Research
Single-Cell Sequencing
Cellular heterogeneity in cancers may underlie differences in treatment responses. Our lab is interested in cellular diversity in medulloblastoma, one of the most common malignant pediatric brain tumor, to understand how cell types within tumors contribute to treatment failure. Medulloblastomas driven by SHH hyperactivation arise from progenitors present during normal cerebellar development. We have sequenced normal cerebella during the peak of postnatal proliferation to establish the normal cell types present during development. We have also sequenced medulloblastomas generated in transgenic mouse models, which closely resemble human medulloblastomas and recapitulate therapy failure observed in patients. Our data can be found under the following link, where users can search for gene expression within our wild-type and tumor datasets to further explore diversity in cerebellar development and medulloblastoma. We hope that this may become a useful tool for researchers to explore gene expression patterns during development and in medulloblastomas with and without treatment.
Aerobic glycolysis in development and tumor formation
Medulloblastomas, like many cancers, depend on different metabolic patterns to support tumor growth. Many of these metabolic processes, including increased lipogenesis and aerobic glycolysis, are remarkably similar to the metabolic programs of neural progenitors. Thus by targeting lipogenesis and glycolysis, we may create more effective treatments for cancer.
Metabolic enzymes such as Hexokinase 2 (Hk2) and Pyruvate kinase M2 (PkM2) are vital in supporting physiological neural progenitor growth of neural progenitor and malignant tumor growth. Although Hk2 and PkM2 are known to be important for growth, the molecular mechanisms underlying metabolic transformation are not well understood. We study how medulloblastoma tumors are able to co-opt these developmental metabolic processes in the hopes of identifying novel targets for anti-tumor therapy.
Anti-apoptotic mechanisms in development and tumor growth
Cerebellar development depends on the interplay between postnatal proliferation of cerebellar granule neuron progenitors (CGNPs) and apoptosis. These opposing processes combine to regulate cerebellar growth. Disruptions in either proliferation or apoptosis can lead to severe neurodevelopmental disorders such as cerebellar hypoplasia or medulloblastoma, the most common malignant pediatric brain tumor. The specific mechanisms regulating these processes in CGNPs is currently unknown.
CGNPs proliferate in the cerebellum in response to Sonic hedgehog (Shh) secreted by nearby neurons, giving rise to the largest population of neurons in the central nervous system. We have found that CGNPs are specially primed for apoptosis and that capacity is conserved in medulloblastoma. The anti-apoptotic protein Bcl-xL normally prevents inappropriate cell death in proliferating CGNPs. Conditional deletion of Bcl-xL in CGNPs induces apoptosis, resulting in cerebellar hypoplasia. Based on these findings, we are investigating whether Shh signaling exerts an anti-apoptotic effect in proliferating CGNPs alongside Bcl-xL and whether the Bcl-xL homolog Mcl-1 also mediates this effect.
Wnt signaling in development and tumor growth
One of the aims in our lab is to study the interplay between cerebellar hypoplasia and medulloblastoma. Both are severe neurological disorders that arise from disrupted neural progenitor regulation. We believe that through understanding normal cerebellar development and the mechanisms behind cerebellar hypoplasia, we’ll be able to produce more targeted, less toxic treatments for medulloblastoma.
Previous studies have shown that GSK-3, an essential kinase in the Wnt signaling pathway, is required to support cortical progenitor proliferation. Deletion of both isoforms of GSK-3 resulted in cerebral hyperplasia, demonstrating that GSK-3 is required to prevent progenitor overgrowth. In light of these studies, we examined whether GSK-3 deletion in the cerebellum would produce hyperplasia and promote medulloblastoma tumorigenesis. We have since found that GSK-3 is required to promote cerebellar progenitor proliferation and that deletion of both isoforms of this gene caused severe cerebellar hypoplasia. We currently aim to understand how GSK-3 regulates cerebellar progenitor proliferation and how GSK-3 can produce opposite effects in brain growth in the cerebrum and cerebellum. Understanding the role GSK-3 plays in cerebellar development will help us develop better medulloblastoma therapies.
DNA repair and apoptotic mechanisms in tumor growth
Microcephaly and medulloblastoma are severe neurological disorders that may result from mutations compromising genomic stability. Ataxia telangiectasia and Rad3-related protein (Atr) normally mitigates proliferation-associated DNA damage and mutations in Atr have been implicated in Seckel syndrome microcephaly. Conditional Atr deletion in mice replicates the microcephalic phenotype seen in Seckel Syndrome patients but particularly affects the cerebellum. Although Atr is known as an important DNA repair protein and its role in microcephaly is well-documented, the precise mechanisms governing DNA damage during growth are unknown.
We have deleted Atr specifically in the cerebellum and found that cerebellar neural progenitors (CGNPs) accumulate DNA damage throughout proliferation, inducing widespread apoptosis. These Atr-deleted CGNPs also exhibited chromosomal abnormalities which became more severe when apoptosis was blocked. More importantly, Atr deletion in medulloblastoma-prone mice prevented tumor formation.