Human Stem Cell-Derived TRPV1-Positive Sensory Neurons: A New Tool to Study Mechanisms of Sensitization

Somatosensation, the detection and transduction of external and internal stimuli such as temperature or mechanical force, is vital to sustaining our bodily integrity. But still, some of the mechanisms of distinct stimuli detection and transduction are not entirely understood, especially when noxious perception turns into chronic pain. Over the past decade major progress has increased our understanding in areas such as mechanotransduction or sensory neuron classification. However, it is in particular the access to human pluripotent stem cells and the possibility of generating and studying human sensory neurons that has enriched the somatosensory research field. Based on our previous work, we describe here the generation of human stem cell-derived nociceptor-like cells. We show that by varying the differentiation strategy, we can produce different nociceptive subpopulations with different responsiveness to nociceptive stimuli such as capsaicin. Functional as well as deep sequencing analysis demonstrated that one protocol in particular allowed the generation of a mechano-nociceptive sensory neuron population, homogeneously expressing TRPV1. Accordingly, we find the cells to homogenously respond to capsaicin, to become sensitized upon inflammatory stimuli, and to respond to temperature stimulation. The efficient and homogenous generation of these neurons make them an ideal translational tool to study mechanisms of sensitization, also in the context of chronic pain.

Das Verfahren geht weit über „die App“ hinaus – Datenschutzfragen von Corona-Tracing-Apps

Seit der Ausbreitung des SARS-CoV-2-Virus in Europa Anfang 2020 wir dan technischen Lösungen zur Eindämmung der Pandemie gearbeitet. Unter den verschiedenen Systementwürfen stechen jene hervor, die damit werben, datenschutzfreundlich und DSGVO-konform zu sein. Die DSGVO selbst verpflichtet die Betreiberïnnen umfangreicher Datenverarbeitungssysteme wie etwa Tracing-Apps zur Anfertigung einer Datenschutz-Folgenabschätzung (DSFA) aufgrund des hohen Risikos für die Rechte- und Freiheiten (Art. 35 DSGVO). Hierbei handelt es sich um eine strukturierte Risikoanalyse, die mögliche grundrechtsrelevante Folgen einer Datenverarbeitung im Vorfeld identifiziert und bewertet.

Wir zeigen in unserer DSFA, dass auch die aktuelle, dezentrale Implementierung der Corona-Warn-App zahlreiche gravierende Schwachstellen und Risiken birgt. Auf der rechtlichen Seite haben wir die Legitimationsgrundlage einer freiwilligen Einwilligung untersucht und formulieren die begründete Forderung, dass der Einsatz einer Tracing-App gesetzlich geregelt werden muss. Weiterhin wurden Maßnahmen zur Verwirklichung von Betroffenenrechten nicht ausreichend betrachtet. Nicht zuletzt ist die Behauptung, ein Datum sei anonym, hoch voraussetzungsreich. Anonymisierung muss als ein kontinuierlicher Vorgang begriffen werden, der eine Abtrennung des Personenbezugs zum Ziel hat und auf dem Zusammenspiel von rechtlichen, organisatorischen und technischen Maßnahmen beruht. Der derzeit vorliegenden Corona-Warn-App fehlt es an einem solchen expliziten Trennungsvorgang. Unsere DSFA zeigt dabei auch die wesentlichen Defizite der offiziellen DSFA der Corona-Warn-App auf.

HESC-derived sensory neurons reveal an unexpected role for PIEZO2 in nociceptor mechanotransduction.. [DOI: 10.1101/741660]

Somatosensation, the detection and transduction of external and internal stimuli, has fascinated scientists for centuries. But still, some of the mechanisms how distinct stimuli are detected and transduced are not entirely understood. Over the past decade major progress has increased our understanding in areas such as mechanotransduction or sensory neuron classification. Additionally, the accessibility to human pluripotent stem cells and the possibility to generate and study human sensory neurons has enriched the somatosensory research field.

Based on our previous work, the generation of functional human mechanoreceptors, we describe here the generation of hESC-derived nociceptor-like cells. We show that by varying the differentiation strategy, we can produce different nociceptive subpopulations. One protocol in particular allowed the generation of a sensory neuron population, homogeneously expressing TRPV1, a prototypical marker for nociceptors. Accordingly, we find the cells to homogenously respond to capsaicin, to become sensitized upon inflammatory stimuli, and to respond to temperature stimulation.

Surprisingly, all of the generated subtypes show mechano-nociceptive characteristics and, quite unexpectedly, loss of mechanotransduction in the absence of PIEZO2.

Human vs. Mouse Nociceptors - Similarities and Differences

The somatosensory system allows us to detect a diverse range of physical and chemical stimuli including noxious ones, which can initiate protective reflexes to prevent tissue damage. However, the sensation of pain can - under pathological circumstances - outlive its usefulness and perpetrate ongoing suffering. Rodent model systems have been tremendously useful to help understand basic mechanisms of pain perception. Unfortunately, the translation of this knowledge into novel therapies has been challenging. We have investigated similarities and differences of human and mouse peptidergic (TRKA expressing) nociceptors using dual-color fluorescence in situ hybridization of dorsal root ganglia. By comparing the transcripts of a selected group of well-established nociceptive markers, we observed significant differences for some of them. We found co-expression of Trpv1, a key player for sensitization and inflammatory pain, with TrkA in a larger population in humans compared to mice. Similar results could be obtained for Na_v1.8 and Na_v1.9, two voltage gated sodium channels implicated in pathological forms of pain. Additionally, co-expression of Ret and TrkA was also found to be more abundant in human neurons. Moreover, the neurofilament heavy polypeptide was detected in all human sensory DRG neurons compared to a more selective expression pattern observed in rodents. To our knowledge, this is the first time that such detailed comparative analysis has been performed and we believe that our findings will direct future experimentation geared to understand the difficulties we face in translating findings from rodent models to humans.

Heteromeric channels formed by TRPC1, TRPC4 and TRPC5 define hippocampal synaptic transmission and working memory

Canonical transient receptor potential (TRPC) channels influence various neuronal functions. Using quantitative high-resolution mass spectrometry, we demonstrate that TRPC1, TRPC4, and TRPC5 assemble into heteromultimers with each other, but not with other TRP family members in the mouse brain and hippocampus. In hippocampal neurons from Trpc1/Trpc4/Trpc5-triple-knockout (Trpc1/4/5^-/-) mice, lacking any TRPC1-, TRPC4-, or TRPC5-containing channels, action potential-triggered excitatory postsynaptic currents (EPSCs) were significantly reduced, whereas frequency, amplitude, and kinetics of quantal miniature EPSC signaling remained unchanged. Likewise, evoked postsynaptic responses in hippocampal slice recordings and transient potentiation after tetanic stimulation were decreased. In vivo, Trpc1/4/5^-/- mice displayed impaired cross-frequency coupling in hippocampal networks and deficits in spatial working memory, while spatial reference memory was unaltered. Trpc1/4/5^-/- animals also exhibited deficiencies in adapting to a new challenge in a relearning task. Our results indicate the contribution of heteromultimeric channels from TRPC1, TRPC4, and TRPC5 subunits to the regulation of mechanisms underlying spatial working memory and flexible relearning by facilitating proper synaptic transmission in hippocampal neurons.

The TRPM2 channel is a hypothalamic heat sensor that limits fever and can drive hypothermia

Body temperature homeostasis is critical for survival and requires precise regulation by the nervous system. The hypothalamus serves as the principal thermostat that detects and regulates internal temperature. We demonstrate that the ion channel TRPM2 [of the transient receptor potential (TRP) channel family] is a temperature sensor in a subpopulation of hypothalamic neurons. TRPM2 limits the fever response and may detect increased temperatures to prevent overheating. Furthermore, chemogenetic activation and inhibition of hypothalamic TRPM2-expressing neurons in vivo decreased and increased body temperature, respectively. Such manipulation may allow analysis of the beneficial effects of altered body temperature on diverse disease states. Identification of a functional role for TRP channels in monitoring internal body temperature should promote further analysis of molecular mechanisms governing thermoregulation and foster the genetic dissection of hypothalamic circuits involved with temperature homeostasis.

Subunit-selective N-Methyl-d-aspartate (NMDA) Receptor Signaling through Brefeldin A-resistant Arf Guanine Nucleotide Exchange Factors BRAG1 and BRAG2 during Synapse Maturation

The maturation of glutamatergic synapses in the CNS is regulated by NMDA receptors (NMDARs) that gradually change from a GluN2B- to a GluN2A-dominated subunit composition during postnatal development. Here we show that NMDARs control the activity of the small GTPase ADP-ribosylation factor 6 (Arf6) by consecutively recruiting two related brefeldin A-resistant Arf guanine nucleotide exchange factors, BRAG1 and BRAG2, in a GluN2 subunit-dependent manner. In young cortical cultures, GluN2B and BRAG1 tonically activated Arf6. In mature cultures, Arf6 was activated through GluN2A and BRAG2 upon NMDA treatment, whereas the tonic Arf6 activation was not detectable any longer. This shift in Arf6 regulation and the associated drop in Arf6 activity were reversed by a knockdown of BRAG2. Given their sequential recruitment during development, we examined whether BRAG1 and BRAG2 influence synaptic currents in hippocampal CA1 pyramidal neurons using patch clamp recordings in acute slices from mice at different ages. The number of AMPA receptor (AMPAR) miniature events was reduced by depletion of BRAG1 but not by depletion of BRAG2 during the first 2 weeks after birth. In contrast, depletion of BRAG2 during postnatal weeks 4 and 5 reduced the number of AMPAR miniature events and compromised the quantal sizes of both AMPAR and NMDAR currents evoked at Schaffer collateral synapses. We conclude that both Arf6 activation through GluN2B-BRAG1 during early development and the transition from BRAG1- to BRAG2-dependent Arf6 signaling induced by the GluN2 subunit switch are critical for the development of mature glutamatergic synapses.

Supralinear dendritic Ca(2+) signalling in young developing CA1 pyramidal cells

Although Ca(2+) is critically important in activity-dependent neuronal development, not much is known about the regulation of dendritic Ca(2+) signals in developing neurons. Here, we used ratiometric Ca(2+) imaging to investigate dendritic Ca(2+) signalling in rat hippocampal pyramidal cells during the first 1-4 weeks of postnatal development. We show that active dendritic backpropagation of Nav channel-dependent action potentials (APs) evoked already large dendritic Ca(2+) transients in animals aged 1 week with amplitudes of ∼150 nm, similar to the amplitudes of ∼160 nM seen in animals aged 4 weeks. Although the AP-evoked dendritic Ca(2+) load increased about four times during the first 4 weeks, the peak amplitude of free Ca(2+) concentration was balanced by a four-fold increase in Ca(2+) buffer capacity κs (∼70 vs. ∼280). Furthermore, Ca(2+) extrusion rates increased with postnatal development, leading to a slower decay time course (∼0.2 s vs. ∼0.1 s) and more effective temporal summation of Ca(2+) signals in young cells. Most importantly, during prolonged theta-burst stimulation dendritic Ca(2+) signals were up to three times larger in cells at 1 week than at 4 weeks of age and much larger than predicted by linear summation, which is attributable to an activity-dependent slow-down of Ca(2+) extrusion. As Ca(2+) influx is four-fold smaller in young cells, the larger Ca(2+) signals are generated using four times less ATP consumption. Taken together, the data suggest that active backpropagations regulate dendritic Ca(2+) signals during early postnatal development. Remarkably, during prolonged AP firing, Ca(2+) signals are several times larger in young than in mature cells as a result of activity-dependent regulation of Ca(2+) extrusion rates.

[Bougie endosonography in the preoperative diagnosis of stenosing esophageal carcinomas]

BACKGROUND AND OBJECTIVE

Nowadays ultrasonic endoscopy is accepted as the most accurate method in the preoperative TNM staging of oesophageal tumour. At the time a diagnosis of oesophageal is made, 25-62% of patients have marked oesophageal stricture due to an advanced stage of the tumour. As a result, it is often impossible to pass a conventional endoscope and the examination is incomplete or a dilator has to be introduced at high risk of perforation or other complications. An ultrasonic oesophagoprobe (Olympus MH 908) with a diameter of 7.9 mm, its tip acting as a dilator has been developed so that even in high-grade oesophageal stricture a complete and low-risk investigation can be undertaken. The value of this instrument has been compared prospectively with that of a standard ultrasonic endoscope in patients with oesophageal stricture due to carcinoma and in relation to the postoperative histology.

PATIENTS AND METHODS

Between May 1996 and February 1997, 62 patients (55 men, 7 women; average age 55.8 [41-82] years) with suspected or histologically confirmed oesophageal carcinoma were examined with the standard ultrasonic endoscope and the new oesophagoprobe. The two independent results were related to the postoperative histology.

RESULTS

It was possible to compare the endoscopic results with the postoperative histology in 47 patients. In 55.8% it was not possible to pass the stricture with the standard ultrasonic endoscope (SE) so that an accuracy of only 41% was obtained in the T stage and 56.4% in the N stage. But with the oesophagoprobe (OP) an accuracy of 74.5% in the T stage and of 63% in the N stage were achieved. The difference in the findings between the two instruments was highly significant (p < 0.001) in those patients in whom the SE could not be passed through the stricture. For the T stage the accuracy was 14.3% vs. 76.2% (SE vs. OP); in the N stage it was 38.1% and 57.2%, respectively. When both instruments could be passed the results were comparable.

CONCLUSIONS

Examination with the ultrasonic oesophagoprobe is a reliable and accurate method free of complications for the preoperative assessment of oesophageal carcinoma with stricture.