Cognitive Dysfunction and Anxiety Resulting from Synaptic Downscaling, Hippocampal Atrophy, and Ventricular Enlargement with Intracerebroventricular Streptozotocin Injection in Male Wistar Rats

Memantine/Rosuvastatin Therapy Abrogates Cognitive and Hippocampal Injury in an Experimental Model of Alzheimer's Disease in Rats: Role of TGF-β1/Smad Signaling Pathway and Amyloid-β Clearance

Alzheimer's disease (AD) is a multifactorial neurodegenerative disorder of complex pathogenesis and multiple interacting signaling pathways where amyloidal-β protein (Aβ) clearance plays a crucial role in cognitive decline. Herein, the current study investigated the possible modulatory effects of memantine/ rosuvastatin therapy on TGF-β1/p-Smad/p21 signaling pathway and their correlation to the blood brain barrier transporters involved in Aβ-clearance and microRNAs as a novel molecular mechanism in AD treatment. AD was induced by a single intracerebroventricular streptozotocin injection (ICV-STZ, 3 mg/kg) in rats and drug therapy was continued for 28 days after AD induction. Efficacy was monitored by applying a battery of behavioral assessments, as well as biochemical, histopathological, molecular and gene expression techniques. The upregulated TGF-β1-signaling in the untreated rats was found to be highly correlated to transporters and microRNAs governing Aβ-efflux; ABCA1/miRNA-26 and LRP1/miRNA-205 expressions, rather than RAGE/miRNA-185 controlling Aβ-influx; an effect that was opposed by the tested drugs and was found to be correlated with the abolished TGF-β1-signaling as well. Combined memantine/rosuvastatin therapy ameliorated the STZ evoked decreases in escape latency and number of crossovers in the Morris water maze test, % spontaneous alternation in the Y-maze test, and discrimination and recognition indices in the object recognition test. The evoked behavioral responses were directly related to the β-amyloid accumulation and the alteration in its clearance. Additionally, drug treatment increased brain glutathione and decreased malondialdehyde levels. These findings were histopathologically confirmed by a marked reduction of gliosis and restoration of neuronal integrity in the CA1 region of the hippocampus of the AD rats. These findings implicated that the memantine/rosuvastatin combination could offer a new therapeutic potential for AD management by abrogating the TGF-β1/p-Smad2/p21 pathway and regulating Aβ-clearance.

The neural basis of neuropsychiatric symptoms in Alzheimer's disease

Neuropsychiatric symptoms (NPS) such as depression, anxiety, apathy and aggression affect up to 90% of Alzheimer's disease (AD) patients. These symptoms significantly increase caregiver stress and institutionalization rates, and more importantly they are correlated with faster cognitive decline. However, the neuronal basis of NPS in AD remains largely unknown. Here, we review current understanding of NPS and related pathology in studies of AD patients and AD mouse models. Clinical studies indicate that NPS prevalence and severity vary across different AD stages and types. Neuroimaging and postmortem studies have suggested that pathological changes in the anterior cingulate cortex, hippocampus, prefrontal cortex, and amygdala are linked to NPS, although the precise mechanisms remain unclear. Studies of AD mouse models have indicated that amyloid-beta and tau-related neurodegeneration in the hippocampus, prefrontal cortex, and anterior cingulate cortex are correlated with NPS-like behavioral deficits. A better understanding of the NPS phenotypes and related pathological changes will pave the way for developing a better management strategy for NPS in AD patients.

MST1 selective inhibitor Xmu-mp-1 ameliorates neuropathological changes in a rat model of sporadic Alzheimer's Disease by modulating Hippo-Wnt signaling crosstalk

Alzheimer's disease (AD), the most prevalent form of dementia, is characterized by progressive cognitive impairment accompanied by aberrant neuronal apoptosis. Reports suggest that the pro-apoptotic mammalian set20-like kinase 1/2 (MST1/2) instigates neuronal apoptosis via activating the Hippo signaling pathway under various stress conditions, including AD. However, whether inhibiting MST1/2 has any therapeutic benefits in AD remains unknown. Thus, we tested the therapeutic effects of intervening MST1/2 activation via the pharmacological inhibitor Xmu-mp-1 in a sporadic AD rat model. Sporadic AD was established in adult rats by intracerebroventricular streptozotocin (ICV-STZ) injection (3 mg/kg body weight). Xmu-mp-1 (0.5 mg/kg/body weight) was administered once every 48 h for two weeks, and Donepezil (5 mg/kg body weight) was used as a reference standard drug. The therapeutic effects of Xmu-mp-1 on ICV-STZ rats were determined through various behavioral, biochemical, histopathological, and molecular tests. At the behavioral level, Xmu-mp-1 improved cognitive deficits in sporadic AD rats. Further, Xmu-mp-1 treatment reduced STZ-associated tau phosphorylation, amyloid-beta deposition, oxidative stress, neurotoxicity, neuroinflammation, synaptic dysfunction, neuronal apoptosis, and neurodegeneration. Mechanistically, Xmu-mp-1 exerted these neuroprotective actions by inactivating the Hippo signaling while potentiating the Wnt/β-Catenin signaling in the AD rats. Together, the results of the present study provide compelling support that Xmu-mp-1 negated the neuronal dysregulation in the rat model of sporadic AD. Therefore, inhibiting MST/Hippo signaling and modulating its crosstalk with the Wnt/β-Catenin pathway can be a promising alternative treatment strategy against AD pathology. This is the first study providing novel mechanistic insights into the therapeutic use of Xmu-mp-1 in sporadic AD.

Neuroprotective Effect of Chlorogenic Acid in an Animal Model of Sporadic Alzheimer's Disease Induced by Streptozotocin

Alzheimer's Disease is a degenerative neurological condition which leads to a decline in memory and cognitive function. Chlorogenic Acid (CGA) presents properties including neuroprotective, antioxidant and anti-inflammatory. The aim of this study was to examine the impact of CGA on cognitive impairments, neuroinflammation and neuronal damage in mice submitted to an experimental model of Sporadic Alzheimer Disease (SAD) induced by intracerebroventricular administration of streptozotocin (ICV-STZ). Male Swiss mice received bilateral ICV-STZ injections (3 mg/Kg) on days 1 and 3. The treatment with CGA (5 mg/Kg, orally) or vehicle (water, orally), was initiated and continued for 26 days, starting 2 h after the second induction procedure. At first, there was no change in serum glucose levels after SAD induction. ICV-STZ induces impairments in aversive, recognition, and spatial memory, while CGA treatment significantly alleviated these memory deficits. Furthermore, locomotor activity, working memory, and anxiety-related activities remained unaffected by the treatments. CGA treatment protects against ICV-STZ-induced increase in the nitrite/nitrate and TBARS levels. ICV-STZ induced a reduction in viable cells, depletion of BDNF, and triggered astrogliosis and microgliosis in the cortex and hippocampus. Treatment with CGA preserves viable cell count in the prefrontal cortex, CA1, and CA3 regions of the hippocampus. Additionally, it prevented BDNF depletion in the prefrontal cortex and hippocampus (CA1, CA3, and DG regions), and mitigated astrogliosis and microgliosis in the prefrontal cortex and hippocampus (CA1, CA3, and DG regions). These findings indicate the neuroprotective effects of CGA, underscoring their potential as therapeutic agents or adjuncts in the treatment of SAD.

Coconut oil ameliorates behavioral and biochemical alterations induced by D-GAL/AlCl3 in rats

Alzheimer's disease (AD) is a chronic, progressive neurodegenerative condition marked by cognitive impairment. Although coconut oil has been shown to be potentially beneficial in reducing AD-related cognitive deficits, information on its mechanism of action is limited. Thus, we investigated the effects of coconut oil on spatial cognitive ability and non-cognitive functions in a rat model of AD induced by G-galactose (D-GAL) and aluminum chloride (AlCl3), and examined the changes in synaptic transmission, cholinergic activity, neurotrophic factors and oxidative stress in this process. The AD model was established by administering D-GAL and AlCl3 for 90 days, while also supplementing with coconut oil during this time. Cognitive and non-cognitive abilities of the rats were evaluated at the end of the 90-day supplementation period. In addition, biochemical markers related to the pathogenesis of the AD were measures in the hippocampus tissue. Exposure to D-GAL/AlCl3 resulted in a reduction in locomotor activity, an elevation in anxiety-like behavior, and an impairment of spatial learning and memory (P < 0.05). The aforementioned behavioral disturbances were observed to coincide with increased oxidative stress and cholinergic impairment, as well as reduced synaptic transmission and levels of neurotrophins in the hippocampus (P < 0.05). Interestingly, treatment with coconut oil attenuated all the neuropathological changes mentioned above (P < 0.05). These findings suggest that coconut oil shows protective effects against cognitive and non-cognitive impairment, AD pathology markers, oxidative stress, synaptic transmission, and cholinergic function in a D-GAL/AlCl3-induced AD rat model.

Anxiety adds the risk of cognitive progression and is associated with axon/synapse degeneration among cognitively unimpaired older adults

BACKGROUND

Mental symptoms have been shown to be associated with dementia. As the most common neuropsychiatric disorder, it is unclear whether and why anxiety increases the risk of cognitive progression in elderly.

METHODS

The aim of this study was to investigate the longitudinal effects of anxiety on cognitive impairment in non-dementia elderly and to explore the underlying biological processes using multi-omics including microarray-based transcriptomics, mass spectrometry-based proteomics and metabolomics, cerebrospinal fluid (CSF) biochemical markers, and brain diffusion tensor imaging (DTI). The Alzheimer's Disease Neuroimaging Initiative (ADNI), Chinese Longitudinal Healthy Longevity Survey (CLHLS) and Shanghai Mental Health Centre (SMHC) cohorts were included.

FINDINGS

Anxiety was found to increase the risk of subsequent cognitive progression in the ADNI, and a similar result was observed in the CLHLS cohort. Enrichment analysis indicated activated axon/synapse pathways and suppressed mitochondrial pathways in anxiety, the former confirmed by deviations in frontolimbic tract morphology and altered levels of axon/synapse markers, and the latter supported by decreased levels of carnitine metabolites. Mediation analysis revealed that anxiety's effect on the longitudinal cognition was mediated by brain tau burden. Correlations of mitochondria-related expressed genes with axon/synapse proteins, carnitine metabolites, and cognitive changes were found.

INTERPRETATION

This study provides cross-validated epidemiological and biological evidence that anxiety is a risk factor for cognitive progression in non-dementia elderly, and that axon/synapse damage in the context of energy metabolism imbalance may contribute to this phenomenon.

FUNDING

The National Natural Science Foundation of China (82271607, 81971682, and 81830059) for data analysis and data collection.