gms | German Medical Science

Objective: The study aims to explore the role of sialylation in protecting retinal ganglion cells (RGCs) and promoting optic nerve regeneration after injury, along with its underlying mechanisms.

Methods. Optic nerve crush (ONC) was conducted on mice, with immunofluorescent staining of retinal sialyltransferases and sialic acid performed at 1, 3, 5, 7 days post-crush (dpc). The sialyltransferases inhibitor 3FAX-PN was intravitreally injected to evaluate its effect on RGC survival post-injury, particularly in αRGCs. AAV-St6gal1 was also intravitreally injected into wild-type mice 14 days before ONC to over-express ST6GAL1. Microglia activation was observed at 5dpc, while RGCs counting and anterograde labeling of regenerating axons were carried out at 14dpc.

Results: scRNA sequencing revealed that αRGCs expressed higher levels of sialyltransferases than other subtypes. Immunofluorescence confirmed that expression of ST6GAL1 and SNA in RGCs progressively and significantly decreased post-injury, with more ST6GAL1 found in αRGCs than non-αRGCs. 3Fax-PN effectively inhibited ST6GAL1, and the reduced level of sialylation exacerbated RGCs death and particularly increased the loss of αRGCs. Concurrently, the number of phagocytic microglia in the ganglion cell layer increased. Overexpression of ST6GAL1 in RGCs via AAV-St6gal1 transfection significantly preserved RGCs survival at 14dpc, and demonstrated robust axon regeneration at two weeks after injury.

Discussion: Polysialylation, considered an inhibitory signal, may modulate microglial phagocytosis of neurons. We hypothesize that the sialylation may protect αRGCs from phagocytosis by microglia, thereby enhancing their survival, and may also alleviate damage to other RGCs. Our preliminary results demonstrate that ST6GAL1 promotes RGC survival and axon regeneration following injury, potentially through the regulation of microglial phagocytosis. Further studies are ongoing to explore the mechanisms in greater detail.