Runxl protects against the pathological progression of osteoarthritis

Runt-related transcription factor-1(Runxl)is required for chondrocyte-to-osteoblast lineage commitment by enhancing both chondrogenesis and osteogenesis during vertebrate development.However,the potential role of Runxl in joint diseases is not well known.In the current study,we aimed to explore the role of Runxl in osteoarthritis induced by anterior cruciate ligament transaction(ACLT)surgery.We showed that chondrocyte-specific Runxl knockout(Runx1f/fCol2a1-Cre)aggravated cartilage destruction by accelerating the loss of proteoglycan and collagen II in early osteoarthritis.Moreover,we observed thinning and ossification of the growth plate,a decrease in chondrocyte proliferative capacity and the loss of bone matrix around the growth plate in late osteoarthritis.We overexpressed Runxl by adeno-associated virus(AAV)in articular cartilage and identified its protective effect by slowing the destruction of osteoarthritis in cartilage in early osteoarthritis and alleviating the pathological progression of growth plate cartilage in late osteoarthritis.ChIP-seq analysis identified new targets that interacted with Runxl in cartilage pathology,and we confirmed the direct interactions of these factors with Runxl by ChIP-qPCR.This study helps us to understand the function of Runxl in osteoarthritis and provides new clues for targeted osteoarthritis therapy.

Disturbed bone remodelling activity varies in different stages of experimental, gradually progressive apical periodontitis in rats

Bone remodelling keeps going through the lifespan of human by bone formation and bone resorption.In the craniofacial region,mandibles act as the main force for biting and chewing,and also become susceptible to a common bone-loss disease,namely,apical periodontitis,once infected dental pulp is not treated timely,during which bone resorption occurs from the apical foramen to the apical bone area.Although conventional root canal treatment(RCT)can remove the most of the infection,chronical apical periodontitis due to incomplete removal of dental pulp and subsequent microleakage will become refractory and more challenging,and this process has scarcely been specifically studied as a bone remodelling issue in rat models.Therefore,to study chronical and refractory apical periodontitis owing to incomplete cleaning of infected dental pulp and microleackage in vivo,we establish a modified rat model of gradually progressive apical periodontitis by sealing residual necrotic dental pulp and introducing limited saliva,which simulates gradually progressive apical periodontitis,as observed in the clinical treatment of chronical and refractory apical periodontitis.We show that bone-loss is inevitable and progressive in this case of apical periodontitis,which confirms again that complete and sound root canal treatment is crucial to halt the progression of chronical and refractory apical periodontitis and promote bone formation.Interestingly,bone remodelling was enhanced at the initial stage of apical periodontitis in this model while reduced with a high osteoblast number afterwards,as shown by the time course study of the modified model.Suggesting that the pathological apical microenvironment reserve its hard tissue formation ability to some degree but in a disturbed manner.Hopefully,our findings can provide insights for future bone regenerative treatment for apical periodontitisassociated bone loss.

Microenvironmental stiffness mediates cytoskeleton re-organization in chondrocytes through laminin-FAK mechanotransduction

Microenvironmental biophysical factors play a fundamental role in controlling cell behaviors including cell morphology,proliferation,adhesion and differentiation,and even determining the cell fate.Cells are able to actively sense the surrounding mechanical microenvironment and change their cellular morphology to adapt to it.Although cell morphological changes have been considered to be the first and most important step in the interaction between cells and their mechanical microenvironment,their regulatory network is not completely clear.In the current study,we generated silicon-based elastomer polydimethylsiloxane(PDMS)substrates with stiff(15:1,PDMS elastomer vs.curing agent)and soft(45:1)stiffnesses,which showed the Young’s moduli of~450 k Pa and 46 kPa,respectively,and elucidated a new path in cytoskeleton re-organization in chondrocytes in response to changed substrate stiffnesses by characterizing the axis shift from the secreted extracellular protein lamininβ1,focal adhesion complex protein FAK to microfilament bundling.We first showed the cellular cytoskeleton changes in chondrocytes by characterizing the cell spreading area and cellular synapses.We then found the changes of secreted extracellular linkage protein,lamininβ1,and focal adhesion complex protein,FAK,in chondrocytes in response to different substrate stiffnesses.These two proteins were shown to be directly interacted by Co-IP and colocalization.We next showed that impact of FAK on the cytoskeleton organization by showing the changes of microfilament bundles and found the potential intermediate regulators.Taking together,this modulation axis of lamininβ1-FAK-microfilament could enlarge our understanding about the interdependence among mechanosensing,mechanotransduction,and cytoskeleton re-organization.