Kenta Maruyama

DNA damage sensor MRE11 recognizes cytosolic double-stranded DNA and induces type i interferon by regulating STING trafficking

Double-stranded DNA (dsDNA) derived from pathogen- or host-damaged cells triggers innate immune responses when exposed to cytoplasm. However, the machinery underlying the primary recognition of intracellular dsDNA is obscure. Here we show that the DNA damage sensor, meiotic recombination 11 homolog A (MRE11), serves as a cytosolic sensor for dsDNA. Cells with a mutation of MRE11 gene derived from a patient with ataxia-telangiectasia–like disorder, and cells in which Mre11 was knocked down, had defects in dsDNA-induced type I IFN production. MRE11 physically interacted with dsDNA in the cytoplasm and was required for activation of stimulator of IFN genes (STING) and IRF3. RAD50, a binding protein to MRE11, was also required for dsDNA responses, whereas NBS1, another binding protein to MRE11, was dispensable. Collectively, our results suggest that the MRE11–RAD50 complex plays important roles in recognition of dsDNA and initiation of STING-dependent signaling, in addition to its role in DNA-damage responses.

Extracellular matrix-inspired growth factor delivery systems for bone regeneration.

Growth factors are very promising molecules to enhance bone regeneration. However, their translation to clinical use has been seriously limited, facing issues related to safety and cost-effectiveness. These problems derive from the vastly supra-physiological doses of growth factor used without optimized delivery systems. Therefore, these issues have motivated the development of new delivery systems allowing better control of the spatiotemporal release and signaling of growth factors. Because the extracellular matrix (ECM) naturally plays a fundamental role in coordinating growth factor activity in vivo, a number of novel delivery systems have been inspired by the growth factor regulatory function of the ECM. After introducing the role of growth factors during the bone regeneration process, this review exposes different issues that growth factor-based therapies have encountered in the clinic and highlights recent delivery approaches based on the natural interaction between growth factor and the ECM.

TRAF Family Member-associated NF-κB Activator (TANK) Is a Negative Regulator of Osteoclastogenesis and Bone Formation

Background: Osteoclasts and osteoblasts are major players in bone metabolism. Results: TRAF family member-associated NF-κB activator (TANK) is induced during osteoclastogenesis and osteoblastogenesis. RANKL-induced osteoclastogenesis was increased in TANK-deficient cells. Osteoblastogenesis was also increased in TANK-deficient mice. Conclusion: TANK is a negative feedback regulator of osteoclastogenesis and osteoblastogenesis. Significance: TANK is a novel suppressor of bone degradation and formation. The differentiation of bone-resorbing osteoclasts is induced by RANKL signaling, and leads to the activation of NF-κB via TRAF6 activation. TRAF family member-associated NF-κB activator (TANK) acts as a negative regulator of Toll-like receptors (TLRs) and B-cell receptor (BCR) signaling by inhibiting TRAF6 activation. Tank−/− mice spontaneously develop autoimmune glomerular nephritis in an IL-6-dependent manner. Despite its importance in the TCRs and BCR-activated TRAF6 inhibition, the involvement of TANK in RANKL signaling is poorly understood. Here, we report that TANK is a negative regulator of osteoclast differentiation. The expression levels of TANK mRNA and protein were up-regulated during RANKL-induced osteoclastogenesis, and overexpression of TANK in vitro led to a decrease in osteoclast formation. The in vitro osteoclastogenesis of Tank−/− cells was significantly increased, accompanied by increased ubiquitination of TRAF6 and enhanced canonical NF-κB activation in response to RANKL stimulation. Tank−/− mice showed severe trabecular bone loss, but increased cortical bone mineral density, because of enhanced bone erosion and formation. TANK mRNA expression was induced during osteoblast differentiation and Tank−/− osteoblasts exhibited enhaced NF-κB activation, IL-11 expression, and bone nodule formation than wild-type control cells. Finally, wild-type mice transplanted with bone marrow cells from Tank−/− mice showed trabecular bone loss analogous to that in Tank−/− mice. These findings demonstrate that TANK is critical for osteoclastogenesis by regulating NF-κB, and is also important for proper bone remodeling.

Strawberry notch homologue 2 regulates osteoclast fusion by enhancing the expression of DC-STAMP

The co-repressor Strawberry notch homolog 2 regulates DC-STAMP expression and osteoclast fusion, and its absence results in osteopetrosis.

Inhibition of IL-1R1/MyD88 signalling promotes mesenchymal stem cell-driven tissue regeneration

Tissue injury and the healing response lead to the release of endogenous danger signals including Toll-like receptor (TLR) and interleukin-1 receptor, type 1 (IL-1R1) ligands, which modulate the immune microenvironment. Because TLRs and IL-1R1 have been shown to influence the repair process of various tissues, we explored their role during bone regeneration, seeking to design regenerative strategies integrating a control of their signalling. Here we show that IL-1R1/MyD88 signalling negatively regulates bone regeneration, in the mouse. Furthermore, IL-1β which is released at the bone injury site, inhibits the regenerative capacities of mesenchymal stem cells (MSCs). Mechanistically, IL-1R1/MyD88 signalling impairs MSC proliferation, migration and differentiation by inhibiting the Akt/GSK-3β/β-catenin pathway. Lastly, as a proof of concept, we engineer a MSC delivery system integrating inhibitors of IL-1R1/MyD88 signalling. Using this strategy, we considerably improve MSC-based bone regeneration in the mouse, demonstrating that this approach may be useful in regenerative medicine applications.

Critical Role of AZI2 in GM-CSF–Induced Dendritic Cell Differentiation

TNFR-associated factor family member–associated NF-κB activator (TANK)–binding kinase 1 (TBK1) is critical for the activation of IFN regulatory factor 3 and type I IFN production upon virus infection. A set of TBK1-binding proteins, 5-azacytidine–induced gene 2 (AZI2; also known as NAP1), TANK, and TBK1-binding protein 1 (TBKBP1), have also been implicated in the production of type I IFNs. Among them, TANK was found to be dispensable for the responses against virus infection. However, physiological roles of AZI2 and TBKBP1 have yet to be clarified. In this study, we found that none of these TBK1-binding proteins is critical for type I IFN production in mice. In contrast, AZI2, but not TBKBP1, is critical for the differentiation of conventional dendritic cells (cDCs) from bone marrow cells in response to GM-CSF. AZI2 controls GM-CSF–induced cell cycling of bone marrow cells via TBK1. GM-CSF–derived DCs from AZI2-deficient mice show severe defects in cytokine production and T cell activation both in vitro and in vivo. Reciprocally, overexpression of AZI2 results in efficient generation of cDCs, and the cells show enhanced T cell activation in response to Ag stimulation. Taken together, AZI2 expression is critical for the generation of cDCs by GM-CSF and can potentially be used to increase the efficiency of immunization by cDCs.

5-azacytidine-induced protein 2 (AZI2) regulates bone mass by fine-tuning osteoclast survival

Background: 5-Azacytidine-induced protein 2 (AZI2) is critical in GM-CSF-induced dendritic cell differentiation. Results: AZI2 deficiency enhances osteoclast survival, leading to decreased bone mass in vivo. Conclusion: AZI2 suppresses osteoclast survival by inhibiting c-Src activation. Significance: This is the first study showing the osteoprotective function of AZI2. 5-Azacytidine-induced protein 2 (AZI2) is a TNF receptor (TNFR)-associated factor family member-associated NF-κB activator-binding kinase 1-binding protein that regulates the production of IFNs. A previous in vitro study showed that AZI2 is involved in dendritic cell differentiation. However, the roles of AZI2 in immunity and its pleiotropic functions are unknown in vivo. Here we report that AZI2 knock-out mice exhibit normal dendritic cell differentiation in vivo. However, we found that adult AZI2 knock-out mice have severe osteoporosis due to increased osteoclast longevity. We revealed that the higher longevity of AZI2-deficient osteoclasts is due to an augmented activation of proto-oncogene tyrosine-protein kinase Src (c-Src), which is a critical player in osteoclast survival. We found that AZI2 inhibits c-Src activity by regulating the activation of heat shock protein 90 (Hsp90), a chaperone involved in c-Src dephosphorylation. Furthermore, we demonstrated that AZI2 indirectly inhibits c-Src by interacting with the Hsp90 co-chaperone Cdc37. Strikingly, administration of a c-Src inhibitor markedly prevented bone loss in AZI2 knock-out mice. Together, these findings indicate that AZI2 regulates bone mass by fine-tuning osteoclast survival.

Plasmodium products persist in the bone marrow and promote chronic bone loss

Plasmodium infection causes chronic inflammation and bone loss through Plasmodium product accumulation in the bone marrow. Plasmodium leftovers cause bone loss Individuals who recover from malarial infection may develop long-term consequences, such as bone loss and growth retardation. Lee et al. now report that Plasmodium by-products retained in the bone marrow lead directly to bone loss. Infection with a mutant Plasmodium that lacked the by-product hemozoin did not induce bone loss. Mechanistically, these products induced MyD88-dependent inflammatory responses in osteoclast and osteoblast precursors, resulting in bone resorption. Treating infected animals with alfacalcidol, a vitamin D3 analog, could prevent this bone loss, suggesting that combining bone therapies with antimalarial drugs may prevent bone loss in infected individuals. Although malaria is a life-threatening disease with severe complications, most people develop partial immunity and suffer from mild symptoms. However, incomplete recovery from infection causes chronic illness, and little is known of the potential outcomes of this chronicity. We found that malaria causes bone loss and growth retardation as a result of chronic bone inflammation induced by Plasmodium products. Acute malaria infection severely suppresses bone homeostasis, but sustained accumulation of Plasmodium products in the bone marrow niche induces MyD88-dependent inflammatory responses in osteoclast and osteoblast precursors, leading to increased RANKL expression and overstimulation of osteoclastogenesis, favoring bone resorption. Infection with a mutant parasite with impaired hemoglobin digestion that produces little hemozoin, a major Plasmodium by-product, did not cause bone loss. Supplementation of alfacalcidol, a vitamin D3 analog, could prevent the bone loss. These results highlight the risk of bone loss in malaria-infected patients and the potential benefits of coupling bone therapy with antimalarial treatment.

Emerging molecules in the interface between skeletal system and innate immunity

Despite the improved treatment of bone destruction, significant unmet medical need remains. For example, there is a limited benefit of continued bisphosphonate therapy for osteoporotic patients, and only minor populations of rheumatoid arthritis patients obtain biologic-free remission. Therefore, the identification of a novel therapeutic target for bone destructive diseases remains an important issue in the field of skeletal biology. To date there has been little progress in identifying osteo-innate-immunological regulators that could be used for the prophylactic treatment of inflammatory bone destruction. Recently, we identified several new molecules that are critical osteo-innate-immunological regulators by using gene targeting technology. These findings may offer an invaluable opportunity to regulate bone-destructive diseases, such as osteoporosis and rheumatoid arthritis.

Mechanistic and structural basis of bioengineered bovine Cathelicidin-5 with optimized therapeutic activity

Peptide-drug discovery using host-defense peptides becomes promising against antibiotic-resistant pathogens and cancer cells. Here, we customized the therapeutic activity of bovine cathelicidin-5 targeting to bacteria, protozoa, and tumor cells. The membrane dependent conformational adaptability and plasticity of cathelicidin-5 is revealed by biophysical analysis and atomistic simulations over 200 μs in thymocytes, leukemia, and E. coli cell-membranes. Our understanding of energy-dependent cathelicidin-5 intrusion in heterogeneous membranes aided in designing novel loss/gain-of-function analogues. In vitro findings identified leucine-zipper to phenylalanine substitution in cathelicidin-5 (1–18) significantly enhance the antimicrobial and anticancer activity with trivial hemolytic activity. Targeted mutants of cathelicidin-5 at kink region and N-terminal truncation revealed loss-of-function. We ensured the existence of a bimodal mechanism of peptide action (membranolytic and non-membranolytic) in vitro. The melanoma mouse model in vivo study further supports the in vitro findings. This is the first structural report on cathelicidin-5 and our findings revealed potent therapeutic application of designed cathelicidin-5 analogues.