MICA: Exosomes and microRNAs regulate neuro-immune interactions in chronic pain

Chronic pain after nerve damage or inflammatory arthritis is a debilitating condition in which the pain experience persists for long time. Pain is a persistent symptom following injury to nerve or in rheumatoid arthritis (RA) whereby pain remains even after suppression of joint disease with medicines. Chronic pain is difficult to treat, with current drugs being relatively ineffective and often having significant side effects. Therefore, a better understanding of the mechanisms responsible for persistence of pain can bring new ideas on how to prevent or attenuate chronic pain and facilitate the development of new medicines. We use mice in our studies as they also demonstrate pain-related behaviour in their hind paws that persists for several weeks in models of joint arthritis and peripheral neuropathy (PN).
Pain is a sign of both RA and PN, where blood cells enter the joint and the injured nerve and produce factors that activate pain nerves: these nerves carry pain signals from the joint or injured nerve to the spinal cord on their way to the brain where pain is felt. We discovered that blood-derived cells are not only in the joint or the injured nerve, but they are also around pain cells outside the joint and injured nerve in a structure that is called dorsal root ganglia (DRG). At this DRG site, far away from the swollen joint and injured nerve, blood-derived cell influence pain nerves and favour pain sensation. In these blood-derived cells we have identified new targets that can be exploited to regulate pain activity and may constitute novel approaches to treating persistent pain. These new targets are small strands of genetic material, produced in the pain cells of the DRG and packaged in small microstructures. Pain cells handover these particles to blood-derived cells to regulate their activity by increasing production of chemicals that increase pain sensitivity. We have identified a new way to target this genetic material within blood-derived cells.
In this project, we will use a variety of methods to assess the activity of blood-derived cells in animal models of pain, and determine the effects of this activity on the nerve cells that carry pain signals. We will then measure readouts of pain when specific activity in blood-derived cells has been either blocked. This study will allow us to determine the therapeutic potential of targets in blood-derived cells for the treatment of persistent pain: both chronic pain after nerve damage or inflammatory arthritis will be studied.

The ultimate aim of our research is to provide new information that will help in the design of novel pain-relieving medicines, thus allowing chronic pain treatments to be more effective to ultimately improve the quality of life of patients.

Chronic inflammatory or neuropathic pain remains undertreated as the efficacy of current strategies is limited by severe side effects. Elucidation of specific mechanisms that underlie chronic pain can open new therapeutic avenues. Pre-clinical studies including ours indicate that neuron interactions with immune cells contribute to chronic pain. Our novel evidence indicates that after peripheral nerve injury dorsal root ganglia (DRG) neurons release extracellular vesicles containing microRNA-21 (miR-21), which are engulfed by macrophages where miR-21 promotes a pro-inflammatory phenotype and the release of pro-nociceptive cytokines. As inhibition of miR-21 prevents neuropathic allodynia, we suggest that delivery of miR-21 antagomir encapsulated in nanoparticles constitutes an original approach to the prevention of neuropathic pain.
In this study, we will identify miR-21 target genes that are regulated in macrophages and contribute to the induction of neuropathic pain. Then, based on the rationale that miR-21 targets may change in neuropathic pain maintenance, we will identify target genes in macrophages at 14 days after nerve injury. Finally, in a model of inflammatory arthritis we will identify miRs which are dysregulated in DRG neurons, affect the phenotype of macrophages, and contribute to the maintenance of pain.

We propose that by comparing and contrasting neuropathic and arthritis pain models we will identify novel mechanisms operative within the DRG, and define specific pathways and mediators, which impact on the chronicity of pain.

By combining microarray analyses with behavior and cell cultures in transgenic mice, macrophage functions and extracellular vesicles characterization, we will define the impact of neuron-derived miRs on macrophage function and phenotype in the DRG in neuropathic and inflammatory allodynia. Furthermore, we will establish whether manipulation of miRs and their target genes in macrophages provides therapeutic analgesia.

Chronic pain constitutes a major clinical issue. In peripheral neuropathies and chronic inflammatory conditions the key symptom reported by patients is pain which is poorly controlled by available analgesics. Thus, there is an unmet clinical need for the development of new strategies that ideally reverse established pain by interfering with the mechanism by which the pain persists.
This proposal aims to advance our understanding of the role of inflammatory cells in the pathology of neuropathic and arthritis pain in order to provide new targets and treatments for therapeutic analgesia.
Besides scientists investigating neuroinflammation mechanisms underlying chronic pain with the aim of identifying new therapeutic targets, a wider group of beneficiaries will use the outputs of the proposed research.

Patients undergoing chronic pain treatment. The findings of this pre-clinical research will have direct relevance to the clinical problem and will provide important evidence for the therapeutic potential of non-coding RNAs as new targets for the treatment of neuropathic and arthritis pain. In the short-term our research could lead to development of a new treatment strategy to reduce the pain associated with neuropathies or arthritis, thus improving patient's quality of life. In the longer-term this research may lead to a clinical trial on the analgesic effect of nanoparticles containing miR-21 antagomir and other miRs in patients with neuropathic pain or suffering from arthritis. Phase I studies using miR mimetics encapsulated in nanoparticle-based formulation have shown minimal side effects and the first-in-man miR-based therapeutic trial in liver cancer patients is ongoing (NCT01829971).

Commercial private sector. The mechanistic insights from this research will provide confidence and real-time guidance to industrial scientists interested in precision medicine. For instance, microRNAs are being considered as robust biomarkers of cancer progression and therapy response. In the short term, the pharmaceutical industry will benefit from our approach. By examining the analgesic efficacy of miR antagomirs and mimics, we will guide drug discovery teams in this area. There is a substantial effort in delucidating the clinical application of miRs with diagnostic and therapeutic potentials in endocrine-related cancer as a single miR can address a multitude of genetic and epigenetic changes that occur in cancer patients. So far, phase I trials with miR-34 and miR-16 mimics, encapsulated in nanoparticle-based formuation to enance drug availability, have shown that drugs were well tolerated. Thus, companies developing miR-based strategies for cancer will find a rationale for exploring miRs with an application for chronic pain. In the longer term, as miR-field progresses our research could lead to a clinical trial of miRs encapsulated in microvesicles for chronic pain. Tissue-specific delivery of miRs may spare essential neuron-macrophage communication, providing a potential therapy with limited side effects.