Expression of lumican in the articular disc of the human temporomandibular joint

Abstract

Lumican belongs to the small leucine-rich repeat proteoglycan (SLRP) gene family and has been reported to exist in the cornea, intervertebral disc and tendon. Lumican plays a significant role in the assembly and regulation of collagen fibres. The human temporomandibular joint (TMJ) disc is made up of fibrocartilage with an extracellular matrix (ECM) composed of collagen and proteoglycans. The existence and behaviour of lumican has not been studied in the human TMJ disc. Therefore, we used immunohistochemical methods to detect lumican, CD34 and vascular endothelial growth factor (VEGF) and histochemical staining with toluidine blue in 13 human TMJ specimens (10 surgically removed and 3 obtained from autopsy). In both the normal and the deformed discs we observed staining with toluidine blue. We found that the area of metachromasia inside the deformed disc was uneven and expression of lumican was strong in the areas negative for metachromasia. Staining of VEGF and CD34 inside the deformed disc was seen. We confirmed the expression of lumican in the human TMJ disc and showed that a large number of fibroblast-like cells existed in the area of strong lumican expression. These new findings about the behaviour of lumican suggest that it may play a key role in the generation of a new collagen network by fibroblast-like cells.

Figure 1

(A, B, C, D) Lumican expression and toluidine blue staining in the human TMJ disc (scale bar = 100 µm). (A) Lumican expression in the normal disc. (B) Metachromasia in the normal disc. (C) Strong lumican expression in the deformed disc (asterics: uneven or weak expression). (D) Metachromasia in the deformed disc (asterics: positive areas). All specimens are sagittal sections.

Figure 2

(A, B, C, D) Immunohistochemical staining of lumican in the TMJ discs (scale bar = 25 µm). (A) The fibroblast-like cells (arrowhead) and the fibrochondrocyte (black arrow), the chondrocyte-like cell (white arrow) in the normal disc (enlargement of circle in Figure 1A). (B) Fibroblast-like cells (arrows) (enlargement of circle in Figure 1C); (C) Fibrochondrocytes (arrows) (enlargement of circle in Figure 1C); (D) Chondrocyte-like cells (arrow) in the deformed disc (enlargement of rectangle in Figure 1C). All specimens are sagital sections.

Figure 3

(A, B, C, D) Immunohistochemical staining of CD34 and VEGF in the TMJ discs (scale bar = 50 µm). (A) Weak CD34 is observed sporadically within the normal disc. (B) Strong CD34 expression is observed in the wall of newly formed capillaries while weak expression is seen in the extracellular matrix. (C) VEGF expression was not found in the normal disc. (D) Strong VEGF expression is seen in the wall of newly formed capillaries. All specimens are sagital sections.