Angiogenic and inflammatory responses following skeletal muscle injury are altered by immune neutralization of endogenous basic fibroblast growth factor, insulin-like growth factor-1 and transforming growth factor-beta 1

Making the case for resistance training in improving vascular function and skeletal muscle capillarization

Through decades of empirical data, it has become evident that resistance training (RT) can improve strength/power and skeletal muscle hypertrophy. Yet, until recently, vascular outcomes have historically been underemphasized in RT studies, which is underscored by several exercise-related reviews supporting the benefits of endurance training on vascular measures. Several lines of evidence suggest large artery diameter and blood flow velocity increase after a single bout of resistance exercise, and these events are mediated by vasoactive substances released from endothelial cells and myofibers (e.g., nitric oxide). Weeks to months of RT can also improve basal limb blood flow and arterial diameter while lowering blood pressure. Although several older investigations suggested RT reduces skeletal muscle capillary density, this is likely due to most of these studies being cross-sectional in nature. Critically, newer evidence from longitudinal studies contradicts these findings, and a growing body of mechanistic rodent and human data suggest skeletal muscle capillarity is related to mechanical overload-induced skeletal muscle hypertrophy. In this review, we will discuss methods used by our laboratories and others to assess large artery size/function and skeletal muscle capillary characteristics. Next, we will discuss data by our groups and others examining large artery and capillary responses to a single bout of resistance exercise and chronic RT paradigms. Finally, we will discuss RT-induced mechanisms associated with acute and chronic vascular outcomes.

Effects of early local administration of high-dose bFGF on a recurrent laryngeal nerve injury model

BACKGROUND

Research on regenerative medicine using basic fibroblast growth factor (bFGF) has recently advanced in the field of laryngology. We previously reported that local administration of bFGF 1 month after recurrent laryngeal nerve (RLN) paralysis compensated for atrophy of the thyroarytenoid muscle. The objective of this study was to elucidate the effects of early bFGF administration on the thyroarytenoid muscle after RLN transection and to investigate the underlying mechanisms.

METHODS

A rat model of RLN paralysis was established in this study. One day after RLN transection, low- (200 ng) or high-dose (2000 ng) bFGF or saline (control) was administered to the thyroarytenoid muscle. The larynges were excised for histological and immunohistochemical examinations at 1, 7, 14, 28, and 56 days after administration.

RESULTS

The cross-sectional thyroarytenoid muscle area was significantly larger in the high-dose group than in the saline and low-dose groups on days 28 and 56. Immunohistochemistry indicated that bFGF significantly increased the number of satellite cells in the thyroarytenoid muscle up to day 14 and that of neuromuscular junctions on days 28 and 56.

CONCLUSIONS

A single, early local administration of high-dose bFGF prevented atrophic changes in the thyroarytenoid muscles by activating satellite cell proliferation and reforming neuromuscular junctions. As increased neuromuscular junctions are expected to maintain myofiber volume, bFGF administration may prevent thyroarytenoid muscle atrophy in the mid to long term.

Evaluation of Safety After Intracordal Basic Fibroblast Growth Factor Injection

OBJECTIVES

Although there are many reports of voice improvement with intracordal trafermin (a basic fibroblast growth factor) injections under local anesthesia, few papers have documented the safety of trafermin. Therefore, we aimed to investigate whether trafermin is safer than control drugs (triamcinolone acetonide) early after intracordal injection under local anesthesia.

METHODS

We conducted a retrospective review from the medical records of patients who underwent intracordal injection with trafermin and triamcinolone acetonide under local anesthesia at our institution. Early postinjective complications were defined as changes in vital signs and chief complaints early after intracordal injection.

RESULTS

A total of 699 and 297 patients underwent intracordal injection under local anesthesia with trafermin and triamcinolone acetonide, respectively. Of these, 227 and 130 patients had early postinjective complications with trafermin and triamcinolone acetonide, retrospectively. The most common complications occurring with trafermin was increased blood pressure in 39 cases (5.58%): 17 cases (2.43%) of blood pressure increase of ≥20 mm Hg. Other complications included pharyngeal discomfort in 37 (5.29%), lightheadedness in 33 (4.72%), and phlegm discharge in 29 (4.15%). Triamcinolone acetonide caused pharyngeal discomfort in 28 patients (9.43%), phlegm discharge in 17 patients (5.72%), lightheadedness in 12 patients (4.04%), sore throat in 11 patients (3.70%), increased blood pressure in 10 patients (3.37%): 7 cases (2.36%) of blood pressure increase of ≥20 mm Hg, and dizziness in seven patients (2.36%). Statistical analysis of the complications between trafermin and triamcinolone acetonide showed no significant differences.

CONCLUSIONS

The proportion of early postinjective complications from intracordal injection of trafermin is no significant difference in that of triamcinolone acetonide. The results suggest that the early postinjective complications are not due to the drug action of trafermin, but rather to complications from the intracordal injection procedures. Intracordal trafermin injection may be safe in the short term.

Changes in serum basic fibroblast growth factor concentration following intracordal injection

Objective

Although many studies have reported improvements in voice outcomes with intracordal trafermin injection, there is a lack of data documenting its changes in serum basic fibroblast growth factor (bFGF) blood concentration. This study examined whether serum bFGF concentrations change after intracordal trafermin injection.

Methods

This retrospective study was conducted at Tokyo Voice Center. We investigated serum bFGF concentrations before and after injection in 40 patients who underwent intracordal trafermin injection. There were 26 males and 14 females, with an age ranging from 13 to 88 years (average 53.25 years). They were diagnosed with paralysis (15 patients), atrophy (15 patients), sulcus (8 patients), and others (2 patients: scar and functional), presenting with severe hoarseness that interfered with daily life.

Results

The mean pre- and post-injective serum bFGF concentration of the 40 patients was 6.689 and 4.658 pg/mL, respectively. The difference in mean serum bFGF concentration between pre- and post-injective was -2.031 pg/mL. The Pearson correlation coefficient was calculated to evaluate the correlation between dosage of trafermin and post-injective serum bFGF concentration, and a moderate correlation was found at r = 0.52. Generalized linear model regression analysis was performed for the purpose of adjusting for confounding among variables. The only variable that showed a statistically predominant association with post-injective serum bFGF concentrations was the dosage of trafermin, with an estimated regression coefficient of 0.048.

Conclusion

In this study, the dosage of trafermin we injected and post-injective serum bFGF concentrations were dose-dependent but the amount of changes in the serum bFGF concentration was negligible within the physiological range. Therefore, as with subcutaneous and wound administration, intracordal trafermin injections may be safe.

Level of Evidence

Level IV.

Spinal Canal and Spinal Cord in Rat Continue to Grow Even after Sexual Maturation: Anatomical Study and Molecular Proposition

Although rodents have been widely used for experimental models of spinal cord diseases, the details of the growth curves of their spinal canal and spinal cord, as well as the molecular mechanism of the growth of adult rat spinal cords remain unavailable. They are particularly important when conducting the experiments of cervical spondylotic myelopathy (CSM), since the disease condition depends on the size of the spinal canal and the spinal cord. Thus, the purposes of the present study were to obtain accurate growth curves for the spinal canal and spinal cord in rats; to define the appropriate age in weeks for their use as a CSM model; and to propose a molecular mechanism of the growth of the adult spinal cord in rats. CT myelography was performed on Lewis rats from 4 weeks to 40 weeks of age. The vertical growth of the spinal canal at C5 reached a plateau after 20 and 12 weeks, and at T8 after 20 and 16 weeks, in males and females, respectively. The vertical growth of the C5 and T8 spinal cord reached a plateau after 24 weeks in both sexes. The vertical space available for the cord (SAC) of C5 and T8 did not significantly change after 8 weeks in either sex. Western blot analyses showed that VEGFA, FGF2, and BDNF were highly expressed in the cervical spinal cords of 4-week-old rats, and that the expression of these growth factors declined as rats grew. These findings indicate that the spinal canal and the spinal cord in rats continue to grow even after sexual maturation and that rats need to be at least 8 weeks of age for use in experimental models of CSM. The present study, in conjunction with recent evidence, proposes the hypothetical model that the growth of rat spinal cord after the postnatal period is mediated at least in part by differentiation of neural progenitor cells and that their differentiation potency is maintained by VEGFA, FGF2, and BDNF.

Effect of Fascia Implantation and Controlled Release of Basic Fibroblast Growth Factor for Muscle Atrophy in Rat Laryngeal Paralysis

OBJECTIVE

To improve lateral thyroarytenoid (TA) muscle atrophy after laryngeal paralysis, reconstruction of the vascular network of the atrophied muscle is necessary. We therefore evaluated whether the controlled release of basic fibroblast growth factor (bFGF) with autologous fascia implantation could affect vascular reconstruction in the lateral TA muscle.

STUDY DESIGN

Animal experiment.

SETTING

Laboratory.

METHODS

Unilateral laryngeal paralysis was induced in 20 rats. The rats were implanted with autologous fascia and a gelatin hydrogel sheet with or without 1 µg of bFGF (fascia and bFGF + fascia groups; n = 5 each) and with only a gelatin hydrogel sheet with bFGF (bFGF group: n = 5). Another group remained untreated (n = 5) at 4 months after paralysis. At 3 months since transplantation, intra- and intergroup comparisons of the muscle volumes and total area of blood vessels in the lateral TA muscle were performed.

RESULTS

When compared with the untreated group, the bFGF + fascia group showed a significant increase in muscle volume (P =.0008) and vascular area (P =.0002) in the lateral TA muscle, whereas the other 2 treated groups demonstrated an insufficient effect.

CONCLUSION

bFGF + fascia implantation showed histologic improvement in severe laryngeal paralysis. We demonstrated that the decrease in lateral TA muscle mass after paralysis might be countered by the reconstruction of the vascular network. Our findings indicate that hypovascular and denervated areas of the laryngeal muscle can be regenerated by the implantation of growth factors and scaffolds with surgical stress.

LEVEL OF EVIDENCE

5.

Limb functional recovery is impaired in fibroblast growth factor-2 (FGF2) deficient mice despite chronic ischaemia-induced vascular growth

FGF2 is a potent stimulator of vascular growth; however, even with a deficiency of FGF2 (Fgf2-/-), developmental vessel growth or ischaemia-induced revascularization still transpires. It remains to be elucidated as to what function, if any, FGF2 has during ischaemic injury. Wildtype (WT) or Fgf2-/- mice were subjected to hindlimb ischaemia for up to 42 days. Limb function, vascular growth, inflammatory- and angiogenesis-related proteins, and inflammatory cell infiltration were assessed in sham and ischaemic limbs at various timepoints. Recovery of ischaemic limb function was delayed in Fgf2-/- mice. Yet, vascular growth response to ischaemia was similar between WT and Fgf2-/- hindlimbs. Several angiogenesis- and inflammatory-related proteins (MCP-1, CXCL16, MMPs and PAI-1) were increased in Fgf2-/- ischaemic muscle. Neutrophil or monocyte recruitment/infiltration was elevated in Fgf2-/- ischaemic muscle. In summary, our study indicates that loss of FGF2 induces a pro-inflammatory microenvironment in skeletal muscle which exacerbates ischaemic injury and delays functional limb use.

Macrophages in inflammation, repair and regeneration

Tissue injury triggers a complex series of cellular responses, starting from inflammation activated by tissue and cell damage and proceeding to healing. By clearing cell debris, activating and resolving inflammation and promoting fibrosis, macrophages play key roles in most, if not all, phases of the response to injury. Recent studies of the mechanisms underlying the initial inflammation and later tissue regeneration and repair revealed that macrophages bridge these processes in part by supporting and activating stem/progenitor cells, clearing damaged tissue, remodeling extracellular matrix to prepare scaffolding for regeneration and promoting angiogenesis. However, macrophages also have a central role in the development of pathology induced by failed resolution (e.g. chronic inflammation) and excessive scarring. In this review, we summarize the activities of macrophages in inflammation and healing in response to acute injury in tissues with differing regenerative capacities. While macrophages lead similar processes in response to tissue injury in these tissues, their priorities and the consequences of their activities differ among tissues. Moreover, the magnitude, nature and duration of injury also greatly affect cellular responses and healing processes. In particular, continuous injury and/or failed resolution of inflammation leads to chronic ailments in which macrophage activities may become detrimental.

Single, high-dose local injection of bFGF improves thyroarytenoid muscle atrophy after paralysis

OBJECTIVES/HYPOTHESIS

Unilateral vocal fold paralysis (UVFP) induces hoarseness due to progressive atrophy of the denervated thyroarytenoid (TA) muscle. Therefore, treatments aimed at regenerating the atrophied TA muscle are required. Basic fibroblast growth factor (bFGF) is involved in muscle development and regeneration. This study aimed to elucidate the effects of bFGF injection on atrophied TA muscle.

STUDY DESIGN

Animal research.

METHODS

A recurrent laryngeal nerve-paralysis rat model was established, and low- (200 ng) or high-dose (2,000 ng) bFGF or saline (control) was injected into the TA muscle 28 days later. The larynges were excised on day 1, 3, 7, 14, and 28 after treatment. The cross-sectional area of the TA muscle in normal and paralyzed sides was compared, and the Ki67-positive (Ki67⁺ ) dividing cells, paired box 7-positive (Pax7⁺ ) satellite cells (SCs), and myogenic differentiation-positive (MyoD⁺ ) myoblasts were counted.

RESULTS

The TA muscle area of animals administered high-dose bFGF increased with time and was significantly larger than that of the saline-injected controls 28 days after treatment (P < .05). The counts of Ki67⁺ and Pax7⁺ cells were the highest on day 1, whereas the MyoD⁺ myoblast count was highest on day 7. These results suggest that bFGF administration into the denervated TA muscles compensated for the atrophied TA muscles by inducing proliferation of SCs and their differentiation to myoblasts.

CONCLUSIONS

A single injection of high-dose bFGF augmented regeneration and differentiation of the atrophied TA muscle by enhancing proliferation and differentiation of muscle SCs, suggesting its possible clinical application in humans with UVFP.

LEVEL OF EVIDENCE

NA Laryngoscope, 130:159-165, 2020.

The role of TGF-β1 during skeletal muscle regeneration

The injury of adult skeletal muscle initiates series of well-coordinated events that lead to the efficient repair of the damaged tissue. Any disturbances during muscle myolysis or reconstruction may result in the unsuccessful regeneration, characterised by strong inflammatory response and formation of connective tissue, that is, fibrosis. The switch between proper regeneration of skeletal muscle and development of fibrosis is controlled by various factors. Amongst them are those belonging to the transforming growth factor β family. One of the TGF-β family members is TGF-β1, a multifunctional cytokine involved in the regulation of muscle repair via satellite cells activation, connective tissue formation, as well as regulation of the immune response intensity. Here, we present the role of TGF-β1 in myogenic differentiation and muscle repair. The understanding of the mechanisms controlling these processes can contribute to the better understanding of skeletal muscle atrophy and diseases which consequence is fibrosis disrupting muscle function.

Insulin-like Growth Factor-II Delays Early but Enhances Late Regeneration of Skeletal Muscle

This study tested whether administration of insulin-like growth factor-II (IGF-II) enhances muscle regeneration. Rat biceps femoris muscle was damaged with notexin and then IGF-II was administered for up to 7 days. Results show that the proportion of nuclei containing or surrounded by immunoreactivity to MyoD, myogenin, and developmental myosin heavy chain (dMHC) is less in the IGF-II treatment group relative to the control group on days 1 (p=0.057), 2 (p=0.034), and 3 (p=0.047), respectively. This indicates a delay in muscle precursor cell (MPC) proliferation and differentiation with IGF-II administration. This effect was not associated with decreased binding capacity of the type 1 IGF receptor, as determined by receptor autoradiography in day 1 muscle sections (NS), but was associated with inhibition of phagocytic processes. The cross-sectional area of regenerating muscle fibers was significantly greater in the IGF-II treatment group than in the control group by day 7 (p=0.0092). The enhancing effect of IGF-II on late muscle regeneration, when the main process taking place is fiber enlargement, coincides with the period in which IGF-II is normally expressed by regenerating muscle, indicating that greater endogenous production of IGF-II would be associated with improved regeneration.

Morphological changes in the cervical muscles of women with chronic whiplash can be modified with exercise-A pilot study

INTRODUCTION

In this preliminary study we determined whether MRI markers of cervical muscle degeneration [elevated muscle fatty infiltration (MFI), cross-sectional area (CSA), and reduced relative muscle CSA (rmCSA)] could be modified with exercise in patients with chronic whiplash.

METHODS

Five women with chronic whiplash undertook 10 weeks of neck exercise. MRI measures of the cervical multifidus (posterior) and longus capitus/colli (anterior) muscles, neck muscle strength, and self-reported neck disability were recorded at baseline and at completion of the exercise program.

RESULTS

Overall significant increases in CSA and rmCSA were observed for both muscles, but significant reductions in MFI were only evident in the cervical multifidus muscle. These changes coincided with increased muscle strength and reduced neck disability.

CONCLUSIONS

MRI markers of muscle morphology in individuals with chronic whiplash appear to be modifiable with exercise.

MeCP2 Affects Skeletal Muscle Growth and Morphology through Non Cell-Autonomous Mechanisms

Rett syndrome (RTT) is an autism spectrum disorder mainly caused by mutations in the X-linked MECP2 gene and affecting roughly 1 out of 10.000 born girls. Symptoms range in severity and include stereotypical movement, lack of spoken language, seizures, ataxia and severe intellectual disability. Notably, muscle tone is generally abnormal in RTT girls and women and the Mecp2-null mouse model constitutively reflects this disease feature. We hypothesized that MeCP2 in muscle might physiologically contribute to its development and/or homeostasis, and conversely its defects in RTT might alter the tissue integrity or function. We show here that a disorganized architecture, with hypotrophic fibres and tissue fibrosis, characterizes skeletal muscles retrieved from Mecp2-null mice. Alterations of the IGF-1/Akt/mTOR pathway accompany the muscle phenotype. A conditional mouse model selectively depleted of Mecp2 in skeletal muscles is characterized by healthy muscles that are morphologically and molecularly indistinguishable from those of wild-type mice raising the possibility that hypotonia in RTT is mainly, if not exclusively, mediated by non-cell autonomous effects. Our results suggest that defects in paracrine/endocrine signaling and, in particular, in the GH/IGF axis appear as the major cause of the observed muscular defects. Remarkably, this is the first study describing the selective deletion of Mecp2 outside the brain. Similar future studies will permit to unambiguously define the direct impact of MeCP2 on tissue dysfunctions.

The geography of fatty infiltrates within the cervical multifidus and semispinalis cervicis in individuals with chronic whiplash-associated disorders

STUDY DESIGN

Cross-sectional.

OBJECTIVES

To quantify the magnitude and distribution of muscle fat infiltration (MFI) within the cervical multifidus and semispinalis cervicis muscles in participants with chronic whiplash-associated disorders (WADs) compared to those who have fully recovered from a whiplash injury and healthy controls.

BACKGROUND

Previous research has established the presence of increased MFI throughout the cervical extensor muscles of individuals with WAD when compared to healthy controls. These changes appear to be greater in the deepest muscles (eg, multifidus and semispinalis cervicis) than in the more superficial muscles. A detailed analysis of the distribution of MFI within these deep extensor muscles in chronic WAD, recovered, and control groups would provide a foundation for further investigation of specific mechanisms, etiologies, and targets for treatments.

METHODS

Fifteen participants (WAD, n = 5; recovered, n = 5; and control, n = 5) were studied using a 3-D fat-water separation magnetic resonance imaging sequence. Bilateral measures of cervical multifidus and semispinalis cervicis MFI in 4 quartiles (1 [medial] to 4 [lateral]) at cervical levels C3 through C7 were included in the analysis. Intrarater and interrater reliability were established. A mixed-model analysis was performed to control for covariates, identify interaction effects, and compare MFI distribution between groups.

RESULTS

The limits of agreement confirmed strong intrarater and interrater agreement at all levels (C3-C7). Sex, age, and body mass index were identified as significant covariates for MFI. Significant interactions were found between group and muscle quartile (P<.001) and between muscle quartile and cervical level (P<.001). Pairwise comparisons for intraquartile MFI between groups revealed significantly greater MFI in the WAD group when compared to the recovered group in the first quartile (P<.001), second quartile (P<.001), and third quartile (P = .03). When compared to the control group, the WAD group had significantly greater MFI in the first quartile (P = .002) and the second quartile (P = .045). The control group had significantly higher MFI in comparison to the recovered group in the first quartile (P = .048).

CONCLUSION

This study provides preliminary data mapping the spatial distribution of MFI in the cervical multifidus and semispinalis cervicis muscles in individuals with chronic WAD, those who have recovered from a whiplash injury, and healthy controls. Muscle fat infiltration is more concentrated in the medial portion of the muscles in all participants. However, the magnitude of MFI in the medial quartiles (1 and 2) is greatest in the chronic WAD group.

Promotion of muscle regeneration by myoblast transplantation combined with the controlled and sustained release of bFGFcpr

Although myoblast transplantation is an attractive method for muscle regeneration, its efficiency remains limited. The efficacy of myoblast transplantation in combination with the controlled and sustained delivery of basic fibroblast growth factor (bFGF) was investigated. Defects of thigh muscle in Sprague-Dawley (SD) rats were created, and GFP-positive myoblasts were subsequently transplanted. The rats were divided into three groups. In control group 1 (C1) only myoblasts were transplanted, while in control group 2 (C2) myoblasts were introduced along with empty gelatin hydrogel microspheres. In the experimental group (Ex), myoblasts were transplanted along with bFGF incorporated into gelatin hydrogel microspheres. Four weeks after transplantation, GFP-positive myoblasts were found to be integrated into the recipient muscle and to contribute to muscle fibre regeneration in all groups. A significantly higher expression level of GFP in the Ex group demonstrated that the survival rate of transplanted myoblasts in Ex was remarkably improved compared with that in C1 and C2. Furthermore, myofibre regeneration, characterized by centralization of the nuclei, was markedly accelerated in Ex. The expression level of CD31 in Ex was higher than that in both C1 and C2, but the differences were not statistically significant. A significantly higher expression level of Myogenin and a lower expression level of MyoD1 were both observed in Ex after 4 weeks, suggesting the promotion of differentiation to myotubes. Our findings suggest that the controlled and sustained release of bFGF from gelatin hydrogel microspheres improves the survival rate of transplanted myoblasts and promotes muscle regeneration by facilitating myogenesis rather than angiogenesis.

Satellite cells and the muscle stem cell niche

Adult skeletal muscle in mammals is a stable tissue under normal circumstances but has remarkable ability to repair after injury. Skeletal muscle regeneration is a highly orchestrated process involving the activation of various cellular and molecular responses. As skeletal muscle stem cells, satellite cells play an indispensible role in this process. The self-renewing proliferation of satellite cells not only maintains the stem cell population but also provides numerous myogenic cells, which proliferate, differentiate, fuse, and lead to new myofiber formation and reconstitution of a functional contractile apparatus. The complex behavior of satellite cells during skeletal muscle regeneration is tightly regulated through the dynamic interplay between intrinsic factors within satellite cells and extrinsic factors constituting the muscle stem cell niche/microenvironment. For the last half century, the advance of molecular biology, cell biology, and genetics has greatly improved our understanding of skeletal muscle biology. Here, we review some recent advances, with focuses on functions of satellite cells and their niche during the process of skeletal muscle regeneration.

Strategies to improve regeneration of the soft palate muscles after cleft palate repair

Children with a cleft in the soft palate have difficulties with speech, swallowing, and sucking. These patients are unable to separate the nasal from the oral cavity leading to air loss during speech. Although surgical repair ameliorates soft palate function by joining the clefted muscles of the soft palate, optimal function is often not achieved. The regeneration of muscles in the soft palate after surgery is hampered because of (1) their low intrinsic regenerative capacity, (2) the muscle properties related to clefting, and (3) the development of fibrosis. Adjuvant strategies based on tissue engineering may improve the outcome after surgery by approaching these specific issues. Therefore, this review will discuss myogenesis in the noncleft and cleft palate, the characteristics of soft palate muscles, and the process of muscle regeneration. Finally, novel therapeutic strategies based on tissue engineering to improve soft palate function after surgical repair are presented.

Transplanted mesoangioblasts require macrophage IL-10 for survival in a mouse model of muscle injury

The aim of this study was to verify whether macrophages influence the fate of transplanted mesoangioblasts--vessel-associated myogenic precursors--in a model of sterile toxin-induced skeletal muscle injury. We have observed that in the absence of macrophages, transplanted mesoangioblasts do not yield novel fibers. Macrophages retrieved from skeletal muscles at various times after injury display features that resemble those of immunoregulatory macrophages. Indeed, they secrete IL-10 and express CD206 and CD163 membrane receptors and high amounts of arginase I. We have reconstituted the muscle-associated macrophage population by injecting polarized macrophages before mesoangioblast injection: alternatively activated, immunoregulatory macrophages only support mesoangioblast survival and function. This action depends on the secretion of IL-10 in the tissue. Our results reveal an unanticipated role for tissue macrophages in mesoangioblast function. Consequently, the treatment of muscle disorders with mesoangioblasts should take into consideration coexisting inflammatory pathways, whose activation may prove crucial for its success.

Body weight and leukocyte infiltration after an acute exercise-related muscle injury in ovariectomized mice treated with estrogen and progesterone

In both rats and mice, an acute skeletal muscle injury leads to leukocyte infiltration in which the leukocytes remove dead fibers and cellular debris, induce a secondary injury, and/or promote myofiber regeneration. Short-term exogenous estrogen treatment attenuates this leukocyte infiltration and prevents body weight gain in rat exercise-induced skeletal muscle injury models. But these estrogen effects may not occur in mice because body weight gain does not consistently occur in ovariectomized mice treated with estrogen. Additionally, progesterone may also attenuate this leukocyte infiltration without affecting body weight. The aim of the current study was to compare body weight and leukocyte infiltration in exercise-injured skeletal muscle of ovariectomized mice treated with exogenous estrogen and progesterone for the short period of 17 days with that of ovariectomized-placebo-treated mice and gonadal-intact male and female mice. There was no significant difference in body weight between the ovariectomized-estrogen-treated and the ovariectomized-placebo-treated mice. The amount of intramuscular leukocyte infiltration of ovariectomized mice treated with estrogen or progesterone was not significantly different from that of ovariectomized-placebo-treated mice. However, in the injured muscle, the mean area of the leukocyte antigen, 7/4, of the ovariectomized-estrogen-treated group was 2-3-fold greater than that of the ovariectomized-placebo-treated, ovariectomized-estrogen-progesterone-treated, and intact male groups (p<.05), suggesting that the 7/4-positive leukocytes of the ovariectomized-estrogen-treated group were larger or had more antigen. In conclusion, ovariectomized mice demonstrate a different body weight and leukocyte response to short-term estrogen treatment than that of ovariectomized rats, and short-term estrogen treatment modulates leukocyte phenotype. These data broaden our understanding of estrogen's effects on body weight and leukocyte infiltration, and may aid in increasing our understanding of how males and females differ in response to acute muscle injury.

Focal myositis--neurogenic phenomenon?

We report four cases of focal myositis. The patients, three men and one woman, had painful muscle hypertrophy, affecting four different sites. MRI confirmed the muscle enlargement and oedema. Electromyography revealed evidence of acute and chronic denervation in all four cases. Muscle biopsy was available in three and confirmed features suggestive of focal myositis. Based on our patient material, we suggest that chronic nerve irritation, such as compression, can lead to muscle hypertrophy which, when prolonged, provokes fibre necrosis and secondary inflammation. Our finding in four patients having hypertrophy involving four different sites, leads us further to suggest that this may be the common mechanism behind focal myositis.

Intramuscular transplantation of muscle-derived stem cells accelerates skeletal muscle healing after contusion injury via enhancement of angiogenesis

BACKGROUND

Muscle contusions are common muscle injuries. Although these injuries are capable of healing, incomplete functional recovery often occurs. Muscle-derived stem cells (MDSCs) are likely derived from blood vessel cells and have a multilineage differentiation potential.

PURPOSE

The aims of this study are (1) to find optimal timing of MDSC transplantation to enhance muscle healing by stimulating muscle regeneration and preventing scar tissue (fibrosis) formation after skeletal muscle contusion injury, and (2) to investigate the role of angiogenesis in the muscle-healing process after MDSC transplantation.

STUDY DESIGN

Controlled laboratory study.

METHODS

Muscle-derived stem cells were injected directly into injured tibialis anterior muscles of mice at various time points (1, 4, and 7 days) after the muscle contusion injury. Muscle regeneration, angiogenesis, and fibrosis formation were evaluated by histology and real-time polymerase chain reaction analysis, and functional recovery was measured by physiologic testing.

RESULTS

Transplantation of MDSCs at 4 days after injury significantly promoted angiogenesis, which was induced by high levels of vascular endothelial growth factor expression at week 1, and significantly increased muscle regeneration and muscle strength by week 2, when compared with the other groups. A decrease in fibrosis formation was observed at week 4, when compared with the other groups, after the transplantation of MDSCs at 4 and 7 days after injury.

CONCLUSION

Intramuscular injection of MDSCs at 4 days after injury improved and accelerated skeletal muscle healing by increasing angiogenesis and decreasing scar tissue formation.

CLINICAL RELEVANCE

These findings could contribute to the development of biologic treatments to aid in muscle healing after muscle injury.

The temporal development of fatty infiltrates in the neck muscles following whiplash injury: an association with pain and posttraumatic stress

BACKGROUND

Radiological findings associated with poor recovery following whiplash injury remain elusive. Muscle fatty infiltrates (MFI) in the cervical extensors on magnetic resonance imaging (MRI) in patients with chronic pain have been observed. Their association with specific aspects of pain and psychological factors have yet to be explored longitudinally.

MATERIALS AND FINDINGS

44 subjects with whiplash injury were enrolled at 4 weeks post-injury and classified at 6 months using scores on the Neck Disability Index as recovered, mild and moderate/severe. A measure for MFI and patient self-report of pain, loss of cervical range of movement and posttraumatic stress disorder (PTSD) were collected at 4 weeks, 3 months and 6 months post-injury. The effects of time and group and the interaction of time by group on MFI were determined. We assessed the mediating effect of posttraumatic stress and cervical range of movement on the longitudinal relationship between initial pain intensity and MFI. There was no difference in MFI across all groups at enrollment. MFI values increased in the moderate/severe group and were significantly higher in comparison to the recovered and mild groups at 3 and 6 months. No differences in MFI values were found between the mild and recovered groups. Initial severity of PTSD symptoms mediated the relationship between pain intensity and MFI at 6 months. Initial ROM loss did not.

CONCLUSIONS

MFI in the cervical extensors occur soon following whiplash injury and suggest the possibility for the occurrence of a more severe injury with subsequent PTSD in patients with persistent symptoms.

Platelet-rich plasma (PRP) to treat sports injuries: evidence to support its use

Tissue repair in musculoskeletal lesions is often a slow and sometimes incomplete process. In sports patients or professional athletes, the impact of musculoskeletal lesions on life and work is great, and the fast recovery of full efficiency and return to competition is of primary importance. The clinical improvement offered by available treatments is not always sufficient for highly demanding patients to return to their previous level of activity. The search for a minimally invasive solution to improve the status of the chondral surface of the injured joint is therefore highly desirable, especially in these patients. Platelet-rich plasma (PRP) is a procedure that allows to obtain a natural concentration of autologous growth factors. The attractive possibility to use the patients' own growth factors to enhance reparative process in tissues with low healing potential, the promising preliminary clinical findings and the safety of these methods, explain the wide application of this biological approach. The aim of this review is to analyse the existing published studies to look for scientific evidence in preclinical studies or in the results obtained through PRP application in humans that supports the efficacy of PRP and its use for the treatment of tendinous, ligamentous, cartilaginous and muscular injuries. The analysis of the literature shows promising preclinical results but contradictory clinical findings for the treatment of sport injuries. High-quality studies are required to confirm these preliminary results and provide scientific evidence to support its use.

Maternal obesity-impaired insulin signaling in sheep and induced lipid accumulation and fibrosis in skeletal muscle of offspring

The prevalence of maternal obesity is increasing rapidly in recent decades. We previously showed that maternal obesity affected skeletal muscle development during the fetal stage. The objective of this study was to evaluate the effects of maternal obesity on the skeletal muscle properties of offspring. Ewes were fed a control diet (100% energy requirement, Con) or an obesogenic diet (150% energy requirement, OB) from 2 mo before pregnancy to weaning. After weaning, the offspring lambs were fed a maintenance diet until 19 mo of age and then ad libitum for 12 wk to measure feed intake. At 22 mo old, the longissimus dorsi (LD) muscle was biopsied. The downstream insulin signaling was lower in OB than Con lambs as shown by reduction in the phosphorylation of protein kinase B, mammalian target of rapamycin, and 4-E binding protein 1. On the other hand, the phosphorylation of protein kinase C and insulin receptor substrate 1 was higher in OB compared to Con lambs. More intramuscular adipocytes were observed in OB compared to Con offspring muscle, and the expression of peroxisome proliferator-activated receptor gamma, an adipocyte marker, was also higher, which was consistent with the higher intramuscular triglyceride content. Both fatty acid transport protein 1 and cluster of differentiation 36 (also known as fatty acid translocase) were increased in the OB group. In addition, higher collagen content was also detected in OB compared to Con offspring. In conclusion, our data show that offspring from obese mothers had impaired insulin signaling in muscle compared with control lambs, which correlates with increased intramuscular triglycerides and higher expression of fatty acid transporters. These data clearly show that maternal obesity impairs the function of the skeletal muscle of offspring, supporting the fetal programming of adult metabolic diseases.

Fibroblast growth factors: biology, function, and application for tissue regeneration

Fibroblast growth factors (FGFs) that signal through FGF receptors (FGFRs) regulate a broad spectrum of biological functions, including cellular proliferation, survival, migration, and differentiation. The FGF signal pathways are the RAS/MAP kinase pathway, PI3 kinase/AKT pathway, and PLCγ pathway, among which the RAS/MAP kinase pathway is known to be predominant. Several studies have recently implicated the in vitro biological functions of FGFs for tissue regeneration. However, to obtain optimal outcomes in vivo, it is important to enhance the half-life of FGFs and their biological stability. Future applications of FGFs are expected when the biological functions of FGFs are potentiated through the appropriate use of delivery systems and scaffolds. This review will introduce the biology and cellular functions of FGFs and deal with the biomaterials based delivery systems and their current applications for the regeneration of tissues, including skin, blood vessel, muscle, adipose, tendon/ligament, cartilage, bone, tooth, and nerve tissues.

Dual and beneficial roles of macrophages during skeletal muscle regeneration

Macrophages are necessary for skeletal muscle regeneration after injury. Muscle recruits inflammatory monocytes/macrophages that switch toward an anti-inflammatory profile upon phagocytosis of debris. In vitro, proinflammatory macrophages stimulate myoblast proliferation, whereas anti-inflammatory macrophages stimulate their differentiation. Thus, macrophages are involved in both phases of skeletal muscle regeneration: first, inflammation and cleansing of necrosis, and then myogenic differentiation and tissue repair.

Inhibition of mammalian muscle differentiation by regeneration blastema extract of Sternopygus macrurus

Tissue regeneration through stem cell activation and/or cell dedifferentiation is widely distributed across the animal kingdom. By comparison, regeneration in mammals is poor and this may reflect a limited dedifferentiation potential of mature cells. Because mammalian myotubes can dedifferentiate in the presence of newt blastema extract, the present study tested the dedifferentiation induction capability of the blastema from the teleost Sternopygus macrurus (SmBE). Our in vitro data showed that SmBE did not induce cell cycle reentry of myonuclei in myotubes. Instead, SmBE caused myotubes to detach and time-lapse imaging analyses characterized the cellular events before their detachment. Furthermore, SmBE enhanced myoblast proliferation and reversibly inhibited their differentiation. These data suggest the presence of protein factors in SmBE that regulate mammalian muscle physiology and differentiation, but do not support the conservation of a dedifferentiation induction capability by the blastema of S. macrurus.

Expression of mRNA for specific fibroblast growth factors associates with that of the myogenic markers MyoD and proliferating cell nuclear antigen in regenerating and overloaded rat plantaris muscle

AIM

To examine the relations between specific fibroblast growth factors (FGFs) and satellite cell activation during muscle regeneration and hypertrophy in vivo, we measured mRNA expression of FGFs and myogenic markers in rat plantaris muscle after bupivacaine administration and synergist ablation.

METHODS

mRNA levels for MyoD, myogenin, proliferating cell nuclear antigen (PCNA), p21, M-cadherin, Pax7, FGF-1, FGF-2, FGF-3, FGF-4, FGF-5, FGF-6, FGF-7, FGF-8 and hepatocyte growth factor (HGF) were measured continually for up to 72 h after bupivacaine administration and synergist ablation. FGF-5, FGF-7 and HGF proteins were immunostained at 72 h after bupivacaine administration.

RESULTS

MyoD and PCNA mRNAs started increasing 24 h after bupivacaine administration. Myogenin, p21, M-cadherin and Pax7 mRNAs started to increase after 48 and 72 h. After synergist ablation, MyoD, PCNA, M-cadherin and Pax7 mRNAs had increased at 24 and 48 h, and myogenin and p21 mRNAs at 12 and 24 h. FGF-1, FGF-7 and HGF mRNAs after the treatments started to increase at the same time as MyoD and PCNA mRNAs. FGF-5 was expressed at the same time as MyoD and PCNA mRNAs after bupivacaine administration but did not after the ablation. FGF-2, FGF-3, FGF-4, FGF-6 and FGF-8 mRNAs were not associated with the expression of the myogenic markers. FGF-7 and HGF proteins were expressed in immature muscle fibre nuclei and the extracellular matrix, but FGF-5 protein was preferentially expressed in extracellular matrix.

CONCLUSION

These results indicate that FGF-1, FGF-7 and HGF are associated with specific myogenic marker expression during muscle regeneration and hypertrophy.

Slc11a1 (Nramp1) alleles interact with acute inflammation loci to modulate wound-healing traits in mice

Lines of mice were obtained by selective breeding for maximum (AIRmax) or minimum (AIRmin) acute inflammation. They present distinct neutrophil influx and show frequency disequilibrium of the solute carrier family 11a member 1 (Slc11a1) alleles. This gene is involved in ion transport at the endosomes within macrophages and neutrophils, interfering in their activation. Homozygous AIRmax and AIRmin sublines for the Slc11a1 gene were produced to examine the interaction of this gene with the acute inflammatory loci. The present work investigated wound-healing traits in AIRmax and AIRmin mice, in F(1) and F(2) intercrosses, and in Slc11a1 sublines. Two-millimeter ear punches were made in the mice and hole closure was measured during 40 days. AIRmax mice demonstrated significant tissue repair while AIRmin mice did not. Significant differences between the responses of male and female mice were also observed. Wound-healing traits demonstrated a correlation with neutrophil influx in F(2) populations. AIRmax( SS )showed higher ear-wound closure than AIRmax( RR ) mice, suggesting that the Slc11a1 S allele favored ear tissue repair. QTL analysis has detected two inflammatory loci modulating ear wound healing on chromosomes 1 and 14. These results suggest the involvement of the acute inflammation modifier QTL in the wound-healing phenotype.

Inflammatory cells do not decrease the ultimate tensile strength of intact tendons in vivo and in vitro: protective role of mechanical loading

Although inflammatory cells and their products are involved in various pathological processes, a possible role in tendon dysfunction has never been convincingly confirmed and extensively investigated. The goal of this study was to determine whether or not an acute inflammatory process deprived of mechanical trauma can induce nonspecific damages to intact collagen fibers. To induce leukocyte accumulation, carrageenan was injected into rat Achilles tendons. We first tested the effect of leukocyte recruitment on the concentrations or activities of matrix metalloproteinases and tissue inhibitors of matrix metalloproteinases. Second, we analyzed at the biochemical, histological, and biomechanical levels the impact of leukocyte invasion on tendons. Finally, collagen bundles isolated from rat-tail tendons were exposed in vitro to mechanical stress and/or inflammatory cells to determine if mechanical loading could protect tendons from the leukocyte proteolytic activity. Carrageenan-induced leukocyte accumulation was associated with an increased matrix metalloproteinase activity and a decreased content of tissue inhibitors of matrix metalloproteinases. However, hydroxyproline content and load to failure did not change significantly in these tendons. Interestingly, mechanical stress, when applied in vitro, protected collagen bundles from inflammatory cell-induced deterioration. Together, our results suggest that acute inflammation does not induce damages to intact and mechanically stressed collagen fibers. This protective effect would not rely on increased tissue inhibitors of matrix metalloproteinases content but would rather be conferred to the intrinsic resistance of mechanically loaded collagen fibers to proteolytic degradation.

Rapid atrophy of the lumbar multifidus follows experimental disc or nerve root injury

STUDY DESIGN

Experimental study of muscle changes after lumbar spinal injury.

OBJECTIVES

To investigate effects of intervertebral disc and nerve root lesions on cross-sectional area, histology and chemistry of porcine lumbar multifidus.

SUMMARY OF BACKGROUND DATA

The multifidus cross-sectional area is reduced in acute and chronic low back pain. Although chronic changes are widespread, acute changes at 1 segment are identified within days of injury. It is uncertain whether changes precede or follow injury, or what is the mechanism.

METHODS

The multifidus cross-sectional area was measured in 21 pigs from L1 to S1 with ultrasound before and 3 or 6 days after lesions: incision into L3-L4 disc, medial branch transection of the L3 dorsal ramus, and a sham procedure. Samples from L3 to L5 were studied histologically and chemically.

RESULTS

The multifidus cross-sectional area was reduced at L4 ipsilateral to disc lesion but at L4-L6 after nerve lesion. There was no change after sham or on the opposite side. Water and lactate were reduced bilaterally after disc lesion and ipsilateral to nerve lesion. Histology revealed enlargement of adipocytes and clustering of myofibers at multiple levels after disc and nerve lesions.

CONCLUSIONS

These data resolve the controversy that the multifidus cross-sectional area reduces rapidly after lumbar injury. Changes after disc lesion affect 1 level with a different distribution to denervation. Such changes may be due to disuse following reflex inhibitory mechanisms.

Immunomodulation of TGF-beta 1 in mdx mouse inhibits connective tissue proliferation in diaphragm but increases inflammatory response: implications for antifibrotic therapy

Irreversible connective tissue proliferation in muscle is a pathological hallmark of Duchenne muscular dystrophy (DMD), a genetic degenerative muscle disease due to lack of the sarcolemmal protein dystrophin. Focal release of transforming growth factor-beta1 (TGF-beta1) is involved in fibrosis development. Murine muscular dystrophy (mdx) is genetically homologous to DMD and histopathological alterations comparable to those in DMD muscles occur in diaphragm of older mdx mice. To investigate the early development of fibrosis and TGF-beta1 involvement, we assessed diaphragms in 6-36-week-old mdx and C57/BL6 (control) mice for fibrosis, and used real-time PCR and ELISA to determine TGF-beta1 expression. Significantly greater fibrosis and TGF-beta1 expression were found in mdx from the 6th week. Mice treated with neutralizing antibody against TGF-beta1 had lower levels of TGF-beta1 protein, reduced fibrosis, unchanged muscles fiber degeneration/regeneration, but increased inflammatory cells (CD4+lymphocytes). These data demonstrate early and progressive fibrosis in mdx diaphragm accompanied by TGF-beta1 upregulation. Reduction of TGF-beta1 appears promising as a therapeutic approach to muscle fibrosis, but further studies are required to evaluate long term effects of TGF-beta1 immunomodulation on the immune system.

A free radical scavenger but not FGF-2-mediated angiogenic therapy rescues myonephropathic metabolic syndrome in severe hindlimb ischemia

The therapeutic use of angiogenic factors shows promise in the treatment of critical limb ischemia; however, its potential for myonephropathic metabolic syndrome (MNMS), a fatal complication caused by arterial reconstruction, has not been elucidated. The objective of this study was to evaluate the effectiveness of recombinant Sendai virus-mediated gene transfer of fibroblast growth factor-2 (FGF-2) directly compared with that of a radical scavenger, MCI-186, in a rat model of MNMS. MNMS was surgically induced by aortic occlusion below renal arteries for 4 h, followed by 6 h of reperfusion. Administration of MCI-186 (twice; iv 5 min before induced ischemia and ip 5 min before reperfusion; 10 mg/kg, respectively), but not FGF-2 gene transfer (once, 48 h before induced ischemia), dramatically prevented the increase of serum biochemical markers as well as the edema of the gastrocnemius muscle. The effect of MCI-186 was accompanied by the marked suppression of the neutrophilic infiltration into the local (muscle) and remote (lung) organs. Although serum and muscular levels of a neutrophil-chemoattractant (growth-related oncogene/cytokine-induced neutrophil chemoattractant-1) were not affected by any treatment, the serum level of soluble intercellular adhesion molecule-1 was decreased by treatment with MCI-186 but not by treatment with FGF-2. These results suggest the distinct mechanism of MNMS from critical limb ischemia without reperfusion. Therefore, radical scavenging should be paid more attention than therapeutic angiogenesis when arterial circulation is reconstructed.

Autologous Bone Marrow-Derived Cells Enhance Muscle Strength Following Skeletal Muscle Crush Injury in Rats

Insufficient post-traumatic skeletal muscle regeneration with consecutive functional deficiency continues to be a serious problem in orthopedic and trauma surgery. Transplantation of autologous muscle precursor cells has shown encouraging results in muscle trauma treatment but is associated with significant donor site morbidity. In contrast to this, bone marrow-derived (BMD) cells can be obtained without any functional deficit by puncture. The goal of this study was to examine whether regular muscle regeneration can be improved by local application of autologous BMD cells in a rat model of blunt skeletal muscle trauma. One week after standardized open blunt crush injury to the left soleus muscle, 10(6) autologous BMD cells were injected into the traumatized muscle of male Sprague Dawley rats. Rats of the control group received saline solution as treatment. Three weeks after application, the fast twitch and tetanic contraction capacity of the soleus muscles was measured bilaterally by stimulating the sciatic nerves. Contraction forces of injured soleus muscles in control animals recovered to 39 +/- 10% (tetanic) and 59 +/- 12% (fast twitch) of the contralateral noninjured soleus muscles (p < 0.001). In contrast, autologous BMD cell injection significantly restored contractile forces to 53 +/- 8% (tetanic) and 72 +/- 13% (fast twitch) compared to those observed in contralateral noninjured soleus muscles. Thus, muscle function was significantly increased by BMD cell treatment (tetanic, p = 0.014; fast twitch, p = 0.05). In conclusion, autologous BMD cell grafting leads to an increase in contraction force, 14% in tetanic and 13% in fast twitch stimulation, demonstrating its potential to improve functional outcome after skeletal muscle crush injury.

Cancer is a functional repair tissue

When a wound occurs, growth and repair genes (GR genes, such as oncogenes, proto-oncogenes, etc.) in surrounding cells are activated and secretion of growth and repair factors (GR factors, such as growth, stem cell, and stimulating factors, etc.) is induced to heal the wound. However, if the wound is persistent due to chronic physical (radiation, electromagnetic field, trauma, particles, etc.), chemical (carcinogens, toxic chemicals, heavy metals etc.) or biological (aging, free radicals, inflammation, nutrient deficiency, bacteria and virus infections, stress, etc.) damage, amplification of GR gene activation in surrounding cells may lead to a clinical cancer. Based on the commonalities between cancer and wound healing, a new hypothesis of cancer is presented: malignancies are not passive mutated useless masses; rather, they are functional tissues produced by GR gene activation to secrete GR factors in an effort to heal persistent wounds in the body. Based on the hypothesis, current cancer treatments aimed at killing cancer cells only may be misguided. The logical extension of the hypothesis is that cancer treatment focused on wound healing by limiting causes of persistent wounds, providing repair cells, GR factors, and substrates required by repair cells may yield more fruitful results than treatments focused on killing cancer cells alone. Spontaneous regressions of cancer, although rare, may be successful examples of serendipitous spontaneous wound healing. Standard therapies aimed at killing cancer cells, should be limited to adjuvant status for limiting symptoms or buying time for completion of the wound healing process. Attempts to destroy cancer cells without healing underlying persistent wounds will allow for eventual recurrence.

IGF-II is up-regulated and myofibres are hypertrophied in regenerating soleus of mice lacking FGF6

Important functions in myogenesis have been proposed for FGF6, a member of the fibroblast growth factor family accumulating almost exclusively in the myogenic lineage. However, the use of FGF6(-/-) mutant mice gave contradictory results and the role of FGF6 during myogenesis remains largely unclear. Using FGF6(-/-) mice, we first analysed the morphology of the regenerated soleus following cardiotoxin injection and showed hypertrophied myofibres in soleus of the mutant mice as compared to wild-type mice. Secondly, to examine the function of the IGF family in the hypertrophy process, we used semiquantitative and real-time RT-PCR assays and Western blots to monitor the expression of the insulin-like growth factors (IGF-I and IGF-II), their receptors [type I IGF receptor (IGF1R) and IGF-II receptor (IGF2R)], and of a binding protein IGFBP-5 in regenerating soleus muscles of FGF6(-/-) knockout mice vs. wild-type mice. In the mutant, both IGF-II and IGF2R, but not IGF-I and IGF1R, were strongly up-regulated, whereas IGFBP5 was down-regulated, strongly suggesting that, in the absence of FGF6, the mechanisms leading to myofibre hypertrophy were mediated specifically by an IGF-II/IGF2R signalling pathway distinct from the classic mechanism involving IGF-I and IGF1R previously described for skeletal muscle hypertrophy. The potential regulating role of IGFBP5 on IGF-II expression is also discussed. This report shows for the first time a specific role for FGF6 in the regulation of myofibre size during a process of in vivo myogenesis.

Cellular and molecular regulation of muscle regeneration

Under normal circumstances, mammalian adult skeletal muscle is a stable tissue with very little turnover of nuclei. However, upon injury, skeletal muscle has the remarkable ability to initiate a rapid and extensive repair process preventing the loss of muscle mass. Skeletal muscle repair is a highly synchronized process involving the activation of various cellular responses. The initial phase of muscle repair is characterized by necrosis of the damaged tissue and activation of an inflammatory response. This phase is rapidly followed by activation of myogenic cells to proliferate, differentiate, and fuse leading to new myofiber formation and reconstitution of a functional contractile apparatus. Activation of adult muscle satellite cells is a key element in this process. Muscle satellite cell activation resembles embryonic myogenesis in several ways including the de novo induction of the myogenic regulatory factors. Signaling factors released during the regenerating process have been identified, but their functions remain to be fully defined. In addition, recent evidence supports the possible contribution of adult stem cells in the muscle regeneration process. In particular, bone marrow-derived and muscle-derived stem cells contribute to new myofiber formation and to the satellite cell pool after injury.

Targeted disruption of the Fgf2 gene does not affect vascular growth in the mouse ischemic hindlimb

Ischemic revascularization involves extensive structural adaptation of the vasculature, including both angiogenesis and arteriogenesis. Previous studies suggest that fibroblast growth factor (FGF)-2 participates in both angiogenesis and arteriogenesis. Despite this, the specific role of endogenous FGF-2 in vascular adaptation during ischemic revascularization is unknown. Therefore, we used femoral artery ligation in Fgf2(+/+) and Fgf2(-/-) mice to test the hypothesis that endogenous FGF-2 is an important regulator of angiogenesis and arteriogenesis in the setting of hindlimb ischemia. Femoral ligation increased capillary and arteriole density in the ischemic calf in both Fgf2(+/+) and Fgf2(-/-) mice. The level of angiographically visible arteries in the thigh was increased in the ischemic hindlimb in all mice, and no significant differences were observed between Fgf2(+/+) and Fgf2(-/-) mice. Additionally, limb perfusion progressively improved to peak values at day 35 postsurgery in both genotypes. Given the equivalent responses observed in Fgf2(+/+) and Fgf2(-/-) mice, we demonstrate that endogenous FGF-2 is not required for revascularization in the setting of peripheral ischemia. Vascular adaptation, including both angiogenesis and arteriogenesis, was not affected by the absence of FGF-2 in this model.

Vascular growth factor expression in a rat model of severe limb ischemia

BACKGROUND

In ischemic tissue hypoxia induces production of vascular growth factors, especially VEGF, which initiate local angiogenesis. Collateralization-or arteriogenesis-occurs at a distance from the ischemic tissue and depends on different growth factors such as FGF-2. A spatial discrepancy in endogenous growth factor production in limb ischemia may have implications for therapeutic angiogenesis. The present study elucidates if such spatial and temporal variation occurs.

MATERIALS AND METHODS

A two-staged procedure was performed to generate severe long-lasting limb ischemia in 60 rats. At 1, 7, 28, and 56 days, subgroups were subjected to perfusion assessment with laser Doppler imaging and angiography. Muscle samples and foot skin were gathered to measure growth factor expression and signs of angiogenesis using immunohistochemistry.

RESULTS

There was an early twofold increase (P < 0.05) in both VEGF and FGF-2 levels in distal muscle from the ischemic leg, but no significant rise in the thigh. The concentrations decreased over time with an exception for VEGF in soleus and FGF-2 in anterior tibial muscle, which remained high. An increased capillarity was noted (P < 0.05) in soleus after 28 days, and the number of BrdU-positive ECs was elevated in all ischemic samples at 56 days. Collateral arteries were observed on the angiograms after 7 days.

CONCLUSIONS

The results suggest that in limb ischemia any major increase in vascular growth factor production is limited to ischemic tissue. The spatial and temporal distribution patterns of growth factor production are complex and to a great extent influenced by inflammation.

Angiogenic gene therapy for experimental critical limb ischemia: acceleration of limb loss by overexpression of vascular endothelial growth factor 165 but not of fibroblast growth factor-2

Recent studies suggest the possible therapeutic effect of intramuscular vascular endothelial growth factor (VEGF) gene transfer in individuals with critical limb ischemia. Little information, however, is available regarding (1) the required expression level of VEGF for therapeutic effect, (2) the related expression of endogenous angiogenic factors, including fibroblast growth factor-2 (FGF-2), and (3) the related adverse effects due to overexpression of VEGF. To address these issues, we tested effects of overexpression of VEGF165 using recombinant Sendai virus (SeV), as directly compared with FGF-2 gene transfer. Intramuscular injection of SeV strongly boosted FGF-2, resulting in significant therapeutic effects for limb salvage with increased blood perfusion associated with enhanced endogenous VEGF expression in murine models of critical limb ischemia. In contrast, VEGF165 overexpression, 5-times higher than that of baseline on day 1, also strongly evoked endogenous VEGF in muscles, resulting in an accelerated limb amputation without recovery of blood perfusion. Interestingly, viable skeletal muscles of either VEGF165- or FGF-2-treated ischemic limbs showed similar platelet-endothelial cell adhesion molecule-1-positive vessel densities. Maturation of newly formed vessels suggested by smooth muscle cell actin-positive cell lining, however, was significantly disturbed in muscles with VEGF. Further, therapeutic effects of FGF-2 were completely diminished by anti-VEGF neutralizing antibody in vivo, thus indicating that endogenous VEGF does contribute to the effect of FGF-2. These results suggest that VEGF is necessary, but should be delicately regulated to lower expression to treat ischemic limb. The therapeutic effect of FGF-2, associated with the harmonized angiogenic effects seen with endogenous VEGF, provides important insights into therapeutic angiogenesis.

Muscle adaptation during distraction osteogenesis in skeletally immature and mature rabbits

The lack of adaptation of muscle is thought to be a major source of complications during distraction osteogenesis (DO). Although adaptation to DO varies with the regimen (lengthening rate >1 mm/day and increase in bone length >20%) muscle contractures associated with DO may be a function of age. We tested this idea by subjecting skeletally mature and skeletally immature rabbits to an aggressive regimen of DO (1.4 mm/day with a 20% increase in tibial length). By using immunofluorescence to assess the presence of neonatal myosin heavy chain in sections from the tibialis anterior, we observed that the generation of new muscle tissue in response to DO was vigorous in young animals (27% positive fibers), whereas it was more muted in adult animals (9.9% positive fibers). This adaptive response was associated with a pronounced proliferation of myoblasts in the young but not in the mature animals. Adult tibialis anterior subjected to DO showed a 50% loss in tetanic and twitch tension whereas those in young animals did not. This correlated with partial denervation of adult but not young muscle, as judged by morphological criteria. These experiments indicate that adaptation to DO depends not only on mechanical variables but also on skeletal maturity.

Mast cell involvement in fibrodysplasia ossificans progressiva

Fibrodysplasia ossificans progressiva (FOP) is a catastrophic genetic disorder of progressive heterotopic ossification associated with dysregulated production of bone morphogenetic protein 4 (BMP4), a potent osteogenic morphogen. Postnatal heterotopic ossification in FOP is often heralded by hectic episodes of severe post-traumatic connective tissue swelling and intramuscular edema, followed by an intense and highly angiogenic fibroproliferative mass. The abrupt appearance, intense size, and rapid intrafascial spread of the edematous preosseous fibroproliferative lesions implicate a dysregulated wound response mechanism and suggest that cells and mediators involved in inflammation and tissue repair may be conscripted in the growth and progression of FOP lesions. The central and coordinate role of inflammatory mast cells and their mediators in tissue edema, wound repair, fibrogenesis, angiogenesis, and tumor invasion prompted us to investigate the potential involvement of mast cells in the pathology of FOP lesions. We show that inflammatory mast cells are present at every stage of the development of FOP lesions and are most pronounced at the highly vascular fibroproliferative stage. Mast cell density at the periphery of FOP lesional tissue is 40- to 150-fold greater than in normal control skeletal muscle or in uninvolved skeletal muscle from FOP patients and 10- to 40-fold greater than in any other inflammatory myopathy examined. These findings document mobilization and activation of inflammatory mast cells in the pathology of FOP lesions and provide a novel and previously unrecognized target for pharmacologic intervention in this extremely disabling disease.

Mast cell proliferation and alterations in bFGF amount and localization are involved in the response of muscle to dystrophin deficiency in hypertrophic feline dystrophy

To test the hypothesis that basic fibroblast growth factor and mast cells play a key role in the phenotypic differences between human dystrophinopathies and hypertrophic feline muscular dystrophy, serial sections of dystrophin-deficient, carrier and normal cat muscle biopsy specimens were examined. They were stained immunohistochemically for dystrophin and different markers of differentiation such as desmin, vimentin and utrophin. Basic fibroblast growth factor was increased in the myofibers of dystrophic cats compared to normal controls and carriers. An association of basic fibroblast growth factor with fiber regeneration and necrosis was shown. The amount of mast cells was markedly increased in muscle tissue of dystrophic cats with a clear predominance of tryptase-positive cells present in large amounts in the endomysium. Mast cells, like basic fibroblast growth factor, were concentrated in areas of muscle fiber regeneration and necrosis. Our data concerning basic fibroblast growth factor and mast cells are consistent with a highly abnormal cellular environment in feline dystrophic muscle with very high levels of basic fibroblast growth factor which is likely modulated by mast cells.

Mechanisms leading to restoration of muscle size with exercise and transplantation after spinal cord injury

We have shown that cycling exercise combined with fetal spinal cord transplantation restored muscle mass reduced as a result of complete transection of the spinal cord. In this study, mechanisms whereby this combined intervention increased the size of atrophied soleus and plantaris muscles were investigated. Rats were divided into five groups (n = 4, per group): control, nontransected; spinal cord transected at T10 for 8 wk (Tx); spinal cord transected for 8 wk and exercised for the last 4 wk (TxEx); spinal cord transected for 8 wk with transplantation of fetal spinal cord tissue into the lesion site 4 wk prior to death (TxTp); and spinal cord transected for 8 wk, exercised for the last 4 wk combined with transplantation 4 wk prior to death (TxExTp). Tx soleus and plantaris muscles were decreased in size compared with control. Exercise and transplantation alone did not restore muscle size in soleus, but exercise alone minimized atrophy in plantaris. However, the combination of exercise and transplantation resulted in a significant increase in muscle size in soleus and plantaris compared with transection alone. Furthermore, myofiber nuclear number of soleus was decreased by 40% in Tx and was not affected in TxEx or TxTp but was restored in TxExTp. A strong correlation (r = 0.85) between myofiber cross-sectional area and myofiber nuclear number was observed in soleus, but not in plantaris muscle, in which myonuclear number did not change with any of the experimental manipulations. 5'-Bromo-2'-deoxyuridine-positive nuclei inside the myofiber membrane were observed in TxExTp soleus muscles, indicating that satellite cells had divided and subsequently fused into myofibers, contributing to the increase in myonuclear number. The increase in satellite cell activity did not appear to be controlled by the insulin-like growth factors (IGF), as IGF-I and IGF-II mRNA abundance was decreased in Tx soleus and plantaris, and was not restored with the interventions. These results indicate that, following a relatively long postinjury interval, exercise and transplantation combined restore muscle size. Satellite cell fusion and restoration of myofiber nuclear number contributed to increased muscle size in the soleus, but not in plantaris, suggesting that cellular mechanisms regulating muscle size differ between muscles with different fiber type composition.

An overexpression of fibroblast growth factor (FGF) and FGF receptor 4 in a severe clinical phenotype of facioscapulohumeral muscular dystrophy

We evaluated the expression of a select panel of growth factors and their receptors, including fibroblast growth factor 1 (FGF-1), fibroblast growth factor 2 (FGF-2), platelet-derived growth factor (PDGF), FGF receptor 1 (FGF-R1), FGF receptor 3 (FGF-R3), FGF receptor 4 (FGF-R4), PDGF receptor alpha (PDGF-Ralpha), PDGF receptor beta (PDGF-Rbeta), and heparan sulfate proteoglycan (HSPG), in muscle biopsy specimens from nine facioscapulohumeral muscular dystrophy (FSHD) patients using immunohistochemistry. Two cases of Duchenne-type muscular dystrophy (DMD), two of Becker-type muscular dystrophy (BMD), and one of limb-girdle-type muscular dystrophy (LGMD) were also investigated. Widespread immunostaining for FGF-1 and FGF-2 on the sarcolemma and overexpression of FGF-R4 in endomysial and perimysial connective tissue were seen in one patient with a severe clinical phenotype of FSHD who had respiratory failure. Standard histochemistry in this patient revealed marked interstitial fibrosis and lobulated fibers. The overexpression of FGF and FGF-R4 in this severe FSHD case may be associated with the muscle fibrosis and disease severity.

Expression of specific white adipose tissue genes in denervation-induced skeletal muscle fatty degeneration

Denervation of skeletal muscle results in rapid atrophy with loss of contractile mass and/or progressive degeneration of muscle fibers which are replaced to a greater or lesser degree by connective and fatty tissues. In this study, we show that denervated rabbit muscles are transformed into a white adipose tissue, depending on their fiber types. This tissue does express LPL, G3PDH and particularly the ob gene, a white adipose tissue-specific marker, and does not express the brown adipose tissue molecular marker UCP1 mRNA.

Systemic administration of acidic fibroblast growth factor ameliorates the ischemic injury of the retina in rats

The central neuroprotective effects against ischemic injury of fibroblast growth factor (FGF), administered either directly into the central nervous system or systemically, is well documented. Here we show in a rat model of transient retinal ischemia that the neuroprotective effect of systemically administered acidic fibroblast growth factor (aFGF, FGF-1) extends to the retina. Histological findings show a lower decrease of retinal ganglion cells and inner nuclear layer cells (P < 0.0001) in animals receiving FGF-1. These results suggest that FGF may function as a natural protection agent during transient retinal ischemia and further document that an efficient neuroprotection of central nervous tissues can be obtained by systemic administration of this protein. Our data may, thus, contribute to the development of novel and safe therapeutic approach for the treatment of the ischemic injury of the retina.