Editors' ChoiceDevelopmental Biology

Preventing Myoblasts from Premature Differentiation

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Science Signaling  24 Jun 2014:
Vol. 7, Issue 331, pp. ec176
DOI: 10.1126/scisignal.2005620

Muscles are formed from myoblasts, which fuse to form the multinucleated muscle fiber. Endocannabinoids, such as anandamide and 2-arachidonoylglycerol (2-AG), stimulate G protein–coupled receptors CB1 and CB2, which activated phospholipase C (PLC) to hydrolyze the phospholipid PIP2. PIP2 promotes the activity of potassium channels necessary for muscle differentiation. Signaling through the CB1 receptor regulates skeletal muscle metabolism. Iannotti et al. determined that endocannabinoid abundance decreased during the differentiation of C2C12 cells, a mouse myoblast cell line. Anandamide abundance decreased in mouse muscles between embryonic day 18 (E18) and postnatal day 4 (P4), then increased at P14, and 2-AG abundance decreased between P4 and P14. CB1 was abundant in C2C12 myoblasts, and its abundance increased in C2C12 cells and primary human skeletal muscle cells upon exposure to differentiation medium. The presence of 2-AG or the CB1 receptor–specific agonist ACEA inhibited differentiation of C2C12 cells and human skeletal muscle cells, based on the abundance of transcripts indicative of differentiation and morphological analysis. Mice genetically deficient in CB1 receptors had more muscle fibrils per muscle with more nuclei in each muscle at E18. At P5, myofibril diameter was increased. In mouse skeletal muscle, the expression of the gene encoding the CB1 receptor decreased and expression of the gene encoding the PIP2-stimulated potassium channel Kv7.4 increased between E18 and P4. Activation of CB1 receptors with ACEA or inhibition of Kv7.4 channels reduced the expression of differentiation markers in C2C12 cells exposed to differentiation medium, and the effects of the two pharmacological agents were not additive, suggesting that these CB1 receptors and Kv7.4 may participate in a common pathway. ACEA reduced the amount of PIP2 in C2C12 cells and the amount of PIP2 that coimmunoprecipitated with Kv7.4 from C2C12 cells. ACEA stimulated C2C12 cell proliferation through a pathway that was not blocked by a PLC inhibitor. Thus, these data indicate that endocannabinoids exert an inhibitory effect on muscle cell differentiation during development through a PLC-dependent pathway that reduces PIP2 and thereby decreases the activity of Kv7.4 channels needed for differentiation, while also stimulating myoblast proliferation through a PLC-independent pathway.

F. A. Iannotti, C. Silvestri, E. Mazzarella, A. Martella, D. Calvigioni, F. Piscitelli, P. Ambrosino, S. Petrosino, G. Czifra, T. Bíró, T. Harkany, M. Taglialatela, V. Di Marzo. The endocannabinoid 2-AG controls skeletal muscle cell differentiation via CB1 receptor-dependent inhibition of Kv7 channels. Proc. Natl. Acad. Sci. U.S.A. 111, E2472–E2481 (2014). [Abstract] [Full Text]

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