α-Chaconine Facilitates Chondrocyte Pyroptosis and Nerve Ingrowth to Aggravate Osteoarthritis Progression by Activating NF-κB Signaling

Abstract

Background: With the rapid growth of the elderly population, the incidence of osteoarthritis (OA) increases annually, which has attracted extensive attention in public health. The roles of dietary intake in controlling joint disorders are perhaps one of the most frequently posed questions by OA patients, while the information about the interaction between dietary intake and OA based on scientific research is limited. α-Chaconine is the richest glycoalkaloid in eggplants such as potatoes. Previous evidence suggests that α-Chaconine is a toxic compound to nervous and digestive systems with potentially severe and fatal consequences for humans and farm animals, but its effect on OA development remains obscure.

Objective: To determine whether α-Chaconine deteriorates OA progression through sensory innervation and chondrocyte pyroptosis via regulating nuclear factor-κB (NF-κB) signaling, providing evidence for a possible linkage between α-Chaconine and OA progression.

Methods: We established a mouse OA model by destabilization of medial meniscus (DMM) surgery and then intra-articular injection of 20 or 100 μM α-Chaconine into the OA mice for 8 and 12 weeks. The severity of OA progression was evaluated by histological staining and radiographic analyses. The expressions of matrix metabolic indicators, Col2, Mmp3, and Mmp13, as well as pyroptosis-related proteins, Nlrp3, Caspase-1, Gsdmd, IL-1β, IL-18, were determined by immunohistochemistry. And the changes in sensory nerve ingrowth and activity of NF-κB signaling were determined by immunofluorescence.

Results: We found that α-Chaconine could exacerbate mouse OA progression, resulting in subchondral sclerosis, osteophyte formation, and higher OARSI scores. Specifically, α-Chaconine could augment cartilage matrix degradation and induce chondrocyte pyroptosis and nerve ingrowth. Mechanistical analysis revealed that α-Chaconine stimulated NF-κB signaling by promoting I-κB α phosphorylation and p65 nuclear translocation.

Conclusion: Collectively, our findings raise the possibility that α-Chaconine intake can boost chondrocyte pyroptosis and nerve ingrowth to potentiate OA progression by activating NF-κB signaling.

Keywords: NF-κB signaling; nerve ingrowth; osteoarthritis; pyroptosis; α-Chaconine.

Graphical abstract

Figure 1

Schematic design of the project.

Figure 2

α-Chaconine (α-Cha) deteriorates OA progression. (A) Safranin O/Fast green staining of cartilage. (B) OARSI scores for cartilage structure damage in (A). (C-C’) Representative three-dimensional images of knee joints. Three-dimensional reconstructions of knee joints in (C) and osteophytes (C’) were used to visualize calcification of meniscus and osteophyte formation 8- and 12-week after DMM surgery. Yellow triangles indicated osteophytes. (D–H) Statistical results of bone morphological parameters in (C). Data were expressed as the mean ± SD. *P < 0.05, **P < 0.01 vs Sham group, ^#P < 0.05, ^##P < 0.01 vs Vehicle group.

Figure 3

α-Chaconine accelerates articular cartilage matrix degradation. (A–C) Immunohistochemistry results of Col2, Mmp3, and Mmp13 proteins. (D–F) The ratios of immunoreactive positive cells of Col2, Mmp3, and Mmp13 in (A–C). Data were expressed as the mean ± SD. **P < 0.01 vs Sham group, ^#P < 0.05, ^##P < 0.01 vs Vehicle group.

Figure 4

α-Chaconine promotes chondrocyte pyroptosis. (A–E) Immunohistochemistry staining results of Nlrp3, Caspase-1, Gsdmd, IL-1β, and IL-18 proteins in articular cartilage 8- and 12-week post-DMM surgery. (F–J) The ratios of immunoreactive positive cells of Nlrp3, Caspase-1, Gsdmd, IL-1β, and IL-18 in (A–E). Data were expressed as the mean ± SD. **P < 0.01 vs Sham group, ^#P < 0.05, ^##P < 0.01 vs Vehicle group.

Figure 5

α-Chaconine recruits sensory nerve ingrowth in subchondral bone. (A and B) Immunofluorescence staining of Cgrp and Netrin-1 in subchondral bone 8- and 12-Week post-surgery. (C and D) Quantification of Cgrp-positive cells and positive staining of Netrin-1 in cartilage. (E and F) Quantification of Cgrp-positive cells and positive staining of Netrin-1 in subchondral bone. Red arrows indicated Cgrp-positive neurons and positive expression of Netrin-1. Data were expressed as the mean ± SD. **P < 0.01 vs Sham group, ^#P < 0.05, ^##P < 0.01 vs Vehicle group.

Figure 6

α-Chaconine activates NF-κB signaling pathway of knee joint. (A and B) Immunofluorescence staining of p65 and p-i-κBα both in articular cartilage and subchondral bone 8 and 12-week post-surgery. (C and D) Quantification of p65 and p-i-κBα positive cells in cartilage. (E and F) Quantification of p65 and p-i-κBα positive cells in subchondral bone. Red arrows indicate the positive expression of p65 and p-i-κBα. Data are expressed as the mean ± SD. **P < 0.01 vs Sham group, ^##P < 0.01 vs Vehicle group.

Figure 7

A schematic diagram illustrating the role of α-Chaconine in exacerbating OA progression.