GRN Gene Research Articles

Frequency and Longitudinal Course of Motor Signs in Genetic Frontotemporal Dementia.

Background and ObjectivesFrontotemporal dementia (FTD) is a highly heritable disorder. The majority of genetic cases are caused by autosomal dominant pathogenic variants in the chromosome 9 open reading frame 72 (c9orf72), progranulin (GRN), and microtubule-associated protein tau (MAPT) gene. As motor disorders are increasingly recognized as part of the clinical spectrum, the current study aimed to describe motor phenotypes caused by genetic FTD, quantify their temporal association, and investigate their regional association with brain atrophy.MethodsWe analyzed baseline visit data of known carriers of a pathogenic variant in the c9orf72, GRN, or MAPT gene from the Genetic Frontotemporal Dementia Initiative cohort study. Principal component analysis with varimax rotation was performed to identify motor sign clusters that were compared with respect to frequency and severity between groups. Associations with cross-sectional atrophy patterns were determined using voxel-wise regression. We applied linear mixed effects models to assess whether groups differed in the association between motor signs and estimated time to symptom onset.ResultsA total of 322 pathogenic variant carriers were included in the analysis: 122 c9orf72 (79 presymptomatic), 143 GRN (112 presymptomatic), and 57 MAPT (43 presymptomatic) pathogenic variant carriers. Principal component analysis revealed 5 motor clusters, which we call progressive supranuclear palsy (PSP)-like, bulbar amyotrophic lateral sclerosis (ALS)-like, mixed/ALS-like, Parkinson disease (PD) like, and corticobasal syndrome–like motor phenotypes. There was no significant group difference in the frequency of signs of different motor phenotypes. However, mixed/ALS-like motor signs were most frequent, followed by PD-like motor signs. Although the PSP-like phenotype was associated with mesencephalic atrophy, the mixed/ALS-like phenotype was associated with motor cortex and corticospinal tract atrophy. The PD-like phenotype was associated with widespread cortical and subcortical atrophy. Estimated time to onset, genetic group and their interaction influenced motor signs. In c9orf72 pathogenic variant carriers, motor signs could be detected up to 25 years before expected symptom onset.DiscussionThese results indicate the presence of multiple natural clusters of motor signs in genetic FTD, each correlated with specific atrophy patterns. Their motor severity depends on time and the affected gene. These clinicogenetic associations can guide diagnostic evaluations and the design of clinical trials for new disease-modifying and preventive treatments.

A novel phenotype in an Italian family with a rare progranulin mutation

IntroductionProgranulin (PGRN) is a secreted glycoprotein encoded in humans by the GRN gene, located on chromosome 17q21. Several nonsense and missense pathogenetic GRN mutations have been described.ObjectiveWe herein describe two sisters carrying a rare GRN mutation with extremely different clinical features and family history of dementia and behavioral disorders, with a novel presentation with stridor and dysphonia.MethodsPatients underwent a multidimensional assessment including neurological and neuropsychological evaluation, structural and functional imaging, and genetic screening.ResultsThe younger sister presented at the age of 64 with inspiratory stridor, dysphonia and exercise-induced dyspnea. Transnasal fiberoptic laryngoscopy showed bilateral adduction of the vocal cords at rest and paradoxical further adduction of the vocal cords during forced inspiration, suggesting the hypothesis of an adductor laryngeal dystonia. The older sister presented at the age of 63 with a rapidly progressive corticobasal syndrome. The only clinical feature common to both sisters was a dysexecutive syndrome. The c.893G > A mutation in exon 9 of GRN was found in heterozygosis in both sisters, causing a missense Arginine to Histidine substitution in position 298 of the protein (p.R298H).ConclusionsOur report supports the pathogenicity of the GRN p.R298H mutation, which is first detected in two members from the same family, showing an extremely different phenotypes. Moreover, we report the first case of an FTD-associated mutation presenting with inspiratory stridor and dysphonia linked to adductor laryngeal dystonia, thus expanding the clinical spectrum of GRN-related disorders.

Distinct cell type-specific protein signatures in GRN and MAPT genetic subtypes of frontotemporal dementia

Frontotemporal dementia is characterized by progressive atrophy of frontal and/or temporal cortices at an early age of onset. The disorder shows considerable clinical, pathological, and genetic heterogeneity. Here we investigated the proteomic signatures of frontal and temporal cortex from brains with frontotemporal dementia due to GRN and MAPT mutations to identify the key cell types and molecular pathways in their pathophysiology. We compared patients with mutations in the GRN gene (n = 9) or with mutations in the MAPT gene (n = 13) with non-demented controls (n = 11). Using quantitative proteomic analysis on laser-dissected tissues we identified brain region-specific protein signatures for both genetic subtypes. Using published single cell RNA expression data resources we deduced the involvement of major brain cell types in driving these different protein signatures. Subsequent gene ontology analysis identified distinct genetic subtype- and cell type-specific biological processes. For the GRN subtype, we observed a distinct role for immune processes related to endothelial cells and for mitochondrial dysregulation in neurons. For the MAPT subtype, we observed distinct involvement of dysregulated RNA processing, oligodendrocyte dysfunction, and axonal impairments. Comparison with an in-house protein signature of Alzheimer’s disease brains indicated that the observed alterations in RNA processing and oligodendrocyte function are distinct for the frontotemporal dementia MAPT subtype. Taken together, our results indicate the involvement of different brain cell types and biological mechanisms in genetic subtypes of frontotemporal dementia. Furthermore, we demonstrate that comparison of proteomic profiles of different disease entities can separate general neurodegenerative processes from disease-specific pathways, which may aid the development of disease subtype-specific treatment strategies.

Abstract 97: Mechanisms of action and regulation of the progranulin/EphA2 axis in mesothelioma

Abstract Mesothelioma is an aggressive tumor with very poor prognosis. The limited availability of therapeutic options for mesothelioma patients suggests the need for a better understanding of mesothelioma biology and the identification of novel therapeutic targets. Progranulin is a pluripotent growth factor whose dysregulation is implicated in several human pathologies including cancer. The pro-tumorigenic activity of progranulin depends on the activation of its functional receptor EphA2. Indeed, in bladder cancer, progranulin promotes EphA2 phosphorylation at Ser897 and triggers EphA2 oncogenic action resulting in increased tumor cell migration, invasion and in vivo tumor growth. Both progranulin and EphA2 are expressed in mesothelioma, with progranulin promoting tumor angiogenesis in a VEGF-independent manner and EphA2 being often mutated or overexpressed. However, in mesothelioma, the potential functional interaction between progranulin and EphA2 is unexplored. Using a panel of mesothelioma cell lines covering all mesothelioma subtypes, we observed increased levels of phosphorylated EphA2 at Ser897 when compared to immortalized normal mesothelial cells, and the levels of phosphorylation positively correlated with progranulin expression. Progranulin-dependent activation of EphA2 in mesothelioma cells promoted the activation of the MAPK and AKT pathways and ERK1/2-dependent EphA2 phosphorylation at Ser897. Transient depletion of progranulin by siRNA approaches as well as GRN gene knock-out by CRISP/Cas9 strategies in mesothelioma cells reduced the activation of the AKT signaling pathway and inhibited the migratory and invasive capabilities of progranulin-depleted cells when compared to parental cells, suggesting that the progranulin/EphA2 axis is oncogenic in mesothelioma. However, EphA2 genetic ablation resulted in an increased basal activation of AKT and MAPK and in progranulin-evoked EphA2-independet AKT/MAPK activation, indicating that alternative membrane receptors might compensate for EphA2 loss and sustain progranulin action in mesothelioma. Using several pharmacological and genetic approaches, we uncovered a role for EGFR and FAK in compensating for EphA2 loss by triggering progranulin-dependent oncogenic signaling in mesothelioma, highlighting a complex functional cross-talk between EphA2, EGFR and FAK in mediating progranulin-dependent tumorigenesis. Thus, these results suggest the need for combinatorial therapeutic approaches to blunt progranulin oncogenic action in mesothelioma. Citation Format: Elisa Ventura, Simone Buraschi, Stephen J. Williams, Antonino Belfiore, Renato V. Iozzo, Antonio Giordano, Andrea Morrione. Mechanisms of action and regulation of the progranulin/EphA2 axis in mesothelioma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 97.

Circ0001470 Acts as a miR-140-3p Sponge to Facilitate the Progression of Embryonic Development through Regulating PTGFR Expression.

Embryonic implantation and development are vital in early pregnancy and assisted reproduction. Circular RNAs (circRNAs) are involved in the two physiological processes and thus regulate animal reproduction. However, their specific regulatory functions and mechanisms remain unclear. Here, a novel circ0001470, originating from the porcine GRN gene, differentially expressed on day 18 versus day 32 of gestation in Meishan and Yorkshire pigs was screened. The circularization characteristic of circ0001470 was identified based on divergent primer amplification, Sanger sequencing, RNase digestion, and RNA nuclear-cytoplasmic fractionation. Functionally, circ0001470 can promote cell proliferation and cycle progression of endometrial epithelial cells (EECs) and also inhibit apoptosis of EECs using CCK-8 assays and flow cytometry analyses. Mechanistically, bioinformatics database prediction, luciferase screening, RNA immunoprecipitation (RIP), RNA-pull down, and FISH co-localization experiments revealed that the circ0001470 acted as a competing endogenous RNA (ceRNA) through sponging miR-140-3p to regulate downstream PTGFR expression. Moreover, in vivo assays revealed that mmu_circGRN promoted embryonic development by affecting the expression of PTGFR, which can activate the MAPK reproduction pathway and facilitate pregnancy maintenance. This study enriched our understanding of circRNAs in embryo implantation and development by deciding the fate of EECs.

Frequency of GRN ‐associated cases in a Russian cohort of patients with frontotemporal dementia

Frontotemporal dementia (FTD) is the second most common cause of early-onset neurodegenerative dementia. Up to 40% of FTD cases are inherited. Mutations in GRN gene are frequent genetic cause of FTD in different population (1-5% of sporadic cases and 5-20% of familial cases). The frequency of this mutation in a Russian cohort of FTD patients has not been studied before. We analyzed DNA samples of patients with FTD for the period from 2014 to 2019 (N=57); 42% of patients had positive family history of dementia. All patients were examined at the Research Center of Neurology and I.M. Sechenov First Moscow State Medical University (Moscow). The distribution by phenotypes is shown in Table 1. GRN mutation screening was performed by Sanger sequencing. In total, 4 pathogenic heterozygous mutations in GRN gene were identified in 5 patients. Two frameshift mutations in exon 9 have not been previously described (Gly384fs*, Cys315fs*). One of these mutations (Gly384fs*) was detected in two unrelated patients with non-fluent variant of primary progressive aphasia (nfvPPA) with the same age at onset and positive family history of dementia, but different rates of the disease progression. Mutation Cys315fs* was detected in one patient with behavioral variant of FTD (bvFTD) without family history. Two other mutations (Gly35fs* and IVS9+1G>A) were previously described, and our patients with these mutations had bvFTD and nfvPPA, respectively. Thus, the frequency of mutation in GRN gene was 8.8%: 12.5% in familial FTD cases and 6% in sporadic cases. GRN mutations were more common in nfvPPA group (17%) compared to bvFTD (7%). Presented are the first data of GRN mutation frequency in Russian patients with FTD. The frequency found is comparable to the data described in other populations. The most frequent disease phenotype in GRN mutation carriers is nfvPPA. Two new frameshift mutations in GRN gene were identified.

A systematic review of progranulin concentrations in biofluids in over 7,000 people: Assessing the pathogenicity of GRN mutations and other influencing factors

AbstractBackgroundHeterozygous mutations in the GRN gene are a major cause of genetic frontotemporal dementia (FTD), accounting for an estimated 5‐10% of all people with FTD. GRN encodes for progranulin, with mutations causing haploinsufficiency, and being associated with significantly lower concentrations of progranulin in biofluids in mutation carriers compared to controls.MethodWe performed a search of the literature (up to December 2019) looking for publications reporting progranulin concentrations within serum, plasma or CSF in any medical condition including FTD and other forms of dementia. We then contacted all authors and asked if they were able to share anonymised data from their study including progranulin concentrations and clinical data including specific mutation if present, clinical diagnosis, age at onset of dementia, sex, and GRN rs5848 polymorphism. Data from 7,071 people was collated and analysed.ResultData on plasma progranulin concentrations measured using the Adipogen assay was available from 3,265 cases. Variability in levels across 109 different GRN mutations was seen and when split into mutation groups, missense variants outside the signal peptide had significantly higher levels compared to all other groups, suggesting that these variants are unlikely to be pathogenic. We established a plasma progranulin cut‐off value of 74.8ng/µL between pathogenic GRN mutation carriers and non‐carriers. We found that the GRN rs5848 polymorphism also affected plasma progranulin levels, with the TT genotype associated with significantly lower levels than CC. Sex differences were also seen, with significantly higher progranulin levels in females than males.ConclusionTogether these findings highlight the variable pathogenicity of different GRN mutations and the importance of considering other factors such as genetic risk factors and sex differences when looking at biofluid concentrations of progranulin. This is of particular relevance in upcoming clinical trials of progranulin‐associated FTD where progranulin levels are being measured as outcome measures.

Retinal biomarkers predict future cognitive performance in progranulin‐haploinsufficient frontotemporal dementia

AbstractBackgroundProgranulin (GRN) haploinsufficiency caused by heterozygous mutations in the GRN gene is a common cause of early‐onset familial frontotemporal dementia (FTD). Our group previously described neuronal ceroid lipofuscinosis‐like features in the retinae of asymptomatic and mildly symptomatic heterozygous GRN mutation carriers (GRN‐carriers). However, additional intraretinal changes, their clinical relevance and utility as biomarkers remain unexplored. We aimed to describe the distinct retinal disease pattern in GRN‐carriers and to investigate the association of retinal change with subsequent brain atrophy and cognitive decline.MethodWe applied optical coherence tomography (OCT) and scanning laser ophthalmoscopy at baseline in 23 GRN‐carriers (age [years, mean+SD]: 62±11, gender [male, N(%)]: 11(48), mean Clinical Dementia Rating (CDR) = 0.5; CDR = 0.0 for 9 subjects) and 85 healthy controls (HCs) (age: 69±15, gender: 42(49)), investigating qualitative and quantitative retinal changes. Linear mixed‐effect models (LME) were used to study the relationships at a group‐level between OCT findings and longitudinal assessments (follow‐up time [months, median(min‐max)]: 28(12‐73)) of cognitive performance including lexical fluency (LF), semantic fluency (SF) and emotion naming (EN). MRI analyses are pending.ResultEight eyes (17%) of five GRN‐carriers (22%) had drusen‐like depositions detectable on OCT. Quantifying macular layers, GRN‐carriers had a thicker outer plexiform layer (OPL: 0.33±0.05mm3, p<0.001), thinner outer nuclear layer (ONL: 0.66±0.07mm3, p = 0.019) and thinner retinal pigment epithelium (RPE: 0.15±0.02mm3, p = 0.039) compared with HC (OPL: 0.30±0.03mm3, ONL: 0.69±0.07mm3, RPE: 0.16±0.01mm3), but no differences in inner retinal layers (confirmed excluding eyes with drusen). The OPL/ONL‐ratio was higher in GRN‐carriers (0.51±0.13) than HC (OPL/ONL‐ratio: 0.44+0.08, B = 0.079, p<0.001). GRN‐carriers with OPL/ONL‐ratio>median at baseline had a faster annualized decline of LF (‐2.60±5.62, B = 0.273, p = 0.002), SF (‐5.70±9.76, B = 0.213, p = 0.035) and EN (0.44±1.24, B = 0.066, p = 0.040) during follow‐up compared to subjects with OPL/ONL‐ratio<median (LF: 4.25±3.50; SF: 0.00±4.32, EN: 2.00±1.83).ConclusionGRN‐haploinsufficiency is associated with retinal phenotypes, including drusen and outer retinal layer thinning, suggestive of photoreceptor degeneration. OPL/ONL‐ratio predicted FTD associated cognitive worsening ‐ and thereby might have potential as biomarker of disease progression in clinical trials.

Tweaking Progranulin Expression: Therapeutic Avenues and Opportunities.

Frontotemporal dementia (FTD) is a neurodegenerative disease, leading to behavioral changes and language difficulties. Heterozygous loss-of-function mutations in progranulin (GRN) induce haploinsufficiency of the protein and are associated with up to one-third of all genetic FTD cases worldwide. While the loss of GRN is primarily associated with neurodegeneration, the biological functions of the secreted growth factor-like protein are more diverse, ranging from wound healing, inflammation, vasculogenesis, and metabolic regulation to tumor cell growth and metastasis. To date, no disease-modifying treatments exist for FTD, but different therapeutic approaches to boost GRN levels in the central nervous system are currently being developed (including AAV-mediated GRN gene delivery as well as anti-SORT1 antibody therapy). In this review, we provide an overview of the multifaceted regulation of GRN levels and the corresponding therapeutic avenues. We discuss the opportunities, advantages, and potential drawbacks of the diverse approaches. Additionally, we highlight the therapeutic potential of elevating GRN levels beyond patients with loss-of-function mutations in GRN.

The Frequency of Genetic Mutations Associated With Behavioral Variant Frontotemporal Dementia in Chinese Han Patients.

BackgroundBehavioral variant frontotemporal dementia (bvFTD) is a clinically heterogeneous syndrome with high heredity. However, the frequencies of mutations associated with bvFTD have yet to be determined. The aim of the current study was to investigate the frequency of Chinese Han patients harboring genetic bvFTD variants.MethodsA total of 49 bvFTD patients selected from our frontotemporal lobar degeneration database, including 14 familial cases belonging to eight families and 35 sporadic cases were consecutively recruited from July 2014 to December 2019 at Xuanwu Hospital (Beijing, China). Whole-exome sequencing (WES) was performed and repeat-primed PCR was used to test samples for the C9orf72 hexanucleotide repeat expansion mutation. The frequency of genetic variants and the pathogenicity of the novel variants were analyzed.ResultsTen pathogenic or likely pathogenic variants were identified in 17 bvFTD patients, including C9orf72 repeat expansions, six previously reported mutations and three novel mutations (MAPT p. R5C, p. D54N, GRN p. P451L). Genetic mutations accounted for 27.9% (12/43) of total cases, 87.5% (7/8) of patients with familial bvFTD, and 14.3% (5/35) with sporadic bvFTD. Pathogenic variants mostly occurred in MAPT gene (20.9%, 9/43), followed by C9orf72 repeat expansions (2.3%, 1/43), GRN gene (2.3%, 1/43) and FUS gene (2.3%, 1/43).ConclusionThere was a high prevalence of genetic variants in Chinese bvFTD patients, highlighting the necessity of genetic testing for bvFTD.

Hyper-religiosity and visual hallucinations in a patient with frontotemporal dementia carrying a double variant in GRN gene

Introduction: Hyper-religiosity has been reported in patients affected by frontotemporal dementia (FTD) with asymmetrical, predominantly right-sided frontotemporal atrophy. Case report: We report a FTD patient carrying a double genetic variant (p.Cys139Arg and c.*78C > T) in the progranulin (GRN) gene who showed an unusual clinical phenotype characterized by hyper-religiosity behavior and visual hallucinations with exclusively religious content. Noteworthy, this patient exhibited a slow clinical and radiological rate of disease progression and a predominantly left-sided frontotemporal atrophy. Discussion and conclusion: The simultaneous presence of these GRN variants in our FTD patient with predominant atrophy in the left (dominant) hemisphere could determine the unusual phenotype with hyper-religiosity and visual hallucinations with exclusively religious content and influence the slow rate of disease progression.

Frequency of frontotemporal dementia-related gene variants in Turkey

Just as its clinical heterogeneity, genetic basis of Frontotemporal dementia (FTD) is also diverse and multiple molecular pathways are thought to be involved in disease pathogenesis. In the present study, FTD- related genes were evaluated in a Turkish cohort of 175 index FTD patients with a gene panel including GRN, MAPT, TARDBP, FUS, CHMP2B and VCP genes. Potential genetic associations were prospected in 16 patients (9.1%); five variants (p.(Gly35Glufs) and p.(Cys253Ter) in GRN; p.(Arg95Cys) in VCP; p.(Met405Val) in TARDBP and p.(Pro636Leu) in MAPT) were classified as pathogenic (P) or likely pathogenic (LP), in four familial and one sporadic patients. Three novel variants in MAPT, CHMP2B and FUS were also identified in familial cases. The most common pathogenic variants were observed in the GRN gene with a frequency of 1.14% (2/175) and this rate was 4.57% (8/175), including variants of uncertain significance (VUS). In this study with the largest cohort of Turkish FTD patients, GRN and MAPT variants were identified as the most common genetic associations; and rare causes like VCP, TARDBP, CHMP2B and FUS variants are recommended to be considered in patients with compatible clinical findings.

Primary Progressive Aphasia Associated With GRN Mutations: New Insights Into the Nonamyloid Logopenic Variant.

To determine relative frequencies and linguistic profiles of primary progressive aphasia (PPA) variants associated with GRN (progranulin) mutations and to study their neuroanatomic correlates. Patients with PPA carrying GRN mutations (PPA-GRN) were selected among a national prospective research cohort of 1,696 patients with frontotemporal dementia, including 235 patients with PPA. All patients with amyloid-positive CSF biomarkers were excluded. In this cross-sectional study, speech/language and cognitive profiles were characterized with standardized evaluations, and gray matter (GM) atrophy patterns using voxel-based morphometry. Comparisons were performed with controls and patients with sporadic PPA. Among the 235 patients with PPA, 45 (19%) carried GRN mutations, and we studied 32 of these. We showed that logopenic PPA (lvPPA) was the most frequent linguistic variant (n = 13, 41%), followed by nonfluent/agrammatic (nfvPPA; n = 9, 28%) and mixed forms (n = 8, 25%). Semantic variant was rather rare (n = 2, 6%). Patients with lvPPA, qualified as nonamyloid lvPPA, presented canonical logopenic deficit. Seven of 13 had a pure form; 6 showed subtle additional linguistic deficits not fitting criteria for mixed PPA and hence were labeled as logopenic-spectrum variant. GM atrophy involved primarily left posterior temporal gyrus, mirroring neuroanatomic changes of amyloid-positive-lvPPA. Patients with nfvPPA presented agrammatism (89%) rather than apraxia of speech (11%). This study shows that the most frequent PPA variant associated with GRN mutations is nonamyloid lvPPA, preceding nfvPPA and mixed forms, and illustrates that the language network may be affected at different levels. GRN testing is indicated for patients with PPA, whether familial or sporadic. This finding is important for upcoming GRN gene-specific therapies.

Human progranulin-expressing mice as a novel tool for the development of progranulin-modulating therapeutics

The granulin protein (also known as, and hereafter referred to as, progranulin) is a secreted glycoprotein that contributes to overall brain health. Heterozygous loss-of-function mutations in the gene encoding the progranulin protein (Granulin Precursor, GRN) are a common cause of familial frontotemporal dementia (FTD). Gene therapy approaches that aim to increase progranulin expression from a single wild-type allele, an area of active investigation for the potential treatment of GRN-dependent FTD, will benefit from the availability of a mouse model that expresses a genomic copy of the human GRN gene. Here we report the development and characterization of a novel mouse model that expresses the entire human GRN gene in its native genomic context as a single copy inserted into a defined locus (Hprt) in the mouse genome. We show that human and mouse progranulin are expressed in a similar tissue-specific pattern, suggesting that the two genes are regulated by similar mechanisms. Human progranulin rescues a phenotype characteristic of progranulin-null mice, the exaggerated and early deposition of the aging pigment lipofuscin in the brain, indicating that the two proteins are functionally similar. Longitudinal behavioural and neuropathological analyses revealed no significant differences between wild-type and human progranulin-overexpressing mice up to 18 months of age, providing evidence that long-term increase of progranulin levels is well tolerated in mice. Finally, we demonstrate that human progranulin expression can be increased in the brain using an antisense oligonucleotide that inhibits a known GRN-regulating micro-RNA, demonstrating that the transgene is responsive to potential gene therapy drugs. Human progranulin-expressing mice represent a novel and valuable tool to expedite the development of progranulin-modulating therapeutics.

Defective Lysosomal Lipid Catabolism as a Common Pathogenic Mechanism for Dementia.

Dementia poses an ever-growing burden to health care and social services as life expectancies have grown across the world and populations age. The most common forms of dementia are Alzheimer's disease (AD), vascular dementia, frontotemporal dementia (FTD), and Lewy body dementia, which includes Parkinson's disease (PD) dementia and dementia with Lewy bodies (DLB). Genomic studies over the past 3 decades have identified variants in genes regulating lipid transporters and endosomal processes as major risk determinants for AD, with the most significant being inheritance of the ε4 allele of the APOE gene, encoding apolipoprotein E. A recent surge in research on lipid handling and metabolism in glia and neurons has established defective lipid clearance from endolysosomes as a central driver of AD pathogenesis. The most prevalent genetic risk factors for DLB are the APOE ε4 allele, and heterozygous loss of function mutations in the GBA gene, encoding the lysosomal catabolic enzyme glucocerebrosidase; whilst heterozygous mutations in the GRN gene, required for lysosomal catabolism of sphingolipids, are responsible for a significant proportion of FTD cases. Homozygous mutations in the GBA or GRN genes produce the lysosomal storage diseases Gaucher disease and neuronal ceroid lipofuscinosis. Research from mouse and cell culture models, and neuropathological evidence from lysosomal storage diseases, has established that impaired cholesterol or sphingolipid catabolism is sufficient to produce the pathological hallmarks of dementia, indicating that defective lipid catabolism is a common mechanism in the etiology of dementia.

Network analysis of the brain proteome of GRN knockout mice reveals pathogenic mechanisms shared in human frontotemporal dementia caused by GRN mutations

AbstractBackgroundMutations in the GRN gene, encoding the progranulin (PGRN) protein, are a common cause of Frontotemporal dementia (FTD) and induce haploinsufficiency of PGRN. PGRN is composed of 7.5 repeating domains called granulins (GRNs 1‐7). PGRN is processed into GRNs within the lysosome, where we hypothesize they are critical for lysosome homeostasis and function. However, it is unclear how decreased levels of lysosomal PGRN/GRNs cause FTD, Alzheimer’s disease, and related neurodegenerative disorders.MethodsWe performed quantitative proteomic analysis of whole‐brain tissue from wild‐type (Grn +/+) and PGRN knockout (Grn ‐/‐) mice at 3‐ and 19‐months of age using 10‐plex Tandem Mass Tag (TMT) isobaric labeling mass spectrometry. Protein changes were validated using immunobloting, immunohistochemistry, and ELISAs.ResultsDeep proteome analysis of mouse brains detected 8,695 proteins. Weighted correlation network analysis (WGCNA) of the brain proteome of Grn ‐/‐ compared to Grn +/+ mice identified 29 modules of highly co‐expressed proteins. In particular, 3 modules strongly correlated to Grn deficiency, increased with age, and were enriched with lysosomal proteins (Gpnmb, Ctsd, Tpp1) and inflammatory proteins (Lgals3, GFAP, CD44). Immunohistochemistry revealed age‐dependent increases in multiple lysosomal proteins and inflammation throughout the Grn ‐/‐ brain, particularly in the thalamus. Importantly, we discovered similar changes in the brain and cerebrospinal fluid (CSF) of individuals with GRN mutations that cause FTD (FTD‐GRN). GPNMB and galectin‐3 (LGALS3) were significantly elevated in the lysates of FTD‐GRN brain. Further, GPNMB levels were significantly increased in human FTD‐GRN CSF compared to controls and other genetic forms of FTD (MAPT and C9orf72).ConclusionsThese data suggest that common pathogenic pathways are dysregulated in human FTD cases with GRN haploinsufficiency and Grn ‐/‐ mice. Moreover, GPNMB is a novel, potential biomarker for FTD. Our findings support the idea that insufficiency of PGRN and GRNs in humans cause FTD, AD, and related neurodegenerative diseases through lysosomal dysfunction and neuroinflammation and suggest novel therapeutic approaches.

Screening for gene mutation in early onset Alzheimer’s disease and frontotemporal dementia: Report from a Serbian tertiary referral center

AbstractBackgroundEarly‐onset dementia (EOD) is conventionally considered to include patients with disease onset before 65 years of age. Alzheimer’s disease (AD) and Frontotemporal dementia (FTD) are two most common forms of degenerative EOD. Our aim was to screen for known gene mutation status in consecutive degenerative EOD patients.MethodTwo hundred and eight consecutive patients diagnosed according to the current clinical criteria for AD and FTD spectrum were recruited from the Neurology Clinic, Clinical Centre of Serbia from 01.04.2012. until 01.04.2017. Patient from AD spectrum were tested for APP, PSEN1, GRN, MAPT and C9ORF72 gene mutation and FTD patients for GRN, MAPT, C9ORF72, VCP, ANG gene mutation.ResultGene mutations were identified in 3.9% of our AD patients: 2.3% patients had mutations in the PSEN1 gene and 1.5% patients in the APP gene. There was no MAPT, GRN and C9ORF72 mutations carriers in our AD cohort. Genetic mutations have been demonstrated in 10.3% of patients with FTD. The most frequent was the hexanucleotide expansion in C9ORF72 (6.4% of all FTD patients), following mutations in GRN, VCP and ANG with the same frequency of (1.3% FTD for each gene). No patient was a MAPT mutation carrier.ConclusionGene mutations were rare causes in our AD cohort. The frequency of carriers was higher in FTD patients‐ mutations were identified in C9ORF72, GRN, VCP and ANG genes. No MAPT mutation carriers were identified in our cohort of patients with degenerative EOD.

An ABCA7 partial deletion and a GRN variant in a semantic variant of primary progressive aphasia patient

AbstractBackground ABCA7 gene (ATP‐binding cassette transporter A7) loss‐of‐function mutations are related to increased risk of suffering Alzheimer’s disease (AD). On the other hand, mutations in GRN (Progranulin) gene are causative of frontotemporal dementia (FTD).MethodsThe proband was a patient diagnosed from semantic variant of primary progressive aphasia. Age at onset was at 50 years‐old, presenting progressive cognitive decline with an important language loss. The MRI showed a left temporal atrophy. AD CSF biomarkers were normal and no familial history of dementia was reported. Next generation sequencing was performed with Illumina NextSeq500. Single nucleotide variants were detected using GATK and copy number variants using ExomeDepth algorithm. Sanger sequencing was performed for GRN variant confirmation and MLPA technique for ABCA7 deletion validation. C9orf72 repeat expansion was studied with a repeat primed PCR and fragment analysis. Biological samples from his mother and a brother were obtained. Commercial ELISA kit was used to measure serum PGRN levels (Adipogen).ResultsPatient showed an ABCA7 partial deletion (exons 17‐47) plus 4 contiguous genes, of a total of 105 kb in size (hg19 chr19:g.1048865_1154298). Deletion was confirmed in the proband and discarded in the proband’s mother and brother by MLPA. Patient and his mother (asymptomatic at 81 yo) were also carriers of a reported GRN variant, p.(Asp33Glu; rs63750742). Progranulin serum levels were normal in the patient and his family members. C9orf72 screening was negative.ConclusionsThe patient harbored two genetic alterations in genes related to dementia risk, although it is unlikely that any of them alone could be responsible of the FTD phenotype. ABCA7 deletion should be de novo or father inherited. ABCA7 protein truncating variant at exon 14 (p.Arg578fs), which has a similar protein consequence, is relatively frequent in control population, although has showed a 1.8‐fold enrichment in AD patients. Moreover, GRN variant does not seem to be pathogenic or low penetrance because proband’s mother is unaffected and serum progranulin levels are normal. In conclusion, these variants per se are likely not sufficient to cause the disease, but rather risk variants of intermediate to high penetrance along with other factors.

Isolated parkinsonism is an atypical presentation of GRN and C9orf72 gene mutations

IntroductionA phenotype of isolated parkinsonism mimicking Idiopathic Parkinson's Disease (IPD) is a rare clinical presentation of GRN and C9orf72 mutations, the major genetic causes of frontotemporal dementia (FTD). It still remains controversial if this association is fortuitous or not, and which clinical clues could reliably suggest a genetic FTD etiology in IPD patients. This study aims to describe the clinical characteristics of FTD mutation carriers presenting with IPD phenotype, provide neuropathological evidence of the mutation's causality, and specifically address their “red flags” according to current IPD criteria. MethodsSeven GRN and C9orf72 carriers with isolated parkinsonism at onset, and three patients from the literature were included in this study. To allow better delineation of their phenotype, the presence of supportive, exclusion and “red flag” features from MDS criteria were analyzed for each case. ResultsAmongst the ten patients (5 GRN, 5 C9orf72), seven fulfilled probable IPD criteria during all the disease course, while behavioral/language or motoneuron dysfunctions occurred later in three. Disease duration was longer and dopa-responsiveness was more sustained in C9orf72 than in GRN carriers. Subtle motor features, cognitive/behavioral changes, family history of dementia/ALS were suggestive clues for a genetic diagnosis. Importantly, neuropathological examination in one patient revealed typical TDP-43-inclusions without alpha-synucleinopathy, thus demonstrating the causal link between FTD mutations, TDP-43-pathology and PD phenotype. ConclusionWe showed that, altogether, family history of early-onset dementia/ALS, the presence of cognitive/behavioral dysfunction and subtle motor characteristics are atypical features frequently present in the parkinsonian presentations of GRN and C9orf72 mutations.

Network Analysis of the Brain Proteome of Grn Knockout Mice Reveals Pathogenic Mechanisms Shared in Human Frontotemporal dementia caused by GRN mutations.

Mutations in the GRN gene, which encodes the progranulin (PGRN) protein, are one of the most common causes of Frontotemporal dementia (FTD) and cause disease through haploinsufficiency of PGRN. PGRN is composed of 7.5 repeating domains termed granulins (GRNs 1–7) that are joined by linker regions. We have recently found that PGRN is processed into ~6kDa GRNs within the lysosome, where we hypothesize they are critical for lysosome homeostasis (Holler et al, eNeuro, 2017 Aug 18;4(4)). However, the molecular mechanisms caused by decreased levels of lysosomal PGRN/GRNs that lead to FTD, Alzheimer’s disease, and other neurodegenerative disorders are still unknown. To gain insight into the mechanisms of FTD pathogenesis, we performed an unbiased quantitative proteomic analysis of whole‐brain tissue from wild‐type (WT) and Progranulin knockout (Grn−/−) mice at 3 and 19‐months of age. We utilized a 10‐plex Tandem Mass Tag (TMT) isobaric labeling mass spectrometry approach for peptide labeling and quantification that enabled a deep proteome analysis of mouse brain and detection of 8,695 proteins. Differential expression analysis of the brain proteome of 3‐month old Grn−/− versus WT mice revealed 29 up and 26 down‐regulated proteins, while 119 proteins were up and 20 proteins were down‐regulated in 19‐month old Grn−/− mice. Then we performed weighted correlation network analysis (WGCNA) on the brain proteome of Grn−/− vs WT mice and identified 29 modules of highly co‐expressed proteins. In particular, 3 modules were strongly correlated to Grn deficiency, increased with age, and were enriched with lysosomal proteins (Ctsd, Fuca2, Tpp1) and inflammatory proteins (Gpnmb, Lgals3, GFAP, CD44, S100a C1qa). Subsequent validation of changes identified through proteomics using western blotting and immunohistochemistry revealed age‐dependent increases in multiple lysosomal proteins (i.e. Cathepsin D and Z) and markers of gliosis (GFAP, IBA1) throughout the brain, with a particularly marked increase in the thalamus in old Grn−/− mice versus age‐matched WT. Next, we asked if similar changes occurred in the biofluids or post‐mortem tissue from individuals with GRN mutations associated with FTD. We found that GPNMB and galectin‐3 (LGALS3) were significantly elevated in the lysates of FTD‐GRN brain samples compared to healthy controls. Total levels of GPNMB were also elevated human FTD‐GRN cerebrospinal fluid and plasma samples compared to controls. These data suggest that common pathogenic pathways are dysregulated in human FTD cases with GRN haploinsufficiency and mice completely deficient for Grn. Moreover, our findings support the idea that insufficiency of PGRN and GRNs in humans may cause FTD, AD and related neurodegenerative diseases through lysosomal dysfunction and neuroinflammation and suggest novel therapeutic approaches.Support or Funding Information1) National Institute of Health NINDS grants (R01NS105971; R01NS093362)2) the Association for Frontotemporal Degeneration grant3) The Bluefield Project to Cure FTD