Intercapillary bridging cells in mouse retina

Purpose Intervascular bridges are fibrous strands that connect neighbouring capillaries. Approximately 0.5% of intervascular bridges in mouse retina present an associated cell. These bridging cells have been described in several tissues; however their identity and functions remain controversial. Methods C57BL/6/6-SJL and CD1 mice retinas were used. Whole-mount formalin-fixed retinas were studied by means of immunohistochemistry and cytochemistry. Isolation of retinal vasculature was achieved by trypsin/pepsin digest technique. Results PAS reaction and the immunolabelling with anti-collagen IV and laminin antibodies revealed that bridging cells were completely surrounded by a basement membrane, connecting two or more neighbouring capillaries. These cells were PECAM-1 negative, a marker of endothelial cells, but strongly tomato lectin positive, a marker shared by endothelial cells and pericytes. Phalloidin, that binds specifically F-actin highly abundant in pericytes, marked also bridging cells. As expected, bridging cells were negative for GFAP and F4-80, a neuroglial and macrophagic marker, respectively. Interestingly, bridging cells expressed the connexin 43 gap junction protein. Conclusion Our results suggest that intercapillary bridging cells are modified pericytes, since they are sourrounded by a basement membrane and express some of pericyte markers. Moreover, retina vasculature lacks innervation. Gap junctions allow ions to move between cells and thus, efficiently provide electrical signal passage through them. Intercapillary bridging cells constitutively expressed the gap junction connexin 43 protein, and this could represent a new way for simultaneous stimulation of different retinal vascular territories.