Liquid-liquid phase separation drives the formation of membrane-less organelles such as stress granule. Aberrant protein phase transition leads to the formation of fibrils and aggregates implicated in various neurodegenerative diseases. We are interested in understanding the molecular mechanisms underlying these aberrant phase transitions and leveraging our understanding of phase transition to develop strategies with therapeutic potential to prevent and reverse these toxic events. We use a combination of biochemistry, molecular biology, cell biology, and biophysics techniques to tackle these problems.

Molecular Mechanism of Protein Phase Transition

It is now universally appreciated that accumulation of misfolded proteins, which can acquire alternative proteotoxic states, causes a series of deleterious molecular events resulting in numerous lethal neurodegenerative diseases. Numerous RNA binding proteins (RBPs) with Prion-like Domains (PrLDs) have been connected via pathology and genetics to the etiology of several neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). Cytoplasmic mislocalization and inclusion formation are common pathological features of these proteinopathies. The PrLDs of these RBPs drive a phase transition into protein-rich reversible liquid droplets that share biophysical properties with RNP granules. “Aging” of these liquid droplets leads to an aberrant phase transition to a more solid-like irreversible fibrillar hydrogel state, which induces neurotoxicity by sequestering RNP cargo and impairing RNP granule function. Elucidating the mechanism of protein aberrant phase transition will be critical for understanding ALS/FTD pathogenesis. We will develop biophysical methods especially single molecule FCS (Fluorescence Correlation Spectroscopy) and single molecule FRET methods to quantitatively understand the molecular mechanism of these transitions. This study will provide a detailed quantitative view of the aberrant phase transition of ALS disease proteins and shed a light on the mechanism of ALS pathogenesis.

Reversing Aberrant Phase Transition in Neurodegenerative Diseases

It is important to develop agents to rescue toxicity by reversing aggregation and aberrant phase transitions. Nuclear import receptors (NIRs) can also function as chaperons and protein disaggregases to rapidly dissolve RBP fibrils and macroscopic hydrogels. Elevating expression of NIRs such as Kapβ2 prevents recruitment of RBPs such as FUS into stress granules, restores nuclear localization, and rescues degeneration caused by disease-linked FUS. Thus, NIRs could be important therapeutic target to restore RBP homeostasis in several fatal neurodegenerative disorders. However, for ALS-linked RBP variants that have mutations in the NLS (Nuclear Localization Signal), the activity of NIR is impaired due to decreased binding affinity. Therefore, it is essential to define how NIR disaggregates RBP fibrils and to potentiate NIR activity against ALS-linked RBP variants.

The second class of agent we aim to develop to antagonize aberrant phase transition is short RNA. RNA binding is essential for RBP function, cellular localization, cytotoxicity and incorporation into stress granules. Consistent with these in vivo results, in vitro studies show that RNA binding contributes to liquid droplet formation of RBP. We hypothesize that RNAs could be designed to reverse aberrant phase transition and aggregation of RBP and rescue proteotoxicity by restoring normal stress granule function. We will study how combinations of these RNAs and NIRs regulate RBP phase transition, which could give us insight on how cell regulates the biophysical properties of RNP granule by its RNA population. This study will provide insights for developing novel RNA therapeutics for ALS as well as other diseases that are characterized by aberrant accumulation of RBPs.

For more information, please visit our lab website:
https://linguolab.wixsite.com/website

PhD in Chemistry, University of Pennsylvania - 2011
BS, Pehing University, Beijing, China 2005

Fellowship

Ellison Medical Foundation and American Federation for Aging Research Postdoctoral Fellowship, 2015
Alzheimer's Association International Research Fellowship, 2016-2019
Target ALS Springboard Fellowship, 2018-2020