Investigating the role of Leucine rich, glioma inactivated 1 (LGI1) in regulating pain sensitivity

Trauma to the nervous system or diseases such as diabetes can injure neurons involved in signalling pain resulting in them becoming over-active and triggering the unpleasant sensation of pain. This type of pain, termed neuropathic pain, is unpleasant, long lasting and results in a poor quality of life for the sufferer. Neuropathic pain is common affecting between 5-10% of people and will become more common with an aging population. Although analgesics are available, this type of pain is particularly resistant to our current treatment strategies leaving the patient with few options. In addition, these drugs cause severe side-effects. This is of course hugely debilitating for the individual, negatively impacting on their way of life. Furthermore, it has significant economic ramifications (treatment costs, time spent off work) and in general is a burden on healthcare services which needs to be addressed. As a result, there is a pressing need to develop new better targeted therapies for the treatment of neuropathic pain. One obstacle has been the lack of translation from basic science findings into the clinic. Here I aim to address this by using patient samples to enhance the clinical relevance of my research findings. Autoantibodies targeting Leucine-rich glioma inactivate 1 (LGI1) are associate with neuropathic pain in patients. This molecule interacts with potassium channels which are important for regulating the activity of neurons involved in signalling pain. I will use these antibodies to determine if disruption of LGI1 is the cause of pain in these patients and whether this protein is a common regulator of neuronal activity and therefore a viable target for the treatment of neuropathic pain as a whole. The aim of my research will be to first assess whether LGI1 impacts on pain sensation by using genetically altered mice which no longer express this protein and assessing their behaviour to sensory stimuli. Using these mice, I will measure the activity of their pain signalling neurons and determine if LGI1 impacts on this activity through its action on potassium channels. Through my collaborations I will obtain LGI1 autoantibodies (-Abs) from a number of patients with neuropathic pain. I will use these samples to develop an animal model in order to ascertain whether these antibodies are causal to the development of neuropathic pain. This study will not only shed light on the role of LGI1 in pain biology, but also autoantibodies as a mechanism to cause abnormal pain sensation in patients. I will use established animal models of nerve injury to better understand the role of LGI1 in the development of neuropathic pain. LGI1 is a secreted molecule and its presence increases/stabilises the activity of potassium channels (therefore decreasing the activity of pain signalling neurons). To test the therapeutic potential of modulating this system, I will create soluble LGI1 protein for use in animals to increase the availability of LGI1 to pain signalling neurons. Using preclinical models, I will test whether LGI1 treatment can reduce neuropathic pain behaviours in mice and therefore determine the analgesic potential of this approach.

These findings will of course directly help neuropathic pain patients with LGI1-Abs, where treatments are already available to reduce antibody levels and could then be used specifically to treat pain. In the wider context, new treatments for neuropathic pain will have huge societal benefits and these findings can be applied to other persistent pain conditions.

Enhanced neuronal excitability is fundamental to neuropathic pain conditions. Therefore, a better understanding of the factors which regulate neuronal activity is paramount to the development of improved pain therapies. Autoantibodies (-Abs) directed against Leucine-rich glioma inactivated 1 (LGI1) are associated with neuropathic pain in patients and these symptoms can be relieved with therapies that reduce antibody levels. LGI1 is a secreted protein which stabilises the expression of Kv1 channels in neuronal membranes and has been shown to regulate neuronal function. However, experimental studies have not yet directly investigated the role of LGI1 in pain. I aim to use my research to better understand the role of LGI1 in regulating neuronal excitability and pain sensitivity. Initially I will characterise the expression of LGI1 in pain signalling neurons and use transgenic mice to specifically ablate LGI1 in neuronal populations at the level of the DRG. The impact of specific LGI1 ablation on sensory function will be assessed using behavioural pain assays. I will test the ability of patient LGI1-Abs to cause neuropathic pain by developing a passive transfer model in mice and measure anatomical, biochemical and molecular outcomes. Electrophysiological approaches will assess the effect of disrupting LGI1 (genetic ablation or LGI1-Abs) on neuronal excitability and mechanistic understanding will be gained by looking at the function and expression of Kv1 channels. To investigate whether LGI1 is important in the more general context of neuropathic pain, I will use a preclinical model of nerve injury. I will generate recombinant LGI1 protein as a novel therapeutic approach for the treatment of pain. I will assess its impact on neuronal activity and apply it to preclinical models with the aim of reversing neuropathic pain behaviours in mice.

The studies set out in this research proposal will have a number of potential beneficiaries.

Academics:
A number of academics will directly benefit from this research during the period of the proposed project and beyond. Through studies of human genetics and basic research, LGI1 is known to have a role in epilepsy, a condition where, similar to neuropathic pain, neuronal hyperexcitability is a fundamental component. Furthermore, other neurological conditions are associated with LGI1 autoantibodies (LGI1-Abs) such as limbic encephalitis, insomnia and cognitive dysfunction. The work proposed in this research grant will lead to a better understanding of the functional role of LGI1 in the nervous system and ascertain why its disruption leads to increased neuronal activity. It will focus on primary sensory neurons an area of the nervous system where LGI1's role has been poorly studied. Therefore findings here could lead to new insights regarding the mechanisms surrounding LGI1 function and be applicable throughout the nervous system. Furthermore, this project will generate new research tools (e.g. recombinant LGI1 protein) which will be directly relevant to other research fields e.g. epilepsy.

Patients:
In the short term this work will benefit LGI1-Abs patients with neuropathic pain. I aim to fully address whether these antibodies are causal to pain by developing a passive transfer model in mice. These findings will aid clinicians in treating patients, where analgesic strategies could be focussed on reducing antibody levels and relieve patients of the need for current analgesics and their harmful side-effects. Neuropathic pain is a hugely debilitating condition and the patients will directly benefit through effective pain relief and increased quality of life. In the longer term this work will also benefit additional neuropathic and chronic pain patients (see sections below).

The pharmaceutical industry:
Pain is a common clinical problem, with inadequate treatment strategies. The pharmaceutical industry has an interest in finding treatments for pain and companies such as AstraZeneca, Biogen, Pfizer, and GSK have current programmes for developing new analgesics. Reducing excessive neuronal activity is paramount to pain treatment and LGI1 is known to regulate neuronal activity in the context of epilepsy. LGI1 is novel to pain and I aim to test the analgesic potential of increasing LGI1 availability to pain signalling neurons through protein application in preclinical models. These findings will be applicable to the treatment of neuropathic pain, as well as other chronic pain conditions and could lead to huge financial gains for this sector as well as a positive economic impact on healthcare services.

Healthcare services and society:
Pain negatively impacts a patient's quality of life, their ability to work and contribute to society. Current analgesics provide insufficient treatment and cause severe side effects resulting in additional healthcare problems. Therefore, pain is a huge financial burden on healthcare systems and society as a whole. For example, in the USA alone the costs associated with persistent pain are massive ($560-635 billion). The development of more effective, better targeted pain therapies will help relieve this burden, resulting in a much-needed financial boost to the healthcare system. Through improved pain relief, individuals will enjoy a better quality of life.

Workforce:
In the long-term improved control of pain will allow patients to return to work. In the short term this research grant will allow me to further develop my technical, research, communication and management skills. By establishing my own research team and attending specific workshops, I will enhance my leadership capabilities. Through my postdoctoral researcher and future team members I will pass on the skills I have gained as I aim to nurture the next generation of pain scientists.