand-gated ion channel nicotinic receptors. The murine embryonic stem cell line CGR8 synthesizes and releases non-neuronal acetylcholine. In the present study a systematic investigation of the expression of nicotinic receptor subunits and muscarinic receptors was performed, when the stem cells were grown in the presence or absence of LIF, as the latter condition induces early differentiation. CGR8 cells expressed multiple nicotinic receptor subtypes (α3, α4, α7, α9, α10, ß1, ß2, ß3, ß4, γ, δ, ε) and muscarinic receptors (M1, M3, M4, M5); M2 was detected only in 2 out of 8 cultures. LIF removal caused a down-regulation only of the α4- and ß4-subunit. In conclusion, more or less the whole repertoire of cholinergic receptors is expressed on the murine embryonic stem cell line CGR8 for mediating cellular signaling of non-neuronal acetylcholine which acts via auto- and paracrine pathways. During early differentiation of the murine CGR8 stem cell signaling via nicotinic receptors containing α4- or ß4 subunits is reduced. Thus, the so-called neuronal α4 nicotine receptor composed of these subunits may be involved in the regulation of pluripotency in this murine stem cell line.

Upregulated acetylcholine synthesis during early differentiation in the embryonic stem cell line CGR8.

Stem cells are used to generate differentiated somatic cells including neuronal cells. Synthesis and release of acetylcholine, a neurotransmitter and widely expressed signaling molecule, were investigated in the murine embryonic stem cell line CGR8 during early differentiation, i.e. in the presence of leukemia inhibitory factor (LIF) to maintain pluripotency and in the absence of LIF to induce early differentiation. CGR8 cells express choline acetyltransferase (ChAT) as demonstrated by measurement of enzyme activity and substantial inhibition by bromoacetylcholine. Pluripotent CGR8 cells showed a ChAT activity of 250 pmol acetylcholine/mg/h, contained 1.1 pmol acetylcholine/106 cells and released about 12.00 pmol acetylcholine/1 x 106 cells/6 h. Removal of LIF induced early differentiation as evidenced by reduced transcription factors Oct-4 and Nanog and a substantial slowing of the proliferation rate. Under this condition acetylcholine synthesis increased to 1640 pmol/mg/h; related to the pluripotent state the content of acetylcholine increased 10-fold and the release to about 32 pmol acetylcholine/1 x 106 cells/6 h. Enzyme kinetic analysis showed a significant increase of the K(m) for the precursor acetyl-CoA and of V(max) without a change of the K(m) for the precursor choline. In conclusion, early differentiation of the stem cell line CGR8 is associated with a substantial increase in ChAT activity and acetylcholine release.