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IGF-I increases bone marrow contribution to adult skeletal muscle and enhances the fusion of myelomonocytic precursors.

Sacco A, Doyonnas R, LaBarge MA, Hammer MM, Kraft P, Blau HM - J. Cell Biol. (2005)

Bottom Line: One responsible cell type involved in this process is a hematopoietic stem cell derivative, the myelomonocytic precursor (MMC).However, the molecular components responsible for this injury-related response remain largely unknown.These results provide novel evidence that a single factor, IGF-I, is sufficient to enhance the fusion of bone marrow derivatives with adult skeletal muscle.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular Pharmacology, Baxter Laboratory in Genetic Pharmacology, Stanford University School of Medicine, Stanford, CA 94305, USA.

ABSTRACT
Muscle damage has been shown to enhance the contribution of bone marrow-derived cells (BMDCs) to regenerating skeletal muscle. One responsible cell type involved in this process is a hematopoietic stem cell derivative, the myelomonocytic precursor (MMC). However, the molecular components responsible for this injury-related response remain largely unknown. In this paper, we show that delivery of insulin-like growth factor I (IGF-I) to adult skeletal muscle by three different methods-plasmid electroporation, injection of genetically engineered myoblasts, and recombinant protein injection-increases the integration of BMDCs up to fourfold. To investigate the underlying mechanism, we developed an in vitro fusion assay in which co-cultures of MMCs and myotubes were exposed to IGF-I. The number of fusion events was substantially augmented by IGF-I, independent of its effect on cell survival. These results provide novel evidence that a single factor, IGF-I, is sufficient to enhance the fusion of bone marrow derivatives with adult skeletal muscle.

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MMCs fuse with differentiated multinucleated myotubes. MMCs were isolated by FACS from fresh bone marrow from GFP transgenic mice, maintained in myoblast GM for 3 d, and co-cultured with Ara-C–treated 3-d-old primary wild-type myotubes, according to Fig. 4 a (3). Immediately after the beginning of the co-culture, we started monitoring the cells using time-lapse confocal microcopy. Arrows indicate muscle cells, and arrowheads indicate MMCs (GFP+) that fuse with each other. The entire time-lapse film of this microscopic field is provided with a single channel of phase contrast and GFP and the merged images (Video 1, available at http://www.jcb.org/cgi/content/full/jcb.200506123/DC1).
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fig5: MMCs fuse with differentiated multinucleated myotubes. MMCs were isolated by FACS from fresh bone marrow from GFP transgenic mice, maintained in myoblast GM for 3 d, and co-cultured with Ara-C–treated 3-d-old primary wild-type myotubes, according to Fig. 4 a (3). Immediately after the beginning of the co-culture, we started monitoring the cells using time-lapse confocal microcopy. Arrows indicate muscle cells, and arrowheads indicate MMCs (GFP+) that fuse with each other. The entire time-lapse film of this microscopic field is provided with a single channel of phase contrast and GFP and the merged images (Video 1, available at http://www.jcb.org/cgi/content/full/jcb.200506123/DC1).

Mentions: Moreover, to determine whether MMCs fuse with either mononucleated myoblasts or with differentiated multinucleated myotubes, we performed time-lapse confocal microscopy. Myotubes were exposed to Ara-C to eliminate contaminating proliferating myoblasts and co-cultured with MMCs (Fig. 4 a, 3). In Fig. 5 (top eight panels), two muscle cells (arrows) are shown fusing together to form a multinucleated myotube. Subsequently, a GFP+ MMC (Fig. 5, arrowhead) fuses with the multinucleated myotube only 5 h after the onset of co-culture (bottom six panels). The entire time-lapse film of this microscopic field is provided with a single channel of phase contrast and GFP and the merged images (Video 1, available at http://www.jcb.org/cgi/content/full/jcb.200506123/DC1). Using time-lapse microscopy in two independent experiments, we detected 12 fusion events, 11 of which occurred with multinucleated myotubes and only 1 with a myoblast. Together, these data demonstrate that bone marrow MMCs can fuse in vitro with multinucleated differentiated myotubes.


IGF-I increases bone marrow contribution to adult skeletal muscle and enhances the fusion of myelomonocytic precursors.

Sacco A, Doyonnas R, LaBarge MA, Hammer MM, Kraft P, Blau HM - J. Cell Biol. (2005)

MMCs fuse with differentiated multinucleated myotubes. MMCs were isolated by FACS from fresh bone marrow from GFP transgenic mice, maintained in myoblast GM for 3 d, and co-cultured with Ara-C–treated 3-d-old primary wild-type myotubes, according to Fig. 4 a (3). Immediately after the beginning of the co-culture, we started monitoring the cells using time-lapse confocal microcopy. Arrows indicate muscle cells, and arrowheads indicate MMCs (GFP+) that fuse with each other. The entire time-lapse film of this microscopic field is provided with a single channel of phase contrast and GFP and the merged images (Video 1, available at http://www.jcb.org/cgi/content/full/jcb.200506123/DC1).
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Related In: Results  -  Collection

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fig5: MMCs fuse with differentiated multinucleated myotubes. MMCs were isolated by FACS from fresh bone marrow from GFP transgenic mice, maintained in myoblast GM for 3 d, and co-cultured with Ara-C–treated 3-d-old primary wild-type myotubes, according to Fig. 4 a (3). Immediately after the beginning of the co-culture, we started monitoring the cells using time-lapse confocal microcopy. Arrows indicate muscle cells, and arrowheads indicate MMCs (GFP+) that fuse with each other. The entire time-lapse film of this microscopic field is provided with a single channel of phase contrast and GFP and the merged images (Video 1, available at http://www.jcb.org/cgi/content/full/jcb.200506123/DC1).
Mentions: Moreover, to determine whether MMCs fuse with either mononucleated myoblasts or with differentiated multinucleated myotubes, we performed time-lapse confocal microscopy. Myotubes were exposed to Ara-C to eliminate contaminating proliferating myoblasts and co-cultured with MMCs (Fig. 4 a, 3). In Fig. 5 (top eight panels), two muscle cells (arrows) are shown fusing together to form a multinucleated myotube. Subsequently, a GFP+ MMC (Fig. 5, arrowhead) fuses with the multinucleated myotube only 5 h after the onset of co-culture (bottom six panels). The entire time-lapse film of this microscopic field is provided with a single channel of phase contrast and GFP and the merged images (Video 1, available at http://www.jcb.org/cgi/content/full/jcb.200506123/DC1). Using time-lapse microscopy in two independent experiments, we detected 12 fusion events, 11 of which occurred with multinucleated myotubes and only 1 with a myoblast. Together, these data demonstrate that bone marrow MMCs can fuse in vitro with multinucleated differentiated myotubes.

Bottom Line: One responsible cell type involved in this process is a hematopoietic stem cell derivative, the myelomonocytic precursor (MMC).However, the molecular components responsible for this injury-related response remain largely unknown.These results provide novel evidence that a single factor, IGF-I, is sufficient to enhance the fusion of bone marrow derivatives with adult skeletal muscle.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular Pharmacology, Baxter Laboratory in Genetic Pharmacology, Stanford University School of Medicine, Stanford, CA 94305, USA.

ABSTRACT
Muscle damage has been shown to enhance the contribution of bone marrow-derived cells (BMDCs) to regenerating skeletal muscle. One responsible cell type involved in this process is a hematopoietic stem cell derivative, the myelomonocytic precursor (MMC). However, the molecular components responsible for this injury-related response remain largely unknown. In this paper, we show that delivery of insulin-like growth factor I (IGF-I) to adult skeletal muscle by three different methods-plasmid electroporation, injection of genetically engineered myoblasts, and recombinant protein injection-increases the integration of BMDCs up to fourfold. To investigate the underlying mechanism, we developed an in vitro fusion assay in which co-cultures of MMCs and myotubes were exposed to IGF-I. The number of fusion events was substantially augmented by IGF-I, independent of its effect on cell survival. These results provide novel evidence that a single factor, IGF-I, is sufficient to enhance the fusion of bone marrow derivatives with adult skeletal muscle.

Show MeSH
Related in: MedlinePlus