Expression of osteocalcin in the patella of experimentally immobilized and remobilized rats

Abstract

The exact mechanisms by which mechanical loading-unloading affects bone tissue are mostly unknown. Recently, osteocalcin, a direct product of osteoblasts, has been shown to reflect the activity of the mineralization phase of the newly formed bone matrix, and therefore, the in situ detection of osteocalcin could be used for studying the effects of physical activity-inactivity on the osteoblast function or bone formation in the target bone. In this study, the effect of various loading states (immobilization and three forms of subsequent remobilization) on the in situ expression of osteocalcin in the rat patellas and their osteotendinous junctions was studied immunohistochemically using a polyclonal rat antiosteocalcin as the primary antibody. Following immobilization for 3 weeks, the immunoreactivity of osteocalcin was markedly decreased or was completely absent in all the patellar areas which normally show intense reaction as a sign of mineralization of the newly formed bone, that is, in the subperiosteal and subchondral regions, in the osteoid tissue that lies on the surface of the trabecular bone, and around the cortical lacunae. The same was true in the mineralized fibrocartilage zone of the osteotendinous junction of the quadriceps tendon. Free remobilization for 8 weeks (free cage activity) could not improve the situation, but after intensified remobilization of the same duration (low and especially high intensity treadmill running) high osteocalcin expression was observed in the above-mentioned anatomic sites. These findings indicate that formation of new bone tissue is rapidly regulated by the loading states of the bone. Higher than normal activity seems to be needed to restore the bone formation from the disuseinduced depression to normal.

Long-Term Outcome and Factors Affecting Prognosis of Extracorporeal Shockwave Therapy for Chronic Refractory Achilles Tendinopathy

“…Retrocalcaneal enthesophytes may be an adaptive response to increased traction in the Achilles tendon [2021]. Increased mechanical loading triggers osteoblastic activity at the tendon attachment site, and physically active people are more likely to exhibit presence of enthesophytes [2223]. Thus, presence of retrocalcaneal enthesophyte may imply that the patient has high activity level and is more liable to overuse injuries.…”

Effects of hindlimb unloading and subsequent reloading on the structure and mechanical properties of Achilles tendon‐to‐bone attachment

“…12,17 To date, Deymier et al (2020) 6 is the only study to have investigated the effects of spaceflight on entheses. Whereas studies have demonstrated that entheses are sensitive to chronic variations in mechanical load, [18][19][20][21][22][23] Deymier et al (2020) 6 reported that spaceflight did not mechanically weaken the supraspinatus tendon enthesis. However, the supraspinatus, a shoulder muscle, is documented as suffering little impact from microgravity.…”

Mechanical Loading in Osteocytes Induces Formation of a Src/Pyk2/MBD2 Complex That Suppresses Anabolic Gene Expression

“…Osteocalcin is an important protein associated with bone formation and its levels in serum directly correlate with measurements of bone mineral density [59] , [60] . Osteocalcin expression is increased in response mechanical loading in both in vivo and in vitro models [61] , [62] . We also analyzed expression of cyclooxygenase-2, runx2, osterix, and osteopontin and found inhibition of Src had no impact on OFSS-induced increases in their expression (data not shown).…”