Transient Receptor Potential Ankyrin 1 Mediates Afferent Signals in the Inflammatory Reflex

Abstract

Survival of an organism requires mechanisms to sense damaging factors in the environment. In mammals, bacterial toxins and inflammatory mediators stimulate nociceptive sensory neurons to activate protective reflexes. Whereas the vagus nerve reflex circuit that protects against damaging inflammation, termed the "inflammatory reflex," was described more than twenty years ago 1,2 , how the vagus nerve detects inflammation to initiate the inflammatory reflex has remained unknown. Here we show that transient receptor potential ankyrin 1 (TRPA1) in sensory vagus neurons is required to sense interleukin-1β (IL-1β), a central cytokine mediator of inflammation and injury. Selective activation of vagus nerve TRPA1 using optopharmacology stimulated the inflammatory reflex to inhibit innate inflammatory responses to bacterial lipopolysaccharide and IL-1β. Proximity ligation assay and immunohistochemistry revealed that IL-1 receptors are coexpressed with TRPA1 in vagus sensory neurons. Whole-cell patch-clamp recordings reveal that TRPA1 is required to mediate IL-1β-dependent depolarization of vagus sensory neurons. Further, TRPA1-deficient mice lack inflammatory reflex attenuation of inflammation, fail to restrain cytokine release, and have significantly enhanced lethality to bacterial sepsis. Therefore, vagus neurons expressing TRPA1 are necessary and sufficient to activate the sensory arc of the inflammatory reflex to protect against harmful inflammation.Reflex neural circuits form the basis for physiological responses when the body is exposed to changing environmental and physiological conditions. The vagus nerve, originating in the brainstem medulla oblongata, is a paired structure that travels through the neck, thorax and abdomen to innervate visceral organs. In humans it is comprised of approximately 100,000 neurons; 80% are sensory, transmitting information to the brainstem in response to changes in the body's internal milieu to stimulate reflex motor signals that regulate heart rate, digestion, and other organ functions. The inflammatory reflex, a vagus circuit that inhibits inflammation to protect tissues from damage, stimulates anti-inflammatory T cells expressing choline acetyltransferase (T ChAT) in the spleen to produce acetylcholine which interacts with 7 nicotinic acetylcholine receptor (7nAChR)-expressing macrophages to inhibit release of TNF, IL-1, HMGB1 and other inflammatory cytokines 1-3 . Electronic stimulation of the inflammatory reflex confers significant protection in preclinical models of arthritis, inflammatory bowel disease, sepsis, and other syndromes, and significantly improves outcomes in clinical trials of rheumatoid arthritis and Crohn's disease 2,4,5 . Despite a detailed mechanistic understanding of signaling in the motor arc of the inflammatory reflex, the afferent arc mechanisms were previously unknown. TRPA1, a polymodal nociceptor cation channel expressed by unmyelinated peptidergic nociceptive C fiber neurons, is stimulated by reactive (hydrogen peroxide, formalin, acrolein) and non-rea...

Involvement of Neural Transient Receptor Potential Channels in Peripheral Inflammation

“…Cinnamaldehyde can also attenuate apoptosis and promote neuronal survival in DRGs due to oxidative stress, by inhibiting NFkB and decreasing ROS (232). Furthermore, direct activation of TRPA1 on the cervical vagus nerve by the optopharmacological molecule optovin reduces systemic inflammation induced by LPS by significantly decreasing serum TNF (125). Interestingly, LPS itself has recently been found to directly activate TRPA1 directly on sensory neurons, inducing a calcium influx, along with vasodilation, pain, and the release of CGRP in a TRPA1 dependent manner (73).…”

Interleukin 1 beta‐induced calcium signaling via TRPA1 channels promotes mitogen‐activated protein kinase‐dependent mesangial cell proliferation

“…29,31 For fibronectin immunostaining in glomerular explants, we used an efficient sieving method previously described by Rush et al (2018). 32 The protocol initially reported for the isolation of rat glomeruli was modified for mice using a smaller size sieve (40 µm) to collect the glomeruli at the last sieving step. The glomeruli were cultured on sterilized glass coverslips for 96 hours before treatment, after which the glomeruli were fixed with 4% formaldehyde for ~15 minutes, permeabilized with 0.5% Triton X-100 for ~15 minutes, blocked with 2% bovine serum albumin for ~1 hour at room temperature and stained overnight with mouse fibronectin antibody at 4°C.…”

“…However, studies have shown that neuronal and nonneuronal transient receptor potential ankyrin 1 (TRPA1), a cation channel, may be involved in the biological activities of IL‐1. TRPA1 and IL1R1 co‐express in mouse nodose sensory neurons and mediate IL‐1β‐induced vagus nerve activity, thermoregulation, and inflammation 22 . Inhibition of TRPA1 channels attenuated IL‐1β production in primary bronchial epithelial cells and reduced cardiac IL‐1β expression level in doxorubicin‐treated mice 23,24 .…”

“…TRPA1 and IL1R1 co-express in mouse nodose sensory neurons and mediate IL-1β-induced vagus nerve activity, thermoregulation, and inflammation. 22 Inhibition of TRPA1 channels attenuated IL-1β production in primary bronchial epithelial cells and reduced cardiac IL-1β expression level in doxorubicin-treated mice. 23,24 TRPA1 agonists upregulated IL-1β in human keratinocytes and rat endometrial cells.…”