Gas6 ameliorates intestinal mucosal immunosenescence to prevent the translocation of a gut pathobiont, Klebsiella pneumoniae, to the liver.

Immunosenescence refers to the development of weakened and/or dysfunctional immune responses associated with aging. Several commensal bacteria can be pathogenic in immunosuppressed individuals. Although Klebsiella pneumoniae is a commensal bacterium that colonizes human mucosal surfaces, the gastrointestinal tract, and the oropharynx, it can cause serious infectious diseases, such as pneumonia, urinary tract infections, and liver abscesses, primarily in elderly patients. However, the reason why K. pneumoniae is a more prevalent cause of infection in the elderly population remains unclear. This study aimed to determine how the host's intestinal immune response to K. pneumoniae varies with age. To this end, the study analyzed an in vivo K. pneumoniae infection model using aged mice, as well as an in vitro K. pneumoniae infection model using a Transwell insert co-culture system comprising epithelial cells and macrophages. In this study, we demonstrate that growth arrest-specific 6 (Gas6), released by intestinal macrophages that recognize K. pneumoniae, inhibits bacterial translocation from the gastrointestinal tract by enhancing tight-junction barriers in the intestinal epithelium. However, in aging mice, Gas6 was hardly secreted under K. pneumoniae infection due to decreasing intestinal mucosal macrophages; therefore, K. pneumoniae can easily invade the intestinal epithelium and subsequently translocate to the liver. Moreover, the administration of Gas6 recombinant protein to elderly mice prevented the translocation of K. pneumoniae from the gastrointestinal tract and significantly prolonged their survival. From these findings, we conclude that the age-related decrease in Gas6 secretion in the intestinal mucosa is the reason why K. pneumoniae can be pathogenic in the elderly, thereby indicating that Gas6 could be effective in protecting the elderly against infectious diseases caused by gut pathogens.

Cancer-derived cholesterol sulfate is a key mediator to prevent tumor infiltration by effector T cells.

Effective tumor immunotherapy requires physical contact of T cells with cancer cells. However, tumors often constitute a specialized microenvironment that excludes T cells from the vicinity of cancer cells, and its underlying mechanisms are still poorly understood. DOCK2 is a Rac activator critical for migration and activation of lymphocytes. We herein show that cancer-derived cholesterol sulfate (CS), a lipid product of the sulfotransferase SULT2B1b, acts as a DOCK2 inhibitor and prevents tumor infiltration by effector T cells. Using clinical samples, we found that CS was abundantly produced in certain types of human cancers such as colon cancers. Functionally, CS-producing cancer cells exhibited resistance to cancer-specific T-cell transfer and immune checkpoint blockade. Although SULT2B1b is known to sulfate oxysterols and inactivate their tumor-promoting activity, the expression levels of cholesterol hydroxylases, which mediate oxysterol production, are low in SULT2B1b-expressing cancers. Therefore, SULT2B1b inhibition could be a therapeutic strategy to disrupt tumor immune evasion in oxysterol-non-producing cancers. Thus, our findings define a previously unknown mechanism for tumor immune evasion and provide a novel insight into the development of effective immunotherapies.

Photopic light-mediated down-regulation of local α1A-adrenergic signaling protects blood-retina barrier in experimental autoimmune uveoretinitis.

We have reported the gateway reflex, which describes specific neural activations that regulate immune cell gateways at specific blood vessels in the central nervous system (CNS). Four types of gateway reflexes exist, all of which induce alterations in endothelial cells at specific vessels of the blood-brain barrier followed by inflammation in the CNS in the presence of CNS-autoreactive T cells. Here we report a new gateway reflex that suppresses the development of retinal inflammation by using an autoreactive T cell-mediated ocular inflammation model. Exposure to photopic light down-regulated the adrenoceptor pathway to attenuate ocular inflammation by suppressing breaching of the blood-retina barrier. Mechanistic analysis showed that exposure to photopic light down-regulates the expression of α1A-adrenoceptor (α1AAR) due to high levels of norepinephrine and epinephrine, subsequently suppressing inflammation. Surgical ablation of the superior cervical ganglion (SCG) did not negate the protective effect of photopic light, suggesting the involvement of retinal noradrenergic neurons rather than sympathetic neurons from the SCG. Blockade of α1AAR signaling under mesopic light recapitulated the protective effect of photopic light. Thus, targeting regional adrenoceptor signaling might represent a novel therapeutic strategy for autoimmune diseases including those that affect organs separated by barriers such as the CNS and eyes.

NEDD4 Is Involved in Inflammation Development during Keloid Formation.

Keloids mark a chronic inflammatory disease characterized by a fibroproliferative disorder of the skin. A genome-wide association study showed that single-nucleotide polymorphism rs8032158 in the neural precursor cell-expressed NEDD4 gene, which has six protein-coding transcript variants (TVs), is genetically linked to keloids. Here, we show that the high frequency of risk allele C in rs8032158 in keloid patients is associated with a selectively higher expression of TV3 of NEDD4 to activate the NF-κB pathway. Comparisons of keloid scars with normal skin samples that do not have the single-nucleotide polymorphism allele and were derived from different anatomical sites showed stronger expressions of NEDD4 TV3 and activated forms of NF-κB and STAT3 in keloid scars. Forced expression or selective knockdown of NEDD4 TV3 increased or decreased NF-κB activation in vitro. Furthermore, NEDD4 knockdown suppressed NF-κB-dependent inflammation development in vivo. Mechanistic analysis showed that NEDD4 TV3 is involved in NF-κB activation through its association with the adaptor protein RIP. These results suggest that NEDD4 TV3 is a potential diagnostic marker and therapeutic target for chronic skin diseases, including keloid.

Gateway reflex: Local neuroimmune interactions that regulate blood vessels.

Neuroimmunology is a research field that intersects neuroscience and immunology, with the larger aim of gaining significant insights into the pathophysiology of chronic inflammatory diseases such as multiple sclerosis. Conventional studies in this field have so far mainly dealt with immune responses in the nervous system (i.e. neuroinflammation) or systemic immune regulation by the release of glucocorticoids. On the other hand, recently accumulating evidence has indicated bidirectional interactions between specific neural activations and local immune responses. Here we discuss one such local neuroimmune interaction, the gateway reflex. The gateway reflex represents a mechanism that translates specific neural stimulations into local inflammatory outcomes by changing the state of specific blood vessels to allow immune cells to extravasate, thus forming the gateway. Several types of gateway reflex have been identified, and each regulates distinct blood vessels to create gateways for immune cells that induce local inflammation. The gateway reflex represents a novel therapeutic strategy for neuroinflammation and is potentially applicable to other inflammatory diseases in peripheral organs.

Bmi1 Regulates IκBα Degradation via Association with the SCF Complex.

Bmi1 is a polycomb group protein and regulator that stabilizes the ubiquitination complex PRC1 in the nucleus with no evidently direct link to the NF-κB pathway. In this study, we report a novel function of Bmi1: its regulation of IκBα ubiquitination in the cytoplasm. A deficiency of Bmi1 inhibited NF-κB-mediated gene expression in vitro and a NF-κB-mediated mouse model of arthritis in vivo. Mechanistic analysis showed that Bmi1 associated with the SCF ubiquitination complex via its N terminus and with phosphorylation by an IKKα/ß-dependent pathway, leading to the ubiquitination of IκBα. These effects on NF-κB-related inflammation suggest Bmi1 in the SCF complex is a potential therapeutic target for various diseases and disorders, including autoimmune diseases.

Gateway reflex: neural activation-mediated immune cell gateways in the central nervous system.

The neural regulation of organs can be categorized as systemic or local. Whereas systemic regulation by the hypothalamus-pituitary-adrenal gland-mediated release of steroid hormones has been well studied, the mechanisms for local regulation have only recently emerged. Two types of local neural regulation are known, the gateway reflex and the inflammatory reflex. The gateway reflex describes a mechanism that converts regional neural stimulations into inflammatory outputs by changing the state of specific blood vessels. Molecularly, the enhancement of NF-κB (nuclear factor kappa-light-chain-enhancer of activated B cells) activity in endothelial cells by neurotransmitters, such as noradrenaline and ATP, induces an enhanced production of pro-inflammatory mediators, including chemokines, which form immune cell gateways at specific vessels. Several types of gateway reflex have been identified, and each regulates distinct organs by creating gateways for autoreactive T cells that induce local inflammation. On the other hand, the inflammatory reflex elicits an anti-inflammatory response through vagal nerves. Here, we summarize recent works on these two local neuro-immune interactions, giving special focus to the gateway reflex.

Brain micro-inflammation at specific vessels dysregulates organ-homeostasis via the activation of a new neural circuit.

Impact of stress on diseases including gastrointestinal failure is well-known, but molecular mechanism is not understood. Here we show underlying molecular mechanism using EAE mice. Under stress conditions, EAE caused severe gastrointestinal failure with high-mortality. Mechanistically, autoreactive-pathogenic CD4+ T cells accumulated at specific vessels of boundary area of third-ventricle, thalamus, and dentate-gyrus to establish brain micro-inflammation via stress-gateway reflex. Importantly, induction of brain micro-inflammation at specific vessels by cytokine injection was sufficient to establish fatal gastrointestinal failure. Resulting micro-inflammation activated new neural pathway including neurons in paraventricular-nucleus, dorsomedial-nucleus-of-hypothalamus, and also vagal neurons to cause fatal gastrointestinal failure. Suppression of the brain micro-inflammation or blockage of these neural pathways inhibited the gastrointestinal failure. These results demonstrate direct link between brain micro-inflammation and fatal gastrointestinal disease via establishment of a new neural pathway under stress. They further suggest that brain micro-inflammation around specific vessels could be switch to activate new neural pathway(s) to regulate organ homeostasis.

EAE Induction by Passive Transfer of MOG-specific CD4+ T Cells.

Experimental autoimmune encephalomyelitis (EAE) is an animal model of multiple sclerosis (MS), which is a chronic inflammatory disease of the central nervous system (CNS). It is characterized by focal demyelination and inflammatory responses mediated by myelin-specific autoreactive CD4+ T cells. Using a passive transfer model of EAE in mice, we have demonstrated that regional specific neural signals by sensory-sympathetic communications create gateways for immune cells at specific blood vessels of the CNS, a phenomenon known as the gateway reflex ( Arima et al., 2012 ; Tracey, 2012; Arima et al., 2013 ; Sabharwal et al., 2014 ; Arima et al., 2015b ). Here we describe protocols for passive transfer model of EAE using freshly isolated (MOG)-specific CD4+ T cells or periodically restimulated MOG-specific CD4+ T cell lines, which are suitable for tracking pathogenic CD4+ T cells in vivo, particularly in the CNS ( Ogura et al., 2008 ; Arima et al., 2012 and 2015b).

Rbm10 regulates inflammation development via alternative splicing of Dnmt3b.

RNA-binding motif 10 (Rbm10) is an RNA-binding protein that regulates alternative splicing, but its role in inflammation is not well defined. Here, we show that Rbm10 controls appropriate splicing of DNA (cytosine-5)-methyltransferase 3b (Dnmt3b), a DNA methyltransferase, to regulate the activity of NF-κB-responsive promoters and consequently inflammation development. Rbm10 deficiency suppressed NF-κB-mediated responses in vivo and in vitro. Mechanistic analysis showed that Rbm10 deficiency decreased promoter recruitment of NF-κB, with increased DNA methylation of the promoter regions in NF-κB-responsive genes. Consistently, Rbm10 deficiency increased the expression level of Dnmt3b2, which has enzyme activity, while it decreased the splicing isoform Dnmt3b3, which does not. These two isoforms associated with NF-κB efficiently, and overexpression of enzymatically active Dnmt3b2 suppressed the expression of NF-κB targets, indicating that Rbm10-mediated Dnmt3b2 regulation is important for the induction of NF-κB-mediated transcription. Therefore, Rbm10-dependent Dnmt3b regulation is a possible therapeutic target for various inflammatory diseases.

A pain-mediated neural signal induces relapse in murine autoimmune encephalomyelitis, a multiple sclerosis model.

Although pain is a common symptom of various diseases and disorders, its contribution to disease pathogenesis is not well understood. Here we show using murine experimental autoimmune encephalomyelitis (EAE), a model for multiple sclerosis (MS), that pain induces EAE relapse. Mechanistic analysis showed that pain induction activates a sensory-sympathetic signal followed by a chemokine-mediated accumulation of MHC class II+CD11b+ cells that showed antigen-presentation activity at specific ventral vessels in the fifth lumbar cord of EAE-recovered mice. Following this accumulation, various immune cells including pathogenic CD4+ T cells recruited in the spinal cord in a manner dependent on a local chemokine inducer in endothelial cells, resulting in EAE relapse. Our results demonstrate that a pain-mediated neural signal can be transformed into an inflammation reaction at specific vessels to induce disease relapse, thus making this signal a potential therapeutic target.

Naïve T Cell Homeostasis Regulated by Stress Responses and TCR Signaling.

The survival of naïve T cells is believed to require signals from TCR-pMHC interactions and cytokines such as IL-7. In contrast, signals that negatively impact naïve T cell survival are less understood. We conducted a forward genetic screening of mice and found a mutant mouse line with reduced number of naïve T cells (T-Red mice). T-Red mice have a point mutation in the Kdelr1 gene, and their naïve T cells show enhanced integrated stress response (ISR), which eventually induces their apoptosis. Therefore, naïve T cells require a KDEL receptor-mediated mechanism that efficiently relieves cellular stress for their survival in vivo. Interestingly, naïve T cells expressing TCR with higher affinity/avidity to self-antigens survive in T-Red mice, suggesting the possible link between TCR-mediated survival and ISR-induced apoptosis. In this article, we discuss the regulation of naïve T cell homeostasis, keeping special attention on the ISR and TCR signal.