Gastrodin attenuates microglia activation through renin-angiotensin system and Sirtuin3 pathway.

Microglia activation and its mediated production of proinflammatory mediators play important roles in different neurodegenerative diseases; hence, modulation of microglia activation has been considered a potential therapeutic strategy to ameliorate neurodegeneration. This study was aimed to determine whether Gastrodin, a common herbal agent known to possess neuroprotective property, can attenuate production of proinflammatory mediators in activated microglia through the renin-angiotensin system (RAS) and Sirtuin3 (SIRT3). Expression of various members of the RAS including ACE, AT1, AT2, and SIRT3 in activated microglia was assessed by immunofluorescence and Western blot in hypoxic-ischemia brain damage (HIBD) in postnatal rats, and in BV-2 microglia in vitro challenged with lipopolysaccharide (LPS) with or without Gastrodin treatment. Expression of NOX-2, a subunit of NADPH oxidase, and proinflammatory mediators including iNOS and TNF-α, was also evaluated. The present results showed that expression of ACE, AT1, NOX-2, iNOS and TNF-α was markedly increased in activated microglia in the corpus callosum of HIBD rats, and in LPS stimulated BV-2 microglia. Remarkably, the expression was markedly attenuated following Gastrodin treatment. Conversely, Gastrodin enhanced AT2 and SIRT3 protein expression. In BV-2 microglia treated with Azilsartan, a specific inhibitor of AT1 (AT1I group), NOX-2 expression was decreased whereas that of SIRT3 in LPS + AT1I and LPS + Gastrodin group was increased when compared with the controls. In LPS + AT1I + Gastrodin group, SIRT3 expression was further augmented. More importantly, Gastrodin effectively reduced caspase 3 protein expression level in the HIBD rats coupled with a significant decrease in caspase 3 positive cells. We conclude that Gastrodin can exert its protective effects against the hypoxic-ischemia brain damage in the present experimental HIBD model. It is suggested that this is mainly through suppression of expression of RAS (except for AT2 and SIRT3) and proinflammatory mediators e.g. TNF-α in activated microglia.

Expression of SIRT3 in various glial cell types in the periventricular white matter in the neonatal rat brain after hypoxia.

Sirtuin 3 (SIRT3) mediates cellular resistance toward various forms of stress. SIRT3 expression in the developing brain, especially its localization in various glial cell types, has not been fully explored. This study aimed to determine SIRT3 expression in the brain of neonatal rats subjected to hypoxia. By immunohistochemistry, immunofluorescence and Western blotting, we show here that SIRT3 expression in the periventricular white matter was up-regulated in hypoxia group compared with the control group at the corresponding time points. Intense SIRT3 expression was detected in microglia at early time points after hypoxia whose cell number was increased with reduced ramifications in hypoxia group compared with the control group. Furthermore, SIRT3 immunoreactivity was obviously enhanced at 24 h, 3 and 7d, but was declined at 14d after hypoxia so that SIRT3 expression between the two groups was comparable. SIRT3 immunofluorescence was also localized in astrocytes labeled with GFAP which was augmented at different time points in hypoxia group. GPAP positive astrocytes exhibited long extending processes being most pronounced at 3d. SIRT3 was moderately expressed at 24 h, 3 and 7d, but was markedly increased at 14d after hypoxia. Moderate SIRT3 expression was also localized in oligodendrocytes labeled with CNPase in the control group. The incidence of CNPase positive oligodendrocytes showing colocalization of SIRT3 increased significantly at 24 h, 3 and 7d after hypoxia. In conclusion, SIRT3 expression was differentially up-regulated in all three major glial cell types following hypoxia. It is suggested that increased SIRT3 expression in the respective glial cell types following hypoxia is involved in different signaling pathways that protect against hypoxic stress in the developing brain.

Herbal Compounds with Special Reference to Gastrodin as Potential Therapeutic Agents for Microglia Mediated Neuroinflammation.

BACKGROUND: Activated microglia play a pivotal role neurodegenerative diseases by producing a variety of proinflammatory mediators including tumor necrosis factor-alpha (TNF-α), interleukin- 1beta (IL-1ß) and nitric oxide (NO) that are toxic to neurons and oligodendrocytes. METHODS: In view of the above, suppression of microglia mediated neuroinflammation is deemed a therapeutic strategy for neurodegenerative diseases. Several potential Chinese herbal extracts have been reported to exert neuroprotective effects against neurodegenerative diseases targeting specifically at the activated microglia. In this connection, the phenolic glucoside gastrodin, a main constituent of the Chinese herbal medicine Gastrodia rhizoma, produced widely in the local community exhibits potential neuroprotective effects through suppression of neurotoxic proinflammatory mediators. RESULTS: Here, we first review the roles of activated microglia in different brain diseases. The effects of gastrodin on activated microglia are then considered. We have identified gastrodin as a putative therapeutic agent as it has been found to suppress microglial activation thus ameliorating neuroinflammation. More importantly, gastrodin downregulates the expression of renin angiotensin system (RAS) and production of proinflammatory mediators. Remarkably, gastrodin promotes Sirtuin 3 (Sirt3) up-regulation and nicotinamide adenine dinucleotide phosphate oxidase-2 (NOX-2) down-regulation after ischemichypoxia in activated microglia mediated by AT1 or AT2 receptors which are angiotensin II receptors subtypes, indicating a possible molecular link between RAS and Sirt3 survival genes. CONCLUSION: This review summarizes the beneficial effects of gastrodin acting on activated microglia along with other herbal compounds. Its efficacy in neuroprotection is consistent with some common herbal products in China.