The Molecular Physiology of the Synapse Laboratory was established in May 2012 at the Biomedical Research Institute Sant Pau in Barcelona.

We are focused in understanding the organization and dynamics of the proteome from synapses of the forebrain, particularly excitatory synapses from the cortex and hippocampus. We want to unravel how synaptic proteome physiology orchestrates synaptic plasticity, ultimately contributing to cognition and behaviour.

Furthermore, we pursue to understand how disruption of normal molecular synaptic physiology can contribute to certain disorders, particularly cognitive disorders such as Intellectual Disability or Autism.

As we are interested in understanding the functioning of the synaptic proteome as a whole we take advantage of a Systems Biology experimental approach, involving mainly mass spectrometry-based proteomics and bioinformatics.

The laboratory research focus can be divided in four secions:

Molecular Organisation and Dynamics of the Synaptic Proteome and its Role in Synaptic Function.

Proteomics profiling of excitatory synapses by mass spectrometry has exposed few thousands of proteins with a potential role in synaptic function. For reviews on this topic please check: Bayes & Grant (Nat. Rev. Neurosci. 2009) and O’Rourke et al. (Nat. Rev. Neurosci. 2012).Considering that, with our current understanding of the synaptic proteome, it is unlikely that all excitatory synapses in the brain will have identical proteomes, several very interesting questions arise from these proteomcis studies:

1. How is the function of these hundreds of molecules coordinated?
2. Are there different types of excitatory synapses based on their proteome? If so, what is their different function?
3. Contrarily, if synaptic proteome composition is a continuum, and therefore all synaptic proteins can reside in any synapse, what laws govern synaptic composition in different physiological conditions?.
4. How does the synaptic proteome vary between brain regions or neurons, throughout development or aging,
5. What is the interplay between synaptic molecular organisation and synaptic electrophysiology?

We are interested in contributing to answer these questions particularly those that tackle proteome dynamics in relation to brain development and synaptic plasticity.

Synaptic Molecular Pathology in Cognitive Disorders

There is a growing body of data suggesting a central role of the synapse in neurodegenerative and psychiatric disorders. The existence of synaptic diseases or “synaptopathies” is increasingly accepted amongst the neuroscience community. Dysfunction in neural communication has been proposed to be involved in disorders as common as intellectual disabilities, Schizophrenia, Parkinson’s disease, Autism or Alzheimer’s disease. Moreover, the ever-increasing number of large-scale genetic studies (i e. comparative genomic hybridization, SNP arrays, exon re-sequencing, etc.) on psychiatric and neurologic disorders is revealing more and more synaptic genes with a previously unknown role in disease.Our own studies on the human PSD have revealed that this neuronal structure is remarkably populated with proteins causing nervous system disease, being particularly relevant to intellectual disabilities (ID) and schizophrenia. It is therefore important to investigate how dysfunctions of the molecular machine that is the PSD contribute to these diseases.Among all these disorders we are especially interested in non-syndromic intellectual disability (NSID) for several reasons. Firstly, ID prevalence in developed countries can be as high as 3%, being the most costly of all diagnoses listed in the International classification of disease (ICD-10) from the World Health Organisation (WHO). Most ID patients have non-syndromic forms, which are characterised by the absence of associated morphologic, radiology or metabolic features. Furthermore, recent studies show that mutations related to glutamatergic function can account for 10-20% of all cases of NSID. Our own data indicates that 25% of the genes related to NSID are found in the PSD (including: SYNGAP1, SHANK2, GRIK2, GRIN1, DLG3, SHANK3, ARHGEF6, CACNG2 or GDI1), pointing in the direction of a preeminent role of the synapse in NSID. Finally, while there are well established pharmacological tools to treat psychiatric diseases such as schizophrenia or mood disorders, very little has been achieved on the therapeutics of intellectual disabilities, which essentially remain untreatable.We believe that understanding the molecular pathology behind NSID will not only help us understand these disorders at the molecular level, but also might result in the identification of proteins or molecular pathways that might become new pharmacological targets to treat these disorders.

Development of Biochemical Methods to Study the Synaptic Proteome at the Microscopic Scale

 In order to advance in the goals outlined in the previous sections we think it is mandatory to be able to adapt current biochemical methods to the smallest scale possible. Ideally we would like to study the synaptic proteome at the microscopic scale, where synaptic activity takes place.Current methodological approaches require the use of relatively large portions of tissue, which in practice means analysing synapses at many different activity states as if they were equivalent. As mentioned previously, our current understanding of the synaptic proteome suggest that this is a dynamic entity, which likely will vary according to synaptic activity. Therefore, the effective synaptic proteome obtained, and this is true for all the proteomics studies performed so far, is an average of all the individual synaptic proteomes found in that tissue. In that process the precious information from the molecular organisation of the synapses at each of these different activity states is essentially lost.Our present approach to tackle this challenge is to take advantage of laser capture microdissection (LCM) technologies. Although LCM can be applied to both histological sections and cell cultures, we are working towards developing methods that use tissue sections, so that we work in conditions that resemble the alive brain as much as possible. LCM allows dissecting fragments of tissue of a few microns of diameter. In our opinion adapting biochemical methods to fractionate the synaptic proteome to the tissue obtained by LCM, and coupling this to mass spectrometry-based proteomics might set the bases to understand the synaptic proteome at an unprecedented resolution.

Evolution of the synaptic proteome at the root of vertebrates

Working with Professor Seth Grant, at Edinburgh University, we have developed an interest on the study of the evolution of the synaptic proteome. This is a research field that has been pioneered by Prof Grant in the past few years.Having established that the synaptic proteome has been highly conserved during mammalian and, most certainly, vertebrate evolution, we thought to investigate its origins at the root of all vertebrates.To achieve this goal we have started a research line on the synaptic proteome of a key organism to investigate the origins of vertebrate evolution: Amphioxus (Branchiostoma spp.). Actually, we are working with the species B. lanceolatum. Amphioxus belong to the same phylum of all vertebrates, the phylum chordate, and present a notochord, a fairly stiff rod of cartilage that extends along the inside of the body, which in vertebrates develops into the spine. Amphioxus are the closest living animals to the common ancestor of all vertebrate species.In the past we have focused our evolutionary work on the postsynaptic density, a large supramolecular protein complex located beneath the postsynaptic membrane of glutamatergic synapses. This structure, which is found in the brain of all vertebrate species including modern fish, can be readily identified by electron microscopy.We have started this research line by investigating if the postsynaptic density does actually exist in amphioxus. This is being analysed by transmission electron microscopy in the nervous cord of post-metamorphic juvenile and adult animals. If this structure exists we will then investigate its proteomic composition with the goal to compare it what we have already seen in vertebrate species.