Stephan N. Witt, PhD
Professor of Biochemistry and Molecular Biology
Bachelor of Fine Arts, 1976-1979 Fine Arts, Tufts University, Medford, Massachusetts
Bachelor of Science, 1979-1981 Chemistry, Union College, Schenectady, New York
PhD, 1982-1988 Biophysical Chemistry, California Institute of Technology, Pasadena, California
(Mentor: Sunney I. Chan)
Postdoctoral Fellow, 1988-1993 Immunochemistry, Stanford University, Stanford, California
(Mentor: Harden M. McConnell)
2001 Yeast Genetics, Cold Spring Harbor Laboratory, Cold Spring Harbor, New York (July 16-August 4)
2009 Analytic and Quantitative Light Microscopy, Marine Biology Lab, Woods Hole, MA (May 5-15)
2014 Statistics in Medicine, Stanford University Open Online Course, (June 24-August 30), Certificate of Completion with Distinction. (9/3/14)
February 23-24, 2023
Dr. Witt served as co-Chair of the NIH Fellowship Study Section: Biophysical, Physiological, Pharmacological, and Bioengineering Neuroscience. (F03B ZRG1 F03B-L (20) L)
February 13, 2023
Dr. Witt is part of a LSUHS team that showed that the menin tumor suppressor is lost in high grade cholangiocarcinomas. Cholangiocarcinoma is a rare and deadly cancer of the bile duct.
Loss of tumor suppressor menin expression in high grade cholangiocarcinomas.
Lairmore TC, Abdulsattar J, De Benedetti A, Shi R, Huang S, Khalil MI, Witt SN.BMC Res Notes. 2023 Feb 13;16(1):15. https://doi.org/10.1186/s13104-023-06282-6
December 08, 2022
Dr. Witt served on the NIH Study Section. Member Conflict: Topics in Neurobiology and Neuropharmacology. (ZRG1 BN-R (02))
June 16-17, 2022
Dr. Witt served on the NIH Fellowship Study Section: Biophysical, Physiological, Pharmacological, and Bioengineering Neuroscience (F03B ZRG1 F03B-L (20) L)
March 1, 2022
Santhan published a paper entitled “α-synuclein inhibits Snx3-retromer retrograde trafficking of the conserved membrane-bound proprotein convertase Kex2 in the secretory pathway of Saccharomyces cerevisiae” in Human Molecular Genetics. This study shows beautifully how alpha-synuclein can disrupt vesicular trafficking in cells.
Santhanasabapathy Rajasekaran et al.
Human Molecular Genetics, Volume 31, Issue 5, 1 March 2022, Pages 705717, https://doi.org/10.1093/hmg/ddab284
February 24-25, 2022
Dr. Witt served the NIH Fellowship Study Section: Biophysical, Physiological, Pharmacological, and Bioengineering Neuroscience. (F03B ZRG1 F03B-L (20) L)
Congratulations to Nirjhar Aloy for being awarded a FWCC predoctoral fellowship of $30,000.
Congratulations to the Witt lab for being awarded a FWCC Idea Award of $50,000 for their investigations of the mechanism by which alpha-synuclein modulates the cell surface expression of adhesion proteins.
October 28-29, 2021
Dr. Witt served on the NIH Fellowship Study Section: Biophysical, Physiological, Pharmacological, and Bioengineering Neuroscience. (F03B ZRG1 F03B-L (20) L)
July 27, 2021
Dr. Witt was awarded a R56 grant from the National Institute of Neurological Disorders and Stroke (NINDS) for his project entitled, “Examining the role of phosphatidylethanolamine and autophagic disruption in Lewy Body Dementias and Parkinson's disease.” Award amount: $642,408
Dr. Witt invited to comment on a paper published in PLOS BIOLOGY.
Trojan horses and tunneling nanotubes enable α-synuclein pathology to spread in Parkinson disease
Santhanasabapathy Rajasekaran, Stephan N. Witt
PLOS Biology: published July 20, 2021 | https://doi.org/10.1371/journal.pbio.3001331
Congratulations to Nirjhar for being awarded a competitive NSF-funded Fellowship to cover the tuition for a set of online summer modules over six days at the Summer Institute of Statistical Genetics at the University of Washington.
June 24-25, 2021
Dr. Witt served on the NIH Cellular and Molecular Biology of Neurodegeneration (CMND) Study Section.
May 26, 2021
Congratulations Sahar! Sahar Shekoohi, a member of the Witt lab, graduated with a PhD and is currently a postdoctoral fellow in the Department of Anesthesiology at LSUHS.
Sahar published a comprehensive characterization of SK-Mel-28, a melanoma cell line, with the gene SNCA knocked out. SNCA codes for the Parkinson’s disease-associated protein alpha-synuclein.
Knocking out alpha-synuclein in melanoma cells dysregulates cellular iron metabolism and suppresses tumor growth. Shekoohi, S., Rajasekaran, S., Patel, P., Yang, S., Liu, W., Huang, S., Yu, X and Witt, S.N. Scientific Reports 2021 Mar 4;11(1):5267. doi: 10.1038/s41598-021-84443-y
October 22-23, 2020
Dr. Witt served on the NIH Fellowship Study Section: Biophysical, Physiological, Pharmacological and Bioengineering Neuroscience. (2020/01 ZRG1 F03B-R (20) L)
Congratulations to Nirjhar for being awarded a competitive NSF-funded Fellowship to cover the tuition for a set of online summer modules over nine days at the Summer Institute of Statistical Genetics at the University of Washington.
Major Research Interests:
α-Synuclein and Parkinson’s disease; α-synuclein and melanoma; protein aggregation; molecular bases of disease; vesicle trafficking
a-Synuclein and Parkinson’s disease
The WITT group uses several organisms (yeast, mice and human cells) to study the mechanism of toxicity of the human Parkinson’s disease-associated protein a-synuclein (a-syn). a-Syn is an intrinsically unfolded protein of unknown function that is the main protein component of Lewy bodies, which are proteinaceous cytoplasmic inclusions in dopamine-producing neurons in individuals who suffer from PD. High expression levels of a-syn or posttranslational modifications of the protein are thought to convert a-syn from a non-toxic protein into a toxic one. There is increasing evidence that the toxic conformation of a-syn is a prion: it acts as a template or seed that converts non-infectious a-syn monomers into infectious oligomers. Examples of ongoing projects include:
(1) a-Syn intracellular trafficking and lipid dyshomeostasis: In eukaryotic cells, wild-type a-syn transits through the endoplasmic reticulum and Golgi apparatus on route to the inner leaflet of the plasma membrane. In neurons, a-syn is thought to promote the fusion of presynaptic vesicles with the presynaptic membrane. We have found that the trafficking of a-syn through the ER is exquisitely sensitive to the level of certain cellular phospholipids, and we are investigating how changes in phospholipid homeostasis alter, and in some cases blocks, a-syn transit through the ER. This work has implications to the mechanism of Lewy body formation.
Figure 1 below shows how a-syn aggregates form in yeast cells that lack the mitochondrial enzyme phosphatidylserine decarboxylase (Psd1/PSD1). The role of this ancient enzyme vis-à-vis a-syn solubility/toxicity is an intense area of our focus.
(2) a-Syn, iron homeostasis, retromer: Many studies over the last 10 years have found a link between a-syn and iron homeostasis. Red blood cells contain relatively high levels of a-syn as well as neurons. Because many of the genes involved in iron homeostasis in human cells are also found in yeast, we are using yeast to investigate the connection between a disruption of cellular iron homeostasis and a-syn toxicity. The findings from yeast are being tested in worms and human cells.
Figure 2 below shows how a-syn inhibits the Snx3-retromer-mediated recycling of Ftr1-Fet3. In yeast, Ftr1-Fet3 is a complex that imports iron into cells. The human orthologs of Fet3 are hephestin and ceruloplasmin.
(3) Inhibitors of a-syn amyloid fiber formation: We have developed a unique method to predict the sequences of short peptides that can inhibit the fibrillization of a-syn. This is a very active area of research in the Witt lab. We have filed a patent disclosure on one of our peptide inhibitors and are actively identifying and characterizing even more potent inhibitors.
(4) a-Syn and melanoma: It is curious that individuals with melanoma (who live) have a 2-fold higher risk of being afflicted with PD than age-matched healthy controls. And it works the other way, that is, individuals with PD have a significantly higher risk of developing melanoma than age-matched individuals without PD. Melanocytes, like dopaminergic neurons, express α-syn. Melanocytes, like dopaminergic neurons, synthesize a pigment (melanin). Some of the most aggressive melanomas also express very high levels of α-syn, as if somehow α-syn promotes growth.
To probe the function of α-syn in melanoma, we used CRISPR/Cas9 to knockout SNCA, the gene that codes for α-syn, in SK-Mel-28 melanoma cells. The SNCA-knockout (KO) clones in culture exhibited a decrease in the transferrin receptor 1 (TfR1), an increase in ferritin, an increase of reactive oxygen species and proliferated slower than control cells. These SNCA-KO clones grafted into SCID mice grew significantly slower than the SK-Mel-28 control cells that expressed α-syn. In the excised SNCA-KO xenografts, TfR1 decreased 3.3fold, ferritin increased 6.2-fold, the divalent metal ion transporter 1 (DMT1) increased threefold, and the iron exporter ferroportin (FPN1) decreased twofold relative to control xenografts. The excised SNCA-KO tumors exhibited significantly more ferric iron and TUNEL staining relative to the control melanoma xenografts. Collectively, depletion of α-syn in SK-Mel-28 cells dysregulates cellular iron metabolism, especially in xenografts, yielding melanoma cells that are deficient in TfR1 and FPN1, that accumulate ferric iron and ferritin, and that undergo apoptosis relative to control cells expressing α-syn. Our model for the dysregulation of iron metabolic proteins in SNCA-KO melanoma cells is shown below (Fig. 3).
- Rajasekaran, S., Peterson, P.P., Liu, Z., Robinson, L.C., and Witt, S.N. (2022) α-Synuclein inhibits Snx3-retromer retrograde trafficking of the conserved membrane-bound proprotein convertase Kex2 in the secretory pathway of Saccharomyces cerevisiae. Human Molecular Genetics Mar 3;31(5):705-717.
- Rajasekaran, S. and Witt, S.N. (2021) Trojan horses and tunneling nanotubes enable a-synuclein pathology to spread in Parkinson’s disease. PLoS Biology 19(7):e3001331
- Shekoohi, S., Rajasekaran, S., Patel, P., Yang, S., Liu, W., Huang, S., Yu, X and Witt, S.N. (2021) Knocking out alpha-synuclein in melanoma cells dysregulates cellular iron metabolism and suppresses tumor growth. Scientific Reports 11, 5267.
- Patel, D, Xu, C., Nagarajan, S., Liu, Z., Hemphill, W.O., Shi, R., Uversky, V.N., Caldwell, G.A., Caldwell, K.A., & Witt, S.N. (2018) Alpha-synuclein inhibits Snx3-retromer-mediated retrograde recycling of iron transporters in S. cerevisiae and C. elegans models of Parkinson’s disease. Human Molecular Genetics 27(9), 1514–1532
- Wang, S., Zhang, S., Liou, L.-C., Ren, Q., Zhang, Z., Caldwell, G.A., Caldwell, K.A., & Witt, S.N. (2014) Phosphatidylethanolamine deficiency disrupts α-synuclein homeostasis in yeast and worm models of Parkinson disease. Proceedings of the National Academy of Sciences USA 111(38): E3976–E3985
- Wang, S., Xu, B., Liou, L.-C., Ren, Q., Huang, S., Luo, Y., Zhang, Z. & Witt, S.N. (2012). α-Synuclein disrupts stress signaling by inhibiting polo-like kinase Cdc5/Plk2. Proceedings of the National Academy of Sciences USA 109, 16119-16124.
- Lee, Y.J., Wang, S., Slone, S.R., Yacoubian, T.A. & Witt, S.N. (2011). Defects in very long chain fatty acid synthesis enhance alpha-synuclein toxicity in a yeast model of Parkinson’s disease. PLoS ONE 6 (1):e15946.
- Liang, J., Clark-Dixon, C., Wang, S., Flower, T.R., Williams-Hart, T., Zweig, R., Robinson, L.C., Tatchell, K. & Witt, S.N. (2008). Novel suppressors of alpha-synuclein toxicity identified using yeast. Human Molecular Genetics 17, 3784-3795.
- Flower, T.R., Clark-Dixon, C., Metoyer, C., Yang, H., Shi, R., Zhang, Z. & Witt, S.N. (2007). YGR198w (YPP1) targets A30P alpha-synuclein to the vacuole for degradation. Journal of Cell Biology 177, 1091-1104.
- Flower, T.R., Chesnokova, L.S., Froelich, C.A., Dixon, C. & Witt, S.N. (2005). Heat shock prevents alpha synuclein-triggered apoptosis in a yeast model of Parkinson’s disease. Journal of Molecular Biology 351, 1081-1100.
Nirjhar earned his MBBS (equivalent to MD in US) from Rajshahi Medical College, Bangladesh, which is one of the leading medical schools in Bangladesh. In his medical career, he practiced as a family physician and as an instructor of Anatomy and Microbiology. Later, he joined a residency program in Cardiovascular and thoracic surgery, where he was doing well. But his strong passion for basic science encouraged him to pursue a career of a physician-scientist and he joined the PhD program in Biochemistry and Molecular Biology at LSUHS.
Nirjhar’s dissertation research is focused on understanding the role of the Parkinson’s disease-associated protein alpha-synuclein in trafficking of multivesicular bodies (MVBs). The central hypothesis of his project is that alpha-synuclein promotes melanoma-metastasis by modulating the trafficking of MVBs and controlling the release of extracellular vesicles. This project has the potential to pave the way for new research in areas of cancer biology.
We are currently accepting applications for Post-doctoral Fellows.
We are currently accepting applications for Graduate students interested in conducting research in the Witt lab.
Undergraduate Research Assistants
We are currently accepting applications from undergraduates.
Medical Students, Residents, and Fellows
The Witt laboratory has a number of research projects available for any Medical Students, Residents, and Fellows interested. Contact the lab for more information.