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Raju V S Rajala, Christopher Kooker, Yuhong Wang, Ammaji Rajala; Pyruvate Kinase M2: Function, Regulation and Role in Rod Photoreceptor cells. Invest. Ophthalmol. Vis. Sci. 2017;58(8):3576.
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© ARVO (1962-2015); The Authors (2016-present)
Pyruvate kinase M2 (PKM2) is a critical enzyme in glycolysis that redirects glucose for anabolic processes instead of oxidative phosphorylation, via tyrosine phosphorylation through growth factor signaling in tumor cells. We recently reported that PKM2 is the major isoform in photoreceptor cells and tyrosine phosphorylation of PKM2 is light-dependent. The biological role of PKM2 in photoreceptor cells is unknown. In the present study, we examined the functional role of PKM2 in rod photoreceptor cells, explored its role in the expression of glycolytic and lipogenic enzymes, and studied its effect on photoreceptor structure and function.
We bred mice expressing Cre-recombinase in rods to mice with a floxed PKM2 gene, generating offspring with a conditional deletion of PKM2 in rod photoreceptors. Cre recombinase expression, PKM2, PKM1, and several rod photoreceptor-specific protein markers were examined by immunoblot and immunohistochemical analysis. Structural changes were determined by hematoxylin and eosin staining of retinal sections and function was measured by electroretinography. Real-time PCR was employed to examine the gene expression of glycolytic and lipogenic enzymes in wild-type and PKM2 knockout mice.
Cre-expression was properly targeted to rod photoreceptor nuclei. Disruption of PKM2 specifically in rods produced an absence of PKM2 expression. Loss of PKM2 did not alter photoreceptor protein expression or rod photoreceptor integrity at 1 month; however, we found decreased scotopic b-wave amplitudes at 2 months. In addition, PKM2 deletion resulted in a compensatory increase in PKM1 expression. We found reduced gene expression of lipogenic enzymes, but not glycolytic enzymes, in PKM2 knockout mice.
Our findings clearly demonstrate that loss of PKM2 expression upregulates PKM1 expression. These results also indicate that PKM2-deficient retinas show reduced lipogenic gene expression, suggesting altered lipid metabolism in photoreceptor cells.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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