Probing the Endocytic Network in Alzheimer’s Disease using Human Neuronal Models
Alzheimer's disease (AD) is a devastating neurodegenerative disorder that is the most common cause of dementia in the elderly and is a tremendous socioeconomic burden. Stem cells derived from human patients can help us discover new therapeutics for AD because individual genetic background is captured in a dish and stem cells can be differentiated into neurons, a relevant cell type to analyze molecular features. My proposal will test whether genes identified with AD risk confer measurable laboratory read-outs characteristic of AD in neurons grown in the laboratory. In particular, I will focus on a particular cellular pathway, the endosomal network, which may become dysfunctional in AD before amyloid and tau deposition are reported.
The overall goal of my project is to use stem cell technology to better understand pathogenic events that may occur early on in neurons that could represent novel therapeutic targets for AD. To accomplish this goal, I will generate human neurons in the lab from patient-derived induced pluripotent stem cells (iPSCs). This powerful technology allows us to capture a patient's unique genetic background in a cell culture dish and derive a relevant human cell type (ie, neurons) to understand cellular processes that might be dysfunctional. In this case, we will study how proteins are trafficked into and around the neurons in a process called endocytosis. We hypothesize that defects in endocytosis may occur upstream of amyloid beta (Aβ) and phosphorylated tau (phospho-tau, or ptau) pathology; thus this cellular pathway may represent an early and novel therapeutic target for AD.
This project will pursue two specific aims: First we will test whether loss of key regulators of endocytosis lead to detectable abnormalities in neurons. To do this, we will use genome engineering techniques to systematically knock-out five receptors that function in the endocytic pathway in iPSCs. We will test whether neurons lacking these receptors have functional deficits and increased levels of Aβ and pTau. Second we have identified patients with AD who have potentially pathogenic variants in one of these receptors, a gene called SORL1. SORL1 is a key regulator of trafficking Aβ and tau through the endosomal network. Using skin cells from these patients, we both generate iPSCs and differentiate neurons, as well as directly convert the skin fibroblast to a neuron, in a process called direct conversion. The iPSC-derived neurons are considered embryonic-like due to the cellular reprograming that happens during their generation. Directly converted neurons maintain the cellular age of the subject from whom the fibroblasts were taken. These experiments will test whether dysfunction in the endocytic network due to variation in SORL1 is present in young neurons and if it is enhanced in neurons that are more indicative of patient age. Together, these experiments will help elucidate the role of SORL1 and related receptors in endocytic dysfunction in AD, and also determine if this pathway is a valid early target for therapeutic intervention.
About the Researcher
My doctoral training in molecular and cellular biology was completed at the University of Washington in June 2009, under the supervision of Dr. Albert R. La Spada. My PhD thesis centered on the role of neuronal autophagy in response to polyglutamine-expanded proteins, a class of mutations that result in inherited neurodegenerative disease. My work resulted in one of the first characterizations of autophagy activation in mammalian neurons and was the first to show a protective role for this mechanism in the polyglutamine disorder known as spinal and bulbar muscular atrophy. I pursued postdoctoral training in the lab of Dr. Lawrence S.B. Goldstein at the University of California, San Diego, specifically to learn stem cell biology and work on neurodegenerative disease in a human system. In the Goldstein lab, in a BrightFocus-supported fellowship, I generated hiPSCs from a cohort of late-onset, AD patients and controls and investigated the effects of a common risk haplotype in the SORL1 gene, which has been associated with AD in population studies. I reasoned that a low- to moderate-effect risk gene would yield detectable biochemical phenotypes in purified hiPSC-derived neurons. My work demonstrated that cell lines harboring risk variants showed a differential effect on SORL1 gene expression after stimulation with neurotrophic factors, and that this directly corresponded to the amount of amyloid beta detected from neuronal cell cultures. I started my independent laboratory at the University of Washington in July of 2016. My current research focuses in two main areas: how genetic risk in endosomal trafficking genes contributes to cellular AD phenotypes in vitro; and how neuronal maturity, function, and age interact to prevent or promote AD pathogenesis in human neurons.
I was first introduced to the field of neurodegenerative disease research over 15 years ago, during one of my first experiences as a summer intern in a lab. I became fascinated with the complexity of the brain and the beauty of looking at neurons in the microscope. To me, watching these beautiful cells dying in degenerative conditions was almost as sad as watching a loved one struggle with cognitive decline in dementia, as had happened to my grandfather. Throughout graduate school and postgraduate training, I have worked to stay on the cutting edge of cell biology in my hopes to uncover new mechanisms that could eventually lead to treatment of these disorders. Now that I am focusing my research program on patient-derived stem cells, I often have the opportunity to meet patients and their family members who are participating in our research by donating their cells or cells from their loved ones. Their generosity is outstanding, and I am constantly amazed by their courage and hope. This provides great incentive to push our work forward in the hopes that we will contribute to the development of novel treatments for Alzheimer's disease. This award at an early stage in my career will be transformative in initiating this push. I would like to express my deep gratitude and appreciation to BrighFocus donors for their support of this project.
First published on: September 25, 2018
Last modified on: March 20, 2020