Activated macrophage-like synoviocytes are resistant to endoplasmic reticulum stress-induced apoptosis in antigen-induced arthritis.
OBJECTIVE
To explore the characteristic expression of endoplasmic reticulum (ER) stress protein in antigen-induced arthritis models and the role of ER stress in arthritis.


METHODS
Effective animal models of rheumatoid arthritis in rabbits and rats were induced by methylated bovine serum albumin and Freund's complete adjuvant. Pathological changes were assessed by magnetic resonance imaging and histological analysis. The expression and localization of ER stress proteins in synovium and peritoneal macrophages (PMΦ) were analyzed by double immunofluorescence staining. RT-PCR was performed to detect mRNA expression of ER stress-related genes. Tumor necrosis factor alpha (TNF-α) and interleukin-1 beta (IL-1β) levels in synoviocytes were measured by RT-PCR and radioimmunoassay.


RESULTS
We found that the ER stress marker BiP was highly up-regulated in arthritis synovium and extensively expressed in fibroblast-like synoviocytes (FLS) and macrophage-like synoviocytes (MLS). The expression of the pro-apoptotic factor CHOP/GADD153 was slightly elevated in inflammatory synovium and mainly localized in FLS, but insignificant in MLS. Unexpectedly, increased expression of CHOP was observed in PMΦ in arthritis rats. Likewise, cleaved caspase-3 was rarely expressed in MLS. In addition, induction of ER stress by tunicamycin resulted in significantly increased expression of pro-inflammatory molecules such as IL-1β and TNF-α in cultured inflammatory FLS.


CONCLUSIONS
Differential activation of the ER stress proteins in synovium MLS may contribute to the resistance of synoviocytes to ER stress-induced apoptosis. Furthermore, ER stress is a potential mediator of arthritis inflammation.
School of Basic Medical Science, Anhui Medical University, 69 Meishan Road, 230032, Hefei, China.
Li-Jie
LJ
Feng
Tong-Cui
TC
Jiang
Cheng-Yue
CY
Zhou
Chang-Liang
CL
Yu
Yu-Jun
YJ
Shen
Jun
J
Li
Yu-Xian
YX
Shen
D000199:Actins / Q000032:analysis; D000818:Animals; D015703:Antigens, CD / Q000032:analysis; D015214:Antigens, Differentiation, Myelomonocytic / Q000032:analysis; D017209:Apoptosis; D001169:Arthritis, Experimental / Q000473:pathology*; D053148:Caspase 3 / Q000378:metabolism; D002478:Cells, Cultured; D059865:Endoplasmic Reticulum Stress; D005260:Female; D053583:Interleukin-1beta / Q000235:genetics; D008262:Macrophage Activation; D008264:Macrophages / Q000502:physiology*; D008279:Magnetic Resonance Imaging; D008297:Male; D011817:Rabbits; D051381:Rats; D017207:Rats, Sprague-Dawley; D013583:Synovial Membrane / Q000166:cytology*; D051742:Transcription Factor CHOP / Q000032:analysis; D014409:Tumor Necrosis Factor-alpha / Q000235:genetics; D000097382:CD68 Molecule
D000199:Actins; D015703:Antigens, CD; D015214:Antigens, Differentiation, Myelomonocytic; D053148:Caspase 3; D053583:Interleukin-1beta; D051742:Transcription Factor CHOP; D014409:Tumor Necrosis Factor-alpha; C067980:CD68 antigen, human; D000097382:CD68 Molecule; C498862:Acta2 protein, rat