Macrophage-derived small extracellular vesicles promote biomimetic mineralized collagen-mediated endogenous bone regeneration

Macrophages play an important role in material-related immune responses and bone formation,but the functionality of macrophage-derived extracellular vesicles(EVs)in material-mediated bone regeneration is still unclear.Here,we evaluated intracellular communication through small extracellular vesicles(sEVs)and its effects on endogenous bone regeneration mediated by biomimetic intrafibrillarly mineralized collagen(IMC).After implantation in the bone defect area,IMC generated more neobone and recruited more mesenchymal stem cells(MSCs)than did extrafibrillarly mineralized collagen(EMC).More CD63+CD90+and CD63+CD163+cells were detected in the defect area in the IMC group than in the EMC group.To determine the functional roles of sEVs,extracellular vesicles from macrophages cultured on different mineralized collagen were isolated,and they showed no morphological differences.However,macrophage-derived sEVs in the IMC group showed an enhanced Young’s modulus and exerted beneficial effects on the osteogenic differentiation of bone marrow MSCs by increasing the expression of the osteoblastic differentiation markers BMP2,BGLAP,COL1,and OSX and calcium nodule formation.Mechanistically,sEVs from IMC-treated macrophages facilitated MSC osteogenesis through the BMP2/Smad5 pathway,and blocking sEV secretion with GW4869 significantly impaired MSC proliferative,immunomodulative and osteogenic potential.Taken together,these findings show that macrophage-derived sEVs may serve as an emerging functional tool in biomaterial-mediated endogenous bone regeneration.

GPCR/endocytosis/ERK signaling/S2R is involved in the regulation of the internalization,mitochondria-targeting and-activating properties of human salivary histatin 1

Human salivary histatin 1(Hst1)exhibits a series of cell-activating properties,such as promoting cell spreading,migration,and metabolic activity.We recently have shown that fluorescently labeled Hst1(F-Hst1)targets and activates mitochondria,presenting an important molecular mechanism.However,its regulating signaling pathways remain to be elucidated.We investigated the influence of specific inhibitors of G protein-coupled receptors(GPCR),endocytosis pathways,extracellular signal-regulated kinases1/2(ERK1/2)signaling,p38 signaling,mitochondrial respiration and Na+/K+-ATPase activity on the uptake,mitochondria-targeting and-activating properties of F-Hst1.We performed a si RNA knockdown(KD)to assess the effect of Sigma-2 receptor(S2R)/Transmembrane Protein 97(TMEM97)—a recently identified target protein of Hst1.We also adopted live cell imaging to monitor the whole intracellular trafficking process of F-Hst1.Our results showed that the inhibition of cellular respiration hindered the internalization of F-Hst1.The inhibitors of GPCR,ERK1/2,phagocytosis,and clathrin-mediated endocytosis(CME)as well as siRNA KD of S2R/TMEM97 significantly reduced the uptake,which was accompanied by the nullification of the promoting effect of F-Hst1 on cell metabolic activity.Only the inhibitor of CME and KD of S2R/TMEM97 significantly compromised the mitochondria-targeting of Hst1.We further showed the intracellular trafficking and targeting process of F-Hst1,in which early endosome plays an important role.Overall,phagocytosis,CME,GPCR,ERK signaling,and S2R/TMEM97 are involved in the internalization of Hst1,while only CME and S2R/TMEM97 are critical for its subcellular targeting.The inhibition of either internalization or mitochondria-targeting of Hst1 could significantly compromise its mitochondria-activating property.