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Do you hear me now? Mechanisms of cellular communication in the trabecular meshwork

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Abstract:

Purpose: Cellular communication in trabecular meshwork (TM) cells is essential in order to regulate aqueous humor outflow and maintain normotensive intraocular pressure. TM cells use various mechanisms to communicate signals between cells, such as secretion of soluble signaling factors. Here, we describe an additional mechanism: the formation of tunneling nanotubes (TNTs), specialized filopodia that transport cellular cargo and organelles directly from one cell to another via a tubular conduit.
Methods: One half of a flask of primary TM cells was labeled with the fluorescent Vybrant dye DiO and the other half with DiD or MitoTracker. The labeled cells were mixed 1:1 and cultured overnight. The next day, cells were fixed and immunostained with CD44 antibodies to label the cell surface. The distribution of Myosin-10 in TM cells was investigated by immunohistochemistry.
Results: Confocal microscopy showed an extended filopodium connecting a DiD-labeled cell to a DiO-labeled cell. At higher magnification, DiD-labeled vesicles were clearly present in the filopodium as well as in the cytoplasm of the DiO-labeled TM cell. In other images, MitoTracker-labeled mitochondria were observed in a DiO-labeled cell. Myosin-10, an unconventional myosin important for TNT formation, was immunolocalized to the tips of filopodia as well as in punctate vesicles along the length of the filopodium and in phagocytic cups.
Conclusions: Our results support the formation of TNTs by TM cells. This allows vesicles and mitochondria to be transferred directly between cells without the need to be secreted extracellularly. This is significant for
cellular communication in the TM because secreted signals are diluted in aqueous humor and washed away into Schlemm’s canal. Moreover, TNTs can extend long distances, allowing cells in different regions of the tissue to receive signals. Cellular communication via TNTs may therefore contribute to the normal homeostatic function of the tissue.

Glaucoma Research 2018-2020, pp. 3-15 #1
Edited by: John R. Samples and Paul A. Knepper
© Kugler Publications, Amsterdam, The Netherlands

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