Intermittent Metabolic Switching and Vascular Cognitive Impairment.

Intermittent fasting (IF), a dietary pattern alternating between eating and fasting periods within a 24-hour cycle, has garnered recognition for its potential to enhance both healthspan and lifespan in animal models and humans. It also shows promise in alleviating age-related diseases, including neurodegeneration. Vascular cognitive impairment (VCI) spans a severity range from mild cognitive deficits to severe cognitive deficits and loss of function in vascular dementia. Chronic cerebral hypoperfusion has emerged as a significant contributor to VCI, instigating vascular pathologies such as microbleeds, blood-brain barrier dysfunction, neuronal loss and white matter lesions. Preclinical studies in rodents strongly suggest that IF has the potential to attenuate pathological mechanisms, including excitotoxicity, oxidative stress, inflammation, and cell death pathways in VCI models. Hence, this supports evaluating IF in clinical trials for both existing and at-risk VCI patients. This review compiles existing data supporting IF's potential in treating VCI-related vascular and neuronal pathologies, emphasizing the mechanisms by which IF may mitigate these issues. Hence providing a comprehensive overview of the available data supporting IF's potential in treating VCI by emphasizing the underlying mechanisms that make IF a promising intervention for VCI.

Role of Mitogen-Activated Protein (MAP) Kinase Pathways in Metabolic Diseases.

Physiological processes that govern the normal functioning of mammalian cells are regulated by a myriad of signalling pathways. Mammalian mitogen-activated protein (MAP) kinases constitute one of the major signalling arms and have been broadly classified into four groups that include extracellular signal-regulated protein kinase (ERK), c-Jun N-terminal kinase (JNK), p38, and ERK5. Each signalling cascade is governed by a wide array of external and cellular stimuli, which play a critical part in mammalian cells in the regulation of various key responses, such as mitogenic growth, differentiation, stress responses, as well as inflammation. This evolutionarily conserved MAP kinase signalling arm is also important for metabolic maintenance, which is tightly coordinated via complicated mechanisms that include the intricate interaction of scaffold proteins, recognition through cognate motifs, action of phosphatases, distinct subcellular localisation, and even post-translational modifications. Aberration in the signalling pathway itself or their regulation has been implicated in the disruption of metabolic homeostasis, which provides a pathophysiological foundation in the development of metabolic syndrome. Metabolic syndrome is an umbrella term that usually includes a group of closely associated metabolic diseases such as hyperglycaemia, hyperlipidaemia, and hypertension. These risk factors exacerbate the development of obesity, diabetes, atherosclerosis, cardiovascular diseases, and hepatic diseases, which have accounted for an increase in the worldwide morbidity and mortality rate. This review aims to summarise recent findings that have implicated MAP kinase signalling in the development of metabolic diseases, highlighting the potential therapeutic targets of this pathway to be investigated further for the attenuation of these diseases.

Inflammasome Activation Mediates Apoptotic and Pyroptotic Death in Astrocytes Under Ischemic Conditions.

Inflammation is a hallmark mechanism of ischemic stroke-induced brain injury. Recent studies have shown that an intracellular multimeric protein complex known as an inflammasome is a key factor for inducing an inflammatory response, and apoptotic and pyroptotic cell death in ischemic stroke. Inflammasome assembly leads to the activation of pro-inflammatory caspases, and the maturation and secretion of pro-inflammatory cytokines IL-1ß and IL-18. While the role of inflammasomes in ischemic stroke-induced neuronal death, and microglial activation and cell death have been established, little is known about the role of inflammasomes in astrocytes under ischemic conditions. In this study, we investigated the expression and activation of inflammasome components in protoplasmic and fibrous astrocytes under ischemic conditions. We found that both protoplasmic and fibrous astrocytes expressed a differential increase in inflammasome protein components, and that their activation promoted maturation of IL-1ß and IL-18, and secretion of IL-1ß, as well as initiating apoptotic and pyroptotic cell death. Pharmacological inhibition of caspase-1 decreased expression of cleaved caspase-1 and production of mature IL-1ß, and protected against inflammasome-mediated apoptotic and pyroptotic cell death. Overall, this study provides novel insights into the role of inflammasome signaling in astrocytes under ischemic conditions.

Chronic cerebral hypoperfusion: a critical feature in unravelling the etiology of vascular cognitive impairment.

Vascular cognitive impairment (VCI) describes a wide spectrum of cognitive deficits related to cerebrovascular diseases. Although the loss of blood flow to cortical regions critically involved in cognitive processes must feature as the main driver of VCI, the underlying mechanisms and interactions with related disease processes remain to be fully elucidated. Recent clinical studies of cerebral blood flow measurements have supported the role of chronic cerebral hypoperfusion (CCH) as a major driver of the vascular pathology and clinical manifestations of VCI. Here we review the pathophysiological mechanisms as well as neuropathological changes of CCH. Potential interventional strategies for VCI are also reviewed. A deeper understanding of how CCH can lead to accumulation of VCI-associated pathology could potentially pave the way for early detection and development of disease-modifying therapies, thus allowing preventive interventions instead of symptomatic treatments.

A mechanistic perspective on the health promoting effects of alcohol - A focus on epigenetics modification.

While the detrimental effects of binge drinking are well recognized, low-to-moderate alcohol consumption may be beneficial to health, although the underlying mechanism(s) remains elusive. In this opinion article, we will examine the effects of low dose alcohol consumption from the perspective of epigenetic modulation. Biochemically, alcohol is metabolized into acetate and subsequently to acetyl-coA, which can modulate histone acetylation levels. While elevated levels of acetyl-CoA are detrimental for longevity, we argue that diminished acetyl-CoA also negatively affects fatty acid biosynthesis and histone acetylation, which play a critical role in gene expression and, ultimately, health span. Since mitochondrial function and glucose metabolism, which provide the main source of nucleocytoplasmic acetyl-CoA, are compromised with age, alcohol-derived acetate could be an alternative source of acetyl-CoA to compensate. Hence, the health benefits of low ethanol consumption may be more pronounced after midlife, since mitochondrial function and/or glucose metabolism are diminished in this phase of the life course. Indeed, various clinical alcohol consumption studies concur with this notion, and have shown that a low dose of regular alcohol intake after midlife brings about various health and survival benefits. The requirement for regular alcohol intake may also reflect the transient nature of ethanol-induced histone acetylation. Conversely, ethanol may also stimulate carcinogenesis by inhibiting DNA methylation, as it was shown to reduce various pathways leading to DNA and histone methylation. However, unlike acetylation, where ethanol directly increases the substrate for acetylation, this effect was only observed in the high alcohol exposure cohort. While alcohol-derived acetate may be beneficial for health after midlife, various detrimental effects of alcohol consumption remain, and hence, we do not advocate excessive drinking to increase acetate. This opinion article establishes a possible role of ethanol-derived acetate in achieving homeostasis and sustaining an organism's health span.

Intermittent Fasting Attenuates Hallmark Vascular and Neuronal Pathologies in a Mouse Model of Vascular Cognitive Impairment.

Background - Chronic cerebral hypoperfusion (CCH) is an important pathophysiological mechanism of vascular cognitive impairment (VCI). The heterogeneous effects of CCH complicate establishing single target therapies against VCI and its more severe form, vascular dementia (VaD). Intermittent fasting (IF) has multiple targets and is neuroprotective across a range of disease conditions including stroke, but its effects against CCH-induced neurovascular pathologies remain to be elucidated. We therefore assessed the effect of IF against CCH-associated neurovascular pathologies and investigated its underlying mechanisms. Methods - Male C57BL/6NTac mice were subjected to either ad libitum feeding (AL) or IF (16 hours of fasting per day) for 4 months. In both groups, CCH was experimentally induced by the bilateral common carotid artery stenosis (BCAS) method. Sham operated groups were used as controls. Measures of leaky microvessels, blood-brain barrier (BBB) permeability, protein expression of tight junctions, extracellular matrix components and white matter changes were determined to investigate the effect of IF against CCH-induced neurovascular pathologies. Results - IF alleviated CCH-induced neurovascular pathologies by reducing the number of leaky microvessels, BBB breakdown and loss of tight junctional proteins. In addition, IF mitigated the severity of white matter lesions, and maintained myelin basic protein levels, while concurrently reducing hippocampal neuronal cell death. Furthermore, IF reduced the CCH-induced increase in levels of matrix metalloproteinase (MMP)-2 and its upstream activator MT1-MMP, which are involved in the breakdown of the extracellular matrix that is a core component of the BBB. Additionally, we observed that IF reduced CCH-induced increase in the oxidative stress marker malondialdehyde, and increased antioxidant markers glutathione and superoxide dismutase. Overall, our data suggest that IF attenuates neurovascular damage, metalloproteinase and oxidative stress-associated pathways, and cell death in the brain following CCH in a mouse model of VCI. Conclusion - Although IF has yet to be assessed in human patients with VaD, our data suggest that IF may be an effective means of preventing the onset or suppressing the development of neurovascular pathologies in VCI and VaD.

Time-restricted feeding modulates the DNA methylation landscape, attenuates hallmark neuropathology and cognitive impairment in a mouse model of vascular dementia.

Objective: Vascular dementia (VaD) is the second most common cause of dementia worldwide. The increasing contribution of lifestyle-associated risk factors to VaD has pointed towards gene-environment interactions (i.e. epigenetics). This study thus aims to investigate the DNA methylation landscape in a chronic cerebral hypoperfusion (CCH) mouse model of VaD. As a nexus between the gene-environment interaction, intermittent fasting (IF) was introduced as a prophylactic intervention. Methods: Bilateral common carotid artery stenosis (BCAS) was used to induce CCH by placing micro-coils of 0.18 mm in each common carotid artery of the mice. The coils were left in the mice for 7, 15 and 30 days to study temporal differences. IF was introduced for 16 h daily for 4 months prior to BCAS. Reduced Representation Bisulfite Sequencing (RRBS) was used to study the DNA methylation landscape. Cognitive impairment was measured using Barnes Maze Test. White matter lesions (WML) and neuronal loss were measured using Luxol fast blue staining and cresyl violet staining respectively. Results: IF mice subjected to CCH displayed significantly better cognitive learning ability and memory, improved neuropathological alterations with reduced WMLs and neuronal loss. Modulation of DNA methylation patterns in the cortex of AL CCH mice was re-modelled and signs of reversal was observed in IF CCH mice across all three timepoints. Conclusions: These findings provide an understanding of how IF may protect the brain against damage caused by CCH and show promise in offering potential beneficial effects in mitigating the neuropathology and cognitive deficits in VaD.

Effects of dietary interventions on telomere dynamics.

Telomeres play a critical role in maintaining cellular fate through tight regulation of cell division and DNA damage or repair. Over the years, it is established that biological ageing is defined by a gradual derangement in functionality, productivity, and robustness of biological processes. The link between telomeres and ageing is highlighted when derangement in telomere biology often leads to premature ageing and concomitant accompaniment of numerous age-associated diseases. Unfortunately, given that ageing is a biologically complicated intricacy, measures to reduce morbidity and improve longevity are still largely in the infancy stage. Recently, it was discovered that dietary habits and interventions might play a role in promoting successful healthy ageing. The intricate relationship between dietary components and its potential to protect the integrity of telomeres may provide unprecedented health benefits and protection against age-related pathologies. However, more focused prospective and follow-up studies with and without interventions are needed to unequivocally link dietary interventions with telomere maintenance in humans. This review aims to summarise recent findings that investigate the roles of nutrition on telomere biology and provide enough evidence for further studies to consider the topic of nutrigenomics and its contributions toward healthy ageing and concomitant strategy against age-associated diseases.

Pathophysiology of blood brain barrier dysfunction during chronic cerebral hypoperfusion in vascular cognitive impairment.

The prevalence of cerebrovascular disease increases with age, placing the elderly at a greater lifetime risk for dementia. Vascular cognitive impairment (VCI) encompasses a spectrum of cognitive deficits from mild cognitive impairment to dementia. VCI and its most severe form, vascular dementia (VaD), is becoming a major public health concern worldwide. As growing efforts are being taken to understand VCI and VaD in animal models and humans, the pathogenesis of the disease is being actively explored. It is postulated that chronic cerebral hypoperfusion (CCH) is a major cause of VCI. CCH activates a molecular and cellular injury cascade that leads to breakdown of the blood brain barrier (BBB) and neurodegeneration. The BBB tightly regulates the movement of substances between the blood and the brain, thereby regulating the microenvironment within the brain parenchyma. Here we illustrate how BBB damage is causal in the pathogenesis of VCI through the increased activation of pathways related to excitotoxicity, oxidative stress, inflammation and matrix metalloproteinases that lead to downstream perivascular damage, leukocyte infiltration and white matter changes in the brain. Thus, CCH-induced BBB damage may initiate and contribute to a vicious cycle, resulting in progressive neuropathological changes of VCI in the brain. This review outlines the molecular and cellular mechanisms that govern BBB breakdown during CCH and highlights the clinical evidence in identifying at-risk VCI patients.

The role of inflammasomes in vascular cognitive impairment.

There is an increasing prevalence of Vascular Cognitive Impairment (VCI) worldwide, and several studies have suggested that Chronic Cerebral Hypoperfusion (CCH) plays a critical role in disease onset and progression. However, there is a limited understanding of the underlying pathophysiology of VCI, especially in relation to CCH. Neuroinflammation is a significant contributor in the progression of VCI as increased systemic levels of the proinflammatory cytokine interleukin-1ß (IL-1ß) has been extensively reported in VCI patients. Recently it has been established that CCH can activate the inflammasome signaling pathways, involving NLRP3 and AIM2 inflammasomes that critically regulate IL-1ß production. Given that neuroinflammation is an early event in VCI, it is important that we understand its molecular and cellular mechanisms to enable development of disease-modifying treatments to reduce the structural brain damage and cognitive deficits that are observed clinically in the elderly. Hence, this review aims to provide a comprehensive insight into the molecular and cellular mechanisms involved in the pathogenesis of CCH-induced inflammasome signaling in VCI.

AIM2 inflammasome mediates apoptotic and pyroptotic death in the cerebellum following chronic hypoperfusion.

Vascular dementia (VaD) is the second most common form of dementia and is caused by vascular pathologies resulting in chronic cerebral hypoperfusion (CCH)- induced brain injury, and ultimately cognitive impairment and memory loss. Several lines of evidence have demonstrated chronic inflammation may be involved in VaD disease progression. It is now recognized that a major contributor to cerebral and systemic chronic inflammation involves the activation of innate immune molecular complexes termed inflammasomes. Whilst previous studies on animal models of VaD have focused on the cortex, hippocampus and striatum, few studies have investigated the effect of CCH on the cerebellum. Emerging studies have found new roles of the cerebellum in cognition, based on its structural interconnectivity with other brain regions and clinical relevance in neuropsychological deficits. In the present study, we conducted our investigation on the cerebellum using a CCH mouse model of VaD following bilateral common carotid artery stenosis (BCAS). This study is the first to characterize an increased expression of inflammasome receptors, adaptor and effector proteins, markers of inflammasome activation, proinflammatory cytokines, and apoptotic and pyroptotic cell death proteins in the cerebellum following CCH. Furthermore, in AIM2 knockout mice, we observed attenuated inflammasome-mediated production of proinflammatory cytokines, apoptosis, and pyroptosis in the cerebellum following CCH. Collectively, our findings provide novel evidence that AIM2 inflammasome activation promotes apoptosis and pyroptosis in the cerebellum following chronic hypoperfusion in a mouse model of VaD.

Intermittent fasting attenuates inflammasome-associated apoptotic and pyroptotic death in the brain following chronic hypoperfusion.

Chronic cerebral hypoperfusion (CCH) has been shown to initiate several inflammatory pathways that can contribute to cognitive deficits and memory loss in vascular cognitive impairment (VCI). Multi-protein complexes termed inflammasomes that may be involved in the inflammatory response to CCH has already been shown to contribute to the inflammatory process and cell death following acute cerebral ischemia. Intermittent fasting (IF) has already been shown to decrease inflammasome activation and protect the brain from ischemic stroke; however, its effects during CCH remains unknown. The present study investigated the impact of IF (16 h of food deprivation daily) for four months on inflammasome-mediated cell death in the cerebellum following CCH in a mouse model of VCI using fourteen to sixteen-week-old male C57BL/6NTac mice. Here we demonstrated that IF decreased inflammasome activation, and initiation of apoptotic and pyroptotic cell death pathways as reflected by the reduction (20-30%) in the expression levels of key effector proteins and cell death markers in the cerebellum following CCH. In summary, our results indicate that IF can attenuate the inflammatory response and cell death pathways in the brain following chronic hypoperfusion in a mouse model of VCI.

Hippocampal transcriptome profiling reveals common disease pathways in chronic hypoperfusion and aging.

Vascular dementia (VaD) is a progressive cognitive impairment of vascular etiology. VaD is characterized by cerebral hypoperfusion, increased blood-brain barrier permeability and white matter lesions. An increased burden of VaD is expected in rapidly aging populations. The hippocampus is particularly susceptible to hypoperfusion, and the resulting memory impairment may play a crucial role in VaD. Here we have investigated the hippocampal gene expression profile of young and old mice subjected to cerebral hypoperfusion by bilateral common carotid artery stenosis (BCAS). Our data in sham-operated young and aged mice reveal an age-associated decline in cerebral blood flow and differential gene expression. In fact, BCAS and aging caused broadly similar effects. However, BCAS-induced changes in hippocampal gene expression differed between young and aged mice. Specifically, transcriptomic analysis indicated that in comparison to young sham mice, many pathways altered by BCAS in young mice resembled those already present in sham aged mice. Over 30 days, BCAS in aged mice had minimal effect on either cerebral blood flow or hippocampal gene expression. Immunoblot analyses confirmed these findings. Finally, relative to young sham mice the cell type-specific profile of genes in both young BCAS and old sham animals further revealed common cell-specific genes. Our data provide a genetic-based molecular framework for hypoperfusion-induced hippocampal damage and reveal common cellular signaling pathways likely to be important in the pathophysiology of VaD.

Natural products as geroprotectors: An autophagy perspective.

Over the past decade, significant attention has been given to repurposing Food and Drug Administration approved drugs to treat age-related diseases. In contrast, less consideration has been given to natural bioactive compounds. Consequently, there have been limited attempts to translate these compounds. Autophagy is a fundamental biological pathway linked to aging, and numerous strategies to enhance autophagy have been shown to extend lifespan. Interestingly, there are a number of natural products that are reported to modulate autophagy, and here we describe a number of them that activate autophagy through diverse molecular and cellular mechanisms. Among these, Urolithin A, Spermidine, Resveratrol, Fatty Acids and Phospholipids, Trehalose and Lithium are featured in detail. Finally, we outline possible strategies to optimise and increase the translatability of natural products, with the overall aim of delaying the ageing process and improving human healthspan.

AIM2 inflammasome mediates hallmark neuropathological alterations and cognitive impairment in a mouse model of vascular dementia.

Chronic cerebral hypoperfusion is associated with vascular dementia (VaD). Cerebral hypoperfusion may initiate complex molecular and cellular inflammatory pathways that contribute to long-term cognitive impairment and memory loss. Here we used a bilateral common carotid artery stenosis (BCAS) mouse model of VaD to investigate its effect on the innate immune response-particularly the inflammasome signaling pathway. Comprehensive analyses revealed that chronic cerebral hypoperfusion induces a complex temporal expression and activation of inflammasome components and their downstream products (IL-1ß and IL-18) in different brain regions, and promotes activation of apoptotic and pyroptotic cell death pathways. Polarized glial-cell activation, white-matter lesion formation and hippocampal neuronal loss also occurred in a spatiotemporal manner. Moreover, in AIM2 knockout mice we observed attenuated inflammasome-mediated production of proinflammatory cytokines, apoptosis, and pyroptosis, as well as resistance to chronic microglial activation, myelin breakdown, hippocampal neuronal loss, and behavioral and cognitive deficits following BCAS. Hence, we have demonstrated that activation of the AIM2 inflammasome substantially contributes to the pathophysiology of chronic cerebral hypoperfusion-induced brain injury and may therefore represent a promising therapeutic target for attenuating cognitive impairment in VaD.

CD137 Ligand-CD137 Interaction is Required For Inflammasome-Associated Brain Injury Following Ischemic Stroke.

The CD137L-CD137 axis is a potent co-stimulatory immune checkpoint regulator that forms a bidirectional signaling pathway between the CD137 ligand (CD137L) and CD137 receptor to regulate immunological activities. This study investigated the potential involvement of the CD137L-CD137 axis on inflammasome-associated brain injury and neurological deficits in a mouse model of focal ischemic stroke. Cerebral ischemia was induced in male C57BL/6J wild-type (WT), CD137L-deficient (CD137L KO) and CD137-deficient (CD137 KO) mice by middle cerebral artery occlusion (MCAO; 60 min), followed by reperfusion (6 h and 24 h). Brain infarct volume and neurological deficit scores were significantly lower in both CD137L KO and CD137 KO mice compared to WT controls. Moreover, CD137L-deficient brains had significantly lower levels of the pyroptotic protein, NT-Gasdermin D, while CD137-deficient brains had significantly lower levels of the pro-apoptotic proteins, cleaved caspase-3, pyroptotic protein, NT-Gasdermin D, and of the secondary pyroptotic protein NT-Gasdermin E, following ischemic stroke. This protection by CD137L and CD137 deletion was associated with a significant decrease in inflammasome signaling. In conclusion, our data provide evidence for the first time that the CD137L-CD137 axis contributes to brain injury and neurological deficits by activating the inflammasome signaling pathway following ischemic stroke.

Evidence that NLRC4 inflammasome mediates apoptotic and pyroptotic microglial death following ischemic stroke.

Stroke is the second leading cause of death in the world and a major cause of long-term disability. Recent evidence has provided insight into a newly described inflammatory mechanism that contributes to neuronal and glial cell death, and impaired neurological outcome following ischemic stroke - a form of sterile inflammation involving innate immune complexes termed inflammasomes. It has been established that inflammasome activation following ischemic stroke contributes to neuronal cell death, but little is known about inflammasome function and cell death in activated microglial cells following cerebral ischemia. Microglia are considered the resident immune cells that function as the primary immune defense in the brain. This study has comprehensively investigated the expression and activation of NLRP1, NLRP3, NLRC4 and AIM2 inflammasomes in isolates of microglial cells subjected to simulated ischemic conditions and in the brain following ischemic stroke. Immunoblot analysis from culture media indicated microglial cells release inflammasome components and inflammasome activation-dependent pro-inflammatory cytokines following ischemic conditions. In addition, a functional role for NLRC4 inflammasomes was determined using siRNA knockdown of NLRC4 and pharmacological inhibitors of caspase-1 and -8 to target apoptotic and pyroptotic cell death in BV2 microglial cells under ischemic conditions. In summary, the present study provides evidence that the NLRC4 inflammasome complex mediates the inflammatory response, as well as apoptotic and pyroptotic cell death in microglial cells under in vitro and in vivo ischemic conditions.

Acute or Delayed Systemic Administration of Human Amnion Epithelial Cells Improves Outcomes in Experimental Stroke.

BACKGROUND AND PURPOSE: Human amnion epithelial cells (hAECs) are nonimmunogenic, nontumorigenic, anti-inflammatory cells normally discarded with placental tissue. We reasoned that their profile of biological features, wide availability, and the lack of ethical barriers to their use could make these cells useful as a therapy in ischemic stroke. METHODS: We tested the efficacy of acute (1.5 hours) or delayed (1-3 days) poststroke intravenous injection of hAECs in 4 established animal models of cerebral ischemia. Animals included young (7-14 weeks) and aged mice (20-22 months) of both sexes, as well as adult marmosets of either sex. RESULTS: We found that hAECs administered 1.5 hours after stroke in mice migrated to the ischemic brain via a CXC chemokine receptor type 4-dependent mechanism and reduced brain inflammation, infarct development, and functional deficits. Furthermore, if hAECs administration was delayed until 1 or 3 days poststroke, long-term functional recovery was still augmented in young and aged mice of both sexes. We also showed proof-of-principle evidence in marmosets that acute intravenous injection of hAECs prevented infarct development from day 1 to day 10 after stroke. CONCLUSIONS: Systemic poststroke administration of hAECs elicits marked neuroprotection and facilitates mechanisms of repair and recovery.