Abstract
Physical exercise has long been recommended as a treatment for osteoarthritis (OA), though its effects vary based on the exercise protocol. Here, we examined whether environmental lighting conditions influence the anti-inflammatory benefits of exercise in a rat model of OA. Moderate-intensity treadmill exercise (Ex) was performed for six weeks under a 12:12 h light/dark (L/D) cycle, and compared against rats housed in a 24 h continuous light (L/L) environment. L/L conditions were associated with serological changes shortly after OA induction, which exacerbated the inflammatory microenvironment in the joint. Differentiation capacity was also impaired in bone precursor cells isolated from normal rats maintained under L/L conditions, despite elevated inflammatory responses. Exercise training under L/L conditions led to increased corticosterone levels in the blood, which exacerbated the progression of cartilaginous and synovial lesions. Osteoporotic phenomena were also observed in exercise-trained rats maintained under L/L conditions, along with inflammation-induced catabolism in the gastrocnemius muscle. Aberrant light/dark cycle conditions were also found to be associated with suppression of splenic Cry1 expression in exercise-trained rats, leading to dysregulation of immune responses. Taken together, these data suggest that lighting condition may be an important environmental factor influencing the exercise-induced benefits on OA.
Highlights
Osteoarthritis (OA) is the most common form of arthritis in older people, leading to functional disability due to pain [1]
We determined the effects of environmental lighting conditions on joint inflammation in vivo
These phenomena represent the early physiological load induced by environmental light stress; arthritis-induced hormonal changes were not observed
Summary
Osteoarthritis (OA) is the most common form of arthritis in older people, leading to functional disability due to pain [1]. Low-to-moderate intensity aerobic exercise has been shown to limit OA-associated pain [5], and multimodal exercise therapy appears more effective in symptomatic control [6,7]; these vigorous activities are not recommended for patients with osteoarthritis [8]. Glucocorticoids are released from the adrenal gland, and are well established as a clock-based stress hormone [15]. Since these two hormones regulate peripheral physiology, by adjusting the internal clock in response to cyclic fluctuations in the environment, their levels should be maintained rhythmically in the body. We sought to determine the effects of environmental lighting conditions on interventional exercise in osteoarthritic rats
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