Proton-activated chloride channel increases endplate porosity and pain in a mouse spine degeneration model
Peng Xue, Weixin Zhang, Mengxi Shen, Junhua Yang, Jiachen Chu, Shenyu Wang, Mei Wan, Junying Zheng, Zhaozhu Qiu, Xu Cao
Peng Xue, Weixin Zhang, Mengxi Shen, Junhua Yang, Jiachen Chu, Shenyu Wang, Mei Wan, Junying Zheng, Zhaozhu Qiu, Xu Cao
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Research Article Bone biology Cell biology

Proton-activated chloride channel increases endplate porosity and pain in a mouse spine degeneration model

Abstract

Chronic low back pain (LBP) can severely affect daily physical activity. Aberrant osteoclast-mediated resorption leads to porous endplates, which allow the sensory innervation that causes LBP. Here, we report that expression of the proton-activated chloride (PAC) channel was induced during osteoclast differentiation in the porous endplates via a RANKL/NFATc1 signaling pathway. Extracellular acidosis evoked robust PAC currents in osteoclasts. An acidic environment of porous endplates and elevated PAC activation–enhanced osteoclast fusion provoked LBP. Furthermore, we found that genetic knockout of the PAC gene Pacc1 significantly reduced endplate porosity and spinal pain in a mouse LBP model, but it did not affect bone development or homeostasis of bone mass in adult mice. Moreover, both the osteoclast bone-resorptive compartment environment and PAC traffic from the plasma membrane to endosomes to form an intracellular organelle Cl channel had a low pH of approximately 5.0. The low pH environment activated the PAC channel to increase sialyltransferase St3gal1 expression and sialylation of TLR2 in the initiation of osteoclast fusion. Aberrant osteoclast-mediated resorption is also found in most skeletal disorders, including osteoarthritis, ankylosing spondylitis, rheumatoid arthritis, heterotopic ossification, and enthesopathy. Thus, elevated Pacc1 expression and PAC activity could be a potential therapeutic target for the treatment of LBP and osteoclast-associated pain.

Authors

Peng Xue, Weixin Zhang, Mengxi Shen, Junhua Yang, Jiachen Chu, Shenyu Wang, Mei Wan, Junying Zheng, Zhaozhu Qiu, Xu Cao

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Figure 4

Extracellular acidosis evokes the ICl, H current in the cell membrane of osteoclasts by activating PAC.

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Extracellular acidosis evokes the ICl, H current in the cell membrane of...
(A) Relative mRNA expression levels of Pacc1 in the cells isolated from Pacc1+/+ mice; cells were cultured in neutral or acidic medium at 1, 3, and 5 days (n = 3). (B and C) Protein levels of PAC in the cells isolated from Pacc1+/+ or Pacc1–/– mice cultured in neural or acidic medium at 1, 3, and 5 days (n = 3). (D) Representative images of coimmunofluorescence staining for PAC (green) and TRAP (red) in human bone section. DAPI (blue). Scale bars: 200 μm and 100 μm. (E) PAC currents monitored by a voltage-ramp protocol at pH 5.5 in the cells isolated from Pacc1+/+ and Pacc1–/– mice; cells were cultured in osteoclastic medium for 3 days. (F) PAC-mediated current densities measured at +100 mV in cells isolated from Pacc1–/– (red) and Pacc1+/+ (black) mice; cells were cultured in osteoclastic medium for 3 days, at pH 5.0, 5.5, 6.0, and 7.3 at 37°C (n ≥7). (E and F) **P < 0.01 and ****P < 0.001 compared with cells isolated from Pacc1+/+ mice. Significance was determined by 2-way ANOVA (A and C) and 1-way ANOVA (F). Data are presented as the mean ± SD.