Russian-Israeli mini-symposium on Molecular Neurobiology

Extensive research in the past two decades has focused on amyloid plaques in Alzheimer’s disease (AD) patients, suggesting that their removal will stop/slow the disease process. These studies neglect to address the possible involvement of calcium handling machineries in the initial stages of functional and structural deterioration of neurons, associated with AD. A role of presenilin, one of the proteins that are mutated in familial AD, in store operated calcium (SOC) entry channel has emerged recently. We will provide evidence for the role of ryanodine receptors associated with calcium stores in plasticity, studied in hippocampal slices of 3XTg mice model of AD. The interaction between presenilin and synaptopodin, a store-related protein residing in dendritic spines was also examined in the 3xTg mice. We have examined the role of presenilin in regulation of ryanodine receptors in both dendrites and spines of cultured hippocampal neurons, using electrophysiological and imaging methodologies. These studies are expected to contribute to the understanding the role of calcium stores in the initial phases of neuronal dysfunctions associated with AD.

Trace amines are endogenous compounds classically regarded as composing beta-phenylethyalmine, p-tyramine, tryptamine, p-octopamine, and some of their metabolites. They are also abundant in common foodstuffs, and can be produced and degraded by the constitutive microbiota. The ability to utilize trace amines has arisen at least twice, with unrelated receptor families present in invertebrates and vertebrates. The term trace amine was coined to reflect the low tissue levels in mammals, however, in invertebrates relatively high levels are present where they serve the role of an invertebrate adrenergic system involved in “fight or flight” responses. Vertebrates express a family of receptors termed trace amine-associated receptors (TAAR). Humans possess 6 functional receptors: TAAR1, TAAR2, TAAR5, TAAR6, TAAR8 and TAAR9. With the exception of TAAR1, TAAR are expressed in olfactory epithelium neurones, where they detect diverse ethological signals including predators, spoiled food, migratory cues, and pheromones. Outside the olfactory system TAAR1 is the most thoroughly studied with both central and peripheral roles. In the brain TAAR1 has been identified as a novel therapeutic target for several neuropsychiatric disorders, including schizophrenia, depression, and addiction. In the periphery TAAR1 shows potential as a novel therapeutic target for diabetes and obesity, and may also regulate immune functions. Recent advances in understanding physiological relevance and pharmacological potential of human TAARs will be discussed. Through this, a picture emerges of an exciting field on the cusp of significant developments, with the potential to identify new therapeutic leads for some of the major unmet medical needs in several areas including neuropsychiatry and metabolic disorders.

It is well established that neurons are plastic and can change the strength of their connections with other neurons depending on their recent history. While many molecular entities involved in plastic processes were already described, the role of a store-operated calcium channel ORAI1 in neuronal plasticity is not known. The store depletion resulted in an increase in stromal interacting molecule 2 (an endoplasmic calcium sensor) association with Orai1 in dendritic spines. The response to the rise in calcium was larger in spines endowed with a cluster of Orai1 molecules than in spines devoid of Orai1. Transfection of neurons with a dominant negative Orai1 resulted in retarded maturation of dendritic spines, a reduction in synaptic connectivity with afferent neurons and a reduction in the ability to undergo morphological changes following induction of chemical long-term potentiation. Similarly, small interfering RNA (siRNA)-treated neurons had fewer mature dendritic spines, and lower rates of mEPSCs compared to scrambled control siRNA-treated neurons. Using dominant negative form of ORAI1, we were able to show that ORAI1 is also needed for formation of new spines following chemical induction of long term potentiation (cLTP), and that this is due to the release of calcium from ryanodine receptor-associated endoplasmic reticulum stores. We propose that when ORAI1 is deficient, there is less calcium in the stores, less releasable calcium and consequently less cLTP and spine formation. Thus, influx of calcium through Orai1 channels facilitates the maturation of dendritic spines and the formation of functional synapses.

To understand a role of a particular molecule, enzyme, cell, or organ it is essential to be able to monitor their amounts or activities in the living systems. But even more important is an ability to modulate them in order to understand how certain molecules and activities affect function. Synthetic biology offers a wide variety of molecular tools allowing precise control over biological processes and functions. Examples are optogenetics and genome editing, both based on trans-kingdom transfer of molecular machines with specific functions normally absent in the target cell or organism. In my talk I will describe our recent advances in two synthetic biology directions. One is thermogenetics where the activity of cells and tissues can be controlled using heat-sensitive ion channels. Another one is metabolic engineering where prokaryotic or fungal enzymes with some unusual activities are introduced into the mammalian cells to modulate key metabolic processes.

Store-operated calcium entry is a critical component of calcium signaling. Store-operated calcium entry through Orai and TRPC channels occurs downstream of Stim calcium sensors activation during intracellular calcium store depletion through IP 3 R. Here we demonstrated that calcium entry is not predefined and strongly depends on interplay between endogenous proteins such as Stim1, Stim2, IP3R, Orai and TRPC.
Our recordings in cell-attached mode have shown that HEK293 or A431 cells contain three types of endogenous store-sensitive calcium channels differing in protein composition, conductance, and selectivity to divalent ions, open time, and number per cell. Furthermore we demonstrated that these channels have different intracellular partners and different regulation modes. We demonstrated that STIM1, STIM2 and IP 3 R differ in the ability to activate these store-operated channels in the following patterns: Orai-dependent channels are regulated by STIM2 or by IP 3 R; TRPC3-containing channels are induced by STIM1; and TRPC1-composed channels are activated by either STIM1, STIM2, or IP 3 R. In our whole-cell experiments with HEK 293 cells, SK-N-SH cells and mouse neurons we observed that STIM2 knockdown changed current-voltage relationship shape resulting in CRAC-like shape.
We suggest that properties of local calcium entry strongly depend on conformational coupling of store-operated calcium entry components and results in wide diversity of cell calcium responses to physiological stimuli.

Recruitment of non-venom genes into venom systems is a known mechanism of venom evolution. While for enzymatic toxins the source of recruitment is clear, the source of neurotoxins in many cases is more obscure. Here we present a striking case of toxin recruitment in the model sea anemone Nematostella vectensis.
Nematostella, similarly to other cnidarians, is venomous and equipped with nematocytes. Significant portion of the Nematostella venom consists of ShK-like toxins loaded into the nematocytes. Recently we found two homologous sequences possessing all typical toxin features: a signal peptide and a propeptide followed by a dibasic processing site and a cysteine-rich mature peptide. These peptides resemble the archetypic ShK toxin from Stichodactyla helianthus and therefore we named them as NveShk-like1 (ShK-l1) and NveShk-like2 (ShK-l2). Both recombinant ShK-l1 and ShK-l2 showed toxic activity on zebrafish larvae, even though ShK-l1 was more potent. However, in situ hybridization experiments resulted into a surprise: only ShK-l1 was localized to nematocytes, whereas ShK-l2 was expressed in various types of neurons. Thus, ShK-l1 is a toxin making part of the venom system while ShK-like2 is a neuropeptide. Since ShK-l2 is a secreted peptide expressed in neurons it may be a new kind of a neurotransmitter. Interestingly, its expression is regulated by two alternative transcription start sites and this feature is conserved in many sea anemones.
Importantly, we present the first example of clear homology between a toxin and a neuropeptide. It is likely that ShK-l1 and ShK-l2 evolved through gene duplication followed by neofunctionalization. As ShK-l2 is highly conserved among sea anemones, whereas ShK-l1 is not, probably the last common ancestor of sea anemones possessed an ShK-l2 paralog and Shk-l1 originated from a gene duplication specific to the lineage of Nematostella.