RESUMO
Müller cells constitute the main glial cell type in the retina where it interacts with virtually all cells displaying relevant functions to retinal physiology. Under appropriate stimuli, Müller cells may undergo dedifferentiation, being able to generate other neural cell types. Here, we show that purified mouse Müller cells in culture express a group of proteins related to the dopaminergic phenotype, including the nuclear receptor-related 1 protein, required for dopaminergic differentiation, as well the enzyme tyrosine hydroxylase. These dopaminergic components are active, since Müller cells are able to synthesize and release dopamine to the extracellular medium. Moreover, Müller-derived tyrosine hydroxylase can be regulated, increasing its activity because of phosphorylation of serine residues in response to agents that increase intracellular cAMP levels. These observations were extended to glial cells obtained from adult monkey retinas with essentially the same results. To address the potential use of dopaminergic Müller cells as a source of dopamine in cell therapy procedures, we used a mouse model of Parkinson's disease, in which mouse Müller cells with the dopaminergic phenotype were transplanted into the striatum of hemi-parkinsonian mice generated by unilateral injection of 6-hydroxydopamine. These cells fully decreased the apomorphine-induced rotational behavior and restored motor functions in these animals, as measured by the rotarod and the forelimb-use asymmetry (cylinder) tests. The data indicate local restoration of dopaminergic signaling in hemi-parkinsonian mice confirmed by measurement of striatal dopamine after Müller cell grafting.
Assuntos
Neurônios Dopaminérgicos/transplante , Células Ependimogliais/transplante , Transtornos Parkinsonianos/patologia , Transtornos Parkinsonianos/terapia , Animais , Cebus , Diferenciação Celular/fisiologia , Células Cultivadas , Corpo Estriado/citologia , Corpo Estriado/fisiologia , Modelos Animais de Doenças , Dopamina/metabolismo , Neurônios Dopaminérgicos/citologia , Neurônios Dopaminérgicos/metabolismo , Células Ependimogliais/citologia , Células Ependimogliais/metabolismo , Feminino , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Transgênicos , Atividade Motora/fisiologia , Membro 2 do Grupo A da Subfamília 4 de Receptores Nucleares/metabolismo , Transtornos Parkinsonianos/metabolismo , Fosforilação/efeitos dos fármacos , Fosforilação/fisiologia , Recuperação de Função Fisiológica/fisiologia , Tirosina 3-Mono-Oxigenase/metabolismoRESUMO
Pituitary Adenylyl Cyclase-Activating Polypeptide (PACAP) is a neuroactive peptide present in the avian retina where it activates adenylyl cyclase (AC) since early in development via PACAP receptors. The synthesis of cAMP in response to PACAP is observed since embryonic day 8/9 (E8/9). After E12, signaling via PACAP receptors desensitizes, reaching very low levels in the mature tissue. We show here that chronic administration of PACAP in vitro desensitizes PACAP-induced cAMP accumulation, while the administration of the PACAP antagonist (PACAP 6-38) re-sensitizes PACAP receptor/cyclase system in vitro and in vivo. Moreover, a twofold increase in the number of tyrosine hydroxylase positive (THâº) cells is observed after in vivo injection of PACAP6-38. NURR1, a transcription factor associated with the differentiation of dopaminergic cells in the CNS, is present in the chick retina in all developmental stages studied. The presence of NURR1 positive cells in the mature tissue far exceeds the number of TH⺠cells, suggesting that these NURR1-positive cells might have the potential to express the dopaminergic phenotype. Our data show that if PACAP signaling is increased in mature retinas, plastic changes in dopaminergic phenotype can be achieved.