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Myogenic-specific ablation of Fgfr1 impairs FGF2-mediated proliferation of satellite cells at the myofiber niche but does not abolish the capacity for muscle regeneration.

Yablonka-Reuveni Z, Danoviz ME, Phelps M, Stuelsatz P - Front Aging Neurosci (2015)

Bottom Line: These prototypic paracrine FGFs transmit their mitogenic effect through the FGFRs, which are transmembrane tyrosine kinase receptors.However, the SC mitogenic response to FGF2 is drastically repressed in isolated myofibers prepared from Fgfr1-ablated mice.Collectively, our study indicates that FGFR1 is important for FGF-mediated proliferation of SCs and its mitogenic role is not compensated by FGFR4 that is also highly expressed in SCs.

View Article: PubMed Central - PubMed

Affiliation: Department of Biological Structure, University of Washington School of Medicine, Seattle WA, USA.

ABSTRACT
Skeletal muscle satellite cells (SCs) are Pax7(+) myogenic stem cells that reside between the basal lamina and the plasmalemma of the myofiber. In mature muscles, SCs are typically quiescent, but can be activated in response to muscle injury. Depending on the magnitude of tissue trauma, SCs may divide minimally to repair subtle damage within individual myofibers or produce a larger progeny pool that forms new myofibers in cases of overt muscle injury. SC transition through proliferation, differentiation and renewal is governed by the molecular blueprint of the cells as well as by the extracellular milieu at the SC niche. In particular, the role of the fibroblast growth factor (FGF) family in regulating SCs during growth and aging is well recognized. Of the several FGFs shown to affect SCs, FGF1, FGF2, and FGF6 proteins have been documented in adult skeletal muscle. These prototypic paracrine FGFs transmit their mitogenic effect through the FGFRs, which are transmembrane tyrosine kinase receptors. Using the mouse model, we show here that of the four Fgfr genes, only Fgfr1 and Fgfr4 are expressed at relatively high levels in quiescent SCs and their proliferating progeny. To further investigate the role of FGFR1 in adult myogenesis, we have employed a genetic (Cre/loxP) approach for myogenic-specific (MyoD(Cre)-driven) ablation of Fgfr1. Neither muscle histology nor muscle regeneration following cardiotoxin-induced injury were overtly affected in Fgfr1-ablated mice. This suggests that FGFR1 is not obligatory for SC performance in this acute muscle trauma model, where compensatory growth factor/cytokine regulatory cascades may exist. However, the SC mitogenic response to FGF2 is drastically repressed in isolated myofibers prepared from Fgfr1-ablated mice. Collectively, our study indicates that FGFR1 is important for FGF-mediated proliferation of SCs and its mitogenic role is not compensated by FGFR4 that is also highly expressed in SCs.

No MeSH data available.


Related in: MedlinePlus

Muscle tissue of adult mR1Δ/Δ/R2Δ/Δ mice retains regenerative activity. Representative images of H&E stained cross sections of TA/EDL from 4-month-old mR1Δ/Δ/R2Δ/Δ mice, showing extensive damage at 7 days post cardiotoxin-induced injury, and progressive recovery at 14 and 21 days post-injury. For each panel, regions delineated in the low magnification image of the whole TA/EDL are shown as higher magnification views (A1–C2) identified with corresponding colored frames; dotted lines in the low magnification images delineate the outer limits of the region that has been effectively injured. Morphology of control contralateral TAs (NaCl-injected, not shown) appeared similar to that of the uninjured muscle depicted in Figure 3. (A) As seen on day 7 post-injury, cardiotoxin injection caused massive myofiber degeneration, resulting in large necrotic regions in which empty remnants of the original myofibers (A1) and infiltration of inflammatory cells (A2) are detected; regions with small regenerating myofibers with central myonuclei (hallmark of regenerating myofibers) were occasionally observed (A2). (B) On day 14 post-injury, regenerating myofibers were more abundant (B2), but regions showing infiltration of inflammatory cells were still occasionally present (B1); asterisk in (B) and (B2) indicates the scar left at the needle injection point. (C) By day 21 post-injury, most of the original injured region showed successful regeneration based on the presence of larger (relative to day 14) myofibers containing central nuclei and overall tissue morphology (C2); infiltration of inflammatory cells was only minimally detected at this stage (C1).
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Figure 4: Muscle tissue of adult mR1Δ/Δ/R2Δ/Δ mice retains regenerative activity. Representative images of H&E stained cross sections of TA/EDL from 4-month-old mR1Δ/Δ/R2Δ/Δ mice, showing extensive damage at 7 days post cardiotoxin-induced injury, and progressive recovery at 14 and 21 days post-injury. For each panel, regions delineated in the low magnification image of the whole TA/EDL are shown as higher magnification views (A1–C2) identified with corresponding colored frames; dotted lines in the low magnification images delineate the outer limits of the region that has been effectively injured. Morphology of control contralateral TAs (NaCl-injected, not shown) appeared similar to that of the uninjured muscle depicted in Figure 3. (A) As seen on day 7 post-injury, cardiotoxin injection caused massive myofiber degeneration, resulting in large necrotic regions in which empty remnants of the original myofibers (A1) and infiltration of inflammatory cells (A2) are detected; regions with small regenerating myofibers with central myonuclei (hallmark of regenerating myofibers) were occasionally observed (A2). (B) On day 14 post-injury, regenerating myofibers were more abundant (B2), but regions showing infiltration of inflammatory cells were still occasionally present (B1); asterisk in (B) and (B2) indicates the scar left at the needle injection point. (C) By day 21 post-injury, most of the original injured region showed successful regeneration based on the presence of larger (relative to day 14) myofibers containing central nuclei and overall tissue morphology (C2); infiltration of inflammatory cells was only minimally detected at this stage (C1).

Mentions: Histological examination of muscle tissues from Fgfr1/Fgfr2-ablated mice showed no apparent differences compared to the control (R1fl/fl/R2fl/fl) mice. Low and high magnification images of H&E stained cross sections processed from TA/EDL of mR1Δ/Δ/R2Δ/Δ and control R1fl/fl/R2fl/fl mice demonstrate for both mouse strains a normal muscle morphology (Figure 3). Next, we analyzed muscle regeneration in mR1Δ/Δ/R2Δ/Δ mice (Figures 4 and 5) following intramuscular administration of cardiotoxin, which specifically destroys the myofibers but preserves SCs (Harris, 2003). As seen in Figure 4, while most of the cardiotoxin-injected muscle tissue did not initiate myofiber formation on day 7 post-injury and still demonstrated large areas of inflammatory cell infiltrations at day 14, by day 21 there was an effective regenerative process throughout the muscle as observed by the characteristic presence of central myonuclei (Figure 4). Our unpublished studies with wildtype adult mice have demonstrated formation of nascent regenerative myofibers by day 7 following cardiotoxin injury and an almost complete myofiber recovery by day 14 post-injury. Hence, it appears that mR1Δ/Δ/R2Δ/Δ injured muscle has a lag in muscle regeneration. Nevertheless, our data (Figures 4 and 5) clearly indicate a thorough regeneration of the injured muscle by day 21 regardless of Fgfr1/Fgfr2 ablation in the myogenic lineage.


Myogenic-specific ablation of Fgfr1 impairs FGF2-mediated proliferation of satellite cells at the myofiber niche but does not abolish the capacity for muscle regeneration.

Yablonka-Reuveni Z, Danoviz ME, Phelps M, Stuelsatz P - Front Aging Neurosci (2015)

Muscle tissue of adult mR1Δ/Δ/R2Δ/Δ mice retains regenerative activity. Representative images of H&E stained cross sections of TA/EDL from 4-month-old mR1Δ/Δ/R2Δ/Δ mice, showing extensive damage at 7 days post cardiotoxin-induced injury, and progressive recovery at 14 and 21 days post-injury. For each panel, regions delineated in the low magnification image of the whole TA/EDL are shown as higher magnification views (A1–C2) identified with corresponding colored frames; dotted lines in the low magnification images delineate the outer limits of the region that has been effectively injured. Morphology of control contralateral TAs (NaCl-injected, not shown) appeared similar to that of the uninjured muscle depicted in Figure 3. (A) As seen on day 7 post-injury, cardiotoxin injection caused massive myofiber degeneration, resulting in large necrotic regions in which empty remnants of the original myofibers (A1) and infiltration of inflammatory cells (A2) are detected; regions with small regenerating myofibers with central myonuclei (hallmark of regenerating myofibers) were occasionally observed (A2). (B) On day 14 post-injury, regenerating myofibers were more abundant (B2), but regions showing infiltration of inflammatory cells were still occasionally present (B1); asterisk in (B) and (B2) indicates the scar left at the needle injection point. (C) By day 21 post-injury, most of the original injured region showed successful regeneration based on the presence of larger (relative to day 14) myofibers containing central nuclei and overall tissue morphology (C2); infiltration of inflammatory cells was only minimally detected at this stage (C1).
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Related In: Results  -  Collection

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Figure 4: Muscle tissue of adult mR1Δ/Δ/R2Δ/Δ mice retains regenerative activity. Representative images of H&E stained cross sections of TA/EDL from 4-month-old mR1Δ/Δ/R2Δ/Δ mice, showing extensive damage at 7 days post cardiotoxin-induced injury, and progressive recovery at 14 and 21 days post-injury. For each panel, regions delineated in the low magnification image of the whole TA/EDL are shown as higher magnification views (A1–C2) identified with corresponding colored frames; dotted lines in the low magnification images delineate the outer limits of the region that has been effectively injured. Morphology of control contralateral TAs (NaCl-injected, not shown) appeared similar to that of the uninjured muscle depicted in Figure 3. (A) As seen on day 7 post-injury, cardiotoxin injection caused massive myofiber degeneration, resulting in large necrotic regions in which empty remnants of the original myofibers (A1) and infiltration of inflammatory cells (A2) are detected; regions with small regenerating myofibers with central myonuclei (hallmark of regenerating myofibers) were occasionally observed (A2). (B) On day 14 post-injury, regenerating myofibers were more abundant (B2), but regions showing infiltration of inflammatory cells were still occasionally present (B1); asterisk in (B) and (B2) indicates the scar left at the needle injection point. (C) By day 21 post-injury, most of the original injured region showed successful regeneration based on the presence of larger (relative to day 14) myofibers containing central nuclei and overall tissue morphology (C2); infiltration of inflammatory cells was only minimally detected at this stage (C1).
Mentions: Histological examination of muscle tissues from Fgfr1/Fgfr2-ablated mice showed no apparent differences compared to the control (R1fl/fl/R2fl/fl) mice. Low and high magnification images of H&E stained cross sections processed from TA/EDL of mR1Δ/Δ/R2Δ/Δ and control R1fl/fl/R2fl/fl mice demonstrate for both mouse strains a normal muscle morphology (Figure 3). Next, we analyzed muscle regeneration in mR1Δ/Δ/R2Δ/Δ mice (Figures 4 and 5) following intramuscular administration of cardiotoxin, which specifically destroys the myofibers but preserves SCs (Harris, 2003). As seen in Figure 4, while most of the cardiotoxin-injected muscle tissue did not initiate myofiber formation on day 7 post-injury and still demonstrated large areas of inflammatory cell infiltrations at day 14, by day 21 there was an effective regenerative process throughout the muscle as observed by the characteristic presence of central myonuclei (Figure 4). Our unpublished studies with wildtype adult mice have demonstrated formation of nascent regenerative myofibers by day 7 following cardiotoxin injury and an almost complete myofiber recovery by day 14 post-injury. Hence, it appears that mR1Δ/Δ/R2Δ/Δ injured muscle has a lag in muscle regeneration. Nevertheless, our data (Figures 4 and 5) clearly indicate a thorough regeneration of the injured muscle by day 21 regardless of Fgfr1/Fgfr2 ablation in the myogenic lineage.

Bottom Line: These prototypic paracrine FGFs transmit their mitogenic effect through the FGFRs, which are transmembrane tyrosine kinase receptors.However, the SC mitogenic response to FGF2 is drastically repressed in isolated myofibers prepared from Fgfr1-ablated mice.Collectively, our study indicates that FGFR1 is important for FGF-mediated proliferation of SCs and its mitogenic role is not compensated by FGFR4 that is also highly expressed in SCs.

View Article: PubMed Central - PubMed

Affiliation: Department of Biological Structure, University of Washington School of Medicine, Seattle WA, USA.

ABSTRACT
Skeletal muscle satellite cells (SCs) are Pax7(+) myogenic stem cells that reside between the basal lamina and the plasmalemma of the myofiber. In mature muscles, SCs are typically quiescent, but can be activated in response to muscle injury. Depending on the magnitude of tissue trauma, SCs may divide minimally to repair subtle damage within individual myofibers or produce a larger progeny pool that forms new myofibers in cases of overt muscle injury. SC transition through proliferation, differentiation and renewal is governed by the molecular blueprint of the cells as well as by the extracellular milieu at the SC niche. In particular, the role of the fibroblast growth factor (FGF) family in regulating SCs during growth and aging is well recognized. Of the several FGFs shown to affect SCs, FGF1, FGF2, and FGF6 proteins have been documented in adult skeletal muscle. These prototypic paracrine FGFs transmit their mitogenic effect through the FGFRs, which are transmembrane tyrosine kinase receptors. Using the mouse model, we show here that of the four Fgfr genes, only Fgfr1 and Fgfr4 are expressed at relatively high levels in quiescent SCs and their proliferating progeny. To further investigate the role of FGFR1 in adult myogenesis, we have employed a genetic (Cre/loxP) approach for myogenic-specific (MyoD(Cre)-driven) ablation of Fgfr1. Neither muscle histology nor muscle regeneration following cardiotoxin-induced injury were overtly affected in Fgfr1-ablated mice. This suggests that FGFR1 is not obligatory for SC performance in this acute muscle trauma model, where compensatory growth factor/cytokine regulatory cascades may exist. However, the SC mitogenic response to FGF2 is drastically repressed in isolated myofibers prepared from Fgfr1-ablated mice. Collectively, our study indicates that FGFR1 is important for FGF-mediated proliferation of SCs and its mitogenic role is not compensated by FGFR4 that is also highly expressed in SCs.

No MeSH data available.


Related in: MedlinePlus