Scientists Uncover Hidden Protein Circuit That Keeps Chronic Pain Switched On

Chronic pain affects hundreds of millions of people worldwide, and for many of them the suffering begins with an injury that should have healed. When a peripheral nerve, the kind of nerve that runs outside the brain and spinal cord, is damaged and fails to recover properly, it can continue firing pain signals long after the original wound is gone. That relentless barrage of signals does not simply pass through the nervous system unnoticed. Over time, it reshapes how the spinal cord and brain process sensory information, leaving sensory and emotion-associated circuits in a state of hyper-reactivity that effectively turns up the volume on pain. Researchers at Boston University Chobanian & Avedisian School of Medicine now report that they have identified a molecular mechanism at the heart of this process, and that blocking it allowed experimental models to return to a calm, normal neurological state.

The discovery centers on a protein called RGS4, which the team found acts as a kind of intracellular circuit governing whether pain sensitivity normalizes after an injury or becomes locked in place. In experiments described in the journal Science Signaling, the researchers blocked RGS4 in the dorsal root ganglia, clusters of sensory nerve cells that innervate the lumbar spinal cord. When they did so in experimental models of neuropathic pain, the nervous system recovered from its abnormal, hypersensitive condition. Conversely, when the scientists increased RGS4 levels, otherwise uninjured models became more sensitive to pain, demonstrating that the protein is not merely a passive marker of injury but an active driver of the transition to persistent pain.

The dorsal root ganglia are a logical place for such a switch to reside. These structures contain the cell bodies of sensory neurons that relay touch, temperature, and pain information from the body toward the spinal cord. Because they sit outside the blood-brain barrier’s protective envelope and outside the central nervous system proper, they are more accessible to targeted therapies than circuits deep within the brain. The Boston University team’s finding that RGS4 operates within these sensory nerve cells suggests that the maintenance of chronic pain may depend on molecular changes occurring in the periphery, rather than exclusively on rewiring within the spinal cord or brain.

RGS4 belongs to a family of regulator of G-protein signaling proteins, molecules that modulate how long intracellular signaling pathways remain active after a receptor on the cell surface is stimulated. By accelerating the deactivation of G-protein signaling, RGS proteins shape the intensity and duration of the messages a neuron sends. In the context of nerve injury, the new research indicates that RGS4 activity contributes to maladaptations, molecular and behavioral changes that keep sensory neurons unusually excitable. Venetia Zachariou, PhD, the Edward Avedisian Professor and chair of the department of pharmacology, physiology & biophysics at the school and the study’s corresponding author, explained that one reason pain may become chronic is that the sensory nerves themselves undergo molecular changes that keep them unusually sensitive.

To establish the protein’s role, the researchers used several groups of experimental models in which they could manipulate RGS4 in different ways. In some groups they removed the protein entirely, in others they reduced it specifically in sensory nerve cells, and in still others they increased its levels. This range of approaches allowed them to test whether the effects they observed were genuinely attributable to RGS4 rather than to compensatory developmental changes or off-target effects. They then assessed the functional consequences across a spectrum of chronic pain conditions, including peripheral nerve injury, postoperative pain, inflammatory pain, and chemotherapy-induced nerve damage, a breadth that strengthens the case that RGS4 is a general mechanism of pain chronification rather than a quirk of a single model.

The results carry particular weight because current treatments for chronic pain remain inadequate. Existing painkillers, including opioids such as morphine, largely mask the sensation of pain rather than addressing the biological processes that sustain it, and they can cause significant side effects, including the risk of dependence that has fueled a public health crisis. Many patients with neuropathic pain find little relief from any available medication. The Boston University team argues that the field needs therapies that interrupt the processes causing pain to persist in the first place, rather than simply dampening pain signals after chronic pain has already taken hold.

Zachariou emphasized that the findings point toward exactly that kind of intervention. Inhibition of RGS4, she noted, can be an effective way to manage neuropathic pain conditions and possibly other forms of chronic pain. Because the pathway can be manipulated in sensory nerve cells outside the brain and spinal cord, it may offer opportunities to develop more targeted treatments while potentially limiting effects elsewhere in the nervous system. That peripheral specificity matters enormously for drug development, since medications that act broadly on the central nervous system often produce sedation, cognitive effects, or addiction liability that limit their usefulness.

Importantly, the researchers also found that the main players controlling the maintenance of chronic pain in their experimental models are expressed in human nerve tissue as well. This conservation across species raises the possibility that RGS4 functions the same way in people, a critical prerequisite for translating the work into clinical therapies. While the study itself was conducted in experimental models, the presence of the relevant molecular machinery in human sensory neurons provides a plausible route from bench to bedside, and it suggests that biomarkers based on RGS4 activity could eventually help identify which patients are most likely to benefit from such treatments.

The broader significance of the work lies in its reframing of what chronic pain is. Rather than viewing persistent pain as simply a louder version of acute pain, the research supports a model in which chronic pain is a disease state sustained by specific, potentially reversible molecular adaptations in sensory neurons. Understanding the detailed mechanisms that control the transition from acute to chronic pain, and the maintenance of chronic pathological pain, the researchers argue, would be essential to guide the development of effective and safer medications. If the maladaptations can be reversed, as the RGS4 experiments suggest, then chronic pain may not be a permanent sentence but a treatable condition.

For patients, the hope is that future therapies built on this discovery could do what morphine and other current analgesics cannot: allow the nervous system itself to reset. Rather than simply masking pain after it becomes chronic, Zachariou said, the team hopes this work contributes to therapies that interrupt the biological processes that cause pain to persist in the first place. The findings appear online in Science Signaling, and the research was supported by National Institutes of Health funding including grants R01NS135775, R01NS117101, F31NS115318, and T32GM159592. As the opioid epidemic continues to highlight the dangers of symptomatic pain relief, mechanistic discoveries like this one offer a glimpse of a different future, one in which the circuits that keep pain alive are switched off at their source.

Subject of Research: The role of the RGS4 protein in dorsal root ganglia sensory neurons in the initiation and maintenance of chronic neuropathic pain

Article Title: BU researchers discover intracellular circuit responsible for chronic pain

Article References: BU researchers discover intracellular circuit responsible for chronic pain. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: chronic pain, neuropathic pain, RGS4, dorsal root ganglia, sensory neurons, Boston University School of Medicine, Science Signaling, peripheral nerve injury, pain chronification, drug targets, G-protein signaling, opioid alternatives