Ultracytochemistry of glycosaminoglycans in the canine knee synovium

Increased physical activity severely induces osteoarthritic changes in knee joints with papain induced sulfate-glycosaminoglycan depleted cartilage

Introduction

Articular cartilage needs sulfated-glycosaminoglycans (sGAGs) to withstand high pressures while mechanically loaded. Chondrocyte sGAG synthesis is regulated by exposure to compressive forces. Moderate physical exercise is known to improve cartilage sGAG content and might protect against osteoarthritis (OA). This study investigated whether rat knee joints with sGAG depleted articular cartilage through papain injections might benefit from moderate exercise, or whether this increases the susceptibility for cartilage degeneration.

Methods

sGAGs were depleted from cartilage through intraarticular papain injections in the left knee joints of 40 Wistar rats; their contralateral joints served as healthy controls. Of the 40 rats included in the study, 20 rats remained sedentary, and the other 20 were subjected to a moderately intense running protocol. Animals were longitudinally monitored for 12 weeks with in vivo micro-computed tomography (μCT) to measure subchondral bone changes and single-photon emission computed tomography (SPECT)/CT to determine synovial macrophage activation. Articular cartilage was analyzed at 6 and 12 weeks with ex vivo contrast-enhanced μCT and histology to measure sGAG content and cartilage thickness.

Results

All outcome measures were unaffected by moderate exercise in healthy control joints of running animals compared with healthy control joints of sedentary animals. Papain injections in sedentary animals resulted in severe sGAG-depleted cartilage, slight loss of subchondral cortical bone, increased macrophage activation, and osteophyte formation. In running animals, papain-induced sGAG-depleted cartilage showed increased cartilage matrix degradation, sclerotic bone formation, increased macrophage activation, and more osteophyte formation.

Conclusions

Moderate exercise enhanced OA progression in papain-injected joints and did not protect against development of the disease. This was not restricted to more-extensive cartilage damage, but also resulted in pronounced subchondral sclerosis, synovial macrophage activation, and osteophyte formation.

Colocalization in vivo and association in vitro of perlecan and elastin

We have colocalized elastin and fibrillin-1 with perlecan in extracellular matrix of tensional and weight-bearing connective tissues. Elastin and fibrillin-1 were identified as prominent components of paraspinal blood vessels, and posterior longitudinal ligament in the human fetal spine and outer annulus fibrosus of the fetal intervertebral disc. We also colocalized perlecan with a synovial elastic basal lamina, where the attached synovial cells were observed to produce perlecan. Elastin, fibrillin-1 and perlecan were co-localized in the intima and media of small blood vessels in the synovium and in human fetal paraspinal blood vessels. Elastic fibers were observed at the insertion point of the anterior cruciate ligament to bone in the ovine stifle joint where they colocalized with perlecan. Elastin has not previously been reported to be spatially associated with perlecan in these tissues. Interactions between the tropoelastin and perlecan heparan sulfate chains were demonstrated using quartz crystal microbalance with dissipation solid phase binding studies. Electrostatic interactions through the heparan sulfate chains of perlecan and core protein mediated the interactions with tropoelastin, and were both important in the coacervation of tropoelastin and deposition of elastin onto perlecan immobilized on the chip surface. This may help us to understand the interactions which are expected to occur in vivo between the tropoelastin and perlecan to facilitate the deposition of elastin and formation of elastic microfibrils in situ and would be consistent with the observed distributions of these components in a number of connective tissues.

Ultrastructural localization of hyaluronic acid in the synovium of the goat knee joint

In the Japanese miniature (Shiba) goat, the synovial membrane contains synoviocytes referred to as type A (macrophage-like cells) and type B cells (fibroblast-like cells) in the intimal layer. Small capillaries and blood vessels of varying sizes were located in the extracellular matrix in the synovial subintima. The type A cells in the synovium possessed numerous vesicles, vacuoles and lysosomes as well as pinocytotic vesicles. These ultrastructural features indicating phagocytosis showed distinct positive reactions following hyaluronan staining. On the other hand, in the type B cells, hyaluronic acids were present in the surface coat of the plasma membrane and its periphery. Additionally, perivascular connective tissue of the small capillaries and blood vessels and interfibrous matrix contained hyaluronan. The results suggest that hyaluronic acid, in the synovial tissue, is synthesized on the plasma membrane of type B cells, and taken up by type A cells. Moreover, hyaluronan is involved in cellular functions in the synovial connective tissue.

Ultracytochemical demonstration of glycoproteins in the canine knee synovium

By various ultracytochemical methods, glycoconjugates of the synoviocytes, the intercellular matrix and the wall of the small capillaries were studied in the synovial intimal tissues of the canine knee joint. Glycoconjugates with vicinal diol groups could be visualized in certain elements of the Golgi complex, lysosomes, vacuoles, the majority of intracellular cytomembranes, the surface coat of the plasma membrane and glycogen particles in type A cells. In type B cells, less-developed Golgi complexes, and fewer lysosomes and vacuoles were present in the cytoplasm than in that of type A cells. In contrast, a large number of cytoplasmic glycogen particles and abundant vicinal diol-containing groups in the surface coat of the plasma membrane became especially obvious in the B cells. Abundant neutral and acidic glycoproteins were observed in fibrous components in the intercellular matrix. In the small capillaries, strongly positive staining intensities for neutral and acidic glycoconjugates were observed in the basement membrane and perivascular connective tissue, as well as in the surface coat of the luminal plasma membrane of the endothelial cells, although to a somewhat weaker degree. Sialic acid, particularly, was notable in the surface coat of the latter cells. In addition, glycoproteins in the type A cells were shown by lectin ultracytochemistry to contain a variety of saccharide residues such as alpha-D-mannose, alpha-D-glucose, alpha-L-fucose, N-acetyl-beta-D-glucosamine, and N-acetyl-neuraminic acid, which were also found in the plasma membrane of the B cells. The properties of the glycoconjugates found are discussed in relation to the basic functions assigned to the synovial membrane of the canine knee joint.