RESUMEN
The neuronal olfactory epithelium undergoes permanent renewal because of environmental aggression. This renewal is partly regulated by factors modulating the level of neuronal apoptosis. Among them, we had previously characterized endothelin as neuroprotective. In this study, we explored the effect of cell survival factor deprivation in the olfactory epithelium by intranasal delivery of endothelin receptors antagonists to rat pups. This treatment induced an overall increase of apoptosis in the olfactory epithelium. The responses to odorants recorded by electroolfactogram were decreased in treated animal, a result consistent with a loss of olfactory sensory neurons (OSNs). However, the treated animal performed better in an olfactory orientation test based on maternal odor compared to non-treated littermates. This improved performance could be due to activity-dependent neuronal survival of OSNs in the context of increased apoptosis level. In order to demonstrate it, we odorized pups with octanal, a known ligand for the rI7 olfactory receptor (Olr226). We quantified the number of OSN expressing rI7 by RT-qPCR and whole mount in situ hybridization. While this number was reduced by the survival factor removal treatment, this reduction was abolished by the presence of its ligand. This improved survival was optimal for low concentration of odorant and was specific for rI7-expressing OSNs. Meanwhile, the number of rI7-expressing OSNs was not affected by the odorization in non-treated littermates; showing that the activity-dependant survival of OSNs did not affect the OSN population during the 10 days of odorization in control conditions. Overall, our study shows that when apoptosis is promoted in the olfactory mucosa, the activity-dependent neuronal plasticity allows faster tuning of the olfactory sensory neuron population toward detection of environmental odorants.
RESUMEN
Apoptosis Inducing Factor (AIF) is a highly conserved, ubiquitous flavoprotein localized in the mitochondrial intermembrane space. In vivo, AIF provides protection against neuronal and cardiomyocyte apoptosis induced by oxidative stress. Conversely in vitro, AIF has been demonstrated to have a pro-apoptotic role upon induction of the mitochondrial death pathway, once AIF translocates to the nucleus where it facilitates chromatin condensation and large scale DNA fragmentation. Given that the aif hypomorphic harlequin (Hq) mutant mouse model displays severe sarcopenia, we examined skeletal muscle from the aif hypomorphic mice in more detail. Adult AIF-deficient skeletal myofibers display oxidative stress and a severe form of atrophy, associated with a loss of myonuclei and a fast to slow fiber type switch, both in "slow" muscles such as soleus, as well as in "fast" muscles such as extensor digitorum longus, most likely resulting from an increase of MEF2 activity. This fiber type switch was conserved in regenerated soleus and EDL muscles of Hq mice subjected to cardiotoxin injection. In addition, muscle regeneration in soleus and EDL muscles of Hq mice was severely delayed. Freshly cultured myofibers, soleus and EDL muscle sections from Hq mice displayed a decreased satellite cell pool, which could be rescued by pretreating aif hypomorphic mice with the manganese-salen free radical scavenger EUK-8. Satellite cell activation seems to be abnormally long in Hq primary culture compared to controls. However, AIF deficiency did not affect myoblast cell proliferation and differentiation. Thus, AIF protects skeletal muscles against oxidative stress-induced damage probably by protecting satellite cells against oxidative stress and maintaining skeletal muscle stem cell number and activation.
Asunto(s)
Factor Inductor de la Apoptosis/fisiología , Apoptosis , Fibras Musculares Esqueléticas/fisiología , Estrés Oxidativo , Animales , Antioxidantes/farmacología , Enfermedades del Sistema Nervioso Autónomo , Western Blotting , Recuento de Células , Diferenciación Celular , Fragmentación del ADN , Etilenodiaminas/farmacología , Técnica del Anticuerpo Fluorescente , Rubor , Hipohidrosis , Técnicas para Inmunoenzimas , Masculino , Ratones , Ratones Endogámicos C57BL , Ratones Endogámicos CBA , Ratones Mutantes , Mitocondrias/efectos de los fármacos , Fibras Musculares Esqueléticas/citología , Fibras Musculares Esqueléticas/efectos de los fármacos , Atrofia Muscular/etiología , Atrofia Muscular/metabolismo , Atrofia Muscular/patología , Compuestos Organometálicos/farmacología , Fenotipo , ARN Mensajero/genética , Especies Reactivas de Oxígeno/metabolismo , Reacción en Cadena en Tiempo Real de la PolimerasaRESUMEN
The objective of this report was to analyse a potential role for FGF6 in muscle resistance to mechanical stress. Normal or regenerating muscles of FGF6 (-/-) mice versus wild-type mice were submitted to different protocols of damaging eccentric contractions (eccentric electrostimulation and intermittent downhill exercise). Then muscular structural properties were analysed by histological and immunochemistry techniques to evaluate the post-injury muscle recovery; their muscle contractile parameters (maximal tetanic force, kinetics properties and fatigue resistance) were assessed. The absence of FGF6 causes (1) a fast-to-slow myofibre type switch in adult control and regenerating Tibialis anterior (TA) muscle; (2) muscle weakness in regenerating muscles in animals submitted to eccentric exercise protocols due to aberrant extensive necrotic zones. These observations point out a crucial and unexpected role for FGF6 in muscle integrity and muscle protection against mechanical stress.
Asunto(s)
Factor 6 de Crecimiento de Fibroblastos/fisiología , Contracción Muscular/genética , Fuerza Muscular/genética , Estimulación Física , Estrés Mecánico , Animales , Factor 6 de Crecimiento de Fibroblastos/genética , Predisposición Genética a la Enfermedad , Ratones , Ratones Endogámicos C57BL , Ratones Noqueados , Contracción Muscular/fisiología , Fibras Musculares Esqueléticas/metabolismo , Fibras Musculares Esqueléticas/fisiología , Fuerza Muscular/fisiología , Músculo Esquelético/metabolismo , Músculo Esquelético/fisiología , Enfermedades Musculares/genética , Regeneración/genética , Regeneración/fisiologíaRESUMEN
Sprouty (Spry) proteins were identified as negative regulators of fibroblast growth factor (FGF) signaling in vertebrates and invertebrates. Given the importance of the FGFs in myogenesis, we performed cardiotoxin injury-induced regeneration experiments on soleus muscles of both, adult control and FGF6 ( - / - ) mutant mice and analyzed the accumulation of Spry (1, 2 and 4) transcripts using semi-quantitative and real-time RT-PCR assays and in situ hybridization. We also analyzed the effects of muscle denervation on the accumulation of Spry transcripts. The three Spry genes begin to be expressed as early as the first stages of muscle regeneration and are characterized by distinct expression patterns. Moreover, Spry gene expression was highly and differentially up-regulated, precociously by the lack of FGF6, and belatedly by muscle denervation strongly suggesting that the transient rise of Spry mRNA accumulation was associated to muscle differentiation. Rescue experiments supported the idea of a specific relationship between FGF6 and Spry 2, both being known for their particular involvement in myogenesis.
Asunto(s)
Factor 6 de Crecimiento de Fibroblastos/metabolismo , Proteínas de la Membrana/biosíntesis , Músculo Esquelético/fisiología , Proteínas Proto-Oncogénicas/metabolismo , Regeneración , Proteínas Adaptadoras Transductoras de Señales , Animales , Factor 6 de Crecimiento de Fibroblastos/genética , Regulación de la Expresión Génica , Péptidos y Proteínas de Señalización Intracelular , Ratones , Ratones Endogámicos C57BL , Ratones Mutantes , Desnervación Muscular , Músculo Esquelético/inervación , Isoformas de Proteínas/biosíntesis , Proteínas Serina-Treonina Quinasas , Proteínas Proto-Oncogénicas/genética , ARN Mensajero/metabolismoRESUMEN
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 analyses of Fgf6 (-/-) mutant mice gave contradictory results and the role of FGF6 during myogenesis remained largely unclear. Recent reports support the concept that FGF6 has a dual function in muscle regeneration, stimulating myoblast proliferation/migration and muscle differentiation/hypertrophy in a dose-dependent manner. The alternative use of distinct signaling pathways recruiting either FGFR1 or FGFR4 might explain the dual role of FGF6 in myogenesis. A role for FGF6 in the maintenance of a reserve pool of progenitor cells in the skeletal muscle has been also strongly suggested. The aim of this review is to summarize our knowledge on the involvement of FGF6 in myogenesis.
Asunto(s)
Factor 6 de Crecimiento de Fibroblastos/fisiología , Desarrollo de Músculos/fisiología , Proteínas Proto-Oncogénicas/fisiología , Animales , Diferenciación Celular , Factor 6 de Crecimiento de Fibroblastos/deficiencia , Factor 6 de Crecimiento de Fibroblastos/genética , Expresión Génica , Hipertrofia , Ratones , Ratones Noqueados , Desarrollo de Músculos/genética , Músculos/metabolismo , Fenotipo , Proteínas Proto-Oncogénicas/deficiencia , Proteínas Proto-Oncogénicas/genética , Receptores de Factores de Crecimiento de Fibroblastos/fisiología , Regeneración , Transducción de Señal , Células Madre/metabolismoRESUMEN
Important functions in myogenesis have been proposed for FGF6, a member of the fibroblast growth factor family accumulating almost exclusively in the myogenic lineage, but its precise role in vivo remains mostly unclear. Here, using FGF6 (-/-) mice and rescue experiments by injection of recombinant FGF6, we dissected the functional role of FGF6 during in vivo myogenesis. We found that the appearance of myotubes was accelerated during regeneration of the soleus of FGF6 (-/-) mice versus wild type mice. This accelerated differentiation was correlated with increased expression of differentiation markers such as CdkIs and calcineurin, as well as structural markers such as MHCI and slow TnI. We showed that an elevated transcript level for calcineurin Aalpha subunit correlated with a positive regulation of calcineurin A activity in regenerating soleus of the FGF6 (-/-) mice. Cyclin D1 and calcineurin were up- and down-regulated, respectively in a dose-dependent manner upon injection of rhFGF6 in regenerating soleus of the mutant mice. We showed an increase of the number of slow oxidative (type I) myofibers, whereas fast oxidative (type IIa) myofibers were decreased in number in regenerating soleus of FGF6 (-/-) mice versus that of wild type mice. In adult soleus, the number of type I myofibers was also higher in FGF6 (-/-) mice than in wild type mice. Taken together these results evidenced a specific phenotype for soleus of the FGF6 (-/-) mice and led us to propose a model accounting for a specific dose-dependent effect of FGF6 in muscle regeneration. At high doses, FGF6 stimulates the proliferation of the myogenic stem cells, whereas at lower doses it regulates both muscle differentiation and muscle phenotype via a calcineurin-signaling pathway.