Age-related secretion of grancalcin by macrophages induces skeletal stem/progenitor cell senescence during fracture healing

Skeletal stem/progenitor cell(SSPC)senescence is a major cause of decreased bone regenerative potential with aging,but the causes of SSPC senescence remain unclear.In this study,we revealed that macrophages in calluses secrete prosenescent factors,including grancalcin(GCA),during aging,which triggers SSPC senescence and impairs fracture healing.Local injection of human rGCA in young mice induced SSPC senescence and delayed fracture repair.Genetic deletion of Gca in monocytes/macrophages was sufficient to rejuvenate fracture repair in aged mice and alleviate SSPC senescence.Mechanistically,GCA binds to the plexin-B2 receptor and activates Arg2-mediated mitochondrial dysfunction,resulting in cellular senescence.Depletion of Plxnb2 in SSPCs impaired fracture healing.Administration of GCA-neutralizing antibody enhanced fracture healing in aged mice.Thus,our study revealed that senescent macrophages within calluses secrete GCA to trigger SSPC secondary senescence,and GCA neutralization represents a promising therapy for nonunion or delayed union in elderly individuals.

“Slow walk”mimetic tensile loading maintains human meniscus tissue resident progenitor cells homeostasis in photocrosslinked gelatin hydrogel

Meniscus,the cushion in knee joint,is a load-bearing tissue that transfers mechanical forces to extracellular matrix(ECM)and tissue resident cells.The mechanoresponse of human tissue resident stem/progenitor cells in meniscus(hMeSPCs)is significant to tissue homeostasis and regeneration but is not well understood.This study reports that a mild cyclic tensile loading regimen of~1800 loads/day on hMeSPCs seeded in 3-dimensional(3D)photocrosslinked gelatin methacryloyl(GelMA)hydrogel is critical in maintaining cellular homeostasis.Experimentally,a“slow walk”biomimetic cyclic loading regimen(10%tensile strain,0.5 Hz,1 h/day,up to 15 days)is applied to hMeSPCs encapsulated in GelMA hydrogel with a magnetic force-controlled loading actuator.The loading significantly increases cell differentiation and fibrocartilage-like ECM deposition without affecting cell viability.Transcriptomic analysis reveals 332 mechanoresponsive genes,clustered into cell senescence,mechanical sensitivity,and ECM dynamics,associated with interleukins,integrins,and collagens/matrix metalloproteinase pathways.The cell-GelMA constructs show active ECM remodeling,traced using a green fluorescence tagged(GFT)-GelMA hydrogel.Loading enhances nascent pericellular matrix production by the encapsulated hMeSPCs,which gradually compensates for the hydrogel loss in the cultures.These findings demonstrate the strong tissue-forming ability of hMeSPCs,and the importance of mechanical factors in maintaining meniscus homeostasis.

Nanosecond pulsed electric fields prime mesenchymal stem cells to peptide ghrelin and enhance chondrogenesis and osteochondral defect repair in vivo

Mesenchymal stem cells(MSCs) are important cell sources in cartilage tissue development and homeostasis,and multiple strategies have been developed to improve MSCs chondrogenic differentiation with an aim of promoting cartilage regeneration.Here we report the effects of combining nanosecond pulsed electric fields(ns PEFs) followed by treatment with ghrelin(a hormone that stimulates release of growth hormone) to regulate chondrogenesis of MSCs.ns PEFs and ghrelin were observed to separately enhance the chondrogenesis of MSCs,and the effects were significantly enhanced when the bioelectric stimulation and hormone were combined,which in turn improved osteochondral tissue repair of these cells within Sprague Dawley rats.We further found that ns PEFs can prime MSCs to be more receptive to subsequent stimuli of differentiation by upregulated Oct4/Nanog and activated JNK signaling pathway.Ghrelin initiated chondrogenic differentiation by activation of ERK1/2 signaling pathway,and RNA-seq results indicated 243 genes were regulated,and JAK-STAT signaling pathway was involved.Interestingly,the sequential order of applying these two stimuli is critical,with ns PEFs pretreatment followed by ghrelin enhanced chondrogenesis of MSCs in vitro and subsequent cartilage regeneration in vivo,but not vice versa.This synergistic prochondrogenic effects provide us new insights and strategies for future cell-based therapies.