Differential Responses of Neural Retina Progenitor Populations to Chronic Hyperglycemia

Abstract

Diabetic retinopathy is a frequent complication of longstanding diabetes, which comprises a complex interplay of microvascular abnormalities and neurodegeneration. Zebrafish harboring a homozygous mutation in the pancreatic transcription factor pdx1 display a diabetic phenotype with survival into adulthood, and are therefore uniquely suitable among zebrafish models for studying pathologies associated with persistent diabetic conditions. We have previously shown that, starting at three months of age, pdx1 mutants exhibit not only vascular but also neuro-retinal pathologies manifesting as photoreceptor dysfunction and loss, similar to human diabetic retinopathy. Here, we further characterize injury and regenerative responses and examine the effects on progenitor cell populations. Consistent with a negative impact of hyperglycemia on neurogenesis, stem cells of the ciliary marginal zone show an exacerbation of aging-related proliferative decline. In contrast to the robust Müller glial cell proliferation seen following acute retinal injury, the pdx1 mutant shows replenishment of both rod and cone photoreceptors from slow-cycling, neurod-expressing progenitors which first accumulate in the inner nuclear layer. Overall, we demonstrate a diabetic retinopathy model which shows pathological features of the human disease evolving alongside an ongoing restorative process that replaces lost photoreceptors, at the same time suggesting an unappreciated phenotypic continuum between multipotent and photoreceptor-committed progenitors.

Embryonic nutritional hyperglycemia decreases cell proliferation in the zebrafish retina

“…However, they analyzed this by using BrdU labeling, which would also be retained by differentiated cells after exiting the cell cycle. Similar observations have been reported in adult mutant models of DR in zebra sh using EdU labeling (Schmitner et al 2021), which, as BrdU, would be also retained by differentiated/mature cells. Thus, our results show for the rst time by using speci c markers of mitotic activity and cell proliferation that nutritional hyperglycemia decreases cell proliferation in progenitor cells of the developing zebra sh retina, which could be an important contributor to the decrease in the number of mature retinal cell types.…”

“…Although DR was initially considered a vascular disease, more recent research has shown that it also is a neurodegenerative disease affecting the neural retina and that cellular changes in the retina precede the clinical features (Cai and McGinnis 2016). DR research using animal models of diabetes/hyperglycemia mainly involves the study of juvenile/adult DR (see Cai and McGinnis 2016), which includes the use of juvenile/adult zebra sh models of DR (Ali et al 2020; Wang et al 2020;Wiggenhauser et al 2020;Schmitner et al 2021). However, the effects of hyperglycemia during early retinal development have been less studied.…”

Retina regeneration: lessons from vertebrates

“…In the case of photoreceptor-specific ablation, when a retinal injury is chronic or not strong enough to activate Müller glia, the rod progenitors respond to damage [ 96 , 97 ]. In the diabetic model of zebrafish with pdx1 homozygous mutation rod and cone cells regenerate from slowly dividing neurod: GFP expressing progenitors with their origin in ONL [ 98 ]. The pancreatic and duodenal homeobox 1 ( pdx1 ) mutant fish represents diabetic features with reduced beta cells and insulin levels along with elevated glucose levels.…”

Beyond Genetics: The Role of Metabolism in Photoreceptor Survival, Development and Repair

“…Given the central role of metabolism, the potential impact of diet and dietary supplements on Müller glia regenerative response has, to the best of our knowledge, not been reported. Interestingly, in zebrafish, in which Müller glia are normally regenerative, Müller glia display a reduced capacity to proliferate and generate new neurons in a genetic model of chronic diabetes ( Schmitner et al, 2021 ). Moreover, altering metabolism in this diabetic model inactivates Notch signaling, an essential component of the regenerative response in the zebrafish retina.…”

“…Moreover, altering metabolism in this diabetic model inactivates Notch signaling, an essential component of the regenerative response in the zebrafish retina. It is important to note, however, that metabolic changes associated with chronic disease are not necessarily directly comparable to changes observed in acute injury models ( Schmitner et al, 2021 ). In the rat, a recent study found that high glucose exposure induces oxidative stress in retinal Müller glia in vitro , and identified Nrf2 as a critical transcription factor in this response ( Albert-Garay et al, 2022 ).…”