MiR-124 Prevents the Microglial Proinflammatory Response by Inhibiting the Activities of TLR4 and Downstream NLRP3 in Palmitic Acid-Treated BV2 Cells

Exploration of the Key Genes Involved in Non-alcoholic Fatty Liver Disease and Possible MicroRNA Therapeutic Targets

Background

MicroRNAs (miRNAs) are promising therapeutic agents for non-alcoholic fatty liver disease (NAFLD). This study aimed to identify key genes/proteins involved in NAFLD pathogenesis and progression and to evaluate miRNAs influencing their expression.

Methods

Gene expression profiles from datasets GSE151158, GSE163211, GSE135251, GSE167523, GSE46300, and online databases were analyzed to identify significant NAFLD-related genes. Then, protein-protein interaction networks and module analysis identified hub genes/proteins, which were validated using real-time PCR in oleic acid-treated HepG2 cells. Functional enrichment analysis evaluated signaling pathways and biological processes. Gene-miRNA interaction networks identified miRNAs targeting critical NAFLD genes.

Results

The most critical overexpressed hub genes/proteins included: TNF, VEGFA, TLR4, CYP2E1, ACE, SCD, FASN, SREBF2, and TGFB1 based on PPI network analysis, of which TNF, TLR4, SCD, FASN, SREBF2, and TGFB1 were up-regulated in oleic acid-treated HepG2 cells. Functional enrichment analysis for biological processes highlighted programmed necrotic cell death, lipid metabolic process response to reactive oxygen species, and inflammation. In the Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis, the highest adjusted P-value signaling pathways encompassed AGE-RAGE in diabetic complications, TNF, and HIF-1 signaling pathways. In gene-miRNA network analysis, miR-16 and miR-124 were highlighted as the miRNAs exerting the most influence on important NAFLD-related genes.

Conclusion

In silico analyses identified NAFLD therapeutic targets and miRNA candidates to guide further experimental investigation.

Analysis of the therapeutic potential of miR-124 and miR-16 in non-alcoholic fatty liver disease

BACKGROUNDS

Non-alcoholic fatty liver disease (NAFLD) is a common condition affecting >25 % of the population worldwide. This disorder ranges in severity from simple steatosis (fat accumulation) to severe steatohepatitis (inflammation), fibrosis and, at its end-stage, liver cancer. A number of studies have identified overexpression of several key genes that are critical in the initiation and progression of NAFLD. MiRNAs are potential therapeutic agents that can regulate several genes simultaneously. Therefore, we transfected cell lines with two key miRNAs involved in targeting NAFLD-related genes.

METHODS

The suppression effects of the investigated miRNAs (miR-124 and miR-16) and genes (TNF, TLR4, SCD, FASN, SREBF2, and TGFβ-1) from our previous study were investigated by real-time PCR in Huh7 and HepG2 cells treated with oleic acid. Oil red O staining and the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) assay were utilized to assess cell lipid accumulation and cytotoxic effects of the miRNAs, respectively. The pro-oxidant-antioxidant balance (PAB) assay was undertaken for miR-16 and miR-124 after cell transfection.

RESULTS

Following transfection of miRNAs into HepG2, oil red O staining showed miR-124 and miR-16 reduced oleic acid-induced lipid accumulation by 35.2 % and 28.6 % respectively (p < 0.05). In Huh7, miR-124 and miR-16 reduced accumulation by 23.5 % and 31.3 % respectively (p < 0.05) but without impacting anti-oxidant activity. Real-time PCR in HepG2 revealed miR-124 decreased expression of TNF by 0.13-fold, TLR4 by 0.12-fold and SREBF2 by 0.127-fold (p < 0.05). miR-16 decreased TLR4 by 0.66-fold and FASN by 0.3-fold (p < 0.05). In Huh7, miR-124 decreased TNF by 0.12-fold and FASN by 0.09-fold (p < 0.05). miR-16 decreased SCD by 0.28-fold and FASN by 0.64-fold (p < 0.05). MTT assays showed, in HepG2, viability was decreased 24.7 % by miR-124 and decreased 33 % by miR-16 at 72 h (p < 0.05). In Huh7, miR-124 decreased viability 42 % at 48 h and 29.33 % at 72 h (p < 0.05), while miR-16 decreased viability by 32.3 % (p < 0.05).

CONCLUSION

These results demonstrate the ability of miR-124 and miR-16 to significantly reduce lipid accumulation and expression of key pathogenic genes associated with NAFLD through direct targeting. Though this requires further in vivo investigation.

Palmitoleic acid protects microglia from palmitate-induced neurotoxicity in vitro

Although palmitoleic acid (POA) is a lipokine with beneficial effects on obesity and is produced as a byproduct from the manufacture of prescription omega-3 fatty acids, its role in nervous system inflammation is still unknown. This study aims to examine the mechanisms and protective effects of POA against palmitic acid (PA)-induced microglial death. PA-induced microglial death was used as a model for POA intervention. Various inhibitors were employed to suppress potential routes of PA entry into the cell. Immunofluorescence staining and Western blotting were conducted to elucidate the protective pathways involved. The results suggest POA has the potential to eliminate PA-induced lactate dehydrogenase (LDH) release, which decreases the overall number of propidium iodide (PI)-positive cells compared with control. Moreover, POA has the potential to significantly increase lipid droplets (LDs) in the cytoplasm, without causing any lysosomal damage. POA inhibited both canonical and non-canonical gasdermin D (GSDMD)-mediated pyroptosis and gasdermin E (GSDME)-mediated pyroptosis, which PA typically induces. Additionally, POA inhibited the endoplasmic reticulum (ER) stress and apoptosis-related proteins induced by PA. Based on the findings, POA can exert a protective effect on microglial death induced by PA via pathways related to pyroptosis, apoptosis, ER stress, and LDs.

Microglial TLR4/NLRP3 Inflammasome Signaling in Alzheimer's Disease

Alzheimer's disease is a pervasive neurodegenerative disease that is estimated to represent approximately 70% of dementia cases worldwide, and the molecular complexity that has been highlighted remains poorly understood. The accumulation of extracellular amyloid-β (Aβ), intracellular neurofibrillary tangles formed by tau hyperphosphorylation, and neuroinflammation are the major pathological features of Alzheimer's disease (AD). Over the years, there has been no apparent breakthrough in drug discovery based on the Aβ and tau hypotheses. Neuroinflammation has gradually become a hot spot in AD treatment research. As the primary cells of innate immunity in the central nervous system, microglia play a key role in neuroinflammation. Toll-like receptor 4 (TLR4) and nucleotide-binding oligomerization domain-like receptor 3 (NLRP3) inflammasomes are vital molecules in neuroinflammation. In the pathological context of AD, the complex interplay between TLR4 and the NLRP3 inflammasomes in microglia influences AD pathology via neuroinflammation. In this review, the effect of the activation and inhibition of TLR4 and NLRP3 in microglia on AD pathology, as well as the cross-talk between TLR4 and the NLRP3 inflammasome, and the influence of essential molecules in the relevant signaling pathway on AD pathology, were expounded. In addition, the feasibility of these factors in representing a potential treatment option for AD has been clarified.

Protective effects of Zishen Huoxue recipe against neuronal injury in the neurovascular unit of rats with vascular dementia by interfering with inflammatory cascade-induced pyroptosis

OBJECTIVE

Chinese herbal formulas show considerable therapeutic benefits in dementia. This study specifically explored the protective action of Zishen Huoxue recipe on the neurovascular unit (NVU) of rats with vascular dementia (VD).

METHODS

VD rat models were established by permanent bilateral common carotid artery occlusion and treated with Zishen Huoxue recipe. In vitro glucose‑oxygen deprivation (OGD)-injured NVU models were established and treated with miR-124-3p agomir or rat medicated serum. The neurological damage, histopathological changes, and neuronal injury in the rat hippocampus were assessed using Morris water maze test and histological stainings. Expression of miR-124-3p was determined using RT-qPCR. The blood-brain barrier/NVU injury, cell pyroptosis, NLRP3 inflammasome activation, and release of inflammatory factors were analyzed mainly by immunofluorescence analysis, TUNEL staining, Western blot, and ELISA. QS-21 (an NLRP3 activator) was used to verify the role of miR-124-3p/NLRP3.

RESULTS

Zishen Huoxue recipe ameliorated the learning/memory deficits, neuronal injury, NVU insults, cell pyroptosis, activation of NLRP3 inflammasome, and extensive secretion of lactate dehydrogenase/IL-1β/IL-18 in VD rats. miR-124-3p was downregulated in VD rats but upregulated after treatment of this recipe. miR-124-3p overexpression ameliorated NVU insults, reduced cell pyroptosis, lowered NLRP3 inflammasome activation, and suppressed inflammatory responses in OGD-injured NVU models. NLRP3 inflammasome activation partly counteracted the amelioration effect of miR-124-3p on pyroptosis. Zishen Huoxue recipe could upregulate miR-124-3p to suppress pyroptosis and protect NVU function.

CONCLUSION

Zishen Huoxue recipe can upregulate miR-124-3p expression to repress the inflammatory cascade-evoked pyroptosis, thereby protecting against neuronal injury in the NVU of VD rats.

Epigenetic regulation in opioid induced hyperalgesia

About 25 million American adults experience pain daily and one of the most commonly prescribed drugs to treat pain are opioids. Prolonged opioid usage and dose escalations can cause a paradoxical response where patients experience enhanced pain sensitivity. This opioid induced hyperalgesia (OIH) is a major hurdle when treating pain in the clinic because its underlying mechanisms are still not fully understood. OIH is also commonly overlooked and lacks guidelines to prevent its onset. Research on pain disorders and opioid usage have recognized potential epigenetic drivers of disease including DNA methylation, histone modifications, miRNA regulation, but their involvement in OIH has not been well studied. This article discusses epigenetic changes that may contribute to pathogenesis, with an emphasis on miRNA alterations in OIH. There is a crucial gap in knowledge including how multiple epigenetic modulators contribute to OIH. Elucidating the epigenetic changes underlying OIH and the crosstalk among these mechanisms could lead to the development of novel targets for the prevention and treatment of this painful phenomena.

The role of pyroptosis in cognitive impairment

Cognitive impairment is a major global disease, manifests as a decline in cognitive functioning and endangers the health of the population worldwide. The incidence of cognitive impairment has increased rapidly with an increasingly aging population. Although the mechanisms of cognitive impairment have partly been elucidated with the development of molecular biological technology, treatment methods are very limited. As a unique form of programmed cell death, pyroptosis is highly pro-inflammatory and is closely associated with the incidence and progression of cognitive impairment. In this review, we discuss the molecular mechanisms of pyroptosis briefly and the research progress on the relationship between pyroptosis and cognitive impairment and its potential therapeutic values, to provide a reference for research in the field of cognitive impairment.

Regulation by noncoding RNAs of local translation, injury responses, and pain in the peripheral nervous system

Neuropathic pain is a chronic condition arising from damage to somatosensory pathways that results in pathological hypersensitivity. Persistent pain can be viewed as a consequence of maladaptive plasticity which, like most enduring forms of cellular plasticity, requires altered expression of specific gene programs. Control of gene expression at the level of protein synthesis is broadly utilized to directly modulate changes in activity and responsiveness in nociceptive pathways and provides an effective mechanism for compartmentalized regulation of the proteome in peripheral nerves through local translation. Levels of noncoding RNAs (ncRNAs) are commonly impacted by peripheral nerve injury leading to persistent pain. NcRNAs exert spatiotemporal regulation of local proteomes and affect signaling cascades supporting altered sensory responses that contribute to hyperalgesia. This review discusses ncRNAs found in the peripheral nervous system (PNS) that are dysregulated following nerve injury and the current understanding of their roles in pathophysiological pain-related responses including neuroimmune interactions, neuronal survival and axon regeneration, Schwann cell dedifferentiation and proliferation, intercellular communication, and the generation of ectopic action potentials in primary afferents. We review progress in the field beyond cataloging, with a focus on the relevant target transcripts and mechanisms underlying pain modulation by ncRNAs.

Palmitic acid induces nDNA release to cytosol and promotes microglial M1 polarization via cGAS-STING signaling pathway

Palmitic acid (PA), the most common statured fatty acid in diets, is involved in peripheral as well as central inflammation. The M1 polarization of microglia plays an important role in PA-induced neuroinflammation. However, it is still unclear on the key factor and molecule mechanism of microglial polarization among it. Thus, we investigated whether the release of self-DNA into the cytoplasm of microglia was a consequence of PA treatment, as in aortic endothelial cells and adipocytes. RT-qPCR and immunofluorescence were performed to detect the status of cytosolic DNA and microglial polarization after PA treatment. We found that the content of cytosolic nDNA rather than mtDNA increased after PA treatment and the M1 polarization of microglia was associated with this. Moreover, the knockdown of cGAS in BV2 microglial cells demonstrated that the cGAS-STING pathway is involved in polarization process. Our results revealed that nDNA and cGAS-STING pathway are critically involved in PA-induced microglial M1 polarization. This mechanism may pose a new insight on targeting microglia may be a promising way to mitigate diet-induced early neuroinflammation.

Asiatic Acid Attenuates Inflammation Induced by Salmonella via Upregulating LncRNA TVX1 in Microglia

Salmonella typhimurium (S.T) induces damage to the central nervous system; however, the role of Asiatic acid (AA) in this is still unknown. Microglia play a role as macrophages to recognize the invaded pathogenic microbes in the brain. The aim of this study was to investigate the protective effect and mechanism of AA on the central nervous system through an in vitro model of S.T infection in microglia. We pre-treated microglia with AA before S.T infection and explored the anti-infection mechanism of AA by sequencing, quantitative reverse transcription PCR (RT-qPCR), and Western blotting. Long non-coding RNA (lncRNA) sequencing demonstrated that inflammation is a major factor in S.T infection of microglia. RT-qPCR data demonstrated that AA inhibited S.T-induced increases in the mRNA levels of the pro-inflammatory factors interleukin (IL)-1β, IL-6, and IL-18. Western blotting demonstrated that AA inhibited S.T-induced activation of the nuclear factor (NF)-κB pathway and activation of the NLR family, pyrin domain-containing 3 (NLRP3) inflammasome. Expression of the lncRNA TVX1 in microglia was decreased by S.T infection and increased by pretreatment with AA. Inhibition of TVX1 expression reversed the anti-inflammatory effect of AA, and overexpression of TVX1 in microglia suppressed S.T-induced inflammation. In conclusion, AA attenuated S.T-induced microglial inflammation by upregulating the expression of the lncRNA TVX1.

MicroRNA: A Linking between Astrocyte Dysfunction, Mild Cognitive Impairment, and Neurodegenerative Diseases

Simple Summary

Neurodegenerative diseases are complex neurological disorders with a high incidence worldwide in older people, increasing hospital visits and requiring expensive treatments. As a precursor phase of neurodegenerative diseases, cognitive impairment needs to be studied to understand the factors that influence its development and improve patients’ quality of life. The present review compiles possible factors and biomarkers for diagnosing mild cognitive impairment based on the most recent studies involving miRNAs. These molecules can direct the gene expression in multiple cells, affecting their behavior under certain conditions, such as stressing factors. This review encourages further research into biomarkers that identify cognitive impairment in cellular models such as astrocytes, which are brain cells capable of maintaining the optimal conditions for the central nervous system functioning.

Abstract

The importance of miRNAs in cellular processes and their dysregulation has taken significant importance in understanding different pathologies. Due to the constant increase in the prevalence of neurodegenerative diseases (ND) worldwide and their economic impact, mild cognitive impairment (MCI), considered a prodromal phase, is a logical starting point to study this public health problem. Multiple studies have established the importance of miRNAs in MCI, including astrocyte regulation during stressful conditions. Additionally, the protection mechanisms exerted by astrocytes against some damage in the central nervous system (CNS) lead to astrocytic reactivation, in which a differential expression of miRNAs has been shown. Nevertheless, excessive reactivation can cause neurodegeneration, and a clear pattern defining the equilibrium point between a neuroprotective or detrimental astrocytic phenotype is unknown. Therefore, the miRNA expression has gained significant attention to understand the maintenance of brain balance and improve the diagnosis and treatment at earlier stages in the ND. Here, we provide a comprehensive review of the emerging role of miRNAs in cellular processes that contribute to the loss of cognitive function, including lipotoxicity, which can induce chronic inflammation, also considering the fundamental role of astrocytes in brain homeostasis.

Neuroendocrine microRNAs linked to energy homeostasis: future therapeutic potential

The brain orchestrates whole-body metabolism through an intricate system involving interneuronal crosstalk and communication. Specifically, a key player in this complex circuitry is the hypothalamus that controls feeding behaviour, energy expenditure, body weight and metabolism, whereby hypothalamic neurons sense and respond to circulating hormones, nutrients, and chemicals. Dysregulation of these neurons contributes to the development of metabolic disorders, such as obesity and type 2 diabetes. The involvement of hypothalamic microRNAs, post-transcriptional regulators of gene expression, in the central regulation of energy homeostasis has become increasingly apparent, although not completely delineated. This review summarizes current evidence demonstrating the regulation of feeding-related neuropeptides by brain-derived microRNAs as well as the regulation of specific miRNAs by nutrients and other peripheral signals. Moreover, the involvement of microRNAs in the central nervous system control of insulin, leptin, and estrogen signal transduction is examined. Finally, the therapeutic and diagnostic potential of microRNAs for metabolic disorders will be discussed and the regulation of brain-derived microRNAs by nutrients and other peripheral signals is considered. Demonstrating a critical role of microRNAs in hypothalamic regulation of energy homeostasis is an innovative route to uncover novel biomarkers and therapeutic candidates for metabolic disorders.

Microglia Pyroptosis: A Candidate Target for Neurological Diseases Treatment

In addition to its profound implications in the fight against cancer, pyroptosis have important role in the regulation of neuronal injury. Microglia are not only central members of the immune regulation of the central nervous system (CNS), but are also involved in the development and homeostatic maintenance of the nervous system. Under various pathological overstimulation, microglia pyroptosis contributes to the massive release of intracellular inflammatory mediators leading to neuroinflammation and ultimately to neuronal damages. In addition, microglia pyroptosis lead to further neurological damage by decreasing the ability to cleanse harmful substances. The pathogenic roles of microglia in a variety of CNS diseases such as neurodegenerative diseases, stroke, multiple sclerosis and depression, and many other neurological disorders have been gradually unveiled. In the context of different neurological disorders, inhibition of microglia pyroptosis by targeting NOD-like receptor family pyrin domain containing (NLRP) 3, caspase-1 and gasdermins (GSDMs) by various chemical agents as well as natural products significantly improve the symptoms or outcome in animal models. This study will provide new ideas for immunomodulatory treatment of CNS diseases.

Cimifugin Ameliorates Lipotoxicity-Induced Hepatocyte Damage and Steatosis through TLR4/p38 MAPK- and SIRT1-Involved Pathways

Objective. Hepatic metabolic disorder induced by lipotoxicity plays a detrimental role in metabolic fatty liver disease pathogenesis. Cimifugin (Cim), a coumarin derivative extracted from the root of Saposhnikovia divaricata, possesses multiple biological properties against inflammation, allergy, and oxidative stress. However, limited study has addressed the hepatoprotective role of Cim. Here, we investigate the protective effect of Cim against lipotoxicity-induced cytotoxicity and steatosis in hepatocytes and clarify its potential mechanisms. Methods. AML-12, a nontransformed mouse hepatocyte cell line, was employed in this study. The cells were incubated with palmitate or oleate to imitate hepatotoxicity or steatosis model, respectively. Results. Cim significantly reversed palmitate-induced hepatocellular injury in a dose-dependent manner, accompanied by improvements in oxidative stress and mitochondrial damage. Cim pretreatment reversed palmitate-stimulated TLR4/p38 MAPK activation and SIRT1 reduction without affecting JNK, ERK1/2, and AMPK pathways. The hepatoprotective effects of Cim were abolished either through activating TLR4/p38 by their pharmacological agonists or genetical silencing SIRT1 via special siRNA, indicating a mechanistic involvement. Moreover, Cim treatment improved oleate-induced hepatocellular lipid accumulation, which could be blocked by either TLR4 stimulation or SIRT1 knockdown. We observed that SIRT1 was a potential target of TLR4 in palmitate-treated hepatocytes, since TLR4 agonist LPS aggravated, whereas TLR4 antagonist CLI-095 alleviated palmitate-decreased SIRT1 expression. SIRT1 knockdown did not affect palmitate-induced TLR4. In addition, TLR4 activation by LPS significantly abolished Cim-protected SIRT1 reduction induced by palmitate. These results collaboratively indicated that TLR4-regulated SIRT1 pathways was mechanistically involved in the protective effects of Cim against lipotoxicity. Conclusion. In brief, we demonstrate the protective effects of Cim against lipotoxicity-induced cell death and steatosis in hepatocytes. TLR4-regulated p38 MAPK and SIRT1 pathways are involved in Cim-protected hepatic lipotoxicity. Cim is a potential candidate for improving hepatic metabolic disorders mediated by lipotoxicity.