RESUMO
The P2X7 receptor/channel responds to extracellular ATP and is associated with neuronal death and neuroinflammation in spinal cord injury and amyotrophic lateral sclerosis. Whether activation of P2X7 directly causes motor neuron death is unknown. We found that cultured motor neurons isolated from embryonic rat spinal cord express P2X7 and underwent caspase-dependent apoptosis when exposed to exceptionally low concentrations of the P2X7 agonist 2'(3')-O-(4-Benzoylbenzoyl)-ATP. The P2X7 inhibitors BBG, oATP, and KN-62 prevented 2'(3')-O-(4-Benzoylbenzoyl)-ATP-induced motor neuron death. The endogenous P2X7 agonist ATP induced motor neuron death at low concentrations (1-100 µM). High concentrations of ATP (1 mM) paradoxically became protective due to degradation in the culture media to produce adenosine and activate adenosine receptors. P2X7-induced motor neuron death was dependent on neuronal nitric oxide synthase-mediated production of peroxynitrite, p38 activation, and autocrine FAS signaling. Taken together, our results indicate that motor neurons are highly sensitive to P2X7 activation, which triggers apoptosis by activation of the well-established peroxynitrite/FAS death pathway in motor neurons.
Assuntos
Apoptose/fisiologia , Neurônios Motores/metabolismo , Ácido Peroxinitroso/metabolismo , Receptores Purinérgicos P2X7/metabolismo , Transdução de Sinais/fisiologia , Receptor fas/metabolismo , Animais , Células Cultivadas , Imunofluorescência , Ratos , Ratos Sprague-Dawley , Reação em Cadeia da Polimerase Via Transcriptase ReversaRESUMO
Mitochondrial dysfunction is one of the pathogenic mechanisms that lead to neurodegeneration in Amyotrophic Lateral Sclerosis (ALS). Astrocytes expressing the ALS-linked SOD1(G93A) mutation display a decreased mitochondrial respiratory capacity associated to phenotypic changes that cause them to induce motor neuron death. Astrocyte-mediated toxicity can be prevented by mitochondria-targeted antioxidants, indicating a critical role of mitochondria in the neurotoxic phenotype. However, it is presently unknown whether drugs currently used to stimulate mitochondrial metabolism can also modulate ALS progression. Here, we tested the disease-modifying effect of dichloroacetate (DCA), an orphan drug that improves the functional status of mitochondria through the stimulation of the pyruvate dehydrogenase complex activity (PDH). Applied to astrocyte cultures isolated from rats expressing the SOD1(G93A) mutation, DCA reduced phosphorylation of PDH and improved mitochondrial coupling as expressed by the respiratory control ratio (RCR). Notably, DCA completely prevented the toxicity of SOD1(G93A) astrocytes to motor neurons in coculture conditions. Chronic administration of DCA (500 mg/L) in the drinking water of mice expressing the SOD1(G93A) mutation increased survival by 2 weeks compared to untreated mice. Systemic DCA also normalized the reduced RCR value measured in lumbar spinal cord tissue of diseased SOD1(G93A) mice. A remarkable effect of DCA was the improvement of grip strength performance at the end stage of the disease, which correlated with a recovery of the neuromuscular junction area in extensor digitorum longus muscles. Systemic DCA also decreased astrocyte reactivity and prevented motor neuron loss in SOD1(G93A) mice. Taken together, our results indicate that improvement of the mitochondrial redox status by DCA leads to a disease-modifying effect, further supporting the therapeutic potential of mitochondria-targeted drugs in ALS.
Assuntos
Esclerose Lateral Amiotrófica/metabolismo , Astrócitos/efeitos dos fármacos , Ácido Dicloroacético/farmacologia , Mitocôndrias/efeitos dos fármacos , Neurônios Motores/efeitos dos fármacos , Superóxido Dismutase/metabolismo , Esclerose Lateral Amiotrófica/tratamento farmacológico , Esclerose Lateral Amiotrófica/genética , Animais , Astrócitos/metabolismo , Morte Celular/efeitos dos fármacos , Sobrevivência Celular/efeitos dos fármacos , Células Cultivadas , Modelos Animais de Doenças , Feminino , Humanos , Masculino , Camundongos , Camundongos Transgênicos , Mitocôndrias/fisiologia , Oxirredução/efeitos dos fármacos , Fosforilação/efeitos dos fármacos , Complexo Piruvato Desidrogenase/metabolismo , Ratos , Superóxido Dismutase/genética , Superóxido Dismutase-1RESUMO
BACKGROUND: During pathology of the nervous system, increased extracellular ATP acts both as a cytotoxic factor and pro-inflammatory mediator through P2X(7) receptors. In animal models of amyotrophic lateral sclerosis (ALS), astrocytes expressing superoxide dismutase 1 (SOD1G93A) mutations display a neuroinflammatory phenotype and contribute to disease progression and motor neuron death. Here we studied the role of extracellular ATP acting through P2X(7) receptors as an initiator of a neurotoxic phenotype that leads to astrocyte-mediated motor neuron death in non-transgenic and SOD1G93A astrocytes. METHODS: We evaluated motor neuron survival after co-culture with SOD1G93A or non-transgenic astrocytes pretreated with agents known to modulate ATP release or P2X(7) receptor. We also characterized astrocyte proliferation and extracellular ATP degradation. RESULTS: Repeated stimulation by ATP or the P2X(7)-selective agonist BzATP caused astrocytes to become neurotoxic, inducing death of motor neurons. Involvement of P2X(7) receptor was further confirmed by Brilliant blue G inhibition of ATP and BzATP effects. In SOD1G93A astrocyte cultures, pharmacological inhibition of P2X(7) receptor or increased extracellular ATP degradation with the enzyme apyrase was sufficient to completely abolish their toxicity towards motor neurons. SOD1G93A astrocytes also displayed increased ATP-dependent proliferation and a basal increase in extracellular ATP degradation. CONCLUSIONS: Here we found that P2X(7) receptor activation in spinal cord astrocytes initiated a neurotoxic phenotype that leads to motor neuron death. Remarkably, the neurotoxic phenotype of SOD1G93A astrocytes depended upon basal activation the P2X(7) receptor. Thus, pharmacological inhibition of P2X(7) receptor might reduce neuroinflammation in ALS through astrocytes.
Assuntos
Trifosfato de Adenosina/metabolismo , Esclerose Lateral Amiotrófica , Astrócitos/metabolismo , Morte Celular/fisiologia , Neurônios Motores/fisiologia , Receptores Purinérgicos P2/metabolismo , Esclerose Lateral Amiotrófica/metabolismo , Esclerose Lateral Amiotrófica/patologia , Esclerose Lateral Amiotrófica/fisiopatologia , Animais , Astrócitos/citologia , Proliferação de Células , Sobrevivência Celular , Células Cultivadas , Técnicas de Cocultura , Humanos , Camundongos , Camundongos Transgênicos , Neurônios Motores/citologia , Mutação , Ratos , Receptores Purinérgicos P2/genética , Receptores Purinérgicos P2X7 , Transdução de Sinais/fisiologia , Superóxido Dismutase/genética , Superóxido Dismutase/metabolismo , Superóxido Dismutase-1RESUMO
Mitochondrial dysfunction and oxidative stress contribute to motor neuron degeneration in amyotrophic lateral sclerosis (ALS). Recent reports indicate that astrocytes expressing the mutations of superoxide dismutase-1 (SOD1) may contribute to motor neuron injury in ALS. Here, we provide evidence that mitochondrial dysfunction in SOD1(G93A) rat astrocytes causes astrocytes to induce apoptosis of motor neurons. Mitochondria from SOD1(G93A) rat astrocytes displayed a defective respiratory function, including decreased oxygen consumption, lack of ADP-dependent respiratory control, and decreased membrane potential. Protein 3-nitrotyrosine was detected immunochemically in mitochondrial proteins from SOD1(G93A) astrocytes, suggesting that mitochondrial defects were associated with nitroxidative damage. Furthermore, superoxide radical formation in mitochondria was increased in SOD1(G93A) astrocytes. Similar defects were found in mitochondria isolated from the spinal cord of SOD1(G93A) rats, and pretreatment of animals with the spin trap 5,5-dimethyl-1-pyrroline N-oxide restored mitochondrial function, forming adducts with mitochondrial proteins in vivo. As shown previously, SOD1(G93A) astrocytes induced death of motor neurons in cocultures, compared with nontransgenic ones. This behavior was recapitulated when nontransgenic astrocytes were treated with mitochondrial inhibitors. Remarkably, motor neuron loss was prevented by preincubation of SOD1(G93A) astrocytes with antioxidants and nitric oxide synthase inhibitors. In particular, low concentrations (approximately 10 nm) of two mitochondrial-targeted antioxidants, ubiquinone and carboxy-proxyl nitroxide, each covalently coupled to a triphenylphosphonium cation (Mito-Q and Mito-CP, respectively), prevented mitochondrial dysfunction, reduced superoxide production in SOD1(G93A) astrocytes, and restored motor neuron survival. Together, our results indicate that mitochondrial dysfunction in astrocytes critically influences motor neuron survival and support the potential pharmacological utility of mitochondrial-targeted antioxidants in ALS treatment.