Regulation and function of the stem cell activation factor Ascl1 in constitutive and injury-induced adult neurogenesis

The purpose of this project is to understand why new nerve cells are produced only in particular areas of the brain and why injuries cannot be repaired in other brain areas. Nerve cells are produced by special cells called stem cells that retain the properties of cells in the embryo to divide and produce various types of specialized cells. Stem cells are only found in limited areas of the brain where they divide throughout life to produce new nerve cells. We have found a protein called Ascl1 that stimulates the divisions of the stem cells and is therefore important for the production of new nerve cells. Our collaborators at the Karolinska Institute in Sweden have also found that the same protein Ascl1 is also present after a stroke in another brain region and in a distinct type of cells called glial cells. Some of these glial cells behave like stem cells when Ascl1 is present after stroke, as they divide and produce new nerve cells, but others do not react to the presence of Ascl1 and fail to produce nerve cells. To help the brain repair the damages caused by strokes, there is clearly a need to improve how glial cells react to the injury and to help them become more like stem cells. For this, we need to understand better how Ascl1 works.
With this project, we want first to understand why Ascl1 is present in stem cells and in some glial cells after a stroke but not in others. We will therefore study the molecules that control in which brain cells Ascl1 is found. Second, we want to understand why, when Ascl1 is present in glial cells, some behave like stem cells and divide while other do not react to the presence of Ascl1 and continue to behave like normal glial cells. Ascl1 is a transcription factor, which means that it controls the activity of many genes in the cells where it is present, and these genes in turn control the behavior of the cells such as their divisions. We will therefore examine the genes that are controlled by Ascl1 in stem cell-like glial cells that respond to Ascl1 and we will find out why the same genes are not controlled by Ascl1 in other glial cells.
We expect our research to lead to a better understanding of how the brain reacts to injuries such as strokes and why it has a limited ability to replace the nerve cells lost with new cells. In the longer term, we hope to have learned enough of the effect of stroke on glial cells to help devise treatments that convert more glial cells into stem cells and help the brain repair itself.

Our main objective in this proposal is to identify and compare the molecular pathways that control the expression and function of the transcription factor Ascl1 in neurogenic stem cells of the adult brain and in astrocytes stimulated by injury. We have previously shown that adult neural stem cells induce the expression of Ascl1 when they become activated and that Ascl1 function is essential for stem cells to exit quiescence and proliferate. Our collaborators have shown that ischemia induces Ascl1 expression in a population of astrocytes restricted to the striatum. However, only a subset of these Ascl1-expressing astrocytes initiates a neurogenic programme.

Here we will use cultures of neural stem cell and astrocyte as well as conditional mutant mice to characterize the signaling pathways that induce Ascl1 expression in activated neural stem cells and activated striatal astrocytes. This will help us understand why Ascl1 is not expressed more broadly by astrocytes in ischemic brains. We will also characterise the gene expression programme activated by Ascl1 in neurogenic astrocytes and we will study the signaling, transcriptional and epigenetic mechanisms responsible for the resistance of non-neurogenic astrocytes to Ascl1 function.

This project will shed new light on two important steps in the activation of neurogenic programmes in the adult brain, the induction of Ascl1 expression and the stimulation by Ascl1 of cell proliferation and neurogenesis. Identifying the pathways that control these two steps in striatal astrocytes will help us decipher mechanisms that limit the neurogenic potential of adult brain astrocytes. In the longer term, our findings will help design strategies that overcome these limitations and stimulate more broadly Ascl1 expression and its activity in astrocytes in response to injury.

Overview:

We propose here to perform basic research with very clear clinical implications in the medium to long term. To progress on the road to clinical applications, it is essential that scientists in academia and industry who might contribute to these developments are made aware of our findings. In the longer term, clinicians and ultimately patients, carers and families will benefit from the design of methods to stimulate brain repair mechanisms that will eventually emerge from our research.

Potential beneficiaries:

The most immediate impact of the project will be on academic researchers studying neural stem cells and astrocytes in animal models. This is a well-established area of research but there are still relatively few studies on molecular mechanisms and particularly intracellular pathways controlling neural stem cell activities and on the mechanisms that limit the neurogenic response of astrocytes to injury. Researchers in these fields will extend our research on the mechanisms controlling neural stem cell activities and limiting the neurogenic response of astrocytes by studying additional models of brain injury and disease as well as human stem cells and astrocytes, to determine whether our results can be generalised to these new models.

Academic researchers who are already engaged in studies to develop treatments for brain injuries and disease will also benefit directly as they will be able to use our results to devise rational strategies to overcome barriers to the production of neurons by astrocytes. In the longer term, researchers in academia or industry will test the robustness and safety of the newly devised protocols in preclinical studies. Clinicians who will conduct the clinical trials will also eventually benefit from our research and from the ensuing translational and preclinical studies performed by others. Ultimately, it is our hope that patients and families will be the greatest beneficiaries of our research.

Arrangements to optimize impact during the course of the project:

Communication and engagement with the scientific and medical beneficiaries will be through conventional scientific presentations, publications and websites. We will broaden the range of scientific conferences that we attend (usually restricted to the fields of Neuroscience or Stem Cell Biology) and will also attend conferences of a more medical character (e.g. Alzheimer's Association International Conference; International Stroke Conference) to access the medical community. Communications with patients groups will be achieved by directly contacting relevant charities in the UK (e.g. Stroke Association; Alzheimer's Society) and abroad to maximise opportunities to communicate our research and engage with patients and families. Our work will be described for the general public through the NIMR/Crick website.
If we find during the course of the project that our results could potentially be used to stimulate the neurogenic response of astrocytes to ischemia, we will immediately take action and consult with the Technology Transfer Officer at NIMR and the Business Manager at MRC Technology (also based on the NIMR campus) who have extensive expertise in patenting and licensing, to consider the need to protect our findings for possible future commercial exploitation, and canvass biotech companies and scientists advising such companies for their interest in collaborating with us. There is strong encouragement at NIMR to maximize commercial exploitation of research through contacts with industry or by starting spin-out companies, e.g. through a recently started Translational Club.