The use of ion-sensitive electrodes and fluorescence imaging in hippocampal slices for studying pathological changes of intracellular Ca2+ regulation

New Perspectives for Developing Therapeutic Bioconjugates of Metabolite-Depleting Enzymes: Lessons Learned Combating Glutamate Excitotoxicity

Glutamate, the main excitatory neurotransmitter in the central nervous system, plays an essential role in several cognitive activities such as memorizing and learning. Excessive glutamate release and disturbance of glutamate homeostasis participates in multiple neuronal pathologies including cerebral ischemia (inadequate blood supply), traumatic brain injury (e.g., from a fall or an accident), multiple sclerosis, epilepsy, migraine, fetal hypoxia, or Alzheimer's disease. Attenuating excitotoxicity by, for example, targeting glutamate receptors has proved to be beneficial in animal models but has largely failed in clinical trials because of toxic side effects. New therapeutic concepts have been explored to reduce the excitotoxic effect caused by the excessive glutamate release by using or stimulating glutamate-depleting enzymes in the bloodstream. These enzymes indirectly act upon the brain by depleting glutamate in the bloodstream, which is believed to siphon it out of the brain. Recent studies have shown that bioconjugate approaches applied to such enzymes exacerbate this therapeutic effect but raise additional questions for future research. This Perspective provides an overview of lessons learned by our group when exploring bioconjugate approaches for combatting glutamate excitotoxicity as an illustration of how research on therapeutic bioconjugates is evolving.

Animal Toxins as Therapeutic Tools to Treat Neurodegenerative Diseases

Neurodegenerative diseases affect millions of individuals worldwide. So far, no disease-modifying drug is available to treat patients, making the search for effective drugs an urgent need. Neurodegeneration is triggered by the activation of several cellular processes, including oxidative stress, mitochondrial impairment, neuroinflammation, aging, aggregate formation, glutamatergic excitotoxicity, and apoptosis. Therefore, many research groups aim to identify drugs that may inhibit one or more of these events leading to neuronal cell death. Venoms are fruitful natural sources of new molecules, which have been relentlessly enhanced by evolution through natural selection. Several studies indicate that venom components can exhibit selectivity and affinity for a wide variety of targets in mammalian systems. For instance, an expressive number of natural peptides identified in venoms from animals, such as snakes, scorpions, bees, and spiders, were shown to lessen inflammation, regulate glutamate release, modify neurotransmitter levels, block ion channel activation, decrease the number of protein aggregates, and increase the levels of neuroprotective factors. Thus, these venom components hold potential as therapeutic tools to slow or even halt neurodegeneration. However, there are many technological issues to overcome, as venom peptides are hard to obtain and characterize and the amount obtained from natural sources is insufficient to perform all the necessary experiments and tests. Fortunately, technological improvements regarding heterologous protein expression, as well as peptide chemical synthesis will help to provide enough quantities and allow chemical and pharmacological enhancements of these natural occurring compounds. Thus, the main focus of this review is to highlight the most promising studies evaluating animal toxins as therapeutic tools to treat a wide variety of neurodegenerative conditions, including Alzheimer's disease, Parkinson's disease, brain ischemia, glaucoma, amyotrophic lateral sclerosis, and multiple sclerosis.

Selective regulation of NR2B by protein phosphatase-1 for the control of the NMDA receptor in neuroprotection

An imbalance between pro-survival and pro-death pathways in brain cells can lead to neuronal cell death and neurodegeneration. While such imbalance is known to be associated with alterations in glutamatergic and Ca²⁺ signaling, the underlying mechanisms remain undefined. We identified the protein Ser/Thr phosphatase protein phosphatase-1 (PP1), an enzyme associated with glutamate receptors, as a key trigger of survival pathways that can prevent neuronal death and neurodegeneration in the adult hippocampus. We show that PP1α overexpression in hippocampal neurons limits NMDA receptor overactivation and Ca²⁺ overload during an excitotoxic event, while PP1 inhibition favors Ca²⁺ overload and cell death. The protective effect of PP1 is associated with a selective dephosphorylation on a residue phosphorylated by CaMKIIα on the NMDA receptor subunit NR2B, which promotes pro-survival pathways and associated transcriptional programs. These results reveal a novel contributor to the mechanisms of neuroprotection and underscore the importance of PP1-dependent dephosphorylation in these mechanisms. They provide a new target for the development of potential therapeutic treatment of neurodegeneration.

Brain slices as models for neurodegenerative disease and screening platforms to identify novel therapeutics

Recent improvements in brain slice technology have made this biological preparation increasingly useful for examining pathophysiology of brain diseases in a tissue context. Brain slices maintain many aspects of in vivo biology, including functional local synaptic circuitry with preserved brain architecture, while allowing good experimental access and precise control of the extracellular environment, making them ideal platforms for dissection of molecular pathways underlying neuronal dysfunction. Importantly, these ex vivo systems permit direct treatment with pharmacological agents modulating these responses and thus provide surrogate therapeutic screening systems without recourse to whole animal studies. Virus or particle mediated transgenic expression can also be accomplished relatively easily to study the function of novel genes in a normal or injured brain tissue context.In this review we will discuss acute brain injury models in organotypic hippocampal and co-culture systems and the effects of pharmacological modulation on neurodegeneration. The review will also cover the evidence of developmental plasticity in these ex vivo models, demonstrating emergence of injury-stimulated neuronal progenitor cells, and neurite sprouting and axonal regeneration following pathway lesioning. Neuro-and axo-genesis are emerging as significant factors contributing to brain repair following many acute and chronic neurodegenerative disorders. Therefore brain slice models may provide a critical contextual experimental system to explore regenerative mechanisms in vitro.