Metallothionein I,II deficient mice do not exhibit significantly worse long-term behavioral outcomes following neonatal hypoxia-ischemia: MT-I,II deficient mice have inherent behavioral impairments

Zinc in Cognitive Impairment and Aging

Zinc, an essential micronutrient for life, was first discovered in 1869 and later found to be indispensable for the normal development of plants and for the normal growth of rats and birds. Zinc plays an important role in many physiological and pathological processes in normal mammalian brain development, especially in the development of the central nervous system. Zinc deficiency can lead to neurodegenerative diseases, mental abnormalities, sleep disorders, tumors, vascular diseases, and other pathological conditions, which can cause cognitive impairment and premature aging. This study aimed to review the important effects of zinc and zinc-associated proteins in cognitive impairment and aging, to reveal its molecular mechanism, and to highlight potential interventions for zinc-associated aging and cognitive impairments.

Spatiotemporal dynamics of γH2AX in the mouse brain after acute irradiation at different postnatal days with special reference to the dentate gyrus of the hippocampus

Gamma H2A histone family member X (γH2AX) is a molecular marker of aging and disease. However, radiosensitivity of the different brain cells, including neurons, glial cells, cells in cerebrovascular system, epithelial cells in pia mater, ependymal cells lining the ventricles of the brain in immature animals at different postnatal days remains unknown. Whether radiation-induced γH2AX foci in immature brain persist in adult animals still needs to be investigated. Hence, using a mouse model, we showed an extensive postnatal age-dependent induction of γH2AX foci in different brain regions at 1 day after whole body gamma irradiation with 5Gy at postnatal day 3 (P3), P10 and P21. P3 mouse brain epithelial cells in pia mater, glial cells in white matter and cells in cerebrovascular system were more radiosensitive at one day after radiation exposure than those from P10 and P21 mice. Persistent DNA damage foci (PDDF) were consistently demonstrated in the brain at 120 days and 15 months after irradiation at P3, P10 and P21, and these mice had shortened lifespan compared to the age-matched control. Our results suggest that early life irradiation-induced PDDF at later stages of animal life may be related to the brain aging and shortened life expectancy of irradiated animals.

Novel Defense by Metallothionein Induction Against Cognitive Decline: From Amyloid β1-42-Induced Excess Zn2+ to Functional Zn2+ Deficiency

The role of metallothioneins (MTs) in cognitive decline associated with intracellular Zn²⁺ dysregulation remains unclear. Here, we report that hippocampal MT induction defends cognitive decline, which was induced by amyloid β_1-42 (Aβ_1-42)-mediated excess Zn²⁺ and functional Zn²⁺ deficiency. Excess increase in intracellular Zn²⁺, which was induced by local injection of Aβ_1-42 into the dentate granule cell layer, attenuated in vivo perforant pathway LTP, while the attenuation was rescued by preinjection of MT inducers into the same region. Intraperitoneal injection of dexamethasone, which increased hippocampal MT proteins and blocked Aβ_1-42-mediated Zn²⁺ uptake, but not Aβ_1-42 uptake, into dentate granule cells, also rescued Aβ_1-42-induced impairment of memory via attenuated LTP. The present study indicates that hippocampal MT induction blocks rapid excess increase in intracellular Zn²⁺ in dentate granule cells, which originates in Zn²⁺ released from Aβ_1-42, followed by rescuing Aβ_1-42-induced cognitive decline. Furthermore, LTP was vulnerable to Aβ_1-42 in the aged dentate gyrus, consistent with enhanced Aβ_1-42-mediated Zn²⁺ uptake into aged dentate granule cells, suggesting that Aβ_1-42-induced cognitive decline, which is caused by excess intracellular Zn²⁺, can more frequently occur along with aging. On the other hand, attenuated LTP under functional Zn²⁺ deficiency in dentate granule cells was also rescued by MT induction. Hippocampal MT induction may rescue cognitive decline under lack of cellular transient changes in functional Zn²⁺ concentration, while its induction is an attractive defense strategy against Aβ_1-42-induced cognitive decline.

Overexpression of Metallothionein-1 Modulates the Phenotype of the Tg2576 Mouse Model of Alzheimer's Disease

Alzheimer's disease (AD) is the most commonly diagnosed dementia, where signs of neuroinflammation and oxidative stress are prominent. In this study we intend to further characterize the roles of the antioxidant, anti-inflammatory, and heavy metal binding protein, metallothionein-1 (MT-1), by crossing Mt1 overexpressing mice with a well-known mouse model of AD, Tg2576 mice, which express the human amyloid-β protein precursor (hAβPP) with the Swedish K670N/M671L mutations. Mt1 overexpression increased overall perinatal survival, but did not affect significantly hAβPP-induced mortality and weight loss in adult mice. Amyloid plaque burden in ∼14-month-old mice was increased by Mt1 overexpression in the hippocampus but not the cortex. Despite full length hAβPP levels and amyloid plaques being increased by Mt1 overexpression in the hippocampus of both sexes, oligomeric and monomeric forms of Aβ, which may contribute more to toxicity, were decreased in the hippocampus of females and increased in males. Several behavioral traits such as exploration, anxiety, and learning were altered in Tg2576 mice to various degrees depending on the age and the sex. Mt1 overexpression ameliorated the effects of hAβPP on exploration in young females, and potentiated those on anxiety in old males, and seemed to improve the rate of spatial learning (Morris water maze) and the learning elicited by a classical conditioning procedure (eye-blink test). These results clearly suggest that MT-1 may be involved in AD pathogenesis.

Behavioral impairments in animal models for zinc deficiency

Apart from teratogenic and pathological effects of zinc deficiency such as the occurrence of skin lesions, anorexia, growth retardation, depressed wound healing, altered immune function, impaired night vision, and alterations in taste and smell acuity, characteristic behavioral changes in animal models and human patients suffering from zinc deficiency have been observed. Given that it is estimated that about 17% of the worldwide population are at risk for zinc deficiency and that zinc deficiency is associated with a variety of brain disorders and disease states in humans, it is of major interest to investigate, how these behavioral changes will affect the individual and a putative course of a disease. Thus, here, we provide a state of the art overview about the behavioral phenotypes observed in various models of zinc deficiency, among them environmentally produced zinc deficient animals as well as animal models based on a genetic alteration of a particular zinc homeostasis gene. Finally, we compare the behavioral phenotypes to the human condition of mild to severe zinc deficiency and provide a model, how zinc deficiency that is associated with many neurodegenerative and neuropsychological disorders might modify the disease pathologies.

Metallothionein-II inhibits lipid peroxidation and improves functional recovery after transient brain ischemia and reperfusion in rats

After transient cerebral ischemia and reperfusion (I/R), damaging mechanisms, such as excitotoxicity and oxidative stress, lead to irreversible neurological deficits. The induction of metallothionein-II (MT-II) protein is an endogenous mechanism after I/R. Our aim was to evaluate the neuroprotective effect of MT-II after I/R in rats. Male Wistar rats were transiently occluded at the middle cerebral artery for 2 h, followed by reperfusion. Rats received either MT (10 μg per rat i.p.) or vehicle after ischemia. Lipid peroxidation (LP) was measured 22 h after reperfusion in frontal cortex and hippocampus; also, neurological deficit was evaluated after ischemia, using the Longa scoring scale. Infarction area was analyzed 72 hours after ischemia. Results showed increased LP in frontal cortex (30.7%) and hippocampus (26.4%), as compared to control group; this effect was fully reversed by MT treatment. Likewise, we also observed a diminished neurological deficit assessed by the Longa scale in those animals treated with MT compared to control group values. The MT-treated group showed a significant (P < 0.05) reduction of 39.9% in the infarction area, only at the level of hippocampus, as compared to control group. Results suggest that MT-II may be a novel neuroprotective treatment to prevent ischemia injury.

The molecular basis of memory

We propose a tripartite biochemical mechanism for memory. Three physiologic components are involved, namely, the neuron (individual and circuit), the surrounding neural extracellular matrix, and the various trace metals distributed within the matrix. The binding of a metal cation affects a corresponding nanostructure (shrinking, twisting, expansion) and dielectric sensibility of the chelating node (address) within the matrix lattice, sensed by the neuron. The neural extracellular matrix serves as an electro-elastic lattice, wherein neurons manipulate multiple trace metals (n > 10) to encode, store, and decode coginive information. The proposed mechanism explains brains low energy requirements and high rates of storage capacity described in multiples of Avogadro number (N(A) = 6 × 10(23)). Supportive evidence correlates memory loss to trace metal toxicity or deficiency, or breakdown in the delivery/transport of metals to the matrix, or its degradation. Inherited diseases revolving around dysfunctional trace metal metabolism and memory dysfunction, include Alzheimer's disease (Al, Zn, Fe), Wilson's disease (Cu), thalassemia (Fe), and autism (metallothionein). The tripartite mechanism points to the electro-elastic interactions of neurons with trace metals distributed within the neural extracellular matrix, as the molecular underpinning of "synaptic plasticity" affecting short-term memory, long-term memory, and forgetting.

Small molecule inhibitor of type I transforming growth factor-β receptor kinase ameliorates the inhibitory milieu in injured brain and promotes regeneration of nigrostriatal dopaminergic axons

Transforming growth factor-β (TGF-β), a multifunctional cytokine, plays a crucial role in wound healing in the damaged central nervous system. To examine effects of the TGF-β signaling inhibition on formation of scar tissue and axonal regeneration, the small molecule inhibitor of type I TGF-β receptor kinase LY-364947 was continuously infused in the lesion site of mouse brain after a unilateral transection of the nigrostriatal dopaminergic pathway. At 2 weeks after injury, the fibrotic scar comprising extracellular matrix molecules including fibronectin, type IV collagen, and chondroitin sulfate proteoglycans was formed in the lesion center, and reactive astrocytes were increased around the fibrotic scar. In the brain injured and infused with LY-364947, fibrotic scar formation was suppressed and decreased numbers of reactive astrocytes occupied the lesion site. Although leukocytes and serum IgG were observed within the fibrotic scar in the injured brain, they were almost absent in the injured and LY-364947-treated brain. At 2 weeks after injury, tyrosine hydroxylase (TH)-immunoreactive fibers barely extended beyond the fibrotic scar in the injured brain, but numerous TH-immunoreactive fibers regenerated over the lesion site in the LY-364947-treated brain. These results indicate that inhibition of TGF-β signaling suppresses formation of the fibrotic scar and creates a permissive environment for axonal regeneration.

Suppression of fibrotic scar formation promotes axonal regeneration without disturbing blood-brain barrier repair and withdrawal of leukocytes after traumatic brain injury

The fibrotic scar containing type IV collagen (Col IV) formed in a lesion site is considered as an obstacle to axonal regeneration, because intracerebral injection of 2,2'-dipyridyl (DPY), an inhibitor of Col IV triple-helix formation, suppresses fibrotic scar formation in the lesion site and promotes axonal regeneration. To determine the role of the fibrotic scar on the healing process of injured central nervous system (CNS), the restoration of blood-brain barrier (BBB) and withdrawal of inflammatory leukocytes were examined in mice subjected to unilateral transection of the nigrostriatal dopaminergic pathway and intracerebral DPY injection. At 5 days after injury, destruction of BBB represented by leakage of Evans blue (EB) and widespread infiltration of CD45-immunoreactive leukocytes was observed around the lesion site, whereas reactive astrocytes increased surrounding the BBB-destroyed area. By 2 weeks after injury, the region of EB leakage and the diffusion of leukocytes were restricted to the inside of the fibrotic scar, and reactive astrocytes gathered around the fibrotic scar. In the DPY-treated lesion site, formation of the fibrotic scar was suppressed (84% decrease in Col IV-deposited area), reactive astrocytes occupied the lesion center, and areas of both EB leakage and leukocyte infiltration decreased by 86%. DPY treatment increased the number of regenerated dopaminergic axons by 2.53-fold. These results indicate that suppression of fibrotic scar formation does not disturb the healing process in damaged CNS, and suggest that this strategy is a reliable tool to promote axonal regeneration after traumatic injury in the CNS.

Enhanced toxicity and ROS generation by doxorubicin in primary cultures of cardiomyocytes from neonatal metallothionein-I/II null mice

The clinical use of doxorubicin (Dox), a potent anticancer drug, is limited by its concurrent dose-dependent cardiotoxicity. We previously found that metallothionein-I/II (MT-I/II) null mice are more vulnerable to Dox-induced cardiomyopathy, but it is unknown whether depletion of MT would sensitize cardiomyocytes to Dox toxicity in vitro since the protective effect of MT still remains controversial. In the present study, a primary culture system of cardiomyocytes from neonatal MT-I/II null (MT(-/-)) and corresponding wild type (MT(+/+)) mice was established to unequivocally determine the effect of MT deficiency on Dox-induced toxicity. MT concentrations in the MT(-/-) cardiomyocytes were about 2.5-fold lower than those in MT(+/+) cardiomyocytes. MT(-/-) cardiomyocytes were more sensitive to Dox-induced cytotoxicity than MT(+/+) cardiomyocytes as measured by morphological alterations, lactate dehydrogenase leakage, cell viability, and apoptosis. Dox time- and concentration-dependently increased reactive oxygen species (ROS) formation in MT(+/+) cardiomyocytes, and this effect was exaggerated in MT(-/-) cardiomyocytes. Antioxidant N-acetylcysteine (NAC) and glutathione (GSH) significantly rescued MT(+/+) but not MT(-/-)cardiomyocytes from Dox-induced cell death and ROS generation. These findings suggest that basal MT provide protection against Dox-induced toxicity in cardiomyocytes, particularly highlight the important role of MT as a cellular antioxidant on scavenging ROS.

Metallothionein enhances angiogenesis and arteriogenesis by modulating smooth muscle cell and macrophage function

OBJECTIVE

In a previous study we identified metallothionein (MT) as a candidate gene potentially influencing collaterogenesis. In this investigation, we determined the effect of MT on collaterogenesis and examined the mechanisms contributing to the effects we found.

METHODS AND RESULTS

Collateral blood flow recovery was assessed using laser Doppler perfusion imaging, and angiogenesis was measured using a Matrigel plug assay. Smooth muscle cells were isolated from MT knockout (KO) mice for functional assays. Gene expression of matrix metalloproteinase-9, platelet-derived growth factor, vascular endothelial growth factor, and Fat cadherin in smooth muscle cells was measured by real-time polymerase chain reaction, and protein levels of vascular endothelial growth factor and matrix metalloproteinase-9 were determined using enzyme-linked immunosorbent assay and Western blot. CD11b(+) macrophages were tested for invasiveness using a real-time impedance assay. Both flow recovery and angiogenesis were impaired in MT KO mice. Proliferation, migration, and invasion were decreased in MT KO smooth muscle cells, and matrix metalloproteinase-9, platelet-derived growth factor, and vascular endothelial growth factor expression were also decreased, whereas FAT-1 cadherin expression was elevated. MT KO CD11b(+) cells were more invasive than wild-type cells.

CONCLUSIONS

MT plays an important role in collateral flow recovery and angiogenesis, an activity that appears to be mediated, in part, by the effects of MT on the functionality of 3 cell types essential for these processes: endothelial cells, smooth muscle cells, and macrophages.

Metallothionein Toxicology: Metal Ion Trafficking and Cellular Protection

The literature is replete with reports about the involvement of metallothionein in host defense against injurious chemical, biological, and physical agents. Yet, metallothionein's functional roles are still being debated. This review addresses the issues that have left the physiological significance of metallothionein in doubt and moves on to assess the MT's importance in cell toxicology. It is evident that the protein is broadly involved in protecting cells from injury due to toxic metal ions, oxidants, and electrophiles. Attention is focused on MT's structural and chemical properties that confer this widespread role in cell protection. Particular emphasis is placed on the implications of finding that metal ion unsaturated metallothionein is commonly present in many cells and tissues and the question, how does selectivity of reaction with metallothionein take place in the cellular environment that includes large numbers of competing metal binding sites and high concentrations of protein and glutathione sulfhydryl groups?