- PhD (Biology) Columbia University 1991
- BSc (Biology) Yale University 1986
Dr. Kraut did her undergraduate degree in Biology at Yale University, and her PhD in molecular biology at Columbia University in New York. Thereafter, she became an EMBO postdoctoral fellow at the Institute of Developmental Biology in Cologne, Germany, and in the Institute of Molecular and Cell Biology in Singapore, where she studied mechanisms of asymmetric cell division in the development of the Drosophila nervous system. Further postdoctoral studies in the California Institute of Technology shifted the focus to intracellular trafficking and neurodegeneration, again in a Drosophila model. Dr. Kraut then returned to Singapore in 2004 as Principle Research Scientist at the Institute of Bioengineering & Nanotechnology, A*STAR, where she developed methods and tools to enable the visualization of sphingolipids and vesicle trafficking in both cellular and whole-animal models of degeneration. In 2009, she joined the faculty of the School of Biological Sciences at Nanyang Technological University.
Dr. Kraut's group is interested in the intracellular trafficking and biophysical behavior of sphingolipids, and the role these lipids play in neurodegeneration. The significance of sphingolipids in neurodegeneration, particularly Alzheimer's disease, is now recognized. The metabolism of these lipids is altered in the disease, and conversely, the cellular content of sphingolipids affects Alzheimer's pathogenesis and production of the disease-causing peptide, Aβ. In spite of the critical involvement of sphingolipids in the disease, and the intense interest this has awakened, the means available to visualize sphingolipids and their trafficking pathways in live cells remain extremely limited. We address this problem by developing fluorescently tagged probes to trace the behaviors of sphingolipids and observe how this changes under neurodegenerative conditions.
We exploit a phenomenon in which plasma membrane "rafts", or nano-scale assemblages of sphingolipids and cholesterol, interact with short peptide motifs within various toxins and viruses, and mediate cellular uptake of the invading pathogen. We have developed a fluorescent probe based on the Sphingolipid Binding Domain (SBD) of Aβ (identified by Fantini et al). The SBD probe is internalized via a raft- and sphingolipid-dependent mechanism. Using time-lapse fluorescence imaging and quantitative colocalization with cellular markers, we have characterized precisely the intracellular trafficking behavior of the SBD probe. We also analyze the biophysical properties of the SBD peptide, using Fluorescence Correlation Spectroscopy (collaboration with Dr. Thorsten Wohland, NUS), Surface Plasmon Resonance, and Atomic Force Microscopy. With this combination of techniques, we have determined that SBD, through interacting with a subset of sphingolipids and cholesterol, marks a small, low-mobility domain at the cell surface that is required for efficient internalization into the cell.
Importantly, the trafficking behavior of SBD and other sphingolipid probes changes drastically under pharmacological treatments that alter lipid metabolism and storage, mimicking neurodegenerative conditions such as Niemann-Pick and the lipid storage diseases. We are now analyzing changes in sphingolipid trafficking, using SBD and other probes, in cellular models of Alzheimer's disease that will be amenable to high throughput analysis. Taking advantage of quantifiable changes in trafficking of these probes, intracellular trafficking analysis will be used as a cell-based drug-screening platform, where automated fluorescence imaging and quantitative colocalization can be applied as a diagnostic readout.
A second interest in the lab is the role of sphingolipids and lysosomal trafficking in neurodegeneration. Neurons and other cells rid themselves of toxic aggregated proteins and damaged organelles by transporting them to degradative autophagosomes and lysosomes. When degradative function is compromised, neurons degenerate. Autophagy is controlled by sphingolipids at a number of levels, but its connection to vesicle transport is not understood. Blue-cheese is an autophagosomal/lysosomal protein in Drosophila that affects both vesicle transport and sphingolipid metabolism (Lim & Kraut, `09; Hebbar & Kraut, in prep). Degenerating motorneurons in blue cheese mutants show a severe impairment in axonal transport of GFP labeled lysosomes, similar to transport defects in mouse models of Alzheimer's disease, suggesting a mechanism whereby failure in axonal transport of a degradative compartment is a primary cause of the pathology. As in the case of Alzheimer's, blue-cheese also affects sphingolipid and cholesterol metabolism in the fly. Our goal is to analyze the relationship between sphingolipid metabolism, neurodegeneration and vesicle transport in this model, using a combination of genetics, live imaging, and sphingolipidomic analysis.