Abstract
Pyruvate kinase M2 (PKM2) is a glycolytic enzyme that is expressed in cancer cells. Its role in tumor metabolism is not definitively established, but investigators have suggested that regulation of PKM2 activity can cause accumulation of glycolytic intermediates and increase flux through the pentose phosphate pathway. Recent evidence suggests that PKM2 also may have non-metabolic functions, including as a transcriptional co-activator in gene regulation. We reported previously that PKM2 is abundant in photoreceptor cells in mouse retinas. In the present study, we conditionally deleted PKM2 (rod-cre PKM2-KO) in rod photoreceptors and found that the absence of PKM2 causes increased expression of PKM1 in rods. Analysis of metabolic flux from U-13C glucose shows that rod-cre PKM2-KO retinas accumulate glycolytic intermediates, consistent with an overall reduction in the amount of pyruvate kinase activity. Rod-cre PKM2-KO mice also have an increased NADPH availability could favor lipid synthesis, but we found no difference in phospholipid synthesis between rod-cre PKM2 KO and PKM2-positive controls. As rod-cre PKM2-KO mice aged, we observed a significant loss of rod function, reduced thickness of the photoreceptor outer segment layer, and reduced expression of photoreceptor proteins, including PDE6β. The rod-cre PKM2-KO retinas showed greater TUNEL staining than wild-type retinas, indicating a slow retinal degeneration. In vitro analysis showed that PKM2 can regulate transcriptional activity from the PDE6β promoter in vitro. Our findings indicate that both the metabolic and transcriptional regulatory functions of PKM2 may contribute to photoreceptor structure, function, and viability.
Highlights
Unlike normal cells, which use glucose for the synthesis of ATP through oxidative phosphorylation, cancer cells utilize glucose to synthesize macromolecular building blocks, such as lipids, proteins, and nucleic acids[1,2]
Conditional deletion of pyruvate kinase M2 (PKM2) in rod photoreceptor cells To determine the functional role of PKM2 in rod photoreceptor cells, we mated the exon 10 floxed PKM2 mice with a transgenic mouse line expressing Crerecombinase under the control of a 4 kb mouse rod opsin promoter (i75-Cre)[13]
We found that opsin properly localized to rod outer segment (OS) (ROSs) in both PKM2 wild-type (Fig. 1B,C) and rod-cre PKM2-KO mice (Fig. 1F,G), suggesting that there was no indication of rod photoreceptor degeneration or mislocalization of opsin in mice at 2 months of age
Summary
Unlike normal cells, which use glucose for the synthesis of ATP through oxidative phosphorylation, cancer cells utilize glucose to synthesize macromolecular building blocks, such as lipids, proteins, and nucleic acids[1,2]. This fuel redirection is thought to be mediated by pyruvate kinase M2 (PKM2), a glycolytic enzyme that dephosphorylates phosphoenolpyruvate (PEP) to pyruvate, the last step in glycolysis[3]. Photoreceptors shed 10% of their outer segment (OS) distal tips to maintain their length for proper function As a result, these cells must synthesize nucleic acids for mRNA production, and lipids
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
