Researchers from multiple international institutions have identified the specific molecular signature of "sleeping nociceptors," a type of pain-sensing nerve cell often inactive but implicated in chronic neuropathic pain. This identification provides a foundational understanding of these neurons at a genetic level and suggests new targets for developing treatments to alleviate persistent pain.
Understanding Sleeping Nociceptors
Sleeping nociceptors are sensory nerve cells that typically remain inactive, being unresponsive to touch or pressure. However, under certain conditions, they can become overactive and fire spontaneously, contributing to chronic pain without an external stimulus. Their cell bodies are located in the dorsal root ganglia, nerve cell clusters near the spine responsible for transmitting sensory signals.
Neuropathic pain, frequently associated with abnormal activity in these cells, affects approximately ten percent of the global population, with estimates indicating it affects around 20% of American adults. Active sleeping nociceptors have been observed in individuals with conditions such as diabetic neuropathy, postherpetic neuralgia, and fibromyalgia.
Prior to this research, while the functional properties of these neurons were known, their precise molecular identity, or genetic fingerprint, remained undefined, which hindered the development of targeted therapies.
Research Methodology
An international team, led by Dr. Angelika Lampert of Uniklinik RWTH Aachen and Dr. Shreejoy Tripathy from the Centre for Addiction and Mental Health (CAMH) and the University of Toronto, conducted the research. The methodology involved simultaneously measuring the electrical behavior and genetic activity of individual neurons.
Co-first author Dr. Jannis Körner utilized Patch-Seq, a technique that combines electrophysiology with single-cell genetic sequencing, to record electrical activity. These data were then integrated with bioinformatics analyses led by co-first author Derek Howard and Dr. Tripathy.
Initial studies were conducted using isolated dorsal root ganglia from pigs, which possess sleeping nociceptors structurally similar to those in humans. Cross-species analyses confirmed that the same molecular markers identified were present in both pig and human sensory neurons. Further validation included psychophysics experiments demonstrating that oncostatin M specifically modulates sleeping nociceptors in human skin.
Molecular Identifiers and Potential Targets
The analyses revealed that sleeping nociceptors possess a distinct molecular signature, which includes:
- The oncostatin M receptor (OSMR)
- The neuropeptide somatostatin (SST)
Additionally, the research identified the ion channel Nav1.9 as highly expressed in sleeping nociceptors, influencing their electrical properties and presenting another potential drug target.
The activation of OSMR by oncostatin M was found to specifically modulate sleeping nociceptors in human skin.
Implications for Treatment
The identification of these molecular characteristics establishes a framework for understanding the molecular basis of neuropathic pain. This work provides specific targets and avenues for the development of new, targeted therapies.
The researchers suggest that selectively quieting these pain-causing neurons, potentially by targeting Nav1.9 or other identified molecules, could lead to novel medications. The team aims to initiate drug discovery projects based on this comprehensive dataset.
Collaborative Effort
The research involved contributions from various institutions including CAMH, Uniklinik RWTH Aachen, The University of Texas at Dallas, the University of Toronto, Harvard Medical School, King's College Hospital in London, and several German universities. The project also included contributions from the NIH-funded PRECISION Network, which focuses on solutions to the opioid crisis. Funding for the study was provided by grants from the NIH, the German Research Foundation, and other organizations.