Identification and targeting of a unique NaV1.7 domain driving chronic pain, 2023, Gomez et al.

[SNT Gatchaman]

Identification and targeting of a unique NaV1.7 domain driving chronic pain
Gomez, Kimberly; Stratton, Harrison J.; Duran, Paz; Loya, Santiago; Tang, Cheng; Calderon-Rivera, Aida; François-Moutal, Liberty; Khanna, May; Madura, Cynthia L.; Luo, Shizhen; McKiver, Bryan; Choi, Edward; Ran, Dongzhi; Boinon, Lisa; Perez-Miller, Samantha; Damaj, M. Imad; Moutal, Aubin; Khanna, Rajesh

Significance
The voltage-gated sodium channel isoform 1.7 (NaV1.7) has been widely implicated in chronic pain. We have discovered a unique intracellular region of NaV1.7 that facilitates its regulation by intracellular auxiliary proteins and which can be targeted to ameliorate chronic pain. Targeting this sequence produces robust reversal of mechanical allodynia in preclinical models of nerve injury, as well as a model of chemotherapy-induced peripheral neuropathy. A plasmid coding for this sequence packaged inside a viral capsid reduced NaV1.7 current density and neuropathic pain. The translational utility of our approach is illustrated by the finding that our genetic therapy reduced NaV1.7 function in macaque DRG neurons, which shares complete sequence homology with human NaV1.7.

Abstract
Small molecules directly targeting the voltage-gated sodium channel (VGSC) NaV1.7 have not been clinically successful. We reported that preventing the addition of a small ubiquitin-like modifier onto the NaV1.7-interacting cytosolic collapsin response mediator protein 2 (CRMP2) blocked NaV1.7 function and was antinociceptive in rodent models of neuropathic pain.

Here, we discovered a CRMP2 regulatory sequence (CRS) unique to NaV1.7 that is essential for this regulatory coupling. CRMP2 preferentially bound to the NaV1.7 CRS over other NaV isoforms. Substitution of the NaV1.7 CRS with the homologous domains from the other eight VGSC isoforms decreased NaV1.7 currents. A cell-penetrant decoy peptide corresponding to the NaV1.7-CRS reduced NaV1.7 currents and trafficking, decreased presynaptic NaV1.7 expression, reduced spinal CGRP release, and reversed nerve injury-induced mechanical allodynia. Importantly, the NaV1.7-CRS peptide did not produce motor impairment, nor did it alter physiological pain sensation, which is essential for survival. As a proof-of-concept for a NaV1.7 -targeted gene therapy, we packaged a plasmid encoding the NaV1.7-CRS in an AAV virus. Treatment with this virus reduced NaV1.7 function in both rodent and rhesus macaque sensory neurons. This gene therapy reversed and prevented mechanical allodynia in a model of nerve injury and reversed mechanical and cold allodynia in a model of chemotherapy-induced peripheral neuropathy.

These findings support the conclusion that the CRS domain is a targetable region for the treatment of chronic neuropathic pain.

Link | PDF (Proceedings of the National Academy of Sciences)

 

[Hutan]

They've reduced the chronic pain of rats without giving them a stern talking to about vicious cycles of fear of movement and deconditioning?

 

[Hutan]

Encoded by the SCN9A gene, NaV1.7 is expressed in nociceptive sensory neurons of the dorsal root ganglion (DRG) (1) and it is a major contributor to human pain signaling (1, 2). Patients carrying activating mutations on SCN9A are burdened with painful heritable syndromes such as inherited erythromelalgia, small-fiber neuropathy, and paroxysmal extreme pain disorder (3). Conversely, SCN9A loss-of-function mutations produce congenital insensitivity to pain (4).

So, NaV1.7 is a type of voltage-gated sodium channel in neurons transmitting the sensation of pain. A protein (CRMP2), when phosphorylated and SUMOlyated, is important in keeping the channel in place on the membrane of the synapse. If you stop the phosphorylation or SUMOlyation, the channel is internalised, and the sensation of pain is not transmitted.

This team found a binding site where the CRMP2 attaches to the channel to activate it. A decoy protein can bind to the channel, but doesn't activate it, stopping the channel from working and so, stopping the pain.

They note that this works with neuropathic pain, but that it doesn't stop physiological pain, which they note is protective. It also doesn't seem to have other bad effects e.g. on motor coordination.

(It's interesting how the authors seem to use 'chronic pain' as a synonym for 'neuropathic pain' - I don't think they are the same things.)

Wikipedia tells me that CRMP2 is expressed in injured neurons (both CNS and peripheral neurons) where it is thought to be associated with nerve regeneration. That all makes sense to me - you damage a nerve, and the CRMP2 activates nerve regeneration and lets you know that you need to protect the tissue.

Wikipedia says:

The expression of CRMPs is altered in neurodegenerative diseases and these proteins likely play an essential role in the pathogenesis of disorders in the nervous system, including Alzheimer's disease, Parkinson's disease, schizophrenia, and many others.

 

[Hutan]

The authors undertook genetic therapy, although I don't think the targeting of that binding site need necessarily be done with genetic therapy:

Viral delivery of the NaV1.7-CRS peptide [the decoy protein] reversed established chronic neuropathic pain, whether from an injury or from a chemotherapeutic agent, but also prevented its development when given before an injury.

We did not observe any signs of toxicity for the duration of our experiment, which lasted for more than one month after the viral injection.

Limitation - in rats, but they think it will work in humans:

Another limitation is that our study primarily relied on rodent pain models, and it has been shown that the pharmacology of NaV1.7 inhibitors can differ between rat and human sensory neurons (27). However, our findings demon- strate that the NaV1.7–CRS interaction is conserved across species, including rat, pig, macaque, and human, suggesting that our obser- vations in rodent tissues may be relevant to human studies.

So, potentially some good options for the control of neuropathic pain

In summary, we discovered a key intracellular domain on NaV1.7, essential for the membrane localization and function of the channel. We demonstrate that this domain can be targeted to reduce the excitability of sensory neurons, spinal neurotransmis- sion and can ultimately abolish chronic neuropathic pain. We expect that the targeting of the CRS domain can be used as a viable strategy for developing future therapeutics that are highly specific and safe for treating chronic pain.

 

[SNT Gatchaman]

So, potentially some good options for the control of neuropathic pain

Yes, interesting that this came out alongside the NEJM papers on NaV1.8 which said that NaV1.7 was proving harder to target effectively. (We had a recent thread on neuropathic pain and microRNAs.)

 

[RedFox]

This is the type of research we should be doing on chronic pain, figuring out the biochemistry of why people experience it. Sometimes (as in fibromyalgic or idiopathic back pain) it occurs in the absence of an obvious injury, perhaps implicating the nervous system.

 

[Hutan]

Of course, people keen on exercise are onto this molecule. I found a study where mice were given regular treadmill exercise, and were found to have reduced phosphorylation of CRMP2:
Treadmill Exercise Reduces Neuroinflammation, Glial Cell Activation and Improves Synaptic Transmission in the Prefrontal Cortex in 3 × Tg-AD Mice, 2022

Spoiler: consideration of whether exercise could reduce relevant phosphorylation of CRMP2

We show that 12-week treadmill exercise beginning in three-month-old mice led to the inhibition of GSK3β kinase activity, decreases in the levels of Aβ oligomers, pro-inflammatory cytokines (IL-1β, IL-6, and TNFα), and the phosphorylation of CRMP2 at Thr514, reduction of microglial and astrocyte activation, and improvement of excitatory and inhibitory synaptic transmission of pyramidal neurons in the prefrontal cortex of 3 × Tg-AD Mice.

In the 2023 study, pain transmission was happening when CRMP2 was phosphorylated.
So, a question is, is phosphorylation of CRMP2 at Thr514 (as was reduced in the exercise mice in the 2022 study) the same as what was happening in the rats with pain in the 2023 study?
The authors of the 2023 study note that CDK5 was doing the phosphorylation, and I found this by googling:

CRMP2 can be phosphorylated at Ser522 by cyclin-dependent kinase 5 (CDK5), which in turn facilitates glycogen synthase kinase 3β (GSK3β)-mediated phosphorylation at Thr509 and Thr514

So, if the mice study is correct, possibly exercise could reduce the phosphorylation of CRMP2, and reduce the activation of the channel transmitting pain signals. Or, the Thr514 site may not have much to do with the functioning of the CRMP2 with respect to the sodium channel for pain transmission.

Edit - I've put this discussion in a spoiler, because, when I looked a bit closer at the mouse study, it turns out that exercise had no effect whatsoever on the phosphorylation of CRMP2 in normal mice. It only had an impact on a specific sort of mouse that supposedly was a model for Alzheimers. So, I don't think the mouse study is evidence for exercise reducing neuropathic pain.

 

[SNT Gatchaman]

See also SARS-CoV-2 N protein interacts with Nav1.7 to promote pathological pain (2025, PAIN)