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

Frese S, Ruebner M, Suhr F, Konou TM, Tappe KA, Toigo M, Jung HH, Henke C, Steigleder R, Strissel PL, Huebner H, Beckmann MW, van der Keylen P, Schoser B, Schiffer T, Frese L, Bloch W, Strick R - PLoS ONE (2015)

Bottom Line: 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.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 erv3.Cellular receptors SLC1A4 and SLC1A5 of Syncytin-1 showed significant decrease of expression in post-competitive muscles compared with the pre-competitive season, but only SLC1A4 protein expression localized throughout the myofiber.

View Article: PubMed Central - PubMed

Affiliation: Institute of Cardiovascular Research and Sport Medicine, Department of Molecular and Cellular Sport Medicine, German Sport University Cologne, Am Sportpark Muengersdorf, Cologne, Germany; University Hospital Zurich, Department of Neurology, Frauenklinikstrasse, Zurich, Switzerland; Institute of Human Movement Sciences and Sport, Exercise Physiology, ETH Zurich, Winterthurerstrasse, Zurich, Switzerland.

ABSTRACT
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 humans 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 human 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 erv3. Immunohistochemistry analyses showed that Syncytin-1 mainly localized to the sarcolemma of myofibers positive for myosin heavy-chain isotypes. Cellular receptors SLC1A4 and SLC1A5 of Syncytin-1 showed significant decrease of expression in post-competitive muscles compared with the pre-competitive season, but only SLC1A4 protein expression localized throughout the myofiber. Erv3 protein was strongly expressed throughout the myofiber, whereas envK1-7 localized to SC nuclei and myonuclei. Syncytin-1 transcription factors, PPARγ and RXRα, 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, SLC1A4 and PAX7 gene regulations along with MyoD1 and myogenin were verified during proliferating or actively-fusing human 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.

No MeSH data available.


Related in: MedlinePlus

Immunostaining of serial cryocut cross-sections in vastus lateralis muscle of cyclist after the pre-competitive season.(A) Muscle fibers are shown, where one area is viewed at a higher magnification (white box) in (B) and (C); (D, E, F) co-immunolocalization of Laminin (green), PAX7 (red) and myonuclei (arrowhead) counterstained with DRAQ5 (blue); the marked area in (A-C) represents the same area as shown in (D–F); SCs (arrows) are indicated. (C) Note that PAX7 positive SC is located between the sarcolemma and the basal lamina of the muscle fibre. Bars: 50 μm (A), 10 μm (B) and 5 μm (C–F).
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pone.0132099.g002: Immunostaining of serial cryocut cross-sections in vastus lateralis muscle of cyclist after the pre-competitive season.(A) Muscle fibers are shown, where one area is viewed at a higher magnification (white box) in (B) and (C); (D, E, F) co-immunolocalization of Laminin (green), PAX7 (red) and myonuclei (arrowhead) counterstained with DRAQ5 (blue); the marked area in (A-C) represents the same area as shown in (D–F); SCs (arrows) are indicated. (C) Note that PAX7 positive SC is located between the sarcolemma and the basal lamina of the muscle fibre. Bars: 50 μm (A), 10 μm (B) and 5 μm (C–F).

Mentions: Additionally, in order to determine PAX7(+) SCs and their localisation in muscle biopsies of the cyclists before the competitive-season, an antibody specific for laminin was used to label the fiber basement membrane. SCs were located between the basal lamina and plasma membrane of the skeletal muscle fiber as previously described [20] [16]. A representative localization of PAX7(+) SCs is shown in Fig 2. Immunostaining for the SC marker myogenin was negative, however myonuclei counterstained with DRAQ5 showed co-localization with PAX7(+) nuclei of SC, indicating an undifferentiated state (Fig 2 and data not shown). Regarding the SC content, a significant decrease of PAX7(+) SCs per muscle fiber (SCS/muscle fibre) as well of the number of SCs as a percentage of the total number of nuclei (SC %) in the post-competitive compared to the pre-competitive season were identified (Fig 1D and Table 1). A relationship was also determined between the change in myonuclear number and change in SCs/fiber (r = –0.91; P < 0.01) throughout the post-competitive-season.


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

Frese S, Ruebner M, Suhr F, Konou TM, Tappe KA, Toigo M, Jung HH, Henke C, Steigleder R, Strissel PL, Huebner H, Beckmann MW, van der Keylen P, Schoser B, Schiffer T, Frese L, Bloch W, Strick R - PLoS ONE (2015)

Immunostaining of serial cryocut cross-sections in vastus lateralis muscle of cyclist after the pre-competitive season.(A) Muscle fibers are shown, where one area is viewed at a higher magnification (white box) in (B) and (C); (D, E, F) co-immunolocalization of Laminin (green), PAX7 (red) and myonuclei (arrowhead) counterstained with DRAQ5 (blue); the marked area in (A-C) represents the same area as shown in (D–F); SCs (arrows) are indicated. (C) Note that PAX7 positive SC is located between the sarcolemma and the basal lamina of the muscle fibre. Bars: 50 μm (A), 10 μm (B) and 5 μm (C–F).
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4495930&req=5

pone.0132099.g002: Immunostaining of serial cryocut cross-sections in vastus lateralis muscle of cyclist after the pre-competitive season.(A) Muscle fibers are shown, where one area is viewed at a higher magnification (white box) in (B) and (C); (D, E, F) co-immunolocalization of Laminin (green), PAX7 (red) and myonuclei (arrowhead) counterstained with DRAQ5 (blue); the marked area in (A-C) represents the same area as shown in (D–F); SCs (arrows) are indicated. (C) Note that PAX7 positive SC is located between the sarcolemma and the basal lamina of the muscle fibre. Bars: 50 μm (A), 10 μm (B) and 5 μm (C–F).
Mentions: Additionally, in order to determine PAX7(+) SCs and their localisation in muscle biopsies of the cyclists before the competitive-season, an antibody specific for laminin was used to label the fiber basement membrane. SCs were located between the basal lamina and plasma membrane of the skeletal muscle fiber as previously described [20] [16]. A representative localization of PAX7(+) SCs is shown in Fig 2. Immunostaining for the SC marker myogenin was negative, however myonuclei counterstained with DRAQ5 showed co-localization with PAX7(+) nuclei of SC, indicating an undifferentiated state (Fig 2 and data not shown). Regarding the SC content, a significant decrease of PAX7(+) SCs per muscle fiber (SCS/muscle fibre) as well of the number of SCs as a percentage of the total number of nuclei (SC %) in the post-competitive compared to the pre-competitive season were identified (Fig 1D and Table 1). A relationship was also determined between the change in myonuclear number and change in SCs/fiber (r = –0.91; P < 0.01) throughout the post-competitive-season.

Bottom Line: 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.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 erv3.Cellular receptors SLC1A4 and SLC1A5 of Syncytin-1 showed significant decrease of expression in post-competitive muscles compared with the pre-competitive season, but only SLC1A4 protein expression localized throughout the myofiber.

View Article: PubMed Central - PubMed

Affiliation: Institute of Cardiovascular Research and Sport Medicine, Department of Molecular and Cellular Sport Medicine, German Sport University Cologne, Am Sportpark Muengersdorf, Cologne, Germany; University Hospital Zurich, Department of Neurology, Frauenklinikstrasse, Zurich, Switzerland; Institute of Human Movement Sciences and Sport, Exercise Physiology, ETH Zurich, Winterthurerstrasse, Zurich, Switzerland.

ABSTRACT
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 humans 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 human 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 erv3. Immunohistochemistry analyses showed that Syncytin-1 mainly localized to the sarcolemma of myofibers positive for myosin heavy-chain isotypes. Cellular receptors SLC1A4 and SLC1A5 of Syncytin-1 showed significant decrease of expression in post-competitive muscles compared with the pre-competitive season, but only SLC1A4 protein expression localized throughout the myofiber. Erv3 protein was strongly expressed throughout the myofiber, whereas envK1-7 localized to SC nuclei and myonuclei. Syncytin-1 transcription factors, PPARγ and RXRα, 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, SLC1A4 and PAX7 gene regulations along with MyoD1 and myogenin were verified during proliferating or actively-fusing human 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.

No MeSH data available.


Related in: MedlinePlus