Neuronal apoptosis, axon damage and synapse loss occur synchronously in acute ocular hypertension

Retinal ganglion cells (RGCs) apoptosis and their axon degeneration are pivotal features in glaucoma. Previous studies suggest that the process of RGCs soma degeneration is distinct from axon degeneration and that both of them lead to vision loss but separately. However, since a normal visual function relies on the integrity of axon, synapse and soma in the retina, a comprehensive understanding of the changes of these neuron components in glaucoma is desired. Therefore, in an acute ocular hypertension (AOH) model in mice, we systematically evaluated retinal neuron soma, axon and synapse alteration at certain time points. We found that ocular hypertension led to a progressive apoptosis of retinal neural cells which proceeded from peripheral to central retina in the wholemount, meanwhile, started in the ganglion cell layer (GCL) and spread to the inner nuclear layer (INL) and then the outer nuclear layer (ONL) as time went on. The type of apoptotic cells was identified as RGCs in GCL, amacrine cells in INL and cone photoreceptor cells in ONL. Axon degeneration was observed at the same time as soma degenerated and also progressed from peripheral to central retina. More interestingly, accumulation of neurofilament in the soma caused by axon transport failure was detected synchronously. We also found that presynaptic and postsynaptic vesicle proteins were downregulated. Taken together, these data support a view that retinal neuronal apoptosis happens not only in RGCs, but also other neurons in laminar layers. Axon damage and synapse loss occur synchronously with soma loss in AOH. The combination of these three parameters might facilitate a systematic evaluation of the disease progression and treatment strategies in glaucoma.