Myogenesis is defined as growth, differentiation and repair of muscles where cell fusion of myoblasts to multinucleated myofibers is one major characteristic. Other cell fusion events in @entity1 are found with bone resorbing osteoclasts and placental syncytiotrophoblasts. No unifying gene regulation for natural cell fusions has been found. We analyzed skeletal muscle biopsies of competitive cyclists for muscle-specific attributes and expression of @entity1 endogenous retrovirus (ERV) envelope genes due to their involvement in cell fusion of osteoclasts and syncytiotrophoblasts. Comparing muscle biopsies from post- with the pre-competitive seasons a significant 2.25-fold increase of myonuclei/mm fiber, a 2.38-fold decrease of fiber area/nucleus and a 3.1-fold decrease of satellite cells (SCs) occurred. We propose that during the pre-competitive season SC proliferation occurred following with increased cell fusion during the competitive season. Expression of twenty-two envelope genes of muscle biopsies demonstrated a significant increase of putative muscle-cell fusogenic genes Syncytin-1 and Syncytin-3, but also for the non-fusogenic @entity16236 . Immunohistochemistry analyses showed that Syncytin-1 mainly localized to the sarcolemma of myofibers positive for myosin heavy-chain isotypes. Cellular receptors @entity19498 and @entity13462 of Syncytin-1 showed significant decrease of expression in post-competitive muscles compared with the pre-competitive season, but only @entity19498 protein expression localized throughout the myofiber. @entity16236 protein was strongly expressed throughout the myofiber, whereas @entity69750 -7 localized to SC nuclei and myonuclei. Syncytin-1 transcription factors, PPARy and @entity13351 , showed no protein expression in the myofiber, whereas the pCREB-Ser133 activator of Syncytin-1 was enriched to SC nuclei and myonuclei. Syncytin-1, Syncytin-3, @entity19498 and @entity4739 gene regulations along with @entity9171 and myogenin were verified during proliferating or actively-fusing @entity1 primary myoblast cell cultures, resembling muscle biopsies of cyclists. Myoblast treatment with anti-Synycytin-1 abrogated cell fusion in vitro. Our findings support functional roles for ERV envelope proteins, especially Syncytin-1, contributing to cell fusion of myotubes.

Long-Term Endurance Exercise in XXXX Stimulates Cell Fusion of Myoblasts along with Fusogenic Endogenous Retroviral Genes In Vivo.

@entity1 :: ('9606', 'Species') :: ['humans', 'human'] @entity9171 :: ('4654', 'Gene') :: ['MyoD1'] @entity13462 :: ('6510', 'Gene') :: ['SLC1A5'] @entity69750 :: ('100616103', 'Gene') :: ['envK1'] @entity19498 :: ('6509', 'Gene') :: ['SLC1A4'] @entity4739 :: ('5081', 'Gene') :: ['PAX7'] @entity16236 :: ('2086', 'Gene') :: ['erv3', 'Erv3'] @entity13351 :: ('6256', 'Gene') :: ['RXRa']
@entity1 :: (9606,Species) :: ['Humans']
