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Yuan Zhu

The brain tumor field moves forward with new findings and a research grant

Yuan Zhu

Yuan Zhu, Ph.D., and other experts completed new research findings evaluating the effects of manipulating the growth-promoting signaling pathways in brain tumors associated with adults and children.

This month, experts at Children’s National Health System made great strides in brain tumor research, specifically in gliomas, glioblastomas and medulloblastomas. Led by Yuan Zhu, Ph.D., the scientific director and Gilbert Endowed Professor of the Gilbert Family Neurofibromatosis Institute and Center for Cancer and Immunology Research at Children’s National, the team completed new research findings evaluating the effects of manipulating the growth-promoting signaling pathways in brain tumors associated with adults and children. Dr. Zhu’s research was recently published in Cell Reports and he was also awarded a U.S. Department of Defense (DoD) grant to gain a better understanding of how low-grade gliomas form. Together, this work moves the needle on developing more effective treatments for these debilitating and life-threatening tumors.

The study

In his recently published paper, Dr. Zhu and his colleagues, including Drs. Seckin Akgul and Yinghua Li, studied glioblastomas, the most common brain tumor in adults, and medulloblastomas, the most common brain tumor found in children, in genetically engineered experimental models. Dr. Zhu found that when they removed the p53 gene (the most commonly mutated tumor suppressor gene in human cancers) in the experimental model’s brain, most developed malignant gliomas and glioblastomas, while Sonic Hedgehog (SHH)-subtype (SHH) medulloblastomas were also observed. They further suppressed the Rictor/mTorc2 molecular pathway that is known in the regulation of tumor growth. This action greatly reduced the incidence of malignant gliomas and extended the survival of the models, validating the concept that Rictor/mTorc2 could be a viable drug target for this lethal brain cancer in adults.

The study also found that the same Rictor/mTorc2 molecular pathway serves the opposite function in SHH medulloblastoma formation, acting as a tumor suppressor. Findings suggest that if the same drug treatment is used for treating SHH medulloblastoma in children, it could potentially have an adverse effect and promote growth of the tumors.

Ultimately, the study demonstrates that Rictor/mTORC2 has opposing functions in glioblastomas in adults and SHH medulloblastomas in children. While drug therapies targeting Rictor/mTORC2 may be successful in adults, the findings reveal the risks of treating children with pediatric brain tumors when using the same therapies.

The grant

Continuing the study of brain tumors, Dr. Zhu recently received a $575,000 grant from DoD to research benign gliomas, with the hope of gaining a greater understanding of how the tumors form. Low-grade gliomas, or benign brain tumors, are the most common brain tumors in children. While not lethal like their high-grade counterpart, these tumors can lead to significant neurological defects, permanently impacting a child’s quality of life. Most commonly, the tumor can impair vision, often leading to blindness.

Since the tumors only occur in children under the age of eight, Dr. Zhu believes they are linked to neural stem or progenitor cells that exist in the optic nerve only during development, or when children are under eight-years-old. To test if his hypothesis is correct, Dr. Zhu will develop a preclinical model that mimics human brain tumors to study the development of the optic nerve. If his theory proves correct, Dr. Zhu’s long-term goal is to develop a strategy that prevents the tumor formation from ever occurring, ultimately preventing vision loss in children. The grant begins in July and will run for three years.

 

Coenzyme Q10

Supplement might help kidney disease

Coenzyme Q10

A research team was able to “rescue” phenotypes caused by silencing the fly CoQ2 gene by providing nephrocytes with a normal human CoQ2 gene, as well as by providing flies with Q10, a popular supplement.

A new study led by Children’s National research scientists shows that coenzyme Q10 (CoQ10), a popular over-the-counter supplement sold for pennies a dose, could alleviate genetic problems that affect kidney function. The work, done in genetically modified fruit flies — a common model for human genetic diseases since people and fruit flies share a majority of genes — could give hope to human patients with problems in the same genetic pathway.

The new study, published April 20 by Journal of the American Society of Nephrology, focuses on genes the fly uses to create CoQ10.

“Transgenic Drosophila that carry mutations in this critical pathway are a clinically relevant model to shed light on the genetic mutations that underlie severe kidney disease in humans, and they could be instrumental for testing novel therapies for rare diseases, such as focal segmental glomerulosclerosis (FSGS), that currently lack treatment options,” says Zhe Han, Ph.D., principal investigator and associate professor in the Center for Cancer & Immunology Research at Children’s National and senior study author.

Nephrotic syndrome (NS) is a cluster of symptoms that signal kidney damage, including excess protein in the urine, low protein levels in blood, swelling and elevated cholesterol. The version of NS that is resistant to steroids is a major cause of end stage renal disease. Of the more than 40 genes that cause genetic kidney disease, the research team concentrated on mutations in genes involved in the biosynthesis of CoQ10, an important antioxidant that protects the cell against damage from reactive oxygen.

Drosophila pericardial nephrocytes perform renal cell functions including filtering of hemolymph (the fly’s version of blood), recycling of low molecular weight proteins and sequestration of filtered toxins. Nephrocytes closely resemble, in structure and function, the podocytes of the human kidney.  The research team tailor-made a Drosophila model to perform the first systematic in vivo study to assess the roles of CoQ10 pathway genes in renal cell health and kidney function.

One by one, they silenced the function of all CoQ genes in nephrocytes. If any individual gene’s function was silenced, fruit flies died prematurely. But silencing three specific genes in the pathway associated with NS in humans – Coq2, Coq6 and Coq8 – resulted in abnormal localization of slit diaphragm structures, the most important of the kidney’s three filtration layers; collapse of membrane channel networks surrounding the cell; and increased numbers of abnormal mitochondria with deformed inner membrane structure.

Journal of the American Society of Nephrology September 2017 cover

The flies also experienced a nearly three-fold increase in levels of reactive oxygen, which the study authors say is a sufficient degree of oxidative stress to cause cellular injury and to impair function – especially to the mitochondrial inner membrane. Cells rely on properly functioning mitochondria, the cell’s powerhouse, to convert energy from food into a useful form. Impaired mitochondrial structure is linked to pathogenic kidney disease.

The research team was able to “rescue” phenotypes caused by silencing the fly CoQ2 gene by providing nephrocytes with a normal human CoQ2 gene, as well as by providing flies with Q10, a readily available dietary supplement. Conversely, a mutant human CoQ2 gene from an patient with FSGS failed to rescue, providing evidence in support of that particular CoQ2 gene mutation causing the FSGS. The finding also indicated that the patient could benefit from Q10 supplementation.

“This represents a benchmark for precision medicine,” Han adds. “Our gene-replacement approach silenced the fly homolog in the tissue of interest – here, the kidney cells – and provided a human gene to supply the silenced function. When we use a human gene carrying a mutation from a patient for this assay, we can discover precisely how a specific mutation – in many cases only a single amino acid change – might lead to severe disease. We can then use this personalized fly model, carrying a patient-derived mutation, to perform drug testing and screening to find and test potential treatments. This is how I envision using the fruit fly to facilitate precision medicine.”

Related resources:
News release: Drosophila effectively models human genes responsible for genetic kidney diseases
Video: Using the Drosophila model to learn more about disease in humans