RESUMEN
Chronically axotomized motoneurons progressively fail to regenerate their axons. Since axonal regeneration is associated with the increased expression of tubulin, actin and GAP-43, we examined whether the regenerative failure is due to failure of chronically axotomized motoneurons to express and sustain the expression of these regeneration associated genes (RAGs). Chronically axotomized facial motoneurons were subjected to a second axotomy to mimic the clinical surgical procedure of refreshing the proximal nerve stump prior to nerve repair. Expression of α1-tubulin, actin and GAP-43 was analyzed in axotomized motoneurons using in situ hybridization followed by autoradiography and silver grain quantification. The expression of these RAGs by acutely axotomized motoneurons declined over several months. The chronically injured motoneurons responded to a refreshment axotomy with a re-increase in RAG expression. However, this response to a refreshment axotomy of chronically injured facial motoneurons was less than that seen in acutely axotomized facial motoneurons. These data demonstrate that the neuronal RAG expression can be induced by injury-related signals and does not require acute deprivation of target derived factors. The transient expression is consistent with a transient inflammatory response to the injury. We conclude that transient RAG expression in chronically axotomized motoneurons and the weak response of the chronically axotomized motoneurons to a refreshment axotomy provides a plausible explanation for the progressive decline in regenerative capacity of chronically axotomized motoneurons.
Asunto(s)
Enfermedades del Nervio Facial , Proteína GAP-43/metabolismo , Regulación de la Expresión Génica/fisiología , Neuronas Motoras/metabolismo , Regeneración Nerviosa/fisiología , Tubulina (Proteína)/metabolismo , Animales , Axotomía , Modelos Animales de Enfermedad , Enfermedades del Nervio Facial/metabolismo , Enfermedades del Nervio Facial/patología , Enfermedades del Nervio Facial/fisiopatología , Proteína GAP-43/genética , Masculino , Neuronas Motoras/patología , Proteínas de Neurofilamentos/genética , Proteínas de Neurofilamentos/metabolismo , ARN Mensajero/metabolismo , Ratas , Ratas Sprague-Dawley , Factores de Tiempo , Tubulina (Proteína)/genéticaRESUMEN
Axotomized motoneurons regenerate their axons regardless of whether axotomy occurs proximally or distally from their cell bodies. In contrast, regeneration of rubrospinal axons into peripheral nerve grafts has been detected after cervical but not after thoracic injury of the rubrospinal tract. By using in situ hybridization (ISH) combined with reliable retrograde tracing methods, we compared regeneration-associated gene expression after proximal and distal axotomy in spinal motoneurons versus rubrospinal neurons. Regardless of whether they were axotomized at the iliac crest (proximal) or popliteal fossa (distal), sciatic motoneurons underwent highly pronounced changes in ISH signals for Growth Associated Protein 43 (GAP-43) (10-20x increase) and neurofilament M (60-85% decrease). In contrast, tubulin ISH signals substantially increased only after proximal axotomy (3-5x increase). To compare these changes in gene expression with those of axotomized rubrospinal neurons, the rubrospinal tract was transected at the cervical (proximal) or thoracic (distal) levels of the spinal cord. Cervically axotomized rubrospinal neurons showed three- to fivefold increases in ISH signals for GAP-43 and tubulins (only transient) and a 75% decrease for neurofilament-M. In sharp contrast, thoracic axotomy had only marginal effects. After implantation of peripheral nerve transplants into the spinal cord injury sites, retrograde labeling with the sensitive retrograde tracer Fluoro-Gold identified regenerating rubrospinal neurons only after cervical axotomy. Furthermore, rubrospinal neurons specifically regenerating into the transplants were hypertrophied and expressed high levels of GAP-43 and tubulins. Taken together, these data support the concept that, even if central nervous system (CNS) axons are presented with a permissive/supportive environment, appropriate cell body responses to injury are a prerequisite for CNS axonal regeneration.
Asunto(s)
Células del Asta Anterior/metabolismo , Axotomía , Vías Eferentes/metabolismo , Proteína GAP-43/metabolismo , Neuronas Motoras/metabolismo , Proteínas de Neurofilamentos/metabolismo , Núcleo Rojo/metabolismo , Degeneración Retrógrada/metabolismo , Tubulina (Proteína)/metabolismo , Animales , Células del Asta Anterior/fisiopatología , Vías Eferentes/fisiopatología , Regulación de la Expresión Génica , Hibridación in Situ , Masculino , Neuronas Motoras/fisiología , Regeneración Nerviosa/fisiología , ARN Mensajero/análisis , Ratas , Ratas Sprague-Dawley , Degeneración Retrógrada/fisiopatología , Médula Espinal/fisiopatología , Médula Espinal/cirugíaAsunto(s)
Regeneración Nerviosa , Neuronas/citología , Tractos Piramidales/citología , Núcleo Rojo/citología , Traumatismos de la Médula Espinal/fisiopatología , Animales , Proteína GAP-43 , Regulación de la Expresión Génica , Glicoproteínas de Membrana/biosíntesis , Glicoproteínas de Membrana/genética , Factores de Crecimiento Nervioso/fisiología , Proteínas del Tejido Nervioso/biosíntesis , Proteínas del Tejido Nervioso/genética , Transferencia de Nervios , Ratas , Receptores de Factor de Crecimiento Nervioso/fisiología , Factores de Transcripción/fisiología , Tubulina (Proteína)/biosíntesis , Tubulina (Proteína)/genéticaRESUMEN
A population-based study of the biology of the thin-level melanoma according to site, Breslow's thickness, and Clark's level was undertaken. Two hundred fifteen patients were studied with a mean follow-up of 41 months. Overall, 23 patients (10.7%) had recurrences, 8 locally, 9 regionally, and 6 systemically, despite an adequate local excision. A multivariate analysis was done. In the patients with thin lesions (less than 1 mm), increasing level (p < 0.002) and head and neck site (p < 0.04) increased the risk of recurrence. Increasing thickness of melanoma up to 1 mm did not influence the risk. This study identifies a group of high-risk melanoma patients for whom adjuvant therapy to decrease recurrences should be studied.