1:Biodonostia Institute; 2:Comparative Neurobiology Laboratory, Cavanilles Institute, University of Valencia, Spain

Neuromuscular junctions (NMJs) are the specific synapse sites between terminal nerves and muscle fibres. Two types of NMJ-capping cells [terminal Schwann cells (tSCs) and Kranocytes] cover these structures. tSCs, the glial component of the synapsis, surround the endplate and maintain the structure of NMJs. Kranocytes, also known as “perisynaptic-fibroblasts”, surround the tSCs, covering a wider tissue area. In response to nerve injury, Kranocytes migrate and create bridges between endplates, which are later colonized by tSCs and axons, to promote the reinnervation process. To date, no study has addressed the interaction of NMJ-capping cells with the immediate muscle fibre microenvironment. Here, we addressed the question if NMJ-capping cells could send and receive information through other sources apart from nerve signalling, and specifically we analysed if they establish connections with the neighbouring capillaries. To this end, iDisco-clarified whole mount skeletal muscles from hindlimbs of C57BL/6 adult mice were analysed by immunofluorescence and confocal microscopy, as well as transmission electron microscopy. Both NMJ-capping cells (tSCs and Kranocytes) were found to establish connections to capillaries, independently to each other, suggesting they are exchanging different types of information. The contacts between tSCs and Kranocytes and the vascular system may represent a novel mechanism of information exchange between NMJs and the muscle fibres that is currently being investigated.

Key words: Neuromuscular junctions (NMJs), tSCs, Kranocytes, vascular network