Joshua M. Shulman, M.D., Ph.D.
Assistant Professor, Departments of Neurology and Molecular and Human Genetics
Functional genomics of Alzheimer's disease and Parkinson's disease; integrative genetic analyses in humans and Drosophila
Recent advances have made the discovery of genetic susceptibility loci for complex human phenotypes a reality, including nervous system disorders. The critical next step will be to definitively identify the responsible genes and understand their functions in both health and disease. Our research integrates genetic investigation in human subjects and model organisms, with the goal of understanding brain function and aging, and improving the treatment of neurologic disease. We focus on Alzheimer’s disease and Parkinson’s disease, two incurable neurodegenerative disorders and experimental paradigms for the age-dependent failure of brain cognitive and motor control in humans.
The clinical manifestation of neurodegenerative disease is the culmination of a multi-tiered pathogenic cascade that evolves over decades—understanding how genetic variants impact this causal chain is essential. Although 2% of the population over age 65 are clinically diagnosed with Parkinson’s disease, the defining pathology of disease (alpha-synuclein Lewy bodies) is discovered in 20% of brains from population-based autopsy studies. We are therefore investigating the impact of genomic variation on directly measured Lewy pathology, neuronal loss in the midbrain substantia nigra, and progressive motor impairment, leveraging human subject cohorts with detailed clinical and pathological data. We also participate in collaborative studies for the functional genetic dissection of Alzheimer’s disease, focusing on the responsible neuropathology, amyloid neuritic plaques and Tau neurofibrillary tangles.
Despite the promise of current human genetic methods, such as genome-wide association studies, they often fail to identify disease susceptibility genes with certainty, instead highlighting broad genomic regions. We are taking advantage of the rapid and powerful genetics available in the fruit fly Drosophila melanogaster in order to accelerate the validation of responsible genes and an understanding of their functions in disease pathogenesis. Expression of human amyloid-beta, Tau, or alpha-synuclein proteins in the fly nervous system recapitulates many core features of Alzheimer’s disease and Parkinson’s disease pathogenesis. We are testing candidate human susceptibility genes for functional genetic interactions in these fly models of neurodegeneration. Implicated molecular pathways are probed in greater depth, using both Drosophila and human genetic approaches. Our strategy has recently identified cell adhesion converging on the cytoskeleton as likely important for Tau-mediated neurodegeneration and Alzheimer’s disease susceptibility, and we are now following up these insights to elucidate the detailed mechanisms.
Susceptibility to neurofibrillary tangles: role of the PTPRD locus and limited pleiotropy with other neuropathologies.
Chibnik LB, White CC, Mukherjee S, Raj T, Yu L, Larson EB, Montine TJ, Keene CD, Sonnen J, Schneider JA, Crane PK, Shulman JM, Bennett DA, De Jager PL