RESUMEN
Injured skeletal muscle generally regenerates less efficiently with age, but little is understood about the effects of ageing on the very early inflammatory and neovascular events in the muscle repair process. This study used a total of 174 whole muscle grafts transplanted within and between young and old mice to analyse the effects of ageing on the early inflammatory response in two strains of mice (BALB/c and SJL/J). There was a very slight delay in the early inflammatory response, and in the appearance of myotubes at day 4 in BALB/c muscle grafted into an old host environment (implicating systemic events). In SJL/J mice, the initial speed of the inflammatory response was slightly delayed with old muscle grafts regardless of host age (implicating muscle-derived factors), while an old host environment transiently affected myogenesis (myotube formation). The slight delays in inflammatory and neovascular responses in old mice did not dramatically impact on the overall formation of new muscle. The neovascular response to injured young and old muscle tissue was further analysed using the corneal micropocket assay. This showed a very clear 1-2 day delay in angiogenesis induced by old versus young BALB/c muscle tissue implanted into the young rat cornea, indicating that new blood vessel formation is at least partly determined by muscle-derived factors. Taken together these results indicate that, while there are slight age-associated delays in inflammation and neovascularisation in response to injured muscle, there is no detrimental effect on myogenesis in the mouse model used in this study.
Asunto(s)
Envejecimiento/fisiología , Músculo Esquelético/lesiones , Regeneración/fisiología , Animales , Córnea/inmunología , Femenino , Inflamación , Masculino , Ratones , Ratones Endogámicos BALB C , Ratones Endogámicos , Músculo Esquelético/fisiología , Músculo Esquelético/trasplante , Neovascularización Fisiológica , Ratas , Ratas Wistar , Especificidad de la Especie , Coloración y Etiquetado , Trasplante Autólogo , Trasplante HomólogoRESUMEN
The expression of laminin isoforms and laminin-binding integrin receptors known to occur in muscle was investigated during myogenic regeneration after crush injury. Comparisons were made between dystrophic 129ReJ dy/dy mice, which have reduced laminin alpha2 expression, and their normal littermates. The overall histological pattern of regeneration after crush injury was similar in dy/dy and control muscle, but proceeded faster in dy/dy mice. In vitro studies revealed a greater yield of mononuclear cells extracted from dy/dy muscle and a reduced proportion of desmin-positive cells upon in vitro cultivation, reflecting the presence of inflammatory cells and "preactivated" myoblasts due to ongoing regenerative processes within the endogenous dystrophic lesions. Laminin alpha1 was not detectable in skeletal muscle. Laminin alpha2 was present in basement membranes of mature myofibers and newly formed myotubes in control and dy/dy muscles, albeit weaker in dy/dy. Laminin alpha2-negative myogenic cells were detected in dy/dy and control muscle, suggesting the involvement of other laminin alpha chains in early myogenic differentiation, such as laminin alpha4 and alpha5 which were both transiently expressed in basement membranes of newly formed myotubes of dy/dy and control mice. Integrin beta1 was expressed on endothelial cells, muscle fibers, and peripheral nerves in uninjured muscle and broadened after crush injury to the interstitium where it occurred on myogenic and nonmyogenic cells. Integrin alpha3 was not expressed in uninjured or regenerating muscle, while integrin alpha6 was expressed mainly on endothelial cells and peripheral nerves in uninjured muscle. Upon crush injury integrin alpha6 increased in the interstitium mainly on nonmyogenic cells, including infiltrating leukocytes, endothelial cells, and fibroblasts. In dy/dy muscle, integrin alpha6 occurred on some newly formed myotubes. Integrin alpha7 was expressed on muscle fibers at the myotendinous junction and showed weak and irregular expression on muscle fibers. After crush injury, integrin alpha7 expression extended to the newly formed myotubes and some myoblasts. However, many myoblasts and newly formed myotubes were integrin alpha7 negative. No marked difference was observed in integrin alpha7 expression between dy/dy and control muscle, either uninjured or after crush injury. Only laminin alpha4 and integrin alpha6 expression patterns were notably different between dy/dy and control muscle. Expression of both molecules was more extensive in dy/dy muscle, especially in the interstitium of regenerating areas and on newly formed myotubes. In view of the faster myogenic regeneration observed in dy/dy mice, the data suggest that laminin alpha4 and integrin alpha6 support myogenic regeneration. However, whether these accelerated myogenic effects are a direct consequence of the reduced laminin alpha2 expression in dy/dy mice, or an accentuation of the ongoing regenerative events in focal lesions in the muscle, requires further investigation.
Asunto(s)
Antígenos CD/metabolismo , Laminina/metabolismo , Músculo Esquelético/metabolismo , Regeneración , Animales , Técnica del Anticuerpo Fluorescente , Técnicas para Inmunoenzimas , Integrina alfa3beta1 , Integrina alfa6 , Integrina alfa6beta1 , Integrinas/metabolismo , Ratones , Músculo Esquelético/lesiones , Músculo Esquelético/fisiología , Isoformas de Proteínas/metabolismo , Regulación hacia ArribaRESUMEN
Skeletal muscles actually surround the dento-alveolar area. However, most dentists would be unaware that they damage skeletal muscle during routine procedures. Simple puncturing of buccinator muscle during an inferior alveolar block kills thousands of fibres. What happens to muscle fibres following such trauma? Pathology texts suggest that skeletal muscle does not regenerate and is replaced by fibrous scar tissue. However, for some decades it has been recognized that muscle fibres do in fact regenerate. In the early 1960s the "satellite" cell was discovered, lying between the muscle cell membrane and the external lamina. After 30 years of intensive research it has been clearly demonstrated that satellite cells are reserve mesenchyme cells which, once the adjacent muscle fibres are damaged, proliferate and provide a new population of young muscle cells, called "myoblasts". Myoblasts rapidly produce muscle specific proteins and fuse together in long chains, called "myotubes", which mature into typical muscle fibres.
Asunto(s)
Músculo Esquelético/fisiopatología , Agujas/efectos adversos , Regeneración/fisiología , Membrana Basal/citología , Membrana Basal/fisiología , División Celular/fisiología , Fusión Celular , Cicatriz/patología , Humanos , Mesodermo/citología , Mesodermo/fisiología , Fibras Musculares Esqueléticas/patología , Fibras Musculares Esqueléticas/fisiología , Proteínas Musculares/fisiología , Músculo Esquelético/lesiones , Músculo Esquelético/patología , Bloqueo Nervioso/efectos adversos , Bloqueo Nervioso/instrumentación , Punciones/efectos adversos , Punciones/instrumentación , Sarcolema/fisiologíaRESUMEN
In mdx mice, a model for Duchenne muscular dystrophy, the timing between the replication of myoblasts and their incorporation into myotubes was determined autoradiographically. Thirty-eight mdx mice aged 23 d were injected with tritiated thymidine to label myoblasts replicating early in the dystrophic process. At intervals from 8 h to 30 d after injection the tibialis anterior muscles were removed, processed for autoradiography and analysed for labelled central myonuclei (derived from the progeny of myoblasts which had been labelled at 23 d). At 8 h after injection there were no labelled central myonuclei, showing that the labelled myoblasts had not fused within this time. At 1 d, 2 % of central myonuclei were labelled, at 2 d, up to 32% were labelled, at 3 d approximately 60% were labelled, and at 4 d the labelling peaked at 74%. In the 27 mice sampled from 5-30 d after injection, the levels of central myonuclear labelling varied enormously: from 1-63%. However, there was a consistent decrease in the numbers of labelled central myonuclei with time. This may have been due to dilution of the relative numbers of labelled myonuclei due to other, nonlabelled, myoblasts replicating after the availability of tritiated thymidine, and fusing. It was also possible that labelled myofibres underwent subsequent necrosis and were eliminated from the muscle. The proposal that a regenerated myofibre can undergo a subsequent cycle of necrosis and regeneration was supported by evidence of some necrotic myofibres with labelled and unlabelled central nuclei. These results have implications for understanding the cellular biology and pathology of dystrophic muscle, particularly in relation to myoblast transfer therapy as a potential treatment of Duchenne muscular dystrophy.
Asunto(s)
Músculo Esquelético/fisiopatología , Distrofia Muscular Animal/fisiopatología , Animales , Autorradiografía , División Celular , Ratones , Ratones Endogámicos mdx , Músculo Esquelético/ultraestructura , Distrofia Muscular Animal/patología , Necrosis , RegeneraciónRESUMEN
In Australia nearly all tertiary education is funded through the Federal Government. With reductions in government spending tertiary education has had to accommodate its share of the cuts. Under such a climate dental schools in Australia face serious financial difficulties, in addition to many other diverse threats, as they head towards the 21st century. Most seriously, and almost uniformly felt, is the diminution of Federal Government funding to a point where the operation of some dental schools remains viable only by way of supplementary funding (direct or in-kind) from State Governments. In this report the authors have developed one possible model of academic, clinical and financial structures of a dental school, based on sound educational and economic grounds, that can overcome some of the short-comings of the paradigm that exists in some schools in Australia. The two key factors underlying the principles of this model for a new style of dental school are flexibility and professional responsibility. Based on the existing academic and economic realities it would be much more appropriate to outsource a significant proportion of the educational and clinical component of a dental school. Highly trained individuals from the dental profession would be invited to provide training in their area of expertise. The role of the dental school would evolve to be like a facilitation centre, organizing the various courses. It would mean that the 'core' curriculum would be the responsibility of the school's academic staff and the outsourced professional members would contribute within the bounds of the basic framework. On the basis of this model a dental school of approximately 225 full-time undergraduate students (50 per year, less some student loss) in a five year programme is planned, and annual staffing costs are estimated at $1.4 million.
Asunto(s)
Facultades de Odontología/tendencias , Australia , Servicios Contratados , Curriculum , Educación en Odontología/economía , Educación en Odontología/organización & administración , Docentes de Odontología , Administración Financiera/economía , Administración Financiera/tendencias , Financiación Gubernamental , Predicción , Humanos , Facultades de Odontología/economía , Facultades de Odontología/organización & administración , Gobierno Estatal , Estudiantes de OdontologíaRESUMEN
Evans blue dye (EBD) identifies areas of increased vascular permeability, which is usually indicative of endothelial damage. Most studies examine EBD-stained areas light-microscopically, but others analyze the cells with the electron microscope. Electron microscopic studies have assumed that EBD itself did not change the ultrastructure of endothelial cells and this hypothesis was tested in the following study. The left iliac arteries of 20 rats were injured with 1-mm vascular clamps for 5 minutes. At 7 and 14 days after clamping, 10 rats for each time were infused intravenously either with normal-saline or EBD, perfused 30 minutes later with fixatives. Then the clamp-injured arteries, contralateral (unclamped) arteries, aortae, and the aortic bifurcations were removed for EM morphometry. In an additional (control) group of 10 rats, with no clamp injuries, 5 were infused with EBD and 5 with normal-saline and all 10 rats were perfused 30 minutes later, as above. EBD caused a significant simplification of the junctional morphology in both normal and regenerating endothelium. It also increased the area fractions of cytoplasmic vesicles in regenerating endothelium. These data demonstrate that EBD causes measurable ultrastructural changes in normal and regenerating endothelium. This effect should be taken into account when using EBD to assess various insults to blood vessels.
Asunto(s)
Colorantes , Endotelio Vascular/ultraestructura , Azul de Evans , Regeneración , Animales , Arterias/fisiología , Arterias/ultraestructura , Femenino , Ratas , Ratas WistarRESUMEN
The identification of myogenic precursor cells (mpc) is a key factor in determining the early events in the myogenesis and regeneration of skeletal muscle. Although satellite cells have long been established as the providers of myoblastic cells, very little is really known (apart from their anatomical location in relation to muscle fibres and their ability to migrate) about the precise role of satellite cells in myogenesis. Numerous techniques for labelling mpc have been devised, but none of these has proven to be completely reliable in firmly establishing the origin of myogenic cells. The use of tritiated thymidine to label DNA in proliferating mpc (which are not specifically distinguishable at the time) and the subsequent location of their labelled progeny in myotube nuclei has revealed a great deal of data on the timing of myogenesis, but not about the nature of mpc themselves. DNA synthesis can also be detected by antibodies to the thymidine analogue, bromodeoxyuridine, and also by antibody staining for proliferating nuclear cell antigen. Like tritiated thymidine, these other markers are not specific for muscle but are general markers for DNA synthesis. In situ hybridisation of various muscle-specific genetic markers and their products has been informative, as has immunolabelling of myogenin, MyoD1 and desmin. Desmin labelling has been particularly instructive in identifying mpc because it is one of the first muscle-specific proteins to be produced in mpc. This review covers some of the techniques mentioned above and their usefulness in determining the early events in myogenesis.
Asunto(s)
ADN/análisis , Desmina/análisis , Músculo Esquelético/citología , Regeneración , Animales , Anticuerpos Monoclonales , Autorradiografía , Biomarcadores/análisis , División Celular , Desmina/inmunología , Humanos , Inmunohistoquímica , Ratones , Músculo Esquelético/química , Músculo Esquelético/fisiología , Células Madre/citologíaRESUMEN
MyoD1 alleles distinguish between the Mm musculus and Mm domesticus subspecies of Mus musculus. SJL/J mice, which belong to the Mm musculus subspecies, are able to regenerate skeletal muscle more efficiently than BALB/c mice which possess the Mm domesticus MyoD1 allele. Hence the possibility that regeneration responses are due to species-specific genetic differences including MyoD1 was investigated in this study. Quantitative morphometric analysis following muscle crush injury of 2 Mm musculus strains, MBK and MGL, has indicated that regeneration phenotype is not species-specific and may not be directly related to MyoD1 alleles. These results contrast with prior investigations conducted in SJL/J and BALB/c mice, and indicate that other genes may have a direct influence on skeletal muscle regeneration.
Asunto(s)
Músculo Esquelético/fisiología , Proteína MioD/genética , Regeneración/fisiología , Alelos , Animales , Masculino , Ratones , Ratones Endogámicos BALB C , Músculo Esquelético/lesiones , Músculo Esquelético/patología , Proteína MioD/fisiología , Fenotipo , Especificidad de la EspecieRESUMEN
BACKGROUND: It is now well established that mature skeletal muscle has the ability to regenerate, and reports on this phenomenon have existed in the research literature for some 40 years. However, it is only relatively recently, largely due to the advances in microsurgery, that practising surgeons can make direct use of the regenerative ability of skeletal muscle. METHODS: Most of the key data on skeletal muscle regeneration have come from experimental studies on muscle grafts in small animal models. One such model is the transplantation of the extensor digitorum muscle of the mouse or rat into the contralateral site, or the relocation of this muscle onto the surface of the tibialis anterior muscle. These and other models, together with the important cellular mechanisms involved in the regeneration of skeletal muscle, are reviewed briefly in this article. RESULTS: Skeletal muscle cells regenerate rapidly in muscle grafts, arising from satellite cells in the surviving peripheral fibres of the graft within 2 days after grafting. The resultant myoblasts progress towards the necrotic graft centre and occupy the area by 5 days. Revascularization commences at 3 days after grafting, but reinnervation takes many weeks to complete. CONCLUSIONS: With the established knowledge on skeletal muscle regeneration, largely gained from experimental studies of muscle grafts; an understanding of these mechanisms should now be fundamental knowledge for today's practising surgeons.
Asunto(s)
Músculo Esquelético/fisiología , Músculo Esquelético/trasplante , Regeneración/fisiología , Animales , Ratones , Músculo Esquelético/irrigación sanguínea , Músculo Esquelético/inervación , Ratas , Trasplante HeterotópicoRESUMEN
The difference in the timing of the regeneration process of skeletal muscle between SJL/J and BALB/c mice was investigated using grafts of whole skeletal muscle (both autografts and allografts). Histological, autoradiographic and immunohistochemical techniques were used in the investigation. Infiltration of leucocytes into autografts, numbers of desmin-positive myogenic cells and myotube formation were all more advanced in the SJL/J compared with BALB/c mice. Furthermore, autoradiographic evidence showed that myoblasts in the SJL/J autografts were synthesising DNA 12 h earlier than myoblasts in BALB/c autografts. In allografts, where SJL/J host mice received BALB/c grafts, and vice versa, leucocyte infiltration and myotube formation occurred earlier in the BALB/c muscles grafted into SJL/J hosts, than in the reverse situation with BALB/c hosts. The results show that, at least for whole muscle grafts, it is the host environment which determines the speed and outcome of the regenerative process.
Asunto(s)
Músculo Esquelético/fisiología , Músculo Esquelético/trasplante , Regeneración , Animales , Autorradiografía , ADN/biosíntesis , Desmina/análisis , Inmunohistoquímica , Leucocitos/fisiología , Masculino , Ratones , Ratones Endogámicos BALB C , Ratones Endogámicos , Músculo Esquelético/metabolismo , Especificidad de la Especie , Factores de Tiempo , Trasplante Autólogo , Trasplante HomólogoRESUMEN
Variation in the regenerative capacity of damaged skeletal muscle between different strains of mice has been well documented but no precise quantitative method has been established to measure directly the phenotypic influences on muscle regeneration. We have developed such a method which allows clear distinction between the regenerative responses in Quackenbush and BALB/c mice. To quantitate regeneration, crushed tibialis anterior muscles taken from Quackenbush, BALB/c and F2 offspring 10 d postinjury were analysed morphometrically by light microscopy. Myotubes in the intermediate crush zone of transverse muscle sections were abundant in Quackenbush but sparse in BALB/c mice. In F2 offspring, regeneration responses reflected those of the parental strains, with no intermediate phenotypes. Statistical analyses indicated a high level of precision and accuracy in the determination of significant differences between regeneration in the different strains and in the F2 offspring. The data presented indicate that this method of quantification of skeletal muscle regeneration may be used for studies on the assessment of the genetic basis for phenotypic variation.
Asunto(s)
Músculo Esquelético/fisiología , Regeneración/fisiología , Animales , Genotipo , Masculino , Métodos , Ratones , Ratones Endogámicos BALB C , Ratones Endogámicos , Músculo Esquelético/patología , Fenotipo , Especificidad de la EspecieRESUMEN
The long-term administration of the beta 2-agonist isoprenaline (at 2 dosages: 100 micrograms/kg or 300 micrograms/kg) was investigated for its effect on the revascularisation and regeneration of skeletal muscle transplants in mice, and also to determine if there was a dose dependent effect. Morphometric, histological and autoradiographic techniques were employed for the investigation. It was found that the accelerated revascularisation observed in a previous short-term study on the effects of isoprenaline did not occur in longer-term usage (as evidenced by autoradiographic and histological results). However, in the present study, the numbers of presumptive satellite cells (identified by autoradiographic examination) were increased at both dosages in the isoprenaline-treated mice. Significant differences were seen in a number of the parameters examined morphometrically, both between the 2 groups which received isoprenaline, and between these groups and the controls (particularly in the volume of regenerated muscle). Dose dependency was therefore evident between the 2 isoprenaline doses and it was concluded that the increased volume of regenerated muscle seen in these transplants was due to the hypertrophic effect of isoprenaline.
Asunto(s)
Agonistas Adrenérgicos beta/administración & dosificación , Isoproterenol/administración & dosificación , Músculo Esquelético/fisiología , Músculo Esquelético/trasplante , Regeneración , Animales , Autorradiografía , Relación Dosis-Respuesta a Droga , Humanos , Lactante , Masculino , Ratones , Ratones Endogámicos BALB C , Músculo Esquelético/irrigación sanguínea , Factores de TiempoRESUMEN
The effects, in vivo, of the exogenous administration of bFGF on myogenesis of regenerating skeletal muscle was assessed either morphometrically or autoradiographically in three separate models of muscle injury in mice: crush-injured, denervated, and dystrophic (mdx) muscles. The bFGF was administered at various doses and different time schedules, sometimes in combination with heparin, into injured tibialis anterior muscles of mice. Delivery of the bFGF was either by direct intramuscular injection or by the sustained release from 888polymers (Hydron or Elvax) implanted into the muscles. The bioactivity of bFGF was confirmed in vitro by measuring its ability to stimulate the proliferation of BALB/c-3T3 fibroblasts and muscle precursor cell lines. The ability of bFGF to stimulate angiogenesis in vivo was confirmed by the implantation of controlled-release polymers containing bFGF into the normally avascular cornea of rats. No measurable effect of bFGF was seen in any of the models of skeletal muscle injury under these experimental conditions, indicating that the availability of biologically active bFGF is not a limiting factor in the regeneration of skeletal muscle following injury.
Asunto(s)
Factor 2 de Crecimiento de Fibroblastos/farmacología , Músculo Esquelético/efectos de los fármacos , Músculo Esquelético/lesiones , Regeneración/efectos de los fármacos , Animales , División Celular/efectos de los fármacos , Núcleo Celular/metabolismo , Células Cultivadas , Córnea/efectos de los fármacos , Desnervación , Portadores de Fármacos/química , Portadores de Fármacos/metabolismo , Factor 2 de Crecimiento de Fibroblastos/administración & dosificación , Factor 2 de Crecimiento de Fibroblastos/análisis , Heparina/metabolismo , Ratones , Ratones Endogámicos BALB C , Ratones Endogámicos mdx , Músculo Esquelético/citología , Músculo Esquelético/metabolismo , Distrofias Musculares/genética , Polivinilos/metabolismo , Ratas , Sucralfato/metabolismoRESUMEN
Endothelial injuries were induced in the left common iliac arteries (1 mm in diameter) of rats, by the placement of 1 mm Scovell-Lewis microvascular clamps for 5 minutes, to create a lesion in which to quantitate the rate and degree of cellular regeneration. The left (clamp-injured) and right (control) iliac arteries from the 15 rats used in this study were viewed with the electron microscope at 2, 7, and 14 days after clamping, and the clamp sites were analysed morphometrically. At 2 days there was only minimal denudation of the endothelium; most cells were disoriented and showed some signs of traumatic injury. By 7 days there was a completely continuous endothelial lining, but there was also evidence of increased cytoplasmic activity in these cells, as well as a statistically significant simplification in their intercellular junctional morphology. These changes persisted at 14 days after injury, but they were less pronounced. Smooth muscle cells in the media were relatively unaffected by the trauma in the first 2 days after clamping. However, they exhibited a change of phenotype from contractile to synthetic by 7 days after injury. By 14 days most smooth muscle cells had reverted back to the contractile phenotype, with little evidence of residual damage. These studies reveal that the reconstitution and regeneration of the endothelium is very rapid following clamp injury, but that significant residual ultrastructural changes in the interendothelial junctions persist for at least 14 days after injury. These findings indicate that there is potential for subsequent pathological changes in sites of vascular clamp injury.
Asunto(s)
Arterias/lesiones , Microcirugia/instrumentación , Instrumentos Quirúrgicos , Cicatrización de Heridas/fisiología , Animales , Arterias/patología , Permeabilidad Capilar/fisiología , Citoplasma/ultraestructura , Endotelio Vascular/lesiones , Endotelio Vascular/patología , Femenino , Arteria Ilíaca/lesiones , Arteria Ilíaca/patología , Procesamiento de Imagen Asistido por Computador , Uniones Intercelulares/ultraestructura , Microscopía Electrónica , Músculo Liso Vascular/lesiones , Músculo Liso Vascular/patología , Ratas , Ratas Wistar , Regeneración/fisiologíaRESUMEN
The angiogenic agent erucamide (cis-13-docosenamide), incorporated into a polymeric biomaterial (Elvax 40P, a copolymer of ethylene and vinyl acetate), was used to determine whether angiogenesis can be increased in the regenerating skeletal muscle, and whether the enhanced revascularization improves the new muscle formation. The angiogenic nature of this lipid was confirmed in a rat cornea-micropocket assay, prior to insertion of small strips of the polymer containing either 3 micrograms, 300 micrograms erucamide or only polymer as a control into the mid-region of crush-injured tibialis anterior (TA) muscles of forty-five adult male BALB/c mice. All TA muscles were sampled ten days after injury and analyzed morphometrically. Statistical analyses of the mean blood vessel area density in lesions from twelve perfused TA muscles (three from each of the erucamide-treated or control group), revealed a dose-dependent angiogenic effect of erucamide: a dosage of 3 micrograms increased mean blood vessel area density to 5.1% compared to 2.0% in controls, due to numerous large caliber, thin-walled vessels, whereas the mean vessel area density in both the 30-micrograms (3.5%) and 300-micrograms (1.5%) doses were similar to controls. However, at all three doses tested, erucamide did not significantly alter the degree of new muscle formation, connective tissue deposition, or removal of necrotic debris.
Asunto(s)
Vasos Sanguíneos/efectos de los fármacos , Córnea/efectos de los fármacos , Ácidos Erucicos/farmacología , Músculo Esquelético/efectos de los fármacos , Polímeros/farmacología , Animales , Relación Dosis-Respuesta a Droga , Masculino , Ratones , Ratones Endogámicos BALB C , Músculo Esquelético/ultraestructura , Ratas , Ratas WistarRESUMEN
The patterns of skeletal muscle precursor cell replication after crush injury were compared by the use of autoradiographic techniques, in young (4-week-old) and old (39-week-old) BALBc and SJL/J mice. Similar comparisons were made between cut and crush lesions in old BALBc muscle. Muscle precursor cell replication commenced at 18-24 h after injury in both young and old muscles from both strains of mice. In young BALBc muscle the peak of myogenic activity at 60 h was 36 h earlier than in old mice. SJL/J muscle responded more rapidly than did BALBc: in young SJL/J the peak myogenic activity was at 46 h (14 h earlier than in young BALBc muscle), and in old SJL/J muscle the peak activity at 72 h was 24 h earlier than in old BALBc muscle. In all mice (both young and old) myogenic cell replication was substantially reduced by 120 h after injury. A comparison of the timing of muscle precursor cell replication in cut and crush lesions in old BALBc mice revealed a more rapid response in the cut lesion; this difference between the lesions is comparable with data from identical lesions in 6-8-week-old BALBc mice (McGeachie and Grounds 1987). However, the peak of myogenic replication in the older mice in the present study was some 26-36 h later than in the younger 6-8-week-old mice. These experiments show that, whilst muscle precursor cell replication commences at approximately the same time (about 24 h) after injury in young and old mice, the peak level of activity is delayed by some 24-36 h in old mice. In addition, the SJL/J mouse strain responds more rapidly and prolifically to muscle injury than does the BALBc strain.
Asunto(s)
Envejecimiento/fisiología , Ratones Endogámicos/fisiología , Músculos/fisiología , Regeneración/fisiología , Animales , División Celular , Femenino , Miembro Posterior/lesiones , Ratones , Ratones Endogámicos BALB C , Músculos/citología , Músculos/lesiones , Especificidad de la Especie , Células Madre/fisiología , Factores de Tiempo , Heridas no Penetrantes/fisiopatología , Heridas Punzantes/fisiopatologíaRESUMEN
Staining for basic fibroblast growth factor (bFGF), a potent mitogen, was examined in muscle recovering from a crush injury and compared between two mouse strains with distinctly different capacities for muscle regeneration to determine if bFGF staining and the steps and outcome of repair were related. Immunofluorescence studies on intact and crushed tibialis anterior muscle were carried out at 0, 1, 3, 6, and 12 h postcrush in SJL/J mice, and at 1, 2, 3, 5, 7, and 11 days after injury in both SJL/J and BALB/c mice (n = 2-4). Disrupted fibers showed increased sarcoplasmic staining for bFGF as little as 3-6 h after injury prior to infiltration with intensely fluorescent mononuclear cells (at 12-24 h). Fiber bFGF was maintained in SJL/J muscles for 2 days, but was lower in most damaged fibers of BALB/c muscles at the same time. Surviving stumps of crushed fibers, once sealed, exhibited sarcoplasmic extensions, some of which stained intensely for bFGF. These processes appeared to connect adjacent fiber stumps, and many were noted in association with aligned mononuclear cells (presumptive myoblasts) at the site of new myotube formation. In representative sections there were more bFGF-positive mononuclear cells present in SJL/J than BALB/c muscles. Intense bFGF localization marked newly regenerating myotubes in both SJL/J and BALB/c muscles, and such myotubes were more frequent and larger in SJL/J muscles. More bFGF was present in regenerating muscles of SJL/J compared with BALB/c mice (with respect to damaged myofibers, mononuclear cells, and myotubes) and this correlates with the superior new muscle formation seen in SJL/J mice. These studies support the idea of a positive relation between bFGF in damaged fibers, the bFGF-positive mononuclear cells, and the speed and success of muscle regeneration.
Asunto(s)
Factor 2 de Crecimiento de Fibroblastos/biosíntesis , Fibras Musculares Esqueléticas/fisiología , Músculo Esquelético/metabolismo , Regeneración , Animales , Cinética , Ratones , Ratones Endogámicos BALB C , Ratones Endogámicos , Músculo Esquelético/lesiones , Músculo Esquelético/fisiologíaRESUMEN
The effect of the beta 2-agonist isoprenaline on the revascularisation and regeneration of skeletal muscle transplants was studied using histological, morphometric and autoradiographic methods. Revascularisation of the transplants was accelerated in the isoprenaline-treated mice as evidenced by histological and autoradiographic results. The numbers of presumptive satellite cells were increased in the isoprenaline-treated mice. Significant increases in muscle cytoplasmic volume, endothelial cell volume, capillary and myofibre numbers, and the numbers of myofibres with peripheral nuclei were also found in transplants removed from the isoprenaline-treated mice (compared with controls). Reductions in myonuclear volume, 'other tissue' volume and numbers of myofibres with no nucleus sectioned were also found in transplants from isoprenaline-treated mice. Although there was an increased volume of regenerated muscle in the transplants, it cannot be concluded that this was because of the earlier transplant revascularisation, as beta 2-agonists have been shown to have a hypertrophic effect on skeletal muscle.
Asunto(s)
Isoproterenol/farmacología , Músculos/trasplante , Regeneración/efectos de los fármacos , Animales , Cobayas , Masculino , Ratones , Ratones Endogámicos BALB C , Músculos/anatomía & histología , Músculos/irrigación sanguíneaRESUMEN
Cell replication in muscle was measured by tritiated thymidine (3H-TdR) incorporation and autoradiography, in mdx mice from 2-44 weeks of age. Pre-mitotic labelling (within 1 h of 3H-TdR injection) was determined in 16 mice aged from 15 to 300 days. In 30 further mdx mice, one leg was irradiated 1 h after 3H-TdR injection to block DNA synthesis. Post-mitotic labelling was measured in both legs 10-15 days later. Between 20 and 60 days of age a very high proportion (up to 2%) of muscle (satellite cell) nuclei were replicating pre-mitotically; from 80-300 days cell replication was detectable but at much lower levels. Centrally placed nuclei within muscle fibres appeared at 24 days, increased rapidly to 50% by 50-100 days, declining thereafter to 25% at 300 days. In post-mitotic samples, labelled myotubes and labelled peripheral muscle nuclei (satellite cell nuclei and myonuclei) appeared at 28 days and were present in the mdx muscles through to 310 days, indicating continued cell replication and muscle regeneration. Myogenic cell replication was both retarded and inhibited by irradiation. These data demonstrate that muscle cell replication in mdx mice commences at about 3 weeks of age, is maximal at 4-8 weeks, but continues at lower levels until at least 44 weeks.
Asunto(s)
Envejecimiento/patología , Músculos/patología , Distrofia Muscular Animal/patología , Animales , Autorradiografía , División Celular/fisiología , Núcleo Celular/ultraestructura , ADN/biosíntesis , Ratones , Ratones Mutantes Neurológicos , Mitosis/fisiología , Distrofia Muscular Animal/genética , Timidina/metabolismoRESUMEN
End-to-end autogenous vein-to-artery grafts in rats have been used extensively as a model for neointimal thickening (hyperplasia), which develops over the first 6 weeks after grafting. This study employed computerised morphometric techniques to analyse 16 grafts, in order to quantitate precisely how the neointima develops. Two important features were described that have not been identified previously, due to the extensive variation in neo-intimal thickness inherent in vein grafts. Firstly, the proximal region of the graft was significantly thicker than the distal region, up until 6 months after grafting. The smooth muscle cells in the graft may have developed more rapidly in the proximal region, due to the altered haemodynamics within the graft. Secondly, within the central region of the graft the characteristic focal nature of neo-intimal hyperplasia was evident throughout the period of the study, but by 6 months the neo-intima tended to be distributed more evenly. By 6 months remodelling of smooth muscle throughout the graft neo-intima had occurred, and the neo-intima had matured to a thickness equivalent to that of the intima plus media of the adjacent iliac artery.