The Role of Lubricin, Irisin and Exercise in the Prevention and Treatment of Osteoarthritis

A Narrative Review on Adipose Tissue and Overtraining: Shedding Light on the Interplay among Adipokines, Exercise and Overtraining

Lifestyle factors, particularly physical inactivity, are closely linked to the onset of numerous metabolic diseases. Adipose tissue (AT) has been extensively studied for various metabolic diseases such as obesity, type 2 diabetes, and immune system dysregulation due to its role in energy metabolism and regulation of inflammation. Physical activity is increasingly recognized as a powerful non-pharmacological tool for the treatment of various disorders, as it helps to improve metabolic, immune, and inflammatory functions. However, chronic excessive training has been associated with increased inflammatory markers and oxidative stress, so much so that excessive training overload, combined with inadequate recovery, can lead to the development of overtraining syndrome (OTS). OTS negatively impacts an athlete's performance capabilities and significantly affects both physical health and mental well-being. However, diagnosing OTS remains challenging as the contributing factors, signs/symptoms, and underlying maladaptive mechanisms are individualized, sport-specific, and unclear. Therefore, identifying potential biomarkers that could assist in preventing and/or diagnosing OTS is an important objective. In this review, we focus on the possibility that the endocrine functions of AT may have significant implications in the etiopathogenesis of OTS. During physical exercise, AT responds dynamically, undergoing remodeling of endocrine functions that influence the production of adipokines involved in regulating major energy and inflammatory processes. In this scenario, we will discuss exercise about its effects on AT activity and metabolism and its relevance to the prevention and/or development of OTS. Furthermore, we will highlight adipokines as potential markers for diagnosing OTS.

Burden of osteoarthritis in China, 1990-2019: findings from the Global Burden of Disease Study 2019

This study aimed to report the most current data on the incidence and disability-adjusted life years (DALY) associated with osteoarthritis in China from 1990 to 2019. Publicly available modelled data from Global Burden of Disease Study (GBD) 2019 were used. The incidence and DALY, due to osteoarthritis in China, stratified by sex, trends of associated risk factors, assess the age, period, and cohort effects on the long-term trends of osteoarthritis incidence and DALY in China from 1990 to 2019. We found that the age-standardized incidence and DALY rates of osteoarthritis in China are higher than the average levels in Asia, Africa, and Oceania. In 2019, the number of cases of osteoarthritis in China was 10,681,311, an increase of 132.66% compared with 1990. the DALY of osteoarthritis in China was 4,724,885 person-years, which was 159.70% higher than that in 1990. In 2019, the incidence and DALY rates of osteoarthritis in China was 750.96/100,000,332.19/100,000. High body-mass as risk factors for osteoarthritis DALY with the population attributable proportion (PAF) increasing steadily from 1990 to 2019. The incidence and DALY rates of three types of osteoarthritis from high to low are osteoarthritis knee, osteoarthritis hand, and osteoarthritis hip. Age-period-cohort model showed that the incidence rate of osteoarthritis in China shows a trend of increasing first and then decreasing with age; concurrently, the DALY rate of osteoarthritis in China increased with age. For the period effect, we found that the period rate ratio (RR) of osteoarthritis incidence and DALY rates kept increasing in the cohort born before 2005-2009, and then, it was gradually reduced by year of birth in the cohort born after 2005-2009. As for cohort effect, the cohort RR of incidence rate of osteoarthritis almost has no change, while the cohort RR of DALY rate of osteoarthritis kept increasing from 1990 to 2019. The burden and impact of osteoarthritis in China are substantial and are increasing. Adopting suitable control and preventive community measures to reduce modifiable risk factors is needed to reduce the current and future burden of osteoarthritis in China. Key Points • This paper analyzes the disease burden of osteoarthritis in China for the first time and discusses the influence on the disease burden of osteoarthritis from the perspectives of age, period, and cohort.

Exercise-induced modulation of myokine irisin on muscle-bone unit in the rat model of post-traumatic osteoarthritis

BACKGROUND AND AIM

Post-traumatic osteoarthritis (PTOA) is a subtype of osteoarthritis (OA). Exercise may produce and release the myokine irisin through muscle fiber contraction. However, the effect of exercise-promoted irisin production on the internal interactions of the muscle-bone unit in PTOA studies remains unclear.

METHODS

Eighteen 8-week-old Sprague-Dawley (SD) rats were randomly divided into three groups: Sham/sedentary (Sham/Sed), PTOA/sedentary (PTOA/Sed), and PTOA/treadmill-walking (PTOA/TW). The PTOA model was established by transection of anterior cruciate ligament (ACLT) and destabilization of medial meniscus (DMM). After 4 weeks of modeling, the PTOA/TW group underwent treadmill exercise (15 m/min, 30 min/d, 5 d/ week, 8 weeks), and the other two groups were free to move in the cage. Evaluation and correlation analysis of muscle, cartilage, subchondral bone and serological indexes were performed after euthanasia.

RESULTS

Eight weeks of treadmill exercise effectively alleviated the trauma-induced OA phenotype, thereby maintaining cartilage and subchondral bone integrity in PTOA, and reducing quadriceps atrophy and myofibril degradation. Exercise reversed the down-regulated expression of peroxisome proliferator-activated receptor-gamma coactivator-1α (PGC-1α) and fibronectin type III structural domain protein 5 (FNDC5) in muscle tissue of PTOA rats, and increased the blood irisin level, and the irisin level was positively correlated with the expression of PGC-1α and FNDC5. In addition, correlation analysis showed that irisin metabolism level was strongly negatively correlated with Osteoarthritis Research Society International (OARSI) and subchondral bone loss, indicating that irisin may be involved in cartilage biology and PTOA-related changes in cartilage and subchondral bone. Moreover, the metabolic level of irisin was strongly negatively correlated with muscle fiber cross-sectional area (CSA), Atrogin-1 and muscle ring-finger protein-1(MuRF-1) expression, suggesting that irisin may alleviate muscle atrophy through autocrine action.

CONCLUSION

Treadmill exercise can alleviate the atrophy and degeneration of muscle fibers in PTOA rats, reduce the degradation of muscle fibrin, promote the expression of serum irisin, and alleviate the degeneration of articular cartilage and subchondral bone loss in PTOA rats. These results indicate that treadmill exercise can affect the process of PTOA by promoting the expression of myokine irisin in rat muscle-bone unit.

Low-intensity pulsed ultrasound irradiation attenuates collagen degradation of articular cartilage in early osteoarthritis-like model mice

PURPOSE

Osteoarthritis (OA) is a combination of degeneration and destruction of articular cartilage due to mechanical stress, secondary synovitis, and bone remodelling. In recent years, early knee OA, a preliminary stage of structural failure in OA, has attracted attention as a potential target for therapy to prevent the onset of OA. Intra-articular administration of monoiodoacetic acid (MIA) induces OA-like symptoms, and low doses of MIA induce early OA like symptoms. In this experiment, a low-dose of MIA was induced to early OA model mice, which were then irradiated with low-intensity pulsed ultrasound (LIPUS) to examine whether LIPUS improves symptoms of early OA.

METHODS

After 4 weeks of LIPUS irradiation, articular cartilage was observed at 1 and 4 weeks. The Osteoarthritis Research Society International (OARSI) scores were calculated using Safranin-O staining results. Cartilage degeneration was detected using Denatured Collagen Detection Reagent (DCDR).

RESULTS

We observed a significant decrease in OARSI scores in the LIPUS irradiated group at week 4. The non-LIPUS group showed widespread areas of double positivity for Type II collagen and DCDR, whereas the LIPUS group showed only a small number of DCDR-positive areas. In addition, macrophage numbers counted in the articular capsule at week 1 showed a significant decrease in the LIPUS irradiated group. Lubricin detection showed that lubricin positive cell number was significantly increased by LIPUS irradiation at week 4.

CONCLUSIONS

These results suggest that LIPUS attenuates cartilage degeneration in early OA by relieving inflammation and enhancing the inhibitory effect of lubricin on cartilage degeneration.