Dylan V Neel, Himanish Basu, Georgia Gunner, and Isaac M Chiu. 5/7/2022. “Catching a killer: Mechanisms of programmed cell death and immune activation in Amyotrophic Lateral Sclerosis.” Immunol Rev.Abstract
In the central nervous system (CNS), execution of programmed cell death (PCD) is crucial for proper neurodevelopment. However, aberrant activation of these pathways in adult CNS leads to neurodegenerative diseases including amyotrophic lateral sclerosis (ALS). How a cell dies is critical, as it can drive local immune activation and tissue damage. Classical apoptosis engages several mechanisms to evoke "immunologically silent" responses, whereas other forms of programmed death such as pyroptosis, necroptosis, and ferroptosis release molecules that can potentiate immune responses and inflammation. In ALS, a fatal neuromuscular disorder marked by progressive death of lower and upper motor neurons, several cell types in the CNS express machinery for multiple PCD pathways. The specific cell types engaging PCD, and ultimate mechanisms by which neuronal death occurs in ALS are not well defined. Here, we provide an overview of different PCD pathways implicated in ALS. We also examine immune activation in ALS and differentiate apoptosis from necrotic mechanisms based on downstream immunological consequences. Lastly, we highlight therapeutic strategies that target cell death pathways in the treatment of neurodegeneration and inflammation in ALS.
Liwen Deng and Isaac M Chiu. 4/20/2022. “A neuropeptide regulates immunity across species.” Neuron, 110, 8, Pp. 1275-1277.Abstract
Communication between the nervous system and immune system is important for regulating immunity in health and disease. Yu et al. (2022) show that neuropeptide Y and its homolog NPF serve as a "language" to facilitate crosstalk between these two systems across species, enabling neurons to downregulate harmful immune responses.
Antonia Wallrapp, Daping Yang, and Isaac M Chiu. 4/2022. “Enteric glial cells mediate gut immunity and repair.” Trends Neurosci, 45, 4, Pp. 251-253.Abstract
In the gut, coordinated cell interactions regulate tissue repair and immunity. How enteric glial cells (EGCs) mediate these processes remained elusive. In a recent paper, Progatzky et al. demonstrate that EGCs interact with immune and mesothelial cells under homeostasis and helminth infection, revealing an indispensable role of an interferon-γ (IFNγ)-EGC-CXCL10 axis in tissue repair.
Swalpa Udit, Kimbria Blake, and Isaac M Chiu. 3/2022. “Somatosensory and autonomic neuronal regulation of the immune response.” Nat Rev Neurosci, 23, 3, Pp. 157-171.Abstract
Bidirectional communication between the peripheral nervous system (PNS) and the immune system is a crucial part of an effective but balanced mammalian response to invading pathogens, tissue damage and inflammatory stimuli. Here, we review how somatosensory and autonomic neurons regulate immune cellular responses at barrier tissues and in peripheral organs. Immune cells express receptors for neuronal mediators, including neuropeptides and neurotransmitters, allowing neurons to influence their function in acute and chronic inflammatory diseases. Distinct subsets of peripheral sensory, sympathetic, parasympathetic and enteric neurons are able to signal to innate and adaptive immune cells to modulate their cellular functions. In this Review, we highlight recent studies defining the molecular mechanisms by which neuroimmune signalling mediates tissue homeostasis and pathology. Understanding the neural circuitry that regulates immune responses can offer novel targets for the treatment of a wide array of diseases.
Nicole J Yang, Jörg Isensee, Dylan V Neel, Andreza U Quadros, Han-Xiong Bear Zhang, Justas Lauzadis, Sai Man Liu, Stephanie Shiers, Andreea Belu, Shilpa Palan, Sandra Marlin, Jacquie Maignel, Angela Kennedy-Curran, Victoria S Tong, Mahtab Moayeri, Pascal Röderer, Anja Nitzsche, Mike Lu, Bradley L Pentelute, Oliver Brüstle, Vineeta Tripathi, Keith A Foster, Theodore J Price, John R Collier, Stephen H Leppla, Michelino Puopolo, Bruce P Bean, Thiago M Cunha, Tim Hucho, and Isaac M Chiu. 2/25/2022. “Anthrax toxins regulate pain signaling and can deliver molecular cargoes into ANTXR2+ DRG sensory neurons.” Nat Neurosci, 25, 2, Pp. 168-179.Abstract
Bacterial products can act on neurons to alter signaling and function. In the present study, we found that dorsal root ganglion (DRG) sensory neurons are enriched for ANTXR2, the high-affinity receptor for anthrax toxins. Anthrax toxins are composed of protective antigen (PA), which binds to ANTXR2, and the protein cargoes edema factor (EF) and lethal factor (LF). Intrathecal administration of edema toxin (ET (PA + EF)) targeted DRG neurons and induced analgesia in mice. ET inhibited mechanical and thermal sensation, and pain caused by formalin, carrageenan or nerve injury. Analgesia depended on ANTXR2 expressed by Nav1.8+ or Advillin+ neurons. ET modulated protein kinase A signaling in mouse sensory and human induced pluripotent stem cell-derived sensory neurons, and attenuated spinal cord neurotransmission. We further engineered anthrax toxins to introduce exogenous protein cargoes, including botulinum toxin, into DRG neurons to silence pain. Our study highlights interactions between a bacterial toxin and nociceptors, which may lead to the development of new pain therapeutics.
Lars E Clark, Sarah A Clark, ChieYu Lin, Jianying Liu, Adrian Coscia, Katherine G Nabel, Pan Yang, Dylan V Neel, Hyo Lee, Vesna Brusic, Iryna Stryapunina, Kenneth S Plante, Asim A Ahmed, Flaminia Catteruccia, Tracy L Young-Pearse, Isaac M Chiu, Paula Montero Llopis, Scott C Weaver, and Jonathan Abraham. 2/2022. “VLDLR and ApoER2 are receptors for multiple alphaviruses.” Nature, 602, 7897, Pp. 475-480.Abstract
Alphaviruses, like many other arthropod-borne viruses, infect vertebrate species and insect vectors separated by hundreds of millions of years of evolutionary history. Entry into evolutionarily divergent host cells can be accomplished by recognition of different cellular receptors in different species, or by binding to receptors that are highly conserved across species. Although multiple alphavirus receptors have been described1-3, most are not shared among vertebrate and invertebrate hosts. Here we identify the very low-density lipoprotein receptor (VLDLR) as a receptor for the prototypic alphavirus Semliki forest virus. We show that the E2 and E1 glycoproteins (E2-E1) of Semliki forest virus, eastern equine encephalitis virus and Sindbis virus interact with the ligand-binding domains (LBDs) of VLDLR and apolipoprotein E receptor 2 (ApoER2), two closely related receptors. Ectopic expression of either protein facilitates cellular attachment, and internalization of virus-like particles, a VLDLR LBD-Fc fusion protein or a ligand-binding antagonist block Semliki forest virus E2-E1-mediated infection of human and mouse neurons in culture. The administration of a VLDLR LBD-Fc fusion protein has protective activity against rapidly fatal Semliki forest virus infection in mouse neonates. We further show that invertebrate receptor orthologues from mosquitoes and worms can serve as functional alphavirus receptors. We propose that the ability of some alphaviruses to infect a wide range of hosts is a result of their engagement of evolutionarily conserved lipoprotein receptors and contributes to their pathogenesis.
Nicole J Yang, Dylan V Neel, Liwen Deng, Michelle Heyang, Angela Kennedy-Curran, Victoria S Tong, Jin Mo Park, and Isaac M Chiu. 8/3/2021. “Nociceptive Sensory Neurons Mediate Inflammation Induced by Edema Toxin.” Front Immunol, 12, Pp. 642373.Abstract
Bacterial products are able to act on nociceptive neurons during pathogenic infection. Neurogenic inflammation is an active part of pain signaling and has recently been shown to impact host-pathogen defense. Bacillus anthracis Edema Toxin (ET) produces striking edema in peripheral tissues, but the cellular mechanisms involved in tissue swelling are not completely understood. Here, we find that nociceptive neurons play a role in ET-induced edema and inflammation in mice. Subcutaneous footpad infection of B. anthracis Sterne caused ET-dependent local mechanical allodynia, paw swelling and body weight gain. Subcutaneous administration of ET induced paw swelling and vascular leakage, the early phases of which were attenuated in the absence of Trpv1+ or Nav1.8+ nociceptive neurons. Nociceptive neurons express the anthrax toxin receptor ANTXR2, but this did not mediate ET-induced edema. ET induced local cytokine expression and neutrophil recruitment, which were dependent in part on Trpv1+ nociceptive neurons. Ablation of Trpv1+ or Nav1.8+ nociceptive neurons also attenuated early increases in paw swelling and body weight gain during live B. anthracis infection. Our findings indicate that nociceptive neurons play an active role in inflammation caused by B. anthracis and Edema Toxin to potentially influence bacterial pathogenesis.
Tiffany Lin, Daisy Quellier, Jeffrey Lamb, Tiphaine Voisin, Pankaj Baral, Felix Bock, Alfrun Schönberg, Rossen Mirchev, Gerald Pier, Isaac Chiu, and Mihaela Gadjeva. 5/6/2021. “Pseudomonas aeruginosa-induced nociceptor activation increases susceptibility to infection.” PLoS Pathog, 17, 5, Pp. e1009557.Abstract
We report a rapid reduction in blink reflexes during in vivo ocular Pseudomonas aeruginosa infection, which is commonly attributed and indicative of functional neuronal damage. Sensory neurons derived in vitro from trigeminal ganglia (TG) were able to directly respond to P. aeruginosa but reacted significantly less to strains of P. aeruginosa that lacked virulence factors such as pili, flagella, or a type III secretion system. These observations led us to explore the impact of neurons on the host's susceptibility to P. aeruginosa keratitis. Mice were treated with Resiniferatoxin (RTX), a potent activator of Transient Receptor Potential Vanilloid 1 (TRPV1) channels, which significantly ablated corneal sensory neurons, exhibited delayed disease progression that was exemplified with decreased bacterial corneal burdens and altered neutrophil trafficking. Sensitization to disease was due to the increased frequencies of CGRP-induced ICAM-1+ neutrophils in the infected corneas and reduced neutrophil bactericidal activities. These data showed that sensory neurons regulate corneal neutrophil responses in a tissue-specific matter affecting disease progression during P. aeruginosa keratitis. Hence, therapeutic modalities that control nociception could beneficially impact anti-infective therapy.
Liwen Deng and Isaac M Chiu. 4/1/2021. “Microbes and pain.” PLoS Pathog, 17, 4, Pp. e1009398. PDF
Tiphaine Voisin, Caroline Perner, Marie-Angele Messou, Stephanie Shiers, Saltanat Ualiyeva, Yoshihide Kanaoka, Theodore J Price, Caroline L Sokol, Lora G Bankova, Frank K Austen, and Isaac M Chiu. 3/30/2021. “The CysLT2R receptor mediates leukotriene C4-driven acute and chronic itch.” Proc Natl Acad Sci U S A, 118, 13.Abstract
Acute and chronic itch are burdensome manifestations of skin pathologies including allergic skin diseases and atopic dermatitis, but the underlying molecular mechanisms are not well understood. Cysteinyl leukotrienes (CysLTs), comprising LTC, LTD, and LTE, are produced by immune cells during type 2 inflammation. Here, we uncover a role for LTC and its signaling through the CysLT receptor 2 (CysLTR) in itch. transcript is highly expressed in dorsal root ganglia (DRG) neurons linked to itch in mice. We also detected in a broad population of human DRG neurons. Injection of leukotriene C (LTC) or its nonhydrolyzable form NMLTC, but neither LTD nor LTE, induced dose-dependent itch but not pain behaviors in mice. LTC-mediated itch differed in bout duration and kinetics from pruritogens histamine, compound 48/80, and chloroquine. NMLTC-induced itch was abrogated in mice deficient for or when deficiency was restricted to radioresistant cells. Itch was unaffected in mice deficient for , , or mast cells (W mice). CysLTR played a role in itch in the MC903 mouse model of chronic itch and dermatitis, but not in models of dry skin or compound 48/80- or -induced itch. In MC903-treated mice, CysLT levels increased in skin over time, and mice showed decreased itch in the chronic phase of inflammation. Collectively, our study reveals that LTC acts through CysLTR as its physiological receptor to induce itch, and CysLTR contributes to itch in a model of dermatitis. Therefore, targeting CysLT signaling may be a promising approach to treat inflammatory itch.
Yiqing Yan, Deepshika Ramanan, Milena Rozenberg, Kelly McGovern, Daniella Rastelli, Brinda Vijaykumar, Omar Yaghi, Tiphaine Voisin, Munir Mosaheb, Isaac Chiu, Shalev Itzkovitz, Meenakshi Rao, Diane Mathis, and Christophe Benoist. 3/9/2021. “Interleukin-6 produced by enteric neurons regulates the number and phenotype of microbe-responsive regulatory T cells in the gut.” Immunity, 54, 3, Pp. 499-513.e5.Abstract
The immune and enteric nervous (ENS) systems monitor the frontier with commensal and pathogenic microbes in the colon. We investigated whether FoxP3 regulatory T (Treg) cells functionally interact with the ENS. Indeed, microbe-responsive RORγ and Helios subsets localized in close apposition to nitrergic and peptidergic nerve fibers in the colon lamina propria (LP). Enteric neurons inhibited in vitro Treg (iTreg) differentiation in a cell-contact-independent manner. A screen of neuron-secreted factors revealed a role for interleukin-6 (IL-6) in modulating iTreg formation and their RORγ proportion. Colonization of germfree mice with commensals, especially RORγ Treg inducers, broadly diminished colon neuronal density. Closing the triangle, conditional ablation of IL-6 in neurons increased total Treg cells but decreased the RORγ subset, as did depletion of two ENS neurotransmitters. Our findings suggest a regulatory circuit wherein microbial signals condition neuronal density and activation, thus tuning Treg cell generation and immunological tolerance in the gut.
Amanda Jacobson, Daping Yang, Madeleine Vella, and Isaac M Chiu. 2/4/2021. “The intestinal neuro-immune axis: crosstalk between neurons, immune cells, and microbes.” Mucosal Immunol.Abstract
The gastrointestinal tract is densely innervated by a complex network of neurons that coordinate critical physiological functions. Here, we summarize recent studies investigating the crosstalk between gut-innervating neurons, resident immune cells, and epithelial cells at homeostasis and during infection, food allergy, and inflammatory bowel disease. We introduce the neuroanatomy of the gastrointestinal tract, detailing gut-extrinsic neuron populations from the spinal cord and brain stem, and neurons of the intrinsic enteric nervous system. We highlight the roles these neurons play in regulating the functions of innate immune cells, adaptive immune cells, and intestinal epithelial cells. We discuss the consequences of such signaling for mucosal immunity. Finally, we discuss how the intestinal microbiota is integrated into the neuro-immune axis by tuning neuronal and immune interactions. Understanding the molecular events governing the intestinal neuro-immune signaling axes will enhance our knowledge of physiology and may provide novel therapeutic targets to treat inflammatory diseases.
Liliana M Sanmarco, Michael A Wheeler, Cristina Gutiérrez-Vázquez, Carolina Manganeli Polonio, Mathias Linnerbauer, Felipe A Pinho-Ribeiro, Zhaorong Li, Federico Giovannoni, Katelyn V Batterman, Giulia Scalisi, Stephanie EJ Zandee, Evelyn S Heck, Moneera Alsuwailm, Douglas L Rosene, Burkhard Becher, Isaac M Chiu, Alexandre Prat, and Francisco J Quintana. 2/2021. “Gut-licensed IFNγ+ NK cells drive LAMP1+ TRAIL+ anti-inflammatory astrocytes.” Nature, 590, 7846, Pp. 473-479.Abstract
Astrocytes are glial cells that are abundant in the central nervous system (CNS) and that have important homeostatic and disease-promoting functions. However, little is known about the homeostatic anti-inflammatory activities of astrocytes and their regulation. Here, using high-throughput flow cytometry screening, single-cell RNA sequencing and CRISPR-Cas9-based cell-specific in vivo genetic perturbations in mice, we identify a subset of astrocytes that expresses the lysosomal protein LAMP1 and the death receptor ligand TRAIL. LAMP1TRAIL astrocytes limit inflammation in the CNS by inducing T cell apoptosis through TRAIL-DR5 signalling. In homeostatic conditions, the expression of TRAIL in astrocytes is driven by interferon-γ (IFNγ) produced by meningeal natural killer (NK) cells, in which IFNγ expression is modulated by the gut microbiome. TRAIL expression in astrocytes is repressed by molecules produced by T cells and microglia in the context of inflammation. Altogether, we show that LAMP1TRAIL astrocytes limit CNS inflammation by inducing T cell apoptosis, and that this astrocyte subset is maintained by meningeal IFNγ NK cells that are licensed by the microbiome.
Valentina N Lagomarsino, Aleksandar D Kostic, and Isaac M Chiu. 12/11/2020. “Mechanisms of microbial–neuronal interactions in pain and nociception.” Neurobiol Pain, 9, Pp. 100056-100056.Abstract
Nociceptor sensory neurons innervate barrier tissues that are constantly exposed to microbial stimuli. During infection, pathogenic microorganisms can breach barrier surfaces and produce pain by directly activating nociceptors. Microorganisms that live in symbiotic relationships with their hosts, commensals and mutualists, have also been associated with pain, but the molecular mechanisms of how symbionts act on nociceptor neurons to modulate pain remain largely unknown. In this review, we will discuss the known molecular mechanisms of how microbes directly interact with sensory afferent neurons affecting nociception in the gut, skin and lungs. We will touch on how bacterial, viral and fungal pathogens signal to the host to inflict or suppress pain. We will also discuss recent studies examining how gut symbionts affect pain. Specifically, we will discuss how gut symbionts may interact with sensory afferent neurons either directly, through secretion of metabolites or neurotransmitters, or indirectly,through first signaling to epithelial cells or immune cells, to regulate visceral, neuropathic and inflammatory pain. While this area of research is still in its infancy, more mechanistic studies to examine microbial-sensory neuron crosstalk in nociception may allow us to develop new therapies for the treatment of acute and chronic pain.
Caroline Perner, Cameron H Flayer, Xueping Zhu, Pamela A Aderhold, Zaynah NA Dewan, Tiphaine Voisin, Ryan B Camire, Ohn A Chow, Isaac M Chiu, and Caroline L Sokol. 11/17/2020. “Substance P Release by Sensory Neurons Triggers Dendritic Cell Migration and Initiates the Type-2 Immune Response to Allergens.” Immunity, 53, 5, Pp. 1063-1077.Abstract

Dendritic cells (DCs) of the cDC2 lineage initiate allergic immunity and in the dermis are marked by their expression of CD301b. CD301b+ dermal DCs respond to allergens encountered in vivo, but not in vitro. This suggests that another cell in the dermis may sense allergens and relay that information to activate and induce the migration of CD301b+ DCs to the draining lymph node (dLN). Using a model of cutaneous allergen exposure, we show that allergens directly activated TRPV1+ sensory neurons leading to itch and pain behaviors. Allergen-activated sensory neurons released the neuropeptide Substance P, which stimulated proximally located CD301b+ DCs through the Mas-related G-protein coupled receptor member A1 (MRGPRA1). Substance P induced CD301b+ DC migration to the dLN where they initiated T helper-2 cell differentiation. Thus, sensory neurons act as primary sensors of allergens, linking exposure to activation of allergic-skewing DCs and the initiation of an allergic immune response.

Meng Wu, Yaobing Chen, Han Xia, Changli Wang, Chin Yee Tan, Xunhui Cai, Yufeng Liu, Fenghu Ji, Peng Xiong, Ran Liu, Yuanlin Guan, Yaqi Duan, Dong Kuang, Sanpeng Xu, Hanghang Cai, Qin Xia, Dehua Yang, Ming-Wei Wang, Isaac M Chiu, Chao Cheng, Philip P Ahern, Liang Liu, Guoping Wang, Neeraj K Surana, Tian Xia, and Dennis L Kasper. 11/10/2020. “Transcriptional and proteomic insights into the host response in fatal COVID-19 cases.” Proc Natl Acad Sci U S A, 117, 45, Pp. 28336-28343.Abstract

Coronavirus disease 2019 (COVID-19), the global pandemic caused by SARS-CoV-2, has resulted thus far in greater than 933,000 deaths worldwide; yet disease pathogenesis remains unclear. Clinical and immunological features of patients with COVID-19 have highlighted a potential role for changes in immune activity in regulating disease severity. However, little is known about the responses in human lung tissue, the primary site of infection. Here we show that pathways related to neutrophil activation and pulmonary fibrosis are among the major up-regulated transcriptional signatures in lung tissue obtained from patients who died of COVID-19 in Wuhan, China. Strikingly, the viral burden was low in all samples, which suggests that the patient deaths may be related to the host response rather than an active fulminant infection. Examination of the colonic transcriptome of these patients suggested that SARS-CoV-2 impacted host responses even at a site with no obvious pathogenesis. Further proteomics analysis validated our transcriptome findings and identified several key proteins, such as the SARS-CoV-2 entry-associated protease cathepsins B and L and the inflammatory response modulator S100A8/A9, that are highly expressed in fatal cases, revealing potential drug targets for COVID-19.

Isabelle A. M. van Thiel, Wouter J. de Jonge, Isaac M Chiu, and Rene M. van den Wijngaard. 6/1/2020. “Microbiota-neuroimmune cross talk in stress-induced visceral hypersensitivity of the bowel.” Am J Physiol Gastrointest Liver Physiol, 318, 6, Pp. G1034-G1041.Abstract

Visceral hypersensitivity of the lower gastrointestinal tract, defined as an increased response to colorectal disten- sion, frequently prompts episodes of debilitating abdominal pain in irritable bowel syndrome (IBS). Although the pathophysiology of IBS is not yet fully elucidated, it is well known that stress is a major risk factor for development and acts as a trigger of pain sensation. Stress modulates both immune responses as well as the gut microbiota and vice versa. Additionally, either microbes themselves or through involvement of the immune system, activate or sensitize afferent nociceptors. In this paper, we review current knowledge on the influence of stress along the gut-brain-microbiota axis and exemplify relevant neuroimmune cross talk mecha- nisms in visceral hypersensitivity, working toward understanding how gut micro- biota-neuroimmune cross talk contributes to visceral pain sensation in IBS patients.

Isaac M Chiu and Asya Rolls. 6/2020. “Editorial overview: Brain, gut and immune system interactions.” Curr Opin Neurobiol, 62, Pp. iii-v. PDF
Coco Chu, David Artis, and Isaac M Chiu. 3/17/2020. “Neuro-immune Interactions in the Tissues.” Immunity, 52, 3, Pp. 464-474.Abstract
The ability of the nervous system to sense environmental stimuli and to relay these signals to immune cells via neurotransmitters and neuropeptides is indispensable for effective immunity and tissue homeostasis. Depending on the tissue microenvironment and distinct drivers of a certain immune response, the same neuronal populations and neuro-mediators can exert opposing effects, promoting or inhibiting tissue immunity. Here, we review the current understanding of the mechanisms that underlie the complex interactions between the immune and the nervous systems in different tissues and contexts. We outline current gaps in knowledge and argue for the importance of considering infectious and inflammatory disease within a conceptual framework that integrates neuro-immune circuits both local and systemic, so as to better understand effective immunity to develop improved approaches to treat inflammation and disease.
Kathy Wang, Omar K Yaghi, Raul German Spallanzani, Xi Chen, David Zemmour, Nicole Lai, Isaac M Chiu, Christophe Benoist, and Diane Mathis. 3/10/2020. “Neuronal, stromal, and T-regulatory cell crosstalk in murine skeletal muscle.” Proc Natl Acad Sci U S A, 117, 10, Pp. 5402-5408.Abstract

A distinct population of Foxp3+CD4+ regulatory T (Treg) cells promotes repair of acutely or chronically injured skeletal muscle. The accumulation of these cells depends critically on interleukin (IL)-33 produced by local mesenchymal stromal cells (mSCs). An intriguing physical association among muscle nerves, IL-33+ mSCs, and Tregs has been reported, and invites a deeper exploration of this cell triumvirate. Here we evidence a striking proximity between IL-33+ muscle mSCs and both large-fiber nerve bundles and small-fiber sensory neurons; report that muscle mSCs transcribe an array of genes encoding neuropeptides, neuropeptide receptors, and other nerve-related proteins; define muscle mSC subtypes that express both IL-33 and the receptor for the calcitonin-gene-related peptide (CGRP); and demonstrate that up- or down-tuning of CGRP signals augments or diminishes, respectively, IL-33 production by muscle mSCs and later accumulation of muscle Tregs. Indeed, a single injection of CGRP induced much of the genetic program elicited in mSCs early after acute skeletal muscle injury. These findings highlight neural/stromal/immune-cell crosstalk in tissue repair, suggesting future therapeutic approaches.