RESUMO
Progression of Alzheimer's disease (AD) is associated with chronic inflammation and microvascular alterations, which can induce impairment of brain perfusion because of vascular pathology and local acidosis. Acidosis can promote amyloidogenesis, which could further contribute to neurodegenerative changes. Nevertheless, there is also evidence that acidosis has neuroprotective effects in hypoxia models. Here we studied the effect of moderate acidosis on beta-amyloid (Abeta)-mediated neurotoxicity. We evaluated morphological changes, cell death, nitrite production and reductive metabolism of hippocampal cultures from Sprague-Dawley rats exposed to Abeta under physiological (pH 7.4) or moderate acidosis (pH 7.15-7.05). In addition, because transforming growth factor beta (TGFbeta) 1 is neuroprotective and is induced by several pathophysiological conditions, we assessed its presence at the different pHs. The exposure of hippocampal cells to Abeta induced a conspicuous reduction of neurites' arborization, as well as increased neuronal death and nitric oxide production. However, Abeta neurotoxicity was significantly attenuated when hippocampal cultures were kept at pH 7.15-7.05, showing a 68% reduction on lactate dehydrogenase release compared with cultures exposed to Abeta at pH 7.4 (P<0.01). Similarly, 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide reduction increased 3.5-fold (P<0.05), and Abeta-induced nitrite production was reduced by 65% when exposed to moderate acidosis compared with basal pH media (P<0.05). At the same time, moderate acidosis decreased intracellular TGFbeta1 precursor (latency associated protein-TGFbeta1) and increased up to fourfold TGFbeta1 bioactivity, detecting a 43% increase in the active TGFbeta levels in cultures exposed to Abeta and moderate acidosis. Inhibition of TGFbeta signaling abolished the neuroprotective effect of moderate acidosis. Our results show that moderate acidosis protected hippocampal cells from Abeta-mediated neurotoxicity through the increased activation and signaling potentiation of TGFbeta.
Assuntos
Acidose/metabolismo , Peptídeos beta-Amiloides/toxicidade , Hipocampo/citologia , Neurônios/efeitos dos fármacos , Fragmentos de Peptídeos/toxicidade , Fator de Crescimento Transformador beta/metabolismo , Peptídeos beta-Amiloides/metabolismo , Análise de Variância , Animais , Azidas , Benzamidas/farmacologia , Tamanho Celular/efeitos dos fármacos , Dioxóis/farmacologia , Embrião de Mamíferos , Feminino , Concentração de Íons de Hidrogênio , L-Lactato Desidrogenase/metabolismo , Óxido Nítrico/metabolismo , Gravidez , Ratos , Ratos Sprague-Dawley , Transdução de Sinais/efeitos dos fármacos , Transdução de Sinais/fisiologia , Sais de Tetrazólio , Tiazóis/antagonistas & inibidores , Fator de Crescimento Transformador beta/antagonistas & inibidores , Tubulina (Proteína)/metabolismoRESUMO
Pro-inflammatory molecules induce glial activation and the release of potentially detrimental factors capable of generating oxidative damage, such as nitric oxide (NO) and superoxide anion (O2.-). Activated glial cells (astrocytes and microglia) are associated to the inflammatory process in neurodegenerative diseases. A strong inflammatory response could escape endogenous control becoming toxic to neurons and contributing to the course of the disease. We evaluated in a hippocampal cells-microglia co-culture model, if the pro-inflammatory condition induced by lipopolysaccharide + interferon-gamma (LPS+IFN-gamma) promoted damage directly or if damage was secondary to glial activation. In addition, we explored the effect of the anti-inflammatory cytokine transforming growth factor-beta1 (TGF-beta1), and pro-inflammatory cytokines, interleukin-1beta (IL-1beta) and tumor necrosis factor-alpha (TNF-alpha) on the regulation of the inflammatory response of microglia. We found that LPS+IFN-gamma-induced damage on hippocampal cultures was dependent on the presence of microglial cells. In hippocampal cultures exposed to LPS+IFN-gamma, TGF-beta1 was induced whereas in microglial cell cultures LPS+IFN-gamma induced the secretion of IL-1beta. TGF-beta1 and IL-1beta but not TNF-alpha decreased the NO production by 70-90%. PD98059, an inhibitor of MAP kinase (MEK), reduced the IFN-gamma-induced NO production by 40%. TGF-beta and IL-1beta reduced the IFN-gamma induced phosphorylation of ERK1,2 by 60% and 40%, respectively. However, the effect of IL-1beta was observed at 30 min and that of TGF-beta1 only after 24 h of exposure. We propose that acting with different timing, TGF-beta1 and IL-1beta can modulate the extracellular signal-regulated kinase ERK1,2, as a common element for different transduction pathways, regulating the amplitude and duration of glial activation in response to LPS+IFN-gamma. Cross-talk among brain cells may be key for the understanding of inflammatory mechanisms involved in pathogenesis of neurodegenerative diseases.