Progranulin insufficiency and TDP-43 overexpression interact to worsen FTD-related phenotypes in mice.
Ontology highlight
ABSTRACT:
ORGANISM(S): Mus musculus
PROVIDER: GSE305500 | GEO | 2026/06/08
REPOSITORIES: GEO
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Project description:Dominant mutations in unrelated genes cause fronto-temporal lobar degeneration with TDP-43 inclusions (FTLD-TDP) and include VCP, which is associated with multisystem proteinopathy (MSP). Conditional inactivation of VCP in postnatal forebrain neurons (VCP cKO) caused cortical brain atrophy, neuronal loss, autophago-lysosomal dysfunction, TDP-43 inclusions and hyperactivity. Quantitative proteomics and single nuclei RNA sequencing on VCP cKO brains identified synaptogenesis and the unfolded protein response as the most decreased and increased pathways respectively. Conditional expression of a single MSP disease mutation, VCP-R155C, in cortical neurons similarly recapitulated features of VCP inactivation and FTLD-TDP. Comparison of transcriptomic and proteomic datasets from genetically defined FTD patients revealed that profiles from GRN carriers were similar to VCP insufficiency. These data support a deficiency in VCP dependent functions as the pathogenic mechanism of FTLD-TDP and reveal an unexpected pathogenic similarity with progranulin deficiency. Enhancing VCP function may be therapeutic in MSP and related forms of FTLD-TDP.
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Project description:Polygenic risk factors influence onset and progression of neurodegenerative diseases, but are difficult to be functionally explored in isolation. Single nucleotide polymorphisms (SNPs) in TMEM106B increase the risk for frontotemporal lobar degeneration (FTLD) of GRN mutation carriers. Currently, it is not clear if progranulin (PGRN) and TMEM106B are synergistically linked and if a gain or a loss-of-function of TMEM106B is responsible for the increased disease risk of patients with PGRN haploinsufficiency. We therefore compared behavioral abnormalities, gene expression patterns, lysosomal activity and TDP-43 pathology in single and double knockout animals. Grn–/–/Tmem106b–/– mice showed a strongly reduced life span and massive motor deficits. Gene expression analysis revealed an upregulation of molecular signatures characteristic for disease associated microglia and autophagy. Dysregulation of maturation of lysosomal proteins as well as a pronounced accumulation of ubiquitinated proteins and wide spread p62 deposition suggest that proteostasis is impaired. Moreover, while single Grn–/– knockouts only occasionally showed TDP-43 pathology, the double knockout mice exhibit robust deposition of phosphorylated TDP-43. Thus, a loss-of-function of TMEM106B may enhance the risk for GRN-associated FTD by reduced protein turnover in the lysosomal/autophagic system.
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Project description:Patients with frontotemporal dementia (FTD) resulting from granulin (GRN) haploinsufficiency have reduced levels of progranulin and exhibit dysregulation in inflammatory and lysosomal networks. Microglia produce high levels of progranulin, and reduction of progranulin in microglia alone is sufficient to recapitulate inflammation, lysosomal dysfunction, and hyperproliferation in a cell-autonomous manner. Therefore, targeting microglial dysfunction caused by progranulin insufficiency represents a potential therapeutic strategy to manage neurodegeneration in FTD. Limitations of current progranulin-enhancing strategies necessitate the discovery of new targets.To identify compounds that can reverse microglial defects in Grn-deficient mouse microglia, we performed a compound screen coupled with high throughput sequencing to assess key transcriptional changes in inflammatory and lysosomal pathways. Positive hits from this initial screen were then further narrowed down based on their ability to rescue cathepsin activity, a critical biochemical readout of lysosomal capacity. The screen identified nor-binaltorphimine dihydrochloride (nor-BNI) and dibutyryl-cAMP, sodium salt (DB-cAMP) as two phenotypic modulators of progranulin deficiency. In addition, nor-BNI and DB-cAMP also rescued cell cycle abnormalities in progranulin-deficient cells. These data highlight the potential of a transcription-based platform for drug screening, and advance two novel lead compounds for FTD.
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