Periodic Reporting for period 4 - SCOPE (Schwann Cell Options for chronic Pain Eradication)
Reporting period: 2024-03-01 to 2025-02-28
The burden of chronic pain is enormous in terms of suffering, disability, health care, and social and economic cost. Due the increase in the aging population, chronic pain is foreseen to increase remarkably in Europe in the near future. Currently available medicines for treating neuropathic pain are often unsatisfactory. Medicines for treating inflammatory pain have gastrointestinal (non-steroidal antiinflammatory drugs, NSAIDs), or cardiovascular [cyclooxygenase-2, (COX2) inhibitors, Coxibs)] liabilities, thus increasing morbidity and mortality in the elderly. The opioid epidemic in the US further highlights the inadequacy of current therapies for chronic pain. Thus, it is urgent to understand the fundamental mechanisms of chronic pain and develop more effective therapies. The overall objectives of our project are to understand the mechanisms underlying chronic pain and identify novel targets for better and safer medicines for chronic pain treatment. Acute pain that resolves quickly is a commonly experienced mechanism of survival. Chronic pain, which may persist for years, is associated with inflammatory diseases, peripheral and central neuropathies, cancer, and other diseases, and is a distinct and debilitating condition that affects 25% of European adults. Although activation of pathways in the central nervous system (CNS) contributes to chronic pain, it commonly has its origin from inflammation or tissue damage in the periphery. The hypothesis underlying the project is that, while acute pain is generated by stimulation of receptors and channels expressed in nociceptor nerve terminals, the subsequent chronic mechanical, thermal, and chemical hypersensitivity, the landmark of chronic pain, is sustained via the critical contribution of Schwann cells. Schwann cells (the counterpart of oligodendrocytes of the CNS) are glial cells that wrap, protect, and nourish peripheral nerve fibers. We hypothesized that these glial cells are targeted by a variety of endogenous or exogenous agents to sustain chronic pain with their repertoire of channels, receptors, and enzymes. The specific objectives of our project are to identify the role of Schwann cells in sustaining chronic pain in different mouse models of human diseases (cancer, nerve damage, inflammation, migraine, and others). To this purpose, we have developed innovative tools to selectively delete (or express) genes and related proteins in Schwann cells. This strategy has enabled the identification of novel targets for better and safer analgesic drugs.
Over the five years of the SCOPE project, we showed a major role of TRPA1 in sensing and amplifying oxidative stress (OxStress) generated by macrophages recruited from the bloodstream following ischemia and reperfusion injury in the mouse hind limb and in a model of chemotherapeutic-induced peripheral neuropathy caused by the drug thalidomide. In the central nervous system, we reported that pain and various markers of demyelination in mouse models of multiple sclerosis were attenuated by antioxidants and TRPA1 antagonists. In a model of cancer pain (using melanoma or lung cancer cells), macrophage colony-stimulating factor expanded endoneurial resident macrophages. The resulting OxStress targeted Schwann cell TRPA1, which amplified OxStress signals to induce pain via neuronal TRPA1. In metastatic bone cancer pain caused by breast cancer in mice, insulin-like growth factor-1 (IGF-1) mediated pain by a similar mechanism involving Schwann cells. Calcitonin gene-related peptide (CGRP), released from trigeminal nerve terminals, mediates neurogenic inflammation—leading to vasodilation, pain hypersensitivity, and migraine pain. However, it remains unclear where CGRP engages its receptor to produce migraine pain. We discovered that CGRP binding to its receptor on Schwann cells, results in receptor internalization in endosomes that sustains pain signal. Schwann cells adjacent to the nerve fibres releasing CGRP are both necessary and sufficient to evoke migraine pain. Fibromyalgia pain, now characterized as ‘nociplastic,’ remains poorly understood. Selective silencing of TRPA1 in Schwann cells reduced allodynia and neuroinflammation (OxStress and macrophage expansion) in the sciatic nerve trunk in a mouse model of fibromyalgia. Endometriosis is characterized by episodes of severe abdominal pain; however, approximately 60% of women also experience headache and other types of pain. The complement component C5a diffuses from pelvic lesions and signals widespread pain via its receptor (C5aR1) on Schwann cells. Prostaglandin E2 (PGE2) is a major mediator of inflammatory pain. However, the mechanisms underlying inflammatory pain remain poorly understood. We discovered that selective silencing of EP2 receptors in Schwann cells eradicated inflammatory pain without affecting inflammation. This unexpected finding decouples inflammatory pain from inflammation and its protective role, opening new avenues for the development of safer, more effective drugs than NSAIDs. Results from the SCOPE project support the hypothesis that Schwann cells integrate signals between nerve fibres and the surrounding environment, thereby promoting hypersensitivity. The Principal Investigator (PI) participated in numerous meetings, from 2021 to 2025: 16 international and 18 national meetings. His collaborators also participated in 7 international and 8 national meetings, during which the results of the SCOPE project were highlighted. The University of Florence organized videos, student meetings, and other outreach events to promote the project's core ideas and findings. Additionally, interviews were conducted with secular press outlets across Europe and the United States. The PI was awarded an ERC Proof-of-Concept grant (GAP-101113466) for the PAIN-CARE project, which builds upon the results obtained from the SCOPE project. To facilitate the technological transfer of the results from both the SCOPE and PAIN-CARE projects, the PI, along with two collaborators (including Romina Nassini) co-founded the academic spinoff FloNext Srl.
In a series of mouse models and in human Schwann cells, we identified diverse cellular and humoral mediators that share a final common pathway involving the generation of oxidative, nitrative, and carbonylic stress (hereafter referred to as OxStress). OxStress engages the transient receptor potential ankyrin 1 (TRPA1), a receptor known for sensing the pungent spice wasabi. TRPA1 functions not only as a sensor of OxStress but also as a robust amplifier of OxStress signals in rodents. The OxStress/TRPA1 pathway is also involved in the development of mechanical allodynia caused by inflammation (such as prostaglandin E2 (PGE2), carrageenan, or complete Freund’s adjuvant). Our results led us to conclude that the pain pathway identified in vivo in mice and rats may be recapitulated at the intracellular level in rodent Schwann cells and, importantly, in human Schwann cells. The SCOPE project provided compelling evidence that Schwann cells are key checkpoints mediating mechanical hypersensitivity, a major mechanism underlying chronic pain. This checkpoint activity is mediated through a series of intracellular mediators that may collectively be referred to as the ‘schwannsome’. We anticipate that individual elements of the ‘schwannsome’ could serve as druggable targets for the development of safer and more effective analgesic medicines.