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A Channel to Nerve Degeneration

Primary Supervisor: Dr Xuming Zhang, Life & Health Sciences

Secondary supervisor: Dr Rhein Parri

PhD project title: A Channel to Nerve Degeneration

University of Registration: Aston University

Project outline:

Afferent nerve fibres are formed by the axons of sensory neurons ensheathed by myelin-forming Schwann cells (SCs). They carry sensory signals to the brain crucial to homeostasis and survival. When nerve fibres are degenerated or injured, often occurring in ageing, obesity and diabetes, peripheral neuropathy (PN) will evolve causing pain, unusual sensations such as numbness and even sensation loss leading ultimately to foot ulcer and amputations. How this damaging process occurs remains elusive, though both sensory neurons and SCs are implicated. Here, we will investigate the molecules mediating PN and the roles of both sensory axons and SCs in this process.

Oxidative stress and nerve inflammation are two hallmark processes causing demyelination and nerve degeneration in PN. They result from altered metabolism and mitochondria dysfunction during ageing and diabetes triggering production of excessive reactive oxygen species (ROS). Accumulated ROS then drives neuroinflammation by activating inflammatory signaling. Interestingly, transient receptor potential melastatin 2 (TRPM2) ion channels are both a metabolic sensor and a sensor for oxidative stress involved in oxidative-stress-induced cell and tissue damage. TRPM2 also mediates immune and inflammatory responses. These prominent functions of TRPM2 align perfectly with the pathological processes of PN, suggesting a pivotal role for TRPM2 in PN. Indeed, TRPM2 is expressed in both sensory axons and SCs, and neuropathic pain in PN was prevented by both pharmacological blockade and genetic deletion of TRPM2. We will investigate the role of TRPM2 in PN and the underlying mechanisms with three objectives.

Firstly, we will investigate the role of TRPM2 in nerve degeneration, oxidative stress and neuroinflammation. We will generate diabetic neuropathy model in wild-type and TRPM2 knockout mice. We will then assess neuropathy behaviours of mice such as pain and gait instability. To examine nerve degeneration, we will stain nerve fibres in the skin with anti-PGP9.5. We will also isolate sciatic nerves to evaluate neuronal damage, demyelination and apoptosis of SCs using histology and apoptosis assay together with qRT-PCR for determination of expression of neuron- and myelin-specific genes. Sciatic nerves will also be used to probe nerve oxidative stress using lipid peroxidation assay and to study neuroinflammation by staining infiltrated macrophage with anti-F4/80. TRPM2-lacking mice likely exhibit reduced nerve degeneration, oxidative stress and neuroinflammation. Secondly, we will determine the role of TRPM2 in nerve firing. Firing frequency determines nerve function. Inhibition of neuropathic pain in PN by blocking TRPM2 suggests a role for TRPM2 in neuronal firing. We will isolate sensory neurons and use current patch clamping to record neuronal firing. We anticipate that altered neuronal firing in diabetic neuropathy is prevented in TRPM2-lacking mice. Thirdly, we will define the separate contributions of TRPM2 in neurons and in SCs to PN. We will use Cre-Lox technology to breed conditional knockout mice in which TRPM2 is selectively deleted in either sensory neurons or SCs. We will then employ the same approaches above to investigate the effect of selective TRPM2 deletion on nerve degeneration, oxidative stress, neuroinflammation and nerve firing.

Altogether, these studies will reveal the novel mechanisms through which TRPM2 mediates PN in two different cell types and suggest TRPM2 as a new target for the treatment of PN.

You will be able to engage our cutting-edge research in a well-funded laboratory with vibrant and stimulating environment, and will have excellent opportunities to learn multi-disciplinary knowledge (neuroscience, immunology, pharmacology and cell biology) and a range of interdisciplinary techniques including gene manipulations, animal behaviour, immunohistology, electrophysiology, qPCR, imaging and cell biology assays to address a prevalent neurologic condition.

References:

  1. Feldman EL et al, Nat. Rev. Dis. Primers 2019, 5, 41.
  2. Yamamoto S et al, Pharmaceuticals (Basel) 2016, 9.

BBSRC Strategic Research Priority: Sustainable Agriculture and Food: Animal Health and Welfare. Understanding the Rules of Life: Neuroscience and behaviour. Integrated Understanding of Health: Ageing

    Techniques that will be undertaken during the project:

    • Immunohistology
    • Cell apoptosis assay (TUNEL)
    • Oxidative stress assay
    • Confocal imaging
    • qRT-PCR
    • Electrophysiology
    • Neuron culture
    • Genotyping and animal behaviour

    Contact: Dr Xuming Zhang, Aston University