Rescue of TDP-43 and neuronal pathologies by peripheral AAV-mediated expression of brain-penetrant progranulin in a mouse model of GRN-linked frontotemporal lobar degeneration
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ABSTRACT: Progranulin (PGRN) haploinsufficiency is a major risk factor for Frontotemporal Lobar Degeneration with TDP-43 pathology (FTLD-TDP). Protein replacement therapeutic strategies are currently in clinical development, intended to restore PGRN levels in the central nervous system and slow or halt disease progression. However, such approaches require repeated dosing. Here, we explored the use of adeno-associated virus (AAV) to achieve sustained expression of a brain penetrant PGRN fusion protein, composed of a single chain variable fragment (scFv) recognizing mouse transferrin receptor (TfR) fused to human PGRN (AAV(L):bPGRN). We evaluated this approach for its ability to rescue pathological phenotypes in a double knockout mouse model lacking both PGRN and TMEM106b. A single administration of AAV(L):bPGRN reduced FTLD-TDP associated pathologies including severe motor function deficits, formation of insoluble, abnormally processed and phosphorylated TDP-43, as well as dysfunctional protein degradation, lipid dysregulation and gliosis.
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.
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.
Project description:Heterozygous mutations in the granulin (GRN) gene result in haploinsufficiency of the progranulin (PGRN) protein, a leading cause of frontotemporal lobar degeneration with TDP-43 aggregates (FTLD-TDP). Polymorphisms in the TMEM106B gene have been associated with disease risk in GRN mutation carriers and protective TMEM106B variants are associated with reduced levels of TMEM106B, suggesting that lowering TMEM106B might be therapeutic in the context of FTLD. Here we tested the impact of full deletion and partial reduction of TMEM106B in mouse and iPSC-derived human cell models of GRN deficiency. In vitro, TMEM106B deletion did not reverse transcriptomic and proteomic profiles in GRN-deficient microglia, with the exception of a small set of immune-related proteins in the NF-κB pathway. In vivo, neither homozygous nor heterozygous Tmem106b deletion normalized disease-associated gene expression in sorted microglia, lipid abnormalities, or histopathology in Grn knock-out mice. Furthermore, Tmem106b reduction with antisense oligonucleotide (ASO) treatment was poorly tolerated in Grn knock-out mice. These data provide novel insight into TMEM106B and GRN function in microglia cells but do not support lowering TMEM106B levels as a viable therapeutic strategy for treating FTLD-GRN.
Project description:Heterozygous mutations in the granulin (GRN) gene result in haploinsufficiency of the progranulin (PGRN) protein, a leading cause of frontotemporal lobar degeneration with TDP-43 aggregates (FTLD-TDP). Polymorphisms in the TMEM106B gene have been associated with disease risk in GRN mutation carriers and protective TMEM106B variants are associated with reduced levels of TMEM106B, suggesting that lowering TMEM106B might be therapeutic in the context of FTLD. Here we tested the impact of full deletion and partial reduction of TMEM106B in mouse and iPSC-derived human cell models of GRN deficiency. In vitro, TMEM106B deletion did not reverse transcriptomic and proteomic profiles in GRN-deficient microglia, with the exception of a small set of immune-related proteins in the NF-κB pathway. In vivo, neither homozygous nor heterozygous Tmem106b deletion normalized disease-associated gene expression in sorted microglia, lipid abnormalities, or histopathology in Grn knock-out mice. Furthermore, Tmem106b reduction with antisense oligonucleotide (ASO) treatment was poorly tolerated in Grn knock-out mice. These data provide novel insight into TMEM106B and GRN function in microglia cells but do not support lowering TMEM106B levels as a viable therapeutic strategy for treating FTLD-GRN.
Project description:Heterozygous mutations in the granulin (GRN) gene result in haploinsufficiency of the progranulin (PGRN) protein, a leading cause of frontotemporal lobar degeneration with TDP-43 aggregates (FTLD-TDP). Polymorphisms in the TMEM106B gene have been associated with disease risk in GRN mutation carriers and protective TMEM106B variants are associated with reduced levels of TMEM106B, suggesting that lowering TMEM106B might be therapeutic in the context of FTLD. Here we tested the impact of full deletion and partial reduction of TMEM106B in mouse and iPSC-derived human cell models of GRN deficiency. In vitro, TMEM106B deletion did not reverse transcriptomic and proteomic profiles in GRN-deficient microglia, with the exception of a small set of immune-related proteins in the NF-κB pathway. In vivo, neither homozygous nor heterozygous Tmem106b deletion normalized disease-associated gene expression in sorted microglia, lipid abnormalities, or histopathology in Grn knock-out mice. Furthermore, Tmem106b reduction with antisense oligonucleotide (ASO) treatment was poorly tolerated in Grn knock-out mice. These data provide novel insight into TMEM106B and GRN function in microglia cells but do not support lowering TMEM106B levels as a viable therapeutic strategy for treating FTLD-GRN.
Project description:The TMEM106B gene, encoding a lysosomal membrane protein, is closely linked with brain aging and neurodegeneration. TMEM106B has been identified as a risk factor for several neurodegenerative diseases characterized by aggregation of the RNA-binding protein TDP-43, including frontotemporal lobar degeneration (FTLD) and limbic-predominant age-related TDP-43 encephalopathy (LATE). To investigate the role of TMEM106B in TDP-43 proteinopathy, we ablated TMEM106B in the TDP-43Q331K knock-in mouse line, which expresses an ALS-linked TDP-43 mutation at endogenous levels. We found that TMEM106B deficiency leads to glial activation, Purkinje cell loss, and behavioral deficits in TDP-43Q331K mice without inducing typical TDP-43 pathology. Interestingly, ablation of TMEM106B results in significant body weight gain, increased fat deposition, and hepatic triglyceride (TG) accumulation in TDP-43Q331K mice. In addition, lipidomic and transcriptome analysis shows a profound alteration in lipid metabolism in the liver of TDP-43Q331KTmem106b-/- mice. Our studies reveal a novel function of TMEM106B and TDP-43 in lipid metabolism and provide new insights into their roles in neurodegeneration.
Project description:PGRN is involved in lysosomal function and is expressed in the brain. Grn knock-out (KO) mice develop several pathologies including lysosomal lipi accumulation, gliosis and neurodegeneration. Here we seek to determine if we can rescue Grn KO pathologies with a peripherally delivered AAV, that targets the liver, and drives expression of full length PGRN fused to a mouse TfR binding scFv (AAV(L):bPGRN. The PGRN fusion protein expressed by this AAV (8D3:PGRN), is brain penetrant. To study this, Grn KO mice were given a single IV injection of either saline or AAV(L):bPGRN at 4 months of age. After 8 months when the mice were 12 months of age, brain samples were collected and bulk RNA sequencing was performed to assess correction of transcriptional changes. Grn wild type (WT) mice treated with saline were also included as a control.
Project description:Many neurodegenerative disorders including Alzheimer’s disease (AD) and frontotemporal lobar degeneration (FTLD) are characterized by abnormal protein deposition and frequently show comorbid pathology. Progranulin (PGRN) is implicated not only in TDP-43 but in tau and alpha-synuclein proteinopathies. However, the underlying mechanisms are unknown. Here, we generated P301S tau transgenic mice with PGRN haploinsufficiency and loss and found that those mice exhibit exacerbated disinhibition phenotype while showing attenuated memory impairment, hippocampal atrophy, and transcriptomic changes. Remarkably, the phenotypic alteration was accompanied by an increase in tau inclusions, which are positive for alpha-synuclein, a PGRN binding partner beta-glucocerebrosidase (GCase), and its substrate glucosylceramide. GCase inhibition or PGRN deficiency enhanced tau aggregation induced by AD-derived tau seeds in neurons. In vitro, GCase and glucosylceramide promoted P301S tau aggregation. Similar co-pathology was observed in AD and FTLD-GRN patients.
Project description:FTLD is the third most common neurodegenerative condition, following only Alzheimer's and Parkinson's diseases. FTLD typically presents in 45-64-year-olds with behavioral changes or progressive decline of language skills. The subtype FTLD-TDP is characterized by certain clinical symptoms and pathological neuronal inclusions detected by TDP-43 immunoreactivity. Here, we extracted amyloid fibrils from brains of four patients, representing four out of five FTLD-TDP subclasses and determined their near-atomic resolution structures by cryo-EM. Unexpectedly, all amyloid fibrils examined are composed of a 135-residue C-terminal fragment of TMEM106B, a lysosomal membrane protein previously implicated as a genetic risk factor for FTLD-TDP. In addition to TMEM106B fibrils, abundant non-fibrillar aggregated TDP-43 is present, as revealed by immunogold labeling. Our observations confirm that FTLD-TDP is an amyloid-involved disease and suggest that amyloid involvement in FTLD-TDP is of protein TMEM106B, rather than of TDP-43.
Project description:The TMEM106B gene, encoding a lysosomal membrane protein, is closely linked with brain aging and neurodegeneration. TMEM106B has been identified as a risk factor for several neurodegenerative diseases characterized by aggregation of the RNA-binding protein TDP-43, including frontotemporal lobar degeneration (FTLD) and limbic-predominant age-related TDP-43 encephalopathy (LATE). To investigate the role of TMEM106B in TDP-43 proteinopathy, we ablated TMEM106B in the TDP-43Q331K knock-in mouse line, which expresses an ALS-linked TDP-43 mutation at endogenous levels. We found that TMEM106B deficiency leads to glial activation, Purkinje cell loss, and behavioral deficits in TDP-43Q331K mice without inducing typical TDP-43 pathology. Interestingly, ablation of TMEM106B results in significant body weight gain, increased fat deposition, and hepatic triglyceride (TG) accumulation in TDP-43Q331K mice. In addition, lipidomic and transcriptome analysis shows a profound alteration in lipid metabolism in the liver of TDP-43Q331KTmem106b-/- mice. Our studies reveal a novel function of TMEM106B and TDP-43 in lipid metabolism and provide new insights into their roles in neurodegeneration.