Investigating the role of astrocytes in regulating brain metabolism

Secondary Supervisor(s): Dr Daniel Fulton

University of Registration: University of Birmingham

BBSRC Research Themes: Understanding the Rules of Life (Neuroscience and Behaviour)

Project Outline

The human brain is always active. The brain consumes 20% of total body energy available, but makes up just 2% of total body weight. A large portion of this energy demand is dedicated to neural signalling processes and the maintenance of ionic gradients which are essential for cell to cell communication. The supply of energy is crucial for brain activity. The high energy demands of the brain makes it particularly susceptible to the dysregulation of bioenergetic processes, redox imbalance, and reduced blood flow or nutrient supply. Astrocytes are the most common cell type in the human brain, and are thought to be capable of supporting and regulating neuronal functions. Astrocytes can take up neurotransmitters, supply neurons with metabolites and respond to inflammatory processes. Astrocytes are also unique in that, they favour aerobic glycolysis and can store glycogen. This is important to enable neuronal function to be sustained under conditions of stress. Dysfunction of astrocytes and alteration in astrocyte metabolism has been implicated in cognitive decline and in neurodegenerative diseases, yet we still do not fully understand their role in supporting neuronal function in the healthy brain. To fully understand how the human brain develops and subsequently functions, it has been critical to create model systems that enable reliable, functionally relevant, and controllable experimentation. Induced pluripotent stem cell (iPSC)-derived models of the brain allow us to achieve this. In previous research, we have created neuron-astrocyte mixed culture models from patient iPSC to investigate how astrocyte metabolism supports neuronal functions. Therefore, these iPSC-derived CNS models offer a tractable system in which to investigate the involvement of neuronal-glial interactions in human brain functions.

Objectives

To use iPSC-derived CNS models to investigate the metabolic interaction between Astrocytes and Neurons to sustain synaptic activity.

1. Characterise substrate utilisation capacity in astrocytes for energy production.

2. Investigate whether neuronal activity can stimulate alterations in astrocyte substrate utilisation and metabolic function.

3. Interrogate signalling cascades that regulate the link between synaptic activity and alterations in astrocyte-neuron metabolic coupling.

Methods

Through the use of iPSC reprogramming, neuronal and astrocytic cells will be created. Cell lineage will be confirmed by qPCR and immunocytochemical staining for typical markers at neural stem cells, neurons and astrocytes. For objective 1, astrocytes will be examined under modified culture conditions (hypoxia, hypoglycaemia, lipid stress) for metabolic flexibility using extracellular flux (seahorse XF) and metabolite analysis. This will provide a deep understanding of how human astrocytes function and respond to ‘environmental’ stimulus. Objective 2 will use microelectrode array (MEA) electrophysiology to understand how electrical activity is impacted by neuronal-astrocyte interactions. To achieve this, we will compare levels of neuronal activity between co-cultures of neurons and astrocytes with neuronal monocultures. To understand the signalling pathways governing astrocyte-neuronal metabolic coupling in objective 3, specific signalling pathways will be stimulated or blocked that link cellular energy sensing to the uptake of metabolites used to generate ATP, for example AMPK, PI3K, insulin receptors and glucose uptake transporters.

Key references

Bonvento, G. and Bolaños, J.P., 2021. Astrocyte-neuron metabolic cooperation shapes brain activity. Cell metabolism, 33(8), pp.1546-1564.

Elsworthy et al., 2021. Amyloid-β precursor protein processing and oxidative stress are altered in human iPSC-derived neuron and astrocyte co-cultures carrying presenillin-1 gene mutations following spontaneous differentiation. Molecular and Cellular Neuroscience, 114, p.103631.