Novel Characterization of Prox-1 Expression on Optic Nerve Astrocytes.

Prox-1 (prospero homeobox protein 1) is a master control gene for lymphatic vessel development and it has been widely used as a marker to detect lymphatic vessels inside and outside the eye. We herein report a novel finding of Prox-1 expression on the astrocytes of the optic nerve, a critical structure that conveys visual information from the retina to the brain. We identified that Prox-1 expressing cells were widely distributed inside the optic nerve. These cells co-expressed both GFAP (glial fibrillary acidic protein) and AQP4 (aquaporin-4) which are typical markers for astrocytes. Interestingly, some of the Prox-1+ cells ensheath CD31+ blood vessels inside the optic nerve and these cells are part of the glymphatic system utilized for ocular fluid circulation. This study not only reveals a novel expression pattern of Prox-1 in the optic nerve but also identifies a new marker for the glymphatic system in this critical structure. Further exploration on this novel phenomenon may re-veal new mechanisms and therapeutic targets for optic nerve-related diseases that affect many patients worldwide.