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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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Recombinant IGF-I protein injection increases the contribution of BMDCs to skeletal muscle. (a) Saline (control) or recombinant IGF-I protein (1, 5, and 10 μg) was injected into the TA muscles of mice that had received a BMT 8 wk earlier, and muscles were harvested 4 wk after protein injection. Immunofluorescence images of transverse sections of muscles injected with saline or 5 μg IGF-I and stained for laminin only (top) or for GFP and laminin (bottom) are shown. Arrows indicate GFP+ myofibers. (b) The total numbers of GFP+ myofibers per transverse section are shown (± SEM). Asterisk indicates values that were significantly different from the control (P < 0.05). P value was determined with a t test. Significance of the values from the dose–response trendline was calculated by using the Pearson correlation coefficient (P < 0.01). Bars, 50 μm.
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fig3: Recombinant IGF-I protein injection increases the contribution of BMDCs to skeletal muscle. (a) Saline (control) or recombinant IGF-I protein (1, 5, and 10 μg) was injected into the TA muscles of mice that had received a BMT 8 wk earlier, and muscles were harvested 4 wk after protein injection. Immunofluorescence images of transverse sections of muscles injected with saline or 5 μg IGF-I and stained for laminin only (top) or for GFP and laminin (bottom) are shown. Arrows indicate GFP+ myofibers. (b) The total numbers of GFP+ myofibers per transverse section are shown (± SEM). Asterisk indicates values that were significantly different from the control (P < 0.05). P value was determined with a t test. Significance of the values from the dose–response trendline was calculated by using the Pearson correlation coefficient (P < 0.01). Bars, 50 μm.

Mentions: To prove definitively that IGF-I protein increases the contribution of BMDCs to muscle, the recombinant IGF-I protein was delivered by intramuscular injection. The commercially available recombinant protein is a purified peptide of 70 amino acids corresponding to exons 3 and 4 of the IGF-I gene, which constitutes the mature processed peptide with domains B, C, A, and D (Bell et al., 1986; Shimatsu and Rotwein, 1987). This delivery system is substantially different from the two methods described in Figs. 1 and 2 because it is transient. Different amounts of IGF-I (1, 5, and 10 μg) were injected into the TA muscles of wild-type mice that had received a BMT with GFP-labeled bone marrow 8 wk earlier, and the muscles of three mice in each group were analyzed 4 wk later. A dose-dependent increase in the number of total GFP+ myofibers per transverse section was observed in IGF-I–injected relative to the saline-injected muscles (P < 0.01; Fig. 3). By contrast, injection of a cytokine, IL-4, recently reported to play a role in the fusion of myoblasts with myocytes to form multinucleated myotubes (Horsley et al., 2003), did not increase the frequency of GFP+ myofibers (unpublished data). The extent of muscle damage assessed as the percentage of centrally nucleated myofibers was 3.3 ± 0.8%, using this mode of IGF-I delivery.


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)

Recombinant IGF-I protein injection increases the contribution of BMDCs to skeletal muscle. (a) Saline (control) or recombinant IGF-I protein (1, 5, and 10 μg) was injected into the TA muscles of mice that had received a BMT 8 wk earlier, and muscles were harvested 4 wk after protein injection. Immunofluorescence images of transverse sections of muscles injected with saline or 5 μg IGF-I and stained for laminin only (top) or for GFP and laminin (bottom) are shown. Arrows indicate GFP+ myofibers. (b) The total numbers of GFP+ myofibers per transverse section are shown (± SEM). Asterisk indicates values that were significantly different from the control (P < 0.05). P value was determined with a t test. Significance of the values from the dose–response trendline was calculated by using the Pearson correlation coefficient (P < 0.01). Bars, 50 μm.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2171272&req=5

fig3: Recombinant IGF-I protein injection increases the contribution of BMDCs to skeletal muscle. (a) Saline (control) or recombinant IGF-I protein (1, 5, and 10 μg) was injected into the TA muscles of mice that had received a BMT 8 wk earlier, and muscles were harvested 4 wk after protein injection. Immunofluorescence images of transverse sections of muscles injected with saline or 5 μg IGF-I and stained for laminin only (top) or for GFP and laminin (bottom) are shown. Arrows indicate GFP+ myofibers. (b) The total numbers of GFP+ myofibers per transverse section are shown (± SEM). Asterisk indicates values that were significantly different from the control (P < 0.05). P value was determined with a t test. Significance of the values from the dose–response trendline was calculated by using the Pearson correlation coefficient (P < 0.01). Bars, 50 μm.
Mentions: To prove definitively that IGF-I protein increases the contribution of BMDCs to muscle, the recombinant IGF-I protein was delivered by intramuscular injection. The commercially available recombinant protein is a purified peptide of 70 amino acids corresponding to exons 3 and 4 of the IGF-I gene, which constitutes the mature processed peptide with domains B, C, A, and D (Bell et al., 1986; Shimatsu and Rotwein, 1987). This delivery system is substantially different from the two methods described in Figs. 1 and 2 because it is transient. Different amounts of IGF-I (1, 5, and 10 μg) were injected into the TA muscles of wild-type mice that had received a BMT with GFP-labeled bone marrow 8 wk earlier, and the muscles of three mice in each group were analyzed 4 wk later. A dose-dependent increase in the number of total GFP+ myofibers per transverse section was observed in IGF-I–injected relative to the saline-injected muscles (P < 0.01; Fig. 3). By contrast, injection of a cytokine, IL-4, recently reported to play a role in the fusion of myoblasts with myocytes to form multinucleated myotubes (Horsley et al., 2003), did not increase the frequency of GFP+ myofibers (unpublished data). The extent of muscle damage assessed as the percentage of centrally nucleated myofibers was 3.3 ± 0.8%, using this mode of IGF-I delivery.

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