Variability in human axon survival

Lead Research Organisation: University of Cambridge
Department Name: Clinical Neurosciences

Abstract

Axons are the long 'wires' that link one nerve cell to another. They are one of the first structures to be lost in almost all degenerative disorders of our brains, spinal cords and nerves. The consequences include pain, disability, loss of memory, hearing and sight in disorders such as Alzheimer's disease, motor neuron disease and multiple sclerosis. Peripheral neuropathies, disorders affecting the network of nerves outside the central nervous system, often resulting from diabetes or the side effects of cancer chemotherapy, are one example of an axonal disorder. Glaucoma, resulting from disruption of the optic nerve by pressure in the eye, is another.

There are two main ways to study axon degeneration. One is in animal or cell culture models. These model systems bring major advantages for research, for example the underlying molecular mechanism can be studied in ways that would not be possible in humans, and drugs can be tested without risk to people. However, these models often do not fully represent the corresponding human disease. They are valid because we share much of our DNA sequence and most types of cells with other mammals, but there are always some limitations.

The second, highly complementary approach is human genetics. Methods for sequencing and analysing human DNA have improved dramatically since the human genome was first sequenced and this is revolutionising our understanding of which genes may cause or contribute to common and rare disorders. However, ultimately these results are correlation rather than proof. Experimental model systems, such as those described above, are needed to extend this research.

By studying axon degeneration in mouse, cell culture and fly models, we have made substantial progress in understanding an important axon degeneration mechanism. Animal models of disease have helped us understand its potential role in human disease and in normal ageing, the single biggest risk factor for many neurodegenerative disorders. Developments in human genetics have independently suggested that the proteins regulating axon degeneration in these model systems play a role in human disease, and generated far more data on how these proteins differ within the human population. The essential next steps are to understand how variations in these proteins within the human population can affect normal protein function, so we will make similar changes in animals or cell culture models to test whether features of the corresponding human diseases emerge. Based on our knowledge of the pathway in mice we are also able to test whether blocking this pathway in various ways can prevent disease.

This work takes important steps towards translating years of progress in axon degeneration in model systems into real understanding of how the pathway malfunctions in human disease and hence towards therapies that can prevent or treat disease.

Technical Summary

We study the pathway of axon degeneration after injury: Wallerian degeneration. Data from animal models suggest related mechanisms influence axon survival in some diseases and in ageing, including multiple sclerosis (MS), peripheral neuropathies (PN), glaucoma and some motor neuron diseases. Early axon loss is also prominent in Alzheimer's disease, Parkinson's disease and ALS. There are no disease-modifying therapies. Here, we address the role of this pathway in human axon survival.

Mutations of five genes are now known to robustly delay Wallerian degeneration in mice and other model organisms but whether a similar phenotype exists in humans has remained an intriguing but unanswered question. Recent GWAS and exome linkage between Wallerian pathway genes and ALS and a painful neuropathy, and animal studies, suggest that such a phenotype could function as a disease modifier. SNP databases indicate polymorphisms likely to delay Wallerian degeneration and others likely to confer an opposite phenotype of axon vulnerability. Our mouse and preliminary human studies support this notion.

We will test which human variants alter axon survival by testing their function in mouse neurons that lack the homologous mouse gene. Using established assays, we will ask whether human variants in a pro-survival protein, NMNAT2, support axon survival and if so how strongly, and whether variants in human SARM1, a pro-degenerative protein, restore rapid Wallerian degeneration when mouse SARM1 is missing. We will then estimate the prevalence of these phenotypes. We will test whether NMNAT2 deficiency is a risk factor for neuropathic pain, and having shown that SARM1 deletion completely rescues nerve growth and early lethality in NMNAT2 null mice, we will test whether it also rescues a premature age-related decline that we find in mice expressing low levels of NMNAT2. These data will complement ongoing GWAS and exome studies to understand the roles of this pathway in human disease.

Planned Impact

The potential non-academic beneficiaries of this project are:
(1) Pharma/biotech companies targeting neurodegenerative disorders where axon degeneration plays an important role. In particular, the move towards personalized medicine will benefit from the type of functional data we will generate. Through our Workshop organization we will also help to stimulate similar work elsewhere resulting in indirect benefit to similar companies. Axon degeneration is a significant event in most neurodegenerative diseases, including some which are highly prevalent and therefore represent major market opportunities for the commercial sector: Alzheimer's disease (lifetime risk 15%), stroke (15%), diabetic neuropathy (7%), glaucoma (2%) and Parkinson's disease (1.5%). There are no disease-modifying treatments. As explained in 'pathways to impact' we will actively engage the commercial sector to ensure this potential is realized, for example through our ongoing CASE studentship with Takeda (Cambridge).
(2) Patients with neurodegenerative disorders and their families. Understanding the genetic basis of disease is crucial. Substantial progress is being made in GWAS and exome studies but functional characterization such as we will carry out (and further stimulate through our Workshop) is vital for knowing which genes are actually causing or contributing to disease and therefore represent the right drug targets. As an increasing component of human disease is recognized to reflect genetic makeup, offering relatives the option to know whether they too are at risk will become more important. While this has important ethical considerations too, moving forward on the technological ability to do this in this work will be an important step.
(3) Lay public interested in nervous system function. In our public engagement activities we find a strong interest in the nervous system among the lay public. While there is only a limited amount that individuals can do about the health of their nervous system, understanding what goes wrong can at least help some patients to come to terms with it, and motivates some healthy individuals to ensure they avoid a lifestyle that places strains on axon survival (e.g., excessive alcohol consumption, obesity, drug abuse).

Publications

10 25 50

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Coleman MP (2020) Programmed axon degeneration: from mouse to mechanism to medicine. in Nature reviews. Neuroscience

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Fricker M (2018) Neuronal Cell Death. in Physiological reviews

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Gilley J (2019) Low levels of NMNAT2 compromise axon development and survival. in Human molecular genetics

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Gilley J (2020) Microinjection of Superior Cervical Ganglion Neurons for Studying Axon Degeneration. in Methods in molecular biology (Clifton, N.J.)

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Gilley J (2019) Low levels of NMNAT2 compromise axon development and survival. in Human molecular genetics

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Loreto A (2020) Axon Degeneration Assays in Superior Cervical Ganglion Explant Cultures. in Methods in molecular biology (Clifton, N.J.)

 
Description BBSRC Industrial Partnership Award
Amount £934,853 (GBP)
Organisation AstraZeneca 
Department Astra Zeneca
Sector Private
Country United States
Start 02/2019 
End 02/2022
 
Description Outreach Award
Amount $150,000 (USD)
Organisation Thompson Family Foundation Initiative 
Sector Charity/Non Profit
Country United States
Start 10/2018 
End 09/2020
 
Title Source data for "Sarm1 Deletion, but Not WldS, Confers Lifelong Rescue in a Mouse Model of Severe Axonopathy" 
Description Source data for figures in associated publication. Each figure panel with analysed data is found as a separate sheet in the excel file. A full descritpion of the datasets and methods can be found in the publication. 
Type Of Material Database/Collection of data 
Year Produced 2017 
Provided To Others? Yes  
 
Description Collaboration on mechanism and prevention of Wallerian degeneration 
Organisation AstraZeneca
Country United Kingdom 
Sector Private 
PI Contribution Basic research into activation mechanism of SARM1
Collaborator Contribution Industrial partnership as part of BBSRC IPA award. Contributes knowledge, discussion, research collaboration, specialised methods such as Mass Spec and chemical synthesis.
Impact BBSRC IPA Award
Start Year 2017
 
Description Generation of mice with 75% reduction in NMNAT2 
Organisation University of Texas Southwestern Medical Center
Country United States 
Sector Academic/University 
PI Contribution Imported gene trap mice with partial knock-down of NMNAT2 from targeted allele and crossed with our own gene trap targeted mice to be used in experiments.
Collaborator Contribution Provided gene trap mice with partial knock-down of NMNAT2 from targeted allele.
Impact We have been monitoring effects of a 75% reduction in NMNAT2 expression during aging.
Start Year 2011
 
Description Giuseppe Orsomando 
Organisation Marche Polytechnic University
Country Italy 
Sector Academic/University 
PI Contribution Expertise and material from axon degeneration models
Collaborator Contribution Expertise in measurement of NAD-related metabolites and enzyme assays
Impact Carpi, F.M., Cortese, M., Orsomando, G., Polzonetti, V., Vincenzetti, S., Moreschini, B., Coleman, M.P., and Magni, G. (2018). Simultaneous quantification of nicotinamide mononucleotide and related pyridine compounds in mouse tissues by UHPLC-MS/MS. Sep Sci plus. 1(1):22-30. -- Di Stefano, M., Loreto A., Orsomando, G., Mori V., Zamporlini, F., Hulse, R.P., Webster, J., Donaldson, L.F., Gering, M., Raffaelli, N., Coleman, M.P., Gilley, J., and Conforti L. (2017). NMN deamidase delays Wallerian degeneration and rescues axonal defects caused by NMNAT2 deficiency in vivo. Current Biology. 27(6):784-794
Start Year 2016
 
Description Prof Richard Piercy 
Organisation Royal Veterinary College (RVC)
Country United Kingdom 
Sector Academic/University 
PI Contribution Expertise in measuring axonal transport
Collaborator Contribution Expertise in equine veterinary science; nerve samples from horses
Impact Dr Robert Adalbert will start a two-year collaboration project with Prof Richard Piercy's group in RVC.
Start Year 2017
 
Description Professor Richard Ribchester 
Organisation University of Edinburgh
Country United Kingdom 
Sector Academic/University 
PI Contribution Characterisation of Sarm1/Nmnat-2 double knockout mice with axonal and neuromuscular synaptic protection.
Collaborator Contribution Professor Richard Ribchester and his group contributed experimental data derived from muscle tension recordings from knockout mice with axonal and synaptic protection.
Impact Gilley, J., Ribchester, R.R., and Coleman, M.P. (2017). Sarm1 deletion, but not WldS, confers lifelong rescue in a mouse model of severe axonopathy. Cell Reports. 21(1):10-16
Start Year 2016
 
Description 19th Annual Packard Center ALS Research Symposium 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Key note speech on the links between Wallerian-like degeneration and various sub-types of ALS and other diseases involving motor axon loss, and also covered what we know about how to stop Wallerian degeneration.
Year(s) Of Engagement Activity 2019
 
Description OPCD Seminar - Oxford 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Professional Practitioners
Results and Impact Talk titled: Mechanisms of axon degeneration in injury and disease, held at Nuffield Department of Clinical Neurosciences. Level 6, West Wing, John Radcliffe Hospital, Oxford OX3 9DU on September 12th 2019
Year(s) Of Engagement Activity 2019
 
Description Poster presentation at Parkinson's Open-day (Saturday 4th November 2017) 
Form Of Engagement Activity Participation in an open day or visit at my research institution
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Patients, carers and/or patient groups
Results and Impact Dr Andrea Loreto and Prof Coleman poster presentation to Parkinson's patients during the open day organised by Prof Roger Barker's Clinic at the John van Geest Centre for Brain Repair. Poster title: Preventing axon loss caused by mitochondrial dysfunction in Parkinson's disease
Year(s) Of Engagement Activity 2017
 
Description Seminar at Cardiff University Dementia Research Institute 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Postgraduate students
Results and Impact I gave a seminar at Cardiff University Dementia Research Institute at the invitation of Owen Peters.
Year(s) Of Engagement Activity 2020
 
Description Seminar at Harvard University 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Postgraduate students
Results and Impact I presented a seminar at Harvard University at the invitation of Roz Segal.
Year(s) Of Engagement Activity 2019
 
Description Suna Kirac Conference, Istanbul 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact I attended and presented at this conference at the invitation of Bob Brown and Nazli Basak. There was an audience of between 100 and 150 people.
Year(s) Of Engagement Activity 2019
 
Description TFFI Retreat 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Industry/Business
Results and Impact Brief talk including updates on our current research collaborations.
Year(s) Of Engagement Activity 2019
 
Description Talk at Hills Road Sixth Form College, Cambridge 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Schools
Results and Impact Presentation to 40 6th form students. Title: The nervous system: the life and death of cells inside your head.
Year(s) Of Engagement Activity 2018
 
Description Univeristy of York Seminar 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Supporters
Results and Impact Seminar speaker at the Univeristy of York, Molecular mechanisms of axon degeneration in injury and disease
Year(s) Of Engagement Activity 2019