Astrocyte apoptosis: implications for neuroprotection.

http://if-pan.krakow.pl/pjp/pdf/2010/5_956.pdf

Quantification of metformin by the HPLC method in brain regions, cerebrospinal fluid and plasma of rats treated with lipopolysaccharide

Accumulation of β-amyloid (Aβ) and resultant inflammation are critical pathological features of Alzheimer disease (AD). Microglia, a primary immune cell in brain, ingests and degrades extracellular Aβ fibrils via the lysosomal system. Autophagy is a catabolic process that degrades native cellular components, however, the role of autophagy in Aβ degradation by microglia and its effects on AD are unknown. Here we demonstrate a novel role for autophagy in the clearance of extracellular Aβ fibrils by microglia and in the regulation of the Aβ-induced NLRP3 (NLR family, pyrin domain containing 3) inflammasome using microglia specific atg7 knockout mice and cell cultures. We found in microglial cultures that Aβ interacts with MAP1LC3B-II via OPTN/optineurin and is degraded by an autophagic process mediated by the PRKAA1 pathway. We anticipate that enhancing microglial autophagy may be a promising new therapeutic strategy for AD.

Autophagy in microglia degrades extracellular β-amyloid fibrils and regulates the NLRP3 inflammasome

Alzheimer'sdisease(AD) is characterized by deposition of amyloid-β (Aβ)plaques, neurofibrillary tangles, andneuronal loss, accompaniedbyneuroinflammation. Neuroinflammatoryprocesses are thought to contribute toAD pathophysiology. Metformin has been reported to have anti-inflammatory efficacy. However, whether metformin is responsible for the anti-neuroinflammationand neuroprotection on APPswe/PS1ΔE9 (APP/PS1) mice remains unclear. Here we showed that metformin attenuated spatial memory deficit, neuron loss in the hippocampus and enhanced neurogenesis in APP/PS1 mice. In addition, metformin administration decreased amyloid-β (Aβ)plaque load and chronic inflammation (activated microglia and astrocytes as well as pro-inflammatory mediators) in the hippocampus and cortex. Further study demonstrated that treatment with metformin enhanced cerebral AMPK activation. Meanwhile, metformin notably suppressed the activation of P65 NF-κB, mTOR and S6K, reduced Bace1 protein expression. Our data suggest that metformin can exert functional recovery of memory deficits and neuroprotective effect on APP/PS1 mice via triggering neurogenesis and anti-inflammation mediated by regulating AMPK/mTOR/S6K/Bace1 and AMPK/P65 NF-κB signaling pathways in the hippocampus, which may contribute to improvement in neurological deficits.

Metformin treatment prevents amyloid plaque deposition and memory impairment in APP/PS1 mice.

AMP-activated protein kinase (AMPK) stimulates energy production via glucose and lipid metabolism, whereas it inhibits energy consuming functions, such as protein and cholesterol synthesis. Increased cytoplasmic AMP and Ca(2+) levels are the major activators of neuronal AMPK signaling. Interestingly, Alzheimer's disease (AD) is associated with several abnormalities in neuronal energy metabolism, for example, decline in glucose uptake, mitochondrial dysfunctions and defects in cholesterol metabolism, and in addition, with problems in maintaining Ca(2+) homeostasis. Epidemiological studies have also revealed that many metabolic and cardiovascular diseases are risk factors for cognitive impairment and sporadic AD. Emerging studies indicate that AMPK signaling can regulate tau protein phosphorylation and amyloidogenesis, the major hallmarks of AD. AMPK is also a potent activator of autophagic degradation which seems to be suppressed in AD. All these observations imply that AMPK is involved in the pathogenesis of AD. However, the responses of AMPK activation are dependent on stimulation and the extent of activating stress. Evidently, AMPK signaling can repress and delay the appearance of AD pathology but later on, with increasing neuronal stress, it can trigger detrimental effects that augment AD pathogenesis. We will outline the potential role of AMPK function in respect to various aspects affecting AD pathogenesis.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1471-4159.2011.07331.x

AMP-activated protein kinase: a potential player in Alzheimer's disease.

Recent evidence suggests that metformin shows beneficial effects in experimental models of neuroinflammatory diseases. The aim of the present study was to determine the effect of metformin on phagocytosis and acidification of lysosomal/endosomal compartments in rat primary microglia in the presence of lipopolysaccharide (LPS) and/or beta-peptides (25–35), (1–40), and (1–42). Metformin increased the phagocytosis of fluorescent microspheres in the presence or absence of all the beta-peptides. However, the drug had no effect on the phagocytosis in LPS-stimulated microglia regardless of the presence of all the beta-peptides. Metformin acidified the lysosomal/endosomal compartments in the presence or absence of the beta-peptide 1–40 in both resting and activated microglia. To elucidate the mechanism of metformin action, we used 5-aminoimidazole-4-carboxamide-1-β-d-ribofuranoside as an activator of adenosine monophosphate-activated protein kinase (AMPK) and compound C as a confirmed pharmacological inhibitor of AMPK. We have shown that metformin increased AMPK activity in microglial cells and that all observed effects are AMPK-dependent because the pretreatment of microglia with compound C reversed the effects of the drug. Since degradation of proteins in lysosomal/endosomal compartments depends largely on their phagocytosis and acidification, metformin may be beneficial in proteinopathies affecting the brain.

/pdf/metformin-increases-phagocytosis-and-acidifies-lysosomal-3aectnrcr5.pdf

Metformin increases phagocytosis and acidifies lysosomal/endosomal compartments in AMPK-dependent manner in rat primary microglia.

Superoxide dismutase 1 and glutathione peroxidase 1 are involved in the protective effect of sulodexide on vascular endothelial cells exposed to oxygen-glucose deprivation

The aim of the present study was to establish whether aniracetam is capable of protecting cultured rat astrocytes against ischemic injury. Treatment of the cultures with aniracetam (1, 10 and 100 mM) during 24 h ischemia simulated in vitro significantly decreased the number of apoptotic cells. The antiapoptotic effects of the drug were confirmed by the increase of intracellular ATP and phosphocreatine (PCr) levels and the inhibition of the caspase-3 activity. Aniracetam also attenuated cellular oxidative stress by decreased production of reactive oxygen species (ROS). These effects were associated with the decrease in levels of c-fos and c-jun mRNA in primary astrocyte cultures exposed to 24 h ischemia. When cultured astrocytes were incubated during 24 h simulated ischemia with wortmannin, a phosphatidylinositol 3-kinase (PI 3-kinase) inhibitor or PD98059, a mitogen-activated protein (MAP)/extracellular signal regulated kinase (ERK) (MEK) inhibitor, the cell apoptosis was accelerated. This effect was antagonized by adding 100 mM aniracetam to the culture medium. These findings suggest that the protective effect of aniracetam is mediated by PI 3-kinase and MEK pathways in the downstream mechanisms.

Aniracetam attenuates apoptosis of astrocytes subjected to simulated ischemia in vitro.

https://link.springer.com/content/pdf/10.1016/S1734-1140(11)70542-4.pdf

Metformin increases phagocytosis and acidifies lysosomal/endosomal compartments in AMPK-dependent manner in rat primary microglia

The present study focused on mechanisms involved in the anti-apoptotic effect of cyclosporin A (CsA) towards ischemic injured astrocytes in vitro [under combined oxygen glucose deprivation (OGD)]. We investigated whether this action might be mediated through activation of extracellular signal regulated kinases 1 and 2 (Erk1/2) or attenuation of calcineurin (CaN) by immunosuppressant in ischemic astrocytes. Additionally, the influence of CsA on phosphorylation of Akt kinase was determined. After 21 days of in vitro culture, astrocytes were subjected to OGD (for 8 h) and CsA (0.25–10 μM); 0.25 μM CsA distinctly stimulated the Erk1/2 pathway in astrocytes exposed to OGD. This protective effect of CsA was strongly associated with CaN inhibition, increased expression of anti-apoptotic factors such as Bcl-XL and NF-κB, as well as suppression of caspase-3 activity. Maximum p-Akt kinase expression was observed following treatment with 1 μM CsA. Finally, we also demonstrated that the beneficial effect of CsA at a concentration of 10 μM is related mainly to strong CaN inhibition. The results obtained suggest that, depending on the concentration used, CsA might act as a protective agent towards ischemia-injured astroglial cells through alternative intracellular pathways associated with increased p-Erk1/2 and p-Akt expression or CaN inactivation.

Calcineurin and Erk1/2-signaling pathways are involved in the antiapoptotic effect of cyclosporin A on astrocytes exposed to simulated ischemia in vitro.

Jakub Adamczyk

Papers

Metformin increases phagocytosis and acidifies lysosomal/endosomal compartments in AMPK-dependent manner in rat primary microglia.

Superoxide dismutase 1 and glutathione peroxidase 1 are involved in the protective effect of sulodexide on vascular endothelial cells exposed to oxygen-glucose deprivation

Aniracetam attenuates apoptosis of astrocytes subjected to simulated ischemia in vitro.

Metformin increases phagocytosis and acidifies lysosomal/endosomal compartments in AMPK-dependent manner in rat primary microglia

Calcineurin and Erk1/2-signaling pathways are involved in the antiapoptotic effect of cyclosporin A on astrocytes exposed to simulated ischemia in vitro.