Changes in Astroglial Water Flow in the Pre-amyloid Phase of the STZ Model of AD Dementia.

Alzheimer's disease (AD) is an age-dependent neurodegenerative disease that is typically sporadic and has a high social and economic cost. We utilized the intracerebroventricular administration of streptozotocin (STZ), an established preclinical model for sporadic AD, to investigate hippocampal astroglial changes during the first 4 weeks post-STZ, a period during which amyloid deposition has yet to occur. Astroglial proteins aquaporin 4 (AQP-4) and connexin-43 (Cx-43) were evaluated, as well as claudins, which are tight junction (TJ) proteins in brain barriers, to try to identify changes in the glymphatic system and brain barrier during the pre-amyloid phase. Glial commitment, glucose hypometabolism and cognitive impairment were characterized during this phase. Astroglial involvement was confirmed by an increase in glial fibrillary acidic protein (GFAP); concurrent proteolysis was also observed, possibly mediated by calpain. Levels of AQP-4 and Cx-43 were elevated in the fourth week post-STZ, possibly accelerating the clearance of extracellular proteins, since these proteins actively participate in the glymphatic system. Moreover, although we did not see a functional disruption of the blood-brain barrier (BBB) at this time, claudin 5 (present in the TJ of the BBB) and claudin 2 (present in the TJ of the blood-cerebrospinal fluid barrier) were reduced. Taken together, data support a role for astrocytes in STZ brain damage, and suggest that astroglial dysfunction accompanies or precedes neuronal damage in AD.

Effect of metformin in hypothalamic astrocytes from an immunocompromised mice model.

Astrocytes are glial cells that play key roles in neuroinflammation, which is a common feature in diabetic encephalopathy and aging process. Metformin is an antidiabetic compound that shows neuroprotective properties, including in inflammatory models, but astroglial signaling pathways involved are still poorly known. Interferons α/ß are cytokines that participate in antiviral responses and the lack of their signaling increases susceptible to viral infections. Here, we investigated the effects of metformin on astrocytes from hypothalamus, a crucial brain region related to inflammatory processes. Astrocyte cultures were derived from interferon α/ß receptor knockout (IFNα/ßR-/-) and wild-type (WT) mice. Metformin did not change the expression of glial fibrillary acidic protein but caused an anti-inflammatory effect by decreasing pro-inflammatory cytokines (tumor necrosis factor-α and interleukin-1ß), as well as increasing gene expression of anti-inflammatory proteins interleukin-10 and Nrf2 (nuclear factor erythroid derived 2 like 2). However, nuclear factor κB p65 and cyclooxygenase 2 were downregulated in WT astrocytes and upregulated in IFNα/ßR-/- astrocytes. AMP-activated protein kinase (AMPK), a molecular target of metformin, was upregulated only in WT astrocytes, while sirtuin 1 increased in both mice models. The expression of inducible nitric oxide synthase was decreased in WT astrocytes and heme oxygenase 1 was increased in IFNα/ßR-/- astrocytes. Although loss of IFNα/ßR-mediated signaling affects some effects of metformin, our results support beneficial roles of this drug in hypothalamic astrocytes. Moreover, paradoxical response of metformin may involve AMPK. Thus, metformin can mediate glioprotection due its effects on age-related disorders in non-diabetic and diabetic encephalopathy individuals.

Differences between cultured astrocytes from neonatal and adult Wistar rats: focus on in vitro aging experimental models.

Astrocytes play key roles regulating brain homeostasis and accumulating evidence has suggested that glia are the first cells that undergo functional changes with aging, which can lead to a decline in brain function. In this context, in vitro models are relevant tools for studying aged astrocytes and, here, we investigated functional and molecular changes in cultured astrocytes obtained from neonatal or adult animals submitted to an in vitro model of aging by an additional period of cultivation of cells after confluence. In vitro aging induced different metabolic effects regarding glucose and glutamate uptake, as well as glutamine synthetase activity, in astrocytes obtained from adult animals compared to those obtained from neonatal animals. In vitro aging also modulated glutathione-related antioxidant defenses and increased reactive oxygen species and cytokine release especially in astrocytes from adult animals. Interestingly, in vitro aged astrocytes from adult animals exposed to pro-oxidant, inflammatory, and antioxidant stimuli showed enhanced oxidative and inflammatory responses. Moreover, these functional changes were correlated with the expression of the senescence marker p21, cytoskeleton markers, glutamate transporters, inflammatory mediators, and signaling pathways such as nuclear factor κB (NFκB)/nuclear factor erythroid 2-related factor 2 (Nrf2)/heme oxygenase 1 (HO-1). Alterations in these genes are remarkably associated with a potential neurotoxic astrocyte phenotype. Therefore, considering the experimental limitations due to the need for long-term maintenance of the animals for studying aging, astrocyte cultures obtained from adult animals further aged in vitro can provide an improved experimental model for understanding the mechanisms associated with aging-related astrocyte dysfunction.

Aging changes the expression of adenosine receptors, insulin-like growth factor 1 (IGF1), and hypoxia-inducible factor 1α (HIF1α) in hypothalamic astrocyte cultures.

The aging process induces neurochemical alterations in different brain regions, including hypothalamus. This pivotal area of the central nervous system (CNS) is crucial for detection and integration of nutritional and hormonal signals from the periphery of the body to maintain metabolic homeostasis. Astrocytes support the CNS homeostasis, energy metabolism, and inflammatory response, as well as increasing evidence has highlighted a critical role of astrocytes in orchestrating hypothalamic functions and in gliocrine system. In this study, we aimed to investigate the age-dependent mRNA expression of adenosine receptors, the insulin-like growth factor 1 receptor (IGF1R), and the hypoxia-inducible factor 1α (HIF1α), in addition to the levels of IGF1 and HIF1α in hypothalamic astrocyte cultures derived from newborn, adult, and aged rats. Our results revealed age-dependent changes in adenosine receptors, as well as a decrease in IGF1R/IGF1 and HIF1α. Of note, adenosine receptors, IGF1, and HIF1α are affected by inflammatory, redox, and metabolic processes, which can remodel hypothalamic properties, as observed in aging brain, reinforcing the role of hypothalamic astrocytes as targets for understanding the onset and/or progression of age-related diseases.

Simvastatin Differentially Modulates Glial Functions in Cultured Cortical and Hypothalamic Astrocytes Derived from Interferon α/ß Receptor Knockout mice.

Astrocytes have key regulatory roles in central nervous system (CNS), integrating metabolic, inflammatory and synaptic responses. In this regard, type I interferon (IFN) receptor signaling in astrocytes can regulate synaptic plasticity. Simvastatin is a cholesterol-lowering drug that has shown anti-inflammatory properties, but its effects on astrocytes, a main source of cholesterol for neurons, remain to be elucidated. Herein, we investigated the effects of simvastatin in inflammatory and functional parameters of primary cortical and hypothalamic astrocyte cultures obtained from IFNα/ß receptor knockout (IFNα/ßR-/-) mice. Overall, simvastatin decreased extracellular levels of tumor necrosis factor-α (TNF-α) and interleukin-1ß (IL-1ß), which were related to a downregulation in gene expression in hypothalamic, but not in cortical astrocytes. Moreover, there was an increase in anti-inflammatory interleukin-10 (IL-10) in both structures. Effects of simvastatin in inflammatory signaling also involved a downregulation of cyclooxygenase 2 (COX-2) gene expression as well as an upregulation of nuclear factor κB subunit p65 (NFκB p65). The expression of cytoprotective genes sirtuin 1 (SIRT1) and nuclear factor erythroid derived 2 like 2 (Nrf2) was also increased by simvastatin. In addition, simvastatin increased glutamine synthetase (GS) activity and glutathione (GSH) levels only in cortical astrocytes. Our findings provide evidence that astrocytes from different regions are important cellular targets of simvastatin in the CNS, even in the absence of IFNα/ßR, which was showed by the modulation of cytokine production and release, as well as the expression of cytoprotective genes and functional parameters.

Serum of COVID-19 patients changes neuroinflammation and mitochondrial homeostasis markers in hippocampus of aged rats.

Patients affected by COVID-19 present mostly with respiratory symptoms but acute neurological symptoms are also commonly observed. Furthermore, a considerable number of individuals develop persistent and often remitting symptoms months after infection, characterizing the condition called long-COVID. Since the pathophysiology of acute and persistent neurological manifestations is not fully established, we evaluated the expression of different genes in hippocampal slices of aged rats exposed to the serum of a post-COVID (sPC) individual and to the serum of patients infected by SARS-CoV-2 [Zeta (sZeta) and Gamma (sGamma) variants]. The expression of proteins related to inflammatory process, redox homeostasis, mitochondrial quality control and glial reactivity was determined. Our data show that the exposure to sPC, sZeta and sGamma differentially altered the mRNA levels of most inflammatory proteins and reduced those of antioxidant response markers in rat hippocampus. Furthermore, a decrease in the expression of mitochondrial biogenesis genes was induced by all serum samples, whereas a reduction in mitochondrial dynamics was only caused by sPC. Regarding the glial reactivity, S100B expression was modified by sPC and sZeta. These findings demonstrate that changes in the inflammatory response and a reduction of mitochondrial biogenesis and dynamics may contribute to the neurological damage observed in COVID-19 patients.

Glioprotective effects of resveratrol in hypothalamic astrocyte cultures obtained from interferon receptor knockout (IFNα/ßR-/-) mice.

Astrocytes play essential roles in the central nervous system (CNS), such as the regulation of glutamate metabolism, antioxidant defenses, and inflammatory/immune responses. Moreover, hypothalamic astrocytes seem to be crucial in the modulation of inflammatory processes, including those related to type I interferon signaling. In this regard, the polyphenol resveratrol has emerged as an important glioprotective molecule to regulate astrocyte functions. Therefore, this study aimed to investigate the immunomodulatory and protective effects of resveratrol in hypothalamic astrocyte cultures obtained from mouse depleted of type I interferon receptors (INF-α/ß-/-), a condition that can impair immune and inflammatory functions. Resveratrol upregulated glutamate transporter and glutamine synthetase gene expression, as well as modulated the release of wide range of cytokines and genes involved in the control of inflammatory response, besides the expression of adenosine receptors, which display immunomodulatory functions. Resveratrol also increased genes associated with redox balance, mitochondrial processes, and trophic factors signaling. The putative genes associated with glioprotective effects of resveratrol, including nuclear factor erythroid derived 2 like 2 (Nrf2), heme oxygenase 1 (HO-1), sirtuin 1 (SIRT1), and phosphoinositide 3-kinase (PI3K)/Akt, were further upregulated by resveratrol. Thus, our data show that resveratrol was able to modulate key genes associated with glial functionality and inflammatory response in astrocyte cultures derived from IFNα/ßR-/- mice. These data are in agreement with previous results, reinforcing its glioprotective effects even in hypothalamic astrocytes with altered inflammatory and immune signaling. Finally, this polyphenol can prepare astrocytes to better respond to injuries, including those associated with neuroimmunology defects.

Age-dependent effects of resveratrol in hypothalamic astrocyte cultures.

OBJECTIVES: The hypothalamus plays critical roles in maintaining brain homeostasis and increasing evidence has highlighted astrocytes orchestrating several of hypothalamic functions. However, it remains unclear how hypothalamic astrocytes participate in neurochemical mechanisms associated with aging process, as well as whether these cells can be a target for antiaging strategies. In this sense, the aim of this study is to evaluate the age-dependent effects of resveratrol, a well-characterized neuroprotective compound, in primary astrocyte cultures derived from the hypothalamus of newborn, adult, and aged rats. METHODS: Male Wistar rats (2, 90, 180, and 365 days old) were used in this study. Cultured astrocytes from different ages were treated with 10 and 100 µM resveratrol and cellular viability, metabolic activity, astrocyte morphology, release of glial cell line-derived neurotrophic factor (GDNF), transforming growth factor ß (TGF-ß), tumor necrosis factor α (TNF-α), interleukins (IL-1ß, IL-6, and IL-10), as well as the protein levels of Nrf2 and HO-1 were evaluated. RESULTS: In vitro astrocytes derived from neonatal, adults, and aged animals changed metabolic activity and the release of trophic factors (GDNF and TGF-ß), as well as the inflammatory mediators (TNF-α, IL-1ß, IL-6, and IL-10). Resveratrol prevented these alterations. In addition, resveratrol changed the immunocontent of Nrf2 and HO-1. The results indicated that the effects of resveratrol seem to have a dose- and age-associated glioprotective role. CONCLUSION: These findings demonstrate for the first time that resveratrol prevents the age-dependent underlying functional reprogramming of in vitro hypothalamic astrocytes, reinforcing its antiaging activity, and consequently, its glioprotective role.

The role of glial cells in Zika virus-induced neurodegeneration.

Zika virus (ZIKV) is a strongly neurotropic flavivirus whose infection has been associated with microcephaly in neonates. However, clinical and experimental evidence indicate that ZIKV also affects the adult nervous system. In this regard, in vitro and in vivo studies have shown the ability of ZIKV to infect glial cells. In the central nervous system (CNS), glial cells are represented by astrocytes, microglia, and oligodendrocytes. In contrast, the peripheral nervous system (PNS) constitutes a highly heterogeneous group of cells (Schwann cells, satellite glial cells, and enteric glial cells) spread through the body. These cells are critical in both physiological and pathological conditions; as such, ZIKV-induced glial dysfunctions can be associated with the development and progression of neurological complications, including those related to the adult and aging brain. This review will address the effects of ZIKV infection on CNS and PNS glial cells, focusing on cellular and molecular mechanisms, including changes in the inflammatory response, oxidative stress, mitochondrial dysfunction, Ca2+ and glutamate homeostasis, neural metabolism, and neuron-glia communication. Of note, preventive and therapeutic strategies that focus on glial cells may emerge to delay and/or prevent the development of ZIKV-induced neurodegeneration and its consequences.

Sulfite Impairs Bioenergetics and Redox Status in Neonatal Rat Brain: Insights into the Early Neuropathophysiology of Isolated Sulfite Oxidase and Molybdenum Cofactor Deficiencies.

Isolated sulfite oxidase (ISOD) and molybdenum cofactor (MoCD) deficiencies are genetic diseases biochemically characterized by the toxic accumulation of sulfite in the tissues of patients, including the brain. Neurological dysfunction and brain abnormalities are commonly observed soon after birth, and some patients also have neuropathological alterations in the prenatal period (in utero). Thus, we investigated the effects of sulfite on redox and mitochondrial homeostasis, as well as signaling proteins in the cerebral cortex of rat pups. One-day-old Wistar rats received an intracerebroventricular administration of sulfite (0.5 µmol/g) or vehicle and were euthanized 30 min after injection. Sulfite administration decreased glutathione levels and glutathione S-transferase activity, and increased heme oxygenase-1 content in vivo in the cerebral cortex. Sulfite also reduced the activities of succinate dehydrogenase, creatine kinase, and respiratory chain complexes II and II-III. Furthermore, sulfite increased the cortical content of ERK1/2 and p38. These findings suggest that redox imbalance and bioenergetic impairment induced by sulfite in the brain are pathomechanisms that may contribute to the neuropathology of newborns with ISOD and MoCD. Sulfite disturbs antioxidant defenses, bioenergetics, and signaling pathways in the cerebral cortex of neonatal rats. CII: complex II; CII-III: complex II-III; CK: creatine kinase; GST: glutathione S-transferase; HO-1: heme oxygenase-1; SDH: succinate dehydrogenase; SO32-: sulfite.

Effects of long-term resveratrol treatment in hypothalamic astrocyte cultures from aged rats.

Aging is intrinsically related to metabolic changes and characterized by the accumulation of oxidative and inflammatory damage, as well as alterations in gene expression and activity of several signaling pathways, which in turn impact on homeostatic responses of the body. Hypothalamus is a brain region most related to these responses, and increasing evidence has highlighted a critical role of astrocytes in hypothalamic homeostatic functions, particularly during aging process. The purpose of this study was to investigate the in vitro effects of a chronic treatment with resveratrol (1 µM during 15 days, which was replaced once every 3 days), a recognized anti-inflammatory and antioxidant molecule, in primary hypothalamic astrocyte cultures obtained from aged rats (24 months old). We observed that aging process changes metabolic, oxidative, inflammatory, and senescence parameters, as well as glial markers, while long-term resveratrol treatment prevented these effects. In addition, resveratrol upregulated key signaling pathways associated with cellular homeostasis, including adenosine receptors, nuclear factor erythroid-derived 2-like 2 (Nrf2), heme oxygenase 1 (HO-1), sirtuin 1 (SIRT1), proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α), and phosphoinositide 3-kinase (PI3K). Our data corroborate the glioprotective effect of resveratrol in aged hypothalamic astrocytes, reinforcing the beneficial role of resveratrol in the aging process.

The Janus face of antipsychotics in glial cells: Focus on glioprotection.

Antipsychotics are commonly prescribed to treat several neuropsychiatric disorders, including schizophrenia, mania in bipolar disorder, autism spectrum disorder, delirium, and organic or secondary psychosis, for example, in dementias such as Alzheimer's disease. There is evidence that typical antipsychotics such as haloperidol are more effective in reducing positive symptoms than negative symptoms and/or cognitive deficits. In contrast, atypical antipsychotic agents have gained popularity over typical antipsychotics, due to fewer extrapyramidal side effects and their theoretical efficacy in controlling both positive and negative symptoms. Although these therapies focus on neuron-based therapeutic schemes, glial cells have been recognized as important regulators of the pathophysiology of neuropsychiatric disorders, as well as targets to improve the efficacy of these drugs. Glial cells (astrocytes, oligodendrocytes, and microglia) are critical for the central nervous system in both physiological and pathological conditions. Astrocytes are the most abundant glial cells and play important roles in brain homeostasis, regulating neurotransmitter systems and gliotransmission, since they express a wide variety of functional receptors for different neurotransmitters. In addition, converging lines of evidence indicate that psychiatric disorders are commonly associated with the triad neuroinflammation, oxidative stress, and excitotoxicity, and that glial cells may contribute to the gliotoxicity process. Conversely, glioprotective molecules attenuate glial damage by generating specific responses that can protect glial cells themselves and/or neurons, resulting in improved central nervous system (CNS) functioning. In this regard, resveratrol is well-recognized as a glioprotective molecule, including in clinical studies of schizophrenia and autism. This review will provide a summary of the dual role of antipsychotics on neurochemical parameters associated with glial functions and will highlight the potential activity of glioprotective molecules to improve the action of antipsychotics.

SARS-CoV-2-Induced Amyloidgenesis: Not One, but Three Hypotheses for Cerebral COVID-19 Outcomes.

The main neuropathological feature of Alzheimer's disease (AD) is extracellular amyloid deposition in senile plaques, resulting from an imbalance between the production and clearance of amyloid beta peptides. Amyloid deposition is also found around cerebral blood vessels, termed cerebral amyloid angiopathy (CAA), in 90% of AD cases. Although the relationship between these two amyloid disorders is obvious, this does not make CAA a characteristic of AD, as 40% of the non-demented population presents this derangement. AD is predominantly sporadic; therefore, many factors contribute to its genesis. Herein, the starting point for discussion is the COVID-19 pandemic that we are experiencing and how SARS-CoV-2 may be able to, both directly and indirectly, contribute to CAA, with consequences for the outcome and extent of the disease. We highlight the role of astrocytes and endothelial cells in the process of amyloidgenesis, as well as the role of other amyloidgenic proteins, such as fibrinogen and serum amyloid A protein, in addition to the neuronal amyloid precursor protein. We discuss three independent hypotheses that complement each other to explain the cerebrovascular amyloidgenesis that may underlie long-term COVID-19 and new cases of dementia.

Early effects of LPS-induced neuroinflammation on the rat hippocampal glycolytic pathway.

Neuroinflammation is a common feature during the development of neurological disorders and neurodegenerative diseases, where glial cells, such as microglia and astrocytes, play key roles in the activation and maintenance of inflammatory responses in the central nervous system. Neuroinflammation is now known to involve a neurometabolic shift, in addition to an increase in energy consumption. We used two approaches (in vivo and ex vivo) to evaluate the effects of lipopolysaccharide (LPS)-induced neuroinflammation on neurometabolic reprogramming, and on the modulation of the glycolytic pathway during the neuroinflammatory response. For this, we investigated inflammatory cytokines and receptors in the rat hippocampus, as well as markers of glial reactivity. Mitochondrial respirometry and the glycolytic pathway were evaluated by multiple parameters, including enzymatic activity, gene expression and regulation by protein kinases. Metabolic (e.g., metformin, 3PO, oxamic acid, fluorocitrate) and inflammatory (e.g., minocycline, MCC950, arundic acid) inhibitors were used in ex vivo hippocampal slices. The induction of early inflammatory changes by LPS (both in vivo and ex vivo) enhanced glycolytic parameters, such as glucose uptake, PFK1 activity and lactate release. This increased glucose consumption was independent of the energy expenditure for glutamate uptake, which was in fact diverted for the maintenance of the immune response. Accordingly, inhibitors of the glycolytic pathway and Krebs cycle reverted neuroinflammation (reducing IL-1ß and S100B) and the changes in glycolytic parameters induced by LPS in acute hippocampal slices. Moreover, the inhibition of S100B, a protein predominantly synthesized and secreted by astrocytes, inhibition of microglia activation and abrogation of NLRP3 inflammasome assembly confirmed the role of neuroinflammation in the upregulation of glycolysis in the hippocampus. Our data indicate a neurometabolic glycolytic shift, induced by inflammatory activation, as well as a central and integrative role of astrocytes, and suggest that interference in the control of neurometabolism may be a promising strategy for downregulating neuroinflammation and consequently for diminishing negative neurological outcomes.

Acute Methylglyoxal-Induced Damage in Blood-Brain Barrier and Hippocampal Tissue.

Methylglyoxal (MG) is a reactive dicarbonyl compound formed mostly via the glycolytic pathway. Elevated blood glucose levels can cause MG accumulation in plasma and cerebrospinal fluid in patients with diabetes mellitus and Alzheimer's disease. Under these disease conditions, the high reactivity of MG leads to modification of proteins and other biomolecules, generating advanced glycation end products (AGEs), which are considered mediators in neurodegenerative diseases. We investigated the integrity of the blood-brain barrier (BBB) and astrocyte response in the hippocampus to acute insult induced by MG when it was intracerebroventricularly administered to rats. Seventy-two hours later, BBB integrity was lost, as assessed by the entry of Evans dye into the brain tissue and albumin in the cerebrospinal fluid, and a decrease in aquaporin-4 and connexin-43 in the hippocampal tissue. MG did not induce changes in the hippocampal contents of RAGE in this short interval, but decreased the expression of S100B, an astrocyte-secreted protein that binds RAGE. The expression of two important transcription factors of the antioxidant response, NF-κB and Nrf2, was unchanged. However, hemeoxigenase-1 was upregulated in the MG-treated group. These data corroborate the idea that hippocampal cells are targets of MG toxicity and that BBB dysfunction and specific glial alterations induced by this compound may contribute to the behavioral and cognitive alterations observed in these animals.

Why antidiabetic drugs are potentially neuroprotective during the Sars-CoV-2 pandemic: The focus on astroglial UPR and calcium-binding proteins.

We are living in a terrifying pandemic caused by Sars-CoV-2, in which patients with diabetes mellitus have, from the beginning, been identified as having a high risk of hospitalization and mortality. This viral disease is not limited to the respiratory system, but also affects, among other organs, the central nervous system. Furthermore, we already know that individuals with diabetes mellitus exhibit signs of astrocyte dysfunction and are more likely to develop cognitive deficits and even dementia. It is now being realized that COVID-19 incurs long-term effects and that those infected can develop several neurological and psychiatric manifestations. As this virus seriously compromises cell metabolism by triggering several mechanisms leading to the unfolded protein response (UPR), which involves endoplasmic reticulum Ca2+ depletion, we review here the basis involved in this response that are intimately associated with the development of neurodegenerative diseases. The discussion aims to highlight two aspects-the role of calcium-binding proteins and the role of astrocytes, glial cells that integrate energy metabolism with neurotransmission and with neuroinflammation. Among the proteins discussed are calpain, calcineurin, and sorcin. These proteins are emphasized as markers of the UPR and are potential therapeutic targets. Finally, we discuss the role of drugs widely prescribed to patients with diabetes mellitus, such as statins, metformin, and calcium channel blockers. The review assesses potential neuroprotection mechanisms, focusing on the UPR and the restoration of reticular Ca2+ homeostasis, based on both clinical and experimental data.

Methylmalonic acid induces inflammatory response and redox homeostasis disruption in C6 astroglial cells: potential glioprotective roles of melatonin and resveratrol.

Methylmalonic acidemia is a neurometabolic disorder biochemically characterized by the accumulation of methylmalonic acid (MMA) in different tissues, including the central nervous system (CNS). In this sense, it has been shown that high levels of this organic acid have a key role in the progressive neurological deterioration in patients. Astroglial cells actively participate in a wide range of CNS functions, such as antioxidant defenses and inflammatory response. Considering the role of these cells to maintain brain homeostasis, in the present study, we investigated the effects of MMA on glial parameters, focusing on redox homeostasis and inflammatory process, as well as putative mediators of these events in C6 astroglial cells. MMA decreased cell viability, glutathione levels, and antioxidant enzyme activities, increased inflammatory response, and changed the expression of nuclear factor erythroid 2-related factor 2 (Nrf2), nuclear factor kappa B (NFκB), peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α), inducible nitric oxide synthase (iNOS), cyclooxygenase 2 (COX-2), and adenosine receptors, suggesting that these transcriptional factors and proteins may underlie the glial responses induced by MMA. Moreover, we also demonstrated the protective roles of melatonin and resveratrol against MMA-induced inflammation and decrease in glutathione levels. In summary, our findings support the hypothesis that astroglial changes are associated with pathogenesis of methylmalonic acidemia. In addition, we showed that these cells might be potential targets for preventive/therapeutic strategies by using molecules, such as melatonin and resveratrol, which mediated glioprotection in this inborn error of metabolism.

Glioprotective Effects of Resveratrol Against BMAA-Induced Astroglial Dysfunctions.

Astroglial cells play important roles in maintaining central nervous system (CNS) homeostasis. The neurotoxin ß-N-methylamino-L-alanine (BMAA) has usually been associated with neurodegeneration due to its toxic effects on neurons. However, little is known about the effects of BMAA on astroglial cells. Resveratrol, a natural polyphenol, represents a potential protective strategy against brain injuries. In the present study, we sought to investigate BMAA-induced astroglial dysfunctions and the glioprotective roles of resveratrol. BMAA did not impair astroglial cellular viability, but increased glutamate uptake, glutamate metabolism into glutamine, and reactive oxygen species production, while decreased glutathione (GSH) and superoxide dismutase (SOD)-based antioxidant defenses and triggers an inflammatory response. In contrast, resveratrol was able to prevent most of these BMAA-induced functional changes in astroglial cells. Moreover, both BMAA and resveratrol modulated the gene expression of molecular pathways associated with glutamate metabolism, redox homeostasis, and inflammatory response, which characterize their roles on astroglial functions. In this regard, BMAA downregulated adenosine receptors, peroxisome proliferator-activated receptor-gamma coactivator 1-alpha (PGC-1α), phosphoinositide-3-kinase (PI3K), and Akt, while resveratrol prevented these effects and upregulated nuclear factor erythroid 2-related factor 2 (Nrf2) and heme oxygenase-1 (HO-1). Our study, for the first time, demonstrates that BMAA directly impacts key astroglial functions, contributing to elucidating the cellular and molecular mechanisms of this toxin in the CNS. In addition, we reinforce the glioprotective effects of resveratrol against BMAA-induced astroglial dysfunctions.

Lipopolysaccharide Induces Gliotoxicity in Hippocampal Astrocytes from Aged Rats: Insights About the Glioprotective Roles of Resveratrol.

Astrocytes may undergo a functional remodeling with aging, acquiring a pro-inflammatory state. In line with this, resveratrol represents an interesting strategy for a healthier brain aging since it can improve glial functions. In the present study, we investigated the glioprotective role of resveratrol against lipopolysaccharide (LPS)-induced gliotoxicity in hippocampal aged astrocytes. Astrocyte cultures were obtained from aged rats (365 days old) and challenged in vitro with LPS in the presence of resveratrol. Cultured astrocytes from newborn rats were used as an age comparative for evaluating LPS gliotoxicity. In addition, aged rats were submitted to an acute systemic inflammation with LPS. Hippocampal astrocyte cultures were also obtained from these LPS-stimulated aged animals to further investigate the glioprotective effects of resveratrol in vitro. Overall, our results show that LPS induced a higher inflammatory response in aged astrocytes, compared to newborn astrocytes. Several inflammatory and gene expression alterations promoted by LPS in aged astrocyte cultures were similar in hippocampal tissue from aged animals submitted to in vivo LPS injection, corroborating our in vitro findings. Resveratrol, in turn, presented anti-inflammatory effects in aged astrocyte cultures, which were associated with downregulation of p21 and pro-inflammatory cytokines, Toll-like receptors (TLRs), and nuclear factor κB (NFκB). Resveratrol also improved astroglial functions. Upregulation of sirtuin 1 (SIRT1), nuclear factor erythroid 2-related factor 2 (Nrf2), and heme oxygenase 1 (HO-1) represent potential molecular mechanisms associated with resveratrol-mediated glioprotection. In summary, our data show that resveratrol can prime aged astrocytes against gliotoxic stimuli, contributing to a healthier brain aging.

Sulforaphane Induces Glioprotection After LPS Challenge.

Sulforaphane is a natural compound that presents anti-inflammatory and antioxidant properties, including in the central nervous system (CNS). Astroglial cells are involved in several functions to maintain brain homeostasis, actively participating in the inflammatory response and antioxidant defense systems. We, herein, investigated the potential mechanisms involved in the glioprotective effects of sulforaphane in the C6 astrocyte cell line, when challenged with the inflammogen, lipopolysaccharide (LPS). Sulforaphane prevented the LPS-induced increase in the expression and/or release of pro-inflammatory mediators, possibly due to nuclear factor κB and hypoxia-inducible factor-1α activation. Sulforaphane also modulated the expressions of the Toll-like and adenosine receptors, which often mediate inflammatory processes induced by LPS. Additionally, sulforaphane increased the mRNA levels of nuclear factor erythroid-derived 2-like 2 (Nrf2) and heme oxygenase-1 (HO1), both of which mediate several cytoprotective responses. Sulforaphane also prevented the increase in NADPH oxidase activity and the elevations of superoxide and 3-nitrotyrosine that were stimulated by LPS. In addition, sulforaphane and LPS modulated superoxide dismutase activity and glutathione metabolism. Interestingly, the anti-inflammatory and antioxidant effects of sulforaphane were blocked by HO1 pharmacological inhibition, suggesting its dependence on HO1 activity. Finally, in support of a glioprotective role, sulforaphane prevented the LPS-induced decrease in glutamate uptake, glutamine synthetase activity, and glial-derived neurotrophic factor (GDNF) levels, as well as the augmentations in S100B release and Na+, K+ ATPase activity. To our knowledge, this is the first study that has comprehensively explored the glioprotective effects of sulforaphane on astroglial cells, reinforcing the beneficial effects of sulforaphane on astroglial functionality.