TRPV1 is mainly functional in the microglia. Its activation, beyond controlling microglia reaction per se, modulated microglia-neuron communication, by promoting release of extracellular vesicles (EVs) from microglia. Indeed, EVs are important mediators of intercellular communication between microglia and brain cells: Maria Cristina Marrone, Annunziato Morabito, Michela Giustizieri, Valerio Chiurchiù, Alessandro Leuti, Marzia Mattioli, Sara Marinelli, Loredana Riganti, Marta Lombardi, Emanuele Murana, Antonio Totaro, Daniele Piomelli, Davide Ragozzino, Sergio Oddi, Mauro Maccarrone, Claudia Verderio & Silvia Marinelli. TRPV1 channels are critical brain inflammation detectors and neuropathic pain biomarkers in mice. Nature Communications 8, Article number: 15292 (2017) doi:10.1038/ncomms15292.
(a–f) Sections of cortical tissue from WT and TRPV1−/− mice, fixed after exposure to ACSF (a,d), ACSF plus vehicle (DMSO; b,e) and ACSF plus 1μM capsaicin (c,f) and immune-processed for iba-1 to stain microglia cells (in red). INSETs are zoom images taken from an area delimited by the yellow square for each condition. (g), Bar graph of percentage of cortical microglia cell phenotype (resting, ameboid, bushy and hypertrophied), in control (grey bars), vehicle- (dark grey bars) and capsaicin- treated (red bars) cortical sections from WT mice. Capsaicin treatment causes a significant shift from ramified and bushy to hypertrophied morphology. (h), Same as in ‘g’ but in cortical sections from TRPV1−/− mice. In these tissues capsaicin fails to induce morphological changes of microglia cells. Note that microglia cells in −/− tissues are already hypertrophied in control conditions (d–f,h).
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