Microglia activation mediates circadian rhythm disruption-induced cognitive impairment in mice

Identification of circadian-sensitive brain structure and its role in cognitive impairment and dementia

BACKGROUND

Circadian disruption has been suggested to induce cognitive impairment and dementia. It remains unknown which brain structures are involved in the pathology.

OBJECTIVE

To investigate which specific brain structure alterations are associated with dementia and cognitive impairment induced by circadian disruption.

METHODS

Circadian disruption was represented by two accelerometer-derived circadian variables, composite phase deviations (CPD) and relative amplitude (RA), separately reflecting circadian disruption in timing and amplitude. The outcomes include brain structures (139 imaging-derived phenotypes), cognitive test performances (seven cognitive tests) and dementia (all-cause dementia, Alzheimer's disease, vascular dementia (AD/VD) and non-AD/VD dementia). Association analysis was used to explore the relationships between circadian disruption and brain structure alterations, cognitive test performances and dementia. Mediation analysis was conducted to investigate which brain structure alterations mediated the cognitive impairment and dementia caused by circadian disruption.

FINDINGS

A total of 88 461 participants (57% female, 62.0±7.8-year old) were included. CPD and RA correlated with substantially different brain structures. All CPD-related brain structures were located in the cerebrum, whereas most RA-related brain structures were located in the cerebellum. Furthermore, only the CPD-related brain structures, including the hippocampus and thalamus, exhibited significant mediation effects accounting for up to 8.6% of the risk for dementia and 13.5% of the risk for cognitive impairment.

CONCLUSIONS

Circadian disruption is associated with brain structural alterations involving dementia and cognitive impairments.

CLINICAL IMPLICATIONS

These results provide a novel insight into the mechanism underlying circadian disruption-induced neurological disorder and may propose potential preventive strategy.

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.

Dysmaturation of sleep state and electroencephalographic activity after hypoxia-ischaemia in preterm fetal sheep

Antenatal hypoxia-ischaemia (HI) in preterm fetal sheep can trigger delayed evolution of severe, cystic white matter injury (WMI), in a similar timecourse to WMI in preterm infants. We therefore examined how severe hypoxia-ischaemia affects recovery of electroencephalographic (EEG) activity. Chronically instrumented preterm fetal sheep (0.7 gestation) received 25 min of complete umbilical cord occlusion (UCO, n = 9) or sham occlusion (controls, n = 9), and recovered for 21 days. HI was associated with a shift to lower frequency EEG activity for the first 5 days with persisting loss of EEG power in the delta and theta bands, and initial loss of power in the alpha and beta bands in the first 14 days of recovery. In the final 3 days of recovery, there was a marked rhythmic shift towards higher frequency EEG activity after UCO. The UCO group spent less time in high-voltage sleep, and in the early evening (7:02 pm ± 47 min) abruptly stopped cycling between sleep states, with a shift to a high frequency state for 2 h 48 min ± 40 min, with tonic electromyographic activity. These findings demonstrate persisting EEG and sleep state dysmaturation after severe hypoxia-ischaemia. Loss of fetal or neonatal sleep state cycling in the early evening may be a useful biomarker for evolving cystic WMI.

Dynamic endocannabinoid-mediated neuromodulation of retinal circadian circuitry

Circadian rhythms are biological rhythms that originate from the "master circadian clock," called the suprachiasmatic nucleus (SCN). SCN orchestrates the circadian rhythms using light as a chief zeitgeber, enabling humans to synchronize their daily physio-behavioral activities with the Earth's light-dark cycle. However, chronic/ irregular photic disturbances from the retina via the retinohypothalamic tract (RHT) can disrupt the amplitude and the expression of clock genes, such as the period circadian clock 2, causing circadian rhythm disruption (CRd) and associated neuropathologies. The present review discusses neuromodulation across the RHT originating from retinal photic inputs and modulation offered by endocannabinoids as a function of mitigation of the CRd and associated neuro-dysfunction. Literature indicates that cannabinoid agonists alleviate the SCN's ability to get entrained to light by modulating the activity of its chief neurotransmitter, i.e., γ-aminobutyric acid, thus preventing light-induced disruption of activity rhythms in laboratory animals. In the retina, endocannabinoid signaling modulates the overall gain of the retinal ganglion cells by regulating the membrane currents (Ca2+, K+, and Cl- channels) and glutamatergic neurotransmission of photoreceptors and bipolar cells. Additionally, endocannabinoids signalling also regulate the high-voltage-activated Ca2+ channels to mitigate the retinal ganglion cells and intrinsically photosensitive retinal ganglion cells-mediated glutamate release in the SCN, thus regulating the RHT-mediated light stimulation of SCN neurons to prevent excitotoxicity. As per the literature, cannabinoid receptors 1 and 2 are becoming newer targets in drug discovery paradigms, and the involvement of endocannabinoids in light-induced CRd through the RHT may possibly mitigate severe neuropathologies.

Neuroinflammation and Neurodegenerative Diseases: How Much Do We Still Not Know?

The term "neuroinflammation" defines the typical inflammatory response of the brain closely related to the onset of many neurodegenerative diseases (NDs). Neuroinflammation is well known, but its mechanisms and pathways are not entirely comprehended. Some progresses have been achieved through many efforts and research. Consequently, new cellular and molecular mechanisms, diverse and conventional, are emerging. In listing some of those that will be the subject of our description and discussion, essential are the important roles of peripheral and infiltrated monocytes and clonotypic cells, alterations in the gut-brain axis, dysregulation of the apelinergic system, alterations in the endothelial glycocalyx of the endothelial component of neuronal vascular units, variations in expression of some genes and levels of the encoding molecules by the action of microRNAs (miRNAs), or other epigenetic factors and distinctive transcriptional factors, as well as the role of autophagy, ferroptosis, sex differences, and modifications in the circadian cycle. Such mechanisms can add significantly to understanding the complex etiological puzzle of neuroinflammation and ND. In addition, they could represent biomarkers and targets of ND, which is increasing in the elderly.

New insight on microglia activation in neurodegenerative diseases and therapeutics

Microglia are immune cells within the central nervous system (CNS) closely linked to brain health and neurodegenerative diseases such as Alzheimer's disease and Parkinson's disease. In response to changes in the surrounding environment, microglia activate and change their state and function. Several factors, example for circadian rhythm disruption and the development of neurodegenerative diseases, influence microglia activation. In this review, we explore microglia's function and the associated neural mechanisms. We elucidate that circadian rhythms are essential factors influencing microglia activation and function. Circadian rhythm disruption affects microglia activation and, consequently, neurodegenerative diseases. In addition, we found that abnormal microglia activation is a common feature of neurodegenerative diseases and an essential factor of disease development. Here we highlight the importance of microglia activation in neurodegenerative diseases. Targeting microglia for neurodegenerative disease treatment is a promising direction. We introduce the progress of methods targeting microglia for the treatment of neurodegenerative diseases and summarize the progress of drugs developed with microglia as targets, hoping to provide new ideas for treating neurodegenerative diseases.