Metabolic mechanisms in oxygen-induced retinopathy: findings from OIR resistant and susceptible mouse strains

Abstract

Purpose : We have previously demonstrated the systemic nature of oxygen-induced retinopathy (OIR) and identified the involvement of serine/one carbon metabolism and upregulation of glutamine-fueled anaplerosis in response to hyperoxia (Singh et. al. 2019 and 2020). In retinal endothelial cells under hyperoxic conditions we also reported the downregulation of the polyamine biosynthetic pathway and the upregulation of the polyamine oxidation pathway (Singh et. al. 2022). To evaluate the importance of these metabolic pathways in the pathogenesis of OIR, we compared them in the OIR resistant and susceptible mouse strains. Based on these findings, we propose a metabolic strategy to prevent OIR in Phase 1.

Methods : We used an established mouse model of oxygen-induced retinopathy (Smith et. al. 1994). Mice were euthanized on P12 and retinas removed. Retinas were extracted with trizol and then treated with DNase. RNA samples were sequenced by Novogene. All the in vivo experiments were performed as per IACUC approved protocols.
For the explant cultures, retinas were cultured in the media containing substrate labeled with stable isotopes for 24h. The labeling pattern of metabolites formed by the catabolism of [¹³C₈] octanoate and [¹³C₁₆] palmitate was measured on a GCMS.

Results : We demonstrate that the BALB/cByJ and C57BL/6J mouse strains differ in their anabolic machinery. Serine-one carbon and polyamine biosynthesis genes showed lower expression, and polyamine degradation enzymes showed higher expression in OIR susceptible retina as compared to OIR resistant retina, when exposed to hyperoxia. We also determined that the retina can use octanoate to replenish TCA cycle metabolites. Additionally, hyperoxia upregulates the entry of carbon from medium-chain and long-chain fatty acids in the cultured retina explants, reversing glutamine-fueled anaplerosis.

Conclusions : Our findings demonstrate oxygen-dependent changes in anabolic pathways. Hyperoxia upregulates β-oxidation of octanoate and palmitate to replenishing TCA, implying these fatty acids can help replenish depleted pools of glutamate and glutamine, and may help preserve biosynthetic precursors in the developing retina. Octanoate accounts for 13% of the free fatty acids in the human body (Ebert et. al. 2003). Based on our findings, we speculate that a non-nitrogenous β-oxidation or anaplerotic strategy may prevent oxygen-induced retinopathy.

This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.