Articular cartilage collagen birefringence is altered concurrent with changes in proteoglycan synthesis during dynamic in vitro loading

Abstract

Introduction:The articular cartilage collagen network and proteoglycans are subject to changes in deteriorating joint diseases. In this study, we exposed articular cartilage plugs to cyclic loading and investigated the properties of collagen network and proteoglycans in different zones of the articular cartilage.Methods: Articular cartilage full-depth plugs were exposed in vitro to 4.1 MPa cyclic (0.5 Hz) loading for 1 to 20 hr and investigated using quantitative microscopic methods (i.e., polarized light microscopy, microspectrophotometry, and autoradiography).Results: The loading caused packing or condensation of the tissue. In histological sections, the height of uncalcified articular cartilage decreased by an average of 12.8% (range, 4 to 19.7%). Loading increased the birefringence of collagen in the superficial cartilage (P Ͻ 0.05), with thickening of the zone up to 41.4% at 20 hr. The thickness of the intermediate zone increased also (22% at 1 hr and 434% at 20 hr). Concomitantly, the birefringence (P Ͻ 0.05) and the thickness of the deep zone decreased (18.5 to 27.8%). Loading for 4 hr increased the 35 S-sulphate incorporation of the cartilage explants by an average of 67% (P Ͻ 0.05). The increase was most significant in the deep cartilage. A simultaneous increase was observed in the proteoglycan concentration of the cartilage; the staining intensity with safranin-O increased by 8.8% (P Ͻ 0.05). After 8 hr loading, this stimulation decreased; at 20 hr, loading caused a clear inhibitory effect on proteoglycan synthesis in the superficial zone.Discussion: According to these results, the chosen loading regimen increased the thickness and collagen orientation in the superficial zone. In contrast, the thickness and birefringence in the deep cartilage were reduced.

Long-term cyclical in vivoloading increases cartilage proteoglycan content in a spatially specific manner: an infrared microspectroscopic imaging and polarized light microscopy study

“…This is in agreement with a previous finding in vitro [27] in which proteoglycan synthesis increased by 102% to 114% in the deep zone after 4 hours of dynamic unconfined loading. The same study, however, found that the stimulatory effect was decreased after 8 hours.…”

Microstructural remodeling of articular cartilage following defect repair by osteochondral autograft transfer

“…In host cartilage overhanging the graft, PI and Γ were lower than in non-overhanging host, suggesting disorganization of existing or new matrix in these more deformed regions. Similar structural features of higher SZ and lower DZ Γ compared to unloaded cartilage occur with normal (subinjurious) cyclic loading of intact adult bovine patellar 38 , and static loading of equine articular cartilage 39 . PLM images and histological staining of host articular cartilage adjacent to a microfracture defect repair in skeletally mature rabbits 40 , and to empty defects in 5-month old sheep 5 , were consistent with flow as well as the novel qPLM structural alterations quantified in the present study.…”

Chondromalacia induced by patellar subluxation: morphological and morphometrical aspects in rabbits

“…Király et al [40], investigated, during dynamic studies using load, alterations of the cartilaginous matrix in the 3 zones using light microscopic , microspectrophotometry and autoradiography. Recently researchers have been applying cationic dyes, such as Safranin O, for the semiquantitative estimation of the glycosaminoglycans in histological sections of the articulate cartilage for microspectrophotometry [41].…”