Microglial REV-ERBα regulates inflammation and lipid droplet formation to drive tauopathy in male mice

Allicin Improves Diet-Induced Nonalcoholic Steatohepatitis and Gut Microbiota Dysbiosis in Mice via the Involvement of the Circadian Clock Gene Rev-erbα

Nonalcoholic Steatohepatitis (NASH) is a progressive liver disease characterized by inflammation and liver damage. Allicin, a bioactive compound derived from garlic, has demonstrated anti-inflammatory and antioxidant properties. This study explores the effects of allicin on NASH and gut microbiota dysbiosis induced by a high-fat, high-fructose diet (HFFD) in mice. Allicin supplementation significantly alleviated hepatic inflammation, improved glucose metabolism, and modulated the circadian rhythm gene Rev-erbα, which plays a critical role in regulating inflammation. The anti-inflammatory effects of allicin were diminished in Si-Rev-erbα-treated HepG2 cells, highlighting the importance of circadian regulation in mediating these effects. Allicin's anti-inflammatory effects were associated with increased levels of short-chain fatty acids (SCFAs) and the restoration of diurnal oscillations in proinflammatory cytokines and gut microbiota composition, particularly in genera, such as Akkermansia, Bacteroidetes, and Lactobacillus. These findings suggest that allicin could be a promising therapeutic approach for managing NASH, liver dysfunction, and related metabolic disorders through the modulation of circadian rhythms and the gut microbiome.

Shuangxia Decoction attenuates sleep disruption in 5×FAD mice through neuroinflammation inhibition: An integrative analysis of transcriptomic and molecular biology investigations

ETHNOPHARMACOLOGICAL RELEVANCE

Alzheimer's disease (AD) is a neurodegenerative disease characterized by memory and learning deficits. Circadian rhythm disruption-induced sleep disruption is frequently observed in AD patients. The Shuangxia Decoction (SXD) comprising Pinellia ternata (Thunb.) Breit. (Banxia) and Prunella vulgaris L. (Xiakucao), has been effectively used to treate sleep disruption for thousands of years. However, the mechanisms by which SXD treated AD through circadian rhythm-related pathways remain unexplored.

AIMS OF THE STUDY

This research sought to determine the efficacy, mechanisms, and active compounds of SXD in AD treatment via an integrative approach.

MATERIALS AND METHODS

We conducted a chronic jet lag (CJL) protocol in wild-type (WT) mice and monitored their rest/activity to compare their rest/activity period among WT, CJL, and CJD + SXD groups. In addition, we evaluated the impact of SXD on the cognitive and Aβ burden of 5 × FAD mice by behavioral tests and Thioflavin staining. The underlying pathway analysis of SXD was revealed through transcriptomic and biology experimental validation. The active compounds of SXD were further analyzed using the UPLC-MS, molecular docking, and cellular thermal shift assay (CESTA).

RESULTS

Our study demonstrated a rapid recovery of rest/activity period in CJL mice following SXD treatment. Additionally, SXD treatment alleviated Aβ plaque accumulation, subsequently preserving cognitive behavior and motor ability in 5 × FAD mice. Moreover, SXD significantly enhanced neuronal synaptic plasticity dendritic plasticity in CA1 neurons of 5 × FAD mice. Transcriptomic analysis showed upregulation of the neuroinflammation-related pathway in 5 × FAD mice. Subsequent heatmap analysis indicated a suppression of inflammatory factor secretion (Cd68, Trem2, IL-6, IL-1β, Cxc3r1, Tnf et al.) and an increase of anti-inflammatory factor secretion (IL4, Ccl19, Ccl21a et al.) following SXD treatment in the 5 × FAD mice. Meanwhile, SXD upregulated positive regulators involved in the circadian rhythm like Bmal1 and Clock, and downregulated negative regulators like Nr1d1. Moreover, microglia exhibited an amoeboid morphology characterized by few processes and rounded cell bodies in 5 × FAD mice, whereas the age-matched SXD group maintained microglia with a ramified appearance. Additionally, our study identified 20 major components of SXD and identified 3-(3,4-Dihydroxyphenyl) lactic acid, Salviaflaside, and Ilexhainanoside D for further molecular docking with REV-ERBα (NR1D1), a commonly used circadian target. Salviaflaside further showed a strong bind with REV-ERBα via CESTA.

CONCLUSIONS

Our findings indicate that SXD may rescue circadian rhythm in 5 × FAD mice through specifically binding to REV-ERBα in microglia to activate the BMAL1/CLOCK pathway, thus inhibiting transcription of inflammatory factors, contributing to alleviating neuroinflammation and impeding AD progression. Our results offer a scientific foundation for developing SXD-based therapies in the early stage of AD, where sleep disruption precedes cognitive decline, offering potential leads for clinical trials to improve sleep quality thus delaying neurodegeneration in AD patients.

Decoding microglial immunometabolism: a new frontier in Alzheimer's disease research

Alzheimer's disease (AD) involves a dynamic interaction between neuroinflammation and metabolic dysregulation, where microglia play a central role. These immune cells undergo metabolic reprogramming in response to AD-related pathology, with key genes such as TREM2, APOE, and HIF-1α orchestrating these processes. Microglial metabolism adapts to environmental stimuli, shifting between oxidative phosphorylation and glycolysis. Hexokinase-2 facilitates glycolytic flux, while AMPK acts as an energy sensor, coordinating lipid and glucose metabolism. TREM2 and APOE regulate microglial lipid homeostasis, influencing Aβ clearance and immune responses. LPL and ABCA7, both associated with AD risk, modulate lipid processing and cholesterol transport, linking lipid metabolism to neurodegeneration. PPARG further supports lipid metabolism by regulating microglial inflammatory responses. Amino acid metabolism also contributes to microglial function. Indoleamine 2,3-dioxygenase controls the kynurenine pathway, producing neurotoxic metabolites linked to AD pathology. Additionally, glucose-6-phosphate dehydrogenase regulates the pentose phosphate pathway, maintaining redox balance and immune activation. Dysregulated glucose and lipid metabolism, influenced by genetic variants such as APOE4, impair microglial responses and exacerbate AD progression. Recent findings highlight the interplay between metabolic regulators like REV-ERBα, which modulates lipid metabolism and inflammation, and Syk, which influences immune responses and Aβ clearance. These insights offer promising therapeutic targets, including strategies aimed at HIF-1α modulation, which could restore microglial function depending on disease stage. By integrating metabolic, immune, and genetic factors, this review underscores the importance of microglial immunometabolism in AD. Targeting key metabolic pathways could provide novel therapeutic strategies for mitigating neuroinflammation and restoring microglial function, ultimately paving the way for innovative treatments in neurodegenerative diseases.

Glia: the cellular glue that binds circadian rhythms and sleep

Glia are increasingly appreciated as serving an important function in the control of sleep and circadian rhythms. Glial cells in Drosophila and mammals regulate daily rhythms of locomotor activity and sleep as well as homeostatic rebound following sleep deprivation. In addition, they contribute to proposed functions of sleep, with different functions mapping to varied glial subtypes. Here, we discuss recent findings in Drosophila and rodent models establishing a role of glia in circadian or sleep regulation of synaptic plasticity, brain metabolism, removal of cellular debris, and immune challenges. These findings underscore the relevance of glia for benefits attributed to sleep and have implications for understanding the neurobiological mechanisms underlying sleep and associated disorders.

Stress causes lipid droplet accumulation in chondrocytes by impairing microtubules

OBJECTIVE

Abnormal mechanical stress is intimately coupled with osteoarthritis. Microtubules play a vital role in the regulation of mechanotransduction and intracellular transport. The purpose of the present study was to investigate the impact of stress-induced microtubule impairment on intracellular transport and lipid droplet (LD) accumulation in chondrocytes.

METHOD

Rats were subjected to unilateral anterior crossbite (UAC), which is inducible for degeneration of temporomandibular joint (TMJ) cartilage. Chondrocytes derived from rat TMJ cartilage were subjected to fluid flow shear stress (FFSS) and analyzed via LCMS/MS-based proteomics. The microtubule destabilization agent nocodazole and/or the microtubule stabilizer docetaxel were used in the UAC and FFSS models.

RESULTS

In both FFSS- and UAC-treated chondrocytes, decreased acetylated α-Tubulin (ac-Tubulin) expression and LD accumulation were observed. Proteomic data revealed increased levels of the LD-associated protein perilipin 3 (Plin3) and decreased levels of cytoskeleton components in FFSS-treated chondrocytes. Live-cell imaging revealed that the colocalization of LDs with lysosomes was significantly decreased after FFSS treatment. Impairment of microtubules by nocodazole reduced the protein level of ac-Tubulin and disrupted the Hsc70-mediated interaction between Plin3 and Lamp2a, as shown by co-IP assays. In contrast, docetaxel reversed the suppression of ac-Tubulin expression, reduced the accumulation of LDs, and decreased the expression of Plin3 in chondrocytes exposed to FFSS and UAC, and docetaxel ameliorated UAC-induced osteoarthritic lesions in the TMJ cartilage.

CONCLUSION

Microtubule impairment under aberrant stress conditions disrupts intracellular transport and blocks lipophagy, causing LD accumulation in chondrocytes. Microtubule stabilization could be a new approach for treating stress-induced cartilage degeneration.

Circadian rhythm, microglia-mediated neuroinflammation, and Alzheimer's disease

Microglia, the brain's resident macrophages, are key mediators of neuroinflammation, responding to immune pathogens and toxins. They play a crucial role in clearing cellular debris, regulating synaptic plasticity, and phagocytosing amyloid-β (Aβ) plaques in Alzheimer's disease (AD). Recent studies indicate that microglia not only exhibit intrinsic circadian rhythms but are also regulated by circadian clock genes, influencing specific functions such as phagocytosis and the modulation of neuroinflammation. Disruption of the circadian rhythm is closely associated with AD pathology. In this review, we will provide an overview of how circadian rhythms regulate microglia-mediated neuroinflammation in the progression of AD, focusing on the pathway from the central nervous system (CNS) and the peripheral immune system. We also discuss potential therapeutic targets, including hormone modulation, lifestyle interventions, and anti-inflammatory therapies, aimed at maintaining brain health in AD. This will shed light on the involvement of circadian rhythm in AD and explore new avenues for AD treatment.

Light Exposure, Physical Activity, and Indigeneity Modulate Seasonal Variation in NR1D1 (REV-ERBα) Expression

Nuclear receptor subfamily 1 group D member 1 (NR1D1 or REV-ERBα) is a crucial element of the circadian clock's transcriptional and translational feedback loop. Understanding its expression in humans is critical for elucidating its role in circadian rhythms and metabolic processes, and in finding potential links to various pathologies. In a longitudinal survey, we examined REV-ERBα expression at 08:00 using a real-time polymerase chain reaction (qRT-PCR) in blood mononuclear cells from Arctic native and non-native residents during equinoxes and solstices. REV-ERBα expression exhibited a pronounced seasonality, peaking at the summer solstice, and reaching a nadir at the winter solstice in both natives and non-natives, with a relatively higher summer peak in natives. After adjusting for age, sex, and body mass index, the amount and timing of light exposure, the amount of physical activity, and indigeneity emerged as significant predictors of REV-ERBα expression.

Dihydroartemisinin requires NR1D1 mediated Rab7 ubiquitination to regulate hepatic stellate cells lipophagy in liver fibrosis

The activation of hepatic stellate cells (HSCs) is a core event in the pathogenesis of liver fibrosis, typically accompanied by the disappearance of lipid droplets (LDs). Reversing the disappearance of HSCs LDs is a strategy to inhibit HSCs activation and alleviate liver fibrosis. Previous studies have shown that nuclear receptor subfamily 1 group d member 1 (NR1D1), as an important component of the biological clock system, is closely related to lipid metabolism. Our previous evidence indicated that Dihydroartemisinin (DHA) can regulate the lipid droplet metabolism of activated HSCs. Moreover, in CCl4 induced liver fibrosis mice, the liver clock gene NR1D1 is dysregulated. On this basis we explored the potential molecular mechanism of DHA inhibiting liver fibrosis through NR1D1. We found that DHA can inhibit liver fibrosis by restoring activated LDs of HSCs through inhibiting HSCs lipophagy. In summary, our study emphasizes the importance of NR1D1 in liver fibrosis and the potential of DHA to regulate NR1D1 in the treatment of liver fibrosis, providing a new direction for the treatment of liver fibrosis.

REV-ERBα Inhibits Osteoclastogenesis and Protects against Alveolar Bone Loss

Circadian rhythm disruption is thought to be associated with periodontitis, and molecular clock genes play critical roles in regulating bone homeostasis. However, the specific contribution of molecular clock genes to alveolar bone resorption caused by periodontitis is poorly understood. In this study, we introduced a novel Periodontitis Circadian Rhythm Score (PeriCRS) model that was established through machine learning using periodontal transcriptomic data from periodontitis clinical cohorts in the Gene Expression Omnibus (GEO) database. This approach revealed the potential regulatory role of circadian rhythm disruption in periodontitis and identified key molecular clock genes associated with alveolar bone destruction. Moreover, we established an experimental periodontitis model with circadian rhythm disturbance via periodontal ligation in mice exposed to a 6-h advanced LD12:12 cycle every 2 d. Our bioinformatics analysis revealed that NR1D1, which encodes REV-ERBα, is a pivotal factor in the impact of circadian rhythm disruption on periodontitis in periodontal tissues. Next, we confirmed the abnormal expression of the molecular clock gene Rev-erbα in inflammatory periodontal tissue in mice and confirmed that circadian rhythm disruption altered REV-ERBα expression. Furthermore, the activation of REV-ERBα with the agonist SR9009 notably decreased RANKL-induced osteoclast differentiation and suppressed the expression of osteoclast-related factors. Subsequent in vivo experiments demonstrated that SR9009 mitigated alveolar bone loss caused by periodontitis. Mechanistically, we found that the IL-22-STAT3 pathway inhibited REV-ERBα expression and modulated RANKL-induced osteoclast differentiation in vitro. Our results elucidate the role of REV-ERBα in osteoclastogenesis and suggest a potential new therapeutic avenue for addressing alveolar bone resorption associated with periodontitis.

Understanding the intricacies of cellular mechanisms in remyelination: The role of circadian rhythm

The term "circadian rhythm" refers to the 24-h oscillations found in various physiological processes in organisms, responsible for maintaining bodily homeostasis. Many neurological diseases mainly involve the process of demyelination, and remyelination is crucial for the treatment of neurological diseases. Current research mainly focuses on the key role of circadian clocks in the pathophysiological mechanisms of multiple sclerosis. Various studies have shown that the circadian rhythm regulates various cellular molecular mechanisms and signaling pathways involved in remyelination. The process of remyelination is primarily mediated by oligodendrocyte precursor cells (OPCs), oligodendrocytes, microglia, and astrocytes. OPCs are activated, proliferate, migrate, and ultimately differentiate into oligodendrocytes after demyelination, involving many key signaling pathway and regulatory factors. Activated microglia secretes important cytokines and chemokines, promoting OPC proliferation and differentiation, and phagocytoses myelin debris that inhibits remyelination. Astrocytes play a crucial role in supporting remyelination by secreting signals that promote remyelination or facilitate the phagocytosis of myelin debris by microglia. Additionally, cell-to-cell communication via gap junctions allows for intimate contact between astrocytes and oligodendrocytes, providing metabolic support for oligodendrocytes. Therefore, gaining a deeper understanding of the mechanisms and molecular pathways of the circadian rhythm at various stages of remyelination can help elucidate the fundamental characteristics of remyelination and provide insights into treating demyelinating disorders.

Upregulation of LXRβ/ABCA1 pathway alleviates cochlear hair cell senescence of C57BL/6 J mice via reducing lipid droplet accumulation

Senescence and loss of cochlear hair cells is an important pathologic basis of age-related hearing loss. Lipid droplet accumulation has previously been shown to play an important role in neurodegeneration; however, its role in age-related hearing loss has not yet been investigated. LXRβ/ABCA1 is a key pathway that regulates lipid metabolism, while its dysfunction can cause abnormal accumulation of lipid droplets in neurons, leading to neurodegeneration. In this study, we found that decreased expression of LXRβ/ABCA1, elevated levels of lipid droplet accumulation, and increased activation of the NLRP3 inflammasome were demonstrated in senescent cochlear hair cells in both animal and cellular models of age-related hearing loss. We then manipulated the LXRβ/ABCA1 pathway transduction of cochlear hair cells. Upregulation of LXRβ/ABCA1 in senescent hair cells was found to reduce the accumulation of lipid droplets, inhibit NLRP3 inflammasome activation, and ultimately alleviate cochlear hair cell senescence. In our study, we also found that NLRP3 inflammasome activation can abrogate the alleviated effect of LXRβ/ABCA1 pathway on the senescence of cochlear hair cells but did not affect the expression of LXRβ/ABCA1.Our study are the first to demonstrate that abnormal lipid droplet accumulation and decreased LXRβ/ABCA1 pathway are observed in cochlear hair cells following the occurrence of age-related hearing loss. Upregulation of LXRβ/ABCA1 in senescent cochlear hair cells can reduce lipid droplet accumulation in cochlear hair cells and alleviate their senescence, which may be related to the inhibition of NLRP3 inflammasome activation. These findings provide potential targets for the treatment of age-related hearing loss.

The glial UDP-glycosyltransferase Ugt35b regulates longevity by maintaining lipid homeostasis in Drosophila

Lipid droplets (LDs) are dynamic organelles essential for lipid storage and organismal survival. Studies have highlighted the importance of glial function in brain LD formation during aging; however, the genes and mechanisms involved remain elusive. Here, we found that Ugt35b, a member of the uridine diphosphate (UDP)-glycosyltransferases that catalyze the transfer of glycosyl groups to acceptors, is highly expressed in glia and crucial for Drosophila lifespan. By integrating multiomics data, we demonstrated that glial Ugt35b plays key roles in regulating glycerolipid and glycerophospholipid metabolism in the brain. Notably, we found that Ugt35b and Lsd-2 are co-expressed in glia and confirmed their protein interaction in vivo. Knockdown of Ugt35b significantly reduced LD formation by downregulating Lsd-2 expression, while overexpression of Lsd-2 partially rescued the shortened lifespan in glial Ugt35b RNAi flies. Our findings reveal the crucial role of glial Ugt35b in regulating LD formation to maintain brain lipid homeostasis and support Drosophila lifespan.

Exploring the link between dystrophic microglia and the spread of Alzheimer's neuropathology

Genetics and other data modalities indicate that microglia play a critical role in Alzheimer's disease progression, but details of the disease-driving influence of microglia are poorly understood. Microglial cells can be parsed into subtypes based on their histological appearance. One subtype of microglia, termed dystrophic microglia, is characterized structurally by fragmented processes and cytoplasmic decay, and their presence has been associated with ageing and neurodegeneration. Recent studies suggest that the interaction between tau proteins and amyloid-β might induce dystrophic changes in microglia, potentially linking amyloid-β and tau pathologies to their effects on these microglia. We developed a study of human brains to test the hypothesis that dystrophic microglia are involved in Alzheimer's disease progression. We speculated that if their presence is unique to Alzheimer's disease neuropathological change, they would be substantially more common in Alzheimer's disease neuropathological change than in neurodegenerative diseases characterized by other proteinopathies, e.g. α-synuclein or transactive response (TAR) DNA-binding protein 43 kDa (TDP-43) pathology. Our analyses used histologically stained sections from five human brain regions of 64 individuals across six disease states, from healthy controls to advanced Alzheimer's disease stages, including comparative conditions such as Lewy body disease and limbic-predominant age-related TDP-43 encephalopathy neuropathological change. Using stereological sampling and digital pathology, we assessed populations of ramified, hypertrophic and dystrophic microglia. We found a significant increase in dystrophic microglia in areas affected early by Alzheimer's disease neuropathological change, suggesting a disease-specific role in neuropathology. Mediation analysis and structural equation modelling suggest that dystrophic microglia might impact the regional spread of Alzheimer's disease neuropathological change. In the mediation model, tau was found to be the initiating factor leading to the development of dystrophic microglia, which was then associated with the spread of amyloid-β and tau. These results suggest that a loss of the protective role of microglia could contribute to the spread of Alzheimer's disease neuropathological change and indicate that further research into preserving microglial function might be warranted.

REV-ERBα inhibitor rescues MPTP/MPP+-induced ferroptosis of dopaminergic neuron through regulating FASN/SCD1 signaling pathway

Circadian disruption is a risk factor for Parkinson's disease (PD). Ferroptosis, a cellular death process, assumes a pivotal role in the degeneration of dopaminergic neurons in PD. Despite its significance, the potential contribution of circadian clock proteins to PD through the modulation of ferroptosis remains elusive. Our investigation unveiled a reduction in the circadian clock protein REV-ERBα in both MPTP/MPP+ and ferroptosis models. REV-ERBα actively promotes ferroptosis by binding to the RORE cis-element and suppressing the transcription of Fasn and Scd1, two genes that inhibit ferroptosis. Notably, inhibiting REV-ERBα exhibited a discernible mitigating effect on ferroptosis and the ensuing dopaminergic neuron damage induced by MPTP/MPP+. Consequently, targeting REV-ERBα emerges as a promising strategy for inhibiting ferroptosis and presents a novel therapeutic avenue for PD.

Targeting selective autophagy in CNS disorders by small-molecule compounds

Autophagy functions as the primary cellular mechanism for clearing unwanted intracellular contents. Emerging evidence suggests that the selective elimination of intracellular organelles through autophagy, compared to the increased bulk autophagic flux, is crucial for the pathological progression of central nervous system (CNS) disorders. Notably, autophagic removal of mitochondria, known as mitophagy, is well-understood in an unhealthy brain. Accumulated data indicate that selective autophagy of other substrates, including protein aggregates, liposomes, and endoplasmic reticulum, plays distinctive roles in various pathological stages. Despite variations in substrates, the molecular mechanisms governing selective autophagy can be broadly categorized into two types: ubiquitin-dependent and -independent pathways, both of which can be subjected to regulation by small-molecule compounds. Notably, natural products provide the remarkable possibility for future structural optimization to regulate the highly selective autophagic clearance of diverse substrates. In this context, we emphasize the selectivity of autophagy in regulating CNS disorders and provide an overview of chemical compounds capable of modulating selective autophagy in these disorders, along with the underlying mechanisms. Further exploration of the functions of these compounds will in turn advance our understanding of autophagic contributions to brain disorders and illuminate precise therapeutic strategies for these diseases.

Loss of CLN3 in microglia leads to impaired lipid metabolism and myelin turnover

Loss-of-function mutations in CLN3 cause juvenile Batten disease, featuring neurodegeneration and early-stage neuroinflammation. How loss of CLN3 function leads to early neuroinflammation is not yet understood. Here, we have comprehensively studied microglia from Cln3∆ex7/8 mice, a genetically accurate disease model. Loss of CLN3 function in microglia leads to lysosomal storage material accumulation and abnormal morphology of subcellular organelles. Moreover, pathological proteomic signatures are indicative of defects in lysosomal function and abnormal lipid metabolism. Consistent with these findings, CLN3-deficient microglia are unable to efficiently turnover myelin and metabolize the associated lipids, showing defects in lipid droplet formation and cholesterol accumulation. Accordingly, we also observe impaired myelin integrity in aged Cln3∆ex7/8 mouse brain. Autophagy inducers and cholesterol-lowering drugs correct the observed microglial phenotypes. Taken together, these data implicate a cell-autonomous defect in CLN3-deficient microglia that impacts their ability to support neuronal cell health, suggesting microglial targeted therapies should be considered for CLN3 disease.

Identification of tauopathy-associated lipid signatures in Alzheimer's disease mouse brain using label-free chemical imaging

There is cumulative evidence that lipid metabolism plays a key role in the pathogenesis of various neurodegenerative disorders including Alzheimer's disease (AD). Visualising lipid content in a non-destructive label-free manner can aid in elucidating the AD phenotypes towards a better understanding of the disease. In this study, we combined multiple optical molecular-specific methods, Fourier transform infrared (FTIR) spectroscopic imaging, synchrotron radiation-infrared (SR-IR) microscopy, Raman and stimulated Raman scattering (SRS) microscopy, and optical-photothermal infrared (O-PTIR) microscopy with multivariate data analysis, to investigate the biochemistry of brain hippocampus in situ using a mouse model of tauopathy (rTg4510). We observed a significant difference in the morphology and lipid content between transgenic (TG) and wild type (WT) samples. Immunohistochemical staining revealed some degree of microglia co-localisation with elevated lipids in the brain. These results provide new evidence of tauopathy-related dysfunction in a preclinical study at a subcellular level.

Microglia, circadian rhythm and lifestyle factors

Microglia, a vital homeostasis-keeper of the central nervous system, perform critical functions such as synaptic pruning, clearance of cellular debris, and participation in neuroinflammatory processes. Recent research has shown that microglia exhibit strong circadian rhythms that not only actively regulate their own immune activity, but also affect neuronal function. Disruptions of the circadian clock have been linked to a higher risk of developing a variety of diseases. In this article we will provide an overview of how lifestyle factors impact microglial function, with a focus on disruptions caused by irregular sleep-wake patterns, reduced physical activity, and eating at the wrong time-of-day. We will also discuss the potential connection between these lifestyle factors, disrupted circadian rhythms, and the role of microglia in keeping brain health. This article is part of the Special Issue on "Microglia".

REV-ERBα Mitigates Astrocyte Activation and Protects Dopaminergic Neurons from Damage

Parkinson's disease (PD) is characterized by astrocyte activation and disruptions in circadian rhythm. Within the astrocyte population, two distinct reactive states exist: A1 and A2. A1 astrocytes are associated with neurotoxicity and inflammation, while A2 astrocytes exhibit neuroprotective functions. Our investigation focused on the role of REV-ERBα, a member of the nuclear receptor superfamily and a key regulator of the circadian clock, in astrocyte activation. We observed that REV-ERBα expression in A1 astrocytes was reduced to one-third of its normal level. Notably, activation of REV-ERBα prompted a transformation of astrocytes from A1 to A2. Mechanistically, REV-ERBα inhibition was linked to the classical NF-κB pathway, while it concurrently suppressed the STAT3 pathway. Furthermore, astrocytes with low REV-ERBα expression were associated with dopaminergic neurons apoptosis. Intriguingly, the opposite effect was observed when using a REV-ERBα agonist, which mitigated astrocyte activation and reduced dopaminergic neuron damage by 50%. In summary, our study elucidates the pivotal role of REV-ERBα in modulating astrocyte function and its potential implications in PD pathogenesis.

Ticking Brain: Circadian Rhythm as a New Target for Cerebroprotection

Circadian rhythm is a master process observed in nearly every type of cell throughout the body, and it macroscopically regulates daily physiology. Recent clinical trials have revealed the effects of circadian variation on the incidence, pathophysiological processes, and prognosis of acute ischemic stroke. Furthermore, core clock genes, the cell-autonomous pacemakers of the circadian rhythm, affect the neurovascular unit-composing cells in a nonparallel manner after the same pathophysiological processes of ischemia/reperfusion. In this review, we discuss the influence of circadian rhythms and clock genes on each type of neurovascular unit cell in the pathophysiological processes of acute ischemic stroke.

Regulation of metabolism by circadian rhythms: Support from time-restricted eating, intestinal microbiota & omics analysis

Circadian oscillatory system plays a key role in coordinating the metabolism of most organisms. Perturbation of genetic effects and misalignment of circadian rhythms result in circadian dysfunction and signs of metabolic disorders. The eating-fasting cycle can act on the peripheral circadian clocks, bypassing the photoperiod. Therefore, time-restricted eating (TRE) can improve metabolic health by adjusting eating rhythms, a process achieved through reprogramming of circadian genomes and metabolic programs at different tissue levels or remodeling of the intestinal microbiota, with omics technology allowing visualization of the regulatory processes. Here, we review recent advances in circadian regulation of metabolism, focus on the potential application of TRE for rescuing circadian dysfunction and metabolic disorders with the contribution of intestinal microbiota in between, and summarize the significance of omics technology.

Targeting dysregulated lipid metabolism for the treatment of Alzheimer's disease and Parkinson's disease: Current advancements and future prospects

Alzheimer's and Parkinson's diseases are two of the most frequent neurological diseases. The clinical features of AD are memory decline and cognitive dysfunction, while PD mainly manifests as motor dysfunction such as limb tremors, muscle rigidity abnormalities, and slow gait. Abnormalities in cholesterol, sphingolipid, and glycerophospholipid metabolism have been demonstrated to directly exacerbate the progression of AD by stimulating Aβ deposition and tau protein tangles. Indirectly, abnormal lipids can increase the burden on brain vasculature, induce insulin resistance, and affect the structure of neuronal cell membranes. Abnormal lipid metabolism leads to PD through inducing accumulation of α-syn, dysfunction of mitochondria and endoplasmic reticulum, and ferroptosis. Great progress has been made in targeting lipid metabolism abnormalities for the treatment of AD and PD in recent years, like metformin, insulin, peroxisome proliferator-activated receptors (PPARs) agonists, and monoclonal antibodies targeting apolipoprotein E (ApoE). This review comprehensively summarizes the involvement of dysregulated lipid metabolism in the pathogenesis of AD and PD, the application of Lipid Monitoring, and emerging lipid regulatory drug targets. A better understanding of the lipidological bases of AD and PD may pave the way for developing effective prevention and treatment methods for neurodegenerative disorders.

Microglial lipid droplet accumulation in tauopathy brain is regulated by neuronal AMPK

The accumulation of lipid droplets (LDs) in aging and Alzheimer's disease brains is considered a pathological phenomenon with unresolved cellular and molecular mechanisms. Utilizing stimulated Raman scattering (SRS) microscopy, we observed significant in situ LD accumulation in microglia of tauopathy mouse brains. SRS imaging, combined with deuterium oxide (D2O) labeling, revealed heightened lipogenesis and impaired lipid turnover within LDs in tauopathy fly brains and human neurons derived from induced pluripotent stem cells (iPSCs). Transfer of unsaturated lipids from tauopathy iPSC neurons to microglia induced LD accumulation, oxidative stress, inflammation, and impaired phagocytosis. Neuronal AMP-activated protein kinase (AMPK) inhibits lipogenesis and promotes lipophagy in neurons, thereby reducing lipid flux to microglia. AMPK depletion in prodromal tauopathy mice increased LD accumulation, exacerbated pro-inflammatory microgliosis, and promoted neuropathology. Our findings provide direct evidence of native, aberrant LD accumulation in tauopathy brains and underscore the critical role of AMPK in regulating brain lipid homeostasis.

A glial circadian gene expression atlas reveals cell type and disease-specific reprogramming in response to amyloid pathology or aging

While circadian rhythm disruption may promote neurodegenerative disease, how aging and neurodegenerative pathology impact circadian gene expression patterns in different brain cell types is unknown. Here, we used translating ribosome affinity purification methods to define the circadian translatomes of astrocytes, microglia, and bulk cerebral cortex, in healthy mouse brain and in the settings of amyloid-beta plaque pathology or aging. Our data reveal that glial circadian translatomes are highly cell type-specific and exhibit profound, context-dependent reprogramming of rhythmic transcripts in response to amyloid pathology or aging. Transcripts involved in glial activation, immunometabolism, and proteostasis, as well as nearly half of all Alzheimer Disease (AD)-associated risk genes, displayed circadian oscillations, many of which were altered by pathology. Amyloid-related differential gene expression was also dependent on time of day. Thus, circadian rhythms in gene expression are cell- and context dependent and provide important insights into glial gene regulation in health, AD, and aging.

Comparative gene regulatory networks modulating APOE expression in microglia and astrocytes

Background

Single-cell technologies have unveiled various transcriptional states in different brain cell types. Transcription factors (TFs) regulate the expression of related gene sets, thereby controlling these diverse expression states. Apolipoprotein E (APOE), a pivotal risk-modifying gene in Alzheimer's disease (AD), is expressed in specific glial transcriptional states associated with AD. However, it is still unknown whether the upstream regulatory programs that modulate its expression are shared across brain cell types or specific to microglia and astrocytes.

Methods

We used pySCENIC to construct state-specific gene regulatory networks (GRNs) for resting and activated cell states within microglia and astrocytes based on single-nucleus RNA sequencing data from AD patients' cortices from the Knight ADRC-DIAN cohort. We then identified replicating TF using data from the ROSMAP cohort. We identified sets of genes co-regulated with APOE by clustering the GRN target genes and identifying genes differentially expressed after the virtual knockout of TFs regulating APOE. We performed enrichment analyses on these gene sets and evaluated their overlap with genes found in AD GWAS loci.

Results

We identified an average of 96 replicating regulators for each microglial and astrocyte cell state. Our analysis identified the CEBP, JUN, FOS, and FOXO TF families as key regulators of microglial APOE expression. The steroid/thyroid hormone receptor families, including the THR TF family, consistently regulated APOE across astrocyte states, while CEBP and JUN TF families were also involved in resting astrocytes. AD GWAS-associated genes (PGRN, FCGR3A, CTSH, ABCA1, MARCKS, CTSB, SQSTM1, TSC22D4, FCER1G, and HLA genes) are co-regulated with APOE. We also uncovered that APOE-regulating TFs were linked to circadian rhythm (BHLHE40, DBP, XBP1, CREM, SREBF1, FOXO3, and NR2F1).

Conclusions

Our findings reveal a novel perspective on the transcriptional regulation of APOE in the human brain. We found a comprehensive and cell-type-specific regulatory landscape for APOE, revealing distinct and shared regulatory mechanisms across microglia and astrocytes, underscoring the complexity of APOE regulation. APOE-co-regulated genes might also affect AD risk. Furthermore, our study uncovers a potential link between circadian rhythm disruption and APOE regulation, shedding new light on the pathogenesis of AD.

Circadian Biology and the Neurovascular Unit

Mammalian physiology and cellular function are subject to significant oscillations over the course of every 24-hour day. It is likely that these daily rhythms will affect function as well as mechanisms of disease in the central nervous system. In this review, we attempt to survey and synthesize emerging studies that investigate how circadian biology may influence the neurovascular unit. We examine how circadian clocks may operate in neural, glial, and vascular compartments, review how circadian mechanisms regulate cell-cell signaling, assess interactions with aging and vascular comorbidities, and finally ask whether and how circadian effects and disruptions in rhythms may influence the risk and progression of pathophysiology in cerebrovascular disease. Overcoming identified challenges and leveraging opportunities for future research might support the development of novel circadian-based treatments for stroke.

Circadian regulation of microglia function: Potential targets for treatment of Parkinson's Disease

Circadian rhythms are involved in the regulation of many aspects of the body, including cell function, physical activity and disease. Circadian disturbance often predates the typical symptoms of neurodegenerative diseases and is not only a non-motor symptom, but also one of the causes of their occurrence and progression. Glial cells possess circadian clocks that regulate their function to maintain brain development and homeostasis. Emerging evidence suggests that the microglial circadian clock is involved in the regulation of many physiological processes, such as cytokine release, phagocytosis, and nutritional and metabolic support, and that disruption of the microglia clock may affect multiple aspects of Parkinson's disease, especially neuroinflammation and α-synuclein processes. Herein, we review recent advances in the circadian control of microglia function in health and disease, and discuss novel pharmacological interventions for microglial clocks in neurodegenerative disorders.

Top 100 most-cited articles on tau protein: a bibliometric analysis and evidence mapping

Background

Tau, a microtubule-associated protein extensively distributed within the central nervous system (CNS), exhibits close associations with various neurodegenerative disorders. Here, we aimed to conduct a qualitative and quantitative bibliometric study of the top 100 most-cited publications on tau protein and reveal the current research hotspots and future perspectives.

Methods

The relevant literature was retrieved from the Web of Science Core Collection. CiteSpace (v6.2.R4) and VOSviewer (1.6.19) were adopted for bibliometric analysis with statistical and visual analysis.

Results

Citations per article ranged from 615 to 3,123, with a median number of 765.5 times. "Neuroscience" emerged as the most extensively researched subject in this field. The USA has emerged as the leading country, with a publication record (n = 65), total citations (n = 66,543), strong centrality (0.29), and extensive international collaborations. Harvard University (n = 11) and the University of California, San Francisco (n = 11) were the top two institutions in terms of publications. Neuron dominated with 13 articles in the 37 high-quality journals. M. Goedert from the MRC Laboratory of Molecular Biology was the most productive (n = 9) and top co-cited (n = 179) author. The most frequently studied keywords were Alzheimer's disease (n = 38). Future research is anticipated to intensify its focus on the pathogenesis of various tau-related diseases, emphasizing the phosphorylation and structural alterations of tau protein, particularly in Alzheimer's disease.

Conclusion

The pathogenesis of various tau-related diseases, including the phosphorylation and structural alterations of the tau protein, will be the primary focus of future research, with particular emphasis on Alzheimer's disease as a central area of investigation.

Circadian Regulation of Apolipoproteins in the Brain: Implications in Lipid Metabolism and Disease

The circadian rhythm is a 24 h internal clock within the body that regulates various factors, including sleep, body temperature, and hormone secretion. Circadian rhythm disruption is an important risk factor for many diseases including neurodegenerative illnesses. The central and peripheral oscillators' circadian clock network controls the circadian rhythm in mammals. The clock genes govern the central clock in the suprachiasmatic nucleus (SCN) of the brain. One function of the circadian clock is regulating lipid metabolism. However, investigations of the circadian regulation of lipid metabolism-associated apolipoprotein genes in the brain are lacking. This review summarizes the rhythmic expression of clock genes and lipid metabolism-associated apolipoprotein genes within the SCN in Mus musculus. Nine of the twenty apolipoprotein genes identified from searching the published database (SCNseq and CircaDB) are highly expressed in the SCN. Most apolipoprotein genes (ApoE, ApoC1, apoA1, ApoH, ApoM, and Cln) show rhythmic expression in the brain in mice and thus might be regulated by the master clock. Therefore, this review summarizes studies on lipid-associated apolipoprotein genes in the SCN and other brain locations, to understand how apolipoproteins associated with perturbed cerebral lipid metabolism cause multiple brain diseases and disorders. This review describes recent advancements in research, explores current questions, and identifies directions for future research.

Minding the Gap: Exploring Neuroinflammatory and Microglial Sex Differences in Alzheimer's Disease

Research into Alzheimer's Disease (AD) describes a link between AD and the resident immune cells of the brain, the microglia. Further, this suspected link is thought to have underlying sex effects, although the mechanisms of these effects are only just beginning to be understood. Many of these insights are the result of policies put in place by funding agencies such as the National Institutes of Health (NIH) to consider sex as a biological variable (SABV) and the move towards precision medicine due to continued lackluster therapeutic options. The purpose of this review is to provide an updated assessment of the current research that summarizes sex differences and the research pertaining to microglia and their varied responses in AD.