Nanoscaled Bionic Periosteum Orchestrating the Osteogenic Microenvironment for Sequential Bone Regeneration.

Periosteum orchestrates bone repair. Previously developed artificial periosteum was mainly focusing on materials modification to simply enhance bone formation, but few were attempting to make the artificial periosteum fit different bone repair stages. Here, we constructed a functionalized periosteum, which was composed of an electrospun scaffold grafted with leptin receptor antibody (LepR-a) and BMP2-loaded hollow MnO2 (h-MnO2) nanoparticles through a polydopamine (PDA)-assisted technique. The bionic periosteum showed suitable mechanical properties and favorable biocompatibility. It effectively recruited skeletal stem cells (SSCs) through antigen-antibody interactions, as in in vitro cell adhesion tests, we observed that more SSCs attached to the LepR-a-grafted periosteum compared to the control group. In vivo, the LepR-a-grafted periosteum covered on the cranial defect in Prx1-Cre/ERT2, -EGFP mice recruited more Prx1-EGFP cells to the fracture site compared to control groups at post-surgery day 3, 7, and 14. Co-staining with Sp7 indicated that most of the recruited Prx1-EGFP cells underwent osteogenic lineage commitment. Sustained BMP2 release from h-MnO2 promoted osteogenesis by accelerating the osteogenic differentiation of recruited SSCs, as demonstrated by alkaline phosphatase (ALP) and alizarin red staining (ARS) in vitro and microcomputed tomography (micro-CT) in vivo. Interestingly, we also observed the growth of osteogenic coupled capillaries (CD31hiEmcnhi) in the bone repair site, which might be induced by increased platelet-derived growth factor-BB (PDGF-BB) in the regenerative microenvironment subsequent to SSCs' differentiation. Taken together, the findings from this study indicate that the multifunctionalized periosteum efficiently recruited and motivated the SSCs in vivo and orchestrated the osteogenic microenvironment for bone repair in a sequence manner. Thus, the construction of the bionic periosteum to couple with natural bone regeneration stages has been demonstrated to be effective in facilitating bone healing.

Mycobacterial secretion systems ESX-1 and ESX-5 play distinct roles in host cell death and inflammasome activation.

During infection of humans and animals, pathogenic mycobacteria manipulate the host cell causing severe diseases such as tuberculosis and leprosy. To understand the basis of mycobacterial pathogenicity, it is crucial to identify the molecular virulence mechanisms. In this study, we address the contribution of ESX-1 and ESX-5--two homologous type VII secretion systems of mycobacteria that secrete distinct sets of immune modulators--during the macrophage infection cycle. Using wild-type, ESX-1- and ESX-5-deficient mycobacterial strains, we demonstrate that these secretion systems differentially affect subcellular localization and macrophage cell responses. We show that in contrast to ESX-1, the effector proteins secreted by ESX-5 are not required for the translocation of Mycobacterium tuberculosis or Mycobacterium marinum to the cytosol of host cells. However, the M. marinum ESX-5 mutant does not induce inflammasome activation and IL-1ß activation. The ESX-5 system also induces a caspase-independent cell death after translocation has taken place. Importantly, by means of inhibitory agents and small interfering RNA experiments, we reveal that cathepsin B is involved in both the induction of cell death and inflammasome activation upon infection with wild-type mycobacteria. These results reveal distinct roles for two different type VII secretion systems during infection and shed light on how virulent mycobacteria manipulate the host cell in various ways to replicate and spread.