Synovial membrane in the temporomandibular joint-Its morphology, function and development

Abstract

This paper reviews recent findings of the synovial membrane, in particular the morphology, function and development of synovial lining cells, in the temporomandibular joint (TMJ). Electron microscopic studies have confirmed the synovial membrane in TMJ consists of macrophage-like type A cells and fibroblast-like type B cells identical to those in other systematic joints. The macrophage-like type A cells react with anti-macrophage and macrophage-derived substances including the major histocompatibility class II molecule, and show a drastic increase in their number in the inflamed synovial membrane. In addition, they have the ability to produce substances involved in the progression of TMJ inflammation such as nitric oxide and inducible nitric oxide synthase. Observation of osteopetrotic mice revealed that macrophage-like type A cells in TMJ are derived from monocyte lineage. Immunocytochemistry for 25kDa heat shock protein was able to depict the entire shape of fibroblast-like type B cells including their unique processes. The expression of an estrogen receptor alpha-immunoreaction in the fibroblast-like type B cells may explain the etiology of temporomandibular disorders at a higher frequency in females than in males, suggesting that TMJ is a target tissue for estrogen. Furthermore, fibroblast-like type B cells are equipped with a basement membrane to serve as an adhesion molecule for the fibroblast-like type B cells to keep their epithelial arrangement. A clear understanding of the morphology of the intact synovial membrane will serve to clarify the etiology and development of temporomandibular disorders.

Expression of caveolin‐1 in the rat temporomandibular joint

“…Its synovial lining layer contains two types of synovial lining cells: macrophage-like type A and fibroblast-like type B cells (for review, see Nozawa-Inoue et al, 2003), as reported in other systemic joints (for review, see Iwanaga et al, 2000). The type A cell is characterized by numerous vacuoles, lysosomes, nuclei with rich heterochromatin, and cell surface filopodia, while the type B cell possesses a well-developed rough endoplasmic reticulum (rER), a nucleus with less chromatin, and cytoplasmic long projections.…”

“…The type A cell is characterized by numerous vacuoles, lysosomes, nuclei with rich heterochromatin, and cell surface filopodia, while the type B cell possesses a well-developed rough endoplasmic reticulum (rER), a nucleus with less chromatin, and cytoplasmic long projections. In addition, some ultrastructural investigations have pointed out that the fibroblast-like type B cells had invaginations reminiscent of caveolae in their cell membrane (Graabaek, 1984;Iwanaga et al, 2000;Nozawa-Inoue et al, 2003). However, both the nature and the functional significance of this structure remain unclear.…”

Immunocytochemical Localization of Caveolin‐3 in the Synoviocytes of the Rat Temporomandibular Joint During Development

“…A series of ultrastructural surveys has agreed that the synovial lining cell layer consists of two kinds of synoviocytes-including macrophage-like type A and fibroblastlike type B cells-which respectively function in the resorption and synthesis/secretion of synovial fluids (for reviews, Iwanaga et al, 2000;Nozawa-Inoue et al, 2003). However, immunoelectron microscopy pointed out the possibility that type B synoviocytes in the TMJ could be further divided into some phenotypes by their immunocytochemical properties (Nozawa-Inoue et al, 1999).…”

“…The synovial membrane in the TMJ consists of a surface synovial lining layer and a connective sublining layer. In addition, the synovial lining layer contains two types of synovial lining cells: macrophage-like type A and fibroblast-like type B cells (for review, see Nozawa-Inoue et al, 2003). The fibroblast-like type B cells have important functions in the production/secretion of type I and II collagens, fibronectin, and glycosaminoglycans-including hyaluronic acid-into the synovial interstitium and fluids.…”

“…In particular, hyaluronic acid plays an essential role in maintaining the viscosity of synovial fluids. Therefore, previous studies have focused on the origin and functions of the fibroblast-like type B cells (Nozawa-Inoue et al, 2003Ikeda et al, 2004;Suzuki et al, 2005Suzuki et al, , 2006. Electron microscopically, the fibroblast-like type B cell is characterized by a well-developed rough endoplasmic reticulum (rER), a nucleus with less heterochromatin, long cytoplasmic projections, and a surrounding basement membrane-like structure in addition to numerous caveolae in the cell membrane.…”