Decoding nociceptor-DC dialogues.

Neuro-immune interactions link physiological and immune responses in host defense. Hanc et al.1 report that nociceptors attract dendritic cells (DCs) via the chemokine (C-C motif) ligand 2 (CCL2), initiate a "sentinel" DC program via the neuropeptide calcitonin gene-related peptide (CGRP), and enhance DC inflammatory responses through direct connections. These neuroimmune units integrate nociceptors' rapid responsiveness with DCs' immune coordination, functioning as an advanced warning system.

Nanophotonics Enable Targeted Photothermal Silencing of Nociceptor Neurons.

The sensory nervous and immune systems work in concert to preserve homeostasis. While this endogenous interplay protects from danger, it may drive chronic pathologies. Currently, genetic engineering of neurons remains the primary approach to interfere selectively with this potentially deleterious interplay. However, such manipulations are not feasible in a clinical setting. Here, this work reports a nanotechnology-enabled concept to silence subsets of unmodified nociceptor neurons that exploits their ability to respond to heat via the transient receptor potential vanilloid type 1 (TRPV1) channel. This strategy uses laser stimulation of antibody-coated gold nanoparticles to heat-activate TRPV1, turning this channel into a cell-specific drug-entry port. This delivery method allows transport of a charged cationic derivative of an N-type calcium channel blocker (CNCB-2) into targeted sensory fibers. CNCB-2 delivery blocks neuronal calcium currents and neuropeptides release, resulting in targeted silencing of nociceptors. Finally, this work demonstrates the ability of the approach to probe neuro-immune crosstalk by targeting cytokine-responsive nociceptors and by successfully preventing nociceptor-induced CD8+ T-cells polarization. Overall, this work constitutes the first demonstration of targeted silencing of nociceptor neuron subsets without requiring genetic modification, establishing a strategy for interfering with deleterious neuro-immune interplays.

FcεR1-expressing nociceptors trigger allergic airway inflammation.

BACKGROUND: Lung nociceptor neurons amplify immune cell activity and mucus metaplasia in response to an inhaled allergen challenge in sensitized mice. OBJECTIVE: We sought to identify the cellular mechanisms by which these sensory neurons are activated subsequent to allergen exposure. METHODS: We used calcium microscopy and electrophysiologic recording to assess whether vagal neurons directly respond to the model allergen ovalbumin (OVA). Next, we generated the first nociceptor-specific FcεR1γ knockdown (TRPV1Cre::FcεR1γfl/fl) mice to assess whether this targeted invalidation would affect the severity of allergic inflammation in response to allergen challenges. RESULTS: Lung-innervating jugular nodose complex ganglion neurons express the high-affinity IgE receptor FcεR1, the levels of which increase in OVA-sensitized mice. FcεR1γ-expressing vagal nociceptor neurons respond directly to OVA complexed with IgE with depolarization, action potential firing, calcium influx, and neuropeptide release. Activation of vagal neurons by IgE-allergen immune complexes, through the release of substance P from their peripheral terminals, directly amplifies TH2 cell influx and polarization in the airways. Allergic airway inflammation is decreased in TRPV1Cre::FcεR1γfl/fl mice and in FcεR1α-/- mice into which bone marrow has been transplanted. Finally, increased in vivo circulating levels of IgE following allergen sensitization enhances the responsiveness of FcεR1 to immune complexes in both mouse jugular nodose complex ganglion neurons and human induced pluripotent stem cell-derived nociceptors. CONCLUSIONS: Allergen sensitization triggers a feedforward inflammatory loop between IgE-producing plasma cells, FcεR1-expressing vagal sensory neurons, and TH2 cells, which helps to both initiate and amplify allergic airway inflammation. These data highlight a novel target for reducing allergy, namely, FcεR1γ expressed by nociceptors.

BASOPHILS ACTIVATE PRURICEPTOR-LIKE VAGAL SENSORY NEURONS.

Vagal sensory neurons convey sensations from internal organs along the vagus nerve to the brainstem. Pruriceptors are a subtype of neurons that transmit itch and induce pruritus. Despite extensive research on the molecular mechanisms of itch, studies focusing on pruriceptors in the vagal ganglia still need to be explored. In this study, we characterized vagal pruriceptor neurons by their responsiveness to pruritogens such as lysophosphatidic acid, ß-alanine, chloroquine, and the cytokine oncostatin M. We discovered that lung-resident basophils produce oncostatin M and that its release can be induced by engagement of FcεRIα. Oncostatin M then sensitizes multiple populations of vagal sensory neurons, including Tac1+ and MrgprA3+ neurons in the jugular ganglia. Finally, we observed an increase in oncostatin M release in mice sensitized to the house dust mite Dermatophagoides pteronyssinus or to the fungal allergen Alternaria alternata, highlighting a novel mechanism through which basophils and vagal sensory neurons may communicate during type I hypersensitivity diseases such as allergic asthma.

Anatomical differences in nociceptor neurons sensitivity.

BACKGROUND: Dorsal Root Ganglia (DRG) neurons are derived from the neural crest and mainly innervate the skin, while Jugular Nodose Complex (JNC) neurons originate from the placode and innervate internal organs. These ganglia are composed of highly heterogeneous groups of neurons aimed at assessing and preserving homeostasis. Among other subtypes, nociceptor neurons are specialized in sensing and responding to environmental dangers. As form typically follows function, we hypothesized that JNC and DRG neurons would be phenotypically and transcriptomically different. METHODS: Mouse JNC and DRG neurons were cultured ex vivo. Using calcium imaging, qPCR and neurite outgrowth assay, we compared the sensitivity of JNC and DRG neurons. Using in-silico analysis of existing RNA sequencing datasets, we confronted our results to transcriptomic differences found between both ganglia. RESULTS: We found drastically different expression levels of Transient Receptor Potential (TRP) channels, growth factor receptors and neuropeptides in JNC and DRG neurons. Functionally, naïve JNC neurons' TRP channels are more sensitive to thermal cues than the ones from DRG neurons. However, DRG neurons showed increased TRP channel responsiveness, neuropeptide release and neurite outgrowth when exposed to Nerve Growth Factor (NGF). In contrast, JNC neurons preferentially responded to Brain-derived neurotrophic factor (BDNF). CONCLUSION: Our data show that JNC and DRG neurons are transcriptomically and functionally unique and that pain sensitivity is different across anatomical sites. Drugs targeting NGF signaling may have limited efficacy to treat visceral pain. Bioelectronics nerve stimulation should also be adjusted to the ganglia being targeted and their different expression profile.

Analysis of Airway Vagal Neurons.

Internal organs, including the airway, are innervated by neurons of the autonomic and sensory nervous systems. The airway-innervating sensory neurons primarily originate from the vagus nerve, whose cell bodies are found, in rodents, in the jugular and nodose ganglia complex (JNC). About half of these sensory neurons expressed the heat-sensing ion channel TRPV1 and evolved to limit tissue damage by detecting chemical, mechanical, or thermal threats and to initiate protective airway reflexes such as coughing and bronchoconstriction. They also help monitor the host homeostasis by sensing nutrients, pressure, and O2 levels and help mount airway defenses by controlling immune and goblet cell activity. To better appreciate the scope of the physiological role and pathological contributions of these neurons, we will review gain and loss-of-function approaches geared at controlling the activity of these neurons. We will also present a method to study transcriptomic changes in airway-innervating neurons and a co-culture approach designed to understand how nociceptors modulate immune responses.

Promoting antigen escape from dendritic cell endosomes potentiates anti-tumoral immunity.

The cross-presenting capacity of dendritic cells (DCs) can be limited by non-specific degradation during endosome maturation. To bypass this limitation, we present in this study a new Accum-based formulation designed to promote endosome-to-cytosol escape. Treatment of primary DCs with Accum linked to the xenoantigen ovalbumin (OVA) triggers endosomal damages and enhances protein processing. Despite multiple challenges using ascending doses of tumor cells, DC prophylactic vaccination results in complete protection due to increased levels of effector CD4 and CD8 T cells as well as high production of pro-inflammatory mediators. When combined with anti-PD-1, therapeutic vaccination using both syngeneic and allogeneic Accum-OVA-pulsed DCs triggers potent anti-tumoral responses. The net outcome culminates in increased CD11c, CD8, and NK infiltration along with a high CD8/Treg ratio. These highly favorable therapeutic effects highlight the promising potential of Accum as a distinct and potent technology platform suitable for the design of next generation cell cancer vaccines.

Nociceptor neurons promote IgE class switch in B cells.

Nociceptors, the high-threshold primary sensory neurons that trigger pain, interact with immune cells in the periphery to modulate innate immune responses. Whether they also participate in adaptive and humoral immunity is, however, not known. In this study, we probed if nociceptors have a role in distinct airway and skin models of allergic inflammation. In both models, the genetic ablation and pharmacological silencing of nociceptors substantially reduced inflammatory cell infiltration to the affected tissue. Moreover, we also found a profound and specific deficit in IgE production in these models of allergic inflammation. Mechanistically, we discovered that the nociceptor-released neuropeptide substance P helped trigger the formation of antibody-secreting cells and their release of IgE. Our findings suggest that nociceptors, in addition to their contributions to innate immunity, play a key role in modulating the adaptive immune response, particularly B cell antibody class switching to IgE.

Neurons and Microglia; A Sickly-Sweet Duo in Diabetic Pain Neuropathy.

Diabetes is a common condition characterized by persistent hyperglycemia. High blood sugar primarily affects cells that have a limited capacity to regulate their glucose intake. These cells include capillary endothelial cells in the retina, mesangial cells in the renal glomerulus, Schwann cells, and neurons of the peripheral and central nervous systems. As a result, hyperglycemia leads to largely intractable complications such as retinopathy, nephropathy, hypertension, and neuropathy. Diabetic pain neuropathy is a complex and multifactorial disease that has been associated with poor glycemic control, longer diabetes duration, hypertension, advanced age, smoking status, hypoinsulinemia, and dyslipidemia. While many of the driving factors involved in diabetic pain are still being investigated, they can be broadly classified as either neuron -intrinsic or -extrinsic. In neurons, hyperglycemia impairs the polyol pathway, leading to an overproduction of reactive oxygen species and reactive nitrogen species, an enhanced formation of advanced glycation end products, and a disruption in Na+/K+ ATPase pump function. In terms of the extrinsic pathway, hyperglycemia leads to the generation of both overactive microglia and microangiopathy. The former incites a feed-forward inflammatory loop that hypersensitizes nociceptor neurons, as observed at the onset of diabetic pain neuropathy. The latter reduces neurons' access to oxygen, glucose and nutrients, prompting reductions in nociceptor terminal expression and losses in sensation, as observed in the later stages of diabetic pain neuropathy. Overall, microglia can be seen as potent and long-lasting amplifiers of nociceptor neuron activity, and may therefore constitute a potential therapeutic target in the treatment of diabetic pain neuropathy.