Generating a Reporter Mouse Line for PGRN and TREM2 Expression
Anika Reifschneider1, Benedikt Wefers2, Anja Capell1, Christian Haass1,2,3
1Biomedical Center (BMC), Biochemistry, Ludwig-Maximilians-Universität München, Munich, Germany; 2German Center for Neurodegenerative Diseases (DZNE), Munich, Germany; 3SyNergy - Munich Cluster for Systems Neurology, Munich, Germany
Increasing evidence has linked inflammation to a number of neurodegenerative disorders including Alzheimer's disease (AD), Parkinson's disease (PD) and frontotemporal dementia (FTD). In the central nervous system microglia, the resident innate immune cells, play a major role in the inflammatory processes and a disease associated microglia population has been identified. However, microglia are highly dynamic and therefore cannot simply be characterized by the two extremes of their activation, the M1 and M2 states. We rather expect numerous functionally distinct microglia populations in both healthy and disease stages.
Progranulin (PGRN), which in the brain is predominantly expressed by microglia, is genetically associated to FTD, but there is also evidence for a disease modulation function in AD. Microglia express different levels of PGRN, depending on their functional status. While resting microglia express low levels of PGRN, its expression is upregulated in activated microglia upon CNS injury. Sequence variants of the triggering receptor expressed on myeloid cells 2 (TREM2), a type 1 trans-membrane protein, were linked to neurodegenerative diseases including AD, FTD and FTD-like syndrome. Like PGRN, TREM2 in the brain is almost exclusively expressed by microglia. TREM2 functions have been linked to chemotaxis, migration, survival, binding of phospholipids and ApoE, proliferation, and others. Although both proteins are upregulated by activated microglia and loss of function of both proteins can lead to a similar neurodegenerative disease, TREM2 deficient microglia are locked in a homeostatic stage, while microglia with loss of PGRN are hyperactivated, indicating partially opposite functions of TREM2 and PGRN in microglia. To follow PGRN and TREM2 expression in vivo we generate reporter mice. Such mice allow us to isolate and characterize microglia subpopulations of either high PGRN or TREM2 expression in healthy and diseased mouse models. The reporters will be introduced into the mouse Grn (mGrn) or mouse Trem2 (mTrem2) locus using the CRISPR/Cas9 system. The P2A, a self-cleaving peptide, ensures multicistronic expression of the fluorescent reporter and PGRN or TREM2.
This work is supported by a fellowship from the Hans and Ilse Breuer Foundation to A.R..