Microglia are central nervous system (CNS) resident macrophages involved in maintaining CNS homeostasis. Importantly, they are also involved in a number of diseases, including Alzheimer?s disease, Huntington?s disease, amyotrophic lateral sclerosis, Parkinson?s disease, multiple sclerosis, infectious diseases and cancer. Despite their importance in health and disease, researchers still lack an experimental model that would enable simple and permanent depletion of microglia to study their functions and their potential as targets for therapy. The principal difficulty in studying microglia is their extensive similarity to other macrophages, which precludes depletion of microglia without concomitant depletion of macrophages. Making use of recent advances in microglia biology, we propose to characterize a transgenic mouse model, termed here Mg-ipKO that enables inducible, permanent, and highly selective depletion of microglia only. The depletion is based on expression of Sall1, a transcription factor expressed in microglia but not in other macrophages/myeloid cells. Sall1-driven expression of Cre recombinase will lead to knockout of CSF-1 receptor (CSF-1R) in microglia. Given that microglia survival is absolutely dependent on CSF-1R, its knockout will lead to depletion of microglia. The depletion will be tamoxifen-inducible and permanent. A similar concept for short- term microglia depletion by Sall1-driven expression of Cre to knockout CSF-1R has recently been proven successful, supporting the feasibility of the approach that we propose. We have recently generated novel Sall1-FRT-Cre transgenic mouse line, and we are currently crossing these mice with two other transgenic mouse lines (obtained from The Jackson Laboratory) to generate final triple transgenic Mg-ipKO mice with the capacity for inducible microglia depletion. We anticipate that we will have generated Mg-ipKO mice by the time funding for this project may start, allowing for an immediate start of experiments with these mice. We propose the specific aim: To characterize microglia depletion and its effects in Mg-ipKO mice. To determine the usefulness of the model, we will induce microglia depletion in adult Mg-ipKO mice by tamoxifen treatment. We will then determine the extent of the depletion and optimize tamoxifen treatment if necessary. Furthermore, we will characterize potential consequences of the depletion on CNS homeostasis (blood-brain barrier integrity, CNS inflammation, astrogliosis) and determine if, over time, the CNS repopulates with microglia that originate from either CNS progenitors, or with macrophages of bone marrow origin. We expect that by the completion of this proposed research we will have developed and characterized an advanced transgenic mouse model for the depletion of microglia that overcomes the limitations of existing approaches and provides a highly useful research tool for multiple biomedical disciplines.
Microglia are immune cells that are found in the central nervous system and are involved in numerous brain diseases, including Alzheimer?s disease, amyotrophic lateral sclerosis, and multiple sclerosis, among others. Currently, there is no animal model that allows permanent and selective deletion of these cells in order to study their role. This project proposes a novel and advanced genetically modified mouse model that addresses this need.
