A key gap remains in our ability to develop successful treatment strategies to prevent photoreceptor (PR) loss and restore vision. To address this gap, we are proposing novel strategies to reprogram metabolism and boost PR survival. PRs have unique metabolic adaptations and utilize aerobic glycolysis to budget their metabolic needs based on nutrient availability, balancing the synthesis of amino acid, nucleotide and lipid precursors with energy generation. PRs perform aerobic glycolysis by expressing hexokinase 2 (HK2) and pyruvate kinase muscle 2 (PKM2). HK2, the first enzyme of glycolysis, acts as an intracellular rheostat, a unique non-enzymatic function that links metabolic status to survival by regulating apoptosis and autophagy. PKM2 is the gatekeeper of energy metabolism and controls aerobic glycolytic flux. HK2 expression is critical for the survival of PRs, as replacing HK2 with HK1 isoform increases apoptosis after stress. Furthermore, replacing low-activity PKM2 with its high-activity isoform PKM1 increases total PKM activity in PRs and boosts survival after nutrient deprivation. The over-arching hypothesis of this proposal is that metabolic reprogramming of PRs, by modulating HKs and PKMs, will enhance survival of stressed PRs, enzymatically by increasing energy generation via glycolysis, and non-enzymatically by inhibiting death signals during energy crisis. The objectives in this project are to: 1) utilize genetic and pharmacologic manipulation of PKM and HK function and prevent retinal detachment induced PR death by metabolic reprograming; and 2) identify non- enzymatic functions of HKs that regulate PR survival during experimental retinal detachment.
Aim 1 : To test the hypothesis that augmenting energy homeostasis by altering PKM function will enhance PR survival during stress. Our hypothesis predicts that increasing total PKM activity provides survival advantage during apoptotic stress by shifting PR metabolism to more efficiently generate ATP from limited energy substrates. These studies will measure glycolytic flux, ATP generation, and cell death in an acute PR stress model upon Pkm1 overexpression or pharmacologic activation of PKM2.
Aim 2 : To test the hypothesis that HK2 is the molecular rheostat that links metabolic status to PR apoptosis and autophagy. Our hypothesis predicts that HK2 links PR metabolic needs to survival and that HK2 to HK1 reprograming will decouple metabolic regulation of apoptosis and autophagy. These studies will identify the links between HK2 and key regulators of apoptosis and autophagy in PRs and will measure the effect of HK2 to HK1 reprogramming on glycolysis, biosynthesis, and PR cell death. Our approach is innovative as we will connect the unique energy metabolism of PRs directly to cell death regulation via manipulating the key mediators of aerobic glycolysis, i.e. PKM2 and HK2. The proposed research is significant in that it will provide critical information on how unique metabolic adaptations of PRs influence cell survival and lay the foundation for future studies exploring the connections between metabolism and PR survival in retinal diseases.
The proposed project is relevant to public health because the goal is to identify novel treatments to improve photoreceptor survival, thus preventing vision loss in many blinding diseases. Photoreceptors have a unique metabolism to address their high demand to meet visual processes, and metabolic dysfunction and energy crisis may be a unifying mechanism of photoreceptor cell death. Therapeutic strategies that target a unifying mechanism in photoreceptor death is expected to be effective for many retinal diseases and restore vision in millions of patients.
