Cyclooxygenase mRNA expression in human patellar tendon at rest and after exercise

Exercise has been shown to acutely elevate several metabolic processes in tendon tissue, including collagen turnover and blood flow, and chronically induce changes in tendon properties. Many of these acute metabolic responses to exercise are regulated by the cyclooxygenase (COX) enzymes. We measured the expression levels of COX-1 [variants 1 and 2 (COX-1v1 and COX-1v2)], COX-2, and the recently discovered intron 1-retaining COX-1 variants (COX-1b(1), COX-1b(2), and COX-1b(3)) at rest and after resistance exercise (RE). Patellar tendon biopsy samples were taken from six individuals (3 men and 3 women) before and 4 h after a bout of RE (3 sets of 10 repetitions at approximately 70% of 1 repetition maximum) and from a separate group of six individuals (3 men and 3 women) before and 24 h after RE and analyzed by real-time RT-PCR. The COX-1 variants were the most abundant COX mRNAs before exercise and remained unchanged (P > 0.05) after exercise. COX-2 was also expressed in tendon tissue at rest and was unchanged (P > 0.05) after exercise. The intron 1-retaining COX-1 variants were not detectable in tendon tissue before or after exercise. COX-1 and COX-2 were expressed at much higher levels by the patellar tendon than by quadriceps skeletal muscle, although the overall COX mRNA expression patterns were similar in skeletal muscle and tendon (COX-1v2 > COX-1v1, P < 0.05; ratio of COX-1 to COX-2 congruent with 4:1). These results suggest that COX-1 and COX-2 are constitutively expressed at relatively high levels in human patellar tendon and are likely targets of COX-inhibiting drugs at rest and after physical activity.