Characterization of released exosomes from satellite glial cells under normal and inflammatory conditions.

Aims Satellite glial cells (SGCs) are non-neuronal cells that entirely surround neurons within sensory ganglia. This unique structure allows SGC-neuron interactions. Altered cross-talk following nerve injury or inflammation is thought to contribute to pathogenesis of chronic pain. Release of extracellular vesicles in form of exosomes has been found to play a key role in cell-cell communication. However, release of exosomes from SGCs and their potential role in modulating pain remain unknown. Hence, this study aimed at identifying and characterizing shed exosomes from SGCs under normal and inflammatory conditions. Methods Fresh primary cultures of rat trigeminal ganglia (TG) were prepared from adult male Sprague-Dawley rats. Danish Animal Inspectorate approved the study protocol. Primary SGCs were kept in culture up to 21 days and were characterized by morphology and immunohistochemistry. Cultured SGCs were monitored under normal and LPS (50 ng/mL) treatment. Collection of conditioned media was performed over time and exosomes were isolated. Particle size distribution and total protein were determined by NTA and LC-MS/MS, respectively. Results SGCs formed small clusters, spread outwards to areas devoid of cells but remained spindle-like in appearance with larger cell bodies. The primary cultures of SGCs were clearly GS positive with a low expression of GFAP. LPS treatment led to higher GFAP expression. Particle size distribution showed that two third of the particles were in the exosomal size range. Upon LPS-stimulation, four proteins (histone H2B, ubiquitin-60S ribosomal, myosin-9, elongation factor 1-alpha) were found exclusively expressed compared to normal treated SGCs. Conclusions For the first time it was demonstrated that SGCs shed extracellular vesicles in exosomal size range. Mysoin-9 was identified as a possible novel marker of SGCs activation under inflammatory conditions. This protein plays a role in cell-cell adhesion and possibly contributes to SGC-SGC cross-talk upon inflammation which may consequently influence the excitability of nearby neurons.