How heterogeneous are oligodendroglia from normal human brain and spinal cord?

The intricacies of the human brain are probably what define us as human, and the oligodendrocytes of the brain are vital in maintaining this. These cells extend processes of their cell membrane to wrap insulating myelin sheaths around nerve fibres, allowing electrical impulses to travel quickly along nerves, and they also nourish the underlying nerve, helping it to survive healthily. This process of myelination happens mostly after birth in humans, and allows the normal development of a baby into an adult. However, it can be disrupted around birth, due to gene defects or premature birth, in adulthood in diseases such as multiple sclerosis and in old age, either in normal ageing, or in other neurodegenerative diseases.

We used to consider all oligodendrocytes as very similar, but we now know that they are likely to exist as different subtypes, perhaps depending on where they came from in development, where they exist in the brain and spinal cord, and depending on the age and sex of the human. They may also change their type in disease. We call this heterogeneity, and the best way to determine how different cells are is to consider them individually. We are now able to examine the RNA messages (which define how a cell behaves) in individual cells, comparing them with other individual cells, and finding out how similar and how different these are using computer programs, allowing thousands of comparisons in an objective way. We can then try and confirm the computer's predictions using techniques to label single RNA molecules, identifying which cells they are in and where they are in brain tissue using antibodies.

In this project, we will extract oligodendrocytes from human post mortem brain and spinal cord tissue from male and female babies, young adults and old adults, from two different brain regions and spinal cord, detect the RNAs in each individual oligodendrocyte and then study the similarities and differences. This will allow us to identify subtypes of oligodendrocytes that behave differently, and that might be more vulnerable to disease or ageing in males and females. In the future, we can then compare oligodendrocytes from people with other oligodendrocyte diseases with these, and develop therapies that target the subtype of oligodendrocytes to help the disease, in a very specific way.

This will be part of the Human Cell Atlas where all data will be stored and pooled from researchers all around the world, allowing free access and collaboration, which the aim of improving and accelerating biological and medical research.

The intricacies of the human brain are probably what define us as human, and the oligodendrocytes of the brain are vital in maintaining this. These cells form the myelin sheaths around nerve axons, allowing fast saltatory nerve conduction, and metabolic support to the underlying axon. Myelination is mostly postnatal, and can be disrupted around birth, due to genetic abnormalities or premature birth, in adulthood in diseases such as multiple sclerosis and in old age, either in normal ageing, or in other neurodegenerative diseases.

We used to consider all oligodendrocytes as very similar, but we now know that they likely exist as different subtypes, depending on their developmental source, final location, the age and sex of the human, and the presence of neurological disease. This heterogeneity can now be studied in individual cells or nuclei by RNA sequencing, comparing each cell to another within and across humans, from post mortem tissue, using bioinformatics, with validation using immunohistochemistry/immunofluorescence and in situ hybridisation on such tissue.

In this project, we will extract oligodendroglial nuclei, from precursors to myelinating cells, from human post mortem brain and spinal cord tissue from male and female fetuses, young adults and old adults, from forebrain, cerebellum and spinal cord, and perform single nuclei RNAseq. We will then analyse these data, pooled with our previous data, and any published and HCA data to better define oligodendroglial subclusters. We will validate them with our previous markers and new markers, and then study the similarities and differences between our sample sets. These differences may define functional differences which confer differential vulnerability to disease or ageing, in central nervous system regions, in males and females. In the future, we can repeat this with disease samples, improving target pathway discovery for white matter disease therapeutics.

Who will benefit from this research?

Patients with white matter diseases: Oligodendrocytes are increasingly implicated in neurodegenerative diseases, especially in diseases such as multiple sclerosis, but also in other diseases such as Parkinsonian diseases and Huntington's disease as well as dementias including cerebral small vessel disease. This research will help define how oligodendrocytes behave in normal brain over the human lifespan, defining differences between regions of the brain and spinal cord, and between males and females, and between patients. This then paves the way for studying these in other diseases, to compare, which we hope will lead to advances in understanding of these diseases and therapeutics.

Researchers: We will provide techniques of how to extract and analyse nuclei from human post mortem tissue, to answer questions as to whether oligodendrocyte heterogeneity exists between ages, sexes and brain and spinal cord region, and provide robust and validated markers for this heterogeneity.

Private sector companies e.g. pharma: interest as to whether there are new targets for therapeutics in neurodegenerative diseases.

Local, national and international policy-makers, for determining best use of funding: interest as to whether therapeutic strategies currently used hold up to scrutiny or whether alternatives might be better pursued and funded.