RANKL and RANK in Cancer Therapy.

Receptor activator of nuclear factor-κB (RANK) and its ligand (RANKL) are key regulators of mammalian physiology such as bone metabolism, immune tolerance and antitumor immunity, and mammary gland biology. Here, we explore the multiple functions of RANKL/RANK in physiology and pathophysiology and discuss underlying principles and strategies to modulate the RANKL/RANK pathway as a therapeutic target in immune-mediated cancer treatment.

A critical relationship between bone and fat: the role of bone marrow adipose-derived RANKL in bone metabolism.

Recent studies have unveiled unique functions of the bone marrow adipose tissue (BMAT), which represent over 10% of the total adipose tissue mass in healthy adults. Increasing evidence is emerging as to how BMAT deposition and osteoporosis are linked under normal and pathophysiological conditions, which is opening up novel treatment avenues. However, the means by which bone marrow adipocytes (BMAs) regulate bone remodeling and their involvement in osteoporosis remained unknown. A study in this issue of EMBO Reports (Hu et al, 2021) and a study in Journal of Clinical Investigation (Yu et al, 2021) reports independently that BMA-derived RANKL regulates osteoclastogenesis and bone remodeling, indicating that excessive RANKL generated by BMAs is an underlying cause for osteoporosis.

Unc93B1 restricts systemic lethal inflammation by orchestrating Toll-like receptor 7 and 9 trafficking.

Toll-like receptor-7 (TLR7) and 9, innate immune sensors for microbial RNA or DNA, have been implicated in autoimmunity. Upon activation, TLR7 and 9 are transported from the endoplasmic reticulum (ER) to endolysosomes for nucleic acid sensing by an ER-resident protein, Unc93B1. Little is known, however, about a role for sensor transportation in controlling autoimmunity. TLR9 competes with TLR7 for Unc93B1-dependent trafficking and predominates over TLR7. TLR9 skewing is actively maintained by Unc93B1 and reversed to TLR7 if Unc93B1 loses preferential binding via a D34A mutation. We here demonstrate that mice harboring a D34A mutation showed TLR7-dependent, systemic lethal inflammation. CD4(+) T cells showed marked differentiation toward T helper 1 (Th1) or Th17 cell subsets. B cell depletion abolished T cell differentiation and systemic inflammation. Thus, Unc93B1 controls homeostatic TLR7 activation by balancing TLR9 to TLR7 trafficking.

Oxidative stress controlling agents are effective for small intestinal injuries induced by non-steroidal anti-inflammatory drugs.

BACKGROUND AND AIM: Video-capsule endoscopy (VCE) has shown that intestinal ulcers are common in non-steroidal anti-inflammatory drugs (NSAIDs) users, although the mechanisms and management have not been clearly defined. To explore the contribution of oxidative stress and potential of anti-oxidants for NSAIDs-induced intestinal ulcers, we assessed human serum oxidative stress balance and the effect of anti-oxidants using a mouse model. METHODS: A total of 30 NSAIDs users (17 aspirin and 13 non-aspirin users) received VCE. Serum reactive oxygen metabolite (d-ROM) and antioxidative OXY-adsorbent test (OXY) were measured. The indomethacin (IND)-induced mouse intestinal ulcer model was used to assess the effect of anti-oxidants. Eight-week-old mice were divided into four groups; control diet and diet including IND (N group), IND and L-carnitine (NC group), and IND and vitamin E (NE group). RESULTS: Serum OXY levels among non-aspirin users were lower in the mucosal injuries positive group than the negative group (P < 0.05). In the mouse models, the degree of mucosal injuries was lower in NC and NE than N (P < 0.01). Serum d-ROM levels were lower in NC and NE than N (P < 0.01), and OXY levels were higher in NC than N and NE (P < 0.01). The degeneration of intestinal mitochondria was mild in NC and NE. The serum KC/CXCL-1 level and hepatic expression of the anti-oxidant molecule Gpx4 were lower in NC than N. CONCLUSIONS: Non-aspirin NSAID-induced intestinal ulcers are related to decreased anti-oxidative stress function. Anti-oxidants, especially L-carnitine, are good candidates for intestinal ulcers.

Endocytosis-free DNA sensing by cell surface TLR9 in neutrophils: rapid defense with autoimmune risks.

TLR9 senses microbial DNA, but may also respond to self-DNA. To prevent the initiation of innate immune responses to self-DNA, TLR9 is thought to sense microbial DNA in endolysosomes, and not at the cell surface. A report by Lindau et al. in this issue of the European Journal of Immunology [Eur. J. Immunol. 2013. 43: 2101-2113] shows that TLR9 is expressed on the surface of human and mouse neutrophils and, furthermore, shows that cell surface TLR9, instead of endosomal TLR9, senses DNA in neutrophils. These findings demonstrate that DNA sensing by TLR9 in neutrophils is quite distinct from that in DCs or macrophages. The unique DNA sensing by cell surface TLR9 in neutrophils may reflect their role in inducing rapid inflammation by degranulation with a minimal role in engulfing microbial products for antigen presentation.

Essential role for Toll-like receptor 7 (TLR7)-unique cysteines in an intramolecular disulfide bond, proteolytic cleavage and RNA sensing.

Toll-like receptor 7 (TLR7) an innate immune sensor for microbial RNA, erroneously responds to self-derived RNA. To avoid autoimmune responses, TLR7 is suggested to be silenced until the N-terminal half of the TLR7 ectodomain (TLR7N) is cleaved off. Resultant truncated TLR7 (TLR7C) is thought to signal microbial RNA. We here show that TLR7N remains associated with TLR7C through a disulfide bond. By N-terminal amino acid sequencing, TLR7C was found to start at 461E or 462A. The newly established monoclonal anti-TLR7N showed that endogenous TLR7 in bone marrow-derived dendritic cells was almost all cleaved and cleaved TLR7N remained in endolysosomes. TLR7N in endolysosomes was linked with TLR7C by a disulfide bond. In contrast, TLR9 did not have a disulfide bond between TLR9N and TLR9C fragments. Among the cysteines unique to the ectodomain of TLR7 but not TLR9 (Cys98, Cys445, Cys475 and Cys722), Cys98 in TLR7N and Cys475 in TLR7C were required for an intramolecular disulfide bond. These cysteines were also needed for proteolytic cleavage of and RNA sensing by TLR7, but not for TLR7 trafficking from endoplasmic reticulum to endosomes. No response was seen in TLR7 mutants lacking the proteolytic cleavage site or TLR7C alone. These results demonstrate requirement for proteolytic cleavage and TLR7N in TLR7 responses and indicate RNA sensing by TLR7N + TLR7C.

Crucial neuroprotective roles of the metabolite BH4 in dopaminergic neurons.

Dopa-responsive dystonia (DRD) and Parkinson's disease (PD) are movement disorders caused by the dysfunction of nigrostriatal dopaminergic neurons. Identifying druggable pathways and biomarkers for guiding therapies is crucial due to the debilitating nature of these disorders. Recent genetic studies have identified variants of GTP cyclohydrolase-1 (GCH1), the rate-limiting enzyme in tetrahydrobiopterin (BH4) synthesis, as causative for these movement disorders. Here, we show that genetic and pharmacological inhibition of BH4 synthesis in mice and human midbrain-like organoids accurately recapitulates motor, behavioral and biochemical characteristics of these human diseases, with severity of the phenotype correlating with extent of BH4 deficiency. We also show that BH4 deficiency increases sensitivities to several PD-related stressors in mice and PD human cells, resulting in worse behavioral and physiological outcomes. Conversely, genetic and pharmacological augmentation of BH4 protects mice from genetically- and chemically induced PD-related stressors. Importantly, increasing BH4 levels also protects primary cells from PD-affected individuals and human midbrain-like organoids (hMLOs) from these stressors. Mechanistically, BH4 not only serves as an essential cofactor for dopamine synthesis, but also independently regulates tyrosine hydroxylase levels, protects against ferroptosis, scavenges mitochondrial ROS, maintains neuronal excitability and promotes mitochondrial ATP production, thereby enhancing mitochondrial fitness and cellular respiration in multiple preclinical PD animal models, human dopaminergic midbrain-like organoids and primary cells from PD-affected individuals. Our findings pinpoint the BH4 pathway as a key metabolic program at the intersection of multiple protective mechanisms for the health and function of midbrain dopaminergic neurons, identifying it as a potential therapeutic target for PD.

Clinical characteristics of drug-induced liver injury in the elderly.

AIM: The average age of Japanese patients with drug-induced liver injury (DILI) is expected to rise as the population ages. The aim of this study was to evaluate the clinical characteristics of DILI in elderly Japanese subjects. METHODS: A total of 142 hospitalized patients with DILI were divided into three groups by age (Group A, < 65 years; Group B, 65-74 years; Group C, >/= 75 years). Patients were examined retrospectively with regard to the number of concomitant drugs, duration of drug intake until onset of DILI, clinical types of DILI, treatment, prognosis, and scores on the diagnostic scale described by Digestive Disease Week, Japan 2004. RESULTS: Patients in Group C used more concomitant drugs (P = 0.0019) compared with patients in Group A. The elderly had a higher frequency of unclear duration of drug intake (P = 0.0020), were more likely to experience cholestatic type DILI (P = 0.033), and underwent more intensive treatment for DILI (P = 0.011). There were fewer cases diagnosed as a "high possibility" of DILI in Group C compared with Group A (P = 0.030) and Group B (P = 0.013). In cases diagnosed as "possible" or "low possibility" of DILI, unclear duration of drug intake was more frequently observed in the elderly (P = 0.0027). CONCLUSION: Elderly patients with DILI show different clinical features than younger patients with DILI. These features should be taken into account in the diagnosis and treatment of DILI in the elderly.

AIF-regulated oxidative phosphorylation supports lung cancer development.

Cancer is a major and still increasing cause of death in humans. Most cancer cells have a fundamentally different metabolic profile from that of normal tissue. This shift away from mitochondrial ATP synthesis via oxidative phosphorylation towards a high rate of glycolysis, termed Warburg effect, has long been recognized as a paradigmatic hallmark of cancer, supporting the increased biosynthetic demands of tumor cells. Here we show that deletion of apoptosis-inducing factor (AIF) in a KrasG12D-driven mouse lung cancer model resulted in a marked survival advantage, with delayed tumor onset and decreased malignant progression. Mechanistically, Aif deletion leads to oxidative phosphorylation (OXPHOS) deficiency and a switch in cellular metabolism towards glycolysis in non-transformed pneumocytes and at early stages of tumor development. Paradoxically, although Aif-deficient cells exhibited a metabolic Warburg profile, this bioenergetic change resulted in a growth disadvantage of KrasG12D-driven as well as Kras wild-type lung cancer cells. Cell-autonomous re-expression of both wild-type and mutant AIF (displaying an intact mitochondrial, but abrogated apoptotic function) in Aif-knockout KrasG12D mice restored OXPHOS and reduced animal survival to the same level as AIF wild-type mice. In patients with non-small cell lung cancer, high AIF expression was associated with poor prognosis. These data show that AIF-regulated mitochondrial respiration and OXPHOS drive the progression of lung cancer.

Cleavage of Toll-Like Receptor 9 Ectodomain Is Required for In Vivo Responses to Single Strand DNA.

Mouse toll-like receptor 9 (TLR9) is an endosomal sensor for single-stranded DNA. TLR9 is transported from the endoplasmic reticulum to endolysosomes by a multiple transmembrane protein Unc93 homolog B1, and proteolytically cleaved at its ectodomain. The structure of TLR9 and its biochemical analyses have shown that the proteolytic cleavage of TLR9 ectodomain enables TLR9-dimerization and TLR9 activation. However, the requirement of TLR9 cleavage in vivo has not been studied. We here show that the 13 amino acids deletion at the cleavage site made TLR9 resistant to proteolytic cleavage. The deletion mutation in the Tlr9 gene impaired TLR9-dependent cytokine production in conventional dendritic cells from the mutant mice. Not only in vitro, in vivo production of inflammatory cytokines (TNF-α and IL-12p40), chemokine (CCR5/RANTES), and type I interferon (IFN-α) induced by administration of TLR9 ligand was also impaired. These results demonstrate that the TLR9 cleavage is required for TLR9 responses in vivo.

Serum-inducible protein (IP)-10 is a disease progression-related marker for non-alcoholic fatty liver disease.

BACKGROUND: The molecular pathogenesis of non-alcoholic steatohepatitis (NASH) is not well defined. The objective of the present study was to identify disease progression-related cytokines and investigate the molecular pathogenesis of such changes in NASH. METHODS: A study population of 20 non-alcoholic fatty liver (NAFL) and 59 NASH patients diagnosed by liver biopsy and 15 healthy volunteers was recruited. The serum pro- and anti-inflammatory cytokines were measured by a multiple enzyme-linked immunosorbent assay. The hepatic mRNA expressions of cytokines were measured by real-time PCR. A monocyte cell line was stimulated with Toll-like receptor (TLR) ligand under a high glucose and insulin condition, and cellular cytokine mRNA expression was quantified. RESULTS: One group of cytokines was higher in NAFL and NASH than in controls, while another group was higher in NASH than in NAFL and controls. The NASH-specific second group included interleukin (IL)-15 and interferon-γ-inducible protein (IP)-10. In particular, IP-10 was higher in NAFL than in controls and higher in NASH than in NAFL and controls. The sensitivity to diagnose NASH was 90%, with specificity of 50%. Insulin resistance reflecting a high glucose and insulin condition resulted in higher IP-10 mRNA expression in the monocyte cell line only with concomitant TLR-2 stimulation. CONCLUSIONS: IP-10 is a sensitive marker of the need for liver biopsy. Insulin resistance with bacteria-related TLR-2 stimulation might induce IP-10 production from monocytes. Insulin resistance and intestinal barrier function should be intensively controlled to prevent progression from NAFL to NASH.

DNase II-dependent DNA digestion is required for DNA sensing by TLR9.

DNase II digests DNA in endolysosomes. In the absence of DNase II, undigested DNA activates cytoplasmic DNA-sensing pathways. Little is known, however, about the role of DNase II in endolysosomal DNA sensing by TLR9. Here we show that DNase II is required for TLR9. We test two types of TLR9 ligands, CpG-A and CpG-B, and show that only CpG-A response is impaired in DNase II-deficient dendritic cells (DCs). Enzymatically inactive DNase II mutants cannot rescue CpG-A responses. DNase II cleaves CpG-A from 20-mer to 11-12-mer. The 3'11-mer CpG-A fragment activates DNase II-deficient DCs. CpG-A shows higher co-localization with LAMP-2(+) lysosomes than CpG-B and induces DNase II localization in LAMP-2(+) lysosomes. Moreover, we demonstrate that DNase II is required for TLR9 activation by bacterial genomic DNA. Taken together, these results demonstrate that TLR9 responds to DNA fragments generated by DNase II.

Targeting cell surface TLR7 for therapeutic intervention in autoimmune diseases.

Toll-like receptor 7 (TLR7) senses microbial-derived RNA but can also potentially respond to self-derived RNA. To prevent autoimmune responses, TLR7 is thought to localize in endolysosomes. Contrary to this view, we show here that TLR7 is present on the cell surface of immune cells and that TLR7 responses can be inhibited by an anti-TLR7 antibody. The anti-TLR7 antibody is internalized with TLR7 and accumulates in endolysosomes as an immune complex. TLR7 responses in dendritic cells, macrophages and B cells are all inhibited by the anti-TLR7 antibody. Furthermore, the anti-TLR7 antibody inhibits in vivo cytokine production induced by a TLR7 ligand. Spontaneous TLR7 activation in Unc93b1(D34A/D34A) mice causes lethal inflammation. Progressive inflammation such as splenomegaly, thrombocytopenia and chronic active hepatitis are ameliorated by anti-TLR7 antibody treatment. These results demonstrate that cell surface TLR7 is a promising target for therapeutic intervention in autoimmune diseases.

An essential role for the N-terminal fragment of Toll-like receptor 9 in DNA sensing.

Toll-like receptor 9 (TLR9) is an innate immune sensor for microbial DNA that erroneously responds to self DNA in autoimmune disease. To prevent autoimmune responses, Toll-like receptor 9 is excluded from the cell surface and silenced until the N-terminal half of the ectodomain (TLR9N) is cleaved off in the endolysosome. Truncated Toll-like receptor 9 (TLR9C) senses ingested microbial DNA, although the precise role of the truncation remains controversial. Here we show that TLR9 is expressed on the surface of splenic dendritic cells. Following the cleavage of TLR9 in the endolysosome, N-terminal half of the ectodomain remains associated with truncated TLR9, forming the complex TLR9N+C. The TLR9-dependent cytokine production by Tlr9(-/-) dendritic cells is rescued by a combination of TLR9N and TLR9C, but not by TLR9C alone. These results demonstrate that the TLR9N+C complex is a bona fide DNA sensor.

Increased myeloid cell responses to M-CSF and RANKL cause bone loss and inflammation in SH3BP2 "cherubism" mice.

While studies of the adaptor SH3BP2 have implicated a role in receptor-mediated signaling in mast cells and lymphocytes, they have failed to identify its function or explain why SH3BP2 missense mutations cause bone loss and inflammation in patients with cherubism. We demonstrate that Sh3bp2 "cherubism" mice exhibit trabecular bone loss, TNF-alpha-dependent systemic inflammation, and cortical bone erosion. The mutant phenotype is lymphocyte independent and can be transferred to mice carrying wild-type Sh3bp2 alleles through mutant fetal liver cells. Mutant myeloid cells show increased responses to M-CSF and RANKL stimulation, and, through mechanisms of increased ERK 1/2 and SYK phosphorylation/activation, they form macrophages that express high levels of TNF-alpha and osteoclasts that are unusually large. M-CSF and RANKL stimulation of myeloid cells that overexpress wild-type SH3BP2 results in similar large osteoclasts. This indicates that the mutant phenotype reflects gain of SH3BP2 function and suggests that SH3BP2 is a critical regulator of myeloid cell responses to M-CSF and RANKL stimulation.