Exercise following joint distraction inhibits muscle wasting and delays the progression of post-traumatic osteoarthritis in rabbits by activating PGC-1α in skeletal muscle

Abstract

Objective: Muscle wasting frequently occurs following joint trauma. Previous research has demonstrated that joint distraction in combination with treadmill exercise (TRE) can mitigate intra-articular inflammation and cartilage damage, consequently delaying the advancement of post-traumatic osteoarthritis (PTOA). However, the precise mechanism underlying this phenomenon remains unclear. Hence, the purpose of this study was to examine whether the mechanism by which TRE following joint distraction delays the progression of PTOA involves the activation of peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α), as well as its impact on muscle wasting.

Methods: Quadriceps samples were collected from patients with osteoarthritis (OA) and normal patients with distal femoral fractures, and the expression of PGC-1α was measured. The hinged external fixator was implanted in the rabbit PTOA model. One week after surgery, a PGC-1α agonist or inhibitor was administered for 4 weeks prior to TRE. Western blot analysis was performed to detect the expression of PGC-1α and Muscle atrophy gene 1 (Atrogin-1). We employed the enzyme-linked immunosorbent assay (ELISA) technique to examine pro-inflammatory factors. Additionally, we utilized quantitative real-time polymerase chain reaction (qRT-PCR) to analyze genes associated with cartilage regeneration. Synovial inflammation and cartilage damage were evaluated through hematoxylin-eosin staining. Furthermore, we employed Masson's trichrome staining and Alcian blue staining to analyze cartilage damage.

Results: The decreased expression of PGC-1α in skeletal muscle in patients with OA is correlated with the severity of OA. In the rabbit PTOA model, TRE following joint distraction inhibited the expressions of muscle wasting genes, including Atrogin-1 and muscle ring finger 1 (MuRF1), as well as inflammatory factors such as interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α) in skeletal muscle, potentially through the activation of PGC-1α. Concurrently, the production of IL-1β, IL-6, TNF-α, nitric oxide (NO), and malondialdehyde (MDA) in the synovial fluid was down-regulated, while the expression of type II collagen (Col2a1), Aggrecan (AGN), SRY-box 9 (SOX9) in the cartilage, and superoxide dismutase (SOD) in the synovial fluid was up-regulated. Additionally, histological staining results demonstrated that TRE after joint distraction reduced cartilage degeneration, leading to a significant decrease in OARSI scores.TRE following joint distraction could activate PGC-1α, inhibit Atrogin-1 expression in skeletal muscle, and reduce C-telopeptides of type II collagen (CTX-II) in the blood compared to joint distraction alone.

Conclusion: Following joint distraction, TRE might promote the activation of PGC-1α in skeletal muscle during PTOA progression to exert anti-inflammatory effects in skeletal muscle and joint cavity, thereby inhibiting muscle wasting and promoting cartilage regeneration, making it a potential therapeutic intervention for treating PTOA.

Keywords: Exercise; Joint distraction; Muscle wasting; PGC-1α; Post-traumatic osteoarthritis.

Fig. 1

Installation of hinged external fixators after PTOA model establishment, and treadmill training for rabbits. a-b The disassembly and installation of the hinged external fixator c PTOA model establishment d-e Joint extension and flexion following joint distraction f The X-ray examination image following the installation of hinged external fixators g The animal treadmill h-i Rabbits exercising on the treadmill

Fig. 2

Decreased expression of PGC-1α in skeletal muscle in patients correlated with OA severity a-b Western blot analysis was performed to detect and quantify the expression of PGC-1α in the quadriceps muscle. c The Spearman’s rank correlation was calculated between the mRNA expression of PGC-1α and the K-L grade

Fig. 3

TRE following joint distraction inhibited muscle wasting and inflammation by activating PGC-1α in the PTOA model. a-b Western blot analysis was conducted to detect and quantify the expression of PGC-1α and Atrogin-1 in the quadriceps muscle. c-d. The qRT-PCR was performed for measuring the mRNA expression of Atrogin-1, MuRF1, IL-1β and TNF-α. e-h Linear regression analyses were performed to analyze the associations between PGC-1α in muscle and Atrogin-1, IL-1β in muscle, IL-1β in the joint cavity and Col2a1. n = 6

Fig. 4

PGC-1α inhibitors can reduce the effect of TRE following joint distraction in suppressing intra-articular inflammation. a The expression of IL-1β, IL-6 and TNF-α was detected by ELISA. b The expression of NO, MDA and SOD was detected by corresponding assay kits. c The synovial tissue was assessed using HE staining and evaluated based on the synovitis score. Scale bar: 50 μm. n = 6

Fig. 5

Inhibitors of PGC-1α weaken the protective effect of cartilage in response to TRE following joint distraction. a The qRT-PCR was performed for measuring the mRNA expression of Col2a1, AGN and SOX-9. b HE staining, Masson’s trichrome staining, and Alcian blue staining were performed from top to bottom to evaluate the pathological changes in cartilage tissue using the OARSI score. Black scale bar: 50 μm. n = 6

Fig. 6

In the premise of joint distraction, TRE could activate PGC-1α and inhibit muscle wasting in skeletal muscles more effectively than NO TRE. a CTX II expression in the blood was detected using ELISA. b IL-1β expression in the joint cavity was detected using ELISA. b The qRT-PCR was performed for measuring the mRNA expression of IL-1β in skeletal muscle. d-e Western blot was performed to detect and quantify the expression of PGC-1α and Atrogin-1 in quadriceps. n = 6