Effect of rottlerin on astrocyte phenotype polarization after trimethyltin insult in the dentate gyrus of mice

The compound (E)-2-(3,4-dihydroxystyryl)-3-hydroxy-4H-pyran-4-one alleviates neuroinflammation and cognitive impairment in a mouse model of Alzheimer's disease

JOURNAL/nrgr/04.03/01300535-202511000-00034/figure1/v/2024-12-20T164640Z/r/image-tiff Previous studies have shown that the compound (E)-2-(3,4-dihydroxystyryl)-3-hydroxy-4H-pyran-4-one (D30), a pyromeconic acid derivative, possesses antioxidant and anti-inflammatory properties, inhibits amyloid-β aggregation, and alleviates scopolamine-induced cognitive impairment, similar to the phase III clinical drug resveratrol. In this study, we established a mouse model of Alzheimer's disease via intracerebroventricular injection of fibrillar amyloid-β to investigate the effect of D30 on fibrillar amyloid-β-induced neuropathology. Our results showed that D30 alleviated fibrillar amyloid-β-induced cognitive impairment, promoted fibrillar amyloid-β clearance from the hippocampus and cortex, suppressed oxidative stress, and inhibited activation of microglia and astrocytes. D30 also reversed the fibrillar amyloid-β-induced loss of dendritic spines and synaptic protein expression. Notably, we demonstrated that exogenous fibrillar amyloid-β introduced by intracerebroventricular injection greatly increased galectin-3 expression levels in the brain, and this increase was blocked by D30. Considering the role of D30 in clearing amyloid-β, inhibiting neuroinflammation, protecting synapses, and improving cognition, this study highlights the potential of galectin-3 as a promising treatment target for patients with Alzheimer's disease.

SIRT3 suppresses vascular endothelial senescence via DHRS2 and contributes to the anti-vascular aging effect of Bazi Bushen capsule

AIMS

Vascular and endothelial aging are significant causes of chronic diseases among the elderly. This study investigated the specific mechanism by which sirtuin 3 (SIRT3) regulates vascular endothelial senescence and the beneficial role of Bazi Bushen capsule (BZBS) in preventing vascular aging.

METHODS

Human umbilical vein endothelial cells and mouse aortic endothelial cells were cultured with D-galactose (D-gal) to induce aging and evaluate the beneficial effects of the SIRT3-dehydrogenase/reductase member 2 (DHRS2) axis on the inhibition of vascular endothelial aging. d-Gal was injected intraperitoneally into wild-type and Sirt3 knockout mice, while BZBS was administered orally. Histochemical staining, immunohistochemistry, and western blotting assays were used to explore the beneficial effects of BZBS against aging-associated vascular remodelling. Endothelial cell function assays were used to evaluate the role of BZBS in suppressing endothelial aging in vitro.

RESULTS

SIRT3 deacetylated DHRS2 and modulated the translation of DHRS2. The SIRT3-DHRS2 axis played an important role in preserving mitochondrial homeostasis and reducing reactive oxygen species generation through suppressing endothelial nitric oxide synthase (eNOS) translocating to mitochondria and eNOS-Thr495 phosphorylation mediated by protein kinase C δ (PKCδ). BZBS mitigated vascular remodelling and relieved endothelial oxidative stress via the SIRT3-DHRS2 axis.

CONCLUSION

SIRT3 activates DHRS2-PKCδ to stop aging in endothelial cells by inhibiting uncoupled eNOS translocating to mitochondria. BZBS rescued vascular aging and endothelial dysfunction via the SIRT3-DHRS2 axis. Revealing a protective mechanism by which SIRT3 inhibits endothelial senescence, this study provides evidence for BZBS in delaying vascular aging.

Extracellular Vesicles Derived from FGF2-Primed Astrocytes Against Mitochondrial and Synaptic Toxicities in Parkinson's Disease

Purpose

Mitochondrial dysfunction associated with neuronal degeneration and subsequent synaptic disconnection are essential for the development of Parkinson's disease (PD). Considering that astrocytes play key roles in synaptogenesis during development, we hypothesized that fibroblast growth factor - 2 (FGF2), a key factor for astrocyte development, could reverse the toxic phenotype of reactive astrocytes, and the extracellular vesicles (EVs) derived from FGF2-primed astrocytes would enhance synaptogenesis in PD model. The present study was to test this hypothesis.

Methods

EVs isolated from FGF2-primed astrocytes (FGF2-EVs) were characterized by transmission electron microscopy and nanoparticle tracking analysis. FGF2-EVs were applied to both in vitro and in vivo models of PD. EVs derived from naïve astrocytes (CON-EV) were used as control. Mitochondrial alterations, neuronal survival, synaptogenesis, and mice behavior were subsequently evaluated by quantitative real-time polymerase chain reaction, Western-blotting, immunohistochemistry, and CatWalk gait analysis. To dissect the underlying mechanisms, proteomic analysis and small interfering RNA (siRNA) mediated gene silencing were adopted.

Results

FGF2 treatment restored the expression of neural progenitor markers and suppressed the levels of A1 astrocytic markers in MPP+ pretreated astrocytes. FGF2-EVs, in comparison with that of CON-EVs, effectively protected neurons from mitochondrial fragmentation and stimulated synaptogenesis, as evidenced by expression of Mitofusin 2 (Mfn2), postsynaptic density protein 95 (PSD-95) and synaptophysin (SYP). Proteomic analysis revealed high enrichment of neural cell adhesion molecule 1 (NCAM1) in FGF2-EVs. Knocking down NCAM1 severely influenced the expression of mitochondrial and synaptic proteins. Furthermore, delivery of FGF2-EVs significantly enhanced the survival of TH+ neurons, the levels of NCAM1 and synaptogenesis in the substantia nigra of PD mice, as well as the locomotion of PD mice.

Conclusion

EVs from FGF2-primed astrocytes are superior in protecting PD mice against mitochondrial and synaptic toxicities, possibly through NCAM1, which could be used as a therapeutic strategy for PD.

Neuroinflammation Involving Endothelin-1 and Platelet-Activating Factor Receptors Contributes To Self-Injurious Behaviors Induced by Bay k-8644 in Adolescent Mice

Bay k-8644, an activator of L-type voltage-gated calcium channels, induces self-injurious behaviors in mice. Although previous studies using animal models have suggested the possible implications of neuroinflammation in self-injurious behaviors, this has not yet been elucidated in the context of Bay k-8644-induced self-injurious behaviors. In this study, Bay k-8644 (50 µg, i.c.v.)-induced self-injurious behaviors were accompanied by increased expression of endothelin (ET)-1, platelet-activating factor (PAF) receptors, and Iba-1 in the striatum. Pretreatment with the ET receptor antagonist bosentan (10 mg/kg, i.p.), the PAF receptor antagonist ginkgolide B (10 mg/kg, i.p.), or the microglial activation inhibitor minocycline (40 mg/kg/day for 5 days, i.p.) significantly inhibited Bay k-8644-induced self-injurious behaviors and microglial activation in the striatum. Interestingly, bosentan also suppressed Bay k-8644-induced PAF receptor expression, indicating that ET-1 may act as an upstream modulator of the PAF signaling under these experimental conditions. Bay k-8644-induced ET-1 expression and consequent pro-inflammatory changes were reversed by the protein kinase C (PKC) inhibitor NPC-15,437 and the Ca2+/calmodulin-dependent kinase II (CaMKII) inhibitor KN-93. Moreover, Bay k-8644-induced self-injurious behaviors and microglial activation were significantly potentiated by exogenous ET-1 administration (10 pmol, i.c.v.) or by weak neuroinflammation in the striatum induced by systemic injection of low-dose lipopolysaccharide (LPS; 1 mg/kg, i.p.). Our results suggest that neuroinflammatory changes associated with ET-1/PAF signaling in the striatum contribute to Bay k-8644-induced self-injurious behaviors.

Beta-sitosterol mitigates cognitive deficit and hippocampal neurodegeneration in mice with trimethyltin-induced toxicity

The present study investigated the neural health benefit of beta-sitosterol (BSS) against trimethyltin (TMT)-induced neurodegeneration in mice. Forty male Institute of Cancer Research (ICR) mice were randomly divided into Sham-veh, TMT-veh, TMT-BSS50, and TMT-BSS100. A one-time intraperitoneal injection of 2.6 mg/kg of TMT was given to mice in TMT groups. Vehicle (veh), BSS 50 mg/kg or BSS 100 mg/kg were orally given for 2 weeks. Spatial learning and memory were evaluated. Brain oxidative status, hippocampal neuropathology, and reactive astrocytes were done. White matter pathology was also evaluated. The results indicated the massy effect of TMT on induced motor ability and spatial memory deficits in accordance with increased neuronal degeneration in Cornus ammonis (CA) 1, CA3, and dentate gyrus (DG) and internal capsule white matter damage. TMT also induced the reduction of reactive astrocytes in CA1 and DG. Brain's catalase activity was significantly reduced by TMT, but not in mice with BSS treatments. Both doses of BSS treatment exhibited improvement in motor ability and spatial memory deficits in accordance with the activation of reactive astrocytes in CA1, CA3, and DG. However, they successfully prevented the increase of neuronal degeneration in CA1 found only with the BSS dose of 100 mg/kg, and it was indicated as the effective dose for neuroprotection in the vulnerable brain area. This study demonstrated mitigative effects of BSS against motor ability and memory deficits with neural health benefits, including a protective effect against CA1 neurodegeneration and a nurturing effect on hippocampal reactive astrocytes.

Exploring the effects of moxibustion on cognitive function in rats with multiple cerebral infarctions from the perspective of glial vascular unit repairing

Objective

This study aimed to explore the effect of moxibustion at Governor Vessel (GV) acupoints, including Baihui (GV 20), Shenting (GV 24) and Dazhui (GV 14) for 14 days on glial vascular unit (GVU) in rats with multiple microinfarctions (MMI), and to explore its action mechanism.

Methods

The effect and mechanism of moxibustion on vascular dementia (VD) were studied in MMI rats by means of behavioral and molecular biology experiments.

Results

Rats receiving MMI showed impairment of memory function, reduction of cerebral blood flow, damage of blood-brain barrier (BBB) integrity and increased brain mass. MMI also increased neuronal degeneration in the hippocampus. Notably, levels of glial fibrillary acidic protein (GFAP) and complement component 3 significantly increased, but those of Connexin43 (CX43) and platelet derived growth factor receptor β (PDGFRβ) significantly decreased in the hippocampus of the rats receiving MMI. Moxibustion, as well as oxiracetam (ORC) treatment improved memory function and neuronal degeneration, ameliorated BBB integrity, increased cerebral blood flow and decreased brain mass. In addition, moxibustion as well as oxiracetam (ORC) treatment reduced the decrease of CX43 protein and increased PDGFRβ protein level in the hippocampus of MMI rats. Moreover, moxibustion treatment reversed MMI-induced increase of the GFAP/CX43 ratio in vascular structural units. Importantly, after PDGFRβ inhibition, VD rats treated with moxibustion had impaired learning and memory, decreased cerebral blood flow, and BBB disruption.

Conclusion

Moxibustion treatment at various GV acupoints improved cerebral blood flow and repaired BBB function in rats with MMI, likely through protecting GVU.

Nimodipine attenuates neuroinflammation and delayed apoptotic neuronal death induced by trimethyltin in the dentate gyrus of mice

L-type voltage-gated calcium channels (L-VGCCs) are thought to be involved in epileptogenesis and acute excitotoxicity. However, little is known about the role of L-VGCCs in neuroinflammation or delayed neuronal death following excitotoxic insult. We examined the effects of repeated treatment with the L-VGCC blocker nimodipine on neuroinflammatory changes and delayed neuronal apoptosis in the dentate gyrus following trimethyltin (TMT)-induced convulsions. Male C57BL/6 N mice were administered TMT (2.6 mg/kg, i.p.), and the expression of the Cav1.2 and Cav1.3 subunits of L-VGCC were evaluated. The expression of both subunits was significantly decreased; however, the astroglial expression of Cav1.3 L-VGCC was significantly induced at 6 and 10 days after TMT treatment. Furthermore, astroglial Cav1.3 L-VGCCs colocalized with both the pro-inflammatory phenotype marker C3 and the anti-inflammatory phenotype marker S100A10 of astrocytes. Nimodipine (5 mg/kg, i.p. × 5 at 12-h intervals) did not significantly affect TMT-induced astroglial activation. However, nimodipine significantly attenuated the pro-inflammatory phenotype changes, while enhancing the anti-inflammatory phenotype changes in astrocytes after TMT treatment. Consistently, nimodipine reduced the levels of pro-inflammatory astrocytes-to-microglia mediators, while increasing the levels of anti-inflammatory astrocytes-to-microglia mediators. These effects were accompanied by an increase in the phosphorylation of extracellular signal-regulated kinase (ERK), supporting our previous finding that p-ERK is a signaling factor that regulates astroglial phenotype changes. In addition, nimodipine significantly attenuated TMT-induced microglial activation and delayed apoptosis of dentate granule neurons. Our results suggest that L-VGCC blockade attenuates neuroinflammation and delayed neurotoxicity following TMT-induced convulsions through the regulation of astroglial phenotypic changes by promoting ERK signaling.

Flaxseed Oil Alleviates Trimethyltin-Induced Cell Injury and Inhibits the Pro-Inflammatory Activation of Astrocytes in the Hippocampus of Female Rats

Exposure to the neurotoxin trimethyltin (TMT) selectively induces hippocampal neuronal injury and astrocyte activation accompanied with resultant neuroinflammation, which causes severe behavioral, cognitive, and memory impairment. A large body of evidence suggests that flaxseed oil (FSO), as one of the richest sources of essential omega-3 fatty acids, i.e., α-linolenic acids (ALA), displays neuroprotective properties. Here, we report the preventive effects of dietary FSO treatment in a rat model of TMT intoxication. The administration of FSO (1 mL/kg, orally) before and over the course of TMT intoxication (a single dose, 8 mg/kg, i.p.) reduced hippocampal cell death, prevented the activation of astrocytes, and inhibited their polarization toward a pro-inflammatory/neurotoxic phenotype. The underlying protective mechanism was delineated through the selective upregulation of BDNF and PI3K/Akt and the suppression of ERK activation in the hippocampus. Pretreatment with FSO reduced cell death and efficiently suppressed the expression of inflammatory molecules. These beneficial effects were accompanied by an increased intrahippocampal content of n-3 fatty acids. In vitro, ALA pretreatment prevented the TMT-induced polarization of cultured astrocytes towards the pro-inflammatory spectrum. Together, these findings support the beneficial neuroprotective properties of FSO/ALA against TMT-induced neurodegeneration and accompanied inflammation and hint at a promising preventive use of FSO in hippocampal degeneration and dysfunction.

Ginsenoside Re protects against kainate-induced neurotoxicity in mice by attenuating mitochondrial dysfunction through activation of the signal transducers and activators of transcription 3 signaling

It was demonstrated that ginsenosides exert anti-convulsive potentials and interleukin-6 (IL-6) is protective from excitotoxicity induced by kainate (KA), a model of temporal lobe epilepsy. Ginsenosides-mediated mitochondrial recovery is essential for attenuating KA-induced neurotoxicity, however, little is known about the effects of ginsenoside Re (GRe), one of the major ginsenosides. In this study, GRe significantly attenuated KA-induced seizures in mice. KA-induced redox changes were more evident in mitochondrial fraction than in cytosolic fraction in the hippocampus of mice. GRe significantly attenuated KA-induced mitochondrial oxidative stress (i.e. increases in reactive oxygen species, 4-hydroxynonenal, and protein carbonyl) and mitochondrial dysfunction (i.e. the increase in intra-mitochondrial Ca2+ and the decrease in mitochondrial membrane potential). GRe or mitochondrial protectant cyclosporin A restored phospho-signal transducers and activators of transcription 3 (STAT3) and IL-6 levels reduced by KA, and the effects of GRe were reversed by the JAK2 inhibitor AG490 and the mitochondrial toxin 3-nitropropionic acid (3-NP). Thus, we used IL-6 knockout (KO) mice to investigate whether the interaction between STAT3 and IL-6 is involved in the GRe effects. Importantly, KA-induced reduction of manganese superoxide dismutase (SOD-2) levels and neurodegeneration (i.e. astroglial inhibition, microglial activation, and neuronal loss) were more prominent in IL-6 KO than in wild-type (WT) mice. These KA-induced detrimental effects were attenuated by GRe in WT and, unexpectedly, IL-6 KO mice, which were counteracted by AG490 and 3-NP. Our results suggest that GRe attenuates KA-induced neurodegeneration via modulating mitochondrial oxidative burden, mitochondrial dysfunction, and STAT3 signaling in mice.

Ramelteon attenuates hippocampal neuronal loss and memory impairment following kainate-induced seizures

Evidence suggests that the neuroprotective effects of melatonin involve both receptor-dependent and -independent actions. However, little is known about the effects of melatonin receptor activation on the kainate (KA) neurotoxicity. This study examined the effects of repeated post-KA treatment with ramelteon, a selective agonist of melatonin receptors, on neuronal loss, cognitive impairment, and depression-like behaviors following KA-induced seizures. The expression of melatonin receptors decreased in neurons, whereas it was induced in astrocytes 3 and 7 days after seizures elicited by KA (0.12 μg/μL) in the hippocampus of mice. Ramelteon (3 or 10 mg/kg, i.p.) and melatonin (10 mg/kg, i.p.) mitigated KA-induced oxidative stress and impairment of glutathione homeostasis and promoted the nuclear translocation and DNA binding activity of Nrf2 in the hippocampus after KA treatment. Ramelteon and melatonin also attenuated microglial activation but did not significantly affect astroglial activation induced by KA, despite the astroglial induction of melatonin receptors after KA treatment. However, ramelteon attenuated KA-induced proinflammatory phenotypic changes in astrocytes. Considering the reciprocal regulation of astroglial and microglial activation, these results suggest ramelteon inhibits microglial activation by regulating astrocyte phenotypic changes. These effects were accompanied by the attenuation of the nuclear translocation and DNA binding activity of nuclear factor κB (NFκB) induced by KA. Consequently, ramelteon attenuated the KA-induced hippocampal neuronal loss, memory impairment, and depression-like behaviors; the effects were comparable to those of melatonin. These results suggest that ramelteon-mediated activation of melatonin receptors provides neuroprotection against KA-induced neurotoxicity in the mouse hippocampus by activating Nrf2 signaling to attenuate oxidative stress and restore glutathione homeostasis and by inhibiting NFκB signaling to attenuate neuroinflammatory changes.

Mechanism of M2 macrophages modulating astrocyte polarization through the TGF-β/PI3K/Akt pathway

Recent studies have revealed that activated astrocytes (AS) are divided into two distinct types, termed A1 and A2. A2 astrocytes are neuroprotective and promote tissue repair and regeneration following spinal cord injury. Whereas, the specific mechanism for the formation of the A2 phenotype remains unclear. This study focused on the PI3K/Akt pathway and examined whether TGF-β secreted by M2 macrophages could mediate A2 polarization by activating this pathway. In this study, we revealed that both M2 macrophages and their conditioned medium (M2-CM) could facilitate the secretion of IL-10, IL-13 and TGF-β from AS, and this effect was significantly reversed after the administration of SB431542 (a TGF-β receptor inhibitor) or LY294002 (a PI3K inhibitor). Moreover, immunofluorescence results demonstrated that TGF-β secreted by M2 macrophages could facilitate the expression of A2 biomarker S100A10 in AS; combined with the results of western blot, it was found that this effect was closely related to the activation of PI3K/Akt pathway in AS. In conclusion, TGF-β secreted by M2 macrophages may induce the conversion of AS to the A2 phenotype through the activation of the PI3K/Akt pathway.

GABAB receptor activation alters astrocyte phenotype changes induced by trimethyltin via ERK signaling in the dentate gyrus of mice

AIMS

We examined the effect of γ-aminobutyric acid (GABA)_B receptor activation on astrocyte phenotype changes induced by trimethyltin (TMT) in the dentate gyrus of mice.

MAIN METHODS

Male C57BL/6N mice received TMT (2.6 mg/kg, i.p.), and the expression of GABA_B receptors was evaluated in the hippocampus. The GABA_B receptor agonist baclofen (2.5, 5, or 10 mg/kg, i.p. × 5 at 12-h intervals) was administered 3-5 days after TMT treatment, and the expression of Iba-1, GFAP, and astrocyte phenotype markers was evaluated 6 days after TMT. SL327 (30 mg/kg, i.p.), an extracellular signal-related kinase (ERK) inhibitor, was administered 1 h after each baclofen treatment.

KEY FINDINGS

TMT insult significantly induced the astroglial expression of GABA_B receptors in the dentate molecular layer. Baclofen significantly promoted the expression of S100A10, EMP1, and CD109, but not that of C3, GGTA1, and MX1 induced by TMT. In addition, baclofen significantly increased the TMT-induced expression of p-ERK in the dentate molecular layer. Interestingly, p-ERK was more colocalized with S100A10 than with C3 after TMT insult, and a significant positive correlation was found between the expression of p-ERK and S100A10. Consistently, SL327 reversed the effect of baclofen on astrocyte phenotype changes. Baclofen also enhanced the TMT-induced astroglial expression of glial cell-derived neurotrophic factor (GDNF), an anti-inflammatory astrocytes-to-microglia mediator, and consequently attenuated Iba-1 expression and delayed apoptotic neuronal death.

SIGNIFICANCE

Our results suggest that GABA_B receptor activation increases S100A10-positive anti-inflammatory astrocytes and astroglial GDNF expression via ERK signaling after TMT excitotoxicity in the dentate molecular layer of mice.

The role of the astrocyte in subarachnoid hemorrhage and its therapeutic implications

Subarachnoid hemorrhage (SAH) is an important public health concern with high morbidity and mortality worldwide. SAH induces cell death, blood−brain barrier (BBB) damage, brain edema and oxidative stress. As the most abundant cell type in the central nervous system, astrocytes play an essential role in brain damage and recovery following SAH. This review describes astrocyte activation and polarization after SAH. Astrocytes mediate BBB disruption, glymphatic–lymphatic system dysfunction, oxidative stress, and cell death after SAH. Furthermore, astrocytes engage in abundant crosstalk with other brain cells, such as endothelial cells, neurons, pericytes, microglia and monocytes, after SAH. In addition, astrocytes also exert protective functions in SAH. Finally, we summarize evidence regarding therapeutic approaches aimed at modulating astrocyte function following SAH, which could provide some new leads for future translational therapy to alleviate damage after SAH.