| BackgroundOsteoarthritis is the most common joint disease,characterized by abnormal bone remodeling of the subchondral bone,non-uniform settlement of the medial and lateral tibial plateaus,cartilage injury and synovial thickening.More than 700 million people in the world suffer from OA,and as a result,there is a huge social and economic consumption and burden.At present,27 million people have been disabled due to OA and it is expected that the number of disabled people will double by 2030.Salubrinal is a chemical synthesis agent that inhibits the dephosphorylation of eukaryotic translation initiation factor 2?(eIF2?).Our previous study confirmed that salubrinal can promote bone wound healing,treat osteoporosis and femoral head necrosis by inhibiting the development of osteoclasts.And some studies showed that salubrinal can protect OA cartilage from damage by inhibiting the expression and activity of inflammatory factors.ObjectiveTo observe the effect of Salubrinal on the subchondral bone of osteoarthritis mice at early stage.In this study,we surgically resected the medial meniscus of the knee jiont in the mice to established an animal model of OA.And investigated whether salubrinal can treat early osteoarthritis by inhibiting abnormal osteoclast activity,modifying subchondral bone remodeling and non-uniform settlement of the medial and lateral tibial plateaus.MethodsExperiment 1: Twenty female C57BL/6 mice(approximately 14 weeks of age)were randomly divided into sham-operated controls group(Sham,n=5),2-week OA model group(2w OA,n=5),4-week OA model group(4w OA,n=5)and 8-week OA model group(8w OA,n=5).The animal model of osteoarthritis was established by surgically resecting the medial meniscus of the knee joint in the mice.The mice were sacrificed at the end of 2 weeks,4 weeks and 8 weeks after operation.The hind leg tissue was isolated and collected.HE staining was used to observe the pathological changes of the knee joints in the early,middle and late stages of OA,to determine whether the OA model was established successfully.Experiment 2: Thirty female C57BL/6 mice(about 14 weeks old)were randomly divided into sham-operated control group(Sham,n=10),2-week OA model group(OA,n=10)and 2-week OA+ Salubrinal group(OA+Sal).The animal model method is same as experiment one.OA+Sal group mice were injected subcutaneously with Salubrinal(1 mg/kg/d)for 2 weeks.Then mice were sacrificed at the end of 2 wks postoperative and the hind leg tissue was separated and collected.Histological staining of HE,Safranine O and tartrate-resistant acid phosphatase(TRAP)was used to observe histomorphological and osteoclast activity changes of the medial and lateral tibial plateaus.Experiment 3: Nine female C57BL/6 mice(approximately 14 weeks of age)were used.The groups and animal modeled were same as the experiment two(n=3).After the mice were sacrificed,bone marrow cells in the bone marrow cavity of the femur and tibia were collected,cultured and induced.The osteoclast formation,migration,and adhesion tests of bone marrow cells were used to examine the development of osteoclasts in each group.ResultsThe experiment results showed that the cartilage surface of the medial tibial plateau was discontinuous at 2w OA,and the tidemark was irregular or even disappeared.The number of chondrocytes was significantly reduced,and a large number of hypertrophic vacuole cells appeared.The lateral tibial plateau cartilage showed a slight fibrosis.The subchondral bone of the medial and lateral tibial plateau appeared uneven changes,and the thickness of the trabecular bone in the subchondral bone was uneven and irregular.Synovial is also thickened significantly.With the increase of modeling time,the wear of cartilage and remodeling of subchondral bone are more and more serious in 4w OA and 8w OA.There was cartilage hyperplasia at the edge of the medial tibial plateau in 4w OA,and the bony osteophyte was formed at 8w.2w Histological and cytological experiment results showed that,compared with Sham group,bone marrow-derived osteoclasts in OA group were significantly activated(P<0.05)and the migratary and adhesive ability were significantly increased(P<0.05).The activity of osteoclasts in subchondral bone was also increased obviously(P<0.05).The OARSI score and calcified cartilage ratio(CC/TAC)were significantly elevated(P<0.05).The bone area fraction(B.Ar/T.Ar)of the medial tibial plateau subchondral bone was increased significantly(P<0.05),but the lateral B.Ar/T.Ar and thickness of subchondral bone plate(SBP)were decreased obviously(P<0.05).Four-segment synovial membrane scores were significantly increased(P<0.05).Compared with OA group,bone marrow-derived osteoclasts development and the migratary and adhesive ability in OA+Sal group were significantly inhibited(P<0.05).The activity of osteoclasts in subchondral bone was also inhibited(P<0.05).OARSI scores and CC/TAC were decreased(P<0.05).Moreover,the inhomogeneous changes of B.Ar/T.Ar and SBP in the medial and lateral tibial plateaus subchondral bone were significantly restored(P<0.05).Four-segment synovial scores were also decreased significantly(P<0.05).By comparing the fold changes between the internal and lateral,we found that compared with Sham group,the OARSI score and the B.Ar/T.Ar(%)fold changes in the medial tibial plateau were significantly higher than those in the lateral tibial plateau(P<0.05).Compared with the OA group,there was no significant difference in the fold changes of OARSI score in the OA+Sal group(P>0.05),while the fold change of B.Ar/T.Ar(%)in medial tibial plateau was significantly lower than that in lateral tibial plateau(P<0.05).ConclusionWe successfully established an animal model of OA by surgically resecting the medial meniscus of the mice knee jiont.And we found that Salubrinal can play a significant role in bone remodeling and non-uniform settlement of tibia plateau subchondral bone at early osteoarthritis stage through regulating osteoclasts development.The current study suggests that salubrinal might potentially be employed as a new therapy for OA. |
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