42 research outputs found
A molecular signature of myalgia in myotonic dystrophy 2
Background: Chronic muscle pain affects close to 20% of the population and is a major health burden. The underlying mechanisms of muscle pain are difficult to investigate as pain presents in patients with very diverse histories. Treatment options are therefore limited and not tailored to underlying mechanisms. To gain insight into the pathophysiology of myalgia we investigated a homogeneous group of patients suffering from myotonic dystrophy type 2 (DM2), a monogenic disorder presenting with myalgia in at least 50% of affected patients. Methods: After IRB approval we performed an observational cross-sectional cohort study and recruited 42 patients with genetically confirmed DM2 plus 20 healthy age and gender matched control subjects. All participants were subjected to an extensive sensory-testing protocol. In addition, RNA sequencing was performed from 12 muscle biopsy specimens obtained from DM2 patients.
Findings: Clinical sensory testing as well as RNA sequencing clearly separated DM2 myalgic from non-myalgia patients and also from healthy controls. In particular pressure pain thresholds were significantly lowered for all muscles tested in myalgic DM2 patients but were not significantly different between non-myalgic patients and healthy controls. The expression of fourteen muscle expressed genes in myalgic patients was significantly up or down-regulated in myalgic compared to non-myalgic DM2 patients. Interpretation: Our data support the idea that molecular changes in the muscles of DM2 patients are associated with muscle pain. Further studies should address whether muscle-specific molecular pathways play a significant role in myalgia in order to facilitate the development of mechanism-based therapeutic strategies to treat musculoskeletal pain
A Probabilistic Model for Estimating the Depth and Threshold Temperature of C-fiber Nociceptors
The subjective experience of thermal pain follows the detection and encoding
of noxious stimuli by primary afferent neurons called nociceptors. However,
nociceptor morphology has been hard to access and the mechanisms of signal
transduction remain unresolved. In order to understand how heat transducers in
nociceptors are activated in vivo, it is important to estimate the
temperatures that directly activate the skin-embedded nociceptor membrane.
Hence, the nociceptor’s temperature threshold must be estimated, which in turn
will depend on the depth at which transduction happens in the skin. Since the
temperature at the receptor cannot be accessed experimentally, such an
estimation can currently only be achieved through modeling. However, the
current state-of-the-art model to estimate temperature at the receptor suffers
from the fact that it cannot account for the natural stochastic variability of
neuronal responses. We improve this model using a probabilistic approach which
accounts for uncertainties and potential noise in system. Using a data set of
24 C-fibers recorded in vitro, we show that, even without detailed knowledge
of the bio-thermal properties of the system, the probabilistic model that we
propose here is capable of providing estimates of threshold and depth in cases
where the classical method fails
Photoswitchable fatty acids enable optical control of TRPV1
Fatty acids (FAs) are not only essential components of cellular energy storage and structure, but play crucial roles in signalling. Here we present a toolkit of photoswitchable FA analogues (FAAzos) that incorporate an azobenzene photoswitch along the FA chain. By modifying the FAAzos to resemble capsaicin, we prepare a series of photolipids targeting the Vanilloid Receptor 1 (TRPV1),a non-selective cation channel known for its role in nociception. Several azo-capsaicin derivatives (AzCAs) emerge as photoswitchable agonists of TRPV1 that are relatively inactive in the dark and become active on irradiation with ultraviolet-A light. This effect can be rapidly reversed by irradiation with blue light and permits the robust optical control of dorsal root ganglion neurons and C-fibre nociceptors with precision timing and kinetics not available with any other technique. More generally, we expect that photolipids will find many applications in controlling biological pathways that rely on protein-lipid interactions
Congenital deafness is associated with specific somatosensory deficits in adolescents
Hearing and touch represent two distinct sensory systems that both rely on the transformation of mechanical force into electrical signals. Here we used a battery of quantitative sensory tests to probe touch, thermal and pain sensitivity in a young control population (14-20 years old) compared to age-matched individuals with congenital hearing loss. Sensory testing was performed on the dominant hand of 111 individuals with normal hearing and 36 with congenital hearing loss. Subjects with congenital deafness were characterized by significantly higher vibration detection thresholds at 10 Hz (2-fold increase, P < 0.001) and 125 Hz (P < 0.05) compared to controls. These sensory changes were not accompanied by any major change in measures of pain perception. We also observed a highly significant reduction (30% compared to controls p < 0.001) in the ability of hearing impaired individual's ability to detect cooling which was not accompanied by changes in warm detection. At least 60% of children with non-syndromic hearing loss showed very significant loss of vibration detection ability (at 10 Hz) compared to age-matched controls. We thus propose that many pathogenic mutations that cause childhood onset deafness may also play a role in the development or functional maintenance of somatic mechanoreceptors
Role of T-type calcium current in identified D-hair mechanoreceptor neurons studied in vitro
Different subsets of dorsal root ganglion (DRG) mechanoreceptors transduce low- and high-intensity mechanical stimuli. It was shown recently that, in vivo, neurotrophin-4 (NT-4)-dependent D-hair mechanoreceptors specifically express a voltage-activated T-type calcium channel (Ca(v)3.2) that may be required for their mechanoreceptive function. Here we show that D-hair mechanoreceptors can be identified in vitro by a rosette-like morphology in the presence of NT-4 and that these rosette neurons are almost all absent in DRG cultures taken from NT-4 knock-out mice. In vitro identification of the D-hair mechanoreceptor allowed us to explore the electrophysiological properties of these cells. We demonstrate that the T-type Ca(v)3.2 channel induced slow membrane depolarization that contributes to lower the voltage threshold for action potential generation and controls spike latency after stimulation of D-hair mechanoreceptors. Indeed, the properties of the T-type amplifier are particularly well suited to explain the high sensitivity of D-hair mechanoreceptors to slowly moving stimuli
USH2A is a Meissner’s corpuscle protein necessary for normal vibration sensing in mice and humans
Fingertip mechanoreceptors comprise sensory neuron endings together with specialized skin cells that form the end-organ. Exquisitely sensitive, vibration-sensing neurons are associated with Meissner’s corpuscles in the skin. In the present study, we found that USH2A, a transmembrane protein with a very large extracellular domain, was found in terminal Schwann cells within Meissner’s corpuscles. Pathogenic USH2A mutations cause Usher’s syndrome, associated with hearing loss and visual impairment. We show that patients with biallelic pathogenic USH2A mutations also have clear and specific impairments in vibrotactile touch perception, as do mutant mice lacking USH2A. Forepaw rapidly adapting mechanoreceptors innervating Meissner’s corpuscles, recorded from Ush2a−/− mice, showed large reductions in vibration sensitivity. However, the USH2A protein was not found in sensory neurons. Thus, loss of USH2A in corpuscular end-organs reduced mechanoreceptor sensitivity as well as vibration perception. Thus, a tether-like protein is required to facilitate detection of small-amplitude vibrations essential for the perception of fine-grained tactile surfaces.The present study was funded by grants from the Deutsche Forschungsgemeinshaft (grant nos. SFB665-B6 to G.R.L., SFB1315 to J.F.A.P. and SFB1158-A01 to S.G.L.) and grants from the European Research Council (grant nos. 789128 to G.R.L. and ERC-2015-CoG-682422 to J.F.A.P.). Additional funding was from the Institute of Health Carlos III (Spanish Ministry of Science and Innovation, grant no. FIS PI16/00539 to J.M.).Peer reviewe
Mother root of Aconitum carmichaelii Debeaux exerts antinociceptive effect in Complete Freund’s Adjuvant-induced mice: roles of dynorphin/kappa-opioid system and transient receptor potential vanilloid type-1 ion channel
Die Effekte von Acid-Sensing Ionkanaele ASIC3 und Stomatin-like Proteinen an Mechanosensation und Noziception
Titelblatt und Inhaltsverzeichnis
Introduction
Materials and Methods
Results
Discussion
Zusammenfassung
ReferencesTransformation of mechanical energy into electrical signals in mechanosensory
neurons is essential for mechanosensation and nociception. This transformation
occurs via sensory transduction channels that are activated by external force.
Recent genetic and electrophysiological studies in Caenorhabditis elegans have
directly shown that the degenerin/epithelial sodium channel (DEG/ENaC) ion
channel subunits, MEC-4 and MEC-10, and the accessory ion channel subunits
MEC-2 and MEC-6 form a sensory transduction ion channel within a
mechanotransduction complex that also includes intra- and extracellular
proteins. In mammals DEG/ENaC ion channel subunits are also proposed to
function as mechanotransducers. Consistent with a function in
mechanosensation, the mammalian acid-sensing ion channel subunit ASIC3 belongs
to the DEG/ENaC family of ion channels; it is highly expressed in
mechanosensory neurons including their peripheral structures; and it has been
shown to be required for normal mechanosensation in mice. MEC-2 protein, which
contains a stomatin-like domain in its central region, interacts and modulates
MEC-4 ion channel activity. Mammalian stomatin-like proteins, like stomatin
and stomatin-like protein (SLP3), might have similar roles. Here we show that
ASIC3 coimmunoprecipitates with stomatin and SLP3 in a heterologous system. We
asked whether the physical interaction between ASIC3 and stomatin proteins has
any effects on mechanotransduction in mechanosensory neurons innervating skin.
To look for a functional interaction between ASIC3 and stomatin in
mechanosensory neurons single fiber analysis of mechanosensitivity in
ASIC3/stomatin double mutant mice in the in vitro skin nerve preparation were
used. The loss of ASIC3 function specifically increases mechanosensitivity in
rapidly adapting mechanoreceptors (RAM) and reduces the sensitivity of
nociceptors, including A-mechanonociceptors (AM) and C-fibers. In comparison,
the additional loss of stomatin does not alter the increased
mechanosensitivity in RAM; however, it slightly decreases the speed of
response (mechanical latency). In addition, AM and C-fibers in ASIC3/stomatin
double mutants show reduced mechanosensitivity that is not significantly
different from the alterations due to loss of ASIC3 alone. However, polymodal
nociceptors (C-MH) in ASIC3/stomatin double mutants show significant decrease
in mechanosensitivity to suprathreshold stimuli compared to C-MH in ASIC3
single mutants. Therefore, the loss of stomatin produced additional alteration
in mechanoreceptor function already altered by loss of ASIC3. The data suggest
that ASIC3 is required for normal mechanoreceptor function and that a weak
functional interaction exists between ASIC3 and stomatin.Die Transformation eines mechanischen Stimulus in einen Nervenimpuls in
sensorischen Neuronen geschieht durch das Aktivieren von
Transduktionsionkanälen in der Zellmembran von Nervenendungen in der Haut.
Dieser Prozess wird Mechanotransduktion genannt. Er spielt eine wichtige Rolle
für den Tastsinn und bei der Entstehung von Schmerz. In den letzten Jahren
wurde durch genetische und electrophysiologische Untersuchungen am
Caenorhabditis elegans (C.elegans) Wurm festgestellt dass die
Ionenkanaluntereinheiten (MEC-4 und MEC-10) der Degenerinen/Epithelialen
Natriumkanäle (DEG/ENaC) und die akzessorischen Ionenkanaluntereinheiten
(MEC-2 und MEC-6) einen sensorischen Transduktionkanal bzw. einen
mechanosensitiven Ionenkanal formen. Dieser mechanosensitive Ionenkanal ist
mit Proteinen aus der extrazellularen Matrix und dem intrazellularen
Cytoskelett verbunden. In Säugetieren sind diese molekularem Grundlagen der
Mechanotransduktion bisher nicht bekannt. Diese Dissertation untersucht, ob
orthologe Moleküle in Säugetieren eine ähnliche Rolle bei der
Mechanotranduktion spielen, wie die Mechanotransduktionsproteine in C.
elegans. Ein orthologes Molekül ist die Ionenkanaluntereinheit acid-sensing
ion channel (ASIC3) der DEG/ENaC Ionenkanäle in Säugern, denn sie ist mit den
Ionenkanal MEC-4 der C. elegans verwandt. Deshalb ist anzunehmen, dass ASIC3
eine ähnliche Funktion bei der Mechanotransduktion hat, wie MEC-4. Hinzu
kommt, dass ähnlich MEC-4 auch ASIC3 in Nervenzellen sowie deren peripheren
Nervenendungen hochexpremiert ist und für eine normale Mechanotransduktion in
Mäusen erforderlich ist. MEC-2 Proteine, die eine Stomatindomäne beinhalten,
interagieren und modulieren die Aktivität des MEC-4 Ionenkanals. Aufgrund der
Homologie von MEC-2 und stomatinähnlichen Proteinen könnten diese ebenfalls
eine solche Rolle spielen. In der vorliegenden Arbeit wird die Rolle von ASIC3
und stomatinähnlichen Proteinen (SLP) bei der Mechanotransduktion in Mäusen
untersucht. Es wird gezeigt, dass eine physikalische Interaktion zwischen
ASIC3 und Stomatin sowie ASIC3 und dem stomatinähnlichen Protein 3 (SLP3) in
einem heterologen System vorliegt. Um zu testen, ob diese Interaktion für die
Mechanotransduktion in sensorischen Neuronen wichtig ist, wurde die in vitro
Haut-Nerv Preparation, in der die Einzelfasermechanosensitivität analysiert
wird, angewendet. Die Mechanosensitivität der verschiedenen Haut-
mechanorezeptoren von normalen Wildtypmäusen wird mit Mäusen verglichen, denen
ASIC3 sowie ASIC3 und Stomatin fehlt. Der Verlust von ASIC3 in Mäusen führt zu
einer Zunahme der Mechanosensitivität von schnelladaptierenden
Mechanorezeptoren (RAM) und zu eine Abnahme der Mechanosensitivität von
A-Mechanonociceptoren (AM) und C-Fasern. Im Vergleich dazu hat der zusätzliche
Verlust von Stomatin keinen Effekt an der Zunahme der Mechanosensitivität in
RAM allerdings wird deren Antwort auf mechanische Reize etwas verlangsamt.
Weiterhin ist die Mechanosensitivität von den AM und C-Fasern in ASIC3
/Stomatin-Mutanten Mäuse vermindert. Diese Verminderung ist jedoch nicht
Signifikant im Vergleich zu ASIC3-Mutaten Mäuse. Andererseits zeigen
polymodale Nociceptoren (C-MH) in ASIC3/Stomatin-Mutanten Mäuse unter starkem
mechanischem Stimulus eine signifikante Verminderung der Mechanosensitivität
im Vergleich zu C-MH in ASIC3-Mutanten. Die Ergebnisse dieser Arbeit zeigen,
dass ASIC3 für eine normale Mechanorezeptorenfunktion in Mäusen notwendig ist.
Die Analyse von Mechanorezeptoren in ASIC3/Stomatin-Mutanten zeigte eine
schwache funktionelle Interaktion zwischen ASIC3 und Stomatin