Abstract
Purpose :
Pyruvate kinase M2 (PKM2) and Lactate dehydrogenase A (LDHA) play pivotal roles in controlling aerobic glycolysis within retinal photoreceptor cells (PR). Much like tumor cells, PR cells divert glucose towards anabolic pathways instead of oxidative phosphorylation. Our prior research has demonstrated that PKM2 and LDHA are primarily expressed in PR cells, and the deletion of these proteins individually leads to age-related degeneration of photoreceptors. In this study, we investigate the collective impact of losing both PKM2 and LDHA on the structure, function, and metabolism of photoreceptor cells within the retina.
Methods :
We generated PKM2/LDHA double knockout (DKO) mice under the control of a retina-specific promoter. Morphological and functional studies were conducted on these mice at 6 and 48 weeks. Immunoblots and immunohistochemical analyses were performed with rhodopsin, rod arrestin, M-opsin, cone arrestin, PKM2, LDHA, PKM1, glial fibrillary acidic protein (GFAP), glutamine synthetase (GS), and measured steady-state levels of metabolites. We used quantitative RT-PCR to assess the expression levels of phosphoenolpyruvate carboxykinase (Pepck), the rate-limiting enzyme in gluconeogenesis, and phosphoglycerate dehydrogenase (Phgdh) in DKO mice.
Results :
The DKO mice exhibited the loss of PKM2/LDHA in PR cells; however, we did not observe any significant difference in morphology and rod and cone function, even up to 48 weeks. Consistent with structure and function preservation, there were no significant differences in the expression of rhodopsin, rod arrestin, M-opsin, and cone arrestin. Loss of PKM2/LDHA resulted in the expression of PKM1 in PR cells. We found significantly reduced levels of Pepck and increased levels of Phgdh in DKO compared to wild-type mice. Steady-state metabolites indicated that DKO mice show increased levels of 3-phosphoglycerate, creatinine, acetyl-coA, nicotinamide riboside (NAD), and phosphoenolpyruvate.
Conclusions :
The increased levels of PKM1 may contribute to the resilience of PR in DKO mice, acting as a regulator of aerobic glycolysis. Surprisingly, the simultaneous loss of PKM2 and LDHA did not negatively impact the structure and function of PR cells. This suggests that manipulating enzymes involved in aerobic glycolysis could be a potential therapeutic strategy for promoting the survival of photoreceptors in retinal diseases.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.