Important collaborations come from synergy between the clinic and the laboratory. This has been the hallmark of Dr. Tifft's research program on glycosphingolipid and glycoprotein storage disorders affecting the central nervous system. These rare, uniformly fatal, lysosomal disorders affect males and females, children and adults and the diagnosis is often delayed years to decades from the onset of symptoms. In a collaboration with Dr. Richard Proia (GDDB/NIDDK) that spans more than 20 years the two have used mouse models of Tay-Sachs and Sandhoff disease to understand the pathogenesis of disease progression and explore therapeutic options.
The collaborators determined that bone marrow transplantation could double the lifespan of Sandhoff disease mice, not by decreasing the storage of GM2 ganglioside, but by inhibiting activation of macrophage-derived microglial cells leading to neuronal apoptosis. This was the first demonstration that inflammation was pivotal in the pathogenesis of lysosomal storage disorders (LSDs) affecting the CNS, an observation that has been subsequently extended to include many neurodegenerative LSDs. Anti-inflammatory compounds have also improved behavior and lifespan in the Sandhoff mouse, further supporting inflammation as an important contributing factor to neurodegeneration.
To further investigate the molecular pathogenesis of these disorders, the Proia/Tifft team have generated induced pluripotent stem (iPS) cells from a patient with infantile Sandhoff disease and used the CRISPR/Cas system to correct the mutation and produce isogenic iPS lines for neuronal differentiation and differential gene expression studies. Likewise, the group has used CRISPR/Cas to create GM1 iPS cells with mutations in the exons most commonly associated with juvenile disease. Isogenic disease and control iPS lines from both diseases have been differentiated into cerebral organoids in culture and faithfully replicate neuronal storage of GM2 and GM1 ganglioside respectively. Abnormally increased cellular proliferation in the visibly larger Sandhoff organoids may explain the megalencephaly observed in infantile GM2 patients.
Using facilities of the NHGRI Mouse Core facility, the group has created and characterized a CRISPR/Cas knock out mouse that recapitulates the skeletal and CNS phenotypes of juvenile GM1 patients. This mouse will be important for ongoing pre-clincial testing of therapeutics for GM1 patients.
GM1 gangliosidosis is a rare disorder caused by the enzyme deficiency of lysosomal b-galactosidase. The researchers have recruited 35 Type II patients for careful phenotyping and longitudinal monitoring of disease progression. In collaboration with Dr. Eva Baker at the NIH Clinical Center Department of Diagnostic Imaging, and Dr. Gilbert Vezina chief of neuroradiology at the Children's National Health System, they have used MRI and MR spectroscopy (specifically volumetrics and quantitation of brain metabolites), the team is able to monitor the disease progression that correlates with neurocognitive decline.
Ongoing work in the laboratory focuses on the mechanisms of neurodegeneration and on the identification of biomarkers of disease progression, including ganglioside quantitation and identification of inflammatory markers in cerebrospinal fluid (CSF), and, in collaboration with Dr. Xuntian Jiang, oligosaccharide profiling by tandem mass spectrometry in urine, plasma, and CSF of GM1 patients.
As director of the Pediatric Undiagnosed Diseases Program (UDP) part of the Undiagnosed Diseases Network of the NIH Common Fund, Dr. Tifft and her team evaluate patients who have long eluded diagnosis at major academic centers throughout the country. The majority of patients have neurologic, often neurodegenerative, disease as part of their symptomatology. By careful clinical phenotyping and use of the latest techniques in next generation sequencing and agnostic screening, the team tries to solve mysterious conditions that may represent very rare presentations of previously described disorders or entirely new disorders. Together with 10 UDN clinical sites across the country and core laboratories for sequencing, metabolomics and generation of model organisms, the UDP is able to investigate the functional consequences of mutations in novel gene candidates and search for additional cases to describe new disease entities.
Glycosphigolipid Disorders Laboratory Members
Jean Johnston, R.N., Research Nurse Coordinator
Precilla D'Souza, P.N.P., D.N.P., Nurse Practitioner
Sangwoo (Ted) Han, Ph.D., Postdoctoral Fellow
Brianna Glase, B.A., Postbaccalaureate Fellow
Robin Yoon B.A., Postbaccalaureate Fellow
Last Updated: September 11, 2018