Summary: The Orai1 class of calcium channels regulates sex differences in immune cell functioning associated with neuroinflammation and neuropathic pain.
Source: Northwestern University
Northwestern Medicine researchers have found that specific calcium channels help regulate sex differences in immune cell function for neuroinflammation and overall neuropathic pain, according to findings published in Scientists progress.
“This study highlights the importance of Orai1-mediated microglial calcium signaling contributing to neuropathic pain. Driskill Graduate Program in Life Sciences (DGP) and co-first author of the study.
Murali Prakriya, Ph.D., professor of pharmacology at Magerstadt and professor of medicine in the division of allergy and immunology, was the study’s senior author.
Microglia are the primary immune cells of the brain and resemble macrophages found in the peripheral immune system. Microglia detect and eliminate harmful pathogens and dying cells and stimulate other immune cells that trigger effective immune responses in the brain. In addition to their surveillance functions, in healthy brains, microglia also influence the formation of synapses, or connections, between neurons, which impact neural circuits and regulate overall cognitive functions.
On the other hand, microglia can also cause persistent neuroinflammation and neuropathic pain, including chronic pain caused by nerve damage, and produce pro-inflammatory cytokines that cause uncontrolled neuroinflammation. Microglia can also cause long-lasting changes in synaptic circuitry in the central nervous system to improve pain sensation, according to Prakriya.
“Signals in the spinal cord that do not normally activate pain circuits are altered such that after nerve injury the same signals are relayed through the spinal cord to the upper brain’s somatosensory brain structure. This change is mediated in part by inflammatory mediators, cytokines produced by spinal microglia,” said Prakriya, who is also a member of the Robert H. Lurie Comprehensive Cancer Center at Northwestern University.
Prakriya’s lab discovered a class of calcium channels called Orai1 channels over a decade ago and since then has continued to study their essential role in immune cell activation.
In the current study, Prakriya’s team aimed to determine what role Orai1 plays in microglial activation and neuropathic pain following nerve injury.
Using Orai1 microglial knockout mouse models, they found that when Orai1 function was blocked or suppressed, Orai1-mediated calcium signaling was lost, ultimately reducing the production of inflammatory cytokines.
“This is an important finding because it implicates Orai1 as a checkpoint, if you will, in the cascade of events that leads to the production of inflammatory cytokines that lead to pain hypersensitivity,” Prakriya said.
Next, the researchers compared measures of pain hypersensitivity after sciatic nerve injury in mouse models. Surprisingly, they identified distinct differences in pain hypersensitivity in male mice compared to female mice lacking Orai1.
Specifically, they found that loss of Orai1 attenuated pain hypersensitivity in male mice, but not in female mice. This has prompted investigators to further investigate the causes of sexual dimorphism in pain perception.
Using spinal cord electrophysiology techniques, they found that in Orai1 knockout male microglial mice, the potentiation, or increased strength, of synaptic transmission that occurs after nerve injury was reduced. Male mice also showed reduced induction of inflammatory cytokines in spinal cord tissue in response to nerve injury, but this was not seen in female mice.
“There is no change in neuropathic pain perception in female mice because there is no change in maladaptive synaptic potentiation that occurs downstream of inflammatory cytokines produced by microglia. Because maladaptive synaptic potentiation is likely the critical step that drives neuropathic pain, it explains why there is attenuation in male but not female mice,” Prakriya said.
Using a microglial staining technique called IBA1 staining, researchers found that although microglial activation was increased equally in male and female mice, inhibited Orai1 function reduced the extent of microglial activation in mice. males but not females.
They then gave male and female mice a small-molecule Orai1 inhibitor compound called CM4620, which is currently being tested in clinical trials, and found that while the drug alleviated neuropathic pain in male mice, it had no no effect on female mice.
The results demonstrate that Orai1 channels are key mediators of microglia-induced neuroinflammation and the sexually dimorphic role of microglia in neuropathic pain, highlighting the importance of developing sex-specific targeted therapies in the future.
“This study highlights striking sex differences in the mechanisms underlying pain hypersensitivity between males and females. We are currently working to determine whether Orai1 signaling can be manipulated in other immune cells to relieve pain in female mice,” Prakriya said.
About this Neuroscience, Inflammation and Neuropathy Research News
Author: Melissa Rohman
Source: Northwestern University
Contact: Melissa Rohman – Northwestern University
Picture: Image is credited to Prakirya Lab
Original research: Free access.
“Regulation of neuropathic pain by Orai1 microglial channelsby Shogo Tsujikawa et al. Scientists progress
Regulation of neuropathic pain by Orai1 microglial channels
Microglia is an important mediator of neuroinflammation, which underlies neuropathic pain. However, the molecular checkpoints controlling microglial reactivity are not well understood.
Here, we investigated the role of Orai1 channels in microglia-mediated neuroinflammation after nerve injury and found that deletion of Orai1 in microglia attenuates Ca2+ signaling and production of inflammatory cytokines by proalgesic agonists. Conditional deletion of Orai1 attenuated microglial proliferation in the dorsal horn, spinal cytokine levels, and potentiation of excitatory neurotransmission after peripheral nerve injury.
These cellular effects were accompanied by an attenuation of pain hyperalgesia in microglial Orai1 knockout mice. A small-molecule Orai1 inhibitor, CM4620, similarly attenuates allodynia in male mice. Unexpectedly, these protective effects were not observed in female mice, revealing sexual dimorphism in Orai1 regulation of microglial reactivity and hyperalgesia.
Together, these results indicate that Orai1 channels are key regulators of the sexually dimorphic role of microglia for neuroinflammation that underlies neuropathic pain.