MicroRNA-153 impairs hippocampal synaptic vesicle trafficking via downregulation of synapsin I in rats following chronic cerebral hypoperfusion

MicroRNAs and Synapse Turnover in Alzheimer's Disease

Alzheimer's Disease (AD) is a progressive neurodegenerative disorder characterized by the accumulation of amyloid-beta plaques and neurofibrillary tangles in the brain, leading to synaptic dysfunction and cognitive decline. Healthy synapses are the crucial for normal brain function, memory restoration and other neurophysiological function. Synapse loss and synaptic dysfunction are two primary events that occur during AD initiation. Synapse lifecycle and/or synapse turnover is divided into five key stages and several sub-stages such as synapse formation, synapse assembly, synapse maturation, synapse transmission and synapse termination. In normal state, the synapse turnover is regulated by various biological and molecular factors for a healthy neurotransmission. In AD, the different stages of synapse turnover are affected by AD-related toxic proteins. MicroRNAs (miRNAs) have emerged as critical regulators of gene expression and have been implicated in various neurological diseases, including AD. Deregulation of miRNAs modulate the synaptic proteins and affect the synapse turnover at different stages. In this review, we discussed the key milestones of synapse turnover and how they are affected in AD. Further, we discussed the involvement of miRNAs in synaptic turnover, focusing specifically on their role in AD pathogenesis. We also emphasized the regulatory mechanisms by which miRNAs modulate the synaptic turnover stages in AD. Current studies will help to understand the synaptic life-cycle and role of miRNAs in each stage that is deregulated in AD, further allowing for a better understanding of the pathogenesis of devastating disease.

Short-Term Memory Deficit Associates with miR-153-3p Upregulation in the Hippocampus of Middle-Aged Mice

The early stages of ageing are a critical time window in which the ability to detect and identify precocious molecular and cognitive markers can make the difference in determining a healthy vs unhealthy course of ageing. Using the 6-different object task (6-DOT), a highly demanding hippocampal-dependent recognition memory task, we classified a population of middle-aged (12-month-old) CD1 male mice in Impaired and Unimpaired based on their short-term memory. This approach led us to identify a different microRNAs expression profile in the hippocampus of Impaired mice compared to Unimpaired ones. Among the dysregulated microRNAs, miR-153-3p was upregulated in the hippocampus of Impaired mice and appeared of high interest for its putative target genes and their possible implication in memory-related synaptic plasticity. We showed that intra-hippocampal injection of the miR-153-3p mimic in adult (3-month-old) mice is sufficient to induce a short-term memory deficit similar to that observed in middle-aged Impaired mice. Overall, these findings unravel a novel role for hippocampal miR-153-3p in modulating short-term memory that could be exploited to prevent early cognitive deficits in ageing.

An in silico approach to identify potential downstream targets of miR-153 involved in Alzheimer's disease

Background: In recent years, microRNAs (miRNAs) have emerged as key players in the pathophysiology of multiple diseases including Alzheimer's disease (AD). Messenger RNA (mRNA) targeting for regulation of gene expression by miRNAs has been implicated in the annotation of disease pathophysiology as well as in the explication of their starring role in contemporary therapeutic interventions. One such miRNA is miR-153 which mediates the survival of cortical neurons and inhibits plaque formation. However, the core mRNA targets of miR-153 have not been fully illustrated. Objective: The present study aimed to elucidate the potential involvement of miR-153 in AD pathogenesis and to reveal its downstream targets. Methods: miRanda was used to identify AD-associated targets of miR-153. TargetScan, PicTar, miRmap, and miRDB were further used to validate these targets. STRING 12 was employed to assess the protein-protein interaction network while Gene ontology (GO) analysis was carried out to identify the molecular functions exhibited by these gene targets. Results: In silico analysis using miRanda predicted five important AD-related targets of miR-153, including APP, SORL1, PICALM, USF1, and PSEN1. All five target genes are negatively regulated by miR-153 and are substantially involved in AD pathogenesis. A protein interaction network using STRING 12 uncovered 30 potential interacting partners for SORL1, PICALM, and USF1. GO analysis revealed that miR-153 target genes play a critical role in neuronal survival, differentiation, exon guidance, amyloid precursor protein processing, and synapse formation. Conclusion: These findings unravel the potential role of miR-153 in the pathogenesis of AD and provide the basis for forthcoming experimental studies.

MiR-153 downregulation alleviates PTSD-like behaviors and reduces cell apoptosis by upregulating the Sigma-1 receptor in the hippocampus of rats exposed to single-prolonged stress

Posttraumatic stress disorder (PTSD) is a psychiatric disorder that may lead to a series of changes in the central nervous system, including impaired synaptic plasticity, neuronal dendritic spine loss, enhanced apoptosis and increased inflammation. However, the specific mechanism of PTSD has not been studied clearly. In the present study, we found that the level of miR-153-3p in the hippocampus of rats exposed tosingle-prolonged stresss (SPS) was upregulated, but its downstream target σ-1R showed a significant decrease. The downregulation of miR-153 could alleviate the PTSD-like behaviors in the rats exposed to SPS, and this effect might be related to the upregulation of σ-1R and PSD95. Furthermore, anti-miR-153 could also increase the dendritic spine density and reduce cell apoptosis in the hippocampus of SPS rats. In addition, we showed that the mTOR signaling pathway might be involved in the regulation of σ-1R in the hippocampus of rats exposed to SPS. The results of this study indicated that miR-153 might alleviate PTSD-like behaviors by regulating cell morphology and reducing cell apoptosis in the hippocampus of rats exposed to SPS by targeting σ-1R, which might be related to the mTOR signaling pathway.

Epigallocatechin-3-Gallate Allosterically Activates Protein Kinase C-α and Improves the Cognition of Estrogen Deficiency Mice

Protein kinase C (PKC) isozymes play essential roles in biological processes, and activation of PKC is proposed to alleviate the symptoms of a variety of diseases. It would be of great significance to find effective pharmacological modulators of PKC isozymes that can be translated for clinical use. Here, using in vitro activity assay, we demonstrated that green tea extract (-)-epigallocatechin-3-gallate (EGCG) dose-dependently activated PKCα with a half effective concentration (EC50) of 0.49 μM. We also performed surface plasmon resonance analysis and found that EGCG binds PKCα with an equilibrium dissociation constant (K_D) value of 4.11 × 10^-6 mol/L. Further computational flexible docking analysis revealed that EGCG interacted with the catalytic C3-C4 domain of PKCα (PDB: 4RA4) through establishing polar hydrogen bonds with V420, T401, E387, and K368 of PKCα, and the benzene ring group of EGCG hydrophobically interacted with the hydrophobic pocket formed by L345, M470, I479, and V353 of PKCα. Interestingly, the PKCα-selective blocker Ro-32-0432 could compete with EGCG for the same substrate-binding pocket of PKCα. Moreover, we found that EGCG dose-dependently improved the spatial memory, object recognition ability, and hippocampal long-term potentiation of ovariectomized mice, which was offset by Ro-32-0432. Collectively, our findings reveal a novel PKCα agonist and open the way to a new perspective on PKCα pharmacology and the treatment of PKCα-related diseases, including cognitive impairment.

Shenzhi Jiannao formula ameliorates vascular dementia in vivo and in vitro by inhibition glutamate neurotoxicity via promoting clathrin-mediated endocytosis

BACKGROUND

Synaptic damage and glutamate excitotoxicity have been implicated in the pathogenesis of vascular dementia (VD). Clathrin, RAB5B and N-methyl-D-aspartic acid receptor 1 (NMDAR1) proteins play a vital role in endocytosis of synaptic vesicles in neurons and glutamate over accumulation. Previous researches have been confirmed that Shenzhi Jiannao (SZJN) formula has an anti-apoptotic and neuroprotective effect in VD, but the underlying mechanisms are still unclear. In this study, we aimed to explore the effect of SZJN formula on cognitive impairment and glutamate excitotoxicity via clathrin-mediated endocytosis (CME) in vivo and in vitro.

METHODS

SZJN formula consists of Panax ginseng C.A.Mey., Anemarrhena asphodeloides Bunge, and Paeonia anomala subsp. veitchii (Lynch) D.Y.Hong & K.Y.Pan. All herbs were prepared into granules. Both common carotid arteries were permanent occluded (2-vessel occlusion, 2VO) in male Sprague Dawley (SD) rats to model VD. One day after operation, the rats began daily treatment with SZJN formula for 2 weeks. The neuroprotective effects of SZJN formula was subsequently assessed by the novel object recognition test, Morris water maze, hematoxylin-eosin (HE) staining and Nissl staining. Glutamate cytotoxicity was assessed by detecting cell viability and cell death of PC12 cells. Immunohistochemistry, immunofluorescence, Western blot, and quantitative real-time PCR were used to detect the expression levels of clathrin, RAB5B, and NMDAR1.

RESULTS

Administration of SZJN formula effectively improved short-term memory and spatial memory. SZJN formula treatment significantly reduced hippocampal neuronal loss, and recovered the arrangement and morphology of neurons and Nissl bodies. Moreover, SZJN formula promoted the proliferation of PC12 cells and inhibited glutamate-induced cell death. The down-regulation of clathrin and RAB5B, as well as the upregulation of NMDAR1 in the brain induced by 2VO or glutamate was also notably reversed by SZJN formula at both the protein and mRNA levels, which may contribute to SZJN formula induced improved neurological function.

CONCLUSIONS

Taken together, our findings provide evidence that the neuroprotective effects of SZJN formula in experimental VD maybe mediated through promoting the expression of clathrin-mediated endocytosis and reducing NMDARs-associated glutamate excitotoxicity. SZJN formula serves as a promising alternative therapy and may be a useful herbal medicine for preventing progression of VD.

AhR/miR-23a-3p/PKCα axis contributes to memory deficits in ovariectomized and normal aging female mice

The mechanism of estrogen deficiency-induced cognitive impairment is still not fully elucidated. In this study, we assessed the effect of microRNA (miRNA) on the memory of long-term estrogen-deficient mice after ovariectomy (OVX) and normal aging. We observed that 5-month OVX and 22-month-old normal aging female mice showed significantly impaired spatial and object recognition memory, declined hippocampal long-term potentiation (LTP), and decreased hippocampal protein kinase C α (PKCα) protein. Quantitative real-time PCR analysis showed upregulated miRNA-23a-3p (miR-23a-3p) in the hippocampus of 5-month OVX and 22-month-old female mice. In vitro, overexpression of miR-23a-3p downregulated PKCα by binding the 3¢ UTRs of Prkca mRNAs, which was prevented by its antisense oligonucleotide AMO-23a. In vivo, adeno-associated virus-mediated overexpression of miR-23a-3p (AAV-pre-miR-23a-3p) suppressed hippocampal PKCα and impaired the memory of mice. Chromatin immunoprecipitation analysis showed that aryl hydrocarbon receptor (AhR) binds the promoter region of miR-23a-3p. The AhR-dependent downregulation of PKCα could be prevented by AMO-23a as well. Furthermore, knockdown of miR-23a-3p using AAV-AMO-23a rescued the cognitive and electrophysiological impairments of OVX and normal aging female mice. We conclude that long-term estrogen deficiency impairs cognition and hippocampal LTP by activating the AhR/miR-23a-3p/PKCα axis. The knockdown of miR-23a-3p may be a potentially valuable therapeutic strategy for estrogen deficiency-induced memory deficits.

Regulatory microRNAs and vascular cognitive impairment and dementia

Vascular cognitive impairment and dementia (VCID) is defined as a progressive dementia disease related to cerebrovascular injury and often occurs in aged populations. Despite decades of research, effective treatment for VCID is still absent. The pathological processes of VCID are mediated by the molecular mechanisms that are partly modulated at the post-transcriptional level. As small endogenous non-coding RNAs, microRNAs (miRs) can regulate target gene expression through post-transcriptional gene silencing. miRs have been reported to play an important role in the pathology of VCID and have recently been suggested as potential novel pharmacological targets for the development of new diagnosis and treatment strategies in VCID. In this review, we summarize the current understanding of VCID, the possible role of miRs in the regulation of VCID and attempt to envision future therapeutic strategies. Since manipulation of miR levels by either pharmacological or genetic approaches has shown therapeutic effects in experimental VCID models, we also emphasize the potential therapeutic value of miRs in clinical settings.

The role of synaptic microRNAs in Alzheimer's disease

Structurally and functionally active synapses are essential for neurotransmission and for maintaining normal synaptic and cognitive functions. Researchers have found that synaptic dysfunction is associated with the onset and progression of neurodegenerative diseases, such as Alzheimer's disease (AD), and synaptic dysfunction is even one of the main physiological hallmarks of AD. MiRNAs are present in small, subcellular compartments of the neuron such as neural dendrites, synaptic vesicles, and synaptosomes are known as synaptic miRNAs. Synaptic miRNAs involved in governing multiple synaptic functions that lead to healthy brain functioning and synaptic activity. However, the precise role of synaptic miRNAs has not been determined in AD progression. This review emphasizes the presence of miRNAs at the synapse, synaptic compartments and roles of miRNAs in multiple synaptic functions. We focused on synaptic miRNAs alteration in AD, and how the modulation of miRNAs effect the synaptic functions in AD. We also discussed the impact of synaptic miRNAs in AD progression concerning the synaptic ATP production, mitochondrial function, and synaptic activity.

Cholinergic Dysfunction Involvement in Chronic Cerebral Hypoperfusion-Induced Impairment of Medial Septum-dCA1 Neurocircuit in Rats

Chronic cerebral hypoperfusion (CCH) is considered a preclinical condition of mild cognitive impairment and thought to precede dementia. However, as the principal cholinergic source of hippocampus, whether the septo-hippocampal neurocircuit was impaired after CCH is still unknown. In this study, we established the CCH rat model by bilateral common carotid artery occlusion (2VO). Under anesthesia, the medial septum (MS) of rats was stimulated to evoke the field excitatory post-synaptic potential (fEPSP) in the pyramidal cell layer of dCA1. Consequently, we observed decreased amplitude of fEPSP and increased paired-pulse ratio (PPR) after 8-week CCH. After tail pinch, we also found decreased peak frequency and shortened duration of hippocampal theta rhythm in 2VO rats, indicating the dysfunction of septo-hippocampal neurocircuit. Besides, by intracerebroventricularly injecting GABAergic inhibitor (bicuculline) and cholinergic inhibitors (scopolamine and mecamylamine), we found that CCH impaired both the pre-synaptic cholinergic release and the post-synaptic nAChR function in MS-dCA1 circuits. These results gave an insight into the role of CCH in the impairment of cholinergic MS-dCA1 neurocircuits. These findings may provide a new idea about the CCH-induced neurodegenerative changes.