Abstract
Purpose :
Proliferative vitreoretinopathy (PVR) represents the greatest risk of failure in retinal detachment repair and portends poor visual outcomes. PVR is triggered by fibrovascular proliferation of retinal pigment epithelium (RPE) on the surface of the retina after the RPE undergoes an epithelial-to-mesenchymal transition (EMT). RPE EMT is accompanied by metabolic reprogramming favoring glycolysis. Pyruvate kinase M2 (PKM2) is a key enzyme of glycolysis whose non-enzymatic functions have been implicated in the glycolytic reprogramming and EMT of other cell types. The importance of PKM2 in RPE EMT and PVR is unknown. Here we sought to understand the role of PKM2-driven glycolysis in triggering RPE EMT, and how pharmacologic modulation of PKM2 alters RPE EMT.
Methods :
To recapitulate loss of cell contact seen early in the PVR process and induce EMT, primary human fetal RPE (hfRPE) were seeded at 10% density. Immunohistochemistry, western blot, and RT-PCR were utilized to assess the expression of EMT markers and phosphorylation of PKM2 in this in vitro model of PVR. The impact of small molecule (ML-265) pharmacologic modulation of PKM2 on the metabolic profile of hfRPE EMT was evaluated with RT-PCR. The therapeutic potential of ML-265 in attenuating RPE EMT was evaluated in several assays.
Results :
HfRPE demonstrated a fibroblastic-like phenotype in this cell culture model of PVR with induction of EMT markers including vimentin, N-cadherin, and TWIST1. PKM2 S37 phosphorylation was increased 7-fold while Y105 phosphorylation was decreased 2.5-fold in the dedifferentiated, fibroblastic-like hfRPE compared to differentiated hfRPE. PKM2 S37 phosphorylation is important for PKM2 dimerization, nuclear translocation, and regulation of glycolytic gene expression via transcriptional co-activation of β-catenin or Hif-1α. Accordingly, the expression of Hif-1α, as well as downstream genes of β-catenin and Hif-1α, such as CCND1, GLUT1, and PDK1, were upregulated in hfRPE EMT. Finally, treatment with ML-265, an allosteric modulator of PKM2 that decreases glycolytic reprogramming, resulted in reduced hfRPE EMT in multiple assays.
Conclusions :
This study suggests a critical role of PKM2 in RPE EMT, the triggering event for PVR. Pharmacologic modulation of PKM2 to halt EMT-driven metabolic reprogramming may be an innovative therapeutic strategy in the prevention of PVR.
This is a 2021 ARVO Annual Meeting abstract.