The Regulatory Role Of Subchondral Osteoblast In The Joint Degenerate Of ACLT Mice

Objective:Osteoarthritis is one of the most common degenerative diseases with high mobility in Orthopaedic worldwide.In addition to the destruction of joint cartilage,osteophyte formation,synovitis,subchondral bone alterations are the vital components in the pathological processes of OA.In past reports,subchondral bone alterations have been considered as a pivotal impact factor of OA though the clear mechanism has not been distinguished yet.Moreover,no study has revealed the potential role of osteoblasts in OA process.Therefore,we designed this investigation to distinguish the modulatory role of subchondral osteoblast in OA process.Methods:In this present study,3 components of investigations were used to revealed the modulatory of osteoblast in OA process:1、On 2 week and 4 week after ACLT,subchondral Ps6(label of mTORC1 signaling)test,micro-CT of subchondral bone,and double IF label(Ps6 and OSX)was measured respectively.2、Establish osteoblast specific conditional knock TSC1 mice model to over-expressed the mTORC1 signaling in osteoblast.Then revealed the joint degeneration and subchondral bone alterations of WT and OSX-TSC1 null mice by histological and image measurements on 2 week post ACLT.Moreover,Rapamycin was used to complete the rescue test;3.Based on component 1&2,reveal SDF-1 expression in subchondral bone by IHC test,meanwhile,the osteoblast from WT mice and OSX-TSC1 null mice was culture respective,reveal the SDF-1 of each type of osteoblast with or without Rapamycin by ELISA and qPCR.In addition,the MEM of each type of osteoblast was co-culture with chondralcytes cell line(ATDC-5),the hypertrophic marker(MMP-13)of ATDC-5 was revealed by Qpcr.Results:1、After 2 weeks post ACLT,the mTORC1 signaling was overexpressed in the subchondral osteoblast in ACLT mice when compared to the SHAM group and enhancement of subchondral osteogenesis was observed in ACLT mice.2、Over-activated mTORC1 signaling in subchondral bone accelerates joint degeneration of ACLT mice and enhance the subchondral osteogenesis as well.In addition,Rapamycin can rescue the joint degeneration and subchondral osteogenesis of OSX-TSC1 null mice.3、SDF-1 was overexpressed in WT or OSX-TSC1 null mice on 2 week post ACLT which was associated with joint degeneration.Meanwhile,inhibiting osteoblastic SDF-1 releasing by Rapamycin can attenuate the hypertrophic of ATDC-5 cell line.Conclusions:In traumatic OA process,the mTORC1 signaling was activating in subchondral osteoblast and therefore stimulated the SDF-1 releasing to accelerate the joint degeneration.As sufficient therapy is absence in OA treatment,the subchondral osteoblastic SDF-1 releasing inhibition may be a promising aspect for OA treatments.