Action of hydrocortisone on the hyaluronic acid of joint fluids in rheumatoid arthritis

Transglutaminase 2 cross-linking activity is linked to invadopodia formation and cartilage breakdown in arthritis

Introduction

The microenvironment surrounding inflamed synovium leads to the activation of fibroblast-like synoviocytes (FLSs), which are important contributors to cartilage destruction in rheumatoid arthritic (RA) joints. Transglutaminase 2 (TG2), an enzyme involved in extracellular matrix (ECM) cross-linking and remodeling, is activated by inflammatory signals. This study was undertaken to assess the potential contribution of TG2 to FLS-induced cartilage degradation.

Methods

Transglutaminase (TGase) activity and collagen degradation were assessed with the immunohistochemistry of control, collagen-induced arthritic (CIA) or TG2 knockdown (shRNA)-treated joint tissues. TGase activity in control (C-FLS) and arthritic (A-FLS) rat FLSs was measured by in situ 5-(biotinamido)-pentylamine incorporation. Invadopodia formation and functions were measured in rat FLSs and cells from normal (control; C-FLS) and RA patients (RA-FLS) by in situ ECM degradation. Immunoblotting, enzyme-linked immunosorbent assay (ELISA), and p3TP-Lux reporter assays were used to assess transforming growth factor-β (TGF-β) production and activation.

Results

TG2 and TGase activity were associated with cartilage degradation in CIA joints. In contrast, TGase activity and cartilage degradation were reduced in joints by TG2 knockdown. A-FLSs displayed higher TGase activity and TG2 expression in ECM than did C-FLSs. TG2 knockdown or TGase inhibition resulted in reduced invadopodia formation in rat and human arthritic FLSs. In contrast, increased invadopodia formation was noted in response to TGase activity induced by TGF-β, dithiothreitol (DTT), or TG2 overexpression. TG2-induced increases in invadopodia formation were blocked by TGF-β neutralization or inhibition of TGF-βR1.

Conclusions

TG2, through its TGase activity, is required for ECM degradation in arthritic FLS and CIA joints. Our findings provide a potential target to prevent cartilage degradation in RA.

Connective tissue metabolism in bone and cartilage of adjuvant arthritic rat

The metabolism of connective tissue matrix components such as glycosaminoglycans and glycoproteins was investigated in normal as well as pathological tissues of bone and cartilage associated with adjuvant arthritis using rat as animal model of the disease. The inflammatory process of adjuvant arthritis was induced in rats with the inoculation of Freund's adjuvant containing heat killed Mycobacterium tuberculosis suspended in paraffin oil. The changes in the metabolism of matrix components in bone and cartilage were examined using radioactive isotopic labeling measurements during the acute as well as chronic phases of arthritic disease. The glycosaminoglycans were fractionated into sulfated and non-sulfated glycosaminoglycans by chemical and enzymic modifications. The biosynthesis of sulfated glycosaminoglycans was evaluated using radioactive labeled (35S)-sulfate. Alterations were demonstrated in the metabolism of connective tissue in the bone and cartilage tissues of arthritic rat. The results obtained showed an increased incorporation of radioactive sulfate in specimens of bone and cartilage during the process of adjuvant arthritis. The contents of sulfated as well as non-sulfated glycosaminoglycans were found to be increased in both the tissues of arthritic rat. Similarly, the amount of total glycosaminoglycans was also found to be increased significantly in the diseased tissues. In addition, various components of tissue glycoproteins such as fucose, sialic acid and total hexose were found to be elevated in insoluble fractions of bone and cartilage during the diseased state. The effects of experimentally induced adjuvant arthritis on the connective tissue were discussed in the light of changes taking place in the metabolism of glycosaminoglycans and glycoproteins in bone and cartilage of arthritic rat.

Suppression of hyaluronic acid synthesis in synovial organ cultures by corticosteroid suspensions

The effects of sparingly soluble corticosteroid suspensions prepared for intraarticular therapy, of their vehicles, and of hydrocortisone on synovial hyaluronic acid (HA) synthesis were compared in organ cultures of normal canine villous synovium. Both hydrocortisone and the corticosteroid suspensions suppressed HA synthesis, as did 2 vehicle components, polysorbate 80 and myristyl-gamma-picrolinium chloride. Cultures of synovium from joints of dogs which, 1 day previously, had been injected with methylprednisolone acetate suspension synthesized less HA than did control cultures from noninjected joints of the same animals. The results indicate that suppression of HA synthesis is a mechanism by which these drugs can act to reduce joint HA content and promote resolution of synovial effusions.