The Dual Role of NaV1.7
in Osteoarthritis

By Alomone Team • March 2024

A novel description of a sodium channel in chondrocytes with potential for pain relief and cartilage protection

Osteoarthritis (OA) is not only a condition affecting hundreds of million people worldwide, but it’s also a debilitating disease as the joint cartilage degrades, which leads to pain and loss of mobility. Coupled with its high prevalence, treatments that halt the progression of OA or help manage pain without opioids are scarce. However, recent research, published in Nature (1), has highlighted the voltage-gated sodium channel (VGSC) NaV1.7 as a potential therapeutic target.

NaV1.7 Expression in OA Chondrocytes

While VGSCs have been previously described in the perception of pain (2), their expression in chondrocytes and how this might relate to OA has been a mystery. To begin answering this question, the researchers looked at VGSCs in human chondrocytes, as well as NaV1.7 in tissue from OA patients. Using RT-qPCR, the researchers demonstrated that that while six VGSCs (CN2A, SCN3A, SCN4A, SCN8A, SCN9A and SCN11A) were expressed in chondrocytes, only NaV1.7 (encoded by the SCN9A gene) showed significant upregulation in OA cartilage. They then ran immunoassays (using our Anti-NaV1.7 (SCN9A) Antibody (#ASC-008) for Western blot and IHC) to show that the upregulation of NaV1.7 was seen at the protein level across different stages of OA severity (Figure 1). These results laid groundwork for the rest of the investigation as they began to link the presence of NaV1.7 with the progression of OA – distinguishing it from NaV1.7’s previously understood role in pain signaling.

Figure 1. OA Chondrocytes Express Elevated Nav1.7 Levels

Adapted from Extended Data Figure 1, Fu et al. (1). a, Expression of 9 distinct VGSCs in the human C28I2 chondrocyte cell line. b, Relative expressions of VGSCs in RNA-sequencing data of human cartilage isolated from OA versus healthy subjects. c, Relative RT-qPCR expression levels of VGSCs expressed in human chondrocytes treated with TNFα or IL-1β. d, RT-qPCR analysis of SCN9A in human cartilage from healthy individuals, and from individuals with early stage (KL1-2) or late stage OA (KL 3-4). e, Western blot expression of NaV1.7 in cartilage from healthy individuals and OA patients with KL grade 1-2 or 3-4 OA. f, Membrane localization of NaV1.7 in human chondrocytes by Western blot. g, Immunohistochemistry (IHC) of NaV1.7 in cartilage from healthy individuals and from individuals with late stage OA; scale bar = 100 µm. h, IHC of NaV1.7 in cartilage collected from mice subjected to sham or DMM surgery; scale bar = 100 µm.

Understanding NaV1.7 by Deletion and Modulation

With NaV1.7’s expression confirmed in chondrocytes, the team moved on to exploring the channel’s specific role in OA. To isolate any specific effects of NaV1.7 on cartilage health and OA progression, they created mouse models with tissue-specific NaV1.7 channel knockouts in dorsal root ganglion (DRG) neurons and in chondrocytes, or in chondrocytes alone. They then used a surgical model of OA known as destabilization of the medial meniscus (DMM) – generally regarded as the ‘gold standard’ for studying the onset and progression of post-traumatic OA (3) – alongside a chemical model using monoiodoacetate (MIA) injection.

Mice lacking NaV1.7 in chondrocytes had significant protection against OA-related cartilage degradation, osteophyte formation, and synovitis in both surgically and chemically induced OA models. These mice also displayed reduced OA-related pain behaviors. Conversely, deleting NaV1.7 in DRG neurons only mitigated pain, without influencing OA’s structural damage.

Since the knockout work showed that NaV1.7 deletion had positive effects, this raised the question whether a pharmacological intervention could produce similar results. To test this, the researchers looked at the effects of NaV1.7 blockade using PF-04856264 (#P-265) – a selective NaV1.7 blocker we make in-house. They found that treating mice with PF-04856264 locally or systemically preserved articular cartilage structure, maintained proteoglycan content, and reduced OA severity – including lower Osteoarthritis Research Society International (OARSI) histopathology scores – and decreased osteophyte formation in both the surgical and chemical OA models. This NaV1.7 blockade also reduced OA pain behavior, increased type II collagen (COL2) levels, and decreased cartilage catabolic markers like MMP13 and aggrecan neoepitope levels (Figure 2).

In summary, PF-04856264 not only preserved cartilage structure but also mitigated OA pain, and it’s this finding that lends real weight to the idea of using a NaV1.7 blocker as a potential therapeutic.

Figure 2. Pharmacological blockade of NaV1.7 is therapeutic against OA histopathology and OA-related pain

Adapted from Extended Data Figure 5, Fu et al. (1). a, Experimental timeline. b, Knee joint histology of DMM-operated WT male mice treated with or without PF-04856264 for 8 weeks; scale bar = 50 µm. c-e, Quantitation of OARSI score (c), osteophyte development (d) and SBP thickness (e) in DMM-operated WT male mice treated with or without PF-04856264 for 8 weeks. f, g, Quantitation of 2 min travel distance (f) and von Frey testing (g) in DMM-operated WT male mice treated with or without PF-04856264 at the indicated time-points after surgery. h, i, IHC (h) and corresponding quantification (i) of Col2, Mmp13, and Aggrecan neoepitope in knee joint sections of DMM operated WT male mice treated with or without PF-04856264 for 8 weeks; scale bar = 50 µm in h. j, Knee joint histology of DMM-operated WT female mice treated with or without PF-04856264 for 8 weeks; scale bar = 50 µm. k-m, Quantitation of OARSI score (k), osteophyte development (l) and SBP thickness (m) in DMM-operated WT female mice treated with or without PF-04856264 for 8 weeks. n, o, Quantitation of 2 min travel distance (n) and von Frey testing (o) in DMM-operated WT female mice treated with or without PF-04856264 at the indicated time-points after surgery.

A Promising Target for OA Treatment

This fascinating study makes a major contribution to how we understand OA at the molecular level, detailing NaV1.7 expression in non-excitable cells like chondrocytes and its involvement in cellular functions crucial for OA progression. In addition, this work has presented NaV1.7 blockade as an intriguing dual-purpose target for OA treatment (Figure 3), offering both disease-modifying benefits and non-addictive pain relief, a novel avenue that will come as a relief to those living with the condition.

Figure 3. NaV1.7 expressed in chondrocytes and DRG neurons contributes to modulating OA joint degradation and pain

Adapted from Figure 2m, Fu et al. (1). Schematic model of NaV1.7 regulation of OA pathophysiology in chondrocytes and DRG neurons. Left panel, NaV1.7 blockade stops Na⁺ influx, stimulating Ca²⁺ influx through NCX1 which leads to protective effects through HSP70 and midkine upregulation. Right panel, NaV1.7 expression in DRG and cartilage contribute to joint histopathology, inflammation, and pain, which are ameliorated via NaV1.7 blockade.

References

1. W. Fu, D. Vasylyev, Y. Bi, M. Zhang, G. Sun, A. Khleborodova, G. Huang, L. Zhao, R. Zhou, Y. Li, S. Liu, X. Cai, W. He, M. Cui, X. Zhao, A. Hettinghouse, J. Good, E. Kim, E. Strauss, P. Leucht, R. Schwarzkopf, E. X. Guo, J. Samuels, W. Hu, M. Attur, S. G. Waxman, C. Liu, NaV1.7 as a chondrocyte regulator and therapeutic target for osteoarthritis. Nature 625, 557–565 (2024). DOI: https://doi.org/10.1038/s41586-023-06888-7.

2. S. D. Dib-Hajj, T. R. Cummins, J. A. Black, S. G. Waxman, Sodium channels in normal and pathological pain. Annu Rev Neurosci 33, 325–347 (2010). DOI: https://doi.org/10.1146/annurev-neuro-060909-153234.

3. K. L. Culley, C. L. Dragomir, J. Chang, E. B. Wondimu, J. Coico, D. A. Plumb, M. Otero, M. B. Goldring, Mouse models of osteoarthritis: surgical model of posttraumatic osteoarthritis induced by destabilization of the medial meniscus. Methods Mol Biol 1226, 143–173 (2015). DOI: https://doi.org/10.1007/978-1-4939-1619-1_12.

Antibodies
Anti-NaV1.7 (SCN9A) Antibody (#ASC-008)

Pharmacological Tools
• Tetrodotoxin citrate (TTX) (#T-550)
• PF-04856264 (#P-265)
• ProTx-II (#STP-100)