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The Identification of CD163 Expressing Phagocytic Chondrocytes in Joint Cartilage and Its Novel Scavenger Role in Cartilage Degradation
Authors:Kai Jiao  Jing Zhang  Mian Zhang  Yuying Wei  Yaoping Wu  Zhong Ying Qiu  Jianjun He  Yunxin Cao  Jintao Hu  Han Zhu  Li-Na Niu  Xu Cao  Kun Yang  Mei-Qing Wang
Abstract:

Background

Cartilage degradation is a typical characteristic of arthritis. This study examined whether there was a subset of phagocytic chondrocytes that expressed the specific macrophage marker, CD163, and investigated their role in cartilage degradation.

Methods

Cartilage from the knee and temporomandibular joints of Sprague-Dawley rats was harvested. Cartilage degradation was experimentally-induced in rat temporomandibular joints, using published biomechanical dental methods. The expression levels of CD163 and inflammatory factors within cartilage, and the ability of CD163+ chondrocytes to conduct phagocytosis were investigated. Cartilage from the knees of patients with osteoarthritis and normal cartilage from knee amputations was also investigated.

Results

In the experimentally-induced degrading cartilage from temporomandibular joints, phagocytes were capable of engulfing neighboring apoptotic and necrotic cells, and the levels of CD163, TNF-α and MMPs were all increased (P<0.05). However, the levels of ACP-1, NO and ROS, which relate to cellular digestion capability were unchanged (P>0.05). CD163+ chondrocytes were found in the cartilage mid-zone of temporomandibular joints and knee from healthy, three-week old rats. Furthermore, an increased number of CD163+ chondrocytes with enhanced phagocytic activity were present in Col-II+ chondrocytes isolated from the degraded cartilage of temporomandibular joints in the eight-week experimental group compared with their age-matched controls. Increased number with enhanced phagocytic activity of CD163+ chondrocytes were also found in isolated Col-II+ chondrocytes stimulated with TNF-α (P<0.05). Mid-zone distribution of CD163+ cells accompanied with increased expression of CD163 and TNF-α were further confirmed in the isolated Col-II+ chondrocytes from the knee cartilage of human patients with osteoarthritis, in contrast to the controls (both P<0.05).

Conclusions

An increased number of CD163+ chondrocytes with enhanced phagocytic activity were discovered within degraded joint cartilage, indicating a role in eliminating degraded tissues. Targeting these cells provides a new strategy for the treatment of arthritis.
Keywords:
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