Toward an understanding of the brain interstitial system and the extracellular proteome in health and autism spectrum disorders

Projektinformationen

SecretAutism

ID Finanzhilfevereinbarung: 101044865

DOI

10.3030/101044865

EK-Unterschriftsdatum 7 November 2022

Startdatum 1 Dezember 2022

Enddatum 30 November 2027

Finanziert unter

• European Research Council (ERC)

Gesamtkosten

€ 1 997 729,00

EU-Beitrag

€ 1 997 729,00

Koordiniert durch

INSTITUTE OF SCIENCE AND TECHNOLOGY AUSTRIA
Austria

Periodic Reporting for period 1 - SecretAutism (Toward an understanding of the brain interstitial system and the extracellular proteome in health and autism spectrum disorders)

Berichtszeitraum: 2022-12-01 bis 2025-05-31

Zusammenfassung vom Kontext und den Gesamtzielen des Projekts

Since the ancient Egyptians, the fluid in the brain has been considered a product of spirits, a pathological signature or inert liquid. Even at the turn of the 19th century, when the cerebrospinal fluid (CSF) was first described as a physiological substance, the CSF and the
interstitial fluid (ISF), the fluid surrounding all the cells of the brain, were considered solely as a cushion. Only more recently studies have begun to show that the compositions of these fluids can have a marked impact on brain development and animal behaviour. A number
of studies have employed omics to demonstrate that the ISF and the CSF are rich in secreted proteins, RNAs and metabolites. However, it is still unclear how these factors influence the development and the function of the brain. Here, we will take a systematic approach to
advance our knowledge about the role of extracellular proteins in the brain in health and disease. Using knowhow in studying the causes of autism spectrum disorders (ASDs) my lab will study the effects of changes in the composition of the extracellular space of the brain
at unprecedented resolution and scale. Specifically, we aim to 1) functionally identify proteins of the extracellular space that modulate neural development; 2) study proteins that are packaged into extracellular vesicles and whose mutations are considered high ASD-risk
factors; 3) analyse -in vivo- the function of HNRNP U, an RNA-binding protein, which we identified in brain extracellular vesicles and whose mutations are tightly linked to neurodevelopmental disorders.

Arbeit, die ab Beginn des Projekts bis zum Ende des durch den Bericht erfassten Berichtszeitraums geleistet wurde, und die wichtigsten bis dahin erzielten Ergebnisse

Little is known about how the intricate extracellular system of the brain regulates and modulates the development and function of neuronal circuitries. Accordingly, through an in-depth literature search on the extracellular role(s) of specific proteins detected in the fluids surrounding brain cells, we found that in the majority of the cases such functions are unknown. These extracellular factors can have a tremendous impact not only on understanding aspects of the healthy brain but also on understanding disorders like ASD. Our study
will contribute to the field of neurosciences in several ways: i) we will identify extracellular and extrinsic components that can affect neuronal network development and function. This research will advance our understanding on how the interstitial system contributes to brain development; ii) our proposal is a step toward unifying and extending efforts that have used -omics to identify extracellular proteins and ASD-risk genes. While several studies analysed the proteomic composition of the fluids surrounding the brain, little is known
about the function of the identified proteins in the extracellular space. Similarly, while several DNA sequencing studies have identified ASD-risk genes, their functional analysis is moving much slower; iii) with this project, we will generate an extensive and systematically-obtained dataset linking the extracellular expression of specific proteins to transcriptomic profiles of neural stem cells and cortical neurons at single cell resolution. This data will represent an important resource by itself; iv) by studying a defined group of ASDrisk genes, we will further our understanding of how their mutation affects the human brain. ASDs affect about 1% of the population. Although in some cases the genetic basis is known, in the majority of the cases we still have only little grasp on how different factors affect brain development in ASDs. This alone represents an important contribution to the neuroscience and medical community; v) our study could potentially lead to the identification of an entire class of treatable ASDs. The CSF and ISF are readily accessible compartments of the brain. Thus, secreted proteins represent promising pharmacological targets and potential paths to modify the course of disorders.

Fortschritte, die über den aktuellen Stand der Technik hinausgehen und voraussichtliche potenzielle Auswirkungen (einschließlich der bis dato erzielten sozioökonomischen Auswirkungen und weiter gefassten gesellschaftlichen Auswirkungen des Projekts)

The extracellular space of the brain parenchyma is filled by the interstitial fluid (ISF) and the extracellular matrix (EM), together constituting the brain interstitial system (ISS). As a whole, the ISS comprises 15-20% of the brain volume and it constitutes the brain microenvironment, offering accommodation to neuronal and glial cells. The ISS is filled with ions, metabolites, peptides, proteins and vesicles. A fraction of the extracellular molecules filling the ISS are locally produced and secreted, while another part has a different
origin and moves into the ISS either from the CSF or from the blood. All the properties of the ISS can also change in response to environmental perturbations (e.g. traumas, infections or even systemic pharmacological treatments), a feature that makes this compartment a very interesting part of the brain. In a nutshell, the ISS is a highly dynamic and complex space connecting the vascular system and neural networks and contacting every brain-resident cell. Interacting with virtually every brain cell, as well as constituting such a large portion of brain tissue, the ISS must play a fundamental role in brain development, information processing and response to changes in the external environment. The importance of extracellular factors is exemplified by the central role of neuropeptides in regulating e.g. circadian rhythm, social and feeding behavior1, or by the role of CSFborne IGF signalling, involved in the regulation of neural stem cell proliferation2 or by the role of Reelin secretion in neuronal migration. In the past years, our group has shown that altering the transport of branched chain amino acids across the blood brain barrier into the ISS results in abnormal dynamics of mRNA translation, reduced neurotransmission and autistic features and motor deficits in mice and humans. This study triggered our attention and our motivation to understand how the composition of extracellular spaces in the brain affects its development and function.