Microglial-Mediated Glycosaminoglycan Catabolism in MPS VII Neuropathology. - Abstract / Project Summary The brain's extracellular matrix (ECM) is a three-dimensional milieu that plays a crucial role in synaptic function and plasticity during development in addition to its regulatory role in axon regeneration and remyelination from injury. Despite its significance, our understanding of how the content of the major brain ECM components, glycosaminoglycans (GAGs) and GAG-modified proteins (proteoglycans), are regulated is limited. Mucopolysaccharidosis VII (MPS VII) is a multi-organelle lysosomal storage disorder caused by the deficiency of β-glucuronidase (GUSB), resulting in neurodevelopmental delay and broad neurological impairment. Our preliminary studies using an MPS VII mouse model that is globally deficient in β-glucuronidase enzyme show prominent intracellular WFA-stained aggregates observed selectively in CD68+ microglia. These results suggest a critical role of microglia-mediated proteoglycan/GAG catabolism in CNS development. These findings lead us to hypothesize that the loss of GUSB function in microglia is a key driver of MPS VII neuropathology. However, there are no existing genetic tools to specifically target and ablate β-glucuronidase activity in microglia. Additionally, there are no existing biomarkers to assay for non-degraded GAGs accumulating intracellularly from the loss of β-glucuronidase activity. The objective of this proposal is to develop new genetic and biochemical tools to test for the importance of microglia-mediated GAG catabolism in the CNS and its dysfunction as a root cause for MPS VII neuropathology. In Aim 1 we will develop and validate new genetic tools to conditionally ablate β- glucuronidase mediated GAG catabolism within microglia and other cells of neural lineage. In Aim 2 we will measure for non-degraded intracellular GAGs that selectively accumulate in MPS brain tissue. Combining these newly generated genetic reagents with the biochemical approach to measure non-degraded intracellular GAGs will allow us to discern and assess microglial mediated GAG catabolism and their dysfunction in MPS VII neuropathology.
