The impact of metallothionein-II on microglial response to tumor necrosis factor-alpha (TNFα) and downstream effects on neuronal regeneration

Metallothionein-2: An emerging target in inflammatory diseases and cancers

Metallothionein-2 (MT-2) was originally discovered as a mediator of zinc homeostasis and cadmium detoxification. However, MT-2 has recently received increased attention because altered expression of MT-2 is closely related to various diseases such as asthma and cancers. Several pharmacological strategies have been developed to inhibit or modify MT-2, revealing its potential as drug target in diseases. Therefore, a better understanding of the mechanisms of MT-2 action is warranted to improve drug development for potential clinical applications. In this review, we highlight recent advances in determining the protein structure, regulation, binding partners, and new functions of MT-2 in inflammatory diseases and cancers.

Comparing RNA-sequencing datasets from astrocytes, oligodendrocytes, and microglia in multiple sclerosis identifies novel dysregulated genes relevant to inflammation and myelination

Central nervous system (CNS) inflammation is a key factor in multiple sclerosis (MS). Invasion of peripheral immune cells into the CNS resulting from an unknown signal or combination of signals results in activation of resident immune cells and the hallmark feature of the disease: demyelinating lesions. These lesion sites are an amalgam of reactive peripheral and central immune cells, astrocytes, damaged and dying oligodendrocytes, and injured neurons and axons. Sustained inflammation affects cells directly located within the lesion site and further abnormalities are apparent diffusely throughout normal-appearing white matter and grey matter. It is only relatively recently, using animal models, new tissue sampling techniques, and next-generation sequencing, that molecular changes occurring in CNS resident cells have been broadly captured. Advances in cell isolation through Fluorescence Activated Cell Sorting (FACS) and laser-capture microdissection together with the emergence of single-cell sequencing have enabled researchers to investigate changes in gene expression in astrocytes, microglia, and oligodendrocytes derived from animal models of MS as well as from primary patient tissue. The contribution of some dysregulated pathways has been followed up in individual studies; however, corroborating results often go unreported between sequencing studies. To this end, we have consolidated results from numerous RNA-sequencing studies to identify and review novel patterns of differentially regulated genes and pathways occurring within CNS glial cells in MS. This article is categorized under: Neurological Diseases > Molecular and Cellular Physiology.

Metallothionein 2 activation by pravastatin reinforces epithelial integrity and ameliorates radiation-induced enteropathy

Background

Radiotherapy or accidental exposure to ionizing radiation causes severe damage of healthy intestinal tissues. Intestinal barrier function is highly sensitive to ionizing radiation, and loss of epithelial integrity results in mucosal inflammation, bacterial translocation, and endotoxemia. Few studies have of epithelial integrity as a therapeutic target to treat radiation toxicity. Here, we examined the effects of pravastatin (PS) and the molecular mechanisms underlying epithelial integrity on radiation-induced enteropathy.

Methods

The radio-mitigative effects of PS were evaluated in a minipig model by quantifying clinical symptoms, and performing histological and serological analyses and mRNA sequencing in intestinal tissues. To evaluate the role of intercellular junctions on radiation damage, we used tight junction regulator and metallothionein 2 (MT2) as treatments in a mouse model of radiation-induced enteropathy. Caco-2 monolayers were used to examine functional epithelial integrityand intercellular junction expression.

Finding

Using a minipig model of pharmaceutical oral bioavailability, we found that PS mitigated acute radiation-induced enteropathy. PS-treated irradiated minipigs had mild clinical symptoms, lower intestinal inflammation and endotoxin levels, and improved gastrointestinal integrity, compared with control group animals. The results of mRNA sequencing analysis indicated that PS treatment markedly influenced intercellular junctions by inhibiting p38 MAPK signaling in the irradiated intestinal epithelium. The PS-regulated gene MT2 improved the epithelial barrier via enhancement of intercellular junctions in radiation-induced enteropathy.

Interpretation

PS regulated epithelial integrity by modulating MT2 in radiation-damaged epithelial cells. These findings suggested that maintenance of epithelial integrity is a novel therapeutic target for treatment of radiation-induced gastrointestinal damage.

Funding

As stated in the Acknowledgments

From the low-density lipoprotein receptor-related protein 1 to neuropathic pain: a potentially novel target

The low-density lipoprotein receptor–related protein 1 plays a major role in the regulation of neuroinflammation, neurodegeneration, neuroregeneration, neuropathic pain, and deficient cognitive functions.

This review describes the roles of the low-density lipoprotein receptor–related protein 1 (LRP-1) in inflammatory pathways, nerve nerve degeneration and -regeneration and in neuropathic pain. Induction of LRP-1 is able to reduce the activation of the proinflammatory NFκB-mediated pathway and the mitogen-activated protein kinase (MAPK) c-Jun N-terminal kinase and p38 signaling pathways, in turn decreasing the production of inflammatory mediators. Low-density lipoprotein receptor-related protein 1 activation also decreases reactive astrogliosis and polarizes microglial cells and macrophages from a proinflammatory phenotype (M1) to an anti-inflammatory phenotype (M2), attenuating the neuroinflammatory environment. Low-density lipoprotein receptor-related protein 1 can also modulate the permeability of the blood–brain barrier and the blood–nerve barrier, thus regulating the infiltration of systemic insults and cells into the central and the peripheral nervous system, respectively. Furthermore, LRP-1 is involved in the maturation of oligodendrocytes and in the activation, migration, and repair phenotype of Schwann cells, therefore suggesting a major role in restoring the myelin sheaths upon injury. Low-density lipoprotein receptor-related protein 1 activation can indirectly decrease neurodegeneration and neuropathic pain by attenuation of the inflammatory environment. Moreover, LRP-1 agonists can directly promote neural cell survival and neurite sprouting, decrease cell death, and attenuate pain and neurological disorders by the inhibition of MAPK c-Jun N-terminal kinase and p38-pathway and activation of MAPK extracellular signal–regulated kinase pathway. In addition, activation of LRP-1 resulted in better outcomes for neuropathies such as Alzheimer disease, nerve injury, or diabetic peripheral neuropathy, attenuating neuropathic pain and improving cognitive functions. To summarize, LRP-1 plays an important role in the development of different experimental diseases of the nervous system, and it is emerging as a very interesting therapeutic target.

Mouse metallothionein-1 and metallothionein-2 are not biologically interchangeable in an animal model of multiple sclerosis, EAE

Mouse metallothionein-1 and 2 (MT1 and MT2) are often considered physiologically equivalent, because they are normally regulated coordinately by a wide range of stimuli, and it is assumed that in vivo they will be normally fully loaded with zinc(ii) (Zn7-MT1/2), although other metal ions, such as copper(i), may be eventually found as well. However, mouse MT2, in contrast to MT1, exhibits a preference for Zn(ii) coordination in comparison to that for Cu(i), which might underlie putatively different biological functions for these two mammalian isoforms. We have characterized the effects of exogenously administered mouse MT1 and MT2, and of transgenic Mt1 overexpression, in an animal model of multiple sclerosis (MS), experimental autoimmune encephalomyelitis (EAE), by active immunization with MOG35-55 peptide. Mice treated daily with MT2 showed a significant amelioration of the clinical course, with decreased peak and cumulative scores and delayed onset of EAE. In contrast, treatment with MT1 or its transgenic overexpression only caused a non-significant trend. MT2 treatment preserved better the myelin of the spinal cord, and the pattern of leukocyte infiltrates and gene expression are compatible with an inhibitory effect on neuroinflammation. Splenocytes from these animals in culture responded adequately to MOG35-55 peptide, but a bias for a Th2 profile seemed to be present in the MT2-treated mice. Interestingly, MT1 but not MT2 decreased the number of cytokines in the serum. The present results indicate that mouse MT1 and MT2 are not biologically interchangeable in the EAE model.

The influence of metallothionein treatment and treadmill running exercise on disease onset and survival in SOD1G93A amyotrophic lateral sclerosis mice

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease, characterised by the degeneration of motor neurons innervating skeletal muscle. The mechanisms underlying neurodegeneration in ALS are not yet fully elucidated, and with current therapeutics only able to extend lifespan by a matter of months there is a clear need for novel therapies to increase lifespan and patient quality of life. Here, we evaluated whether moderate-intensity treadmill exercise and/or treatment with metallothionein-2 (MT2), a neuroprotective protein, could improve survival, behavioural or neuropathological outcomes in SOD1^G93A familial ALS mice. Six-week-old female SOD1^G93A mice were allocated to one of four treatment groups: MT2 injection, i.m.; moderate treadmill exercise; neither MT2 nor exercise; or both MT2 and exercise. MT2-treated mice survived around 3% longer than vehicle-treated mice, with this mild effect reaching statistical significance in Cox proportional hazards analysis once adjusted for potential confounders. Mixed model body weight trajectories over time indicated that MT2-treated mice, with or without exercise, reached maximum body weight at a later age, suggesting a delay in disease onset of around 4% compared to saline-treated mice. Exercise alone did not significantly increase survival or delay disease onset, and neither exercise nor MT2 substantially ameliorated gait abnormalities or muscle strength loss. We conclude that neither exercise nor MT2 treatment was detrimental in female SOD1^G93A mice, and further study could determine whether the mild effect of peripheral MT2 administration on disease onset and survival could be improved via direct administration of MT2 to the central nervous system.

Protein-protein interactions underlying the behavioral and psychological symptoms of dementia (BPSD) and Alzheimer's disease

Alzheimer’s Disease (AD) is a devastating neurodegenerative disorder currently affecting 45 million people worldwide, ranking as the 6^th highest cause of death. Throughout the development and progression of AD, over 90% of patients display behavioral and psychological symptoms of dementia (BPSD), with some of these symptoms occurring before memory deficits and therefore serving as potential early predictors of AD-related cognitive decline. However, the biochemical links between AD and BPSD are not known. In this study, we explored the molecular interactions between AD and BPSD using protein-protein interaction (PPI) networks built from OMIM (Online Mendelian Inheritance in Man) genes that were related to AD and two distinct BPSD domains, the Affective Domain and the Hyperactivity, Impulsivity, Disinhibition, and Aggression (HIDA) Domain. Our results yielded 8 unique proteins for the Affective Domain (RHOA, GRB2, PIK3R1, HSPA4, HSP90AA1, GSK3beta, PRKCZ, and FYN), 5 unique proteins for the HIDA Domain (LRP1, EGFR, YWHAB, SUMO1, and EGR1), and 6 shared proteins between both BPSD domains (APP, UBC, ELAV1, YWHAZ, YWHAE, and SRC) and AD. These proteins might suggest specific targets and pathways that are involved in the pathogenesis of these BPSD domains in AD.

Metallothionein-I + II Reduces Oxidative Damage and Apoptosis after Traumatic Spinal Cord Injury in Rats

After spinal cord injury (SCI), some self-destructive mechanisms start leading to irreversible neurological deficits. It is known that oxidative stress and apoptosis play a major role in increasing damage after SCI. Metallothioneins I and II (MT) are endogenous peptides with known antioxidant, neuroprotective capacities. Taking advantage of those capacities, we administered exogenous MT to rats after SCI in order to evaluate the protective effects of MT on the production of reactive oxygen species (ROS) and lipid peroxidation (LP), as markers of oxidative stress. The activities of caspases-9 and -3 and the number of annexin V and TUNEL-positive cells in the spinal cord tissue were also measured as markers of apoptosis. Rats were subjected to either sham surgery or SCI and received vehicle or two doses of MT (10 μg per rat) at 2 and 8 h after surgical procedure. The results showed a significant increase in levels of MT protein by effect of SCI and SCI plus treatment at 12 h, while at 24 h an increase of MT was observed only in the injury plus treatment group (p < 0.05). ROS production was decreased by effect of MT in lesioned tissue; likewise, we observed diminished LP levels by MT effect both in the sham group and in the group with SCI. Also, the results showed an increase in the activity of caspase-9 due to SCI, without changes by effect of MT, as compared to the sham group. Caspase-3 activity was increased by SCI, and again, MT treatment reduced this effect only at 24 h after injury. Finally, the results of the number of cells positive to annexin V and TUNEL showed a reduction due to MT treatment both at 24 and 72 h after the injury. With the findings of this work, we conclude that exogenously administered MT has antioxidant and antiapoptotic effects after SCI.

Expression Profiles of Metallothionein I/II and Megalin in Cuprizone Model of De- and Remyelination

Copper chelator cuprizone (CPZ) is neurotoxicant, which selectively disrupts oligodendroglial respiratory chain, leading to oxidative stress and subsequent apoptosis. Demyelination is, however, followed by spontaneous remyelination owing to the activation of intrinsic CNS repair mechanisms. To explore the participation of metallothioneins (MTs) in these processes, in this study we analyzed the expression profiles of MT-I/II and their receptor megalin (low-density lipoprotein receptor related protein-2) in the brain of mice subjected to different protocols of CPZ feeding. Experiments were performed in female C57BL/6 mice fed with 0.25% CPZ during 1, 3 and 5 weeks. They were sacrificed immediately after feeding with CPZ or 2 weeks after the withdrawal of CPZ. The data showed that CPZ-induced demyelination was followed by high astrogliosis and enhanced expression of MTs and megalin in white (corpus callosum and internal capsule) and gray matter of the brain (cortex, hippocampus, and cerebellum). Moreover, in numerous cortical neurons and progenitor cells the signs of MT/megalin interactions and Akt1 phosphorylation was found supporting the hypothesis that MTs secreted from the astrocytes might directly affect the neuronal differentiation and survival. Furthermore, in mice treated with CPZ for 5 weeks the prominent MTs and megalin immunoreactivities were found on several neural stem cells and oligodendrocyte progenitors in subgranular zone of dentate gyrus and subventricular zone of lateral ventricles pointing to high modulatory effect of MTs on adult neuro- and oligodendrogenesis. The data show that MT I/II perform important cytoprotective and growth-regulating functions in remyelinating processes activated after toxic demyelinating insults.