The host immune response to bone biomaterials is vital in determining scaffold fates and bone regeneration outcomes. The nanometer-scale interface of biomaterials, which independently controls physical inputs to cells, regulates osteogenic differentiation of stem cells and local immune response. Herein, we fabricated biomimetic hierarchical intrafibrillarly mineralized collagen (HIMC) with a bone-like staggered nanointerface and investigated its immunomodulatory properties and mesenchymal stem cell (MSC) recruitment during endogenous bone regeneration. The acquired HIMC potently induced neo-bone formation by promoting CD68+CD163+ M2 macrophage polarization and CD146+STRO-1+ host MSC recruitment in critical-sized bone defects. Mechanistically, HIMC facilitated M2 macrophage polarization and interleukin (IL)-4 secretion to promote MSC osteogenic differentiation. An anti-IL4 neutralizing antibody significantly reduced M2 macrophage-mediated osteogenic differentiation of MSCs. Moreover, HIMC-loaded-IL-4 implantation into critical-sized mandible defects dramatically enhanced bone regeneration and CD68+CD163+ M2 macrophage polarization. The depletion of monocyte/macrophages by clodronate liposomes significantly impaired bone regeneration by HIMC, but did not affect MSC recruitment. Thus, in emulating natural design, the hierarchical nanointerface possesses the capacity to recruit host MSCs and promote endogenous bone regeneration by immunomodulation of macrophage polarization through IL-4.

Background: Macrophage M1 polarization plays a pivotal role in inflammatory diseases. Progranulin (PGRN) has potential anti-inflammation action, however, the effect of PGRN on macrophage M1 polarization has been poorly studied. Our study aimed to investigate the effect of PGRN on lipopolysaccharide (LPS)-induced macrophage M1 polarization and clarify the underlying mechanisms. Methods: RAW264.7 cells were polarized to M1 macrophage by LPS with or without recombinant PGRN (rPGRN) and tumor necrosis factor alpha antibody (anti-TNF-α). A cell counting kit-8 assay (CCK-8), flow cytometry, Quantitative Real-Time PCR assay (q-PCR), Western blot assay and enzyme-linked immunosorbent assay (ELISA) were used to determine the effect of different treatments on cell proliferation, expression of surface phenotype marker and expressions and secretion of inflammatory cytokines. The activation of NF-κB/mitogen-activated protein kinase (MAPK) pathways and the nuclear translocation of NF-κB p65 were detected by Western blot and immunofluorescence respectively. THP-1 and primary bone marrow-derived monocytes (BMDMs) were also used to demonstrate effect of PGRN on expressions and secretion of inflammatory cytokines induced by LPS. Results: In RAW264.7 cells, rPGRN at concentrations below 80 ng/ml significantly promoted cell proliferation in dose dependent fashion. rPGRN significantly inhibited LPS-induced change of phenotype (CD86/CD206 ratio) and function (tumor necrosis factor (TNF-α) and inducible nitric oxide synthase (iNOS) expressions). LPS-stimulated secretion of TNF-α and activated phosphorylation of IKKα/β, IкBα, p65, JNK and p38 and the nucleus translocation of NF-кB p65 were also significantly downregulated by rPGRN. In addition, recombinant TNF-α (rTNF-α) significantly boosted TNF-α and iNOS expression vs the control group. Moreover, anti-TNF-α significantly inhibited LPS-induced TNF-α and iNOS expression. In THP-1 and BMDM cells, reversing effect of rPGRN on LPS-enhanced expressions of TNF-α and iNOS and secretion of TNF-α was further demonstrated.

Tendon injuries disrupt the balance between stability and mobility, causing compromised functions and disabilities. The regeneration of mature, functional tendons remains a clinical challenge. Here, we perform transcriptional profiling of tendon developmental processes to show that the extracellular matrix-associated protein periostin (Postn) contributes to the maintenance of tendon stem/progenitor cell (TSPC) functions and promotes tendon regeneration. We show that recombinant periostin (rPOSTN) promotes the proliferation and stemness of TSPCs, and maintains the tenogenic potentials of TSPCs in vitro. We also find that rPOSTN protects TSPCs against functional impairment during long-term passage in vitro. For in vivo tendon formation, we construct a biomimetic parallel-aligned collagen scaffold to facilitate TSPC tenogenesis. Using a rat full-cut Achilles tendon defect model, we demonstrate that scaffolds loaded with rPOSTN promote endogenous TSPC recruitment, tendon regeneration and repair with native-like hierarchically organized collagen fibers. Moreover, newly regenerated tendons show recovery of mechanical properties and locomotion functions.