Advanced Osteoarthritis in Humans Is Associated With Altered Collagen VI Expression and Upregulation of ER-stress Markers Grp78 and Bag-1

Abstract

; and Summa Health Systems, Akron, Ohio (IG) S U M M A R Y To test the hypothesis that a perturbation of endoplasmic reticulum (ER) function is involved in the pathogenesis of osteoarthritis (OA), articular cartilage was isolated from non-OA patients secondary to resection of osteo-or chondrosarcomas. Intra-joint samples of minimal and advanced osteoarthritic cartilage were isolated from patients undergoing total knee arthroplasty and scored for disease severity. Glucose-regulated protein-78 (grp78) and bcl-2-associated athanogene-1 (bag-1) were detected via immunofluorescence as markers of non-homeostatic ER function. Additionally, the expression of type VI collagen and its integrin receptor, NG2, was determined to examine cartilage matrix health and turnover. There was an upregulation of grp78 in advanced OA, and variable expression in minimal OA. Non-OA cartilage was consistently grp78 negative. The downstream regulator bag-1 was also upregulated in OA compared with normal cartilage. Collagen VI was mainly cellassociated in non-OA cartilage, with a more widespread distribution observed in OA cartilage along with increased intracellular staining intensity. The collagen VI integral membrane proteoglycan receptor NG2 was downregulated in advanced OA compared with its patientmatched minimally involved cartilage sample. These results suggest that chondrocytes exhibit ER stress during OA, in association with upregulation of a large secreted molecule, type VI collagen. (J Histochem Cytochem 57:923-931, 2009) K E Y W O R D S osteoarthritis cartilage ER stress bag-1 grp78 collagen VI NG2 OSTEOARTHRITIS (OA) IS A PROGRESSIVE DISEASE, with changes in chondrocyte gene expression and extracellular matrix (ECM) composition occurring before macroscopic structural damage is observed (Hamerman 1989). Articular chondrocytes in OA exhibit a hypermetabolic phenotype, with studies describing highly proliferative clonal chondrocytes, along with the upand downregulation of ECM molecules such as aggrecan

Metabolic Labeling of Chondrocytes for the Quantitative Analysis of the Interleukin-1-beta-mediated Modulation of Their Intracellular and Extracellular Proteomes

“…31 Hallmarks of osteoarthritic cartilage are the degradation of ECM components and the destruction of this pericellular microenvironment. 32 Previous studies have shown increased amounts of COL6 in osteoarthritic cartilage, 33,34 depicting those modifications in the collagenous network that occur in degenerated cartilage. Our group has previously described an intracellular increase of this protein in OA chondrocytes.…”

Endoplasmic reticulum stress induces the expression of COX-2 through activation of eIF2α, p38-MAPK and NF-κB in advanced glycation end products stimulated human chondrocytes

“…When protein folding is disturbed, GRP78 synthesis is increased and GRP78 subsequently binds to misfolded proteins to prevent them from forming aggregates and assists them to refold properly [3]. Bag-1 has recently been shown to be a downstream regulator of ER stress in chondrocytes [4]. It is now well established that overexpression of Bag-1 protects chondrocytes from ER stress [4,5].…”

“…Bag-1 has recently been shown to be a downstream regulator of ER stress in chondrocytes [4]. It is now well established that overexpression of Bag-1 protects chondrocytes from ER stress [4,5]. Therefore elevated expressions of GRP78 and Bag-1 are considered to be reliable markers of ER stress [3,4].…”

“…It is now well established that overexpression of Bag-1 protects chondrocytes from ER stress [4,5]. Therefore elevated expressions of GRP78 and Bag-1 are considered to be reliable markers of ER stress [3,4]. The ER stress response is suggested to contribute in several human diseases, including osteoarthritis (OA) and rheumatoid arthritis (RA) [2].…”

A preclinical evaluation of an autologous living hyaline-like cartilaginous graft for articular cartilage repair: a pilot study

“…Under normal conditions, this protein occurs primarily in the pericellular matrix that surrounds the chondrocytes throughout the different zones. In OA cartilage, it was reported that the expression and overall distribution of type VI collagen increases in the lower middle and upper deep zones 45,46 . In the results presented in Fig.…”