Piezo2 voltage-block regulates mechanical pain sensitivity.

PIEZO2 is a trimeric mechanically-gated ion channel expressed by most sensory neurones in the dorsal root ganglia. Mechanosensitive PIEZO2 channels are also genetically required for normal touch sensation in both mice and humans. We previously showed that PIEZO2 channels are also strongly modulated by membrane voltage. Specifically, it is only at very positive voltages that all channels are available for opening by mechanical force. Conversely, most PIEZO2 channels are blocked at normal negative resting membrane potentials. The physiological function of this unusual biophysical property of PIEZO2 channels, however, remained unknown. We characterized the biophysical properties of three PIEZO2 ion channel mutations at an evolutionarily conserved Arginine (R2756). Using genome engineering in mice we generated Piezo2R2756H/R2756H and Piezo2R2756K/R2756K knock-in mice to characterize the physiological consequences of altering PIEZO2 voltage sensitivity in vivo. We measured endogenous mechanosensitive currents in sensory neurones isolated from the dorsal root ganglia and characterized mechanoreceptor and nociceptor function using electrophysiology. Mice were also assessed behaviourally and morphologically. Mutations at the conserved Arginine (R2756) dramatically changed the biophysical properties of the channel relieving voltage block and lowering mechanical thresholds for channel activation. Piezo2R2756H/R2756H and Piezo2R2756K/R2756K knock-in mice that were homozygous for gain of function mutations were viable and were tested for sensory changes. Surprisingly, mechanosensitive currents in nociceptors, neurones that detect noxious mechanical stimuli, were substantially sensitized in Piezo2 knock-in mice, but mechanosensitive currents in most mechanoreceptors that underlie touch sensation were only mildly affected by the same mutations. Single-unit electrophysiological recordings from sensory neurones innervating the glabrous skin revealed that rapidly-adapting mechanoreceptors that innervate Meissner's corpuscles exhibited slightly decreased mechanical thresholds in Piezo2 knock-in mice. Consistent with measurements of mechanically activated currents in isolated sensory neurones essentially all cutaneous nociceptors, both fast conducting Aδ-mechanonociceptors and unmyelinated C-fibre nociceptors were substantially more sensitive to mechanical stimuli and indeed acquired receptor properties similar to ultrasensitive touch receptors in Piezo2 knock-in mice. Mechanical stimuli also induced enhanced ongoing activity in cutaneous nociceptors in Piezo2 knock-in mice and hyper-sensitive PIEZO2 channels were sufficient alone to drive ongoing activity, even in isolated nociceptive neurones. Consistently, Piezo2 knock-in mice showed substantial behaviourally hypersensitivity to noxious mechanical stimuli. Our data indicate that ongoing activity and sensitization of nociceptors, phenomena commonly found in human chronic pain syndromes, can be driven by relieving the voltage-block of PIEZO2 ion channels. Indeed, membrane depolarization caused by multiple noxious stimuli may sensitize nociceptors by relieving voltage-block of PIEZO2 channels.

Lack of evidence for participation of TMEM150C in sensory mechanotransduction.

The membrane protein TMEM150C has been proposed to form a mechanosensitive ion channel that is required for normal proprioceptor function. Here, we examined whether expression of TMEM150C in neuroblastoma cells lacking Piezo1 is associated with the appearance of mechanosensitive currents. Using three different modes of mechanical stimuli, indentation, membrane stretch, and substrate deflection, we could not evoke mechanosensitive currents in cells expressing TMEM150C. We next asked if TMEM150C is necessary for the normal mechanosensitivity of cutaneous sensory neurons. We used an available mouse model in which the Tmem150c locus was disrupted through the insertion of a LacZ cassette with a splice acceptor that should lead to transcript truncation. Analysis of these mice indicated that ablation of the Tmem150c gene was not complete in sensory neurons of the dorsal root ganglia (DRG). Using a CRISPR/Cas9 strategy, we made a second mouse model in which a large part of the Tmem150c gene was deleted and established that these Tmem150c-/- mice completely lack TMEM150C protein in the DRGs. We used an ex vivo skin nerve preparation to characterize the mechanosenstivity of mechanoreceptors and nociceptors in the glabrous skin of the Tmem150c-/- mice. We found no quantitative alterations in the physiological properties of any type of cutaneous sensory fiber in Tmem150c-/- mice. Since it has been claimed that TMEM150C is required for normal proprioceptor function, we made a quantitative analysis of locomotion in Tmem150c-/- mice. Here again, we found no indication that there was altered gait in Tmem150c-/- mice compared to wild-type controls. In summary, we conclude that existing mouse models that have been used to investigate TMEM150C function in vivo are problematic. Furthermore, we could find no evidence that TMEM150C forms a mechanosensitive channel or that it is necessary for the normal mechanosensitivity of cutaneous sensory neurons.

Oral fatty acid taste sensitivity in healthy young individuals of both sexes is related to body mass index and soluble CD36 serum levels / La sensibilidad oral a ácidos grasos en jóvenes sanos de ambos sexos está relacionada con el índice de masa corporal y los niveles séricos de sCD36

Introduction: CD36 is a membrane protein that functions as a lingual receptor for lipids. The soluble CD36 fraction (sCD36) may correlate oral fatty acid fat taste sensitivity to body mass index (BMI) and adiposity. Objectives: to determine if the oral fatty acid taste sensitivity in healthy young individuals of both sexes is related to serum sCD36 levels, adiposity and BMI. Methods: a cross-sectional study was conducted in 72 healthy young individuals (18-25 years). Serum sCD36 was quantified for all subjects. Oral fatty acid taste sensitivity was determined using an ascending series of the three-alternate forced choice methodology. Additionally, BMI was calculated using anthropometry, and adiposity was determined by bioelectric impedance analysis. Results: there was a positive correlation between BMI and the oral fatty acid taste sensitivity threshold (r = 0.277, p < 0.05) and a negative correlation between BMI and serum sCD36 levels (r = -0.035, p < 0.01). Adiposity negatively correlated with the sCD36 levels only in women (r = -0.359, p < 0.05). The threshold for oral sensitivity to fatty acids in overweight individuals was 1.0 (IQR 1.16) mM vs 0.2 (IQR 0.29) mM in healthy weight individuals (p < 0.05), while sCD36 levels were 26.1 pg/ml (IQR 32.9) and 77.97 pg/ml (IQR 560.66) in overweight and normal weight individuals, respectively (p < 0.05). Conclusions: BMI positively correlates with the oral sensitivity threshold of fatty acids and negatively correlates with serum sCD36 levels. The threshold of oral sensitivity to fatty acids was significantly higher in overweight subjects, while sCD36 levels were significantly higher in the group of normal weight individuals

Introducción: CD36 es una proteína de membrana que funciona como receptor lingual para lípidos. La fracción soluble del CD36 (sCD36) podría correlacionar la sensibilidad gustativa a los ácidos grasos orales con el índice de masa corporal (IMC) y con la adiposidad. Objetivos: determinar si la sensibilidad gustativa a ácidos grasos orales se relaciona con los niveles séricos de sCD36, la adiposidad y el IMC en jóvenes de ambos sexos. Métodos: estudio transversal en 72 adultos jóvenes (18-25 años). Se cuantificaron los niveles séricos de sCD36 para todos los sujetos. Se determinó la sensibilidad gustativa a los ácidos grasos orales usando la prueba triangular discriminatoria de concentraciones escaladas. Adicionalmente, se calculó el IMC usando antropometría y se determinó la adiposidad por análisis de bioimpedancia. Resultados: se encontró correlación positiva entre el IMC y el umbral de sensibilidad gustativa a los ácidos grasos orales (r = 0,277, p < 0,05) y una correlación negativa entre el IMC y los niveles séricos de sCD36 (r = -0,035, p < 0,01). La adiposidad, solo en mujeres se correlacionó negativamente con los niveles de sCD36 (r = -0,359, p < 0,05). El umbral para la sensibilidad gustativa a ácidos grasos orales en sujetos con sobrepeso fue 1,0 (IQR 1,16) mM vs. 0,2 (IQR 0,29) mM en sujetos con peso normal (p < 0,05), mientras que los niveles séricos de sCD36 fueron de 26,1 pg/ml (IQR 32,9) en sujetos con sobrepeso y 77,97 pg/ml (IQR 560,66) en sujetos con peso normal, respectivamente (p < 0,05). Conclusiones: el IMC se correlaciona positivamente con el umbral para la sensibilidad oral a los ácidos grasos y negativamente se correlaciona con los niveles séricos de sCD36. El umbral de sensibilidad oral a los ácidos grasos fue significativamente mayor en sujetos con sobrepeso, mientras que los niveles de sCD36 fueron significativamente más altos en el grupo de sujetos con peso normal

Oral fatty acid taste sensitivity in healthy young individuals of both sexes is related to body mass index and soluble CD36 serum levels.

INTRODUCTION: Introduction: CD36 is a membrane protein that functions as a lingual receptor for lipids. The soluble CD36 fraction (sCD36) may correlate oral fatty acid fat taste sensitivity to body mass index (BMI) and adiposity. Objectives: to determine if the oral fatty acid taste sensitivity in healthy young individuals of both sexes is related to serum sCD36 levels, adiposity and BMI. Methods: a cross-sectional study was conducted in 72 healthy young individuals (18-25 years). Serum sCD36 was quantified for all subjects. Oral fatty acid taste sensitivity was determined using an ascending series of the three-alternate forced choice methodology. Additionally, BMI was calculated using anthropometry, and adiposity was determined by bioelectric impedance analysis. Results: there was a positive correlation between BMI and the oral fatty acid taste sensitivity threshold (r = 0.277, p < 0.05) and a negative correlation between BMI and serum sCD36 levels (r = -0.035, p < 0.01). Adiposity negatively correlated with the sCD36 levels only in women (r = -0.359, p < 0.05). The threshold for oral sensitivity to fatty acids in overweight individuals was 1.0 (IQR 1.16) mM vs 0.2 (IQR 0.29) mM in healthy weight individuals (p < 0.05), while sCD36 levels were 26.1 pg/ml (IQR 32.9) and 77.97 pg/ml (IQR 560.66) in overweight and normal weight individuals, respectively (p < 0.05). Conclusions: BMI positively correlates with the oral sensitivity threshold of fatty acids and negatively correlates with serum sCD36 levels. The threshold of oral sensitivity to fatty acids was significantly higher in overweight subjects, while sCD36 levels were significantly higher in the group of normal weight individuals.

INTRODUCCIÓN: Introducción: CD36 es una proteína de membrana que funciona como receptor lingual para lípidos. La fracción soluble del CD36 (sCD36) podría correlacionar la sensibilidad gustativa a los ácidos grasos orales con el índice de masa corporal (IMC) y con la adiposidad. Objetivos: determinar si la sensibilidad gustativa a ácidos grasos orales se relaciona con los niveles séricos de sCD36, la adiposidad y el IMC en jóvenes de ambos sexos. Métodos: estudio transversal en 72 adultos jóvenes (18-25 años). Se cuantificaron los niveles séricos de sCD36 para todos los sujetos. Se determinó la sensibilidad gustativa a los ácidos grasos orales. Adicionalmente, se calculó el IMC usando antropometría y se determinó la adiposidad por análisis de bioimpedancia. Resultados: se encontró correlación positiva entre el IMC y el umbral de sensibilidad gustativa a los ácidos grasos orales (r = 0,277, p < 0,05) y una correlación negativa entre el IMC y los niveles séricos de sCD36 (r = −0,035, p < 0,01). La adiposidad, solo en mujeres se correlacionó negativamente con los niveles de sCD36 (r = −0,359, p < 0,05). El umbral para la sensibilidad gustativa a ácidos grasos orales en sujetos con sobrepeso fue 1,0 (IQR 1,16) mM vs. 0,2 (IQR 0,29) mM en sujetos con peso normal (p < 0,05), mientras que los niveles séricos de sCD36 fueron de 26,1 pg/ml (IQR 32,9) en sujetos con sobrepeso y 77,97 pg/ml (IQR 560,66) en sujetos con peso normal, respectivamente (p < 0,05). Conclusiones: el IMC se correlaciona positivamente con el umbral para la sensibilidad oral a los ácidos grasos y negativamente se correlaciona con los niveles séricos de sCD36. El umbral de sensibilidad oral a los ácidos grasos fue significativamente mayor en sujetos con sobrepeso, mientras que los niveles de sCD36 fueron significativamente más altos en el grupo de sujetos con peso normal.