Biology subjects

Julius, D.

Publications and source records attributed to Julius, D..

10 recordsLinked to original sources

bioRxiv2025

The structural basis of cold sensitivity

Thermosensitive TRP ion channels enable somatosensory nerve fibers to detect changes in our thermal environment over a wide physiologic range 1-3. In mammals, the menthol receptor, TRPM8, is activated by temperatures below [~]26{degrees}C and is essential for the perception of cold or chemical cooling agents 4-6. A fascinating, yet still unachieved goal is to elucidate structural mechanisms whereby TRPM8 or other thermosensitive channels are gated by changes in ambient temperature. Recent studies using cryogenic electron microscopy (cryo-EM) have attempted to address this challenging question but are limited by difficulties in visualizing temperature-evoked conformational substates or assessing the energetic landscape governing gating transitions 7,8. Here, we close this gap by using cryo-EM to visualize TRPM8 channels in cellular membranes, where bona fide menthol- and cold-evoked open states are captured. We identify a novel semi-swapped architecture in which interdigitation of channel subunits is substantially rearranged following repositioning of the S6 transmembrane helix and elements of the pore region. By combining this structural analysis with thermodynamic measurements using hydrogen-deuterium exchange mass spectrometry (HDX-MS), we are able to pinpoint the pore and TRP helices as key regions undergoing stimulus-evoked conformational dynamics that drive channel gating. Structural mechanisms associated with activation are validated by comparison of human TRPM8 with the menthol-sensitive, but relatively cold-insensitive avian orthologue. We propose a free energy landscape to explain channel gating by cold or cooling agents.

biophysics↗

bioRxiv2025

A Cellular Basis for Heightened Gut Sensitivity in Females

Visceral pain disorders, such as irritable bowel syndrome, exhibit a marked female prevalence. Enhanced signaling between enterochromaffin (EC) cells in the gut epithelium and mucosal sensory nerve fibers likely contributes to this sex bias. Here, we identify a novel estrogen-responsive paracrine pathway in which two enteroendocrine cell types, PYY-expressing L-cells and serotonergic EC cells, communicate to increase gut sensitivity in females. We demonstrate that ER estrogen signaling upregulates the bacterial metabolite SCFA receptor Olfr78 on colonic L-cells, increasing PYY release and their sensitivity to acetate. Elevated PYY acts on neighboring EC cells via NPY1R, thereby enhancing serotonin release and gut pain. We propose that hormonal fluctuations, in conjunction with internal (stress) or environmental (diet) factors, amplify this local estrogen-responsive colonic circuit, resulting in maladaptive gut sensitivity.

physiology↗

bioRxiv2024

Metabolic tuning facilitates nociceptor resilience to excitotoxicity

The capsaicin receptor, TRPV1, mediates the detection of harmful chemical and thermal stimuli. Overactivation of TRPV1 can lead to cellular damage or death through excitotoxicity, a phenomenon associated with painful neuropathy and the paradoxical use of capsaicin as an analgesic. We exploited capsaicin-evoked death to conduct a systematic analysis of excitotoxicity through a genome-wide CRISPRi screen, thereby revealing a comprehensive network of regulatory pathways. We show that decreased expression of mitochondrial electron transport chain (ETC) components protects against capsaicin-induced toxicity by mitigating calcium imbalance and mitochondrial reactive oxygen species production via distinct pathways. Interestingly, TRPV1+ sensory neurons in adult mice maintain lower expression of ETC components and can better tolerate excitotoxicity and oxidative stress compared to other sensory neuron subtypes. We further confirm the regulatory roles of the ETC in sensory neurons through gain-of-function and loss-of-function experiments. These findings implicate ETC tuning as a cellular protective strategy against sensory excitotoxicity.

cell biology↗

bioRxiv2024

Crypt and Villus Enterochromaffin Cells are Distinct Stress Sensors in the Gut

The crypt-villus structure of the small intestine serves as an essential protective barrier, with its integrity monitored by the guts sensory system. Enterochromaffin (EC) cells, which are rare sensory epithelial cells that release serotonin (5-HT), surveil the mucosal environment and signal both within and outside the gut. However, it remains unclear whether EC cells in intestinal crypts and villi respond to different stimuli and elicit distinct responses. In this study, we introduce a new reporter mouse model to observe the release and propagation of serotonin in live intestines. Using this system, we show that crypt EC cells exhibit two modes of serotonin release: transient receptor potential A1 (TRPA1)-dependent tonic serotonin release that controls basal ionic secretion, and irritant-evoked serotonin release that activates gut sensory neurons. Furthermore, we find that a thick protective mucus layer prevents TRPA1 receptors on crypt EC cells from responding to luminal irritants such as reactive electrophiles; if this mucus layer is compromised, then crypt EC cells become susceptible to activation by luminal irritants. On the other hand, villus EC cells detect oxidative stress through TRPM2 channels and co-release serotonin and ATP to activate nearby gut sensory fibers. Our work highlights the physiological importance of intestinal architecture and differential TRP channel expression in sensing noxious stimuli that elicit nausea and/or pain sensations in the gut.

physiology↗

bioRxiv2023

Endogenous Opioid Signaling Regulates Proliferation of Spinal Cord Ependymal Cells

After injury, mammalian spinal cords develop scars to seal off the damaged area and prevent further injury. However, excessive scarring can hinder neural regeneration and functional recovery (1, 2). These competing actions underscore the importance of developing therapeutic strategies to dynamically modulate the extent of scar formation. Previous research on scar formation has primarily focused on the role of astrocytes, but recent evidence suggests that ependymal cells also participate. Ependymal cells normally form the epithelial layer encasing the central canal, but they undergo massive proliferation and differentiation into astroglia following certain types of injury, becoming a core component of scars (3-7). However, the mechanisms regulating ependymal proliferation in vivo in both healthy and injured conditions remain unclear. Here, we uncover an intercellular kappa ({kappa}) opioid signaling pathway that controls endogenous ependymal proliferation. Specifically, we detect expression of the {kappa} opioid receptor, OPRK1, in a functionally under-characterized cell type called cerebrospinal fluid-contacting neurons (CSF-cNs). We also discover a neighboring cell population that express the cognate ligand, prodynorphin (PDYN). Importantly, OPRK1 activation excites CSF-cNs, and systemic administration of a {kappa} antagonist enhances ependymal proliferation in uninjured spinal cords in a CSF-cN-dependent manner. Moreover, injecting a {kappa} agonist reduces the proliferation induced by dorsal hemisection. Altogether, our data suggest a regulatory mechanism whereby PDYN+ cells tonically release {kappa} opioids to stimulate CSF-cNs, which in turn suppress ependymal proliferation. This endogenous pathway provides a mechanistic basis for the potential use of {kappa} opiates in modulating scar formation and treating spinal cord injuries.

neuroscience↗

bioRxiv2023

Allosteric regulation of TRPV1 by the inflammatory lipid, LPA

TRP ion channels are modulated by phosphoinositide lipids, but the underlying structural mechanisms remain unclear. The capsaicin- and heat-activated receptor, TRPV1, has served as a model for deciphering lipid modulation, which is relevant to understanding how pro-algesic agents enhance channel activity in the setting of inflammatory pain. Identification of a pocket within the TRPV1 transmembrane core has provided initial clues as to how phosphoinositide lipids bind to and regulate the channel. Here we show that this regulatory pocket can accommodate diverse lipid species, including the inflammatory lipid lysophosphatidic acid (LPA), whose actions are determined by their specific modes of binding. Furthermore, we show that an empty pocket channel lacking an endogenous phosphoinositide lipid assumes an agonist-like state, even at low temperature, substantiating the concept that phosphoinositide lipids serve as negative TRPV1 modulators whose ejection from the binding pocket is a critical step towards activation by thermal or chemical stimuli.

biochemistry↗

bioRxiv2022

TRPV1 drugs alter core body temperature via central projections of primary afferent sensory neurons

TRPV1, a capsaicin- and heat-sensitive ion channel, is expressed by peripheral nociceptors and has been implicated in various inflammatory and neuropathic pain conditions. Although pharmacological modulation of TRPV1 has attracted therapeutic interest, their utility is limited because TRPV1 agonists and antagonists thus far examined show thermo-modulatory side effects in animal models and human clinical trials. These on-target effects may result from the perturbation of TRPV1 receptors on nociceptors, which transduce signals to central thermoregulatory circuits and also release pro-inflammatory factors from their peripheral terminals, such as the vasodilative neuropeptide calcitonin gene-related peptide (CGRP). Alternatively, they may originate from the modulation of TRPV1 on vascular smooth muscle cells (vSMCs), where channel activation promotes arteriole constriction. Here, we ask which of these pathways is most responsible for the body temperature perturbations elicited by TRPV1 drugs in vivo. We address this question by selectively eliminating TRPV1 expression in sensory neurons or vSMCs and show that only the former abrogates agonist-induced hypothermia and antagonist-induced hyperthermia. Furthermore, lesioning the central projections of TRPV1-positive sensory nerve fibers also abrogates drug-mediated thermo-modulation, whereas eliminating CGRP has no effect. Thus, TRPV1 drugs alter core body temperature by modulating sensory input to the central nervous system, rather than through peripheral actions on the vasculature. These findings suggest how mechanically distinct TRPV1 antagonists may diminish inflammatory pain without affecting core body temperature.

physiology↗

bioRxiv2022

Gut Enterochromaffin Cells are Critical Drivers of Visceral Pain and Anxiety

Gastrointestinal (GI) discomfort is a hallmark of most gut disorders and represents a significant component of chronic visceral pain 1. For the growing population afflicted by irritable bowel syndrome (IBS), GI hypersensitivity and pain persist long after signs of tissue injury have resolved 2. IBS also exhibits a strong sex bias afflicting women three-fold more than men 1. Identifying the molecules, cells, and circuits that mediate both the acute and persistent phases of visceral pain is a critical first step in understanding how environmental and endogenous factors produce long-term changes in the nervous system or associated tissues to engender chronic pain syndromes 3,4. Enterochromaffin (EC) cells within the gut epithelium are exceedingly rare sensory neuroendocrine cells that detect and transduce noxious stimuli to nearby nerve endings via serotonin. Here, we manipulate murine EC cell activity using genetic strategies to ascertain their contributions to visceral pain. We show that acute EC cell activation is sufficient to elicit hypersensitivity to gut distension and necessary for the sensitizing actions of isovalerate, a bacterially derived short-chain fatty acid irritant associated with inflammatory GI disorders. Remarkably, prolonged EC cell activation by itself is sufficient to produce persistent visceral hypersensitivity, even in the absence of an instigating inflammatory episode. Perturbing the activity of these rare EC cells led to a marked increase in anxiety-like behaviors that normalized after blocking serotonergic signaling. Sex differences were also observed accross a range of assays indicating that females have a higher baseline visceral sensitivity. Our findings validate a critical role for EC cell-mucosal afferent signaling in acute and persistent GI pain while highlighting mechanistically defined genetic models for studying visceral hypersensitivity, sex differences, and associated behaviors.

physiology↗

bioRxiv2019

Mechanisms governing irritant-evoked activation and calcium modulation of TRPA1

The TRPA1 ion channel is a chemosensory receptor that is critical for detecting noxious chemical agents that elicit or exacerbate pain or itch. Here we use structural and electrophysiological methods to elucidate how a broad class of reactive electrophilic irritants activate TRPA1 through a two-step cysteine modification mechanism that promotes local conformational changes leading to widening of the selectivity filter to enhance calcium permeability and opening of a cytoplasmic gate. We also identify a calcium binding pocket that is remarkably conserved across TRP channel subtypes and accounts for all aspects of calcium-dependent TRPA1 regulation, including potentiation, desensitization, and activation by metabotropic receptors. These findings provide a structural basis for understanding how endogenous or exogenous chemical agents activate a broad-spectrum irritant receptor directly or indirectly through a cytoplasmic second messenger.

biophysics↗

bioRxiv2018

Structural insight into TRPV5 channel function and modulation

TRPV5 (transient receptor potential vanilloid) is a unique calcium-selective TRP channel that is essential for calcium homeostasis. TRPV5 and its close homologue TRPV6 do not exhibit thermosensitivity or ligand-dependent activation, unlike other TRPV channels, but are constitutively opened at physiological membrane potentials. Here, we report high resolution electron cryo-microscopy (cryo-EM) structures of truncated and full length TRPV5 in lipid nanodisc, as well as a TRPV5 W583A mutant structure and a complex structure of TRPV5 with calmodulin (CaM). These structures highlight and explain functional differences between the thermosensitive and calcium-selective TRPV channels. An extended S1-S2 linker folds on top of the channel that might shield it from modulation by extracellular factors. Resident lipid densities in the homologous vanilloid pocket are different from those previously found in TRPV1, supporting a comparatively more rigid architecture of TRPV5. A ring of tryptophan residues (W583) at the bottom of the pore coordinates a density and mutation of W583 resultes in opening of the lower gate. Moreover, we provide structural insight into the calcium-dependent channel inactivation and propose a flexible stoichiometry for TRPV5 and CaM binding.

biophysics↗