Development of a CRISPR screening platform in microglia to elucidate mechanisms of neurodegeneration
Nina M Draeger1, Chao Wang2, Claire Clelland2, Wayne W Poon3, Li Gan2, Martin Kampmann1
1Department of Biochemistry and Biophysics, Institute for Neurodegenerative Diseases and California Institute for Quantitative Biomedical Research, University of California, San Francisco, CA, 94158, USA; 2Gladstone Institute of Neurological Disease, Department of Neurology, University of California, San Francisco, CA 94158, USA; 3Institute for Memory Impairments and Neurological Disorders, University of California Irvine, Irvine, CA 92697, USA
Increasing evidence suggests an important role for microglia in the development and progression of neurodegenerative diseases, with neuroinflammation being a crucial hallmark. However, activated microglia can be neuroprotective or amplify neurodegenerative processes making it even more important to study the detailed neuron-microglia interplay in these diseases.
By integrating either CRISPR interference (CRISPRi) or CRISPR activation (CRISPRa) into iPSCs, we have developed novel genetic screening tools to interrogate loss- or gain-of-function genome-wide. We can derive neurons from these iPSCs and in co-culture with either primary mouse microglia or iPSC-derived microglia, use this innovative discovery platform to identify key neuronal and microglial factors relevant for neurodegeneration.
The first application of our discovery platform is to identify the role of microglia in pathological tau propagation, a process thought to drive progression of tauopathies. Recent studies suggest that tau propagation between neurons is enhanced by microglia which was confirmed in our co-culture model: tau aggregation is increased in iPSC-derived neurons co-cultured with rodent microglia when compared to neurons cultured alone. Moreover, tau aggregates are detected in a high proportion of microglia. This aggregation phenotype will be applied to a CRISPRi-based screen in iPSC-derived neurons to unravel the mechanisms behind enhanced neuronal tau aggregation and spreading. A similar screen will be performed with iPSC-derived microglia. These complementary screens will comprehensively investigate microglia-neuronal interactions in the context of neurodegeneration. Dissecting the different pathways by which microglia can affect neuronal dysfunctions may lead to novel therapeutic targets.