Embryonic nutritional hyperglycemia decreases cell proliferation in the zebrafish retina

Diabetic retinopathy (DR) is one of the leading causes of blindness in the world. While there is a major focus on the study of juvenile/adult DR, the effects of hyperglycemia during early retinal development are less well studied. Recent works in embryonic zebrafish models of nutritional hyperglycemia revealed that hyperglycemia leads to decreased cell numbers of mature retinal cell types, which has been related to a modest increase in apoptotic cell death and altered cell differentiation (Singh et al. 2019; Titialii-Torres and Morris 2022). However, how embryonic hyperglycemia impacts cell proliferation in developing retinas remains still unknown. Here, we exposed zebrafish embryos to 50 mM glucose from 10 hours postfertilization (hpf) to 5 days postfertilization (dpf). First, we confirmed that hyperglycemia increases apoptotic death and decreases the rod and Müller glia population in the retina of 5 dpf zebrafish. Interestingly, the increase in cell death was mainly observed in the ciliary marginal zone (CMZ), where most of the proliferating cells are located. To analyze the impact of hyperglycemia in cell proliferation, mitotic activity was first quantified using pH3 immunolabeling, which revealed a significant decrease in mitotic cells in the retina (mainly in the CMZ) at 5 dpf. A significant decrease in cell proliferation in the outer nuclear and ganglion cell layers of the central retina in hyperglycemic animals was also detected using the proliferation marker PCNA. Overall, our results show that nutritional hyperglycemia decreases cellular proliferation in the developing retina, which could contribute significantly to the decline in the number of mature retinal cells.