Enriched Environment-Induced Neuroprotection against Cerebral Ischemia-Reperfusion Injury Might Be Mediated via Enhancing Autophagy Flux and Mitophagy Flux

Mitophagy in acute central nervous system injuries: regulatory mechanisms and therapeutic potentials

Acute central nervous system injuries, including ischemic stroke, intracerebral hemorrhage, subarachnoid hemorrhage, traumatic brain injury, and spinal cord injury, are a major global health challenge. Identifying optimal therapies and improving the long-term neurological functions of patients with acute central nervous system injuries are urgent priorities. Mitochondria are susceptible to damage after acute central nervous system injury, and this leads to the release of toxic levels of reactive oxygen species, which induce cell death. Mitophagy, a selective form of autophagy, is crucial in eliminating redundant or damaged mitochondria during these events. Recent evidence has highlighted the significant role of mitophagy in acute central nervous system injuries. In this review, we provide a comprehensive overview of the process, classification, and related mechanisms of mitophagy. We also highlight the recent developments in research into the role of mitophagy in various acute central nervous system injuries and drug therapies that regulate mitophagy. In the final section of this review, we emphasize the potential for treating these disorders by focusing on mitophagy and suggest future research paths in this area.

Environmental enrichment: a neurostimulatory approach to aging and ischemic stroke recovery and rehabilitation

Environmental enrichment (EE) represents a robust experimental framework exploring the intricate interplay between genes and the environment in shaping brain development and function. EE is recognized as a non-invasive intervention, easily translatable to elderly human cohorts, and extrapolated from research on animal aging models. Age is the most important risk factor for ischemic stroke. Research indicates that EE, characterized by increased sensory, cognitive, and social stimulation, leads to structural changes in the brain, such as enhanced dendritic complexity and synaptic density, particularly in the hippocampus and cortex. Tailored EE interventions for elderly stroke survivors include cognitively stimulating activities and participation in social groups. These interventions enhance cognitive function and support recovery by promoting neural repair. Additionally, EE helps to mitigate sensory deficits commonly observed in older adults, ultimately improving mental performance and quality of life. EE has shown promise in preventing relapse, enhancing attention, reducing anxiety, forestalling age-related DNA methylation alterations, and amplifying neurogenesis through heightened neural progenitor cell (NPC) populations. Aligning preclinical studies with clinical trials can enhance neurorehabilitation conditions for stroke patients, thereby optimizing the environments in which they recover. This can be achieved through the concerted efforts of multidisciplinary teams working collaboratively. This review explores how EE specifically impacts the aging brain and ischemic stroke, a major age-related neurological disorder with global health implications. The potential of enviro-mimetics and relevant clinical studies on EE's effects on ischemic stroke survivors are discussed. This review enhances our understanding of the effects of EE on aging and ischemic stroke, motivating further research aimed at refining strategies for stroke management and recovery.

Mechanisms Associated with Mitophagy and Ferroptosis in Cerebral Ischemia-reperfusion Injury

Ischemic stroke (IS) constitutes a major threat to human health. Vascular recanalization by intravenous thrombolysis and mechanical thrombolysis remain the most significant and effective methods for relief of ischemia. Key elements of these treatments include achieving blood-vessel recanalization, restoring brain-tissue reperfusion, and preserving the ischemic penumbra. However, in achieving the therapeutic goals of vascular recanalization, secondary damage to brain tissue from cerebral ischemia-reperfusion injury (CIRI) must also be addressed. Despite advancements in understanding the pathological processes associated with CIRI, effective interventions to prevent its onset and progression are still lacking. Recent research has indicated that mitophagy and ferroptosis are critical mechanisms in the development of CIRI, and significantly contribute to the onset and progression of IS and CIRI because of common targets and co-occurrence mechanisms. Therefore, exploring and summarizing the potential connections between mitophagy and ferroptosis during CIRI is crucial. In the present review, we mainly focused on the mechanisms of mitochondrial autophagy and ferroptosis, and their interaction, in the development of CIRI. We believe that the data show a strong relationship between mitochondrial autophagy and ferroptosis with interactive regulation. This information may underpin new potential approaches for the prevention and treatment of IS and subsequent CIRI.

A Scoping Review of Preclinical Environmental Enrichment Protocols in Models of Poststroke to Set the Foundations for Translating the Paradigm to Clinical Settings

The translation of the highly effective Environmental Enrichment (EE) paradigm from preclinical animal models to human clinical settings has been slow and showed inconsistent results. The primary translational challenge lies in defining what constitutes an EE for humans. To tackle this challenge, this study conducted a scoping review of preclinical EE protocols to explore what constitutes EE for animal models of stroke, laying the foundation for the translation of EE to human application. A systematic search was conducted in the MEDLINE, PsycINFO, and Web of Science databases to identify studies that conducted an EE intervention in the post-stroke animal model. A total of 116 studies were included in the review. A critical reflection of the characteristics of the included studies revealed that EE for post-stroke is a strategy that frequently modifies the animals' daily environment to create a richness of spatial, structural, and/or social opportunities to engage in a variety of daily life-related motor, cognitive, and social exploratory activities. These activities are relevant to the inhabiting individual and involve the activation of the body function(s) affected by the stroke. This review also identified six principles that underpinned the EE protocols: complexity (spatial and social), variety, novelty, targeting needs, scaffolding, and integration of rehabilitation tasks. These findings can be used as steppingstones to define what constitutes EE in human clinical applications and to develop a set of principles that can inform the design of EE protocols for patients after a stroke.

Relationship between enriched environment and neurodegeneration: a review from mechanism to therapy

Enriched environment (EE), as a non-pharmacological intervention, has garnered considerable attention for its potential to ameliorate neurodegenerative diseases (NDs). This review delineated the impact of EE on the biological functions associated with NDs, emphasizing its role in enhancing neural plasticity, reducing inflammation, and bolstering cognitive performance. We discussed the molecular underpinnings of the effects of EE, including modulation of key signaling pathways such as extracellular regulated kinase 1/2 (ERK1/2), mitogen-activated protein kinases (MAPK), and AMPK/SIRT1, which were implicated in neuroprotection and synaptic plasticity. Additionally, we scrutinized the influence of EE on epigenetic modifications and autophagy, processes pivotal to ND pathogenesis. Animal models, encompassing both rodents and larger animals, offer insights into the disease-modifying effects of EE, underscoring its potential as a complementary approach to pharmacological interventions. In summary, EE emerges as a promising strategy to augment cognitive function and decelerate the progression of NDs.

Calycosin Ameliorates Neuroinflammation via TLR4-Mediated Signal Following Cerebral Ischemia/Reperfusion Injury in vivo and in vitro

Background

Cerebral ischemia-reperfusion injury (CIRI) is a key pathophysiological process that leads to stroke mortality, with TLR4-mediated inflammation playing a crucial role. Our previous research highlighted the neuroprotective effects of the phytoestrogen calycosin on CIRI, although the precise mechanism remains unclear. This study aimed to explore the effects of calycosin on the HMGB1/TLR4/NF-κB signaling pathway in rat models of CIRI, both in vivo and in vitro.

Methods

In vivo, a rat CIRI model was established using middle cerebral artery occlusion (MCAO), inducing ischemia for 1.5 h followed by 24 h of reperfusion. Calycosin was administered intraperitoneally 1 h after ischemia. Neurological deficits and brain infarct volumes were evaluated. Histological changes and key protein expressions around the ischemic penumbra were assessed by H&E staining and immunofluorescence. In vitro, primary neurons and PC12 cells were subjected to oxygen-glucose deprivation/reoxygenation (OGD/R) to mimic CIRI. Cell viability was measured using a CCK8 assay, and alterations in HMGB1/TLR4/NF-κB pathway components were analyzed using qRT-PCR, Western blotting, and ELISA.

Results

In the MCAO rat model, calycosin significantly reduced neurological deficits and infarct sizes, and improved brain tissue damage following reperfusion. Similarly, in the OGD/R model, calycosin attenuated neuronal injury in PC12 cells and in primary neurons. Additionally, calycosin inhibited LPS-induced activation of the HMGB1/TLR4/NF-κB signaling pathway in PC12 cells. Both in vitro and in vivo studies have shown that calycosin effectively downregulates HMGB1 and TLR4 expression, decreases NF-κB and IκB phosphorylation, and reduces the secretion of inflammatory cytokines such as IL-6 and IL-18.

Conclusion

These findings suggest that calycosin mitigates cerebral ischemia-reperfusion injury and neuroinflammation by inhibiting the HMGB1/TLR4/NF-κB signaling pathway, thereby providing neuroprotection.

Esculetin attenuates cerebral ischemia-reperfusion injury and protects neurons through Nrf2 activation in rats

Nuclear factor erythroid 2 (NF-E2)-related factor 2 (Nrf2) is a key transcription factor in the antioxidant response and is associated with various chronic diseases. The aim of this study was to explore the action of esculetin, a natural dihydroxy coumarin, on attenuating middle cerebral artery occlusion (MCAO) and reperfusion, and whether its effect is dependent on Nrf2 activation, as well as nuclear factor-kappa B (NF-κB) inhibition. Two doses of esculetin (20 and 40 mg/kg) were tested on rats with MCAO reperfusion. Neurological deficiency, oxidative stress, and pathological analyses were performed to evaluate its effect. An in vitro analysis was also used to confirm whether its action was dependent on the Nrf2/HO-1/NQO-1 pathway. Compared with MCAO reperfusion rats, esculetin improved infarct volume and increased normal-shaped neuron cells by decreasing tumor necrosis factor-alpha (TNF-α), interleukin (IL)-6, and IL-1β levels. The oxidative stress parameter malondialdehyde (MDA) decreased and the activity of superoxide dismutase (SOD) and glutathione/glutathione disulfide (GSH/GSSG) ratio increased after esculetin treatment. Moreover, esculetin inhibited NF-κB activation induced by MCAO. In vitro, hypoxia/reoxygenation (H/R) impaired the viability of rat neuron cells and esculetin showed a neuron protection effect on cells. Nrf2 inhibitor Brusatol inhibited the activation of Nrf2, heme oxygenase-1 (HO-1), and NAD(P)H quinone oxidoreductase 1 (NQO-1) caused by esculetin and abolished its protection effect. Esculetin protected cerebral neurons from ischemia-reperfusion injury by inhibiting NF-κB and Nrf2/HO-1/NQO-1 activation.

Dorsal dentate gyrus mediated enriched environment-induced anxiolytic and antidepressant effects in cortical infarcted mice

Anxiety and depression are the most common mental health disorders worldwide, each affecting around 30% stroke survivors. These complications not only affect the functional recovery and quality of life in stroke patients, but also are distressing for caregivers. However, effective treatments are still lacking. Enriched environment (EE), characterized with novel and multi-dimensional stimulation, has been reported to exert therapeutic effects on physical and cognitive function. In addition, EE also had potential positive effects on emotional disorders after ischemic stroke; however, the underling mechanisms have not been well elucidated. This study aimed to explore the effectiveness of EE on emotional disorders after cerebral ischemia and its underling mechanism. Sensorimotor cortical infarction was induced by photothrombosis with stable infarct location and volume, resulting in motor dysfunction, anxiety and depression-like behaviors in mice, with decreased ALFF and ReHo values and decreased c-fos expression in the infarction area and adjacent regions. Seven days' EE treatment significantly improved motor function of contralateral forelimb and exhibited anxiolytic and antidepressant effects in infarcted mice. Compared to the mice housing in a standard environment, those subjected to acute EE stimulation had significantly increased ALFF and ReHo values in the bilateral somatosensory cortex (S1, S2), dorsal dentate gyrus (dDG), dorsal CA1 of hippocampus (dCA1), lateral habenular nucleus (LHb), periaqueductal gray (PAG), ipsilateral primary motor cortex (M1), retrosplenial cortex (RSC), parietal association cortex (PtA), dorsal CA3 of hippocampus (dCA3), claustrum (Cl), ventral pallidum (VP), amygdala (Amy), and contralateral auditory cortex (Au). Some of, but not all, the ipsilateral brain regions mentioned above showed accompanying increases in c-fos expression with the most significant changes in the dDG. The number of FosB positive cells in the dDG, decreased in infarcted mice, was significantly increased after chronic EE treatment. Chemogenetic activation of dDG neurons reduced anxiety and depressive-like behaviors in infarcted mice, while neuronal inhibition resulted in void of the anxiolytic and antidepressant effects of EE. Altogether, these findings indicated that dDG neurons may mediate EE-triggered anxiolytic and antidepressant effects in cortical infarcted mice.

Environmental Enrichment for Stroke and Traumatic Brain Injury: Mechanisms and Translational Implications

Acquired brain injuries, such as ischemic stroke, intracerebral hemorrhage (ICH), and traumatic brain injury (TBI), can cause severe neurologic damage and even death. Unfortunately, currently, there are no effective and safe treatments to reduce the high disability and mortality rates associated with these brain injuries. However, environmental enrichment (EE) is an emerging approach to treating and rehabilitating acquired brain injuries by promoting motor, sensory, and social stimulation. Multiple preclinical studies have shown that EE benefits functional recovery, including improved motor and cognitive function and psychological benefits mediated by complex protective signaling pathways. This article provides an overview of the enriched environment protocols used in animal models of ischemic stroke, ICH, and TBI, as well as relevant clinical studies, with a particular focus on ischemic stroke. Additionally, we explored studies of animals with stroke and TBI exposed to EE alone or in combination with multiple drugs and other rehabilitation modalities. Finally, we discuss the potential clinical applications of EE in future brain rehabilitation therapy and the molecular and cellular changes caused by EE in rodents with stroke or TBI. This article aims to advance preclinical and clinical research on EE rehabilitation therapy for acquired brain injury. © 2024 American Physiological Society. Compr Physiol 14:5291-5323, 2024.

A bibliometric analysis of research foci and trends in cerebral ischemia-reperfusion injury involving autophagy during 2008 to 2022

BACKGROUND

Cerebral ischemia-reperfusion injury (CIRI) is a complex pathophysiological process that typically occurs during the treatment of ischemia, with limited therapeutic options. Autophagy plays a vital role during the reperfusion phase and is a potential therapeutic target for preventing and treating cerebral ischemia-reperfusion injury.

METHODS

We conducted a comprehensive search of the Web of Science Core Collection for publications related to cerebral ischemia-reperfusion injury with autophagy, published between January 1, 2008, and January 1, 2023. We analyzed the selected publications using VOSviewer, CiteSpace, and other bibliometric tools.

RESULTS

Our search yielded 877 relevant publications. The field of autophagy in cerebral ischemia-reperfusion injury has grown rapidly since 2016. China has been the leading contributor to publications, followed by the USA and Iran. Chen Zhong and Qin Zhenghong have been influential in this field but have yet to reach all groups. In addition, there has been a shortage of collaboration among authors from different institutions. Our literature and keyword analysis identified Neurovascular protection (#11 Neuroprotective, #13 Neurovascular units, etc) and Inflammation (NLRP3 inflammasome) as popular research directions. Furthermore, the terms "Blood-Brain Barrier," "Mitophagy," and "Endoplasmic reticulum stress" have been frequently used and may be hot research topics in the future.

CONCLUSIONS

The role of autophagy in cerebral ischemia-reperfusion injury remains unclear, and the specific mechanisms of drugs used to treat ischemia-reperfusion injury still need to be explored. This work outlines the changing trends in investigating cerebral ischemia-reperfusion injury involving autophagy and suggests future lines of inquiry.

The environmental enrichment ameliorates chronic cerebral hypoperfusion-induced cognitive impairment by activating autophagy signaling pathway and improving synaptic function in hippocampus

BACKGROUND

Chronic cerebral hypoperfusion (CCH) is a frequently observed underlying pathology of both Alzheimer's disease (AD) and vascular dementia (VD), which is a common consequence of cerebral blood flow (CBF) dysregulation. Synaptic damage has been proven as a crucial causative factor for CCH-related cognitive impairment. This study aimed to investigate the neuroprotective impact of environmental enrichment (EE) intervention on CCH-induced synaptic destruction and the consequent cognitive impairment. Furthermore, the underlying mechanism of this neuroprotective effect was explored to provide new insights into therapeutic interventions for individuals suffering from AD or VD.

METHODS

In this experiment, all rats were initially acclimatized to a standard environment (SE) for a period of one week. On the seventh day, rats underwent either bilateral common carotid artery occlusion (2VO) surgery or sham surgery (Sham) before being subjected to a four-week procedure of exposure to an EE, except for the control group. During the EE or SE procedure, intraperitoneal injection of chloroquine (CQ) into rats was performed once daily for four weeks. Following this, cognitive function was assessed using the Morris water maze (MWM) test. The synapse ultrastructure was subsequently observed using transmission electron microscopy. Expression levels of autophagy-related proteins (LC3, LAMP1, and P62) and synapse-related proteins (Synapsin I and PSD-95) were detected through Western blotting. Finally, immunofluorescence was used to examine the expression levels of Synapsin I and PSD-95 and the colocalization of LAMP-1 and LC3 in the hippocampus.

RESULTS

After undergoing 2VO, rats exposed to SE exhibited cognitive impairment, autophagic dysfunction, and synapse damage. The synapse damage was evidenced by ultrastructural damage and degradation of synapse-related proteins. However, these effects were significantly mitigated by exposure to an EE intervention. Moreover, the intervention led to an improvement in autophagic dysfunction.

CONCLUSION

The study found that EE had a positive impact on CCH-induced synaptic damage. Specifically, EE was found to increase synaptic plasticity-associated proteins and postsynaptic density thickness, while decreasing synaptic space. This multifaceted effect resulted in an amelioration of CCH-induced cognitive impairment. It was shown that this beneficial outcome was mediated via the activation of the autophagy-lysosomal pathway. Overall, the findings suggest that EE may have a therapeutic potential for cognitive impairments associated with CCH through autophagy-mediated synaptic improvement.

Enriched environment attenuates ferroptosis after cerebral ischemia/reperfusion injury by regulating iron metabolism

Preventing neuronal death after ischemic stroke (IS) is crucial for neuroprotective treatment, yet current management options are limited. Enriched environment (EE) is an effective intervention strategy that promotes the recovery of neurological function after cerebral ischemia/reperfusion (I/R) injury. Ferroptosis has been identified as one of the mechanisms of neuronal death during IS, and inhibiting ferroptosis can reduce cerebral I/R injury. Our previous research has demonstrated that EE reduced ferroptosis by inhibiting lipid peroxidation, but the underlying mechanism still needs to be investigated. This study aims to explore the potential molecular mechanisms by which EE modulates iron metabolism to reduce ferroptosis. The experimental animals were randomly divided into four groups based on the housing environment and the procedure the animals received: the sham-operated + standard environment (SSE) group, the sham-operated + enriched environment (SEE) group, the ischemia/reperfusion + standard environment (ISE) group, and the ischemia/reperfusion + enriched environment (IEE) group. The results showed that EE reduced IL-6 expression during cerebral I/R injury, hence reducing JAK2-STAT3 pathway activation and hepcidin expression. Reduced hepcidin expression led to decreased DMT1 expression and increased FPN1 expression in neurons, resulting in lower neuronal iron levels and alleviated ferroptosis. In addition, EE also reduced the expression of TfR1 in neurons. Our research suggested that EE played a neuroprotective role by modulating iron metabolism and reducing neuronal ferroptosis after cerebral I/R injury, which might be achieved by inhibiting inflammatory response and down-regulating hepcidin expression.

Targeting neuronal mitophagy in ischemic stroke: an update

Cerebral ischemia is a neurological disorder associated with complex pathological mechanisms, including autophagic degradation of neuronal mitochondria, or termed mitophagy, following ischemic events. Despite being well-documented, the cellular and molecular mechanisms underlying the regulation of neuronal mitophagy remain unknown. So far, the evidence suggests neuronal autophagy and mitophagy are separately regulated in ischemic neurons, the latter being more likely activated by reperfusional injury. Specifically, given the polarized morphology of neurons, mitophagy is regulated by different neuronal compartments, with axonal mitochondria being degraded by autophagy in the cell body following ischemia-reperfusion insult. A variety of molecules have been associated with neuronal adaptation to ischemia, including PTEN-induced kinase 1, Parkin, BCL2 and adenovirus E1B 19-kDa-interacting protein 3 (Bnip3), Bnip3-like (Bnip3l) and FUN14 domain-containing 1. Moreover, it is still controversial whether mitophagy protects against or instead aggravates ischemic brain injury. Here, we review recent studies on this topic and provide an updated overview of the role and regulation of mitophagy during ischemic events.

Demand Coupling Drives Neurodegeneration: A Model of Age-Related Cognitive Decline and Dementia

The societal burden of Alzheimer's Disease (AD) and other major forms of dementia continues to grow, and multiple pharmacological agents directed towards modifying the pathological "hallmarks" of AD have yielded disappointing results. Though efforts continue towards broadening and deepening our knowledge and understanding of the mechanistic and neuropathological underpinnings of AD, our previous failures motivate a re-examination of how we conceptualize AD pathology and progression. In addition to not yielding effective treatments, the phenotypically heterogeneous biological processes that have been the primary area of focus to date have not been adequately shown to be necessary or sufficient to explain the risk and progression of AD. On the other hand, a growing body of evidence indicates that lifestyle and environment represent the ultimate level of causation for AD and age-related cognitive decline. Specifically, the decline in cognitive demands over the lifespan plays a central role in driving the structural and functional deteriorations of the brain. In the absence of adequate cognitive stimulus, physiological demand-function coupling leads to downregulation of growth, repair, and homeostatic processes, resulting in deteriorating brain tissue health, function, and capacity. In this setting, the heterogeneity of associated neuropathological tissue hallmarks then occurs as a consequence of an individual's genetic and environmental background and are best considered downstream markers of the disease process rather than specific targets for direct intervention. In this manuscript we outline the evidence for a demand-driven model of age-related cognitive decline and dementia and why it mandates a holistic approach to dementia treatment and prevention that incorporates the primary upstream role of cognitive demand.