RESUMO
Nervous tissue is characterized by a tight structural association between glial cells and neurons. It is well known that glial cells support neuronal functions, but their role under pathologic conditions is less well understood. Here, we addressed this question in vivo using an experimental model of retinal ischemia and transgenic mice for glia-specific inhibition of soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE)-dependent exocytosis. Transgene expression reduced glutamate, but not ATP release from single Müller cells, impaired glial volume regulation under normal conditions and reduced neuronal dysfunction and death in the inner retina during the early stages of ischemia. Our study reveals that the SNARE-dependent exocytosis in glial cells contributes to neurotoxicity during ischemia in vivo and suggests glial exocytosis as a target for therapeutic approaches.
Assuntos
Exocitose/genética , Isquemia/complicações , Degeneração Neural/etiologia , Retina/patologia , Células Ganglionares da Retina/metabolismo , Proteínas SNARE/metabolismo , Animais , Proteínas de Ligação ao Cálcio/metabolismo , Modelos Animais de Doenças , Doxiciclina/uso terapêutico , Células Ependimogliais/metabolismo , Proteína Glial Fibrilar Ácida/genética , Proteína Glial Fibrilar Ácida/metabolismo , Ácido Glutâmico/metabolismo , Filamentos Intermediários/metabolismo , Isquemia/patologia , Luz , Camundongos , Camundongos Transgênicos , Proteínas dos Microfilamentos/metabolismo , Proteína Quinase C-alfa/metabolismo , Receptores Purinérgicos P2Y1/deficiência , Receptores Purinérgicos P2Y1/genética , Proteínas SNARE/genética , Fator A de Crescimento do Endotélio Vascular/metabolismoRESUMO
Glial cells in the diseased nervous system undergo a process known as reactive gliosis. Gliosis of retinal Müller glial cells is characterized by an upregulation of glial fibrillary acidic protein and frequently by a reduction of inward K(+) current amplitudes. Purinergic signaling is assumed to be involved in gliotic processes. As previously shown, lack of the nucleotide receptor P2Y1 leads to an altered regulation of K(+) currents in Müller cells of the ischemic retina. Here, we asked first whether this effect is mediated by the IP3 receptor subtype 2 (IP3R2) known as the major downstream signaling target of P2Y1 in Müller cells. The second question was whether lack of IP3R2 affects neuronal survival in the control and ischemic retina. Ischemia was induced in wild type and IP3R2-deficient (IP 3 R2 (-/-)) mice by transient elevation of the intraocular pressure. Immunostaining and TUNEL labelling were used to quantify neuronal cell loss. The downregulation of inward K(+) currents in Müller cells from ischemic IP 3 R2 (-/-) retinae was less strong than in wild type animals. The reduction of the number of cells in the ganglion cell layer and of calretinin- and calbindin-positive cells 7 days after ischemia was similar in wild type and IP 3 R2 (-/-) mice. However, IP3R2 deficiency led to an increased number of TUNEL-positive cells in the outer nuclear layer at 1 day and to an enhanced postischemic loss of photoreceptors 7 days after ischemia. This implies that IP3R2 is involved in some but not all aspects of signaling in Müller cells after an ischemic insult.