PHGDH supports liver ceramide synthesis and sustains lipid homeostasis

Yun Pyo Kang,Min Liu,Bo-Hyun Choi,James J Saller,Aimee Falzone,Paloma González-Sánchez,Jonathan L Coloff,Gina M DeNicola,Florian A Karreth

doi:10.1186/s40170-020-00212-x

Abstract

Backgroundd-3-phosphoglycerate dehydrogenase (PHGDH), which encodes the first enzyme in serine biosynthesis, is overexpressed in human cancers and has been proposed as a drug target. However, whether PHGDH is critical for the proliferation or homeostasis of tissues following the postnatal period is unknown.MethodsTo study PHGDH inhibition in adult animals, we developed a knock-in mouse model harboring a PHGDH shRNA under the control of a doxycycline-inducible promoter. With this model, PHGDH depletion can be globally induced in adult animals, while sparing the brain due to poor doxycycline delivery.ResultsWe found that PHGDH depletion is well tolerated, and no overt phenotypes were observed in multiple highly proliferative cell compartments. Further, despite detectable knockdown and impaired serine synthesis, liver and pancreatic functions were normal. Interestingly, diminished PHGDH expression reduced liver serine and ceramide levels without increasing the levels of deoxysphingolipids. Further, liver triacylglycerol profiles were altered, with an accumulation of longer chain, polyunsaturated tails upon PHGDH knockdown.ConclusionsThese results suggest that dietary serine is adequate to support the function of healthy, adult murine tissues, but PHGDH-derived serine supports liver ceramide synthesis and sustains general lipid homeostasis.

Highlights

D-3-phosphoglycerate dehydrogenase (PHGDH), which encodes the first enzyme in serine biosynthesis, is overexpressed in human cancers and has been proposed as a drug target
Generation of an inducible model for systemic PHGDH knockdown In order to evaluate the requirement for serine biosynthesis in normal, proliferating adult tissues, we generated a mouse model in which an Small hairpin RNA (shRNA) targeting PHGDH is linked to GFP and expressed in a doxycycline-inducible manner (Fig. 1a)
Because doxycycline levels achieved in the mouse brain are an order of magnitude lower than in plasma [23], this model is expected to spare the brain and avoid the previously reported brain toxicity associated with PHGDH knockout. shRNA, rtTA3 dual allele mice were placed on a 200 ppm doxycycline-containing diet containing serine and glycine

Summary

Introduction

D-3-phosphoglycerate dehydrogenase (PHGDH), which encodes the first enzyme in serine biosynthesis, is overexpressed in human cancers and has been proposed as a drug target. PHGDH activity is increased in many cancer cells as a consequence of genomic amplification, transcriptional upregulation, posttranslational modification, and allosteric regulation [7, 9, 15, 22, 24, 32, 34, 40]. Whole animal PHGDH deletion is embryonic lethal in mice as a consequence of overall developmental retardation and brain defects [48]. Targeted deletion of PHGDH in endothelial cells is lethal (2020) 8:6 shortly after birth as a consequence of vascular defects due to compromised heme synthesis and mitochondrial function [42]. Whether PHGDH is critical for the proliferation or homeostasis of other tissues following the postnatal period is unknown

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Discussion

Conclusion