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IMPDH2 filaments protect from neurodegeneration in AMPD2 deficiency

ABSTRACT: Metabolic dysregulation is one of the most common causes of pediatric neurodegenerative disorders. However, how the disruption of ubiquitous and essential metabolic pathways predominantly affect neural tissue remains unclear. Here we use a mouse model of AMPD2 deficiency to study cellular and molecular mechanisms that lead to selective neuronal vulnerability to purine metabolism imbalance. We show that AMPD deficiency in mice primarily leads to hippocampal dentate gyrus degeneration despite causing a generalized reduction of brain GTP levels. Remarkably, we uncover that neurodegeneration resistant regions of the hippocampus accumulate micron sized filaments of IMPDH2, the rate limiting enzyme in GTP synthesis. In contrast, IMPDH2 filaments are barely detectable in the dentate gyrus, which show a progressively neuroinflammation and neurodegeneration. Furthermore, using a human AMPD2 neural cell culture model, we show that blocking IMPDH2 polymerization with a dominant negative IMPDH2 variant impairs AMPD2 deficient neural progenitor growth. Together, our findings suggest that IMPDH2 polymerization prevents detrimental GTP deprivation caused by AMPD2 deficiency, providing resistance to neurodegeneration. This data opens the possibility of exploring the involvement of IMPDH2 assembly as a therapeutic intervention for neurodegeneration.

ORGANISM(S): Mus musculus

PROVIDER: GSE253045 | GEO | 2024/01/16

REPOSITORIES: GEO

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Project description:Sanfilippo syndrome type B (MPS III B) is an autosomal recessive, neurodegenerative disease of children, characterized by profound mental retardation and dementia. The primary cause is mutation in the NAGLU gene, resulting in deficiency of N-acetylglucosaminidase and lysosomal accumulation of heparan sulfate. In the mouse model of MPS III B, neurons and microglia display the characteristic vacuolation of lysosomal storage of undegraded substrate, but neurons in the medial entorhinal cortex (MEC) display accumulation of several additional substances. We used whole genome microarray analysis to examine differential gene expression in MEC neurons isolated by laser capture microdissection from Naglu -/- and Naglu +/- mice. Neurons from the lateral entorhinal cortex (LEC) were used as tissue controls. The highest increase in gene expression (6- to 7-fold between mutant and control) in MEC and LEC neurons was that of Lyzs, which encodes lysozyme, but accumulation of lysozyme protein was seen in MEC neurons only. Because of a report that lysozyme induced the formation of hyperphosphorylated tau (P-tau) in cultured neurons, we searched for P-tau by immunohistochemistry. P-tau was found in MEC of Naglu -/- mice, in the same neurons as lysozyme. In older mutant mice, it was also seen in the dentate gyrus, an area important for memory. Electron microscopy of dentate gyrus neurons showed cytoplasmic inclusions of paired helical filaments - P-tau aggregates characteristic of tauopathies, a group of age-related dementias that includes Alzheimer disease. Our findings indicate that the Sanfilippo syndrome type B should also be considered a tauopathy. Two-condition experiment, Naglu-/- (affected) vs. Naglu+/- (unaffected control) of neurons from two adjacent brain regions: medial entorhinal cortex (MEC) and lateral entorhinal cortex (LEC). Biological replicates: 3 MEC Naglu-/-, 3 MEC Naglu+/-, 3 LEC Naglu-/- and 3 LEC Naglu+/-. Comparisons were made between 3 pairs of mutant and control female littermates for MEC and LEC neurons with dye switch duplicates, for a total of 12 microarrays.

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IMPDH2 filaments protect from neurodegeneration in AMPD2 deficiency

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