Deterioration of cognitive function after transient cerebral ischemia with amyloid-β infusion-possible amelioration of cognitive function by AT2 receptor activation

TXNIP/NLRP3 aggravates global cerebral ischemia-reperfusion injury-induced cognitive decline in mice

Global cerebral ischemia/reperfusion (GCI/R) injury poses a risk for cognitive decline, with neuroinflammation considered pivotal in this process. This study aimed to unravel the molecular mechanisms underlying GCI/R injury and propose a potential therapeutic strategy for associated cognitive deficits. Utilizing bioinformatics analysis of a public microarray profile (GSE30655 and GSE80681) in cerebral ischemic mice, it was observed that neuroinflammation emerged as a significant gene ontology item, with an increase in the expression of thioredoxin-interacting protein (TXNIP) and NLRP3 genes. Experimental models involving bilateral occlusion of the common carotid arteries in mice revealed that GCI/R induced cognitive impairment, along with a time-dependent increase in TXNIP and NLRP3 levels. Notably, TXNIP knockdown alleviated cognitive dysfunction in mice. Furthermore, the introduction of adeno-associated virus injection with TXNIP knockdown reduced the number of activated microglia, apoptosis neurons, and levels of oxidative stress and inflammatory cytokines in the hippocampus. Collectively, these findings underscore the significance of TXNIP/NLRP3 in the hippocampus in exacerbating cognitive decline due to GCI/R injury, suggesting that TXNIP knockdown holds promise as a therapeutic strategy.

Targeting the Renin-Angiotensin System (RAS) for Neuropsychiatric Disorders

BACKGROUND

Neuropsychiatric disorders, such as mood disorders, schizophrenia, and Alzheimer's disease (AD) and related dementias, are associated to significant morbidity and mortality worldwide. The pathophysiological mechanisms of neuropsychiatric disorders remain to be fully elucidated, which has hampered the development of effective therapies. The Renin Angiotensin System (RAS) is classically viewed as a key regulator of cardiovascular and renal homeostasis. The discovery that RAS components are expressed in the brain pointed out a potential role for this system in central nervous system (CNS) pathologies. The understanding of RAS involvement in the pathogenesis of neuropsychiatric disorders may contribute to identifying novel therapeutic targets.

AIMS

We aim to report current experimental and clinical evidence on the role of RAS in physiology and pathophysiology of mood disorders, schizophrenia, AD and related dementias. We also aim to discuss bottlenecks and future perspectives that can foster the development of new related therapeutic strategies.

CONCLUSION

The available evidence supports positive therapeutic effects for neuropsychiatric disorders with the inhibition/antagonism of the ACE/Ang II/AT1 receptor axis or the activation of the ACE2/Ang-(1-7)/Mas receptor axis. Most of this evidence comes from pre-clinical studies and clinical studies lag much behind, hampering a potential translation into clinical practice.

Deeper cerebral hypoperfusion leads to spatial cognitive impairment in mice

BACKGROUND

Vascular cognitive impairment (VCI) is the second-leading cause of dementia worldwide, which is caused by cerebrovascular diseases or relevant risk factors. However, there are no appropriate animal models, which can be used to study changes of neuropathology in the human VCI. To better understand the development of VCI, we modified three mouse models of chronical vascular diseases, and further compared the advantage and disadvantage of these models. We hope to establish a more suitable mouse model mimicking VCI in human beings.

METHODS

Adult male C57/BL6 mice (n=98) were used and animals underwent transient bilateral common carotid arteries occlusion (tBCCAO), or bilateral common carotid artery stenosis (BCAS), or right unilateral common carotid artery occlusion, respectively. Haemodynamic changes of surface cerebral blood flow (CBF) were examined up to 4 weeks. Spatial cognitive impairment was evaluated to determine the consequence of chronic cerebral ischaemia.

RESULTS

These mouse models showed different extents of CBF reduction and spatial reference memory impairment from 1 week up to 4 weeks postoperation compared with the control group (p<0.05). We found that (1) bilaterally ligation of common carotid artery caused decrease of 90% CBF in C57/BL6 mice (p<0.05) and caused acute instead of prolonged impairment of spatial reference memory (p<0.05); (2) unilateral ligation of common carotid artery did not cause severe ipsilateral ischaemia as seen in the tBCCAO mice and caused minor but significant spatial reference memory disturbance (p<0.05); and (3) 20% decrease in the bilateral CBF did not cause spatial reference memory impairment 4 weeks postoperation (p>0.05), while 30% decrease in bilateral or unilateral CBF led to significant memory disturbance in mice (p<0.05).

CONCLUSION

We demonstrated that BCAS using 0.16/0.18 mm microcoils is an alternative VCI mouse model when studying the mechanism and developing therapy of VCI.

Preventive Effect of Hippocampal Sparing on Cognitive Dysfunction of Patients Undergoing Whole-Brain Radiotherapy and Imaging Assessment of Hippocampal Volume Changes

Objective

Preventive effect of hippocampal sparing on cognitive dysfunction of patients undergoing whole-brain radiotherapy and imaging assessment of hippocampal volume changes.

Methods

Forty patients with brain metastases who attended Liaoning Cancer Hospital from January 2018 to December 2019 were identified as research subjects and were randomly divided into a control group and an experimental group, with 20 cases in each group. The control group was treated with whole-brain radiotherapy (WBRT), and the experimental group was treated with hippocampal sparing-WBRT (HS-WBRT). The Montreal Cognitive Assessment (MoCA) score, Eastern Cooperative Oncology Group (ECOG) score, cancer quality-of-life questionnaire (QLQ-C3O) score, hippocampal volume changes, and prognosis of the two groups were compared.

Results

The MoCA scores decreased in both groups at 3, 6, and 12 months after radiotherapy, with significantly higher scores in the experimental group than in the control group (P < 0.05). After radiotherapy, both groups had lower ECOG scores, with those in the experimental group being significantly lower than those in the control group (P < 0.05). After radiotherapy, the QLQ-C30 score was elevated in both groups, and that of the experimental group was significantly higher than that of the control group (P < 0.05). The experimental group outperformed the control group in terms of the prognosis (P < 0.05). The hippocampal volume of the control group was significantly smaller than that of the experimental group (P < 0.05).

Conclusion

The application of hippocampal sparing in patients receiving whole-brain radiotherapy is effective in preventing cognitive dysfunction, improving the quality of life and prognosis of patients, and avoiding shrinkage of hippocampal volume.

Neurovascular Alterations in Vascular Dementia: Emphasis on Risk Factors

Vascular dementia (VaD) constitutes the second most prevalent cause of dementia in the world after Alzheimer’s disease (AD). VaD regroups heterogeneous neurological conditions in which the decline of cognitive functions, including executive functions, is associated with structural and functional alterations in the cerebral vasculature. Among these cerebrovascular disorders, major stroke, and cerebral small vessel disease (cSVD) constitute the major risk factors for VaD. These conditions alter neurovascular functions leading to blood-brain barrier (BBB) deregulation, neurovascular coupling dysfunction, and inflammation. Accumulation of neurovascular impairments over time underlies the cognitive function decline associated with VaD. Furthermore, several vascular risk factors, such as hypertension, obesity, and diabetes have been shown to exacerbate neurovascular impairments and thus increase VaD prevalence. Importantly, air pollution constitutes an underestimated risk factor that triggers vascular dysfunction via inflammation and oxidative stress. The review summarizes the current knowledge related to the pathological mechanisms linking neurovascular impairments associated with stroke, cSVD, and vascular risk factors with a particular emphasis on air pollution, to VaD etiology and progression. Furthermore, the review discusses the major challenges to fully elucidate the pathobiology of VaD, as well as research directions to outline new therapeutic interventions.

Angiotensin II and Amyloid-β Synergistically Induce Brain Vascular Smooth Muscle Cell Senescence

BACKGROUND

Amyloid-β (Aβ) induces cerebrovascular damage and is reported to stimulate endothelial cell senescence. We previously demonstrated that angiotensin II (Ang II)-promoted vascular senescence. We examined the possible cross-talk between Ang II and Aβ in regulating brain vascular smooth muscle cell (BVSMC) senescence.

METHODS

BVSMCs were prepared from adult male mice and stimulated with Ang II (0, 0.1, 1, 10, and 100 nmol/l) and/or Aβ 1-40 (0, 0.1, 0.3, 0.5, 1, 3, and 5 µmol/l) for the indicated times. Cellular senescence was evaluated by senescence-associated β-galactosidase staining.

RESULTS

Treatment with Ang II (100 nmol/l) or Aβ (1 µmol/l) at a higher dose increased senescent cells compared with control at 6 days. Treatment with Ang II (10 nmol/l) or Aβ (0.5 µmol/l) at a lower dose had no effect on senescence whereas a combined treatment with lower doses of Ang II and Aβ significantly enhanced senescent cells. This senescence enhanced by lower dose combination was markedly blocked by valsartan (Ang II type 1 receptor inhibitor) or TAK-242 (Aβ receptor TLR4 inhibitor) treatment. Moreover, lower dose combination caused increases in superoxide anion levels and p-ERK expression for 2 days, NF-κB activity, p-IκB, p-IKKα/β, p16 and p53 expression for 4 days, and an obvious decrease in pRb expression. These changes by lower dose combination, except in p-IκB expression and NF-κB activity, were significantly inhibited by pretreatment with U0126 (ERK inhibitor).

CONCLUSIONS

Ang II and Aβ synergistically promoted BVSMC senescence at least due to enhancement of the p-ERK-p16-pRb signaling pathway, oxidative stress, and NF-κB/IκB activity.

Differentially expressed genes accompanying neurobehavioral deficits in a modified rat model of vascular dementia

Vascular dementia refers to the progressive loss of memory and other cognitive functions. The heterogeneity of cerebrovascular disease renders it challenging to elucidate the neuropathological substrates and mechanisms underlying vascular dementia. In this study, we performed neurobehavioral tests, RNA sequencing (RNA-seq), and quantitative real-time polymerase chain reaction (qRT-PCR) tests to evaluate a rat model of modified two-vessel occlusion (2-VO) and identify the differentially expressed genes in the hippocampus of 2-VO versus sham rats by Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) annotations. Compared with the sham group, the 2-VO group revealed significantly reduced spontaneous motor behaviors, a lack of exploration for new objects, and varying degrees of spatial memory impairment. Although the genetic background of vascular dementia is well established for monogenic disorders, the relationship between key regulatory genes and signaling pathways remains obscure. Using RNA-seq and bioinformatic analyses, we identified 58 upregulated genes and 137 downregulated genes in the hippocampus of 2-VO rats compared to sham rats. Results were confirmed by qRT-PCR. ErbB3, a gene mainly involved in cranial nervous system development, negative regulation of neuronal apoptosis, and signal transduction, was downregulated in the hippocampus of 2-VO rats compared to sham rats. Moreover, ERBB3 plays an important role in neuron-protecting ERBB and PI3K-AKT signaling pathways, both of which were found to be enriched by GO and KEGG functional pathway analyses. Understanding the molecular mechanisms of vascular dementia may help establish potential treatment targets for cognitive deficits.

Cerebral artery dilation during transient ischemia is impaired by amyloid β deposition around the cerebral artery in Alzheimer's disease model mice

Transient ischemia is an exacerbation factor of Alzheimer's disease (AD). We aimed to examine the influence of amyloid β (Aβ) deposition around the cerebral (pial) artery in terms of diameter changes in the cerebral artery during transient ischemia in AD model mice (APPNL-G-F) under urethane anesthesia. Cerebral vasculature and Aβ deposition were examined using two-photon microscopy. Cerebral ischemia was induced by transient occlusion of the unilateral common carotid artery. The diameter of the pial artery was quantitatively measured. In wild-type mice, the diameter of arteries increased during occlusion and returned to their basal diameter after re-opening. In AD model mice, the artery response during occlusion differed depending on Aβ deposition sites. Arterial diameter changes at non-Aβ deposition site were similar to those in wild-type mice, whereas they were significantly smaller at Aβ deposition site. The results suggest that cerebral artery changes during ischemia are impaired by Aβ deposition.

Defective mitophagy in Alzheimer's disease

Alzheimer's disease (AD) is a progressive, mental illness without cure. Several years of intense research on postmortem AD brains, cell and mouse models of AD have revealed that multiple cellular changes are involved in the disease process, including mitochondrial abnormalities, synaptic damage, and glial/astrocytic activation, in addition to age-dependent accumulation of amyloid beta (Aβ) and hyperphosphorylated tau (p-tau). Synaptic damage and mitochondrial dysfunction are early cellular changes in the disease process. Healthy and functionally active mitochondria are essential for cellular functioning. Dysfunctional mitochondria play a central role in aging and AD. Mitophagy is a cellular process whereby damaged mitochondria are selectively removed from cell and mitochondrial quality and biogenesis. Mitophagy impairments cause the progressive accumulation of defective organelle and damaged mitochondria in cells. In AD, increased levels of Aβ and p-tau can induce reactive oxygen species (ROS) production, causing excessive fragmentation of mitochondria and promoting defective mitophagy. The current article discusses the latest developments of mitochondrial research and also highlights multiple types of mitophagy, including Aβ and p-tau-induced mitophagy, stress-induced mitophagy, receptor-mediated mitophagy, ubiquitin mediated mitophagy and basal mitophagy. This article also discusses the physiological states of mitochondria, including fission-fusion balance, Ca²⁺ transport, and mitochondrial transport in normal and diseased conditions. Our article summarizes current therapeutic interventions, like chemical or natural mitophagy enhancers, that influence mitophagy in AD. Our article discusses whether a partial reduction of Drp1 can be a mitophagy enhancer and a therapeutic target for mitophagy in AD and other neurological diseases.