Inhibition of the Rho/ROCK pathway prevents neuronal degeneration in vitro and in vivo following methylmercury exposure

Therapeutic potential of 4-phenylbutyric acid against methylmercury-induced neuronal cell death in mice

Methylmercury (MeHg) is an environmental neurotoxin that induces damage to the central nervous system and is the causative agent in Minamata disease. The mechanisms underlying MeHg neurotoxicity remain largely unknown, and there is a need for effective therapeutic agents, such as those that target MeHg-induced endoplasmic reticulum (ER) stress and the unfolded protein response (UPR), which is activated as a defense mechanism. We investigated whether intraperitoneal administration of the chemical chaperone, 4-phenylbutyric acid (4-PBA), at 120 mg/kg/day can alleviate neurotoxicity in the brains of mice administered 50 ppm MeHg in drinking water for 5 weeks. 4-PBA significantly reduced MeHg-induced ER stress, neuronal apoptosis, and neurological symptoms. Furthermore, 4-PBA was effective even when administered 2 weeks after the initiation of exposure to 30 ppm MeHg in drinking water. Our results strongly indicate that ER stress and the UPR are key processes involved in MeHg toxicity, and that 4-PBA is a novel therapeutic candidate for MeHg-induced neurotoxicity.

Fasudil, a ROCK inhibitor, prevents neuropathic pain in Minamata disease model rats

Methylmercury (MeHg), an environmental toxicant, is known to cause sensory impairment by inducing neurodegeneration of sensory nervous systems. However, in recent years, it has been revealed that neuropathic pain occurs in the chronic phase of MeHg poisoning, that is, in current Minamata disease patients. Our recent study using Minamata disease model rats demonstrated that MeHg-mediated neurodegeneration in the sensory nervous system may induce inflammatory microglia production in the dorsal horn of the spinal cord and subsequent somatosensory cortical rewiring, leading to neuropathic pain. We hypothesized that inhibition of the Rho-associated coiled coil-forming protein kinase (ROCK) pathway could prevent MeHg-induced neuropathic pain because the ROCK pathway is known to be involved in inducing the production of inflammatory microglia. Here, we showed for the first time that Fasudil, a ROCK inhibitor, can prevent neuropathic pain in Minamata disease model rats. In this model, Fasudil significantly suppressed nerve injury-induced inflammatory microglia production in the dorsal horn of the spinal cord and prevented subsequent somatosensory cortical rewiring. These results suggest that the ROCK pathway is involved in the onset and development of neuropathic pain in the chronic phase of Minamata disease, and that its inhibition is effective in pain prevention.

ROCK2 Inhibition: A Futuristic Approach for the Management of Alzheimer's Disease

Neurons depend on mitochondrial functions for membrane excitability, neurotransmission, and plasticity.Mitochondrialdynamicsare important for neural cell maintenance. To maintain mitochondrial homeostasis, lysosomes remove dysfunctionalmitochondria through mitophagy. Mitophagy promotes mitochondrial turnover and prevents the accumulation of dysfunctional mitochondria. In many neurodegenerative diseases (NDDs), including Alzheimer's disease (AD), mitophagy is disrupted in neurons.Mitophagy is regulated by several proteins; recently,Rho-associated coiled-coil containing protein kinase 2 (ROCK2) has been suggested to negatively regulate the Parkin-dependent mitophagy pathway.Thus, ROCK2inhibitionmay bea promising therapyfor NDDs. This review summarizesthe mitophagy pathway, the role of ROCK2in Parkin-dependentmitophagyregulation,and mitophagy impairment in the pathology of AD. We further discuss different ROCK inhibitors (synthetic drugs, natural compounds,and genetherapy-based approaches)and examine their effects on triggering neuronal growth and neuroprotection in AD and other NDDs. This comprehensive overview of the role of ROCK in mitophagy inhibition provides a possible explanation for the significance of ROCK inhibitors in the therapeutic management of AD and other NDDs.

Effect of methylmercury on fetal neurobehavioral development: an overview of the possible mechanisms of toxicity and the neuroprotective effect of phytochemicals

Methylmercury (MeHg) is a global environmental pollutant with neurotoxic effects. Exposure to MeHg via consumption of seafood and fish can severely impact fetal neurobehavioral development even when MeHg levels in maternal blood are as low as about 5 μg/L, which the mother tolerates well. Persistent motor dysfunctions and cognitive deficits may result from trans-placental exposure. The present review summarizes current knowledge on the mechanisms of MeHg toxicity during the period of nervous system development. Although cerebellar Purkinje cells are MeHg targets, the actions of MeHg on thiol components in the neuronal cytoskeleton as well as on mitochondrial enzymes and induction of disturbances of glutamate signaling can impair extra-cerebellar functions, also at levels well tolerated by adult individuals. Numerous herbal substances possess neuroprotective effects, predominantly represented by natural polyphenolic molecules that might be utilized to develop natural drugs to alleviate neurotoxicity symptoms caused by MeHg or other Hg compounds.

Cross-tissue analysis of blood and brain epigenome-wide association studies in Alzheimer's disease

To better understand DNA methylation in Alzheimer's disease (AD) from both mechanistic and biomarker perspectives, we performed an epigenome-wide meta-analysis of blood DNA methylation in two large independent blood-based studies in AD, the ADNI and AIBL studies, and identified 5 CpGs, mapped to the SPIDR, CDH6 genes, and intergenic regions, that are significantly associated with AD diagnosis. A cross-tissue analysis that combined these blood DNA methylation datasets with four brain methylation datasets prioritized 97 CpGs and 10 genomic regions that are significantly associated with both AD neuropathology and AD diagnosis. An out-of-sample validation using the AddNeuroMed dataset showed the best performing logistic regression model includes age, sex, immune cell type proportions, and methylation risk score based on prioritized CpGs in cross-tissue analysis (AUC = 0.696, 95% CI: 0.616 - 0.770, P-value = 2.78 × 10^-5). Our study offers new insights into epigenetics in AD and provides a valuable resource for future AD biomarker discovery.

Cellular Conditions Responsible for Methylmercury-Mediated Neurotoxicity

Methylmercury (MeHg) is a widely known environmental pollutant that causes severe neurotoxicity. MeHg-induced neurotoxicity depends on various cellular conditions, including differences in the characteristics of tissues and cells, exposure age (fetal, childhood, or adulthood), and exposure levels. Research has highlighted the importance of oxidative stress in the pathogenesis of MeHg-induced toxicity and the site- and cell-specific nature of MeHg-induced neurotoxicity. The cerebellar granule cells and deeper layer cerebrocortical neurons are vulnerable to MeHg. In contrast, the hippocampal neurons are resistant to MeHg, even at high mercury accumulation levels. This review summarizes the mechanisms underlying MeHg-mediated intracellular events that lead to site-specific neurotoxicity. Specifically, we discuss the mechanisms associated with the redox ability, neural outgrowth and synapse formation, cellular signaling pathways, epigenetics, and the inflammatory conditions of microglia.

Exploring the therapeutic promise of targeting Rho kinase in rheumatoid arthritis

Rheumatoid arthritis (RA) is a prevalent systemic autoimmune disease caused by dysregulated inflammatory reactions, T lymphocyte invasion into the joints, and articular thickening. Immune cells, primarily tumor necrosis factor-alpha (TNF-α) and chemokines (interleukin or IL-1), which are predominantly generated by activated macrophages cells, have also been involved with the pathogenesis of rheumatoid arthritis. Rho GTPases are integral factors of biochemical cascades utilized by antigens, and also by cellular receptors, cytokines, and chemokines, to modulate inflammatory reactions, according to growing data. The Rho family is a group of G proteins that govern a variety of biological and physiological activities such as mobility, actin stress fiber production, growth, and polarity. Research suggests that the Rho A and Rho-associated coiled-coil kinase (ROCK) regulatory cascade could be essential in several autoimmune conditions, including RA. ROCK is activated in the synovial of rheumatoid arthritis patients, while the blocking of ROCK with fasudil could also decrease IL-6, TNF-α, and IL-1. This review covers current developments in understanding the overactivation of Rho enzyme activity in RA suppressed by ROCK inhibitors which can be utilized for the treatment of autoimmune disease. We offer an outline of the function of ROCK inhibitors in immune cells and discuss findings which emphasize the rising participation of this category of kinases within the pathological process of autoimmune disorders. Assuming the potential ability of ROCK as a therapeutic, we define approaches that might be used to inhibit Rho kinase activity in rheumatoid disorders.

Local delivery of RhoA siRNA by PgP nanocarrier reduces inflammatory response and improves neuronal cell survival in a rat TBI model

Traumatic brain injury (TBI) is a leading cause of death and disability with complex pathophysiology including prolonged neuroinflammation, apoptosis, and glial scar formation. The upregulation of RhoA is a key factor in the pathological development of secondary injury following TBI. Previously, we developed a novel cationic, amphiphilic copolymer, poly (lactide-co-glycolide)-graft-polyethylenimine (PgP), as a nanocarrier for delivery of therapeutic nucleic acids. In a rat compression spinal cord injury model, delivery of siRNA targeting RhoA (siRhoA) by PgP resulted in RhoA knockdown; reduced astrogliosis and inflammation; and promoted axonal regeneration/sparing. Here, we evaluated the effect of RhoA knockdown by PgP/siRhoA nanoplexes in a rat controlled cortical impact TBI model. A single intraparenchymal injection of PgP/siRhoA nanoplexes significantly reduced RhoA expression, lesion volume, neuroinflammation, and apoptosis, and increased neuronal survival in the ipsilateral cortex. These results suggest that PgP/siRhoA nanoplexes can efficiently knockdown RhoA expression in the injured brain and reduce secondary injury.

DNA methyltransferase- and histone deacetylase-mediated epigenetic alterations induced by low-level methylmercury exposure disrupt neuronal development

Methylmercury (MeHg) is a chemical substance that causes adverse effects on fetal development. However, the molecular mechanisms by which environmental MeHg affects fetal development have not been clarified. Recently, it has been suggested that the toxic effects of chemicals on fetal development are related alterations in epigenetics, such as DNA methylation and histone modification. In order to analyze the epigenetic effects of low-level MeHg exposure on neuronal development, we evaluated neuronal development both in vivo and in vitro. Pregnant mice (C57BL/6J) were orally administrated 3 mg/kg of MeHg once daily from embryonic day 12-14. Fetuses were removed on embryonic day 19 and brain tissues were collected. LUHMES cells were treated with 1 nM of MeHg for 6 days and collected on the last day of treatment. In both in vivo and in vitro samples, MeHg significantly suppressed neurite outgrowth. Decreased acetylated histone H3 (AcH3) levels and increased histone deacetylase (HDAC) 3 and HDAC6 levels were observed in response to MeHg treatment in both in vivo and in vitro experiments. In addition, increased DNA methylation and DNA methyltransferase 1 (DNMT1) levels were observed in both in vivo and in vitro experiments. The inhibition of neurite outgrowth resulting from MeHg exposure was restored by co-treatment with DNMT inhibitor or HDAC inhibitors. Our results suggest that neurological effects such as reduced neurite outgrowth due to low-level MeHg exposure result from epigenetic changes, including a decrease in AcH3 via increased HDAC levels and an increase in DNA methylation via increased DNMT1 levels.

Inhibition of microRNA-10b-5p up-regulates HOXD10 to attenuate Alzheimer's disease in rats via the Rho/ROCK signalling pathway

OBJECTIVE

It is believed that microRNAs (miRNAs) participate in the pathogenesis of Alzheimer's disease (AD), but the specified function of miR-10b-5p in the disease has not been thoroughly understood. Thereafter, this research aimed to assess the function of miR-10b-5p in AD.

METHODS

Rat AD models were established by injected with amyloid-β_1-42 (Aβ_1-42), which were mainly treated with lentivirus-miR-10b-5p inhibitor, or lentivirus-overexpressed homeobox D10 (HOXD10). MiR-10b-5p, HOXD10, RhoA, ROCK1 and ROCK2 expression in rat hippocampal tissues were determined. Afterwards, the behaviour of rats was tested, and neuronal apoptosis, pathological injury, and inflammatory factors and oxidative stress-related factors were all assessed. Finally, the target relation between miR-10b-5p and HOXD10 was detected.

RESULTS

MiR-10b-5p was upregulated while HOXD10 was downregulated, and the Rho/ROCK signalling pathway was activated in hippocampal tissues of rats with AD. Inhibition of miR-10b-5p could attenuate the neuronal apoptosis, pathological injury, inflammation reaction, and oxidative stress by elevating HOXD10 and inhibiting the Rho/ROCK signalling pathway in AD rats. Moreover, HOXD10 was targeted by miR-10b-5p.

CONCLUSION

Inhibited miR-10b-5p decelerated the development of AD by promoting HOXD10 and inactivating the Rho/ROCK signalling pathway, and our findings may contribute to the exploration of AD treatment.

Decreased plasma thiol antioxidant capacity precedes neurological signs in a rat methylmercury intoxication model

The main target organ for MeHg is the nervous system, and its neurological dysfunction remains irreversible. Therefore, predictive biomarkers associated with individual susceptibility to MeHg and future clinical severity are needed to protect against the progression of MeHg toxicity. In this study, we demonstrated that plasma thiol antioxidant capacity (-SHp) is a useful predictive biomarker associated with future clinical severity using MeHg-intoxicated rats administered 1 mg/kg/day for 4 weeks. Blood samples were collected from the subclavian vein of each rat once a week to examine total blood mercury concentrations and the levels of plasma oxidative stress markers. Time course analyses of the correlation between these weekly blood examination values and hind limb crossing signs score after 4 weeks of MeHg exposure were performed, and plasma -SHp levels after 2 weeks of MeHg exposure showed strong correlations with future hind limb crossing sign scores. Neuropathological changes also developed in parallel with hind limb crossing sign scores. Quantitative analysis of vacuolar areas in the spinal cord showed a strong correlation with hind limb crossing sign scores. In conclusion, evaluation of plasma -SHp levels allowed us to detect individuals at risk for health damage and could protect the sensitive population against MeHg toxicity.

Methylmercury Poisoning Induces Cardiac Electrical Remodeling and Increases Arrhythmia Susceptibility and Mortality

This study aims to investigate the cardiac electrical remodeling associated with intoxication by methylmercury (MeHg). We evaluated the chronic effects of MeHg on in vivo electrocardiograms and on ex vivo action potentials and depolarizing (I_Ca-L) and repolarizing (I_to) currents. The acute effect of MeHg was evaluated on HEK293 cells expressing human ERG, Kv4.3 and KCNQ1/KCNE1 channels. Chronic MeHg treatment increased QTc and T_peak–T_end interval duration, prolonged action potential duration and decreased amplitude of I_to and I_Ca-L. In addition, heterologously expressed I_hKv4.3, I_hERG or I_hKCNQ1/KCNE1 decreased after acute exposure to MeHg at subnanomolar range. The introduction of the in vitro effects of MeHg in a computer model of human ventricular action potentials triggered early afterdepolarizations and arrhythmia. In conclusion, cardiac electrical remodeling induced by MeHg poisoning is related to the reduction of I_to and I_Ca-L. The acute effect of MeHg on hKv4.3; hERG and hKCNQ1/KCNE1 currents and their transposition to in silico models show an association between MeHg intoxication and acquired Long QT Syndrome in humans. MeHg can exert its high toxicity either after chronic or acute exposure to concentrations as low as picomolar.

Fasudil, a Rho-Associated Coiled Coil-Forming Protein Kinase Inhibitor, Recovers Methylmercury-Induced Axonal Degeneration by Changing Microglial Phenotype in Rats

Methylmercury (MeHg) is an environmental neurotoxicant that induces neuropathological changes. In this study, we established chronic MeHg-intoxicated rats. These rats survived, and sustained MeHg-induced axonal degeneration, including the dorsal root nerve and the dorsal column of the spinal cord; these changes persisted 12 weeks after MeHg withdrawal. We demonstrated for the first time the restorative effect of Fasudil, a specific inhibitor of Rho-associated coiled coil-forming protein kinase, on axonal degeneration and corresponding neural dysfunction in the established chronic MeHg-intoxicated rats. To investigate the mechanism of this restorative effect, we focused on the expression of Rho protein families. This was supported by our previous study, which demonstrated that cotreatment with Fasudil prevented axonal degeneration by mitigating neurite extension/retraction incoordination caused by MeHg-induced suppression of Rac1 in vitro and in subacute MeHg-intoxicated rats. However, the mechanism of the restorative effect of Fasudil on axonal degeneration in chronic MeHg-intoxicated rats differed from MeHg-mediated neuritic extension/retraction incoordination. We found that the restorative effect of Fasudil was caused by the Fasudil-induced change of microglial phenotype, from proinflammatory to anti-inflammatory; moreover, Fasudil suppressed Rho-associated coiled coil-forming protein kinase activity. Treatment with Fasudil decreased the expression of proinflammatory factors, including tumor necrosis factor-α, inducible nitric oxide synthase, interleukin-1β, and interleukin-6; furthermore, it inactivated the nuclear factor kappa-light-chain-enhancer of activated B cells pathway. Additionally, Fasudil treatment was associated with increased levels of anti-inflammatory factors arginase-1 and interleukin-10. These results suggest that Rho-associated coiled coil-forming protein kinase inhibition may recover MeHg-mediated axonal degeneration and neural dysfunction in chronic MeHg intoxication.

Angiopoietin-like 4 binds neuropilins and cooperates with VEGF to induce diabetic macular edema

The majority of patients with diabetic macular edema (DME), the most common cause of vision loss in working-age Americans, do not respond adequately to current therapies targeting VEGFA. Here, we show that expression of angiopoietin-like 4 (ANGPTL4), a HIF-1-regulated gene product, is increased in the eyes of diabetic mice and patients with DME. We observed that ANGPTL4 and VEGF act synergistically to destabilize the retinal vascular barrier. Interestingly, while ANGPTL4 modestly enhanced tyrosine phosphorylation of VEGF receptor 2, promotion of vascular permeability by ANGPTL4 was independent of this receptor. Instead, we found that ANGPTL4 binds directly to neuropilin 1 (NRP1) and NRP2 on endothelial cells (ECs), leading to rapid activation of the RhoA/ROCK signaling pathway and breakdown of EC-EC junctions. Treatment with a soluble fragment of NRP1 (sNRP1) prevented ANGPTL4 from binding to NRP1 and blocked ANGPTL4-induced activation of RhoA as well as EC permeability in vitro and retinal vascular leakage in diabetic animals in vivo. In addition, sNRP1 reduced the stimulation of EC permeability by aqueous fluid from patients with DME. Collectively, these data identify the ANGPTL4/NRP/RhoA pathway as a therapeutic target for the treatment of DME.

ROCK2 regulates autophagy in the hippocampus of rats after subarachnoid hemorrhage

The role of autophagy in subarachnoid hemorrhage (SAH) remains unclear. This study aimed to investigate the role of ROCK2 in the regulation of hippocampus autophagy after SAH. Thirty-six Sprague-Dawley rats were randomly divided into three groups - the sham group, the SAH group, and the SAH+ ROCK2 inhibitor group (or the drug group) - and analyzed through a behavior test. The hippocampus tissues were analyzed using immunochemistry and western blot analysis. We observed injured morphology in the hippocampus and impaired learning and memory ability in the rats in the SAH group, accompanied by upregulated ROCK2 expression and increased beclin-1 and LC3-II expression. Compared with the SAH group, we observed normal morphology in the hippocampus and better learning and memory ability in the rats in the drug group, accompanied by downregulated ROCK2 expression and increased beclin-1 and LC3-II expression. SAH activates autophagy in the hippocampus, but this could be inhibited by ROCK2. Inhibition of ROCK2 promotes autophagy and reduces the injury in the hippocampus, leading to the recovery of learning and memory ability following SAH. ROCK2 may represent a new target for the treatment of SAH.

Dynamic blebbing: A bottleneck to human embryonic stem cell culture that can be overcome by Laminin-Integrin signaling

This study characterizes dynamic and apoptotic blebbing in human embryonic stem cells (hESC), identifies dynamic blebbing as a bottleneck to successful cell attachment during passaging, and demonstrates that dynamic blebbing can be rapidly stopped by plating cells on recombinant human laminin. In freshly plated hESC, dynamic and apoptotic blebbing differed in time of occurrence, bleb retraction rate, mitochondrial membrane potential, and caspase 3&7 activation. While dynamic blebbing can be controlled with drugs that inhibit myosin II, these methods have off-target effects and are not suitable for clinical applications. Recombinant human laminin-521 or addition of laminin-111 to Matrigel provided a safe method to drastically decrease dynamic blebbing and improve cell attachment with proteins normally found in the inner cell mass. Inhibition of focal adhesion kinase, which is activated by binding of integrins to laminin, prolonged dynamic blebbing and inhibited attachment. These data show that hESC bind rapidly to laminins through an integrin, which activates focal adhesion kinase that in turn downregulates dynamic blebbing. Laminins enabled hESC to rapidly attach during passaging, improved plating efficiency, enabled passaging of single pluripotent stem cells, and avoided use of inhibitors that have non-specific off-target effects. These data provide a strategy for improving hESC culture using biologically safe recombinant human proteins.

Oxidative stress, caspase-3 activation and cleavage of ROCK-1 play an essential role in MeHg-induced cell death in primary astroglial cells

Methylmercury is a toxic environmental contaminant that elicits significant toxicity in humans. The central nervous system is the primary target of toxicity, and is particularly vulnerable during development. Rho-associated protein kinase 1 (ROCK-1) is a major downstream effector of the small GTPase RhoA and a direct substrate of caspase-3. The activation of ROCK-1 is necessary for membrane blebbing during apoptosis. In this work, we examined whether MeHg could affect the RhoA/ROCK-1 signaling pathway in primary cultures of mouse astrocytes. Exposure of cells with 10 μM MeHg decreased cellular viability after 24 h of incubation. This reduction in viability was preceded by a significant increase in intracellular and mitochondrial reactive oxygen species levels, as well as a reduced NAD⁺/NADH ratio. MeHg also induced an increase in mitochondrial-dependent caspase-9 and caspase-3, while the levels of RhoA protein expression were reduced or unchanged. We further found that MeHg induced ROCK-1 cleavage/activation and promoted LIMK1 and MYPT1 phosphorylation, both of which are the best characterized ROCK-1 downstream targets. Inhibiting ROCK-1 and caspases activation attenuated the MeHg-induced cell death. Collectively, these findings are the first to show that astrocytes exposed to MeHg showed increased cleavage/activation of ROCK-1, which was independent of the small GTPase RhoA.

Endoplasmic reticulum stress preconditioning modifies intracellular mercury content by upregulating membrane transporters

Endoplasmic reticulum (ER) stress preconditioning protects cells against methylmercury (MeHg) cytotoxicity by inducing integrated stress responses such as eIF2α phosphorylation, ATF4 accumulation, and nonsense-mediated mRNA decay (NMD) suppression. Here we demonstrated that ER stress preconditioning results in the upregulation of membrane transporters, leading to a decrease in intracellular mercury content. Our analyses showed that ER stress preconditioning upregulated the expression of methionine transporters that affect the cellular influx of MeHg, LAT1, LAT3, and SNAT2; and a membrane transporter that affects the efflux of MeHg, ABCC4, in MeHg-susceptible myogenic cells. Among these, ABCC4 transporter expression exhibited the greatest elevation. The functional significance of ABCC4 transporter in the efflux of MeHg was shown by the ABCC4 inhibition study. Additionally, we identified the role of phospho-eIF2α/ATF4 pathway in the upregulation of LAT1, SNAT2, and ABCC4 and the role of NMD suppression in LAT3 upregulation. Further, we detected that ER stress preconditioning amplified membrane transporter expression most likely through the translation of the upregulated mRNAs caused by ATF4-dependent transcription and NMD suppression. Taken together, these results suggested that the phospho-eIF2α/ATF4 pathway activation and NMD suppression may represent therapeutic targets for the alleviation of MeHg cytotoxicity by enhancing mercury efflux besides inducing protective stress responses.

Methylmercury Causes Blood-Brain Barrier Damage in Rats via Upregulation of Vascular Endothelial Growth Factor Expression

Clinical manifestations of methylmercury (MeHg) intoxication include cerebellar ataxia, concentric constriction of visual fields, and sensory and auditory disturbances. The symptoms depend on the site of MeHg damage, such as the cerebellum and occipital lobes. However, the underlying mechanism of MeHg-induced tissue vulnerability remains to be elucidated. In the present study, we used a rat model of subacute MeHg intoxication to investigate possible MeHg-induced blood-brain barrier (BBB) damage. The model was established by exposing the rats to 20-ppm MeHg for up to 4 weeks; the rats exhibited severe cerebellar pathological changes, although there were no significant differences in mercury content among the different brain regions. BBB damage in the cerebellum after MeHg exposure was confirmed based on extravasation of endogenous immunoglobulin G (IgG) and decreased expression of rat endothelial cell antigen-1. Furthermore, expression of vascular endothelial growth factor (VEGF), a potent angiogenic growth factor, increased markedly in the cerebellum and mildly in the occipital lobe following MeHg exposure. VEGF expression was detected mainly in astrocytes of the BBB. Intravenous administration of anti-VEGF neutralizing antibody mildly reduced the rate of hind-limb crossing signs observed in MeHg-exposed rats. In conclusion, we demonstrated for the first time that MeHg induces BBB damage via upregulation of VEGF expression at the BBB in vivo. Further studies are required in order to determine whether treatment targeted at VEGF can ameliorate MeHg-induced toxicity.

Methylmercury and brain development: A review of recent literature

Methylmercury (MeHg) is a potent environmental pollutant, which elicits significant toxicity in humans. The central nervous system (CNS) is the primary target of toxicity, and is particularly vulnerable during development. Maternal exposure to MeHg via consumption of fish and seafood can have irreversible effects on the neurobehavioral development of children, even in the absence of symptoms in the mother. It is well documented that developmental MeHg exposure may lead to neurological alterations, including cognitive and motor dysfunction. The neurotoxic effects of MeHg on the developing brain have been extensively studied. The mechanism of toxicity, however, is not fully understood. No single process can explain the multitude of effects observed in MeHg-induced neurotoxicity. This review summarizes the most current knowledge on the effects of MeHg during nervous system development considering both, in vitro and in vivo experimental models. Considerable attention was directed towards the role of glutamate and calcium dyshomeostasis, mitochondrial dysfunction, as well as the effects of MeHg on cytoskeletal components/regulators.

MARCKS is involved in methylmercury-induced decrease in cell viability and nitric oxide production in EA.hy926 cells

Methylmercury (MeHg) is a persistent environmental contaminant that has been reported worldwide. MeHg exposure has been reported to lead to increased risk of cardiovascular diseases; however, the mechanisms underlying the toxic effects of MeHg on the cardiovascular system have not been well elucidated. We have previously reported that mice exposed to MeHg had increased blood pressure along with impaired endothelium-dependent vasodilation. In this study, we investigated the toxic effects of MeHg on a human endothelial cell line, EA.hy926. In addition, we have tried to elucidate the role of myristoylated alanine-rich C kinase substrate (MARCKS) in the MeHg toxicity mechanism in EA.hy926 cells. Cells exposed to MeHg (0.1-10 µM) for 24 hr showed decreased cell viability in a dose-dependent manner. Treatment with submaximal concentrations of MeHg decreased cell migration in the wound healing assay, tube formation on Matrigel and spontaneous nitric oxide (NO) production of EA.hy926 cells. MeHg exposure also elicited a decrease in MARCKS expression and an increase in MARCKS phosphorylation. MARCKS knockdown or MARCKS overexpression in EA.hy926 cells altered not only cell functions, such as migration, tube formation and NO production, but also MeHg-induced decrease in cell viability and NO production. These results suggest the broad role played by MARCKS in endothelial cell functions and the involvement of MARCKS in MeHg-induced toxicity.

Inhibition of prostaglandin E2 receptor EP3 mitigates thrombin-induced brain injury

Prostaglandin E2 EP3 receptor is the only prostaglandin E2 receptor that couples to multiple G-proteins, but its role in thrombin-induced brain injury is unclear. In the present study, we exposed mouse hippocampal slice cultures to thrombin in vitro and injected mice with intrastriatal thrombin in vivo to investigate the role of EP3 receptor in thrombin-induced brain injury and explore its underlying cellular and molecular mechanisms. In vitro, EP3 receptor inhibition reduced thrombin-induced hippocampal CA1 cell death. In vivo, EP3 receptor was expressed in astrocytes and microglia in the perilesional region. EP3 receptor inhibition reduced lesion volume, neurologic deficit, cell death, matrix metalloproteinase-9 activity, neutrophil infiltration, and the number of CD68(+) microglia, but increased the number of Ym-1(+) M2 microglia. RhoA-Rho kinase levels were increased after thrombin injection and were decreased by EP3 receptor inhibition. In mice that received an intrastriatal injection of autologous arterial blood, inhibition of thrombin activity with hirudin decreased RhoA expression compared with that in vehicle-treated mice. However, EP3 receptor activation reversed this effect of hirudin. These findings show that prostaglandin E2 EP3 receptor contributes to thrombin-induced brain damage via Rho-Rho kinase-mediated cytotoxicity and proinflammatory responses.

Methylmercury upregulates RE-1 silencing transcription factor (REST) in SH-SY5Y cells and mouse cerebellum

Methylmercury (MeHg) is a highly neurotoxic compound that, in adequate doses, can cause damage to the brain, including developmental defects and in severe cases cell death. The RE-1-silencing transcription factor (REST) has been found to be involved in the neurotoxic effects of environmental pollutants such as polychlorinated biphenyls (PCBs). In this study, we investigated the effects of MeHg treatment on REST expression and its role in MeHg-induced neurotoxicity in neuroblastoma SH-SY5Y cells. We found that MeHg exposure caused a dose- and time- dependent apoptotic cell death, as evidenced by the appearance of apoptotic hallmarks including caspase-3 processing and annexin V uptake. Moreover, MeHg increased REST gene and gene product expression. MeHg-induced apoptotic cell death was completely abolished by REST knockdown. Interestingly, MeHg (1μM/24h) increased the expression of REST Corepressor (Co-REST) and its binding with REST whereas the other REST cofactor mammalian SIN3 homolog A transcription regulator (mSin3A) was not modified. In addition, we demonstrated that the acetylation of histone protein H4 was reduced after MeHg treatment and was critical for MeHg-induced apoptosis. Accordingly, the pan-histone deacetylase inhibitor trichostatin-A (TSA) prevented MeHg-induced histone protein H4 deacetylation, thereby reverting MeHg-induced neurotoxic effect. Male mice subcutaneously injected with 10mg/kg of MeHg for 10 days showed an increase in REST expression in the granule cell layer of the cerebellum together with a decrease in histone H4 acetylation. Collectively, we demonstrated that methylmercury exposure can cause neurotoxicity by activating REST gene expression and H4 deacetylation.

The role of the Rho/ROCK signaling pathway in inhibiting axonal regeneration in the central nervous system

The Rho/Rho-associated coiled-coil containing protein kinase (Rho/ROCK) pathway is a major signaling pathway in the central nervous system, transducing inhibitory signals to block regeneration. After central nervous system damage, the main cause of impaired regeneration is the presence of factors that strongly inhibit regeneration in the surrounding microenvironment. These factors signal through the Rho/ROCK signaling pathway to inhibit regeneration. Therefore, a thorough understanding of the Rho/ROCK signaling pathway is crucial for advancing studies on regeneration and repair of the injured central nervous system.

Nanotherapeutic strategies for the treatment of Alzheimer's disease

Alzheimer's disease (AD), the most common form of dementia, is now representing one of the largest unmet medical needs. However, no effective treatment is now available to impede the progression of AD or delay its onset. There are two major challenges for the development of effective therapy for AD. First, the exact cause for AD onset is still unknown. Second, brain drug delivery is significantly hindered by the blood-brain barrier (BBB). In this review, we will summarize the pathological understanding about AD and the related treatments, compare BBB and its effect on brain drug delivery under normal and AD conditions and review the nanotherapeutic strategies that have been developed for AD therapy in recent years.

siRNA as a tool to improve the treatment of brain diseases: Mechanism, targets and delivery

As the population ages, brain pathologies such as neurodegenerative diseases and brain cancer increase their incidence, being the need to find successful treatments of upmost importance. Drug delivery to the central nervous system (CNS) is required in order to reach diseases causes and treat them. However, biological barriers, mainly blood-brain barrier (BBB), are the key obstacles that prevent the effectiveness of possible treatments due to their ability to strongly limit the perfusion of compounds into the brain. Over the past decades, new approaches towards overcoming BBB and its efflux transporters had been proposed. One of these approaches here reviewed is through small interfering RNA (siRNA), which is capable to specifically target one gene and silence it in a post-transcriptional way. There are different possible functional proteins at the BBB, as the ones responsible for transport or just for its tightness, which could be a siRNA target. As important as the effective silence is the way to delivery siRNA to its anatomical site of action. This is where nanotechnology-based systems may help, by protecting siRNA circulation and providing cell/tissue-targeting and intracellular siRNA delivery. After an initial overview on incidence of brain diseases and basic features of the CNS, BBB and its efflux pumps, this review focuses on recent strategies to reach brain based on siRNA, and how to specifically target these approaches in order to treat brain diseases.

Antenatal taurine improves neuronal regeneration in fetal rats with intrauterine growth restriction by inhibiting the Rho-ROCK signal pathway

The Rho-ROCK signal pathway is an important mediator of inhibitory signals that blocks central nervous cell regeneration. Here, we investigated whether antenatal taurine improved neuronal regeneration in fetal rats with intrauterine growth restriction (IUGR) by inhibiting this pathway. Thirty pregnant rats were randomly divided into three groups: control, IUGR, and IUGR + antenatal taurine supplementation (taurine group). The mRNA levels of Ras homolog gene A (Rho A), Rho-associated coiled-coil forming protein kinase 2 (ROCK2), and proliferating cell nuclear antigen (PCNA) were detected using real-time quantitative PCR. RhoA, ROCK2 and PCNA-positive cells were counted using immunohistochemistry. Antenatal taurine supplementation decreased RhoA and Rock2 mRNA expression, increased PCNA mRNA expression, and significantly decreased RhoA, ROCK2-positive and increased PCNA-positive cell counts in IUGR fetal rat brain tissues (p < 0.05). Thus, antenatal taurine supplementation inhibited the expression of key Rho-ROCK signal molecules and improved IUGR fetal brain development.

Design of dual inhibitors of ROCK-I and NOX2 as potential leads for the treatment of neuroinflammation associated with various neurological diseases including autism spectrum disorder

Inhibition of both ROCK-I and NOX2 to treat neuroinflammation could be very effective in the treatment of progressive neurological disorders like AD, ASD and FXS.

Design of novel rho kinase inhibitors using energy based pharmacophore modeling, shape-based screening, in silico virtual screening, and biological evaluation

Rho-associated protein kinase (ROCK) plays a key role in regulating a variety of cellular processes, and dysregulation of ROCK signaling or expression is implicated in numerous diseases and infections. ROCK proteins have therefore emerged as validated targets for therapeutic intervention in various pathophysiological conditions such as diabetes-related complications or hepatitis C-associated pathogenesis. In this study, we report on the design and identification of novel ROCK inhibitors utilizing energy based pharmacophores and shape-based approaches. The most potent compound 8 exhibited an IC50 value of 1.5 μM against ROCK kinase activity and inhibited methymercury-induced neurotoxicity of IMR-32 cells at GI50 value of 0.27 μM. Notably, differential scanning fluorometric analysis revealed that ROCK protein complexed with compound 8 with enhanced stability relative to Fasudil, a validated nanomolar range ROCK inhibitor. Furthermore, all compounds exhibited ≥96 μM CC50 (50% cytotoxicity) in Huh7 hepatoma cells, while 6 compounds displayed anti-HCV activity in HCV replicon cells. The identified lead thus constitutes a prototypical molecule for further optimization and development as anti-ROCK inhibitor.

Rho family GTPases: key players in neuronal development, neuronal survival, and neurodegeneration

The Rho family of GTPases belongs to the Ras superfamily of low molecular weight (∼21 kDa) guanine nucleotide binding proteins. The most extensively studied members are RhoA, Rac1, and Cdc42. In the last few decades, studies have demonstrated that Rho family GTPases are important regulatory molecules that link surface receptors to the organization of the actin and microtubule cytoskeletons. Indeed, Rho GTPases mediate many diverse critical cellular processes, such as gene transcription, cell–cell adhesion, and cell cycle progression. However, Rho GTPases also play an essential role in regulating neuronal morphology. In particular, Rho GTPases regulate dendritic arborization, spine morphogenesis, growth cone development, and axon guidance. In addition, more recent efforts have underscored an important function for Rho GTPases in regulating neuronal survival and death. Interestingly, Rho GTPases can exert either a pro-survival or pro-death signal in neurons depending upon both the cell type and neurotoxic insult involved. This review summarizes key findings delineating the involvement of Rho GTPases and their effectors in the regulation of neuronal survival and death. Collectively, these results suggest that dysregulation of Rho family GTPases may potentially underscore the etiology of some forms of neurodegenerative disease such as amyotrophic lateral sclerosis.

Rho-kinase as a therapeutic target in vascular diseases: striking nitric oxide signaling

Rho GTPases are a globular, monomeric group of small signaling G-protein molecules. Rho-associated protein kinase/Rho-kinase (ROCK) is a downstream effector protein of the Rho GTPase. Rho-kinases are the potential therapeutic targets in the treatment of cardiovascular diseases. Here, we have primarily discussed the intriguing roles of ROCK in cardiovascular health in relation to nitric oxide signaling. Further, we highlighted the biphasic effects of Y-27632, a ROCK inhibitor under shear stress, which acts as an agonist of nitric oxide production in endothelial cells. The biphasic effects of this inhibitor raised the question of safety of the drug usage in treating cardiovascular diseases.

Alteration in MARCKS phosphorylation and expression by methylmercury in SH-SY5Y cells and rat brain

The molecular mechanisms mediating methylmercury (MeHg)-induced neurotoxicity are not completely understood. Because myristoylated alanine-rich C kinase substrate (MARCKS) plays an essential role in the differentiation and development of neuronal cells, we studied the alteration of MARCKS expression and phosphorylation in MeHg-induced neurotoxicity of neuroblastoma SH-SY5Y cells and in the rat brain. Exposure to MeHg induced a decrease in cell viability of SH-SY5Y cells, which was accompanied by a significant increase in phosphorylation and a reduction in MARCKS expression. Pretreatment of cells with a protein kinase C inhibitor or an extracellular Ca(2+) chelator suppressed MeHg-induced MARCKS phosphorylation. In MARCKS knock-down cells, MeHg-induced cell death was significantly augmented in comparison to control siRNA. In brain tissue from MeHg-treated rats, MARCKS phosphorylation was enhanced in the olfactory bulb in comparison to control rats. The present study may indicate that alteration in MARCKS expression or phosphorylation has consequences for MeHg-induced neurotoxicity.

Rac1 selective activation improves retina ganglion cell survival and regeneration

In adult mammals, after optic nerve injury, retinal ganglion cells (RGCs) do not regenerate their axons and most of them die by apoptosis within a few days. Recently, several strategies that activate neuronal intracellular pathways were proposed to prevent such degenerative processes. The rho-related small GTPase Rac1 is part of a complex, still not fully understood, intracellular signaling network, mediating in neurons many effects, including axon growth and cell survival. However, its role in neuronal survival and regeneration in vivo has not yet been properly investigated. To address this point we intravitreally injected selective cell-penetrating Rac1 mutants after optic nerve crush and studied the effect on RGC survival and axonal regeneration. We injected two well-characterized L61 constitutively active Tat-Rac1 fusion protein mutants, in which a second F37A or Y40C mutation confers selectivity in downstream signaling pathways. Results showed that, 15 days after crush, both mutants were able to improve survival and to prevent dendrite degeneration, while the one harboring the F37A mutation also improved axonal regeneration. The treatment with F37A mutant for one month did not improve the axonal elongation respect to 15 days. Furthermore, we found an increase of Pak1 T212 phosphorylation and ERK1/2 expression in RGCs after F37A treatment, whereas ERK1/2 was more activated in glial cells after Y40C administration. Our data suggest that the selective activation of distinct Rac1-dependent pathways could represent a therapeutic strategy to counteract neuronal degenerative processes in the retina.

Diabetes and overexpression of proNGF cause retinal neurodegeneration via activation of RhoA pathway

Our previous studies showed positive correlation between accumulation of proNGF, activation of RhoA and neuronal death in diabetic models. Here, we examined the neuroprotective effects of selective inhibition of RhoA kinase in the diabetic rat retina and in a model that stably overexpressed the cleavage-resistance proNGF plasmid in the retina. Male Sprague-Dawley rats were rendered diabetic using streptozotosin or stably express cleavage-resistant proNGF plasmid. The neuroprotective effects of the intravitreal injection of RhoA kinase inhibitor Y27632 were examined in vivo. Effects of proNGF were examined in freshly isolated primary retinal ganglion cell (RGC) cultures and RGC-5 cell line. Retinal neurodegeneration was assessed by counting TUNEL-positive and Brn-3a positive retinal ganglion cells. Expression of proNGF, p75^NTR, cleaved-PARP, caspase-3 and p38MAPK/JNK were examined by Western-blot. Activation of RhoA was assessed by pull-down assay and G-LISA. Diabetes and overexpression of proNGF resulted in retinal neurodegeneration as indicated by 9- and 6-fold increase in TUNEL-positive cells, respectively. In vitro, proNGF induced 5-fold cell death in RGC-5 cell line, and it induced >10-fold cell death in primary RGC cultures. These effects were associated with significant upregulation of p75^NTR and activation of RhoA. While proNGF induced TNF-α expression in vivo, it selectively activated RhoA in primary RGC cultures and RGC-5 cell line. Inhibiting RhoA kinase with Y27632 significantly reduced diabetes- and proNGF-induced activation of proapoptotic p38MAPK/JNK, expression of cleaved-PARP and caspase-3 and prevented retinal neurodegeneration in vivo and in vitro. Taken together, these results provide compelling evidence for a causal role of proNGF in diabetes-induced retinal neurodegeneration through enhancing p75^NTR expression and direct activation of RhoA and p38MAPK/JNK apoptotic pathways.

Investigation of the performance of PEG-PEI/ROCK-II-siRNA complexes for Alzheimer's disease in vitro

Recent studies have showed inhibiting ROCK promoted axonal regeneration and suppressing ROCK-II decreased Aβ formation, suggesting ROCK is a potential target for the treatment of Alzheimer's disease. Because ROCK-II mRNA is abundantly expressed in brain, we targeted ROCK-II mRNA using a siRNA approach. To suppress ROCK-II mRNA expression, we synthesized PEG-PEI/ROCK-II-siRNA complexes and transfected C17.2 neural stem cells in vitro. The characteristics of the complexes were tested using a gel retardation assay. Particle size and zeta potential were examined using dynamic light scattering and the morphology of the complexes were observed by transmission electron microscopy. The toxicity was detected by an MTT assay and transfection efficiency was determined by flow cytometry. Laser confocal microscopy was employed to investigate the cell uptake of the complexes. RT-PCR and western blotting were used to verify the effect of gene silencing. Our results indicated that the characteristics of the complexes depended on the N/P ratios. At a high N/P ratio, PEG-PEI could completely condense the siRNA into small-sized uniform particles. However, high N/P ratios are accompanied with high cytotoxicity. Because of high transfection efficiency and low cytotoxicity, N/P=50 was chosen to transfect C17.2 cells in vitro. Laser confocal microscopy showed that ROCK-II-siRNA with green fluorescence was mainly distributed in the cytoplasm and synapses. Moreover, ROCK-II-siRNA was successfully released from the lysosome. RT-PCR and western blotting demonstrated effective gene silencing. These results indicated that PEG-PEI/ROCK-II-siRNA complexes effectively suppressed ROCK-II mRNA expression, providing the basis for future research in vivo.

A method for rapid dose-response screening of environmental chemicals using human embryonic stem cells

INTRODUCTION

Human embryonic stem cells (hESC) provide an invaluable model for assessing the effects of environmental chemicals and drugs on human prenatal development. However, hESC are difficult to adapt to 96-well plate screening assays, because they survive best when plated as colonies, which are difficult to count and plate accurately. The purpose of this study is to present an experimental method and analysis procedure to accomplish reliable screening of toxicants using hESC.

METHODS

We present a method developed to rapidly and easily determine the number of cells in small colonies of hESC spectrophotometerically and then accurately dispense equivalent numbers of cells in 96-well plates. The MTT assay was used to evaluate plating accuracy, and the method was tested using known toxicants.

RESULTS

The quality of the plate set-up and analysis procedure was evaluated with NIH plate validation and assessment software. All statistical parameters measured by the software were acceptable, and no drift or edge effects were observed. The 96-well plate MTT assay with hESC was tested by performing a dose-response screen of commercial products, which contain a variety of chemicals. The screen was done using single wells/dose, and the reliability of this method was demonstrated in a subsequent screen of the same products repeated three times. The single and triple screens were in good agreement, and NOAELs and IC(50)s could be determined from the single screen. The effects of vapor from volatile chemicals were studied, and methods to monitor and avoid vapor effects were incorporated into the assay.

DISCUSSION

Our method overcomes the difficulty of using hESC for reliable quantitative 96-well plate assays. It enables rapid dose-response screening using equipment that is commonly available in laboratories that culture hESC. This method could have a broad application in studies of environmental chemicals and drugs using hESC as models of prenatal development.

Differing effects of toxicants (methylmercury, inorganic mercury, lead, amyloid β, and rotenone) on cultured rat cerebrocortical neurons: differential expression of rho proteins associated with neurotoxicity

Methylmercury (MeHg), inorganic mercury (IHg), lead (Pb), amyloid-β peptide (Aβ), and rotenone (RTN) are well-known toxicants. Here, we demonstrate that these five toxicants exhibit differing effects on cerebrocortical neurons. The concentration responsible for 30% loss of viability (EC30) values 3 days after exposure was approximately 100nM for MeHg, IHg, and RTN and 10μM for Aβ. Neuritic degeneration and subsequent apoptotic cell death were observed in these toxicant-treated cells. In contrast, the EC30 value 3 days after exposure to Pb was > 10μM. We clarified the differential expression of Ras homolog gene (Rho) family proteins (Ras-related C3 botulinum toxin substrate 1 [Rac1], cell division cycle 42, and Ras homolog gene family, member A [RhoA]) upon exposure to these five toxicants. Exposure to 100nM MeHg, IHg, or RTN downregulated the expression of Rac1, related to neuritic extension, but did not affect RhoA, related to retraction. At a higher concentration (1μM), IHg and RTN also acted through the suppression of Rac1, whereas increased MeHg toxicity was not associated with the expression of Rho family proteins. On the other hand, Pb and Aβ showed no effects on the expression of Rho proteins. Modification of the balance of neuritic extension and retraction by the suppression of Rho A rescued the neurotoxicity of 100nM MeHg, IHg, and RTN. The results indicate that the imbalance of neuritic extension and retraction by the suppression of Rac1 by 100nM MeHg, IHg, and RTN causes cerebrocortical neuron axonal degeneration and cell death. By contrast, the neurotoxicities of Pb, Aβ, and MeHg (at higher concentrations) are conferred by other toxic mechanisms.