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Mesenchymal stem cell-derived extracellular vesicles (MSC-EVs) have obvious advantages over MSC therapy. But the strong procoagulant properties of MSC-EVs pose a potential risk of thromboembolism, an issue that remains insufficiently explored. In this study, we systematically investigated the procoagulant activity of large EVs derived from human umbilical cord MSCs (UC-EVs) both in vitro and in vivo. UC-EVs were isolated from cell culture supernatants. Mice were injected with UC-EVs (0.125, 0.25, 0.5, 1, 2, 4 μg/g body weight) in 100 μL PBS via the tail vein. Behavior and mortality were monitored for 30 min after injection. We showed that these UC-EVs activated coagulation in a dose- and tissue factor-dependent manner. UC-EVs-induced coagulation in vitro could be inhibited by addition of tissue factor pathway inhibitor. Notably, intravenous administration of high doses of the UC-EVs (1 μg/g body weight or higher) led to rapid mortality due to multiple thrombus formations in lung tissue, platelets, and fibrinogen depletion, and prolonged prothrombin and activated partial thromboplastin times. Importantly, we demonstrated that pulmonary thromboembolism induced by the UC-EVs could be prevented by either reducing the infusion rate or by pre-injection of heparin, a known anticoagulant. In conclusion, this study elucidates the procoagulant characteristics and mechanisms of large UC-EVs, details the associated coagulation risk during intravenous delivery, sets a safe upper limit for intravenous dose, and offers effective strategies to prevent such mortal risks when high doses of large UC-EVs are needed for optimal therapeutic effects, with implications for the development and application of large UC-EV-based as well as other MSC-EV-based therapies., (© 2024. The Author(s), under exclusive licence to Shanghai Institute of Materia Medica, Chinese Academy of Sciences and Chinese Pharmacological Society.)

Few therapies can reverse the proangiogenic activity of senescent mesenchymal stromal/stem cells (MSCs). In this study, we investigated the effects of rapamycin on the proangiogenic ability of senescent human umbilical cord MSCs (UCMSCs). An in vitro replicative senescent cell model was established in cultured UCMSCs. We found that late passage (P25 or later) UCMSCs (LP-UCMSCs) exhibited impaired proangiogenic abilities. Treatment of P25 UCMSCs with rapamycin (900 nM) reversed the senescent phenotype and notably enhanced the proangiogenic activity of senescent UCMSCs. In a nude mouse model of hindlimb ischemia, intramuscular injection of rapamycin-treated P25 UCMSCs into the ischemic limb significantly promoted neovascularization and ischemic limb salvage. We further analyzed the changes in the expression of angiogenesis-associated genes in rapamycin-primed MSCs and found higher expression of several genes related to angiogenesis, such as VEGFR2 and CTGF/CCN2, in primed cells than in unprimed MSCs. Taken together, our data demonstrate that rapamycin is a potential drug to restore the proangiogenic activity of senescent MSCs, which is of importance in treating ischemic diseases and tissue engineering., (© 2022. The Author(s), under exclusive licence to Shanghai Institute of Materia Medica, Chinese Academy of Sciences and Chinese Pharmacological Society.)

Objective: To investigate the feasibility of using human umbilical cord blood derived mesenchymal stem cells (UCB-MSCs) and demineralized bone matrix (DBM) scaffolds to repair critical-sized calvarial defects in athymic rats., Methods: Human UCB-MSCs were isolated, expanded and osteogenically induced in vitro. Osteogenic differentiation of UCB-MSCs was evaluated by Alizarin Red staining and measurement of calcium content respectively, and then the cells were seeded onto DBM scaffolds. Bilateral full-thickness defects (5 mm in diameter) of parietal bone were created in an athymic rat model. The defects were either repaired with UCB-MSC/DBM constructs (experimental group) or with DBM scaffolds alone (control group). Animals were harvested at 6 and 12 weeks post-implantation respectively, and defect repair was evaluated with gross observation, micro-CT measurement and histological analysis., Results: Micro-CT showed that new bone was formed in the experimental group at 6 weeks post-implantation, while no sign of new bone formation was observed in the control group. At 12 weeks post-transplantation, scaffolds had been degraded almost completely in both sides. It was shown that an average of (78.19 +/- 6.45)% of each defect volume had been repaired in experimental side; while in the control side, only limited bone formed at the periphery of the defect. Histological examination revealed that the defect was repaired by trabecular bone tissue in experimental side at 12 weeks, while only fibrous connection was observed in the control group., Conclusions: Tissue-engineered bone composed of osteogenically-induced human UCB-MSCs on DBM scaffolds could successfully repair the critical-sized calvarial defects in athymic rat models.

Objective: To study the possibility and mechanism of construction of tissue engineered bone with human bone marrow mesenchymal stem cells (hBMSCs) as seeding cells and partially demineralized bone matrix (pDBM) as scaffold., Methods: hBMSCs are cultured and mutiplified. The 4th grade hBMSCs are seeded on the pDBM, the growth and adhesion of hBMSCs on pDBM are observed under scanning electro microscope. The adhesion efficiency is assessed. The complexes are implanted in the nude mice subcutaneously, the pDBM without cells as control. The grafts are taken out on the 8th and 12th week., Results: There is new bone formation on the 8th and 12th week in complex group. There is a layer of osteoblast like cells adhered on the surface of most of the new bone, which suggest the possibility of intramembranous ossification. There is no bone formation in control group., Conclusions: Tissue engineered bone can be constructed with hBMScs and pDBM in vivo, and the mechanism of which could be intramembranous ossification.

Objective: To investigate the feasibility of human bone marrow mesenchymal stem cells (hBMSCs) in vitro differentiation into vascular smooth muscle cells with induction of platelet-derived growth Factor BB (PDGF-BB)., Methods: Bone marrow mesenchymal stem cells of adult healthy donors were separated from iliac crest aspiration and expanded in DMEM-LG medium. Cells at passage 1 were transferred to EGM-2 medium containing PDGF-BB (20 ng/ml) and cultured for 14 days. The expression of SM alpha-actin, SM calponin, SMMHC and SM 22alpha were detected by immunofluorescence and observed with fluorescence microscope. mRNA expression of SMalpha-actin, SM calponin, SMMHC as well as SM 22alpha was analyzed by RT-PCR. The method of Western-Blot was applied to determine protein expression of SM 22alpha. Cells with induction were observed for the expression of SM alpha-actin,SM calponin,SMMHC by FACs analysis., Results: With the induction of PDGF-BB, the morphology of cells changed to a spindle fibroblastic appearance. By fluorescence microscope observation, expression of SM alpha-actin, SM calponin and SMMHC was found intracellularly in PDGF-BB treated hBMSCs at 14 days. Western-Blot detection confirmed SM 22alpha expression by 14 days induction. RT-PCR of characteristic vascular smooth muscle cells related genes, such as SM alpha-actin, SM calponin, SMMHC and SM 22alpha revealed differentiation of vascular smooth muscle cells phenotype in monolayer culture upon stimulation with PDGF-BB for 14 days. The positive expression of SM alpha-actin, SM calponin and SMMHC in induced cells was significantly higher than that in non-induced cells (P < 0.05, n=3)., Conclusion: These results suggested hBMSCs could be differentiated into vascular smooth muscle cell phenotype with PDGF-BB induction in vitro.

Objective: To repair segmental mandibular defects with autogenous bone marrow stromal cells (BMSCs) and coralline hydroxyapatite., Methods: Isolated BMSCs were in vitro expanded and osteogenically induced. In 11 canines, a 3 cm segmental mandibular defect in right mandible was created. Five canine's defects were repaired with cell-scaffold constructs made from induced BMSCs and coralline hydroxyapatite (CHA); Others were repaired with CHA as control. The engineered bone was evaluated by X-ray, CT, gross and histological examination, biomechanical test 12, 26, 32 weeks post-operation respectively., Results: BMSCs grew well on the CHA. X-ray and CT images showed better callus formation at connection sites in experimental group over time while worse formation at connection sites eventually in control group. At 32 weeks post-operation in experimental group, the defects were well repaired grossly. Histologically, there were bony healing and lamellar bone formation, in experimental group fibrous healing and woven bone formation in control group. Biomechanical test revealed no significant difference between experimental group and normal control group., Conclusions: Canine segmental mandibular defects can be ultimately repaired with the tissue-engineered bone generated by autogenous osteogenic BMSCs and CHA scaffold.

Purpose: To explore the ectopic osteogenic abilities of bone marrow stromal cells (BMSCs) on different scaffold materials in nude mice., Methods: Canine BMSCs in vitro cultured were seeded at the density of 1x10(6)cells/cm(2) onto scaffolds of freeze-dried demineralized bone matrix (fdDBM), tricalcium phosphate (TCP), 200microm coralline hydroxyapatite (CH200) and 500microm coralline hydroxyapatite (CH500). The cell adherence and growth on the materials were examined by SEM and H&E staining after 4 to 7 days of in vitro culturing. To observe the ectopic osteogenic capacity, four 10mmx5mmx2mm cell/scaffold complexes (fdDBM, TCP, CH200, CH500) and a blank control scaffold (fdDBM only) were implanted subcutaneously into each of athymic mice (n=8). The implants were harvested after 9 weeks and H&E stained. Newly formed trabecular bone volume (TBV) was measured by IMAGER-PRO PLUS software, and statistical analysis was performed by ANOVA with SAS software., Results: Canine BMSCs adhered to all 4 types of scaffolds and spread well in their pores 7-8 days after seeding. Athymic subcutaneous ectopic osteogenesis were observed in all the specimens of TCP, CH200, CH500 but were observed only in 75% of BMSCs/fdDBM and 25% of fdDBM. The TCP group showed significant higher TBV percentage (28.2%+/-2.86) than CH200 group (24.1%+/-4.12) and CH500 group (18.1%+/-4.66) (P<0.01)., Conclusions: BMSCs adhered to all 4 scaffolds. When combined with BMSCs, TCP exhibited the greatest osteogenic potential, which indicates that it might be an excellent scaffold material in the field of bone tissue engineering. Supported by National 973 Project (G1999054300) and National Natural Science Foundation of China(30271426).

Objective: To evaluate the influence of mechanical stress on chondrogenesis of in vitro cultured porcine bone marrow stem cells (BMSC)., Methods: Porcine BMSC of passage 2 were seeded onto a cylinder-shaped PGA/PLA scaffold, 8mm in diameter and 3mm in thickness, at a density of 5 x 10(7)/cm(3). After the cell-scaffold constructs were cultured for one week, the primary medium, high-glucose DMEM medium with 10% fetal bovine serum (FBS), was replaced by chondrogenically inductive medium containing TGFbeta(1) (10 ng/ml), IGF-I (50 ng/ml), and dexamethasone (40 ng/ml) in addition to DMEM+10% FBS. The constructs were randomly divided into three groups according to the imposed stress: experimental group A in which a centrifugal stress was imposed at 100 g, 30 min, 2/d; experimental group B in which a rotative stress was imposed at 80 rpm, 8 h/d by a shaker; and control group in which the constructs were statically cultured. The gross view, histology, histochemistry, immunohistochemistry and glycosaminoglycan (GAG) content were evaluated after 4 and 8 weeks respectively., Results: Four weeks later, the constructs in both experimental groups maintained their original sizes and shapes. Histology showed nodular lacuna-like structures, in company with GAG deposition and collagen synthesis. In addition, collagen type II was detected by immunohistochemistry. In the control group, however, the constructs shrunk to a little smaller size than those in the experimental groups, and histological staining showed a little amount of lacuna. Eight weeks later, the constructs in both experimental groups still maintained the original sizes and shapes with good elasticity. HE staining showed massive lacuna-like structures in most areas of the construct and extracellular matrix deposited evenly. Fibrous tissues were only observed in some areas. Safranin-O staining showed massive GAG formation and Masson staining showed much more collagen formation than those in the control group. Immunohistochemical staining of collagen type II showed strong positive expression. In the control group the constructs showed massive fibrous tissues, with a small amount of lacuna-like structures in the peripheral areas. GAG contents in the 2 experimental groups were 5.98 mg/g and 5.62 mg/g respectively, both significantly higher than that in the control group (4.73 mg/g) without a difference between the 2 experimental groups., Conclusion: Mechanical stress promotes chondrogenesis and cartilage maturation of BMSC in vitro.