Progranulin Mutations Research Articles

Early detection of neuropsychiatric, language and motor symptoms in genetic frontotemporal dementia (FTD): Defining prodromal FTD

AbstractBackgroundThe prodromal stage of genetic frontotemporal dementia (FTD) is currently poorly defined. Whilst the majority of people with genetic FTD develop behavioural symptoms, a number of people present with primary progressive aphasia (PPA), neuropsychiatric symptoms, parkinsonism, including corticobasal syndrome (CBS) or progressive supranuclear palsy (PSP), or amyotrophic lateral sclerosis (ALS). Such variable phenotypes pose a barrier to clearer definitions of prodromal FTD.Methods1139 people have been recruited to the Genetic FTD Initiative (GENFI), a deep phenotyping international multicentre cohort study of FTD. Clinical data on symptoms within the language, neuropsychiatric and motor domains have been collected on presymptomatic and symptomatic mutation carriers, as well as mutation‐negative controls using the GENFI Symptom Scales.Results Language: In the symptomatic phase, 19 participants met Gorno‐Tempini diagnostic criteria for primary progressive aphasia (PPA), the majority (17) of whom had a progranulin (GRN) mutation. The phenotype in these cases was either nonfluent variant (8) or did not meet criteria for a specific variant (9). Additionally, 42 presymptomatic participants had subtle early language problems. Neuropsychiatric: Symptoms were reported most frequently in symptomatic C9orf72 mutation carriers (91.7% of all symptomatic C9orf72 carriers) and to a lesser extent in GRN and MAPT mutation carriers. Depression and anxiety were common in mutation‐negative controls (14%) as well as mutation carriers. Motor: ALS and FTD‐ALS were most frequent in C9orf72‐associated FTD (12.5% of all symptomatic C9orf72 carriers). Parkinsonism (including PSP and CBS) was present to a lesser extent in C9orf72, GRN, and MAPT mutation carriers.ConclusionsLanguage, neuropsychiatric and motor features are common in genetic FTD and will need to be included in any prodromal staging system. Improved, operationalised measurement of such symptoms will allow improved stratification of individuals, and aid clinical trials. Future work should unravel the temporal trajectory of such symptoms within each form of genetic FTD.

TDP‐43 proteinopathy in the retina of patients with frontotemporal lobar degeneration

Frontotemporal lobar degeneration (FTLD) is a clinically and pathologically heterogeneous disease. The distinct underlying pathologies include aggregation of TDP-43, tau and FUS. Currently, no ante-mortem biomarkers are available to distinguish between the different pathological subtypes, providing challenges for diagnosis and therapeutic interventions. As an extension of the brain, the retina displays similarities in terms of anatomy and functionality. The accessibility of the retina provides a 'window' into the brain and a great potential for noninvasive imaging of neurodegenerative changes in patients. The aim of this study is to assess the presence of TDP-43 in the retina.Post-mortem retina tissue was obtained from donors with FTLD-TDP (n=6), of which 3 donors carried a C9orf72 repeat expansion, one progranulin (PRGN) mutation and two sporadic donors. We also included donors with FTLD-tau (n=5), FTLD-FUS (n=1) , AD with limbic TDP-43 depositions (n=2), and donors with ALS-TDP (n=2). Immunohistochemical stainings were performed for panTDP-43, phosphorylated TDP-43 (pTDP-43), p62, and dipeptides (polyGA and polyGP).In C9orf72 and PRGN mutation carriers, as well as one sporadic FTLD-TDP donor, TDP-43 inclusions were observed in the outer plexiform layer of the retina. One sporadic donor showed granular TDP-43 deposits in amacrine cells. No TDP-43 inclusions were observed in FTLD-tau, ALS and AD donors. Interestingly, all C9orf72 mutation carriers showed abundant presence of p62 and dipeptide inclusions in the inner nuclear layer of the retina.Manifestations of TDP-43 and dipeptide pathology are present in the retina of patients with FTLD-TDP. No TDP-43 inclusions are present in the retina of ALS or AD patients with limbic TDP-43 pathology, suggesting that retinal TDP-43 pathology is specific for FTLD-TDP. With the advances in ocular imaging techniques these findings provide opportunities for non-invasive retinal imaging for diagnosis and monitoring progression of FTLD-TDP.

Transcriptomic and Network Meta-Analysis of Frontotemporal Dementias.

Frontotemporal lobar degeneration (FTLD), also known as frontotemporal dementia (FTD), results in a progressive decline in executive function, leading to behavioral changes, speech problems, and movement disorders. FTD is the second most common cause of young-onset dementia affecting approximately 50–60,000 Americans. FTD exists in familial and sporadic forms, with GRN progranulin and C9orf72 mutations being the most common causes. In this study, we compared the sporadic and familial transcriptome within the cerebellum, frontal cortex, hippocampus, and Brodmann’s area 8 of patients with FTD to determine genes and pathways involved in the disease process. Most dysregulated genes expression occurred in the frontal cortex and Brodmann’s area 8 for genetic and sporadic forms of FTD, respectively. A meta-analysis revealed 50 genes and 95 genes are dysregulated in at least three brain regions in patients with familial mutations and sporadic FTD patients, respectively. Familial FTD genes centered on the Wnt signaling pathway, whereas genes associated with the sporadic form of FTD centered on MAPK signaling. The results reveal the similarities and differences between sporadic and familial FTD. In addition, valproic acid and additional therapeutic agents may be beneficial in treating patients with FTD.

Serum neurofilament light chain as a surrogate of cognitive decline in sporadic and familial frontotemporal dementia.

Neurofilament light chain (NfL) has recently been proposed as a promising biomarker in frontotemporal dementia (FTD). We investigated the correlation of both cerebrospinal fluid (CSF) and serum NfL with detailed neuropsychological data and cognitive decline in a cohort of sporadic and familial FTD. CSF and serum NfL, as well as conventional CSF Alzheimer's disease (AD) biomarkers (Aβ42, t-Tau, p-Tau181), were determined in 63 FTD patients (30 sporadic-FTD, 20 with progranulin (GRN) mutations [FTD-GRN], 13 with chromosome 9 open reading frame 72 [C9orf72] expansions [C9orf72-FTD]), 37 AD patients, and 31 neurologic controls. Serum NfL was also quantified in 37 healthy individuals. Correlations between baseline CSF and serum NfL levels, standardized neuropsychological tests, and the rate of cognitive decline in FTD patients were assessed. CSF and serum NfL presented with significantly higher levels in FTD than in AD patients and both control groups. Within FTD subtypes, genetic cases, and particularly FTD-GRN, had higher CSF and serum NfL levels. Significant correlations between NfL levels and overall cognitive function, abstract reasoning (CSF and serum), executive functions, memory, and language (serum) were found. A relationship between increased baseline CSF and serum NfL and a decay in cognitive performance over time was also observed. Our findings highlight the potential of serum NfL as a useful surrogate end point of disease severity in upcoming targeted treatments.

Single-cell multimodal analysis in a case with reduced penetrance of Progranulin-Frontotemporal Dementia

We identified an autosomal dominant progranulin mutation carrier without symptoms of dementia in her lifetime (Reduced Penetrance Mutation Carrier, RedPenMC). This resistance to develop expected pathology presents a unique opportunity to interrogate neurodegenerative mechanisms. We performed multimodal single-nuclei analyses of post-mortem frontal cortex from RedPenMC, including transcriptomics and global levels of chromatin marks. RedPenMC had an increased ratio of GRN-expressing microglia, higher levels of activating histone mark H3k4me3 in microglia and lower levels of the repressive chromatin marks H3k9me1 and H3k9me3 in the frontal cortex than her affected mutation carrier son and evidence of higher protein levels of progranulin in both plasma and brain homogenates. Although the study is limited to one case, the results support that restoring brain progranulin levels may be sufficient to escape neurodegeneration and FTD. In addition to previously identified modifier genes, it is possible that epigenetic marks may contribute to the increased progranulin expression in cases of reduced penetrance. These findings may stimulate similar follow-up studies and new therapeutic approaches.

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.

Delivering progranulin to neuronal lysosomes protects against excitotoxicity

Loss-of-function mutations in progranulin (GRN) are a major genetic cause of frontotemporal dementia (FTD), possibly due to loss of progranulin’s neurotrophic and anti-inflammatory effects. Progranulin promotes neuronal growth and protects against excitotoxicity and other forms of injury. It is unclear if these neurotrophic effects are mediated through cellular signaling or through promotion of lysosomal function. Progranulin is a secreted proprotein that may activate neurotrophic signaling through cell-surface receptors. However, progranulin is efficiently trafficked to lysosomes and is necessary for maintaining lysosomal function. To determine which of these mechanisms mediates progranulin’s protection against excitotoxicity, we generated lentiviral vectors expressing progranulin (PGRN) or lysosome-targeted progranulin (L-PGRN). L-PGRN was generated by fusing the LAMP-1 transmembrane and cytosolic domains to the C-terminus of progranulin. L-PGRN exhibited no detectable secretion, but was delivered to lysosomes and processed into granulins. PGRN and L-PGRN protected against NMDA excitotoxicity in rat primary cortical neurons, but L-PGRN had more consistent protective effects than PGRN. L-PGRN’s protective effects were likely mediated through the autophagy-lysosomal pathway. In control neurons, an excitotoxic dose of NMDA stimulated autophagy, and inhibiting autophagy with 3-methyladenine reduced excitotoxic cell death. L-PGRN blunted the autophagic response to NMDA and occluded the protective effect of 3-methyladenine. This was not due to a general impairment of autophagy, as L-PGRN increased basal autophagy and did not alter autophagy after nutrient starvation. These data show that progranulin’s protection against excitotoxicity does not require extracellular progranulin, but is mediated through lysosomes, providing a mechanistic link between progranulin’s lysosomal and neurotrophic effects.

Neuronal VCP loss of function recapitulates FTLD-TDP pathology.

SUMMARYThe pathogenic mechanism by which dominant mutations in VCP cause multisystem proteinopathy (MSP), a rare neurodegenerative disease that presents as fronto-temporal lobar degeneration with TDP-43 inclusions (FTLD-TDP), remains unclear. To explore this, we inactivate VCP in murine postnatal forebrain neurons (VCP conditional knockout [cKO]). VCP cKO mice have cortical brain atrophy, neuronal loss, autophago-lysosomal dysfunction, and TDP-43 inclusions resembling FTLD-TDP pathology. Conditional expression of a single disease-associated mutation, VCP-R155C, in a VCP null background similarly recapitulates features of VCP inactivation and FTLD-TDP, suggesting that this MSP mutation is hypomorphic. Comparison of transcriptomic and proteomic datasets from genetically defined patients with FTLD-TDP reveal that progranulin deficiency and VCP insufficiency result in similar profiles. These data identify a loss of VCP-dependent functions as a mediator of FTLD-TDP and reveal an unexpected biochemical similarity with progranulin deficiency.

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.

FTD-PSP is an Unusual Clinical Phenotype in A Frontotemporal Dementia Patient with A Novel Progranulin Mutation.

Progranulin (GRN) mutations are a major cause of frontotemporal dementia (FTD); the spectrum of clinical phenotypes of FTD is much more extensive than previously reported. The frequency and locations of GRN mutations in Chinese patients with FTD remain uncertain. We performed cDNA sequencing in one sporadic male patient who initially presented FTD symptoms. Brain magnetic resonance imaging (MRI) and positron emission computed tomography/computed tomography (PET/CT) were applied to further confirm the diagnosis of FTD from this patient. Cellular apoptosis and survival test were performed to identify the function of GRN. We identified one novel missense GRN mutation (c.1498G>A, p.V500I) in this patient, who initially presented typical behavioral-variant frontotemporal dementia (bvFTD) features but then presented progressive supranuclear palsy (PSP) clinical characteristics 5 years after onset. Besides, WT GRN protein showed an adequate trophic stimulus to preserve the survival of SH-SY5Y cells in the medium free of serum, while GRN mutation (c.1498G>A, p.V500I) may impair the ability of supporting cell survival. This study owns significant implications for genetic counseling and clinical heterogeneity. We illustrate the fact that FTD presenting features of bvFTD and PSP in one patient could be considered as a specific phenotype in patients with GRN mutations. GRN p.V500I led to the neuronal degeneration in vitro; this finding provides a significant evidence that this mutation may be a new causative mutation in patients with FTD.

Clinical and Neuroimaging Aspects of Familial Frontotemporal Lobar Degeneration Associated with MAPT and GRN Mutations.

Numerous kindreds with familial frontotemporal lobar degeneration have been linked to mutations in microtubule-associated protein tau (MAPT) or progranulin (GRN) genes. While there are many similarities in the clinical manifestations and associated neuroimaging findings, there are also distinct differences. In this review, we compare and contrast the demographic/inheritance characteristics, histopathology, pathophysiology, clinical aspects, and key neuroimaging findings between those with MAPT and GRN mutations.

Preclinical development of PR006, a gene therapy for the treatment of frontotemporal dementia with progranulin mutations

AbstractBackgroundFrontotemporal dementia (FTD) caused by GRN haploinsufficiency (FTD‐GRN) represents 5‐10% of all FTD cases. GRN encodes progranulin, a glycoprotein that is essential for normal lysosomal function and neuronal survival. FTD‐GRN patients exhibit approximately 50‐70% reduction in progranulin levels. We are developing PR006, an AAV vector designed to deliver the GRN gene, for FTD‐GRN patients with a goal of slowing or stopping disease progression. We aimed to evaluate the efficacy of PR006 in preclinical models of FTD‐GRN.MethodWe evaluated the efficacy of PR006 in vitro using neurons differentiated from human induced pluripotent stem cells (iPSCs). iPSC‐derived neurons from individuals carrying GRN mutations exhibit reduced progranulin levels and decreased activation of the lysosomal enzyme cathepsin D. Additionally, we assessed the therapeutic effects of PR006 in vivo using a Grn knockout (KO) mouse model of FTD‐GRN. Grn KO mice exhibit progressive brain‐wide lipofuscinosis, ubiquitin accumulation, microgliosis, and neuroinflammation. PR006 was administered by intracerebroventricular (ICV) injection to Grn KO mice, and vector biodistribution, progranulin levels, lysosomal alterations, and neuroinflammation were assessed. Nonhuman primates (NHPs) were used to assess the safety and tolerability of PR006.ResultPR006 transduction in iPSC‐derived FTD‐GRN mutation carrier neurons resulted in robust, dose‐dependent secretion of progranulin and restored cathepsin D maturation. In the Grn KO mouse model, ICV PR006 treatment was well‐tolerated and resulted in broad vector biodistribution and increased progranulin expression in biofluids and tissues. PR006 treatment in the Grn KO mouse model decreased lipofuscinosis, ubiquitin accumulation, and expression of neuroinflammatory markers in the brains of these animals. PR006 treatment in NHPs was well‐tolerated and resulted in broad vector biodistribution and progranulin expression in the central nervous system and the periphery.ConclusionThese in vitro and in vivo preclinical studies demonstrated that PR006 effectively increased expression of progranulin and reduced pathological features of FTD‐GRN, supporting clinical development of PR006 for patients with this disease.

Lipid metabolism dysfunction in progranulin mutation carriers: Unbiased metabolomics reveals strong relationship to clinical status in FTLD

AbstractBackgroundHeterozygous progranulin (GRN) mutations are an important cause of familial Frontotemporal Lobar Degeneration (f‐FTLD) associated with TDP‐43 pathology. The cellular role of progranulin remains unclear, but alterations in lipid metabolism and lysosomal function have been suggested. Better understanding the pathophysiology of progranulin deficiency is critical as several clinical trials are underway in this population, and fluid biomarkers are urgently needed to assess pharmacodynamic effects. Therefore, we conducted an unbiased metabolomic analysis in GRN mutation carriers and family member controls, and identified at least two classes of lipids altered in symptomatic GRN carriers.MethodsMatched plasma and CSF samples were obtained from GRN mutation carriers (46 plasma, 36 CSF) and age‐matched blood relatives (36 plasma, 18 CSF). Untargeted metabolite detection was conducted via LC‐MS/MS in both plasma (1389 compounds) and CSF (508 compounds) by Metabolon. To identify important compounds in differentiating these groups, we conducted an unbiased analysis between family controls, asymptomatic carriers, and symptomatic carriers using univariate one‐way ANOVA with post‐hoc Fisher’s LSD corrected for false discovery rate (FDR) and partial least squares ‐ discriminant analysis (PLS‐DA, Metaboanalyst). For compounds identified by this unbiased approach, correlation with measures of disease severity was analyzed via linear regression, controlling for age and gender.ResultsIn plasma, 22 compounds were identified as significant in discriminating between groups via ANOVA (FDR<0.05), and 17/22 were also identified by PLS‐DA (VIP>2.4). Of these, 21/22 compounds were lipids; 11 were sphingomyelins. Comparatively, in the relatively lipid‐poor CSF samples, 6/15 compounds identified by PLS‐DA (VIP>2.0) were phosphatidylcholines. Pathway impact analysis revealed a large impact from the GRN mutation on sphingolipids in plasma and glycerophospholipids in CSF. In secondary analyses, sphingomyelins were elevated in plasma from symptomatic carriers, while phosphatidylcholines were decreased in CSF. Secondary analyses showed these compounds were correlated with clinical measures of disease severity, including MoCA and CDR+NACC‐FTLD.ConclusionIncreased plasma concentration of sphingomyelin and decreased CSF phosphatidylcholines are both associated with worse clinical status in FTLD‐GRN. These findings suggest that impaired lipid metabolism could play a pathogenic role in FTLD‐GRN. Targeted lipidomic measures in plasma and CSF may potentially reveal useful clinical trial biomarkers.

High frequency of progranulin mutations in Caribbean Hispanic families with dementia

AbstractBackgroundProgranulin (GRN) mutations cause frontotemporal dementia (FTD) and have been implicated in causing a variety of clinical neuro‐degenerative syndromes, including Alzheimer’s disease (AD) but it is hypothesized that these presentations all result from TDP‐43 pathology. We estimated the frequency of GRN mutations in multiplex families with dementia in the Dominican Republic and in New York.MethodsWe analyzed GRN mutations from whole genome sequencing data in 1941 individuals from 307 multiplex Caribbean Hispanic families with dementia. We prioritized rare (MAF<0.05 in GnomAD exomes and genomes) GRN variants annotated as having moderate‐high functional effect. Identified variants were cross‐referenced with FTD mutations found in Orphanet, MedGen, SNOMED and OMIM databases. GRN mutation carriers further were assessed for clinical and behavioral symptoms.ResultsWe identified 27 rare, moderate‐high impact variants in GRN in the Caribbean Hispanic families. Six mutations (rs63750723, rs368705304, rs63750479, rs63750412, rs63751294, rs25647) were previously reported as associated with FTD and were found with MAF<0.05 in the GnomAD genomes. 92 individuals (4.7%) from 45 families carried at least one of the six previously reported GRN variants. Of these 47 (51 %) were initially thought to have Alzheimer’s Disease with an average age at onset of 77.8 (±8.93) and the remaining 46 were unaffected (average age of last healthy exam= 65.05 (±8.4)). Aggression and psychosis were frequently observed behavioral symptoms in the demented patients consistent with FTD phenotype.ConclusionsIn this study we observed a higher than expected frequency of damaging GRN mutations in families multiply affected by dementia. The majority of demented individuals were thought to have Alzheimer’s disease initially. Further analyses of phenotype‐genotype correlations should provide insight into impact of GRN mutations among Caribbean Hispanics.

Elevated levels of extracellular vesicles in progranulin-deficient mice and FTD-GRN Patients.

ObjectiveThe goal of this study was to investigate the effect of progranulin insufficiency on extracellular vesicles (EVs), a heterogeneous population of vesicles that may contribute to progression of neurodegenerative disease. Loss‐of‐function mutations in progranulin (GRN) are a major cause of frontotemporal dementia (FTD), and brains from GRN carriers with FTD (FTD‐GRN) exhibit signs of lysosomal dysfunction. Lysosomal dysfunction may induce compensatory increases in secretion of exosomes, EVs secreted from the endolysosomal system, so we hypothesized that progranulin insufficiency would increase EV levels in the brain.MethodsWe analyzed levels and protein contents of brain EVs from Grn–/– mice, which model the lysosomal abnormalities of FTD‐GRN patients. We then measured brain EVs in FTD‐GRN patients. To assess the relationship of EVs with symptomatic disease, we measured plasma EVs in presymptomatic and symptomatic GRN mutation carriers.Results Grn–/– mice had elevated brain EV levels and altered EV protein contents relative to wild‐type mice. These changes were age‐dependent, occurring only after the emergence of pathology in Grn–/– mice. FTD‐GRN patients (n = 13) had elevated brain EV levels relative to controls (n = 5). Symptomatic (n = 12), but not presymptomatic (n = 7), GRN carriers had elevated plasma EV levels relative to controls (n = 8).InterpretationThese data show that symptomatic FTD‐GRN patients have elevated levels of brain and plasma EVs, and that this effect is modeled in the brain of Grn–/– mice after the onset of pathology. This increase in EVs could influence FTD disease progression, and provides further support for EVs as potential FTD biomarkers.

Microglial burden, activation and dystrophy patterns in frontotemporal lobar degeneration

BackgroundMicroglial dysfunction is implicated in frontotemporal lobar degeneration (FTLD). Although studies have reported excessive microglial activation or senescence (dystrophy) in Alzheimer’s disease (AD), few have explored this in FTLD. We examined regional patterns of microglial burden, activation and dystrophy in sporadic and genetic FTLD, sporadic AD and controls.MethodsImmunohistochemistry was performed in frontal and temporal grey and white matter from 50 pathologically confirmed FTLD cases (31 sporadic, 19 genetic: 20 FTLD-tau, 26 FTLD-TDP, four FTLD-FUS), five AD cases and five controls, using markers to detect phagocytic (CD68-positive) and antigen-presenting (CR3/43-positive) microglia, and microglia in general (Iba1-positive). Microglial burden and activation (morphology) were assessed quantitatively for each microglial phenotype. Iba1-positive microglia were assessed semi-quantitatively for dystrophy severity and qualitatively for rod-shaped and hypertrophic morphology. Microglia were compared in each region between FTLD, AD and controls, and between different pathological subtypes of FTLD, including its main subtypes (FTLD-tau, FTLD-TDP, FTLD-FUS), and subtypes of FTLD-tau, FTLD-TDP and genetic FTLD. Microglia were also compared between grey and white matter within each lobe for each group.ResultsThere was a higher burden of phagocytic and antigen-presenting microglia in FTLD and AD cases than controls, but activation was often not increased. Burden was generally higher in white matter than grey matter, but activation was greater in grey matter. However, microglia varied regionally according to FTLD subtype and disease mechanism. Dystrophy was more severe in FTLD and AD than controls, and more severe in white than grey matter, but this also varied regionally and was particularly extensive in FTLD due to progranulin (GRN) mutations. Presence of rod-shaped and hypertrophic microglia also varied by FTLD subtype.ConclusionsThis study demonstrates regionally variable microglial involvement in FTLD and links this to underlying disease mechanisms. This supports investigation of microglial dysfunction in disease models and consideration of anti-senescence therapies in clinical trials.

Loss of Tmem106b exacerbates FTLD pathologies and causes motor deficits in progranulin-deficient mice.

Progranulin (PGRN) and transmembrane protein 106B (TMEM106B) are important lysosomal proteins implicated in frontotemporal lobar degeneration (FTLD) and other neurodegenerative disorders. Loss-of-function mutations in progranulin (GRN) are a common cause of FTLD, while TMEM106B variants have been shown to act as disease modifiers in FTLD. Overexpression of TMEM106B leads to lysosomal dysfunction, while loss of Tmem106b ameliorates lysosomal and FTLD-related pathologies in young Grn-/- mice, suggesting that lowering TMEM106B might be an attractive strategy for therapeutic treatment of FTLD-GRN. Here, we generate and characterize older Tmem106b-/- Grn-/- double knockout mice, which unexpectedly show severe motor deficits and spinal cord motor neuron and myelin loss, leading to paralysis and premature death at 11-12months. Compared to Grn-/- , Tmem106b-/- Grn-/- mice have exacerbated FTLD-related pathologies, including microgliosis, astrogliosis, ubiquitin, and phospho-Tdp43 inclusions, as well as worsening of lysosomal and autophagic deficits. Our findings confirm a functional interaction between Tmem106b and Pgrn and underscore the need to rethink whether modulating TMEM106B levels is a viable therapeutic strategy.

Patients with progranulin mutations overlap with the progressive dysexecutive syndrome: towards the definition of a frontoparietal dementia phenotype.

Patients with progranulin mutations overlap with the progressive dysexecutive syndrome: towards the definition of a frontoparietal dementia phenotype.

Variability of clinical syndromes and cerebral glucose metabolism in symptomatic frontotemporal lobar degeneration associated with progranulin mutations

Objective: The aims of our study were to describe the clinical phenotype and to characterize the cerebral glucose metabolism patterns as measured with fluordesoxyglucose-positron emission tomography (FDG-PET) in symptomatic FTLD-patients with different GRN variants. Methods: For this study, data were included from all patients (n = 10) of a single-center FTLD registry study who had a pathogenic GRN variant and who had undergone a cerebral FDG-PET scan. Results: An overt variability of clinical phenotypes was identified with half of the cases being not unambiguously classifiable into one of the clinical FTLD subtypes. Furthermore, GRN + patients showed a considerable inter-individual variability of FDG uptake pattern. In half of the GRN + patients, metabolic changes expanded from frontal and temporal brain regions to parietal brain regions including the posterior cingulate cortex. Striking asymmetry without a preference for either hemisphere was overt in half of GRN + cases. Conclusion: We conclude that GRN mutations cause variable patterns of neurodegeneration that often exceed the anatomical boundaries of the frontotemporal brain regions and produce clinical syndromes that cannot clearly be classified into one of the subtypes as defined by the diagnostic criteria.

Loss of TMEM106B leads to myelination deficits: implications for frontotemporal dementia treatment strategies.

Genetic variants that define two distinct haplotypes at the TMEM106B locus have been implicated in multiple neurodegenerative diseases and in healthy brain ageing. In frontotemporal dementia (FTD), the high expressing TMEM106B risk haplotype was shown to increase susceptibility for FTD with TDP-43 inclusions (FTD-TDP) and to modify disease penetrance in progranulin mutation carriers (FTD-GRN). To elucidate the biological function of TMEM106B and determine whether lowering TMEM106B may be a viable therapeutic strategy, we performed brain transcriptomic analyses in 8-month-old animals from our recently developed Tmem106b-/- mouse model. We included 10 Tmem106b+/+ (wild-type), 10 Tmem106b+/- and 10 Tmem106-/- mice. The most differentially expressed genes (153 downregulated and 60 upregulated) were identified between Tmem106b-/- and wild-type animals, with an enrichment for genes implicated in myelination-related cellular processes including axon ensheathment and oligodendrocyte differentiation. Co-expression analysis also revealed that the most downregulated group of correlated genes was enriched for myelination-related processes. We further detected a significant loss of OLIG2-positive cells in the corpus callosum of Tmem106b-/- mice, which was present already in young animals (21 days) and persisted until old age (23 months), without worsening. Quantitative polymerase chain reaction revealed a reduction of differentiated but not undifferentiated oligodendrocytes cellular markers. While no obvious changes in myelin were observed at the ultrastructure levels in unchallenged animals, treatment with cuprizone revealed that Tmem106b-/- mice are more susceptible to cuprizone-induced demyelination and have a reduced capacity to remyelinate, a finding which we were able to replicate in a newly generated Tmem106b CRISPR/cas9 knock-out mouse model. Finally, using a TMEM106B HeLa knock-out cell line and primary cultured oligodendrocytes, we determined that loss of TMEM106B leads to abnormalities in the distribution of lysosomes and PLP1. Together these findings reveal an important function for TMEM106B in myelination with possible consequences for therapeutic strategies aimed at lowering TMEM106B levels.