Luteolin induces microRNA-132 expression and modulates neurite outgrowth in PC12 cells

Luteolin for neurodegenerative diseases: a review

Neurodegenerative diseases such as Parkinson's disease, Alzheimer's disease, Huntington's disease, and multiple sclerosis affect millions of people around the world. In addition to age, which is a key factor contributing to the development of all neurodegenerative diseases, genetic and environmental components are also important risk factors. Current methods of treating neurodegenerative diseases are mostly symptomatic and do not eliminate the cause of the disease. Many studies focus on searching for natural substances with neuroprotective properties that could be used as an adjuvant therapy in the inhibition of the neurodegeneration process. These compounds include flavonoids, such as luteolin, showing significant anti-inflammatory, antioxidant, and neuroprotective activity. Increasing evidence suggests that luteolin may confer protection against neurodegeneration. In this review, we summarize the scientific reports from preclinical in vitro and in vivo studies regarding the beneficial effects of luteolin in neurodegenerative diseases. Luteolin was studied most extensively in various models of Alzheimer's disease but there are also several reports showing its neuroprotective effects in models of Parkinson's disease. Though very limited, studies on possible protective effects of luteolin against Huntington's disease and multiple sclerosis are also discussed here. Overall, although preclinical studies show the potential benefits of luteolin in neurodegenerative disorders, clinical evidence on its therapeutic efficacy is still deficient.

Neurotrophic Natural Products

Neurotrophins (NGF, BDNF, NT3, NT4) can decrease cell death, induce differentiation, as well as sustain the structure and function of neurons, which make them promising therapeutic agents for the treatment of neurodegenerative disorders. However, neurotrophins have not been very effective in clinical trials mostly because they cannot pass through the blood-brain barrier owing to being high-molecular-weight proteins. Thus, neurotrophin-mimic small molecules, which stimulate the synthesis of endogenous neurotrophins or enhance neurotrophic actions, may serve as promising alternatives to neurotrophins. Small-molecular-weight natural products, which have been used in dietary functional foods or in traditional medicines over the course of human history, have a great potential for the development of new therapeutic agents against neurodegenerative diseases such as Alzheimer's disease. In this contribution, a variety of natural products possessing neurotrophic properties such as neurogenesis, neurite outgrowth promotion (neuritogenesis), and neuroprotection are described, and a focus is made on the chemistry and biology of several neurotrophic natural products.

The Neuroprotective Effects of Flavonoid Fisetin against Corticosterone-Induced Cell Death through Modulation of ERK, p38, and PI3K/Akt/FOXO3a-Dependent Pathways in PC12 Cells

The overactive hypothalamic-pituitary-adrenal (HPA) axis is believed to trigger the overproduction of corticosterone, leading to neurotoxicity in the brain. Fisetin is a flavonoid commonly found in fruits and vegetables. It has been suggested to possess various biological activities, including antioxidant, anti-inflammatory, and neuroprotective effects. This study aims to explore the potential neuroprotective properties of fisetin against corticosterone-induced cell death and its underlying molecular mechanism in PC12 cells. Our results indicate that fisetin, at concentrations ranging from 5 to 40 μM, significantly protected PC12 cells against corticosterone-induced cell death. Fisetin effectively reduced the corticosterone-mediated generation of reactive oxygen species (ROS) in PC12 cells. Fisetin treatments also showed potential in inhibiting the corticosterone-induced apoptosis of PC12 cells. Moreover, inhibitors targeting MAPK/ERK kinase 1/2 (MEK1/2), p38 MAPK, and phosphatidylinositol 3-kinase (PI3K) were found to significantly block the increase in cell viability induced by fisetin in corticosterone-treated cells. Consistently, fisetin enhanced the phosphorylation levels of ERK, p38, Akt, and c-AMP response element-binding protein (CREB) in PC12 cells. Additionally, it was found that the diminished levels of p-CREB and p-ERK by corticosterone can be restored by fisetin treatment. Furthermore, the investigation of crosstalk between ERK and CREB revealed that p-CREB activation by fisetin occurred through the ERK-independent pathway. Moreover, we demonstrated that fisetin effectively counteracted the corticosterone-induced nuclear accumulation of FOXO3a, an apoptosis-triggering transcription factor, and concurrently promoted FOXO3a phosphorylation and its subsequent cytoplasmic localization through the PI3K/Akt pathway. In conclusion, our findings indicate that fisetin exerts its neuroprotective effect against corticosterone-induced cell death by modulating ERK, p38, and the PI3K/Akt/FOXO3a-dependent pathways in PC12 cells. Fisetin emerges as a promising phytochemical for neuroprotection.

Pachira macrocarpa Schltdl. & Cham., HPLC Profile, and Neuroprotective Potential via Regulation of JNK, miRNA132, and miRNA-125b

In this study, we investigated the polyphenolic profile of Pachira macrocarpa Schltdl. & Cham. by HPLC analysis and we also isolated three compounds from the ethyl acetate leaf extract, which were identified by different spectral data as vitexin 1, luteolin 2, and ferulic acid 3. Moreover, we investigated the three isolated compounds and the plant extract for their therapeutic potential against AlCl3 exposure-induced neurotoxicity in rats. This investigation aims to determine whether vitexin, luteolin, and ferulic acid in Pachira macrocarpa Schltdl. & Cham. extract (P. macrocarpa) have the ability to treat AlCl3-induced brain toxicity in rats. Six groups of rats were created: group 1 (normal group), group 2 treated with AlCl3, and groups 3, 4, 5, and 6 treated with AlCl3 with vitexin, luteolin, ferulic acid, and P. macrocarpa extract, respectively, for 28 days. Neurotoxicity was assessed by measuring plasma IL-8 and IL-33 as well as brain superoxide dismutase (SOD), glutathione reductase (GSR), B-cell lymphoma-2 (BcL-2), B-cell lymphoma-2 associated-x (Bax), and neurogranin using the ELISA technique and c-Jun N-terminal kinase (JNK), miRNA-125b, and miRNA-132 levels using western blot and PCR. HPLC analysis identified major phenolics and flavonoids. Among the phenolics identified, chlorogenic acid was prevalent (2159.14 μg/g), and regarding flavonoids, rutin was prevalent (204.69 μg/g). A significant elevation of IL-8 and IL-33 as well as brain Bax, neurogranin, and JNK levels and of miRNA-125b gene expression levels was observed following AlCl3 exposure. However, significant depletion of SOD, GSR, BcL-2, total protein, and miRNA-132 gene expression was observed in AlCl3-treated rats. Administration of the P. macrocarpa extract and its isolated compounds significantly increased SOD, GSR, BcL-2, total protein, and miRNA132 gene expression and decreased IL-8 and IL-33 as well as brain Bax, neurogranin, and JNK levels and brain miRNA-125b gene expression compared to AlCl3-treated rats. P. macrocarpa extract and its isolated compounds ameliorated AlCl3-induced oxidative stress and neurotoxicity in rats.

Dietary Flavonoids and Adult Neurogenesis: Potential Implications for Brain Aging

Adult neurogenesis deficiency has been proposed to be a common hallmark in different age-related neurodegenerative diseases. The administration of flavonoids is currently reported as a potentially beneficial strategy for preventing brain aging alterations, including adult neurogenesis decline. Flavonoids are a class of plant-derived dietary polyphenols that have drawn attention for their neuroprotective and pro-cognitive effects. Although they undergo extensive metabolism and localize in the brain at low concentrations, flavonoids are now believed to improve cerebral vasculature and interact with signal transduction cascades involved in the regulation of adult neurogenesis. Furthermore, many dietary flavonoids have been shown to reduce oxidative stress and neuroinflammation, improving the neuronal microenvironment where adult neurogenesis occurs. The overall goal of this review is to summarize the evidence supporting the role of flavonoids in modulating adult neurogenesis as well as to highlight how these dietary agents may be promising candidates in restoring healthy brain function during physiological and pathological aging.

Therapeutics for mitochondrial dysfunction-linked diseases in Down syndrome

Genome-wide deregulation contributes to mitochondrial dysfunction and impairment in oxidative phosphorylation (OXPHOS) mechanism resulting in oxidative stress, increased production of reactive oxygen species (ROS) and cell death in individuals with Down syndrome (DS). The cells, which require more energy, such as muscles, brain and heart are greatly affected. Impairment in mitochondrial network has a direct link with patho-mechanism at cellular and systemic levels at the backdrop of generalized metabolic perturbations in individuals with DS. Myriads of clinico-phenotypic features, including intellectual disability, early aging and neurodegeneration, and Alzheimer disease (AD)-related dementia are inevitable in DS-population where mitochondrial dysfunctions play the central role. Collectively, the mitochondrial abnormalities and altered energy metabolism perturbs several signaling pathways, particularly related to neurogenesis, which are directly associated with cognitive development and early onset of AD in individuals with DS. Therefore, therapeutic challenges for amelioration of the mitochondrial defects were perceived to improve the quality of life of the DS population. A number of pharmacologically active natural compounds such as polyphenols, antioxidants and flavonoids have shown convincing outcome for reversal of the dysfunctional mitochondrial network and oxidative metabolism, and improvement in intellectual skill in mouse models of DS and humans with DS.

Luteolin Induced Hippocampal Neuronal Pyroptosis Inhibition by Regulation of miR-124-3p/TNF-α/TRAF6 Axis in Mice Affected by Breast-Cancer-Related Depression

Background

Breast-cancer-related depression (BCRD) is associated with an increased mortality rate among breast cancer (BC) survivors. Luteolin has many pharmacological effects, particularly in the treatment of BC. In this study, we aimed to explore the anti-BCRD activity of luteolin and its underlying functional mechanism.

Methods

A BCRD mouse model was induced by injecting 4T1 cells and corticosterone (COR). Behavioral test, terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) staining, Nissl staining, immunofluorescence, reverse-transcription quantitative PCR (RT-qPCR), and western blotting were used to study the effect of luteolin in mice with BCRD in vivo. A COR-induced neuron injury model was established in HT-22 cells in vitro. The role of miR-124-3p in the anti-BCRD effects of luteolin was studied using a miR-124-3p inhibitor.

Results

Luteolin significantly reduced the size and weight of the tumor, increased the mice entry frequency in the symmetrical sector, and reduced the duration of immobility in the tail suspension and forced swimming tests of mice affected by BCRD. Simultaneously, apoptosis of hippocampal neurons was inhibited, and the number of Nissl bodies increased with luteolin treatment. In addition, luteolin resulted in the upregulation of miR-124-3p expression in the hippocampus and downregulated the expression of tumor necrosis factor-α (TNF-α) and TNF receptor-associated factor 6 (TRAF6), as well as lowered the phosphorylation levels of nuclear factor-kappa B (NF-κB) and IkappaB (IκB). Luteolin also inhibited pyroptosis of hippocampal neurons in mice affected by BCRD, as revealed by the low protein levels of NOD-like receptor protein 3 (NLRP3), caspase-1, gasdermin D-N (GSDMD-N), interleukin (IL)-1β, and IL-18. However, the miR-124-3p inhibitor significantly reversed the therapeutic effect of luteolin on COR-induced HT-22 cells.

Conclusion

Our study demonstrated that the anti-BCRD function of luteolin was mediated by regulating the miR-124-3p/TNF-α/TRAF6-related pathway and inhibiting neuronal cell pyroptosis and subsequent inflammation. Therefore, luteolin may be a potential drug candidate in the treatments of BCRD.

Luteolin stimulates the NGF-induced neurite outgrowth in cultured PC12 cells through binding with NGF and potentiating its receptor signaling

Luteolin, a flavonoid in fruits and vegetables, has neurotrophic functions without a well-characterized mechanism. Here, we hypothesize a direct interaction of luteolin with nerve growth factor (NGF); as such, the functionality of the NGF could be potentiated. The direct binding of luteolin with NGF was validated by ultra-filtration, Biacore, and docking analyses. In cultured PC12 cells, application of luteolin in combination with a low dose of NGF potentiated the NGF-induced differentiation of neurons by an increase of the differentiated cell number to 25.4 ± 4.8% (p < 0.01), as well as the increased expression of neurofilaments by 119 ± 32.1% (p < 0.05), 191 ± 12.6% (p < 0.01), and 110 ± 23.4% (p < 0.05) for NF68, NF160 and NF200, respectively. The co-treatment induced the phosphorylations of tropomyosin receptor kinase A (TrkA), extracellular signal-regulated kinase 1/2 (ERK1/2), protein kinase B (Akt), phospholipase C-γ1 (PLCγ1), and cAMP response element-binding protein (CREB) by 2 to 3 fold: these induced phosphorylations were mimicking that of a high dose of NGF. Moreover, the application of the TrkA inhibitor, K252a, blocked the luteolin-mediated induction of neurofilament expression and neurite outgrowth in cultured PC12 cells, suggesting the target specificity. The result supports the development of luteolin as a therapeutic, or preventive, agent for NGF insufficiency-associated neurodegenerative diseases.

Extracellular vesicles synchronize cellular phenotypes of differentiating cells

During embryonic development, cells differentiate in a coordinated manner, aligning their fate decisions and differentiation stages with those of surrounding cells. However, little is known about the mechanisms that regulate this synchrony. Here we show that cells in close proximity synchronize their differentiation stages and cellular phenotypes with each other via extracellular vesicle (EV)-mediated cellular communication. We previously established a mouse embryonic stem cell (ESC) line harbouring an inducible constitutively active protein kinase A (CA-PKA) gene and found that the ESCs rapidly differentiated into mesoderm after PKA activation. In the present study, we performed a co-culture of Control-ESCs and PKA-ESCs, finding that both ESC types rapidly differentiated in synchrony even when PKA was activated only in PKA-ESCs, a phenomenon we named 'Phenotypic Synchrony of Cells (PSyC)'. We further demonstrated PSyC was mediated by EVs containing miR-132. PKA-ESC-derived EVs and miR-132-containing artificial nano-vesicles similarly enhanced mesoderm and cardiomyocyte differentiation in ESCs and ex vivo embryos, respectively. PSyC is a new form of cell-cell communication mediated by the EV regulation of neighbouring cells and could be broadly involved in tissue development and homeostasis.

Role of luteolin in overcoming Parkinson's disease

Parkinson's disease (PD) is the second most common neurodegenerative disorder affecting elderly people (>60 years old) worldwide. There is no permanent cure for the disease but the symptomatic relief can be obtained by using dopamine agonists besides L-dopa therapy. The longer use of the drugs is associated with several side effects. Hence, the researchers have made a considerable attention toward the development of neuroprotective agents from plants. A number of phytochemicals have been demonstrated for their protective effects in various in vitro, in vivo, and clinical studies. In this context, luteolin, a flavone which is present in fruits and vegetables has been attributed to a number of pharmacological properties including neuroprotective. The present review demonstrates the bioavailability, oral absorption, and mechanism of action against PD.

Neuronal Development-Related miRNAs as Biomarkers for Alzheimer's Disease, Depression, Schizophrenia and Ionizing Radiation Exposure

Radiation exposure may induce Alzheimer's disease (AD), depression or schizophrenia. A number of experimental and clinical studies suggest the involvement of miRNA in the development of these diseases, and also in the neuropathological changes after brain radiation exposure. The current literature review indicated the involvement of 65 miRNAs in neuronal development in the brain. In the brain tissue, blood, or cerebral spinal fluid (CSF), 11, 55, or 28 miRNAs are involved in the development of AD respectively, 89, 50, 19 miRNAs in depression, and 102, 35, 8 miRNAs in schizophrenia. We compared miRNAs regulating neuronal development to those involved in the genesis of AD, depression and schizophrenia and also those driving radiation-induced brain neuropathological changes by reviewing the available data. We found that 3, 11, or 8 neuronal developmentrelated miRNAs from the brain tissue, 13, 16 or 14 miRNAs from the blood of patient with AD, depression and schizophrenia respectively were also involved in radiation-induced brain pathological changes, suggesting a possibly specific involvement of these miRNAs in radiation-induced development of AD, depression and schizophrenia respectively. On the other hand, we noted that radiationinduced changes of two miRNAs, i.e., miR-132, miR-29 in the brain tissue, three miRNAs, i.e., miR- 29c-5p, miR-106b-5p, miR-34a-5p in the blood were also involved in the development of AD, depression and schizophrenia, thereby suggesting that these miRNAs may be involved in the common brain neuropathological changes, such as impairment of neurogenesis and reduced learning memory ability observed in these three diseases and also after radiation exposure.

Luteolin-induced vasorelaxation in uterine arteries from normal pregnant rats

BACKGROUND

The flavonoid, luteolin, promotes vasorelaxation in various arteries through endothelial-dependent and independent mechanisms. Although there is growing interest in the vasoactive effects of flavonoids on maternal vascular function during pregnancy, it is unknown whether luteolin elicits vasorelaxation in the uterine circulation. We tested the hypothesis that luteolin induces vasorelaxation via endothelial-dependent mechanisms in uterine arteries from normal pregnant rats during late gestation.

METHODS

Uterine arteries and aortas were isolated from Sprague-Dawley rats at gestational day 19 and prepared for wire myography.

RESULTS

The potency of luteolin-induced vasorelaxation was examined between uterine arteries and the aortas. By 50 µM of luteolin, there was complete relaxation (100.5 ± 5.2%) in uterine arteries as compared to aortas (27.5 ± 10.0%). Even the highest concentration of 100 µM luteolin produced less than half relaxation (43.6 ± 8.6%) in aortas compared to uterine arteries. We then explored if luteolin-induced vasorelaxation in uterine arteries from pregnant rats was mediated by endothelial-dependent vasorelaxation pathways, including nitric oxide synthase (NOS), cyclooxygenase (COX), or potassium (K⁺) channels. Blocking these pathways with N(G)-Nitro-l-arginine methyl ester hydrochloride (L-NAME), indomethacin, or tetraethylammonium (TEA)/high potassium chloride (KCl), respectively, did not alter luteolin responses in uterine arteries from pregnant rats. These findings suggested that endothelial factors may not mediate luteolin-induced vasorelaxation in uterine arteries during pregnancy. Indeed, experiments where the endothelium was removed did not alter luteolin-induced vasorelaxation in uterine arteries during pregnancy.

CONCLUSIONS

Luteolin directly promotes vasorelaxation in the medial smooth muscle layer of uterine arteries during normal pregnancy.

MicroRNA-135a-5p Promotes the Functional Recovery of Spinal Cord Injury by Targeting SP1 and ROCK

Emerging evidence indicates that microRNAs play a pivotal role in neural remodeling after spinal cord injury (SCI). This study aimed to investigate the mechanisms of miR-135a-5p in regulating the functional recovery of SCI by impacting its target genes and downstream signaling. The gene transfection assay and luciferase reporter assay confirmed the target relationship between miR-135a-5p and its target genes (specificity protein 1 [SP1] and Rho-associated kinase [ROCK]1/2). By establishing the H₂O₂-induced injury model, miR-135a-5p transfection was found to inhibit the apoptosis of PC12 cells by downregulating the SP1 gene, which subsequently induced downregulation of pro-apoptotic proteins (Bax, cleaved caspase-3) and upregulation of anti-apoptotic protein Bcl-2. By measuring the neurite lengths of PC12 cells, miR-135a-5p transfection was found to promote axon outgrowth by downregulating the ROCK1/2 gene, which subsequently caused upregulation of phosphate protein kinase B (AKT) and phosphate glycogen synthase kinase 3β (GSK3β). Use of the rat SCI models showed that miR-135a-5p could increase the Basso, Beattie, and Bresnahan (BBB) scores, indicating neurological function recovery. In conclusion, the miR-135a-5p-SP1-Bax/Bcl-2/caspase-3 and miR-135a-5p-ROCK-AKT/GSK3β axes are involved in functional recovery of SCI by regulating neural apoptosis and axon regeneration, respectively, and thus can be promising effective therapeutic strategies in SCI.

A Pharmacological Appraisal of Neuroprotective and Neurorestorative Flavonoids Against Neurodegenerative Diseases

BACKGROUND & OBJECTIVE

Alzheimer's disease (AD) and Parkinson's disease (PD) affect an increasing number of the elderly population worldwide. The existing treatments mainly improve the core symptoms of AD and PD in a temporary manner and cause alarming side effects. Naturally occurring flavonoids are well-documented for neuroprotective and neurorestorative effects against various neurodegenerative diseases. Thus, we analyzed the pharmacokinetics of eight potent natural products flavonoids for the druggability and discussed the neuroprotective and neurorestorative effects and the underlying mechanisms.

CONCLUSION

This review provides valuable clues for the development of novel therapeutics against neurodegenerative diseases.

Novel extraction techniques and pharmaceutical activities of luteolin and its derivatives

Luteolin is a 3', 4', 5, 7 tetra hydroxyl flavonoid that exits in many plants, fruits, and vegetable. Many methods of extraction, isolation, and purification are being used, and therapeutic properties are being under discussion due to its valuable role in nutrition and human health. In this review, we have summarized conventional and novel extraction techniques from most recent research on luteolin, its derivatives, and its biological activities. Maceration, soxhlet, reflux, hydrodistillation, ultrasound-assisted extraction, microwave-assisted extraction, ultrasound microwave-assisted extraction, enzyme-assisted extraction, supercritical fluid extraction, and high-speed counter-current chromatography extraction techniques are being used for isolation and purification of these phytochemicals. The anti-inflammatory, anti-cancer, antioxidant, antiviral, heart protective, neurological impairments protection, anti-aging, and whiting properties have been discussed in this review. The literature suggests luteolin and its derivative has many promising health benefits and its therapeutic activity is strongly associated with isolating and purifying solvents and extraction techniques. PRACTICAL APPLICATIONS: This review aims to highlight the sources, novel extraction techniques, and pharmaceutical properties of luteolin. This review provides enough knowledge about how to get maximum extraction yield of luteolin using the novel extraction techniques. Because its therapeutic activity is strongly associated with isolating and purifying solvents and techniques.

Luteolin induces hippocampal neurogenesis in the Ts65Dn mouse model of Down syndrome

Studies have shown that the natural flavonoid luteolin has neurotrophic activity. In this study, we investigated the effect of luteolin in a mouse model of Down syndrome. Ts65Dn mice, which are frequently used as a model of Down syndrome, were intraperitoneally injected with 10 mg/kg luteolin for 4 consecutive weeks starting at 12 weeks of age. The Morris water maze test was used to evaluate learning and memory abilities, and the novel object recognition test was used to assess recognition memory. Immunohistochemistry was performed for the neural stem cell marker nestin, the astrocyte marker glial fibrillary acidic protein, the immature neuron marker DCX, the mature neuron marker NeuN, and the cell proliferation marker Ki67 in the hippocampal dentate gyrus. Nissl staining was used to observe changes in morphology and to quantify cells in the dentate gyrus. Western blot assay was used to analyze the protein levels of brain-derived neurotrophic factor (BDNF) and phospho-extracellular signal-regulated kinase 1/2 (p-ERK1/2) in the hippocampus. Luteolin improved learning and memory abilities as well as novel object recognition ability, and enhanced the proliferation of neurons in the hippocampal dentate gyrus. Furthermore, luteolin increased expression of nestin and glial fibrillary acidic protein, increased the number of DCX⁺ neurons in the granular layer and NeuN⁺ neurons in the subgranular region of the dentate gyrus, and increased the protein levels of BDNF and p-ERK1/2 in the hippocampus. Our findings show that luteolin improves behavioral performance and promotes hippocampal neurogenesis in Ts65Dn mice. Moreover, these effects might be associated with the activation of the BDNF/ERK1/2 pathway.

Attenuation of Morphine Withdrawal Syndrome by Prosopis Farcta Extract and Its Bioactive Component Luteolin in Comparison with Clonidine in Rats

Background

Today, the plant Prosopis farcta is frequently used for traditional medicinal purposes. The aim of this study was the identification of luteolin in P. farcta extract (PFE) and to evaluate its effect on morphine discontinuation syndrome in rats.

Material/Methods

Using high-performance liquid chromatography (HPCL), luteolin was evaluated in PFE. The frequency of behavioral symptoms of morphine withdrawal (jumping, rearing, and teeth chattering) induced by naloxone challenge were illustrated in morphine-dependent rats receiving PFE, luteolin, saline, or clonidine. LD50 of PFE and luteolin was 540 mg/kg and 150 mg/kg, respectively. Signs of behavioral morphine withdrawal in rats were significantly inhibited by chronic co-administration of PFE, luteolin, or clonidine with morphine.

Results

This study showed that PFE was less effective than clonidine at a dose of 100 mg/kg, and at doses of 200 mg/kg and 300 mg/kg it was comparable to clonidine, and did not show a significant difference in the reduction of morphine withdrawal symptoms. Luteolin was comparable in 30 mg/kg, 60 mg/kg, and 90 mg/kg with clonidine to reduce the frequency of morphine withdrawal symptoms. PFE can be used as a source of luteolin.

Conclusions

The study findings suggest that PFE and luteolin might reduce the signs of narcotic withdrawal. Due to a similar effect to clonidine, its mechanism of action might be through the protein kinase A pathway and might have human therapeutic potential.

Luteolin alleviates LPS-induced bronchopneumonia injury in vitro and in vivo by down-regulating microRNA-132 expression

Bronchopneumonia is a common multiple infection disease under 2 years old. Luteolin is a natural flavonoid widely distributed in plants with anti-inflammatory effect. This study aimed to explore the effects of luteolin on lipopolysaccharide (LPS)-induced bronchopneumonia injury in vitro and in vivo. Firstly, the viability and apoptosis of human bronchial epithelial BEAS-2B cells after luteolin treatment were assessed. Then, cells were treated with 10 μM LPS to simulate inflammatory injury. The potential protective effects of luteolin on LPS-induced BEAS-2B cell inflammatory injury were detected. Moreover, after LPS and/or luteolin treatment, the expression of microRNA-132 (miR-132) in BEAS-2B cells was measured. The roles of miR-132 in protective activity of luteolin were investigated. Finally, the LPS-induced bronchopneumonia murine model was established and the anti-inflammatory effects of luteolin in vivo were analyzed. The results showed that LPS decreased BEAS-2B cell viability, increased cell apoptosis and enhanced inflammatory cytokines expression. Luteolin alleviated the LPS-induced viability loss, apoptosis and elevated expression of inflammatory cytokines in a dose-dependent manner. Moreover, luteolin alleviated the LPS-induced miR-132 expression increase in BEAS-2B cells. Overexpression of miR-132 reversed the protective effects of luteolin on LPS-induced inflammatory injury. Mechanistically, luteolin mitigated LPS-induced activation of NF-κB signaling pathway by down-regulation of miR-132. Furthermore, we also found that luteolin alleviated LPS-induced bronchopneumonia model in vivo. In conclusion, this study revealed that luteolin alleviated LPS-induced bronchopneumonia injury in vitro and in vivo through down-regulating miR-132. These findings provide theoretical basis for deeply exploring the treatment of bronchopneumonia in children by using luteolin.

Ketamine administered pregnant rats impair learning and memory in offspring via the CREB pathway

Ketamine has been reported to impair the capacity for learning and memory. This study examined whether these capacities were also altered in the offspring and investigated the role of the CREB signaling pathway in pregnant rats, subjected to ketamine-induced anesthesia. On the 14^th day of gestation (P14), female rats were anesthetized for 3 h via intravenous ketamine injection (200 mg/Kg). Morris water maze task, contextual and cued fear conditioning, and olfactory tasks were executed between the 25^th to 30^th day after birth (B25-30) on rat pups, and rats were sacrificed on B30. Nerve density and dendritic spine density were examined via Nissl’s and Golgi staining. Simultaneously, the contents of Ca²⁺/Calmodulin-Dependent Protein Kinase II (CaMKII), p-CaMKII, CaMKIV, p-CaMKIV, Extracellular Regulated Protein Kinases (ERK), p-ERK, Protein Kinase A (PKA), p-PKA, cAMP-Response Element Binding Protein (CREB), p-CREB, and Brain Derived Neurotrophic Factor (BDNF) were detected in the hippocampus. We pretreated PC12 cells with both PKA inhibitor (H89) and ERK inhibitor (SCH772984), thus detecting levels of ERK, p-ERK, PKA, p-PKA, p-CREB, and BDNF. The results revealed that ketamine impaired the learning ability and spatial as well as conditioned memory in the offspring, and significantly decreased the protein levels of ERK, p-ERK, PKA, p-PKA, p-CREB, and BDNF. We found that ERK and PKA (but not CaMKII or CaMKIV) have the ability to regulate the CREB-BDNF pathway during ketamine-induced anesthesia in pregnant rats. Furthermore, ERK and PKA are mutually compensatory for the regulation of the CREB-BDNF pathway.

Response of Myeloid Leukemia Cells to Luteolin is Modulated by Differentially Expressed Pituitary Tumor-Transforming Gene 1 (PTTG1) Oncoprotein

Luteolin, a flavonoid nutraceutical abundant in vegetables and fruits, exhibits a wide range of bioactive properties, including antioxidant, anti-inflammatory and anti-cancer activities. Pituitary tumor-transforming gene 1 (PTTG1), an oncoprotein that regulates cell proliferation, is highly expressed in several types of cancer cells including leukemia. In this study, we aim to investigate the anti-cancer effects of luteolin on cells with differential PTTG1 expression and their underlying mechanisms in human myeloid leukemia cells. Methyl thiazolyl tetrazolium (MTT) assay data showed that luteolin (25–100 μM) significantly reduced cell viability in THP-1, HL-60 and K562 cells but did not affect normal peripheral blood mononuclear cells (PBMCs). Flow cytometric analysis and Western blot data demonstrated that luteolin induced a stronger apoptosis on undifferentiated myeloid leukemia cells with higher PTTG1 protein levels than on 12-myristate 13-acetate (PMA)- or all-trans-retinoic acid (ATRA)-differentiated cells with lower PTTG1 expression. Furthermore, PTTG1 knockdown by shRNA in leukemia cells suppressed cell proliferation, arrested cell-cycle progression and impaired the effectiveness of luteolin on cell-cycle regulation. Moreover, PTTG1-knockdown cells with luteolin exposure presented a reduction of the apoptotic proteins and maintained higher levels of the anti-apoptotic proteins such as Mcl-1, Bcl-2 and p21, which exhibited greater resistance to apoptosis. Finally, microarray analysis showed that 20 genes associated with cell proliferation, such as CXCL10, VEGFA, TNF, TP63 and FGFR1, were dramatically down-regulated in PTTG1-knockdown cells. Our current findings clearly demonstrate that luteolin-triggered leukemic cell apoptosis is modulated by the differential expression of the PTTG1. PTTG1 oncoprotein overexpression may modulate cell proliferation-related regulators and enhance the response of myeloid leukemia cells to luteolin. Luteolin is beneficial for the treatment of cancer cells with highly expressed PTTG1 oncoprotein.

Fisetin Exerts Antioxidant and Neuroprotective Effects in Multiple Mutant hSOD1 Models of Amyotrophic Lateral Sclerosis by Activating ERK

Oxidative stress exhibits a central role in the course of amyotrophic lateral sclerosis (ALS), a progressive neurodegenerative disease commonly found to include a copper/zinc superoxide dismutase (SOD1) gene mutation. Fisetin, a natural antioxidant, has shown benefits in varied neurodegenerative diseases. The possible effect of fisetin in ALS has not been clarified as of yet. We investigated whether fisetin affected mutant hSOD1 ALS models. Three different hSOD1-related mutant models were used: Drosophila expressing mutant hSOD1^G85R, hSOD1^G93A NSC34 cells, and transgenic mice. Fisetin treatment provided neuroprotection as demonstrated by an improved survival rate, attenuated motor impairment, reduced ROS damage and regulated redox homeostasis compared with those in controls. Furthermore, fisetin increased the expression of phosphorylated ERK and upregulated antioxidant factors, which were reversed by MEK/ERK inhibition. Finally, fisetin reduced the levels of both mutant and wild-type hSOD1 in vivo and in vitro, as well as the levels of detergent-insoluble hSOD1 proteins. The results indicate that fisetin protects cells from ROS damage and improves the pathological behaviors caused by oxidative stress in disease models related to SOD1 gene mutations probably by activating ERK, thereby providing a potential treatment for ALS.

Advances in Roles of miR-132 in the Nervous System

miR-132 is an endogenous small RNA and controls post-transcriptional regulation of gene expression via controlled degradation of mRNA or transcription inhibition. In the nervous system, miR-132 is significant for regulating neuronal differentiation, maturation and functioning, and widely participates in axon growth, neural migration, and plasticity. The miR-132 is affected by factors like mRNA expression, functional redundancy, and signaling cascades. It targets multiple downstream molecules to influence physiological and pathological neuronal activities. MiR-132 can influence the pathogenesis of many diseases, especially in the nervous system. The dysregulation of miR-132 results in the occurrence and exacerbation of neural developmental, degenerative diseases, like Alzheimer’s disease, Parkinson’s disease and epilepsy, neural infection and psychiatric disorders including disturbance of consciousness, cognition and memory, depression and schizophrenia. Regulation of miR-132 expression relieves symptoms, alleviates severity and finally effects a cure. This review aims to discuss the clinical potentials of miR-132 in the nervous system.

An Important Function of Petrosiol E in Inducing the Differentiation of Neuronal Progenitors and in Protecting Them against Oxidative Stress

Insufficient endogenous neurotrophin supply contributes to neurodegeneration. Meanwhile, neuronal injuries are also attributed to oxidative stress upon toxin exposure. Thus, reconstruction neurite extension and antioxidative stress are the potential strategies for ameliorating neuronal injuries. However, there is no well-defined therapeutic developed in this regard. In search of such therapeutics, Petrosiol E is identified here as a potent inducer to guide the differentiation of neuronal progenitor cells. Petrosiol E also considerably promotes embryonic stem cell differentiation into neural ectoderm features. Moreover, Petrosiol E reveals an antioxidant function to protect cells from oxidative stress induced by arsenic. Moreover, the molecular mechanism underlying Petrosiol E-induced neuronal differentiation is uncovered: (a) enhancement of NF-E2-related factor 2 (Nrf 2) activity in driving neuronal differentiation; (b) diminishment of oxidative stress. Petrosiol E activates the mitogen-activated protein kinase and serine/threonine kinase signaling to enhance the activity of Nrf 2. As a result of enhanced Nrf 2 activity, neuronal differentiation is accelerated, and the cellular antioxidation responses are also enforced, even under arsenic-induced neurotoxicity. Together, the combined results unveil a desirable role of Petrosiol E in driving neuronal differentiation and in combating oxidative stress. This study would open an avenue to develop new therapeutics based on Petrosiol compounds to treat neurodegenerative diseases.

Luteolin, a natural flavonoid, inhibits methylglyoxal induced apoptosis via the mTOR/4E-BP1 signaling pathway

Methylglyoxal (MG) accumulation has been observed in human cerebrospinal fluid and body tissues under hyperglycaemic conditions. Recent research has demonstrated that MG-induces neuronal cell apoptosis, which promotes the development of diabetic encephalopathy. Our previous animal study has shown that luteolin, a natural flavonoid, attenuates diabetes-associated cognitive dysfunction. To further explore the neuroprotective properties of luteolin, we investigated the inhibitive effect of luteolin on MG-induced apoptosis in PC12 neuronal cells. We found that MG inhibited cell viability in a dose-dependent manner and induced apoptosis in PC12 cells. Pretreatment with Luteolin significantly elevated cell viability, reduced MG-induced apoptosis, inhibited the activation of the mTOR/4E-BP1 signaling pathway, and decreased pro-apoptotic proteins, Bax, Cytochrome C as well as caspase-3. Furthermore, we found that pretreatment with the mTOR inhibitor, rapamycin, significantly reduced the expression of the pro-apoptotic protein Bax. Therefore, these observations unambiguously suggest that the inhibitive effect of Luteolin against MG-induced apoptosis in PC12 cells is associated with inhibition of the mTOR/4E-BP1 signaling pathway.

Functional integration of complex miRNA networks in central and peripheral lesion and axonal regeneration

New players are emerging in the game of peripheral and central nervous system injury since their physiopathological mechanisms remain partially elusive. These mechanisms are characterized by several molecules whose activation and/or modification following a trauma is often controlled at transcriptional level. In this scenario, microRNAs (miRNAs/miRs) have been identified as main actors in coordinating important molecular pathways in nerve or spinal cord injury (SCI). miRNAs are small non-coding RNAs whose functionality at network level is now emerging as a new level of complexity. Indeed they can act as an organized network to provide a precise control of several biological processes. Here we describe the functional synergy of some miRNAs in case of SCI and peripheral damage. In particular we show how several small RNAs can cooperate in influencing simultaneously the molecular pathways orchestrating axon regeneration, inflammation, apoptosis and remyelination. We report about the networks for which miRNA-target bindings have been experimentally demonstrated or inferred based on target prediction data: in both cases, the connection between one miRNA and its downstream pathway is derived from a validated observation or is predicted from the literature. Hence, we discuss the importance of miRNAs in some pathological processes focusing on their functional structure as participating in a cooperative and/or convergence network.

Derivatives of caffeic acid, a natural antioxidant, as the basis for the discovery of novel nonpeptidic neurotrophic agents

Neurodegenerative disorders, such as Parkinson's disease and Alzheimer's disease, threaten the lives of millions of people and the number of affected patients is constantly growing with the increase of the aging population. Small molecule neurotrophic agents represent promising therapeutics for the pharmacological management of neurodegenerative diseases. In this study, a series of caffeic acid amide analogues with variable alkyl chain lengths, including ACAF3 (C3), ACAF4 (C4), ACAF6 (C6), ACAF8 (C8) and ACAF12 (C12) were synthesized and their neurotrophic activity was examined by different methods in PC12 neuronal cells. We found that all caffeic acid amide derivatives significantly increased survival in PC12 neuronal cells in serum-deprived conditions at 25μM, as measured by the MTT assay. ACAF4, ACAF6 and ACAF8 at 5µM also significantly enhanced the effect of nerve growth factor (NGF) in inducing neurite outgrowth, a sign of neuronal differentiation. The neurotrophic effects of amide derivatives did not seem to be mediated by direct activation of tropomyosin receptor kinase A (TrkA) receptor, since K252a, a potent TrkA antagonist, did not block the neuronal survival enhancement effect. Similarly, the active compounds did not activate TrkA as measured by immunoblotting with anti-phosphoTrkA antibody. We also examined the effect of amide derivatives on signaling pathways involved in survival and differentiation by immunoblotting. ACAF4 and ACAF12 induced ERK1/2 phosphorylation in PC12 cells at 5 and 25µM, while ACAF12 was also able to significantly increase AKT phosphorylation at 5 and 25µM. Molecular docking studies indicated that compared to the parental compound caffeic acid, ACAF12 exhibited higher binding energy with phosphoinositide 3-kinase (PI3K) as a putative molecular target. Based on Lipinski's rule of five, all of the compounds obeyed three molecular descriptors (HBD, HBA and MM) in drug-likeness test. Taken together, these findings show for the first time that caffeic amides possess strong neurotrophic effects exerted via modulation of ERK1/2 and AKT signaling pathways presumably by activation of PI3K and thus represent promising agents for the discovery of neurotrophic compounds for management of neurodegenerative diseases.

miR-124 promotes the neuronal differentiation of mouse inner ear neural stem cells

MicroRNAs (miRNAs or miRs) act as key regulators in neuronal development, synaptic morphogenesis and plasticity. However, their role in the neuronal differentiation of inner ear neural stem cells (NSCs) remains unclear. In this study, 6 miRNAs were selected and their expression patterns during the neuronal differentiation of inner ear NSCs were examined by RT-qPCR. We demonstrated that the culture of spiral ganglion stem cells present in the inner ears of newborn mice gave rise to neurons in vitro. The expression patterns of miR-124, miR-132, miR-134, miR-20a, miR-17-5p and miR-30a-5p were examined during a 14-day neuronal differentiation period. We found that miR-124 promoted the neuronal differentiation of and neurite outgrowth in mouse inner ear NSCs, and that the changes in the expression of tropomyosin receptor kinase B (TrkB) and cell division control protein 42 homolog (Cdc42) during inner ear NSC differentiation were associated with miR-124 expression. Our findings indicate that miR-124 plays a role in the neuronal differentiation of inner ear NSCs. This finding may lead to the development of novel strategies for restoring hearing in neurodegenerative diseases.

Luteolin inhibited proliferation and induced apoptosis of prostate cancer cells through miR-301

Luteolin is a falvonoid compound derived from Lonicera japonica Thunb. Numerous reports have demonstrated that luteolin has anticancer effects on many kinds of tumors. This study investigated the effects of luteolin on prostate cancer (PCa), assessing the PC3 and LNCaP cells. The cell viability and apoptosis were assessed by performing Cell Counting Kit-8 assay and Annexin V–fluorescein isothiocyanate/propidium iodide double staining. Luteolin was found to inhibit androgen-sensitive and androgen-independent PCa cell lines’ growth and induced apoptosis. To uncover the exact mechanisms and molecular targets, microRNA (miR) array analysis was performed. miR-301 was found to be markedly downregulated. Then, the expression of miR-301 was retrospectively analyzed in the primary PCa tissues by quantitative reverse transcription polymerase chain reaction and in situ hybridization methods. According to the quantitative reverse transcription polymerase chain reaction results of miR-301, the 54 PCa patients were divided into two groups: high and low miR-301 groups. The division indicator is a relative expression ≥5. Compared to the low-expression group, high miR-301 expression was associated with a significantly shorter overall survival (P=0.029). The proapoptotic gene, DEDD2, was predicted to be the direct target of miR-301. It was clarified in accordance with bioinformatics and luciferase activity analyses. The overexpression of miR-301 by plasmid decreased the luteolin effect. Taken together, these results suggest that luteolin inhibits PCa cell proliferation through miR-301, the poor predictive factor of PCa.

Modulation of neurotrophic signaling pathways by polyphenols

Polyphenols are an important class of phytochemicals, and several lines of evidence have demonstrated their beneficial effects in the context of a number of pathologies including neurodegenerative disorders such as Alzheimer’s and Parkinson’s disease. In this report, we review the studies on the effects of polyphenols on neuronal survival, growth, proliferation and differentiation, and the signaling pathways involved in these neurotrophic actions. Several polyphenols including flavonoids such as baicalein, daidzein, luteolin, and nobiletin as well as nonflavonoid polyphenols such as auraptene, carnosic acid, curcuminoids, and hydroxycinnamic acid derivatives including caffeic acid phentyl ester enhance neuronal survival and promote neurite outgrowth in vitro, a hallmark of neuronal differentiation. Assessment of underlying mechanisms, especially in PC12 neuronal-like cells, reveals that direct agonistic effect on tropomyosin receptor kinase (Trk) receptors, the main receptors of neurotrophic factors including nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) explains the action of few polyphenols such as 7,8-dihydroxyflavone. However, several other polyphenolic compounds activate extracellular signal-regulated kinase (ERK) and phosphoinositide 3-kinase (PI3K)/Akt pathways. Increased expression of neurotrophic factors in vitro and in vivo is the mechanism of neurotrophic action of flavonoids such as scutellarin, daidzein, genistein, and fisetin, while compounds like apigenin and ferulic acid increase cyclic adenosine monophosphate response element-binding protein (CREB) phosphorylation. Finally, the antioxidant activity of polyphenols reflected in the activation of Nrf2 pathway and the consequent upregulation of detoxification enzymes such as heme oxygenase-1 as well as the contribution of these effects to the neurotrophic activity have also been discussed. In conclusion, a better understanding of the neurotrophic effects of polyphenols and the concomitant modulations of signaling pathways is useful for designing more effective agents for management of neurodegenerative diseases.

Luteolin and Apigenin Attenuate 4-Hydroxy-2-Nonenal-Mediated Cell Death through Modulation of UPR, Nrf2-ARE and MAPK Pathways in PC12 Cells

Luteolin and apigenin are dietary flavones and exhibit a broad spectrum of biological activities including antioxidant, anti-inflammatory, anti-cancer and neuroprotective effects. The lipid peroxidation product 4-hydroxy-2-nonenal (4-HNE) has been implicated as a causative agent in the development of neurodegenerative disorders. This study investigates the cytoprotective effects of luteolin and apigenin against 4-HNE-mediated cytotoxicity in neuronal-like catecholaminergic PC12 cells. Both flavones restored cell viability and repressed caspase-3 and PARP-1 activation in 4-HNE-treated cells. Luteolin also mitigated 4-HNE-mediated LC3 conversion and reactive oxygen species (ROS) production. Luteolin and apigenin up-regulated 4-HNE-mediated unfolded protein response (UPR), leading to an increase in endoplasmic reticulum chaperone GRP78 and decrease in the expression of UPR-targeted pro-apoptotic genes. They also induced the expression of Nrf2-targeted HO-1 and xCT in the absence of 4-HNE, but counteracted their expression in the presence of 4-HNE. Moreover, we found that JNK and p38 MAPK inhibitors significantly antagonized the increase in cell viability induced by luteolin and apigenin. Consistently, enhanced phosphorylation of JNK and p38 MAPK was observed in luteolin- and apigenin-treated cells. In conclusion, this result shows that luteolin and apigenin activate MAPK and Nrf2 signaling, which elicit adaptive cellular stress response pathways, restore 4-HNE-induced ER homeostasis and inhibit cytotoxicity. Luteolin exerts a stronger cytoprotective effect than apigenin possibly due to its higher MAPK, Nrf2 and UPR activation, and ROS scavenging activity.

Effect of laminin-binding BDNF on induction of recurrent laryngeal nerve regeneration by miR-222 activation of mTOR signal pathway

BACKGROUND AND AIM

Recurrent laryngeal nerve injury is a common severe complication in neck surgery, which can cause varying degrees of vocal fold paralysis and respiratory tract problems. In present study, the effects of laminin-binding brain derived neurotrophic factor (LBD-BDNF) on recurrent laryngeal nerve regeneration were explored and its possible mechanism was investigated.

METHODS

LBD-BDNF or NAT-BDNF (BDNF without LBD binding) treatment was performed in laryngeal nerve injured rabbits for sixteen weeks. The laryngeal nerve was removed, and histological examination as well as laryngeal electromyography was employed to evaluate its morphology and function of conduction. PC12 cells were cultured to investigate the mechanisms underlying the effects of LBD-BDNF. Neurite outgrowth, proliferation and migration were determined in nerve cells. The expression of miRNAs and protein of mTOR was quantified by real-time PCR and western blotting respectively.

RESULTS

In vivo experiments, LBD-BDNF significantly improved the histological structure and function of recurrent laryngeal nerve compared with NAT-BDNF. LBD-BDNF also markedly promoted neurite outgrowth, proliferation and migration in PC12 cells in vitro experiments. The levels of miR-222 and p-mTOR were up-regulated by LBD-BDNF treatment in both in vivo and in vitro experiments. miR-222 inhibitor attenuated the expression of phosphorylated mTOR and miR-222 mimic enhanced its expression in PC12 cells. In addition, the improved nerve conduction by LBD-BDNF was canceled by miR-222 inhibitor, and the mTOR inhibitor reversed the effects of miR-222 inhibitor on LBD-BDNF treated cells.

CONCLUSIONS

The present study revealed that LBD-BDNF promoted the recurrent laryngeal nerve regeneration in laryngeal nerve injured rabbits. The underlying mechanism was closely related to activation of p-mTOR by miR-222.

Up-Regulation of miR-34a Expression in Response to the Luteolin-Induced Neurite Outgrowth of PC12 Cells

Luteolin (3',4',5,7-tetrahydroxyflavone), a flavonoid found in several vegetables and fruits, has been reported to possess neurotrophic activities that are associated with its capacity to promote neuronal survival and differentiation. In the present study, we report for the first time a genomewide screen for microRNAs (miRNAs) regulated during the luteolin-mediated neurite outgrowth of PC12 cells. We found that after luteolin treatment, the abundance of 16 miRNAs was markedly up-regulated and that of 3 miRNAs was down-regulated in PC12 cells. The induction of miR-34a by luteolin was the most pronounced among these differentially expressed miRNAs. The correlation between miR-34a down-regulation and decreased luteolin-mediated neurite outgrowth may indicate a mechanism by which miR-34a may act as a modulator of neuronal differentiation. Furthermore, we found that luteolin enhanced the phosphorylation of p53 at Ser15, which was associated with the promotion of miR-34a transcription and neurite outgrowth. Moreover, the level of sirtuin 1 (SIRT1), a known miR-34a target, was reduced during luteolin-induced neurite outgrowth. In turn, the level of acetylated p53, a substrate of SIRT1, was correspondingly increased in luteolin-treated PC12 cells. In addition to p53 activation, we further identified that luteolin-induced miR-34a transcription and neurite outgrowth involved the activation of the JNK and p38 MAPK pathways. However, the inhibition of JNK and p38 MAPK activation did not block luteolin-induced p53 activation in PC12 cells. Our findings suggested that the activation of both p53-dependent and p53-independent miR-34a/SIRT1 pathways plays a critical role in the mechanisms underlying luteolin-induced neuritogenesis.

Inhibition of miR-134 Protects Against Hydrogen Peroxide-Induced Apoptosis in Retinal Ganglion Cells

MicroRNAs (miRNAs) have been suggested to play an important role in neurological diseases. Particularly, miR-134 is reportedly involved in regulating neuron survival. However, the association between miR-134 and retinal ganglion cell (RGC) survival under adverse stimulus has not been extensively investigated. In this study, we aimed to explore the role and underlying mechanism of miR-134 in regulating RGC apoptosis in response to hydrogen peroxide (H2O2) treatment. Results showed that the expression of miR-134 dose- and time-dependently increased in RGC after H2O2 treatment. H2O2-induced RGC apoptosis was significantly attenuated by the inhibition of miR-134 expression by antagomiR-134 and was enhanced by miR-134 overexpression. Luciferase reporter assay revealed a direct interaction between miR-134 and the 3'-untranslated region of cyclic AMP-response element-binding protein (CREB), a critical transcription factor for neuronal protection. In H2O2-treated RGCs, the inhibition of miR-134 significantly elevated the expression of CREB and its downstream genes, including brain-derived neurotrophic factor (BDNF) and Bcl-2. Furthermore, the inhibition of miR-134 also increased the expression of miR-132, a rapid response gene downstream of CREB. In addition, the target gene of miR-132, acetylcholinesterase was expectedly decreased by miR-134 inhibition. However, the overexpression of miR-134 exerted an opposite effect. The knockdown of CREB apparently abolished the protective effect of miR-134 inhibition against H2O2-induced RGC apoptosis. The increased expression of BDNF and Bcl-2 induced by miR-134 inhibition was also abrogated by CREB knockdown. Overall, our results suggested that the downregulation of miR-134 can effectively protect against H2O2-induced RGC apoptosis by negatively modulating CREB expression.

BDNF-ERK-CREB signalling mediates the role of miR-132 in the regulation of the effects of oleanolic acid in male mice

BACKGROUND

Although previous study has demonstrated that brain-derived neurotrophic factor (BDNF) is involved in the antidepressant-like effect of oleanolic acid, there is little information regarding the details of the molecular mechanism involved in this effect.

METHODS

We used a chronic unpredictable mild stress (CUMS) model to test the antidepressant-like effect of oleanolic acid on depressant-like behaviour, miR-132 expression and synaptic protein expression in the male mouse hippocampus. Furthermore, we explored the possible signalling pathways associated with miR-132 expression that mediate the effect of oleanolic acid on neuronal proliferation.

RESULTS

The results demonstrated that a 3-week treatment with oleanolic acid ameliorated CUMS-induced anhedonic and anxiogenic behaviours. Furthermore, we found that oleanolic acid led to the BDNF-related phosphorylation and activation of extracellular signal-regulated kinases (ERK) and cyclic adenosine monophosphate response element binding protein (CREB), which was associated with the upregulation of miR-132 and hippocampal neuronal proliferation. Moreover, experiments with an miR-132 antagomir revealed that targeting miR-132 led to inhibition of neuronal proliferation and the postsynaptic density protein 95, but did not affect presynaptic protein synapsin I.

LIMITATIONS

Several other stimuli can also induce CREB phosphorylation in the hippocampus. Thus, regulation of miR-132 may not be restricted to neurotrophic signalling.

CONCLUSION

Our results show that oleanolic acid induces the upregulation of miR-132, which serves as an important regulator of neurotrophic actions, mainly through the activation of the hippocampal BDNF-ERK-CREB signalling pathways.

Luteolin modulates 6-hydroxydopamine-induced transcriptional changes of stress response pathways in PC12 cells

The neurotoxin 6-hydroxydopamine (6-OHDA), which causes transcriptional changes associated with oxidative and proteotoxic stress, has been widely used to generate an experimental model of Parkinson's disease. The food-derived compound luteolin has multi-target actions including antioxidant, anti-inflammatory and neurotrophic activities. The aim of this study is to investigate how luteolin affects 6-OHDA-mediated stress response pathways. The results showed that when PC12 cells were pre-treated with luteolin (20 µM) 30 min prior to 6-OHDA (100 µM) exposure, 6-OHDA-induced ROS overproduction, cytotoxicity, caspase-3 activation, and mRNA expression of BIM, TRB3 and GADD34 were significantly attenuated. Moreover, 6-OHDA-mediated cell cycle arrest and transcription of p53 target genes, p21, GADD45α and PUMA, were reduced by luteolin. Luteolin also significantly down-regulated 6-OHDA-mediated unfolded protein response (UPR), leading to decreases in phospho-eIF2α, ATF4, GRP78 and CHOP. In addition, luteolin attenuated 6-OHDA-induced Nrf2-mediated HO-1 and GCLC. Taken together, these results suggest that diminishing intracellular ROS formation and down-regulation of p53, UPR and Nrf2-ARE pathways may be involved in the neuroprotective effect of luteolin.

MicroRNA-132 is enriched in developing axons, locally regulates Rasa1 mRNA, and promotes axon extension

Developing axons can locally synthesize proteins, with roles in axon growth, guidance, and regeneration, but the mechanisms that regulate axonal mRNA translation are not well understood. MicroRNAs (miRNAs) are important regulators of translation but have still been little characterized in developing axons. Here we study mouse dorsal root ganglion (DRG) axons and show that their extension is impaired by conditional deficiency of the miRNA-processing enzyme Dicer in vitro and in vivo. A screen for axonal localization identifies a specific set of miRNAs preferentially enriched within the developing axon. High axonal expression and preferential localization were observed for miR-132, a miRNA previously known for roles in dendrites and dysregulation in major neurologic diseases. miR-132 knockdown reduced extension of cultured DRG axons, whereas overexpression increased extension. Mechanistically, miR-132 regulated the mRNA for the Ras GTPase activator Rasa1, a novel target in neuronal function. Moreover, miR-132 regulation of Rasa1 translation was seen in severed axons, demonstrating miRNA function locally within the axon. miR-132 expression in DRGs peaked in the period of maximum axon growth in vivo, consistent with its effect on axon growth, and suggesting a role as a developmental timer. Together, these findings identify miR-132 as a positive regulator of developing axon extension, acting through repression of Rasa1 mRNA, in a mechanism that operates locally within the axon.

Regulation of LH receptor mRNA binding protein by miR-122 in rat ovaries

LH receptor (LHR) expression in the ovary is regulated by the RNA binding protein, (LHR mRNA binding protein [LRBP]), which has been identified as being mevalonate kinase. This study examined the role of microRNA miR-122 in LRBP-mediated LHR mRNA expression. Real-time PCR analysis of ovaries from pregnant mare serum gonadotropin/human chorionic gonadotropin (hCG)-primed female rats treated with hCG to down-regulate LHR expression showed that an increase in miR-122 expression preceded LHR mRNA down-regulation. The expression of miR-122 and its regulation was confirmed using fluorescent in situ hybridization of the frozen ovary sections using 5'-fluorescein isothiocyanate-labeled miR-122 locked nucleic acid probe. The increased expression of miR-122 preceded increased expression of LRBP mRNA and protein, and these increases were followed by LHR mRNA down-regulation. Inhibition of protein kinase A (PKA) and ERK1/2 signaling pathways by H89 and UO126, respectively, attenuated the hCG-mediated up-regulation of miR-122 levels. This was also confirmed in vitro using human granulosa cells. These results suggest the possibility that hCG-mediated miR-122 expression is mediated by the activation of cAMP/PKA/ERK signaling pathways. Inhibition of miR-122 by injection of the locked nucleic acid-conjugated antagomir of miR-122 abrogated the hCG-mediated increases in LRBP protein expression. Because it has been previously shown that miR-122 regulates sterol regulatory element-binding proteins (SREBPs) and SREBPs, in turn, regulate LRBP expression, the role of SREBPs in miR-122-mediated increase in LRBP expression was then examined. The levels of active forms of both SREBP-1a and SREBP-2 were increased in response to hCG treatment, and the stimulatory effect was sustained up to 4 hours. Taken together, our results suggest that hCG-induced down-regulation of LHR mRNA expression is mediated by activation of cAMP/PKA/ERK pathways to increase miR-122 expression, which then increases LRBP expression through the activation of SREBPs.

Neurotrophic action of 5-hydroxylated polymethoxyflavones: 5-demethylnobiletin and gardenin A stimulate neuritogenesis in PC12 cells

Polymethoxyflavones (PMFs) exhibit a broad spectrum of biological properties, including anticancer, antiatherogenic, and neuroprotective effects. The aim of this study is to investigate the neurotrophic effects of 5-demethylnobiletin, a hydroxylated PMF found in citrus plants, and gardenin A, a synthetic PMF analogue, on neurite outgrowth and neuronal differentiation in PC12 cells. The results of this study showed that 5-demethylnobiletin and gardenin A (10-20 μM) potently induce neurite outgrowth in PC12 cells, accompanied by the expression of neuronal differentiation and synapse formation marker proteins, growth-associated protein-43 (GAP-43), and synaptophysin. We observed that the addition of K252a, a TrKA antagonist, significantly inhibited NGF-induced neurite outgrowth in PC12 cells, but 5-demethylnobiletin- or gardenin A-induced neurite outgrowth was not affected. Treatment with 5-demethylnobiletin and gardenin A markedly induced the phosphorylation of both cyclic AMP response element-binding protein (CREB) and CRE-mediated transcription, which was suppressed through the administration of the inhibitor 2-naphthol AS-E phosphate (KG-501) or using CREB siRNA. Furthermore, our results showed that MAPK/ERK kinase 1/2 (MEK1/2), protein kinase A (PKA), and protein kinase C (PKC) inhibitors blocked the CRE transcription activity and neurite outgrowth induced through 5-demethylnobiletin or gardenin A. Consistently, increased ERK phosphorylation and PKA and PKC activities were observed in PC12 cells treated with 5-demethylnobiletin or gardenin A. These results reveal for the first time that 5-demethylnobiletin and gardenin A promote neuritogenesis through the activation of MAPK/ERK-, PKC-, and PKA-dependent, but not TrkA-dependent, CREB signaling pathways in PC12 cells.

Identification of particular groups of microRNAs that positively or negatively impact on beta cell function in obese models of type 2 diabetes

AIMS/HYPOTHESIS

MicroRNAs are key regulators of gene expression involved in health and disease. The goal of our study was to investigate the global changes in beta cell microRNA expression occurring in two models of obesity-associated type 2 diabetes and to assess their potential contribution to the development of the disease.

METHODS

MicroRNA profiling of pancreatic islets isolated from prediabetic and diabetic db/db mice and from mice fed a high-fat diet was performed by microarray. The functional impact of the changes in microRNA expression was assessed by reproducing them in vitro in primary rat and human beta cells.

RESULTS

MicroRNAs differentially expressed in both models of obesity-associated type 2 diabetes fall into two distinct categories. A group including miR-132, miR-184 and miR-338-3p displays expression changes occurring long before the onset of diabetes. Functional studies indicate that these expression changes have positive effects on beta cell activities and mass. In contrast, modifications in the levels of miR-34a, miR-146a, miR-199a-3p, miR-203, miR-210 and miR-383 primarily occur in diabetic mice and result in increased beta cell apoptosis. These results indicate that obesity and insulin resistance trigger adaptations in the levels of particular microRNAs to allow sustained beta cell function, and that additional microRNA deregulation negatively impacting on insulin-secreting cells may cause beta cell demise and diabetes manifestation.

CONCLUSIONS/INTERPRETATION

We propose that maintenance of blood glucose homeostasis or progression toward glucose intolerance and type 2 diabetes may be determined by the balance between expression changes of particular microRNAs.