Investigation of non-vascular NG2 expressing cells in the adult mouse retina after ischemia-reperfusion injury

Abstract

Nerve/glial antigen 2 (NG2) protein is a single membrane-spanning proteoglycan that is expressed by pericytes, polydendrocytes and some microglia/macrophage (Iba1+/NG2+) in central nervous system. Non-vascular NG2 expressing cells (polydendrocytes & Iba1+/NG2+ cells) in the brain are shown to be multi-potential and have been implicated in neurodegenerative diseases. However, existence and function of possible non-vascular NG2 expressing cells in ocular diseases has not been reported. In the present study, we performed immunocytochemical analysis and identified non-vascular NG2+ cell type in a mouse glaucomatous model characterised with degeneration of retinal ganglion cells (RGCs) induced by acute ocular hypertension. Male C57BL/6N mice aged 6-10 weeks were exposed to acute ocular hypertension by increasing ocular pressure for 1 hour followed by reperfusion for 1 day leading to retinal ischemia/reperfusion (I/R) injury. In normal retina, NG2 expression was restricted to pericytes around blood vessels. However, after injury, we observed some non-vascular NG2 expressing cells away from blood vessels in brain parachyma, and some with ameboid appearance showed close association with RGCs. Interestingly, majority of non-vascular NG2+ cells also expressed Iba-1 (Iba1+/NG2+), which were only found after retinal I/R injury. The source and the role of the non-vascular NG2 expressing cells with respect to injured RGCs are now being under investigation.