Background: Spinal cord injury (SCI) can lead to severe motor and sensory dysfunction with high disability and mortality. In recent years, mesenchymal stem cell (MSC)-secreted nano-sized exosomes have shown great potential for promoting functional behavioral recovery following SCI. However, MSCs are usually exposed to normoxia in vitro, which differs greatly from the hypoxic micro-environment in vivo. Thus, the main purpose of this study was to determine whether exosomes derived from MSCs under hypoxia (HExos) exhibit greater effects on functional behavioral recovery than those under normoxia (Exos) following SCI in mice and to seek the underlying mechanism. Methods: Electron microscope, nanoparticle tracking analysis (NTA), and western blot were applied to characterize differences between Exos and HExos group. A SCI model in vivo and a series of in vitro experiments were performed to compare the therapeutic effects between the two groups. Next, a miRNA microarray analysis was performed and a series of rescue experiments were conducted to verify the role of hypoxic exosomal miRNA in SCI. Western blot, luciferase activity, and RNA-ChIP were used to investigate the underlying mechanisms. Results: Our results indicate that HExos promote functional behavioral recovery by shifting microglial polarization from M1 to M2 phenotype in vivo and in vitro. A miRNA array showed miR-216a-5p to be the most enriched in HExos and potentially involved in HExos-mediated microglial polarization. TLR4 was identified as the target downstream gene of miR-216a-5p and the miR-216a-5p/TLR4 axis was confirmed by a series of gain-and loss-offunction experiments. Finally, we found that TLR4/NF-κB/PI3K/AKT signaling cascades may be involved in the modulation of microglial polarization by hypoxic exosomal miR-216a-5p. Conclusion: Hypoxia preconditioning represents a promising and effective approach to optimize the therapeutic actions of MSC-derived exosomes and a combination of MSC-derived exosomes and miRNAs may present a minimally invasive method for treating SCI.

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Spinal cord injury (SCI) can cause severe irreversible motor dysfunction and even death. Neural stem cell (NSC) transplantation can promote functional recovery after acute SCI in experimental animals, but numerous issues, including low-transplanted cell survival rate, cell de-differentiation, and tumor formation need to be resolved before routine clinical application is feasible. Recent studies have shown that transplanted stem cells facilitate regeneration through release of paracrine factors. Small extracellular vesicles (sEVs), the smallest known membrane-bound nanovesicles, are involved in complex intercellular communication systems and are an important vehicle for paracrine delivery of therapeutic agents. However, the application of NSC-derived small extracellular vesicles (NSC-sEVs) to SCI treatment has not been reported. We demonstrate that NSC-sEVs can significantly reduce the extent of SCI, improve functional recovery, and reduce neuronal apoptosis, microglia activation, and neuroinflammation in rats. Furthermore, our study suggests that NSC-sEVs can regulate apoptosis and inflammatory processes by inducing autophagy. In brief, NSC-sEVs increased the expression of the autophagy marker proteins LC3B and beclin-1, and promoted autophagosome formation. Following NSC-sEV infusion, the SCI area was significantly reduced, and the expression levels of the proapoptotic protein Bax, the apoptosis effector cleaved caspase-3, and the pro-inflammatory cytokines TNF-α, IL-1β, and IL-6 were significantly reduced, whereas the expression level of the anti-apoptotic protein Bcl-2 was upregulated. In the presence of the autophagy inhibitor 3MA, however, these inhibitory effects of NSC-sEVs on apoptosis and neuroinflammation were significantly reversed. Our results show for the first time that NSC-sEV treatment has the potential to reduce neuronal apoptosis, inhibit neuroinflammation, and promote functional recovery in SCI model rats at an early stage by promoting autophagy.

Approximately 10% of bone fractures do not heal satisfactorily, leading to significant clinical and socioeconomic implications. Recently, the role of macrophages in regulating bone marrow stem cell (BMSC) differentiation through the osteogenic pathway during fracture healing has attracted much attention.Methods: The tibial monocortical defect model was employed to determine the critical role of macrophage scavenger receptor 1 (MSR1) during intramembranous ossification (IO) in vivo. The potential functions and mechanisms of MSR1 were explored in a co-culture system of bone marrow-derived macrophages (BMDMs), RAW264.7 cells, and BMSCs using qPCR, Western blotting, immunofluorescence, and RNA sequencing.Results: In this study, using the tibial monocortical defect model, we observed delayed IO in MSR1 knockout (KO) mice compared to MSR1 wild-type (WT) mice. Furthermore, macrophage MSR1 mediated PI3K/AKT/GSK3β/β-catenin signaling increased ability to promote osteogenic differentiation of BMSCs in the co-culture system. We also identified proliferator-activated receptor gamma coactivator 1-alpha (PGC1α) as the target gene for macrophage MSR1-activated PI3K/AKT/GSK3β/β-catenin pathway in the co-culture system that facilitated M2-like polarization by enhancing mitochondrial oxidative phosphorylation.Conclusion: Our findings revealed a previously unrecognized function of MSR1 in macrophages during fracture repair. Targeting MSR1 might, therefore, be a new therapeutic strategy for fracture repair.

Aims: In the NOD-like receptor (NLR) family, the pyrin domain containing 3 (NLRP3) inflammasome is closely related to the progression of atherosclerosis. This study aimed to assess the effects of curcumin on NLRP3 inflammasome in phorbol 12-myristate 13-acetate (PMA)-induced macrophages and explore its underlying mechanism.Methods: Human monocytic THP-1 cells were pretreated with curcumin for 1 h and subsequently induced with PMA for 48 h. Total protein was collected for Western blot analysis. Cytokine interleukin (IL)-1β release and nuclear factor kappa B (NF-κB) p65 translocation were detected by ELISA assay and cellular NF-κB translocation kit, respectively.Results: Curcumin significantly reduced the expression of NLRP3 and cleavage of caspase-1 and IL-1β secretion in PMA-induced macrophages. Moreover, Bay (a NF-κB inhibitor) treatment considerably suppressed the expression of NLRP3 inflammasome in PMA-induced THP-1 cells. Curcumin also markedly inhibited the upregulation of toll-like receptor 4 (TLR4), myeloid differentiation factor 88 (MyD88), phosphorylation level of IκB-α, and activation of NF-κB in PMA-induced macrophages. In addition, purinergic 2X7 receptor (P2X7R) siRNA was administered, and it significantly decreased NLRP3 inflammasome expression in PMA-induced macrophages. Furthermore, curcumin reversed PMA-stimulated P2X7R activation, which further reduced the expression of NLRP3 and cleavage of caspase-1 and IL-1β secretion. Silencing of P2X7R using siRNA also suppressed the activation of NF-κB pathway in PMA-induced macrophages, but P2X7R-silenced cells did not significantly decrease the expression of TLR4 and MyD88.Conclusion: Curcumin inhibited NLRP3 inflammasome through suppressing TLR4/MyD88/NF-κB and P2X7R pathways in PMA-induced macrophages.

MicroRNAs and autophagy play critical roles in cardiac hypoxia/reoxygenation (H/R)‐induced injury. Here, we investigated the function of miR‐21 in regulating autophagy and identified the potential molecular mechanisms involved. To determine the role of miR‐21 in regulating autophagy, H9c2 cells were divided into the following six groups: control group, H/R group, (miR‐21+ H/R) group, (miR‐21‐negative control + H/R) group, (BEZ235+ H/R) group and (miR‐21+ BEZ235+ H/R) group. The cells underwent hypoxia for 1 hr and reoxygenation for 3 hrs. Cell count kit‐8 was used to evaluate cell function and apoptosis was analysed by Western blotting. Western blotting and transmission electron microscopy were used to investigate autophagy. We found that miR‐21 expression was down‐regulated, and autophagy was remarkably increased in H9c2 cells during H/R injury. Overexpression of miR‐21 with a miR‐21 precursor significantly inhibited autophagic activity and decreased apoptosis, accompanied by the activation of the AKT/mTOR pathway. In addition, treatment with BEZ235, a novel dual Akt/mTOR inhibitor, resulted in a significant increase in autophagy and apoptosis. However, we found that miR‐21‐mediated inhibition of apoptosis and autophagy was partly independent of Akt/mTOR activation, as demonstrated in cells treated with both miR‐21 and BEZ235. We showed that miR‐21 could inhibit H/R‐induced autophagy and apoptosis, which may be at least partially mediated by the Akt/mTOR signalling pathway.

The evolution of a child’s skin microbiome is associated with the development of the immune system and skin environment. As only few studies have analyzed the microbiota in young children, we investigated changes in the skin microbiota of children (158 subjects; ≤10 years old) and compared the microbiota structures between children and their mothers using 16S rRNA gene amplicon sequencing. Sample location and age were the primary factors determining a child’s skin bacterial composition, which differed significantly among the face, ventral forearm, and calf. Relative abundances of Streptococcus and Granulicatella were negatively correlated with age, and the alpha diversity at all body sites examined increased during the first 10 years of life, especially on the face. The facial bacterial composition of 10-year-old children was strongly associated with delivery mode at birth. Among mother-child pairs (50 pairs), the relative abundances of most bacterial genera in children were more similar to those of their own mothers than those of unrelated women. The data indicated that age and site were significantly associated with microbial composition and that maternal factors determine the child’s microbiome. Further research is needed to characterize the effects of maturation of the infant microbiome on health in adulthood.

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