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David Julius

Publications and source records attributed to David Julius.

At least 19 recordsLinked to original sources
PubMed2025

Mitochondrial activity tunes nociceptor resilience to excitotoxicity.

The capsaicin receptor, TRPV1, mediates the detection of noxious chemical and thermal stimuli by nociceptors, primary sensory neurons of the pain pathway. Overactivation of TRPV1 leads to cellular damage or death through calcium entry and excitotoxicity. We have exploited this phenomenon 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 and other challenges by mitigating both calcium imbalance and the generation of mitochondrial reactive oxygen species via distinct pathways. Moreover, we confirm the regulatory roles of the ETC in sensory neurons through gain-of-function and loss-of-function experiments. Interestingly, TRPV1+ sensory neurons maintain lower expression of ETC components and can better tolerate excitotoxicity and oxidative stress compared with other sensory neuron subtypes, implicating ETC tuning as an intrinsic cellular strategy that protects nociceptors against excitotoxicity.

Mitochondria↗
PubMed2006

TRP channel activation by reversible covalent modification.

Allyl isothiocyanate, the pungent principle of wasabi and other mustard oils, produces pain by activating TRPA1, an excitatory ion channel on sensory nerve endings. Isothiocyanates are membrane-permeable electrophiles that form adducts with thiols and primary amines, suggesting that covalent modification, rather than classical lock-and-key binding, accounts for their agonist properties. Indeed, we show that thiol reactive compounds of diverse structure activate TRPA1 in a manner that relies on covalent modification of cysteine residues within the cytoplasmic N terminus of the channel. These findings suggest an unusual paradigm whereby natural products activate a receptor through direct, reversible, and covalent protein modification.

Calcium Channels↗
PubMed2006

The P2Y12 receptor regulates microglial activation by extracellular nucleotides.

Microglia are primary immune sentinels of the CNS. Following injury, these cells migrate or extend processes toward sites of tissue damage. CNS injury is accompanied by release of nucleotides, serving as signals for microglial activation or chemotaxis. Microglia express several purinoceptors, including a G(i)-coupled subtype that has been implicated in ATP- and ADP-mediated migration in vitro. Here we show that microglia from mice lacking G(i)-coupled P2Y(12) receptors exhibit normal baseline motility but are unable to polarize, migrate or extend processes toward nucleotides in vitro or in vivo. Microglia in P2ry(12)(-/-) mice show significantly diminished directional branch extension toward sites of cortical damage in the living mouse. Moreover, P2Y(12) expression is robust in the 'resting' state, but dramatically reduced after microglial activation. These results imply that P2Y(12) is a primary site at which nucleotides act to induce microglial chemotaxis at early stages of the response to local CNS injury.

Adenosine Diphosphate↗
PubMed2006

Spider toxins activate the capsaicin receptor to produce inflammatory pain.

Bites and stings from venomous creatures can produce pain and inflammation as part of their defensive strategy to ward off predators or competitors. Molecules accounting for lethal effects of venoms have been extensively characterized, but less is known about the mechanisms by which they produce pain. Venoms from spiders, snakes, cone snails or scorpions contain a pharmacopoeia of peptide toxins that block receptor or channel activation as a means of producing shock, paralysis or death. We examined whether these venoms also contain toxins that activate (rather than inhibit) excitatory channels on somatosensory neurons to produce a noxious sensation in mammals. Here we show that venom from a tarantula that is native to the West Indies contains three inhibitor cysteine knot (ICK) peptides that target the capsaicin receptor (TRPV1), an excitatory channel expressed by sensory neurons of the pain pathway. In contrast with the predominant role of ICK toxins as channel inhibitors, these previously unknown 'vanillotoxins' function as TRPV1 agonists, providing new tools for understanding mechanisms of TRP channel gating. Some vanillotoxins also inhibit voltage-gated potassium channels, supporting potential similarities between TRP and voltage-gated channel structures. TRP channels can now be included among the targets of peptide toxins, showing that animals, like plants (for example, chilli peppers), avert predators by activating TRP channels on sensory nerve fibres to elicit pain and inflammation.

Animals↗
PubMed2006

Coiled coils direct assembly of a cold-activated TRP channel.

Transient receptor potential (TRP) channels mediate numerous sensory transduction processes and are thought to function as tetramers. TRP channel physiology is well studied; however, comparatively little is understood regarding TRP channel assembly. Here, we identify an autonomously folded assembly domain from the cold- and menthol-gated channel TRPM8. We show that the TRPM8 cytoplasmic C-terminal domain contains a coiled coil that is necessary for channel assembly and sufficient for tetramer formation. Cell biological experiments indicate that coiled-coil formation is required for proper channel maturation and trafficking and that the coiled-coil domain alone can act as a dominant-negative inhibitor of functional channel expression. Our data define an authentic TRP modular assembly domain, establish a clear role for coiled coils in ion channel assembly, demonstrate that coiled-coil assembly domains are a general feature of TRPM channels, and delineate a new tool that should be of general use in dissecting TRPM channel function.

Amino Acid Sequence↗
PubMed2006

Neuroanatomical evidence for segregation of nerve fibers conveying light touch and pain sensation in Eimer's organ of the mole.

Talpid moles are small insectivores that live in dark underground tunnels. They depend heavily on touch to navigate and find food. Most species have an array of complex epidermal sensory structures called Eimer's organs that cover the tip of the nose. In this study, the anatomy of Eimer's organ was examined in the coast mole and star-nosed mole by using the fluorescent styryl pyridinium dye AM1-43 and immunocytochemical staining for neurofilament 200 and substance P. In addition, DiI was used to label neural components of Eimer's organ. AM1-43 labeled all of the Eimer's organ receptors after systemic injection, suggesting a role in mechanotransduction. Immunostaining with neurofilament 200 and substance P labeled distinct subtypes of sensory fibers. Substance P labeled a group of free nerve endings along the outer edge of Eimer's organ, indicating a nociceptive role for these fibers. In contrast, neurofilament 200 labeled a more central set of nerve endings, suggesting that these fibers function as low-threshold mechanoreceptors. By labeling subsets of trigeminal afferents distant from the receptor array with DiI, we revealed innervation patterns indicating that one afferent supplies the outer, substance P-positive set of free nerve endings, whereas several afferents differentially innervate the central free nerve endings. Our results suggest that the free nerve endings innervating Eimer's organ are largely mechanosensitive and may play an important role in the rapid sensory discrimination observed in these species.

Afferent Pathways↗
PubMed2006

TRPA1 mediates the inflammatory actions of environmental irritants and proalgesic agents.

TRPA1 is an excitatory ion channel targeted by pungent irritants from mustard and garlic. TRPA1 has been proposed to function in diverse sensory processes, including thermal (cold) nociception, hearing, and inflammatory pain. Using TRPA1-deficient mice, we now show that this channel is the sole target through which mustard oil and garlic activate primary afferent nociceptors to produce inflammatory pain. TRPA1 is also targeted by environmental irritants, such as acrolein, that account for toxic and inflammatory actions of tear gas, vehicle exhaust, and metabolic byproducts of chemotherapeutic agents. TRPA1-deficient mice display normal cold sensitivity and unimpaired auditory function, suggesting that this channel is not required for the initial detection of noxious cold or sound. However, TRPA1-deficient mice exhibit pronounced deficits in bradykinin-evoked nociceptor excitation and pain hypersensitivity. Thus, TRPA1 is an important component of the transduction machinery through which environmental irritants and endogenous proalgesic agents depolarize nociceptors to elicit inflammatory pain.

Acrolein↗
PubMed2005

A neuropeptide courier for delta-opioid receptors?

The delta-opioid receptor and the precursor protein of a neuropeptide, substance P, are colocalized in the large dense-core vesicles of pain-sensing neurons. In this issue of Cell, report that trafficking of the delta-opioid receptor to these vesicles depends on its physical interaction with the substance P domain of its precursor polyprotein (protachykinin). Moreover, in mice lacking this precursor, the contribution of the delta-opioid receptor to pain processing is dramatically altered. These observations suggest a new role for peptide precursors as sorting signals in vesicular transport.

Animals↗
PubMed2005

Pungent products from garlic activate the sensory ion channel TRPA1.

Garlic belongs to the Allium family of plants that produce organosulfur compounds, such as allicin and diallyl disulfide (DADS), which account for their pungency and spicy aroma. Many health benefits have been ascribed to Allium extracts, including hypotensive and vasorelaxant activities. However, the molecular mechanisms underlying these effects remain unknown. Intriguingly, allicin and DADS share structural similarities with allyl isothiocyanate, the pungent ingredient in wasabi and other mustard plants that induces pain and inflammation by activating TRPA1, an excitatory ion channel on primary sensory neurons of the pain pathway. Here we show that allicin and DADS excite an allyl isothiocyanate-sensitive subpopulation of sensory neurons and induce vasodilation by activating capsaicin-sensitive perivascular sensory nerve endings. Moreover, allicin and DADS activate the cloned TRPA1 channel when expressed in heterologous systems. These and other results suggest that garlic excites sensory neurons primarily through activation of TRPA1. Thus different plant genera, including Allium and Brassica, have developed evolutionary convergent strategies that target TRPA1 channels on sensory nerve endings to achieve chemical deterrence.

Allyl Compounds↗
PubMed2005

Selective blockade of the capsaicin receptor TRPV1 attenuates bone cancer pain.

Cancer colonization of bone leads to the activation of osteoclasts, thereby producing local tissue acidosis and bone resorption. This process may contribute to the generation of both ongoing and movement-evoked pain, resulting from the activation of sensory neurons that detect noxious stimuli (nociceptors). The capsaicin receptor TRPV1 (transient receptor potential vanilloid subtype 1) is a cation channel expressed by nociceptors that detects multiple pain-producing stimuli, including noxious heat and extracellular protons, raising the possibility that it is an important mediator of bone cancer pain via its capacity to detect osteoclast- and tumor-mediated tissue acidosis. Here, we show that TRPV1 is present on sensory neuron fibers that innervate the mouse femur and that, in an in vivo model of bone cancer pain, acute or chronic administration of a TRPV1 antagonist or disruption of the TRPV1 gene results in a significant attenuation of both ongoing and movement-evoked nocifensive behaviors. Administration of the antagonist had similar efficacy in reducing early, moderate, and severe pain-related responses, suggesting that TRPV1 may be a novel target for pharmacological treatment of chronic pain states associated with bone cancer metastasis.

Activating Transcription Factor 3↗
PubMed2004

A Nobel for smell.

Explore the source record for details and available documents.

History, 20th Century↗
PubMed2004

The super-cooling agent icilin reveals a mechanism of coincidence detection by a temperature-sensitive TRP channel.

TRPM8, a member of the transient receptor potential family of ion channels, depolarizes somatosensory neurons in response to cold. TRPM8 is also activated by the cooling agents menthol and icilin. When exposed to menthol or cold, TRPM8 behaves like many ligand-gated channels, exhibiting rapid activation followed by moderate Ca(2+)-dependent adaptation. In contrast, icilin activates TRPM8 with extremely variable latency followed by extensive desensitization, provided that calcium is present. Here, we show that, to achieve full efficacy, icilin requires simultaneous elevation of cytosolic Ca2+, either via permeation through TRPM8 channels or by release from intracellular stores. Thus, two stimuli must be paired to elicit full channel activation, illustrating the potential for coincidence detection by TRP channels. Determinants of icilin sensitivity map to a region of TRPM8 that corresponds to the capsaicin binding site on the noxious heat receptor TRPV1, suggesting a conserved molecular logic for gating of these thermosensitive channels by chemical agonists.

Acetylcholine↗
PubMed2004

Uropathic observations in mice expressing a constitutively active point mutation in the 5-HT3A receptor subunit.

Mutant mice with a hypersensitive serotonin (5-HT)3A receptor were generated through targeted exon replacement. A valine to serine mutation (V13'S) in the channel-lining M2 domain of the 5-HT3A receptor subunit rendered the 5-HT3 receptor 70-fold more sensitive to serotonin and produced constitutive activity when combined with the 5-HT3B subunit. Mice homozygous for the mutant allele (5-HT3Avs/vs) had decreased levels of 5-HT3A mRNA. Measurements on sympathetic ganglion cells in these mice showed that whole-cell serotonin responses were reduced, and that the remaining 5-HT3 receptors were hypersensitive. Male 5-HT3Avs/vs mice died at 2-3 months of age, and heterozygous (5-HT3Avs/+) males and homozygous mutant females died at 4-6 months of age from an obstructive uropathy. Both male and female 5-HT3A mutant mice had urinary bladder mucosal and smooth muscle hyperplasia and hypertrophy, whereas male mutant mice had additional prostatic smooth muscle and urethral hyperplasia. 5-HT3A mutant mice had marked voiding dysfunction characterized by a loss of micturition contractions with overflow incontinence. Detrusor strips from 5-HT3Avs/vs mice failed to contract to neurogenic stimulation, despite overall normal responses to a cholinergic agonist, suggestive of altered neuronal signaling in mutant mouse bladders. Consistent with this hypothesis, decreased nerve fiber immunoreactivity was observed in the urinary bladders of 5-HT3Avs/vs compared with 5-HT3A wild-type (5-HT3A+/+) mice. These data suggest that persistent activation of the hypersensitive and constitutively active 5-HT3A receptor in vivo may lead to excitotoxic neuronal cell death and functional changes in the urinary bladder, resulting in bladder hyperdistension, urinary retention, and overflow incontinence.

Animals↗
PubMed2004

Immunoreactive TRPV-2 (VRL-1), a capsaicin receptor homolog, in the spinal cord of the rat.

The vanilloid receptor-like 1 protein (VRL-1, also called TRPV2) is a member of the TRPV family of proteins and is a homolog of the capsaicin/vanilloid receptor (VR1, or TRPV1). Although VRL-1 does not bind capsaicin, like VR1 it is activated by noxious heat (>52 degrees C). Unlike VR1, however, VRL-1 is primarily expressed by medium- and large-diameter primary afferents, which suggests that nociceptive processing is but one of the functions to which VRL-1 contributes. To provide information on the diverse spinal circuits that are engaged by these VRL-1-expressing primary afferents, we completed a detailed immunocytochemical map of VRL-1 in rat spinal cord, including light and electron microscopic analysis, and generated a more comprehensive neurochemical characterization of VRL-1-expressing primary afferents. Consistent with previous reports, we found that VRL-1 and VR1 are expressed in different dorsal root ganglion (DRG) cell bodies. Almost all VRL-1-expressing cells labeled for N52 (a marker of myelinated afferents), consistent with VRL-1 expression in Adelta and Abeta fibers. EM analysis of the DRG and dorsal roots confirmed this and revealed two categories of neurons based on the intensity of immunolabeling. The densest VRL-1 immunoreactivity in the spinal cord was found in lamina I, inner lamina II, and laminae III/IV. This is consistent with the expression of VRL-1 by myelinated nociceptors that target laminae I and IIi and in nonnociceptive Abeta fibers that target laminae III/IV. Dorsal rhizotomy reduced, but did not eliminate, the immunostaining in all dorsal horn laminae, which indicates that VRL-1 expression derives from both DRG cells and from neurons intrinsic to the brain or spinal cord. Spinal hemisection reduced immunostaining of the ipsilateral dorsal columns in segments rostral to the lesion and in the dorsal column nuclei, presumably from the loss of ascending Abeta afferents, but there was no change caudal to the lesion. Thus, supraspinal sources of dorsal horn VRL-1 immunoreactivity are likely not significant. Although we never observed VRL-1 immunostaining in cell bodies in the superficial dorsal horn, there was extensive labeling of motoneurons and ventral root efferents-in particular, in an extremely densely labeled population at the lumbosacral junction. Finally, many ependymal cells surrounding the central canal were intensely labeled. These results emphasize that VRL-1, in contrast to VR1, is present in a diverse population of neurons and undoubtedly contributes to numerous functions in addition to nociceptive processing.

Animals↗
PubMed2004

Mustard oils and cannabinoids excite sensory nerve fibres through the TRP channel ANKTM1.

Wasabi, horseradish and mustard owe their pungency to isothiocyanate compounds. Topical application of mustard oil (allyl isothiocyanate) to the skin activates underlying sensory nerve endings, thereby producing pain, inflammation and robust hypersensitivity to thermal and mechanical stimuli. Despite their widespread use in both the kitchen and the laboratory, the molecular mechanism through which isothiocyanates mediate their effects remains unknown. Here we show that mustard oil depolarizes a subpopulation of primary sensory neurons that are also activated by capsaicin, the pungent ingredient in chilli peppers, and by Delta(9)-tetrahydrocannabinol (THC), the psychoactive component of marijuana. Both allyl isothiocyanate and THC mediate their excitatory effects by activating ANKTM1, a member of the TRP ion channel family recently implicated in the detection of noxious cold. These findings identify a cellular and molecular target for the pungent action of mustard oils and support an emerging role for TRP channels as ionotropic cannabinoid receptors.

Animals↗
PubMed2004

Changes in anxiety-related behaviors and hypothalamic-pituitary-adrenal activity in mice lacking the 5-HT-3A receptor.

The serotonin-3 (5-HT-3A) receptor has been localized in limbic and brainstem structures that regulate anxiety-related behavior and hypothalamic-pituitary-adrenal (HPA) activity, but its role in regulating anxiety-related behaviors is equivocal, and evidence for its role in regulating HPA activity is limited. Therefore, we used 5-HT-3A receptor knockout (KO) mice to further study these issues. Behavior in the elevated plus maze, open field, light-dark box and after Pavlovian fear conditioning was examined in addition to HPA activity under basal and acute stress conditions. Compared to age-matched adult male wild-type (WT) controls, adult male KO mice exhibited increased distance traveled in the open arms of the elevated plus maze, consistent with decreased measures of anxiety. There were no differences between the two genotypes in exploratory behavior in the open field or light-dark test. KO mice displayed enhanced fear conditioning indexed by fear-induced freezing behavior. KO mice displayed lower adrenocorticotropin (ACTH) responses to restraint or lipopolysaccharide (LPS). In addition, lower vasopressin mRNA in the paraventricular nucleus of the hypothalamus (PVN) and higher corticotropin-releasing hormone (CRH) mRNA in the central amygdala were observed in KO compared to WT mice. Therefore, deletion of the 5-HT-3A receptor revealed an important role for this receptor in regulating HPA responses to acute stress and a potential interaction between the 5-HT-3A receptor and CRH in the amygdala. Together, these data suggest that the 5-HT-3A receptor does not have a unitary role in the regulation of anxiety- and fear-related behaviors but has a potentially substantial role in the regulation of HPA activity.

Amygdala↗