Immunofluorescence Analysis of NF-kB and iNOS Expression in Different Cell Populations during Early and Advanced Knee Osteoarthritis.

Marko Ostojic,Violeta Soljic,Katarina Vukojevic,Ante Zevrnja

doi:10.3390/ijms22126461

Abstract

Synovitis of the knee synovium is proven to be a precursor of knee osteoarthritis (OA), leading to a radiologically advanced stage of the disease. This study was conducted to elucidate the expression pattern of different inflammatory factors—NF-kB, iNOS, and MMP-9 in a subpopulation of synovial cells. Thirty synovial membrane intra-operative biopsies of patients (ten controls, ten with early OA, and ten with advanced OA, according to the Kellgren–Lawrence radiological score) were immunohistochemically stained for NF-kB, iNOS, and MMP9, and for different cell markers for macrophages, fibroblasts, leukocytes, lymphocytes, blood vessel endothelial cells, and blood vessel smooth muscle cells. The total number of CD68+/NF-kB+ cells/mm2 in the intima of early OA patients (median = 2359) was significantly higher compared to the total number of vimentin+/Nf-kB+ cells/mm2 (median = 1321) and LCA+/NF-kB+ cells/mm2 (median = 64) (p < 0.001 and p < 0.0001, respectively). The total number of LCA+/NF-kB+ cells/mm2 in the subintima of advanced OA patients (median = 2123) was significantly higher compared to the total number of vimentin+/NF-kB+ cells/mm2 (median = 14) and CD68+/NF-kB+ cells/mm2 (median = 29) (p < 0.0001). The total number of CD68+/iNOS+ cells/mm2 in the intima of both early and advanced OA patients was significantly higher compared to the total number of vimentin+/iNOS+ cells/mm2 and LCA+/iNOS+ cells/mm2 (p < 0.0001 and p < 0.001, respectively). The total number of CD68+/MMP-9+ cells/mm2 in the intima of both early and advanced OA patients was significantly higher compared to the total number of vimentin+/MMP-9+ cells/mm2 and CD5+/MMP-9+ cells/mm2 (p < 0.0001). Macrophages may have a leading role in OA progression through the NF-kB production of inflammatory factors (iNOS and MMP-9) in the intima, except in advanced OA, where leukocytes could have a dominant role through NF-kB production in subintima. The blocking of macrophageal and leukocyte NF-kB expression is a possible therapeutic target as a disease modifying drug.

Highlights

Osteoarthritis (OA) is the most common disease of the synovial joints that mostly affects older adults
Synovitis has been radiologically proven to be a prognostic factor for OA development [37,38], and innate immunity plays a paramount role in early OA advancement [28]
Our previous study showed the higher grade of synovitis in patients with radiologically early OA compared to advanced eOA [11]

Summary

Introduction

Osteoarthritis (OA) is the most common disease of the synovial joints that mostly affects older adults. It indicates chronic degenerative changes in the articular cartilage that perpetuate pathological changes in other parts of the joint in a cascade manner [1]. The synovial membrane contains resident cells such as macrophage-like synoviocytes (MLS), fibroblast-like synoviocytes (FLS), endothelium and smooth muscle cells of blood vessels, and non-resident, inflammatory cells, such as lymphocytes and plasmacells. It has two layers; the intima, the thin layer where the macrophages and fibroblasts are located, and the subintima, the supportive stroma [9]. Clinically, synovitis grade is greatly associated with the severity of pain, joint dysfunction, and cartilage loss in OA [14,15]

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