A novel role for the chemokine lymphotactin and its receptor in trigeminal sensitisation

Chemokines are a large family of small secreted proteins that regulate the migration of white blood cells with a well-established role in coordinating immune responses in peripheral tissues. However, within the last decade a range of studies has demonstrated that chemokines also have wide-reaching effects in the nervous system, where they have been shown to have diverse effects in a range of processes, regulating development, inflammation and communication between cells. Consequently, they have been implicated in a variety of disease states including multiple sclerosis, Parkinson's, Huntingdon's and Alzheimer's diseases, and chronic pain. This proposal focuses on a relatively little-studied member of the large chemokine family. Our recent work provides the first demonstration that this particular chemokine and its receptor are expressed in the nervous system. Evidence from other studies now clearly shows that chemokines can initiate and maintain increased activity within peripheral and central pain pathways and thus contribute to the development of chronic pain. This raises the possibility that the chemokine we propose to study may also be important in the development of chronic pain and other diseases. We will investigate the role of the chemokine in pain from the mouth and face; as this area is supplied by the trigeminal nerve, pain from this region is known as trigeminal pain. The overall aims of the study are to determine which components of the trigeminal pain pathway express the chemokine and its receptor, and to investigate its role in increased activity in this pathway. This will enable us to establish its potential contribution to the development of chronic pain in the oro-facial region. Initially we will determine the expression of the chemokine and its receptor in specific cell types within normal rat trigeminal tissues that are involved in pain initiation and processing, including the tooth pulp, a branch of the trigeminal nerve, and elements of central pain pathways. We will then establish how their expression is altered in two conditions, nerve injury and inflammation, known to produce increased activity in pain pathways. This activity plays a key role in the initiation of chronic pain. We will determine whether levels of expression correlate with the time course of development of increased activity, as determined in our previous studies. We have access to unique archives of human tissues stemming from our provision of a national service for advice and management of patients who sustain trigeminal nerve injuries, and from treatment of patients with dental pain. We will use this tissue to examine the expression of the chemokine and receptor in human tooth pulps and injured nerves from patients with known clinical pain histories, enabling us to establish whether expression at sites of nerve injury or inflammation in human tissue correlates with the presence of pain. We will also carry out a series of functional studies to determine the effects of this chemokine within a region of the brainstem involved in the central processing of trigeminal pain. These studies will establish whether the chemokine is able to influence activity in different cell types in this region and investigate how it may modulate signalling between and within cells. Thus we will be able to establish whether this molecule is capable of enhancing activity in the central nervous system, and identify any potential role in modifying activity in central pain pathways. This project will enable us to determine any putative role for this chemokine within peripheral and central pain pathways and establish whether either the chemokine or its receptor may provide a target for novel analgesics. This, in turn, may lead to the development of novel therapies for chronic pain and potentially other neurological conditions for which there is currently no reliable treatment, thus substantially improving quality of life for patients.

Several chemokines have recently been identified within the nervous system, where they have been shown to have diverse effects, regulating neuronal development, neuroinflammation and synaptic transmission, and have been implicated in the initiation and maintenance of exaggerated pain states. Recent work in Prof Boissonade's laboratory provides the first demonstration that the relatively little-studied chemokine, lymphotactin (XCL1), and its receptor (XCR1) are expressed in the nervous system. The overall aim of this study is therefore to characterise for the first time the expression of XCL1 and XCR1 in the trigeminal system, and to investigate their putative role in hyperexcitability, signalling and trigeminal pain. We will characterise XCR1 and XCL1 expression in normal rat trigeminal tissues (tooth pulp, lingual nerve, trigeminal ganglion and trigeminal nucleus) and identify specific structures demonstrating expression, eg neuronal structures, immune cells and glial cells. We will also determine in our established animal models, whether XCR1 and XCL1 expression are altered by nerve injury or inflammation and establish any correlation with the development of hyperexcitability. We will examine the expression of the XCL1 and XCR1 in human tooth pulps and injured nerves using our unique archives of human tissues from patients with known clinical pain histories. This will enable us to establish whether expression at sites of nerve injury or inflammation correlates with the presence of pain. The above will be achieved using a range of immunocytochemical and image analysis techniques. Using an in-vitro trigeminal slice preparation we will determine whether XCL1 activates intracellular signalling molecules, eg p38 and ERK, in the trigeminal nucleus within specific cell types, eg astrocytes, microglia or neurones, and probe the cellular mechanisms of XCL1-induced activation.

All research scientists working in the very broad field of chemokine research will benefit from this research. In addition to their well-established role in co-ordinating peripheral inflammatory responses, it is now increasingly clear that chemokines play a fundamental role in signalling within the nervous system, and they have been shown to be involved in diverse events including neuronal development, neuroinflammation and synaptic transmission. Thus there will be a wide range of scientists who will benefit from this research; these are discussed in detail in the Academic Beneficiaries section. The wider beneficiaries are discussed below. Patients with pain and other neurological disease: Because of their wide-reaching roles in the nervous system, chemokines have been implicated the pathogenesis of numerous neurological conditions including multiple sclerosis, Parkinson's, Huntingdon's and Alzheimer's diseases, and chronic pain. Our study will provide the first description of the distribution and neuromodulatory effects of a relatively little-studied chemokine within the nervous system, focusing on areas related to trigeminal pain. However, neuromodulatory effects of this chemokine are likely to be wide-reaching, thus there is potential that this molecule and its receptor may represent a therapeutic target for a range of conditions. If this leads to the development of novel therapies with improved side effect profiles, it could provide a substantially improved quality of life for patients. Many of the conditions described above are more prevalent in the older population and thus any novel drugs may contribute to improved health during ageing. In order to ensure that our data is as widely disseminated as possible, we will inform research scientists in all relevant fields through publication in a broad spectrum of high impact journals with copies made available through PubMed Central, and present data at wide-ranging international conferences. We will identify other collaborators with interest in other neurological areas to carry out further studies, and inform clinicians and patient user groups as appropriate (see Pathways to Impact). Pharmaceutical Industry: The data from the proposed study will potentially provide information regarding targets for the development of therapies for a wide range of neurological disorders (see above). The increased prevalence of these disorders due to the ageing population, coupled with a lack of drugs to cater for these disorders, has resulted in considerable interest in the development of novel therapeutics to address these areas of unmet clinical need. The interest of our industrial partner, Pfizer, lies primarily in the identification of targets for novel analgesics. However, as described above, there is considerable scope for any novel targets identified in this project to be utilised for the development of therapies for other neurological disorders. The research staff: The research staff employed on this grant will gain interdisciplinary expertise as a result of this collaborative project. In addition, working with our industrial collaborators will enable them to gain a broader perspective, particularly with respect to the field of drug discovery. Our interest in wide dissemination of our findings will bring opportunities to publish in new areas, and enable work to be presented to a diverse audience, which will strengthen and develop the direction of their careers.