Rapamycin regulates cholesterol biosynthesis and cytoplasmic ribosomal proteins in hippocampus and temporal lobe of APP/PS1 mouse

Effect and Mechanism of Rapamycin on Cognitive Deficits in Animal Models of Alzheimer's Disease: A Systematic Review and Meta-analysis of Preclinical Studies

Background

Alzheimer's disease (AD), the most common form of dementia, remains long-term and challenging to diagnose. Furthermore, there is currently no medication to completely cure AD patients. Rapamycin has been clinically demonstrated to postpone the aging process in mice and improve learning and memory abilities in animal models of AD. Therefore, rapamycin has the potential to be significant in the discovery and development of drugs for AD patients.

Objective

The main objective of this systematic review and meta-analysis was to investigate the effects and mechanisms of rapamycin on animal models of AD by examining behavioral indicators and pathological features.

Methods

Six databases were searched and 4,277 articles were retrieved. In conclusion, 13 studies were included according to predefined criteria. Three authors independently judged the selected literature and methodological quality. Use of subgroup analyses to explore potential mechanistic effects of rapamycin interventions: animal models of AD, specific types of transgenic animal models, dosage, and periodicity of administration.

Results

The results of Morris Water Maze (MWM) behavioral test showed that escape latency was shortened by 15.60 seconds with rapamycin therapy, indicating that learning ability was enhanced in AD mice; and the number of traversed platforms was increased by 1.53 times, indicating that the improved memory ability significantly corrected the memory deficits.

CONCLUSIONS

Rapamycin therapy reduced age-related plaque deposition by decreasing AβPP production and down-regulating β-secretase and γ-secretase activities, furthermore increased amyloid-β clearance by promoting autophagy, as well as reduced tau hyperphosphorylation by up-regulating insulin-degrading enzyme levels.

Rapamycin Responds to Alzheimer's Disease: A Potential Translational Therapy

Alzheimer's disease (AD) is a sporadic or familial neurodegenerative disease of insidious onset with progressive cognitive decline. Although numerous studies have been conducted or are underway on AD, there are still no effective drugs to reverse the pathological features and clinical manifestations of AD. Rapamycin is a macrolide antibiotic produced by Streptomyces hygroscopicus. As a classical mechanistic target of rapamycin (mTOR) inhibitor, rapamycin has been shown to be beneficial in a variety of AD mouse and cells models, both before the onset of disease symptoms and the early stage of disease. Although many basic studies have demonstrated the therapeutic effects of rapamycin in AD, many questions and controversies remain. This may be due to the variability of experimental models, different modes of administration, dose, timing, frequency, and the availability of drug-targeting vehicles. Rapamycin may delay the development of AD by reducing β-amyloid (Aβ) deposition, inhibiting tau protein hyperphosphorylation, maintaining brain function in APOE ε4 gene carriers, clearing chronic inflammation, and improving cognitive dysfunction. It is thus expected to be one of the candidates for the treatment of Alzheimer's disease.

Beyond the amyloid hypothesis: how current research implicates autoimmunity in Alzheimer's disease pathogenesis

The amyloid hypothesis has so far been at the forefront of explaining the pathogenesis of Alzheimer's Disease (AD), a progressive neurodegenerative disorder that leads to cognitive decline and eventual death. Recent evidence, however, points to additional factors that contribute to the pathogenesis of this disease. These include the neurovascular hypothesis, the mitochondrial cascade hypothesis, the inflammatory hypothesis, the prion hypothesis, the mutational accumulation hypothesis, and the autoimmunity hypothesis. The purpose of this review was to briefly discuss the factors that are associated with autoimmunity in humans, including sex, the gut and lung microbiomes, age, genetics, and environmental factors. Subsequently, it was to examine the rise of autoimmune phenomena in AD, which can be instigated by a blood-brain barrier breakdown, pathogen infections, and dysfunction of the glymphatic system. Lastly, it was to discuss the various ways by which immune system dysregulation leads to AD, immunomodulating therapies, and future directions in the field of autoimmunity and neurodegeneration. A comprehensive account of the recent research done in the field was extracted from PubMed on 31 January 2022, with the keywords "Alzheimer's disease" and "autoantibodies" for the first search input, and "Alzheimer's disease" with "IgG" for the second. From the first search, 19 papers were selected, because they contained recent research on the autoantibodies found in the biofluids of patients with AD. From the second search, four papers were selected. The analysis of the literature has led to support the autoimmune hypothesis in AD. Autoantibodies were found in biofluids (serum/plasma, cerebrospinal fluid) of patients with AD with multiple methods, including ELISA, Mass Spectrometry, and microarray analysis. Through continuous research, the understanding of the synergistic effects of the various components that lead to AD will pave the way for better therapeutic methods and a deeper understanding of the disease.

A Simple Computational Approach to Identify Potential Drugs for Multiple Sclerosis and Cognitive Disorders from Expert Curated Resources

Multiple sclerosis, a disease of central nervous system leads to potential disability. In the USA, one million cases are diagnosed with multiple sclerosis in 2019. Multiple sclerosis is identified as one of the diseases causing global burden. Cognitive disorder is highly prevalent among 43-70% of multiple sclerosis patients. However, treating cognitive disorder in multiple sclerosis patients is mostly ignored and this leads to several complications. We utilized various expert curated resources to identify potential drugs for multiple sclerosis and cognitive disorder, with specific focus on identifying drugs that are capable of treating both the conditions. We used simple text mining techniques to compile two databases, disease-drug association database and gene-drug interaction database from various existing standard resources. Our study suggests four drugs, Baclofen, Levodopa, Minocycline, and Vitamin B12, for treating both multiple sclerosis and cognitive disorder. In addition, our approach suggests six drugs for multiple sclerosis and 10 drugs for cognitive disorder. We obtained pharmacologist opinion on the drugs suggested for each condition and provided literature evidence for our claim. Here, we present our computational approach as a protocol such that it can be applied to other comorbid diseases that did not gain much attention so far.

Rapamycin activates mitophagy and alleviates cognitive and synaptic plasticity deficits in a mouse model of Alzheimer's disease

Alzheimer's disease (AD) is a chronic neurodegenerative disease, which is characterized by cognitive and synaptic plasticity damage. Rapamycin is an activator of autophagy/mitophagy, which plays an important role in identifying and degrading damaged mitochondria. The aim of this study was to investigate the effect of rapamycin on cognitive and synaptic plasticity defects induced by AD, and further explore if the underlying mechanism was associated with mitophagy. The results show that rapamycin increases parkin-mediated mitophagy and promotes fusion of mitophagosome and lysosome in the APP/PS1 mouse hippocampus. Rapamycin enhances learning and memory viability, synaptic plasticity and the expression of synapse related proteins, and impedes Cytochrome C-mediated apoptosis, decreases oxidative status and recovers mitochondrial function in APP/PS1 mice. The data suggest that rapamycin effectively alleviates AD-like behaviors and synaptic plasticity deficits in APP/PS1 mice, which is associated with enhanced mitophagy. Our findings possibly uncover an important function of mitophagy in eliminating damaged mitochondria to attenuate Alzheimer's disease-associated pathology.

Rapamycin restores brain vasculature, metabolism, and blood-brain barrier in an inflammaging model

Rapamycin (RAPA) is found to have neuro-protective properties in various neuroinflammatory pathologies, including brain aging. With magnetic resonance imaging (MRI) techniques, we investigated the effect of RAPA in a lipopolysaccharide (LPS)-induced inflammaging model in rat brains. Rats were exposed to saline (control), or LPS alone or LPS combined with RAPA treatment (via food over 6 weeks). Arterial spin labeling (ASL) perfusion imaging was used to measure relative cerebral blood flow (rCBF). MR spectroscopy (MRS) was used to measure brain metabolite levels. Contrast-enhanced MRI (CE-MRI) was used to assess blood-brain barrier (BBB) permeability. Immunohistochemistry (IHC) was used to confirm neuroinflammation. RAPA restored NF-κB and HIF-1α to normal levels. RAPA was able to significantly restore rCBF in the cerebral cortex post-LPS exposure (p < 0.05), but not in the hippocampus. In the hippocampus, RAPA was able to restore total creatine (Cr) acutely, and N-acetyl aspartate (NAA) at 6 weeks, post-LPS. Myo-inositol (Myo-Ins) levels were found to decrease with RAPA treatment acutely post-LPS. RAPA was also able to significantly restore the BBB acutely post-LPS in both the cortex and hippocampus (p < 0.05 for both). RAPA was found to increase the percent change in BOLD signal in the cortex at 3 weeks, and in the hippocampus at 6 weeks post-LPS, compared to LPS alone. RAPA treatment also restored the neuronal and macro-vascular marker, EphB2, back to normal levels. These results indicate that RAPA may play an important therapeutic role in inhibiting neuroinflammation by normalizing brain vascularity, BBB, and some brain metabolites, and has a high translational capability.

Repositioning of Immunomodulators: A Ray of Hope for Alzheimer's Disease?

Alzheimer's disease (AD) is the most common age-related neurodegenerative disorder characterized by cognitive decline and by the presence of amyloid β plaques and neurofibrillary tangles in the brain. Despite recent advances in understanding its pathophysiological mechanisms, to date, there are no disease-modifying therapeutic options, to slow or halt the evolution of neurodegenerative processes in AD. Current pharmacological treatments only transiently mitigate the severity of symptoms, with modest or null overall improvement. Emerging evidence supports the concept that AD is affected by the impaired ability of the immune system to restrain the brain's pathology. Deep understanding of the relationship between the nervous and the immune system may provide a novel arena to develop effective and safe drugs for AD treatment. Considering the crucial role of inflammatory/immune pathways in AD, here we discuss the current status of the immuno-oncological, immunomodulatory and anti-TNF-α drugs which are being used in preclinical studies or in ongoing clinical trials by means of the drug-repositioning approach.

Astaxanthin Improved the Cognitive Deficits in APP/PS1 Transgenic Mice Via Selective Activation of mTOR

Astaxanthin (Ast) is an effective neuroprotective and antioxidant compound used to treat Alzheimer's disease (AD); however, the underlying in vivo molecular mechanisms remain unknown. In this study, we report that Ast can activate the mammalian target of rapamycin (mTOR) pathway in the 8-month-old APP/PS1 transgenic mouse model of AD. Our results suggest that Ast could ameliorate the cognitive defects in APP/PS1 mice by activating the mTOR pathway. Moreover, mTOR activation perturbed the mitochondrial dynamics, increased the synaptic plasticity after 21 days of treatment with Ast (10 mg/kg/day), and increased the expression of Aβ-degrading enzymes, mitochondrial fusion, and synapse-associated proteins and decreased the expression of mitochondrial fission proteins. Intraperitoneal injection of the mTOR inhibitor, rapamycin, abolished the effects of Ast. In conclusion, Ast activates the mTOR pathway, which is necessary for mitochondrial dynamics and synaptic plasticity, leading to improved learning and memory. Our results support the use of Ast for the treatment of cognitive deficits. Graphical abstract In summary, Ast ameliorates cognitive deficits via facilitating the mTOR-dependent mitochondrial dynamics and synaptic damage, and reducing Aβ accumulation. This model supports the use of Ast for the treatment of cognitive deficits.

Study on the mechanism of curcumin to reduce the inflammatory response of temporal lobe in Alzheimer's disease by regulating miR-146a

BACKGROUND

To explore the potential mechanism of curcumin in the treatment of Alzheimer's disease and clarify the role of miR-146a in the neuroinflammatory response to Alzheimer's disease.

METHODS

Clinical case study: 20 AD patients and 20 age-gender matched non-inflammatory and non-dementia patients in the department of neurology of our hospital were included, peripheral venous blood and cerebrospinal fluid were collected, and mir-146a levels in peripheral blood and cerebrospinal fluid were detected by real-time fluorescence quantitative PCR. Animal experimental study group: There were 3 groups, including APP/PS1 mice control group, APP/PS1 mice low-dose curcumin treatment group, and C57BL/6J mice wild-type (WT) control group, with 10 mice in each group. mir-146a levels in mice brain tissue were detected by quantitative real-time PCR. Aβ, APP, complement factor H (CFH) and M1 microglia labeled IL-1 β and iNOS in temporal lobe tissues of mice were detected by using Westernblot method.

RESULTS

The plasma miRNA-146a level in AD group was 39.10 ±12.97 fmol/L, and that in control group was 60.54 ±13.16 fmol/L. The plasma miRNA-146a level in AD group was significantly lower than that in control group. The level of miRNA-146a in cerebrospinal fluid of AD group (25.16 ± 5.16 fmol/L) was significantly higher than that of control group (11.35 ±3.58 fmol/L). After treatment with low dose curcumin, the level of miRNA-146a in APP/PS1 mice decreased significantly, and the expression of A β and APP/PS1 in temporal lobe of mice detected by Western blot decreased significantly, the levels of IL-1 β and iNOS protein decreased significantly, and the protein of CFH increased signifanctly.

CONCLUSIONS

miRNA-146a can be used as one of the potential biomarkers of AD. Low dose curcumin can significantly reduce the level of neuropro-inflammatory miR-146A, up-regulate the expression of CFH protein, inhibit the phenotype of M1 microglia, and play a role in the treatment of AD by promoting the phagocytosis and clearance mechanism of A β.