Disrupting Serine Synthesis for Pediatric Medulloblastoma Therapy Restricted; Files Only

Abstract

Medulloblastomas, the most prevalent malignant brain tumor in children, originate from the cerebellum and pose significant challenges due to their propensity to metastasize through the central nervous system. One of the most common types of neurons that resides in the cerebellum, the cerebellar granular neurons, is primarily regulated by the Sonic Hedgehog pathway. Dysregulation of this pathway has been known to contribute to the development of medulloblastomas. The genes, Phgdh and Shmt1, are expressed during the SHH-driven proliferation, and their patterns of expression suggest that they play an important role in the pathogenesis of tumors. This study sought to 1) understand whether SHH induces PHGDH and SHMT1 and 2) how these genes could affect medulloblastoma growth. Mice were bred to induce a mutant of the Smoothened (SMO) protein, a key player in the SHH pathway, resulting in the development of SHH medulloblastomas, termed G-Smo mice. We utilized Western blotting to quantify PHGDH and SHMT1 protein levels in G-Smo mice injected with vismodegib, an inhibitor of the SHH pathway. To understand how these genes could alter tumor growth, we compared tumors in 1) G-Smo mice, 2) G-Smo/Shmt1-KO, 3) G-Smo/Phgdh f/f, and 4) G-Smo/P&S-KO. We sectioned and immunostained brains with tumors using antibodies for the proliferation marker, phosphorylated-Rb, apoptosis marker, cC3, and differentiation marker, NEUROD1. The stained cells were annotated and counted using Tissue Studio. Our study found that SHH induces SHMT1 expression. We also found that there were significantly higher proliferative cells in G-Smo Phgdh f/f, SHMT1 -/- compared to G-Smo mice and significantly fewer differentiated cells in G-Smo Phgdh f/f mice compared to G-Smo controls. There were no significant differences in apoptotic cells between genotypes. Further investigation into these mechanisms of tumor metabolism will allow for the development of novel, targeted therapies for medulloblastomas.   

Table of Contents

Introduction..............................................................................................................1

Methods...................................................................................................................8

Results.....................................................................................................................10

Discussion................................................................................................................11

Conclusions............................................................................................................14

References...............................................................................................................16

Figures.....................................................................................................................20

Figure 1a Sonic Hedgehog Signaling Pathway ………….……….……….……….……...3

Figure 1b Serine Synthesis Pathway …………….……….……….……….………..….5

Figure 2 Comparing PHGDH and SHMT1 protein expression during Sonic Hedgehog Inhibition in            wild-type and G-Smo

mice ……….……….……….……….……….……..….20

Figure 3 NEUROD1, PhosphoRb, and Cleaved-Caspase 3 Cell Counts in G-Smo mice ……….. .21

Figure 4 Apoptosis staining in Phgdh and Shmt1 deleted mice ……….……….………...…. 22

Figure 5 Differentiation in Phgdh and Shmt1 deleted mice ……….……….……….……….22

Figure 6 Proliferation staining in Phgdh and Shmt1 deleted mice ……….……….…………..23

About this Honors Thesis

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School	Emory College
Department	Neuroscience and Behavioral Biology
Degree	B.S.
Submission	Honors Thesis
Language	English
Research Field	Biology, Neuroscience
Keyword	Cancer Biology Medulloblastoma
Committee Chair / Thesis Advisor	Gershon, Timothy, Emory University
Committee Members	Cafferty, Patrick, Emory University Roeser, Andrea, Emory University

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