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The extracellular aggregation of insoluble protein deposits of amyloid-β (Aβ) into plaques and the hyperphosphorylation of the intracellular protein tau leading to neurofibrillary tangles are the main pathological hallmarks of Alzheimer' s disease (AD). Both Aβ and tau are metal-binding proteins. Essential trace metals such as zinc, copper, and iron play important roles in healthy brain function but altered homeostasis and distribution have been linked to neurodegenerative diseases and aging. In addition, the presence of non-essential trace metals such as aluminum has been associated with AD. Trace metals and abnormal metal metabolism can influence protein aggregation, synaptic signaling pathways, mitochondrial function, oxidative stress levels, and inflammation, ultimately resulting in synapse dysfunction and neuronal loss in the AD brain. Herein we provide an overview of metals and metal-binding proteins and their pathophysiological role in AD.

In the last years, research has shown that zinc ions play an essential role in the physiology of brain function. Zinc acts as a potent neuromodulatory agent and signaling ions, regulating healthy brain development and the function of both neurons and glial cells. Therefore, the concentration of zinc within the brain and its cells is tightly controlled. Zinc transporters are key regulators of (extra-) cellular zinc levels, and deregulation of zinc homeostasis and zinc transporters has been associated with neurodegenerative and neuropsychiatric disorders. However, to date, the presence of specific family members and their subcellular localization within brain cells have not been investigated in detail. Here, we analyzed the expression of all zinc transporters (ZnTs) and Irt-like proteins (ZIPs) in the rat brain. We further used primary rat neurons and rat astrocyte cell lines to differentiate between the expression found in neurons or astrocytes or both. We identified ZIP4 expressed in astrocytes but significantly more so in neurons, a finding that has not been reported previously. In neurons, ZIP4 is localized to synapses and found in a complex with major postsynaptic scaffold proteins of excitatory synapses. Synaptic ZIP4 reacts to short-term fluctuations in local zinc levels. We conclude that ZIP4 may have a so-far undescribed functional role at excitatory postsynapses.

Autism Spectrum Disorders (ASD) are caused by a combination of genetic predisposition and nongenetic factors. Among the nongenetic factors, maternal immune system activation and zinc deficiency have been proposed. Intriguingly, as a genetic factor, copy-number variations in S100B, a pro-inflammatory damage-associated molecular pattern (DAMP), have been associated with ASD, and increased serum S100B has been found in ASD. Interestingly, it has been shown that increased S100B levels affect zinc homeostasis in vitro. Thus, here, we investigated the influence of increased S100B levels in vitro and in vivo during pregnancy in mice regarding zinc availability, the zinc-sensitive SHANK protein networks associated with ASD, and behavioral outcomes. We observed that S100B affects the synaptic SHANK2 and SHANK3 levels in a zinc-dependent manner, especially early in neuronal development. Animals exposed to high S100B levels in utero similarly show reduced levels of free zinc and SHANK2 in the brain. On the behavioral level, these mice display hyperactivity, increased stereotypic and abnormal social behaviors, and cognitive impairment. Pro-inflammatory factors and zinc-signaling alterations converge on the synaptic level revealing a common pathomechanism that may mechanistically explain a large share of ASD cases.

The diagnostic criteria and treatment approaches of autism spectrum disorders (ASD) have changed greatly over the years. Currently, diagnosis is conducted mainly by observational screening tools that measure a child' s social and cognitive abilities. The two main tools used in the diagnosis of ASD are DSM-5 and M-CHAT, which examine persistent deficits in interaction and social communication, and analyze responses to "yes/no" items that cover different developmental domains to formulate a diagnosis. Treatment depends on severity and comorbidities, which can include behavioral training, pharmacological use, and dietary supplement. Behavior-oriented treatments include a series of programs that aim to re-condition target behaviors, and develop vocational, social, cognitive, and living skills. However, to date, no single or combination treatments have been able to reverse ASD completely. This chapter provides an overview of the current diagnostic and treatment strategies of ASD.