Plasma progranulin levels predict progranulin mutation status in frontotemporal dementia patients and asymptomatic family members

Progranulin measurement with a new automated method: a step forward in the diagnostic approach to neurodegenerative disorders

OBJECTIVES

Mutations in the GRN gene encoded glycoprotein progranulin (PGRN), cause 5-10 % of all cases of frontotemporal lobar degeneration (FTLD). The aim of our study was to verify the analytical and clinical performance of an automated chemiluminescent immunoassay method for PGRN measurement recently developed (Chorus Evo, Diesse Diagnostica, Italy).

METHODS

Five plasma pools and residual plasma samples (K2EDTA) from 25 control subjects (11 males, 62-79 years; 14 females, 54-76 years) and 151 patients (70 males, 53-81 years; 81 females, 44-82 years) with different neurodegenerative disorders (NDs), were assayed. In 61 out of 151 patients, genetic GRN screening was carried.

RESULTS

Within-run imprecision (CV%) ranged from 3.8 % (11.5 pg/L) to 10.8 % (2.5 pg/L), and between-run, from 5.6 % (68.7 pg/L) to 10.7 % (2.8 pg/L). At genetic screening, 3 out of 61 patients were classified as GRN+ carriers, 18 as "other mutations" and 40 as "no-mutations" carriers. The PGRN median level in GRN+ carriers (15.9 pg/L) was significantly lower than that in control subjects (32.8 pg/L; p=0.006), in GRN- (27.50 pg/L; p=0.007), in other mutation carriers (24.80 pg/L; p=0.05) and in NDs patients (22.40 pg/L; p=0.05) ROC analysis, demonstrates the accuracy of progranulin levels in discriminating between "GRN+" and "GRN-" carriers (AUC 0.985) as well as "GRN+" and "other mutations" carriers (AUC 0.870).

CONCLUSIONS

The new automated progranulin method, for robust analytical performance, is suitable for use in the clinical setting, supporting clinicians in making a differential diagnosis in patients with neurodegenerative disorder.

Progranulin deficiency in the brain: the interplay between neuronal and non-neuronal cells

Heterozygous mutations in GRN gene lead to insufficient levels of the progranulin (PGRN) protein, resulting in frontotemporal dementia (FTD) with TAR DNA-binding protein 43 (TDP-43) inclusions, classified pathologically as frontotemporal lobar degeneration (FTLD-TDP). Homozygous GRN mutations are exceedingly rare and cause neuronal ceroid lipofuscinosis 11, a lysosomal storage disease with onset in young adulthood, or an FTD syndrome with late-onset manifestations. In this review, we highlight the broad spectrum of clinical phenotypes associated with PGRN deficiency, including primary progressive aphasia and behavioral variant of frontotemporal dementia. We explore these phenotypes alongside relevant rodent and in vitro human models, ranging from the induced pluripotent stem cell-derived neural progenitors, neurons, microglia, and astrocytes to genetically engineered heterotypic organoids containing both neurons and astrocytes. We summarize advantages and limitations of these models in recapitulating the main FTLD-GRN hallmarks, highlighting the role of non-cell-autonomous mechanisms in the formation of TDP-43 pathology, neuroinflammation, and neurodegeneration. Data obtained from patients' brain tissues and biofluids, in parallel with single-cell transcriptomics, demonstrate the complexity of interactions among the highly heterogeneous cellular clusters present in the brain, including neurons, astrocytes, microglia, oligodendroglia, endothelial cells, and pericytes. Emerging evidence has revealed that PGRN deficiency is associated with cell cluster-specific, often conserved, genetic and molecular phenotypes in the central nervous system. In this review, we focus on how these distinct cellular populations and their dysfunctional crosstalk contribute to neurodegeneration and neuroinflammation in FTD-GRN. Specifically, we characterize the phenotypes of lipid droplet-accumulating microglia and alterations of myelin lipid content resulting from lysosomal dysfunction caused by PGRN deficiency. Additionally, we consider how the deregulation of glia-neuron communication affects the exchange of organelles such as mitochondria, and the removal of excess toxic products such as protein aggregates, in PGRN-related neurodegeneration.

ASO-mediated knock-down of GPNMB in mutant-GRN and in Grn-deficient peripheral myeloid cells disrupts lysosomal function and immune responses

BACKGROUND

GPNMB has been discussed as a potential therapeutic target in GRN-mediated neurodegeneration, based on the observed reproducible upregulation in FTD-GRN cerebrospinal fluid (CSF) and post-mortem brain. However, the functional impacts of up-regulated GPNMB are currently unknown, and it is currently unclear if targeting GPNMB will be protective or deleterious. Increases in GPNMB seen in FTD-GRN are reproduced in brains of aged Grn-deficient mice. Importantly, although brains of young Grn-deficient mice do not exhibit upregulated Gpnmb expression, peripheral immune cells of these mice exhibit increased Gpnmb expression as young as 5-to-6 months, suggesting the effects of Grn-deficiency in the periphery proceed those in the brain. Grn-deficiency is known to alter peripheral immune cell function, including impaired autophagy and altered cytokine secretion. GPNMB has potential effects on these processes, but has never been studied in peripheral immune cells of patients or preclinical models. Informing the functional significance of GPNMB upregulation in Grn-deficient states in myeloid cells has potential to inform GPNMB as a therapeutic candidate.

METHODS

The effects of GPNMB knock-down via antisense oligonucleotide (ASO) were assessed in peripheral blood mononuclear cells (PBMCs) from 25 neurologically healthy controls (NHCs) and age- and sex-matched FTD-GRN patients, as well as peritoneal macrophages (pMacs) from progranulin-deficient (Grn -/-) and B6 mice. Lysosomal function, antigen presentation and MHC-II processing and recycling were assessed, as well as cytokine release and transcription.

RESULTS

ASO-mediated knock-down of GPNMB increased lysosomal burden and IL1β cytokine secretion in FTD-GRN carriers and NHCs monocytes. ASO-mediated knock-down of Gpnmb in Grn-deficient macrophages decreased lysosomal pan-cathepsin activity and protein degradation. In addition, ASO-mediated knock-down of Gpnmb increased MHC-II surface expression, which was driven by decreased MHC-II uptake and recycling, in macrophages from Grn-deficient females. Finally, ASO-mediated knock-down of Gpnmb dysregulated IFN γ -stimulated IL6 cytokine transcription and secretion by mouse macrophages due to the absence of regulatory actions of the Gpnmb extracellular fragment (ECF).

CONCLUSIONS

Our data herein reveal that GPNMB has a regulatory effect on multiple immune effector functions, including capping inflammation and immune responses in myeloid cells, potentially via secretion of its ECF. Therefore, in progranulin-deficient states, the marked upregulation in GPNMB transcript and protein may represent a compensatory mechanism to preserve lysosomal function in myeloid cells. These novel findings indicate that targeted depletion of GPNMB in FTD-GRN would not be a rational therapeutic strategy because it is likely to dysregulate important immune cell effector functions mediated by GPNMB. Specifically, our data indicate that therapeutic strategies inhibiting GPNMB levels and/or activity may worsen the effects of GRN deficiency.

Immunological Fluid Biomarkers in Frontotemporal Dementia: A Systematic Review

Dysregulated immune activation plays a key role in the pathogenesis of neurodegenerative diseases, including frontotemporal dementia (FTD). This study reviews immunological biomarkers associated with FTD and its subtypes. A systematic search of PubMed and Web of Science was conducted for studies published before 1 January 2025, focusing on immunological biomarkers in CSF or blood from FTD patients with comparisons to healthy or neurological controls. A total of 124 studies were included, involving 6686 FTD patients and 202 immune biomarkers. Key findings include elevated levels of GFAP and MCP1/CCL2 in both CSF and blood and consistently increased CHIT1 and YKL-40 in CSF. Complement proteins from the classical activation pathway emerged as promising targets. Distinct immune markers were found to differentiate FTD from Alzheimer's disease (AD) and amyotrophic lateral sclerosis (ALS), with GFAP, SPARC, and SPP1 varying between FTD and AD and IL-15, HERV-K, NOD2, and CHIT1 differing between FTD and ALS. A few markers, such as Galectin-3 and PGRN, distinguished FTD subtypes. Enrichment analysis highlighted IL-10 signaling and immune cell chemotaxis as potential pathways for further exploration. This study provides an overview of immunological biomarkers in FTD, emphasizing those most relevant for future research on immune dysregulation in FTD pathogenesis.

A novel c.1468 G > A GRN mutation causes frontotemporal dementia in a Chinese Han family

BACKGROUND/PURPOSE

GRN mutations act as causative factors in patients with FTD clinical phenotype or FTD pathology and exhibit high clinical heterogeneity. The discovery of these mutations and the analysis of their associations with resembling Alzheimer's disease should be critical to understand the pathogenesis of FTD.

METHODS

Clinical analysis, neuroimaging, target region capture and high-throughput sequencing were performed in a family of 3 generations. The underlying Alzheimer's pathology was evaluated by using biomarker evidence obtained from cerebrospinal fluid (CSF) amyloid testing, 18F-florbetapir (AV-45) PET imaging and FDG18-positron emission tomography imaging.

RESULTS

Through target region capture and high-throughput sequencing, a three-generation family was able to identify a heterozygous G to A point mutation at position 490 (c.1468)G > A, which led to a valine to methionine substitution (V490M) at exon 12. This unique missense mutation was found at codon 1468. Eight members of the proband's family-two sisters and the proband himself-had the mutation found by Sanger sequencing. Interestingly, biomarker tests for amyloid in the proband's cerebrospinal fluid (CSF) indicated pathology consistent with Alzheimer's disease (AD). The mutation was expected to have a high likelihood of being pathogenic.

CONCLUSIONS

We firstly reported a novel mutation in the GRN gene at codon 490 (V490M) in exon 12 in a China FTD family. The CSF biomarker alterations of the proband revealed a reduction in Aβ42 and the Aβ42/Aβ40 ratio. The analysis of mutation might support the role of GRN in patients with FTD and contribute to the discovery of a new pathological mechanism underlying the disease.

Proteomic analysis reveals distinct cerebrospinal fluid signatures across genetic frontotemporal dementia subtypes

We used an untargeted mass spectrometric approach, tandem mass tag proteomics, for the identification of proteomic signatures in genetic frontotemporal dementia (FTD). A total of 238 cerebrospinal fluid (CSF) samples from the Genetic FTD Initiative were analyzed, including samples from 107 presymptomatic (44 C9orf72, 38 GRN, and 25 MAPT) and 55 symptomatic (27 C9orf72, 17 GRN, and 11 MAPT) mutation carriers as well as 76 mutation-negative controls ("noncarriers"). We found shared and distinct proteomic alterations in each genetic form of FTD. Among the proteins significantly altered in symptomatic mutation carriers compared with noncarriers, we found that a set of proteins including neuronal pentraxin 2 and fatty acid binding protein 3 changed across all three genetic forms of FTD and patients with Alzheimer's disease from previously published datasets. We observed differential changes in lysosomal proteins among symptomatic mutation carriers with marked abundance decreases in MAPT carriers but not other carriers. Further, we identified mutation-associated proteomic changes already evident in presymptomatic mutation carriers. Weighted gene coexpression network analysis combined with gene ontology annotation revealed clusters of proteins enriched in neurodegeneration and glial responses as well as synapse- or lysosome-related proteins indicating that these are the central biological processes affected in genetic FTD. These clusters correlated with measures of disease severity and were associated with cognitive decline. This study revealed distinct proteomic changes in the CSF of patients with genetic FTD, providing insights into the pathological processes involved in the disease. In addition, we identified proteins that warrant further exploration as diagnostic and prognostic biomarker candidates.

Blood-Based Biomarkers in Frontotemporal Dementia: A Narrative Review

This narrative review explores the current landscape of blood biomarkers in Frontotemporal dementia (FTD). Neurofilament light chain (NfL) may be useful in the differentiation of behavioral variant FTD from primary psychiatric disorders (PPDs) or dementia with Lewy bodies (DLB). In prodromal FTD and presymptomatic mutation carriers (GRN, MAPT, C9orf72), elevated NfL may herald pheno-conversion to full-blown dementia. Baseline NfL correlates with steeper neuroanatomical changes and cognitive, behavioral and functional decline, making NfL promising in monitoring disease progression. Phosphorylated neurofilament heavy chain (pNfH) levels have a potential limited role in the demarcation of the conversion stage to full-blown FTD. Combined NfL and pNfH measurements may allow a wider stage stratification. Total tau levels lack applicability in the framework of FTD. p-tau, on the other hand, is of potential value in the discrimination of FTD from Alzheimer's dementia. Progranulin concentrations could serve the identification of GRN mutation carriers. Glial fibrillary acidic protein (GFAP) may assist in the differentiation of PPDs from behavioral variant FTD and the detection of GRN mutation carriers (additional research is warranted). Finally, TAR DNA-binding protein-43 (TDP-43) appears to be a promising diagnostic biomarker for FTD. Its potential in distinguishing TDP-43 pathology from other FTD-related pathologies requires further research.

Carboxy-terminal blockade of sortilin binding enhances progranulin gene therapy, a potential treatment for frontotemporal dementia

Frontotemporal dementia is commonly caused by loss-of-function mutations in the progranulin gene. Potential therapies for this disorder have entered clinical trials, including progranulin gene therapy and drugs that reduce progranulin interactions with sortilin. Both approaches ameliorate functional and pathological abnormalities in mouse models of progranulin insufficiency. Here we investigated whether modifying the progranulin carboxy terminus to block sortilin interactions would improve the efficacy of progranulin gene therapy. We compared the effects of treating progranulin-deficient mice with gene therapy vectors expressing progranulin with intact sortilin interactions, progranulin with the carboxy terminus blocked to reduce sortilin interactions, or GFP control. We found that expressing carboxy-terminally blocked progranulin generated higher levels of progranulin both at the injection site and in more distant regions. Carboxy-terminally blocked progranulin was also more effective at ameliorating microgliosis, microglial lipofuscinosis, and lipid abnormalities including ganglioside accumulation and loss of bis(monoacylglycero)phosphate lipids. Finally, only carboxy-terminally blocked progranulin reduced plasma neurofilament light chain, a biomarker of neurodegeneration, in progranulin-deficient mice. These results demonstrate that modifying the progranulin cargo to block sortilin interactions may be important for increasing the effectiveness of progranulin gene therapy.

One-sentence Summary

The effectiveness of progranulin gene therapy in models of FTD is improved by blocking the protein's carboxy terminus, which prevents sortilin binding.

An anti-sortilin affibody-peptide fusion inhibits sortilin-mediated progranulin degradation

Heterozygous loss-of-function mutations in the GRN gene are a common cause of frontotemporal dementia. Such mutations lead to decreased plasma and cerebrospinal fluid levels of progranulin (PGRN), a neurotrophic factor with lysosomal functions. Sortilin is a negative regulator of extracellular PGRN levels and has shown promise as a therapeutic target for frontotemporal dementia, enabling increased extracellular PGRN levels through inhibition of sortilin-mediated PGRN degradation. Here we report the development of a high-affinity sortilin-binding affibody-peptide fusion construct capable of increasing extracellular PGRN levels in vitro. By genetic fusion of a sortilin-binding affibody generated through phage display and a peptide derived from the progranulin C-terminus, an affinity protein (A3-PGRNC15*) with 185-pM affinity for sortilin was obtained. Treating PGRN-secreting and sortilin-expressing human glioblastoma U-251 cells with the fusion protein increased extracellular PGRN levels up to 2.5-fold, with an EC50 value of 1.3 nM. Our results introduce A3-PGRNC15* as a promising new agent with therapeutic potential for the treatment of frontotemporal dementia. Furthermore, the work highlights means to increase binding affinity through synergistic contribution from two orthogonal polypeptide units.

ASO-mediated knockdown of GPNMB in mutant- GRN and Grn -deficient peripheral myeloid cells disrupts lysosomal function and immune responses

Background

Increases in GPNMB are detectable in FTD- GRN cerebrospinal fluid (CSF) and post-mortem brain, and brains of aged Grn -deficient mice. Although no upregulation of GPNMB is observed in the brains of young Grn -deficient mice, peripheral immune cells of these mice do exhibit this increase in GPNMB. Importantly, the functional significance of GPNMB upregulation in progranulin-deficient states is currently unknown. Given that GPNMB has been discussed as a potential therapeutic target in GRN -mediated neurodegeneration, it is vital for the field to determine what the normal function of GPNMB is in the immune system, and whether targeting GPNMB will elicit beneficial or deleterious effects.

Methods

The effects of GPNMB knock-down via antisense oligonucleotide (ASO) were assessed in peripheral blood mononuclear cells (PBMCs) from 25 neurologically healthy controls (NHCs) and age- and sex-matched FTD- GRN patients, as well as peritoneal macrophages (pMacs) from progranulin-deficient ( Grn -/- ) and B6 mice. Lysosomal function, antigen presentation and MHC-II processing and recycling were assessed, as well as cytokine release and transcription.

Results

We demonstrate here that ASO-mediated knockdown of GPNMB increases lysosomal burden and cytokine secretion in FTD-GRN carrier and neurologically healthy controls (NHCs) monocytes. ASO-mediated knockdown of GPNMB in Grn -deficient macrophages decreased lysosomal pan-cathepsin activity and protein degradation. In addition, ASO-mediated knockdown of GPNMB increased MHC-II surface expression, which was driven by decreased MHC-II uptake and recycling, in macrophages from Grn -deficient females. Finally, ASO-mediated knockdown of GPNMB dysregulated IFNγ-stimulated cytokine transcription and secretion by mouse macrophages due to the absence of regulatory actions of the GPNMB extracellular fragment (ECF).

Conclusions

Our data herein reveals that GPNMB has a regulatory effect on multiple immune effector functions, including capping inflammation and immune responses in myeloid cells via secretion of its ECF. Therefore, in progranulin-deficient states, the drastic upregulation in GPNMB transcript and protein may represent a compensatory mechanism to preserve lysosomal function in myeloid cells. These novel findings indicate that targeted depletion in FTD- GRN would not be a rational therapeutic strategy because it is likely to dysregulate important immune cell effector functions.

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

BACKGROUND

Pathogenic heterozygous mutations in the progranulin gene (GRN) are a key cause of frontotemporal dementia (FTD), leading to significantly reduced biofluid concentrations of the progranulin protein (PGRN). This has led to a number of ongoing therapeutic trials aiming to treat this form of FTD by increasing PGRN levels in mutation carriers. However, we currently lack a complete understanding of factors that affect PGRN levels and potential variation in measurement methods. Here, we aimed to address this gap in knowledge by systematically reviewing published literature on biofluid PGRN concentrations.

METHODS

Published data including biofluid PGRN concentration, age, sex, diagnosis and GRN mutation were collected for 7071 individuals from 75 publications. The majority of analyses (72%) had focused on plasma PGRN concentrations, with many of these (56%) measured with a single assay type (Adipogen) and so the influence of mutation type, age at onset, sex, and diagnosis were investigated in this subset of the data.

RESULTS

We established a plasma PGRN concentration cut-off between pathogenic mutation carriers and non-carriers of 74.8 ng/mL using the Adipogen assay based on 3301 individuals, with a CSF concentration cut-off of 3.43 ng/mL. Plasma PGRN concentration varied by GRN mutation type as well as by clinical diagnosis in those without a GRN mutation. Plasma PGRN concentration was significantly higher in women than men in GRN mutation carriers (p = 0.007) with a trend in non-carriers (p = 0.062), and there was a significant but weak positive correlation with age in both GRN mutation carriers and non-carriers. No significant association was seen with weight or with TMEM106B rs1990622 genotype. However, higher plasma PGRN levels were seen in those with the GRN rs5848 CC genotype in both GRN mutation carriers and non-carriers.

CONCLUSIONS

These results further support the usefulness of PGRN concentration for the identification of the large majority of pathogenic mutations in the GRN gene. Furthermore, these results highlight the importance of considering additional factors, such as mutation type, sex and age when interpreting PGRN concentrations. This will be particularly important as we enter the era of trials for progranulin-associated FTD.

Genetic Factors Associated with the Development of Neuropathy in Type 2 Diabetes

Neuropathy is a serious and frequent complication of type 2 diabetes (T2DM). This study was carried out to search for genetic factors associated with the development of diabetic neuropathy by whole exome sequencing. For this study, 24 patients with long-term type 2 diabetes with neuropathy and 24 without underwent detailed neurological assessment and whole exome sequencing. Cardiovascular autonomic function was evaluated by cardiovascular reflex tests. Heart rate variability was measured by the triangle index. Sensory nerve function was estimated by Neurometer and Medoc devices. Neuropathic symptoms were characterized by the neuropathy total symptom score (NTSS). Whole exome sequencing (WES) was performed on a Thermo Ion GeneStudio S5 system determining the coding sequences of approximately 32,000 genes comprising 50 million base pairs. Variants were detected by Ion Reporter software and annotated using ANNOVAR, integrating database information from dbSNP, ClinVar, gnomAD, and OMIM. Integrative genomics viewer (IGV) was used for visualization of the mapped reads. We have identified genetic variants that were significantly associated with increased (22-49-fold) risk of neuropathy (rs2032930 and rs2032931 of recQ-mediated genome instability protein 2 (RMI2) gene), rs604349 of myosin binding protein H like (MYBPHL) gene and with reduced (0.07-0.08-fold) risk (rs917778 of multivesicular body subunit 12B (MVB12B) and rs2234753 of retinoic acid X receptor alpha (RXRA) genes). The rs2032930 showed a significant correlation with current perception thresholds measured at 5 Hz and 250 Hz for n. medianus (p = 0.042 and p = 0.003, respectively) and at 5 Hz for n. peroneus (p = 0.037), as well as the deep breath test (p = 0.022) and the NTSS (p = 0.023). The rs2032931 was associated with current perception thresholds (p = 0.003 and p = 0.037, respectively), deep breath test (p = 0.022), and NTSS (p = 0.023). The rs604349 correlated with values measured at 2000 (p = 0.049), 250 (p = 0.018), and 5 Hz (p = 0.005) for n. medianus, as well as warm perception threshold measured by Medoc device (p = 0.042). The rs2234753 showed correlations with a current perception threshold measured at 2000 Hz for n. medianus (p = 0.020), deep breath test (p = 0.040), and NTSS (p = 0.003). There was a significant relationship between rs91778 and cold perception threshold (p = 0.013). In our study, genetic variants have been identified that may have an impact on the risk of neuropathy developing in type 2 diabetic patients. These results could open up new opportunities for early preventive measures and might provide targets for new drug developments in the future.

A 3'UTR Insertion Is a Candidate Causal Variant at the TMEM106B Locus Associated With Increased Risk for FTLD-TDP

Background and Objectives

Single-nucleotide variants near TMEM106B associate with the risk of frontotemporal lobar dementia with TDP-43 inclusions (FTLD-TDP) and Alzheimer disease (AD) in genome-wide association studies (GWASs), but the causal variant at this locus remains unclear. Here, we asked whether a novel structural variant on TMEM106B is the causal variant.

Methods

An exploratory analysis identified structural variants on neurodegeneration-related genes. Subsequent analyses focused on an Alu element insertion on the 3'UTR of TMEM106B. This study included data from longitudinal aging and neurogenerative disease cohorts at Stanford University, case-control cohorts in the Alzheimer Disease Sequencing Project (ADSP), and expression and proteomics data from Washington University in St. Louis (WUSTL). Four hundred thirty-two individuals from 2 Stanford aging cohorts were whole-genome long-read and short-read sequenced. A total of 16,906 samples from ADSP were short-read sequenced. Genotypes, transcriptomics, and proteomics data were available in 1,979 participants from an aging and dementia cohort at WUSTL. Selection criteria were specific to each cohort. In primary analyses, the linkage disequilibrium between the TMEM106B locus variants in the FTLD-TDP GWAS and the 3'UTR insertion was estimated. We then estimated linkage by ancestry in the ADSP and evaluated the effect of the TMEM106B lead variant on mRNA and protein levels.

Results

The primary analysis included 432 participants (52.5% female, age range 45-92 years). We identified a 316 bp Alu insertion overlapping the TMEM106B 3'UTR tightly linked with top GWAS variants rs3173615(C) and rs1990622(A). In ADSP European ancestry participants, this insertion is in equivalent linkage with rs1990622(A) (R2 = 0.962, D' = 0.998) and rs3173615(C) (R2 = 0.960, D' = 0.996). In African ancestry participants, the insertion is in stronger linkage with rs1990622(A) (R2 = 0.992, D' = 0.998) than with rs3173615(C) (R2 = 0.811, D' = 0.994). In public data sets, rs1990622 was consistently associated with TMEM106B protein levels but not with mRNA expression. In the WUSTL data set, rs1990622 is associated with TMEM106B protein levels in plasma and CSF, but not with TMEM106B mRNA expression.

Discussion

We identified a novel Alu element insertion in the 3'UTR of TMEM106B in tight linkage with the lead FTLD-TDP risk variant. The lead variant is associated with TMEM106B protein levels, but not expression. The 3'UTR insertion is a lead candidate for the causal variant at this complex locus, pending confirmation with functional studies.

Antisense oligonucleotides targeting the miR-29b binding site in the GRN mRNA increase progranulin translation

Heterozygous GRN (progranulin) mutations cause frontotemporal dementia (FTD) due to haploinsufficiency, and increasing progranulin levels is a major therapeutic goal. Several microRNAs, including miR-29b, negatively regulate progranulin protein levels. Antisense oligonucleotides (ASOs) are emerging as a promising therapeutic modality for neurological diseases, but strategies for increasing target protein levels are limited. Here, we tested the efficacy of ASOs as enhancers of progranulin expression by sterically blocking the miR-29b binding site in the 3' UTR of the human GRN mRNA. We found 16 ASOs that increase progranulin protein in a dose-dependent manner in neuroglioma cells. A subset of these ASOs also increased progranulin protein in iPSC-derived neurons and in a humanized GRN mouse model. In FRET-based assays, the ASOs effectively competed for miR-29b from binding to the GRN 3' UTR RNA. The ASOs increased levels of newly synthesized progranulin protein by increasing its translation, as revealed by polysome profiling. Together, our results demonstrate that ASOs can be used to effectively increase target protein levels by partially blocking miR binding sites. This ASO strategy may be therapeutically feasible for progranulin-deficient FTD as well as other conditions of haploinsufficiency.

Analytical and clinical validation of a blood progranulin ELISA in frontotemporal dementias

OBJECTIVES

Heterozygous mutations in the granulin (GRN) gene may result in haploinsufficiency of progranulin (PGRN), which might lead to frontotemporal dementia (FTD). In this study, we aimed to perform analytical and clinical validation of a commercial progranulin kit for clinical use.

METHODS

Analytical validation parameters including assay precision, selectivity, measurement range, dilution linearity, interferences and sample stability were tested according to previously described procedures. For clinical validation, PGRN levels were measured in plasma from 32 cognitively healthy individuals, 52 confirmed GRN mutation carriers, 25 C9orf72 mutation carriers and 216 patients with different neurodegenerative diseases of which 70 were confirmed as non-mutation carriers.

RESULTS

Among the analytical validation parameters, assay precision and repeatability were very stable (coefficients of variation <7 %). Spike recovery was 96 %, the measurement range was 6.25-400 μg/L and dilution linearity ranged from 1:50-1:200. Hemolysis did not interfere with progranulin levels, and these were resistant to freeze/thaw cycles and storage at different temperatures. For the clinical validation, the assay was capable of distinguishing GRN mutation carriers from controls and non-GRN mutation carriers with very good sensitivity and specificity at a cut-off of 57 μg/L (97 %, 100 %, respectively).

CONCLUSIONS

In this study, we demonstrate robust analytical and diagnostic performance of this commercial progranulin kit for implementation in clinical laboratory practice. This easy-to-use test allows identification of potential GRN mutation carriers, which may guide further evaluation of the patient. This assay might also be used to evaluate the effect of novel PGRN-targeting drugs and therapies.

Regulation of extracellular progranulin in medial prefrontal cortex

Progranulin is a secreted pro-protein that has anti-inflammatory and neurotrophic effects and is necessary for maintaining lysosomal function. Mutations in progranulin (GRN) are a major cause of frontotemporal dementia. Most pathogenic GRN mutations cause progranulin haploinsufficiency, so boosting progranulin levels is a promising therapeutic strategy. Progranulin is constitutively secreted, then taken up and trafficked to lysosomes. Before being taken up from the extracellular space, progranulin interacts with receptors that may mediate anti-inflammatory and growth factor-like effects. Modifying progranulin trafficking is a viable approach to boosting progranulin, but progranulin secretion and uptake by cells in the brain is poorly understood and may involve distinct mechanisms from other parts of the body. Understanding the cell types and processes that regulate extracellular progranulin in the brain could provide insight into progranulin's mechanism of action and inform design of progranulin-boosting therapies. To address this question we used microdialysis to measure progranulin in interstitial fluid (ISF) of mouse medial prefrontal cortex (mPFC). Grn+/- mice had approximately 50% lower ISF progranulin than wild-type mice, matching the reduction of progranulin in cortical tissue. Fluorescent in situ hybridization and immunofluorescence confirmed that microglia and neurons are the major progranulin-expressing cell types in the mPFC. Studies of conditional microglial (Mg-KO) and neuronal (N-KO) Grn knockout mice revealed that loss of progranulin from either cell type results in approximately 50% reduction in ISF progranulin. LPS injection (i.p.) produced an acute increase in ISF progranulin in mPFC. Depolarizing cells with KCl increased ISF progranulin, but this response was not altered in N-KO mice, indicating progranulin secretion by non-neuronal cells. Increasing neuronal activity with picrotoxin did not increase ISF progranulin. These data indicate that microglia and neurons are the source of most ISF progranulin in mPFC, with microglia likely secreting more progranulin per cell than neurons. The acute increase in ISF progranulin after LPS treatment is consistent with a role for extracellular progranulin in regulating inflammation, and may have been driven by microglia or peripheral immune cells. Finally, these data indicate that mPFC neurons engage in constitutive progranulin secretion that is not acutely changed by neuronal activity.

Rare exonic variant affects GRN splicing and contributes to frontotemporal lobar degeneration

Heterozygous loss-of-function (LOF) mutations in the progranulin gene (GRN) cause frontotemporal lobar degeneration (FTLD) by a mechanism of haploinsufficiency. For most missense mutations, the contribution to FTLD is however unclear. We studied the pathogenicity of rare GRN missense mutations using patient biomaterials. We identified a new mutation in GRN, c.1178 A>C, in a patient with a diagnosis of primary progressive aphasia. Neuropathological examination of autopsied brain showed FTLD with TAR DNA-binding protein 43 (FTLD-TDP) type A pathology with concomitant Alzheimer's disease pathology. Serum progranulin protein levels were reduced to levels comparable to known LOF mutations. The mutation is in the last codon of exon 10, in the splice donor sequence. Our data provide evidence that the mutation leads to aberrant splicing, resulting in a frameshift (p.(Glu393AlafsTer31)) and consequently nonsense-mediated mRNA decay. Our finding demonstrates that carefully examining sequencing data around splice sites is needed since this mutation was annotated as a missense mutation. Unraveling the pathogenicity of variants of unknown significance is important for clinical diagnosis and genetic counseling.

Latozinemab, a novel progranulin-elevating therapy for frontotemporal dementia

BACKGROUND

Heterozygous loss-of-function mutations in the progranulin (PGRN) gene (GRN) cause a reduction in PGRN and lead to the development of frontotemporal dementia (FTD-GRN). PGRN is a secreted lysosomal chaperone, immune regulator, and neuronal survival factor that is shuttled to the lysosome through multiple receptors, including sortilin. Here, we report the characterization of latozinemab, a human monoclonal antibody that decreases the levels of sortilin, which is expressed on myeloid and neuronal cells and shuttles PGRN to the lysosome for degradation, and blocks its interaction with PGRN.

METHODS

In vitro characterization studies were first performed to assess the mechanism of action of latozinemab. After the in vitro studies, a series of in vivo studies were performed to assess the efficacy of a mouse-cross reactive anti-sortilin antibody and the pharmacokinetics, pharmacodynamics, and safety of latozinemab in nonhuman primates and humans.

RESULTS

In a mouse model of FTD-GRN, the rodent cross-reactive anti-sortilin antibody, S15JG, decreased total sortilin levels in white blood cell (WBC) lysates, restored PGRN to normal levels in plasma, and rescued a behavioral deficit. In cynomolgus monkeys, latozinemab decreased sortilin levels in WBCs and concomitantly increased plasma and cerebrospinal fluid (CSF) PGRN by 2- to threefold. Finally, in a first-in-human phase 1 clinical trial, a single infusion of latozinemab caused a reduction in WBC sortilin, tripled plasma PGRN and doubled CSF PGRN in healthy volunteers, and restored PGRN to physiological levels in asymptomatic GRN mutation carriers.

CONCLUSIONS

These findings support the development of latozinemab for the treatment of FTD-GRN and other neurodegenerative diseases where elevation of PGRN may be beneficial. Trial registration ClinicalTrials.gov, NCT03636204. Registered on 17 August 2018, https://clinicaltrials.gov/ct2/show/NCT03636204 .

Patients with sporadic FTLD exhibit similar increases in lysosomal proteins and storage material as patients with FTD due to GRN mutations

Loss of function progranulin (GRN) mutations are a major autosomal dominant cause of frontotemporal dementia (FTD). Patients with FTD due to GRN mutations (FTD-GRN) develop frontotemporal lobar degeneration with TDP-43 pathology type A (FTLD-TDP type A) and exhibit elevated levels of lysosomal proteins and storage material in frontal cortex, perhaps indicating lysosomal dysfunction as a mechanism of disease. To investigate whether patients with sporadic FTLD exhibit similar signs of lysosomal dysfunction, we compared lysosomal protein levels, transcript levels, and storage material in patients with FTD-GRN or sporadic FTLD-TDP type A. We analyzed samples from frontal cortex, a degenerated brain region, and occipital cortex, a relatively spared brain region. In frontal cortex, patients with sporadic FTLD-TDP type A exhibited similar increases in lysosomal protein levels, transcript levels, and storage material as patients with FTD-GRN. In occipital cortex of both patient groups, most lysosomal measures did not differ from controls. Frontal cortex from a transgenic mouse model of TDP-opathy had similar increases in cathepsin D and lysosomal storage material, showing that TDP-opathy and neurodegeneration can drive these changes independently of progranulin. To investigate these changes in additional FTLD subtypes, we analyzed frontal cortical samples from patients with sporadic FTLD-TDP type C or Pick's disease, an FTLD-tau subtype. All sporadic FTLD groups had similar increases in cathepsin D activity, lysosomal membrane proteins, and storage material as FTD-GRN patients. However, patients with FTLD-TDP type C or Pick's disease did not have similar increases in lysosomal transcripts as patients with FTD-GRN or sporadic FTLD-TDP type A. Based on these data, accumulation of lysosomal proteins and storage material may be a common aspect of end-stage FTLD. However, the unique changes in gene expression in patients with FTD-GRN or sporadic FTLD-TDP type A may indicate distinct underlying lysosomal changes among FTLD subtypes.

C9orf72 expansions are the most common cause of genetic frontotemporal dementia in a Southeast Asian cohort

OBJECTIVE

Frontotemporal dementia (FTD) encompasses a spectrum of neurodegenerative disorders, including behavioural variant FTD (bvFTD), semantic variant primary progressive aphasia (svPPA) and non-fluent variant PPA (nfvPPA). While a strong genetic component is implicated in FTD, genetic FTD in Asia is less frequently reported. We aimed to investigate the frequency of Southeast Asian FTD patients harbouring known genetic FTD variants.

METHODS

A total of 60 FTD-spectrum patients (25 familial and 35 sporadic) from Singapore and the Philippines were included. All underwent next-generation sequencing and repeat-primed PCR for C9orf72 expansion testing. Neurofilament light chain (NfL) levels were measured in a subset of patients.

RESULTS

Overall, 26.6% (16/60 cases) carried pathogenic or likely pathogenic variants in a FTD-related gene, including: MAPT Gln351Arg (n = 1); GRN Cys92Ter (n = 1), Ser301Ter (n = 2), c.462 + 1G > C (n = 1); C9orf72 expansion (35-70 repeats; n = 8); TREM2 Arg47Cys (n = 1); and OPTN frameshift insertion (n = 2). Genetic mutations accounted for 48% (12/25) of patients with familial FTD, and 11.4% (4/35) of patients with sporadic FTD. C9orf72 repeat expansions were the most common genetic mutation (13.3%, 8/60), followed by GRN (6.7%, 4/60) variants. Within mutation carriers, plasma NfL was highest in a C9orf72 expansion carrier, and CSF NfL was highest in a GRN splice variant carrier.

INTERPRETATION

In our cohort, genetic mutations are present in one-quarter of FTD-spectrum cases, and up to half of those with family history. Our findings highlight the importance of wider implementation of genetic testing in FTD patients from Southeast Asia.

GRN Missense Variants and Familial Alzheimer's Disease: Two Case Reports

BACKGROUND

Progranulin protein (GRN) is a growth factor, encoded by the GRN (Granulin precursor) gene, involved in several functions including inflammation, wound repair, signal transduction, proliferation, and tumorigenesis. Mutations in GRN gene are usually the genetic etiology of frontotemporal dementia (FTD), but different studies reported GRN mutations in Alzheimer 's disease (AD) patients.

OBJECTIVE

Here, we analyzed FTD linked gene GRN in 23 patients with a clinical diagnosis of AD and a family history of AD (FAD), not carrying mutations in AD candidate genes (PSEN 1, PSEN 2, and APP). In addition, Microtubule-associated protein tau (MAPT) gene was studied too. All patients underwent an extensive neuropsychological battery.

METHODS

Genetic analyses were performed thought PCR assay and sequencing. Variants were annotated with ANNOVAR and allele frequency was checked on population databases. In silico prediction tools were consulted to check nonsynonymous variants and their effect on protein function and structure. The clinical data were retrospectively collected from medical records.

RESULTS

Genetic screening of MAPT and GRN in 23 FAD patients highlighted two rare different variants in two probands (2/23 = 8,7%) located in GRN gene: R433W (p.Arg433Trp) and C521Y (p.Cys521Tyr). The R433W and C521Y are variants with uncertain significant, that are predicted to affect GRN protein structure and function, with a possible damaging effect.

CONCLUSIONS

Our data provide evidence of the importance of GRN genetic analysis also in the study of familial AD.

Early Diagnosis of Alzheimer's Disease with Blood Test; Tempting but Challenging

The increasing prevalence of Alzheimer's disease (AD) has led to a health crisis. According to official statistics, more than 55 million people globally have AD or other types of dementia, making it the sixth leading cause of death. It is still difficult to diagnose AD and there is no definitive diagnosis yet; post-mortem autopsy is still the only definite method. Moreover, clinical manifestations occur very late in the course of disease progression; therefore, profound irreversible changes have already occurred when the disease manifests. Studies have shown that in the preclinical stage of AD, changes in some biomarkers are measurable prior to any neurological damage or other symptoms. Hence, creating a reliable, fast, and affordable method capable of detecting AD in early stage has attracted the most attention. Seeking clinically applicable, inexpensive, less invasive, and much more easily accessible biomarkers for early diagnosis of AD, blood-based biomarkers (BBBs) seem to be an ideal option. This review is an inclusive report of BBBs that have been shown to be altered in the course of AD progression. The aim of this report is to provide comprehensive insight into the research status of early detection of AD based on BBBs.

Searching for Biomarkers in Proliferative Diabetic Retinopathy: Amphiregulin and Progranulin

Objective

Diabetic retinopathy is a common diabetic microvascular problem. Its diagnosis and classification are based on visible changes in clinical fundus examination. However, the discovery of possible vitreous biomarkers in patients with proliferative and nonproliferative diabetic retinopathy may guide both the differentiation and degree of retinopathy. Biomarkers that will be accepted can be also a treatment target. Amphiregulin (AREG) promotes proliferative and regenerative activity and repairs most cell types by binding and activating epidermal growth factor receptors. Progranulin (PGRN) has complex functions in many physiological and pathological processes. Thus, this study aimed to report vitreous AREG and PGRN levels in patients with diabetes and proliferative retinopathy and compare the results with those without diabetes.

Methods

Thirty-three eyes of 33 patients with proliferative diabetic retinopathy and 31 eyes of 31 patients without diabetes were included in this study. Vitreous humor samples were collected from all patients at the time of pars plana vitrectomy surgery immediately before the surgical procedure. Vitreous AREG and PGRN values were determined by the ELISA method.

Results

The mean AREG and PGRN values were similar in the groups (p=0.427, p=0.459, respectively).

Conclusions

The results demonstrated that vitreous AREG and PGRN levels have no significant relationship with proliferative diabetic retinopathy.

Cerebrospinal Fluid Biomarker Profile in TDP-43-Related Genetic Frontotemporal Dementia

Cerebrospinal fluid (CSF) biomarkers, namely total tau, phospho-tau and amyloid beta peptides, have received much attention specifically regarding Alzheimer’s disease (AD), since they can detect the biochemical fingerprint of AD and serve as a diagnostic tool for accurate and early diagnosis during life. In the same way, biomarkers for other neurodegenerative disease pathologies are also needed. We present a case series of six patients with genetic frontotemporal dementia (FTD), with TDP-43 underlying proteinopathy, in an attempt to assess TDP-43 as a novel biomarker alone and in combination with established AD biomarkers for this specific patient group, based on the principles of personalized and precision medicine. Our results indicate that genetic TDP-43-FTD is characterized by increased CSF TPD-43 and increased TDP-43 × τΤ/τP-181 combination. Hence, TDP-43 combined with tau proteins could be a useful tool for the diagnosis of genetic FTD with TDP-43 underling histopathology, supplementing clinical, neuropsychological and imaging data.

Overexpression of progranulin increases pathological protein accumulation by suppressing autophagic flux

Progranulin (PGRN) haploinsufficiency from autosomal dominant mutations in the PGRN gene causes frontotemporal lobar degeneration, which is characterized by cytoplasmic inclusions predominantly containing TDP-43 (FTLD-TDP). PGRN supplementation for patients with a PGRN gene mutation has recently been proposed as a therapeutic strategy to suppress FTLD-TDP. However, it currently remains unclear whether excessive amounts of PGRN are beneficial or harmful. We herein report the effects of PGRN overexpression on autophagic flux in a cultured cell model. PGRN overexpression increased the level of an autophagosome marker without promoting autophagosome formation and decreased the signal intensity of an autolysosome marker, indicating the suppression of autophagic flux due to reductions in the formation of autolysosomes. Assessments of lysosome numbers and biogenesis using LysoTracker and cells stably expressing TFEB-GFP, respectively, indicated that PGRN overexpression increased the lysosome numbers without lysosomal biogenesis. These results suggest that PGRN overexpression suppressed autophagic flux by inhibiting autophagosome-lysosome fusion. Moreover, PGRN overexpression enhanced polyglutamine aggregation and aggregate-prone TDP-43 accumulation, indicating that the suppression of autophagic flux by excessive amounts of PGRN worsens the pathology of neurodegenerative diseases.

New insights and therapeutic opportunities for progranulin-deficient frontotemporal dementia

Frontotemporal dementia (FTD) is the second most common form of dementia. It affects the frontal and temporal lobes of the brain and has a highly heterogeneous clinical representation with patients presenting with a wide range of behavioral, language, and executive dysfunctions. Etiology of FTD is complex and consists of both familial and sporadic cases. Heterozygous mutations in the GRN gene, resulting in GRN haploinsufficiency, cause progranulin (PGRN)-deficient FTD characterized with cytoplasmic mislocalization of TAR DNA-binding protein 43 kDa (TDP-43) aggregates. GRN codes for PGRN, a secreted protein that is also localized in the endolysosomes and plays a critical role in regulating lysosomal homeostasis. How PGRN deficiency modulates immunity and causes TDP-43 pathology and FTD-related neurodegeneration remains an active area of intense investigation. In the current review, we discuss some of the significant progress made in the past two years that links PGRN deficiency with microglial-associated neuroinflammation, TDP-43 pathology, and lysosomal dysfunction. We also review the opportunities and challenges toward developing therapies and biomarkers to treat PGRN-deficient FTD.

Serum progranulin is not associated with rs5848 polymorphism in Korean patients with neurodegenerative diseases

Low serum progranulin (PGRN) is known to be associated with granulin (GRN) gene mutation and T alleles of GRN rs5848 polymorphism. However, there have been only a few Asian studies exploring these. We investigated the serum PGRN levels, rs5848 genotypes, and their relations with cerebrospinal fluid (CSF) Alzheimer’s disease (AD) biomarkers in the Korean population. Serum PGRN levels, GRN rs5848 polymorphism, and GRN mutations were evaluated in 239 participants (22 cognitively unimpaired participants and 217 patients with neurodegenerative diseases). CSF AD biomarkers were also evaluated in 214 participants. There was no significant difference in the serum PGRN levels among the diagnostic groups. We could not find any GRN mutation carrier in our sample. The differences in the frequencies of the rs5848 genotypes among the clinical groups or the effects of the rs5848 genotypes on serum PGRN were not observed. There was no correlation between the serum PGRN level or rs5848 genotype and CSF AD biomarkers. Neither the T allele nor the TT genotype had an effect on the development of AD. Our results showed that serum PGRN levels were not associated with rs5848 genotypes, indicating that multiple single nucleotide polymorphisms might affect PGRN concentrations in an ethnicity-specific manner.

Exploring Neurofilament Light Chain and Exosomes in the Genetic Forms of Frontotemporal Dementia

Differential diagnosis of neurological disorders and their subtype classification are challenging without specific biomarkers. Genetic forms of these disorders, typified by an autosomal dominant family history, could offer a window to identify potential biomarkers by exploring the presymptomatic stages of the disease. Frontotemporal dementia (FTD) is the second cause of dementia with an age of onset < 65, and its most common mutations are in GRN, C9orf72, and MAPT genes. Several studies have demonstrated that the main proteins involved in FTD pathogenesis can be secreted in exosomes, a specific subtype of extracellular vesicles able to transfer biomolecules between cells avoiding cell-to-cell contact. Neurofilament light chain (NfL) levels in central nervous system have been advocated as biomarkers of axonal injury. NfL concentrations have been found increased in FTD and have been related to disease severity and prognosis. Little information on the relationship between NfL and exosomes in FTD has been collected, deriving mainly from traumatic brain injury. Current review deals with this matter in the attempt to provide an updated discussion of the role of NfL and exosomes as biomarkers of genetic forms of FTD.

Interactions Between Weight Loss and Plasma Neurodegenerative Markers for Determining Cognitive Decline Among Community-Dwelling Older Adults

This study aimed to investigate the interaction between weight loss (WL) and plasma amyloid-β 42/40 (Aβ 42/40), neurofilament light chain (NfL), progranulin, and their association with cognitive decline over time among older adults. This 5-year observational approach included 470 participants from the Multidomain Alzheimer Preventive Trial, mean age 76.8 years (SD = 4.5), 59.4% women. WL was defined as ≥5% decrease over the first year. Biomarkers were measured at 12 months. Cognitive function was assessed yearly from 12 months onward by Mini-Mental State Examination (MMSE); Clinical Dementia Rating sum of boxes (CDR-SB); a composite score based on Category Naming Test; Digit Symbol Substitution Test; 10 MMSE orientation items (MMSEO) and free and total recall of the Free and Cued Selective Reminding test; and these tests individually. Twenty-seven participants (5.7%) presented WL. In adjusted analyses, combined WL + lower Aβ 42/40 (≤0.103, lowest quartile) was related with more pronounced 4-year cognitive decline according to CDR-SB (p < .0001) and MMSEO (p = .021), compared with non-WL + higher Aβ 42/40. WL + higher NfL (>94.55 pg/mL, highest quartile) or progranulin (>38.4 ng/mL, 3 higher quartiles) were related with higher cognitive decline according to CDR-SB, MMSE, MMSEO, and composite score (all p < .03), compared with non-WL + lower NfL or higher progranulin. Regrouping progranulin quartiles (Q1-Q3 vs Q4) revealed higher cognitive decline among the WL + lower progranulin group compared with non-WL + lower progranulin. In conclusion, 1-year WL was associated with subsequent higher 4-year cognitive decline among older adults presenting low Aβ 42/40 or high NfL. Future studies combining plasma biomarker assessments and body weight surveillance may be useful for identifying people at risk of cognitive impairment. Clinical trial number: NCT00672685.

Conceptual framework for the definition of preclinical and prodromal frontotemporal dementia

The presymptomatic stages of frontotemporal dementia (FTD) are still poorly defined and encompass a long accrual of progressive biological (preclinical) and then clinical (prodromal) changes, antedating the onset of dementia. The heterogeneity of clinical presentations and the different neuropathological phenotypes have prevented a prior clear description of either preclinical or prodromal FTD. Recent advances in therapeutic approaches, at least in monogenic disease, demand a proper definition of these predementia stages. It has become clear that a consensus lexicon is needed to comprehensively describe the stages that anticipate dementia. The goal of the present work is to review existing literature on the preclinical and prodromal phases of FTD, providing recommendations to address the unmet questions, therefore laying out a strategy for operationalizing and better characterizing these presymptomatic disease stages.

Stratifying the Presymptomatic Phase of Genetic Frontotemporal Dementia by Serum NfL and pNfH: A Longitudinal Multicentre Study

OBJECTIVE

Although the presymptomatic stages of frontotemporal dementia (FTD) provide a unique chance to delay or even prevent neurodegeneration by early intervention, they remain poorly defined. Leveraging a large multicenter cohort of genetic FTD mutation carriers, we provide a biomarker-based stratification and biomarker cascade of the likely most treatment-relevant stage within the presymptomatic phase: the conversion stage.

METHODS

We longitudinally assessed serum levels of neurofilament light (NfL) and phosphorylated neurofilament heavy (pNfH) in the Genetic FTD Initiative (GENFI) cohort (n = 444), using single-molecule array technique. Subjects comprised 91 symptomatic and 179 presymptomatic subjects with mutations in the FTD genes C9orf72, GRN, or MAPT, and 174 mutation-negative within-family controls.

RESULTS

In a biomarker cascade, NfL increase preceded the hypothetical clinical onset by 15 years and concurred with brain atrophy onset, whereas pNfH increase started close to clinical onset. The conversion stage was marked by increased NfL, but still normal pNfH levels, while both were increased at the symptomatic stage. Intra-individual change rates were increased for NfL at the conversion stage and for pNfH at the symptomatic stage, highlighting their respective potential as stage-dependent dynamic biomarkers within the biomarker cascade. Increased NfL levels and NfL change rates allowed identification of presymptomatic subjects converting to symptomatic disease and capture of proximity-to-onset. We estimate stage-dependent sample sizes for trials aiming to decrease neurofilament levels or change rates.

INTERPRETATION

Blood NfL and pNfH provide dynamic stage-dependent stratification and, potentially, treatment response biomarkers in presymptomatic FTD, allowing demarcation of the conversion stage. The proposed biomarker cascade might pave the way towards a biomarker-based precision medicine approach to genetic FTD. ANN NEUROL 2021.

Autosomal Dominant Frontotemporal Lobar Degeneration in a Filipino Family with Progranulin Mutation

BACKGROUND

Compared to Western populations, familial frontotemporal lobar degeneration (FTLD) is rare among Asians. Progranulin (GRN) gene mutation, which is a major cause of FTLD, is likewise rare. We present a family with FTLD from the Philippines with an autosomal dominant pattern of inheritance and GRN mutation and briefly review reports of GRN mutations in Asia.

CASE PRESENTATION

The proband is 66 years old with progressive nonfluent aphasia (PNFA)-corticobasal syndrome . We assessed 3 generations of her pedigree and found 11 affected relatives with heterogenous phenotypes, usually behavioral variant frontotemporal dementia (FTD) and PNFA. Neuroimaging showed atrophy and hypometabolism consistent with FTD syndromes. White matter hyperintensities were seen in affected members even in the absence of vascular risk factors. A GRN mutation R110X was found in 6 members, 3 with symptoms and 3 were asymptomatic. Plasma GRN was low (<112 ng/mL) in all mutation carriers. No mutations were found in microtubule-associated protein tau, APP, PSEN1, and PSEN2 genes, and all were APOE3.

CONCLUSION

This is the first Filipino family with autosomal dominant FTD documented with GRN mutation. Identifying families and cohorts would contribute to therapeutic developments in an area with FTD-GRN.

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.

Genetic variants in progranulin upstream open reading frames increase downstream protein expression

Premature termination codon (PTC) mutations in the granulin gene (GRN) lead to loss-of-function (LOF) of the progranulin protein (PGRN), causing frontotemporal lobar degeneration (FTLD) by haploinsufficiency. GRN expression is regulated at multiple levels, including the 5' untranslated region (UTR). The main 5' UTR of GRN and an alternative 5' UTR, contain upstream open reading frames (uORFs). These mRNA elements generally act as cis-repressors of translation. Disruption of each uORF of the alternative 5' UTR, increases protein expression with the 2 ATG-initiated uORFs being capable of initiating translation. We performed targeted sequencing of the uORF regions in a Flanders-Belgian cohort of patients with frontotemporal dementia (FTD) and identified 2 genetic variants, one in each 5' UTR. Both variants increase downstream protein levels, with the main 5' UTR variant rs76783532 causing a significant 1.5-fold increase in protein expression. We observed that the presence of functional uORFs in the alternative 5' UTR act as potential regulators of PGRN expression and demonstrate that genetic variation within GRN uORFs can alter their function.

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.

Effect of the Histone Deacetylase Inhibitor FRM-0334 on Progranulin Levels in Patients With Progranulin Gene Haploinsufficiency: A Randomized Clinical Trial

IMPORTANCE

Histone deacetylase inhibitors have been repeatedly shown to elevate progranulin levels in preclinical models. This report describes the first randomized clinical trial of a histone deacetylase inhibitor in frontotemporal dementia (FTD) resulting from progranulin (GRN) gene variations.

OBJECTIVE

To characterize the safety, tolerability, plasma pharmacokinetics, and pharmacodynamic effects of oral FRM-0334 on plasma progranulin and other exploratory biomarkers, including fluorodeoxyglucose (FDG)-positron emission tomography (PET), in individuals with GRN haploinsufficiency.

DESIGN, SETTING, AND PARTICIPANTS

In this randomized, double-blind, placebo-controlled, dose-escalating, phase 2a safety, tolerability, and pharmacodynamic clinical study, 2 doses of a histone deacetylase inhibitor (FRM-0334) were administered to participants with prodromal to moderate FTD with granulin variations. Participants were recruited from January 13, 2015, to April 13, 2016. The study included 27 participants with prodromal (n = 8) or mild-to-moderate symptoms of FTD (n = 19) and heterozygous pathogenic variations in GRN and was conducted at multiple centers in North America, the UK, and the European Union. Data were analyzed from June 9, 2019, to May 13, 2021.

INTERVENTIONS

Daily oral placebo (n = 5), 300 mg of FRM-0334 (n = 11), or 500 mg of FRM-0334 (n = 11) was administered for 28 days.

MAIN OUTCOMES AND MEASURES

Primary outcomes were safety and tolerability of FRM-0334 and its peripheral pharmacodynamic effect on plasma progranulin. Secondary outcomes were the plasma pharmacokinetic profile of FRM-0334 and its pharmacodynamic effect on cerebrospinal fluid progranulin. Exploratory outcomes were FDG-PET, FTD clinical severity, and cerebrospinal fluid biomarkers (neurofilament light chain [NfL], amyloid β 1-42, phosphorylated tau 181, and total tau [t-tau]).

RESULTS

A total of 27 participants (mean [SD] age, 56.6 [10.5] years; 16 women [59.3%]; 26 White participants [96.3%]) with GRN variations were randomized and completed treatment. FRM-0334 was safe and well tolerated but did not affect plasma progranulin (4.3 pg/mL per day change after treatment; 95% CI, -10.1 to 18.8 pg/mL; P = .56), cerebrospinal fluid progranulin (0.42 pg/mL per day; 95% CI, -0.12 to 0.95 pg/mL; P = .13), or exploratory pharmacodynamic measures. Plasma FRM-0334 exposure did not increase proportionally with dose. Brain FDG-PET data were available in 26 of 27 randomized participants. In a cross-sectional analysis of 26 individuals, bifrontal cortical FDG hypometabolism was associated with worse Clinical Dementia Rating (CDR) plus National Alzheimer's Coordinating Center frontotemporal lobar degeneration sum of boxes score (b = -3.6 × 10-2 standardized uptake value ratio [SUVR] units/CDR units; 95% CI, -4.9 × 10-2 to -2.2 × 10-2; P < .001), high cerebrospinal fluid NfL (b = -9.2 × 10-5 SUVR units/pg NfL/mL; 95% CI, -1.3 × 10-4 to -5.6 × 10-5; P < .001), and high CSF t-tau (-7.2 × 10-4 SUVR units/pg t-tau/mL; 95% CI, -1.4 × 10-3 to -9.5 × 10-5; P = .03).

CONCLUSIONS AND RELEVANCE

In this randomized clinical trial, the current formulation of FRM-0334 did not elevate PRGN levels, which could reflect a lack of efficacy at attained exposures, low bioavailability, or some combination of the 2 factors. Bifrontal FDG-PET is a sensitive measure of symptomatic GRN haploinsufficiency. International multicenter clinical trials of FTD-GRN are feasible.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT02149160.

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.

Lysosome dysfunction as a cause of neurodegenerative diseases: Lessons from frontotemporal dementia and amyotrophic lateral sclerosis

Frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS) are fatal neurodegenerative disorders that are thought to exist on a clinical and pathological spectrum. FTD and ALS are linked by shared genetic causes (e.g. C9orf72 hexanucleotide repeat expansions) and neuropathology, such as inclusions of ubiquitinated, misfolded proteins (e.g. TAR DNA-binding protein 43; TDP-43) in the CNS. Furthermore, some genes that cause FTD or ALS when mutated encode proteins that localize to the lysosome or modulate endosome-lysosome function, including lysosomal fusion, cargo trafficking, lysosomal acidification, autophagy, or TFEB activity. In this review, we summarize evidence that lysosomal dysfunction, caused by genetic mutations (e.g. C9orf72, GRN, MAPT, TMEM106B) or toxic-gain of function (e.g. aggregation of TDP-43 or tau), is an important pathogenic disease mechanism in FTD and ALS. Further studies into the normal function of many of these proteins are required and will help uncover the mechanisms that cause lysosomal dysfunction in FTD and ALS. Mutations or polymorphisms in genes that encode proteins important for endosome-lysosome function also occur in other age-dependent neurodegenerative diseases, including Alzheimer's (e.g. APOE, PSEN1, APP) and Parkinson's (e.g. GBA, LRRK2, ATP13A2) disease. A more complete understanding of the common and unique features of lysosome dysfunction across the spectrum of neurodegeneration will help guide the development of therapies for these devastating diseases.

Systematic Review: Genetic, Neuroimaging, and Fluids Biomarkers for Frontotemporal Dementia Across Latin America Countries

Frontotemporal dementia (FTD) includes a group of clinically, genetically, and pathologically heterogeneous neurodegenerative disorders, affecting the fronto-insular-temporal regions of the brain. Clinically, FTD is characterized by progressive deficits in behavior, executive function, and language and its diagnosis relies mainly on the clinical expertise of the physician/consensus group and the use of neuropsychological tests and/or structural/functional neuroimaging, depending on local availability. The modest correlation between clinical findings and FTD neuropathology makes the diagnosis difficult using clinical criteria and often leads to underdiagnosis or misdiagnosis, primarily due to lack of recognition or awareness of FTD as a disease and symptom overlap with psychiatric disorders. Despite advances in understanding the underlying neuropathology of FTD, accurate and sensitive diagnosis for this disease is still lacking. One of the major challenges is to improve diagnosis in FTD patients as early as possible. In this context, biomarkers have emerged as useful methods to provide and/or complement clinical diagnosis for this complex syndrome, although more evidence is needed to incorporate most of them into clinical practice. However, most biomarker studies have been performed using North American or European populations, with little representation of the Latin American and the Caribbean (LAC) region. In the LAC region, there are additional challenges, particularly the lack of awareness and knowledge about FTD, even in specialists. Also, LAC genetic heritage and cultures are complex, and both likely influence clinical presentations and may modify baseline biomarker levels. Even more, due to diagnostic delay, the clinical presentation might be further complicated by both neurological and psychiatric comorbidity, such as vascular brain damage, substance abuse, mood disorders, among others. This systematic review provides a brief update and an overview of the current knowledge on genetic, neuroimaging, and fluid biomarkers for FTD in LAC countries. Our review highlights the need for extensive research on biomarkers in FTD in LAC to contribute to a more comprehensive understanding of the disease and its associated biomarkers. Dementia research is certainly reduced in the LAC region, highlighting an urgent need for harmonized, innovative, and cross-regional studies with a global perspective across multiple areas of dementia knowledge.

C9orf72 deficiency promotes microglial-mediated synaptic loss in aging and amyloid accumulation

C9orf72 repeat expansions cause inherited amyotrophic lateral sclerosis (ALS)/frontotemporal dementia (FTD) and result in both loss of C9orf72 protein expression and production of potentially toxic RNA and dipeptide repeat proteins. In addition to ALS/FTD, C9orf72 repeat expansions have been reported in a broad array of neurodegenerative syndromes, including Alzheimer's disease. Here we show that C9orf72 deficiency promotes a change in the homeostatic signature in microglia and a transition to an inflammatory state characterized by an enhanced type I IFN signature. Furthermore, C9orf72-depleted microglia trigger age-dependent neuronal defects, in particular enhanced cortical synaptic pruning, leading to altered learning and memory behaviors in mice. Interestingly, C9orf72-deficient microglia promote enhanced synapse loss and neuronal deficits in a mouse model of amyloid accumulation while paradoxically improving plaque clearance. These findings suggest that altered microglial function due to decreased C9orf72 expression directly contributes to neurodegeneration in repeat expansion carriers independent of gain-of-function toxicities.

Neurodegenerative Disease Risk in Carriers of Autosomal Recessive Disease

Genetics has driven significant discoveries in the field of neurodegenerative diseases (NDDs). An emerging theme in neurodegeneration warrants an urgent and comprehensive update: that carrier status of early-onset autosomal recessive (AR) disease, typically considered benign, is associated with an increased risk of a spectrum of late-onset NDDs. Glucosylceramidase beta (GBA1) gene mutations, responsible for the AR lysosomal storage disorder Gaucher disease, are a prominent example of this principle, having been identified as an important genetic risk factor for Parkinson disease. Genetic analyses have revealed further examples, notably GRN, TREM2, EIF2AK3, and several other LSD and mitochondria function genes. In this Review, we discuss the evidence supporting the strikingly distinct allele-dependent clinical phenotypes observed in carriers of such gene mutations and its impact on the wider field of neurodegeneration.

Progranulin in neurodegenerative dementia

Long-term or severe lack of protective factors is important in the pathogenesis of neurodegenerative dementia. Progranulin (PGRN), a neurotrophic factor expressed mainly in neurons and microglia, has various neuroprotective effects such as anti-inflammatory effects, promoting neuron survival and neurite growth, and participating in normal lysosomal function. Mutations in the PGRN gene (GRN) have been found in several neurodegenerative dementias, including frontotemporal lobar degeneration (FTLD) and Alzheimer's disease (AD). Herein, PGRN deficiency and PGRN hydrolytic products (GRNs) in the pathological changes related to dementia, including aggregation of tau and TAR DNA-binding protein 43 (TDP-43), amyloid-β (Aβ) overproduction, neuroinflammation, lysosomal dysfunction, neuronal death, and synaptic deficit have been summarized. Furthermore, as some therapeutic strategies targeting PGRN have been developed in various models, we highlighted PGRN as a potential anti-neurodegeneration target in dementia.

Neuroinflammation is highest in areas of disease progression in semantic dementia

Despite epidemiological and genetic data linking semantic dementia to inflammation, the topography of neuroinflammation in semantic dementia, also known as the semantic variant of primary progressive aphasia, remains unclear. The pathology starts at the tip of the left temporal lobe where, in addition to cortical atrophy, a strong signal appears with the tau PET tracer 18F-flortaucipir, even though the disease is not typically associated with tau but with TDP-43 protein aggregates. Here, we characterized the topography of inflammation in semantic variant primary progressive aphasia using high-resolution PET and the tracer 11C-PBR28 as a marker of microglial activation. We also tested the hypothesis that inflammation, by providing non-specific binding targets, could explain the 18F-flortaucipir signal in semantic variant primary progressive aphasia. Eight amyloid-PET-negative patients with semantic variant primary progressive aphasia underwent 11C-PBR28 and 18F-flortaucipir PET. Healthy controls underwent 11C-PBR28 PET (n = 12) or 18F-flortaucipir PET (n = 12). Inflammation in PET with 11C-PBR28 was analysed using Logan graphical analysis with a metabolite-corrected arterial input function. 18F-flortaucipir standardized uptake value ratios were calculated using the cerebellum as the reference region. Since monoamine oxidase B receptors are expressed by astrocytes in affected tissue, selegiline was administered to one patient with semantic variant primary progressive aphasia before repeating 18F-flortaucipir scanning to test whether monoamine oxidase B inhibition blocked flortaucipir binding, which it did not. While 11C-PBR28 uptake was mostly cortical, 18F-flortaucipir uptake was greatest in the white matter. The uptake of both tracers was increased in the left temporal lobe and in the right temporal pole, as well as in regions adjoining the left temporal pole such as insula and orbitofrontal cortex. However, peak uptake of 18F-flortaucipir localized to the left temporal pole, the epicentre of pathology, while the peak of inflammation 11C-PBR28 uptake localized to a more posterior, mid-temporal region and left insula and orbitofrontal cortex, in the periphery of the damage core. Neuroinflammation, greatest in the areas of progression of the pathological process in semantic variant primary progressive aphasia, should be further studied as a possible therapeutic target to slow disease progression.

Pharmacotherapy for Frontotemporal Dementia

Frontotemporal dementia is a heterogeneous spectrum of neurodegenerative disorders. The neuropathological inclusions are tau proteins, TAR DNA binding protein 43 kDa-TDP-43, or fused in sarcoma-ubiquitinated inclusions. Genetically, several autosomal mutations account for the heritability of the disorder. Phenotypically, frontotemporal dementia can present with a behavioral variant or a language variant called primary progressive aphasia. To date, there are no approved symptomatic or disease-modifying treatments for frontotemporal dementia. Currently used therapies are supported by low-level of evidence (mostly uncontrolled) studies. The off-label use of drugs is also limited by their side-effect profile including an increased risk of confusion, parkinsonian symptoms, and risk of mortality. Emerging disease-modifying treatments currently target the progranulin and the expansion on chromosome 9 open reading frame 72 genes as well as tau deposits. Advancing our understanding of the pathophysiology of the disease and improving the design of future clinical trials are much needed to optimize the chances to obtain positive outcomes.

FTLD Treatment: Current Practice and Future Possibilities

While behavioral variant frontotemporal dementia (bvFTD) and primary progressive aphasia (PPA) remain unrelenting and universally fatal conditions, there is a framework for supportive treatment in patients diagnosed with these frontotemporal dementia (FTD) syndromes and the larger spectrum of clinical syndromes associated with frontotemporal lobar degeneration (FTLD) pathology on autopsy. A managing physician has an important role in weighing therapeutic options, organizing caregiver support, and framing long-term expectations for patients and caregivers. Additionally, a dedicated neurologist may assist patients and caregivers in navigating a growing range of FTD research, including exciting opportunities in clinical therapeutic trials. This chapter will review current therapeutic options for patients with bvFTD and PPA and detail the landscape of potential new disease-modifying therapies targeting the pathophysiology or FTLD.

Blood Biomarkers in Frontotemporal Dementia: Review and Meta-Analysis

Biomarkers in cerebrospinal fluid (CSF) are useful in the differential diagnosis between frontotemporal dementia (FTD) and Alzheimer’s dementia (AD), but require lumbar puncture, which is a moderately invasive procedure that can cause anxiety to patients. Gradually, the measurement of blood biomarkers has been attracting great interest. Testing blood instead of CSF, in order to measure biomarkers, offers numerous advantages because it negates the need for lumbar puncture, it is widely available, and can be repeated, allowing the prediction of disease course. In this study, a systematic review of the existing literature was conducted, as well as meta-analysis with greater emphasis on the most studied biomarkers, p-tau and progranulin. The goal was to give prominence to evidence regarding the use of plasma biomarkers in clinical practice.

Unravelling Genetic Factors Underlying Corticobasal Syndrome: A Systematic Review

Corticobasal syndrome (CBS) is an atypical parkinsonian presentation characterized by heterogeneous clinical features and different underlying neuropathology. Most CBS cases are sporadic; nevertheless, reports of families and isolated individuals with genetically determined CBS have been reported. In this systematic review, we analyze the demographical, clinical, radiological, and anatomopathological features of genetically confirmed cases of CBS. A systematic search was performed using the PubMed, EMBASE, and Cochrane Library databases, included all publications in English from 1 January 1999 through 1 August 2020. We found forty publications with fifty-eight eligible cases. A second search for publications dealing with genetic risk factors for CBS led to the review of eight additional articles. GRN was the most common gene involved in CBS, representing 28 out of 58 cases, followed by MAPT, C9ORF72, and PRNP. A set of symptoms was shown to be significantly more common in GRN-CBS patients, including visuospatial impairment, behavioral changes, aphasia, and language alterations. In addition, specific demographical, clinical, biochemical, and radiological features may suggest mutations in other genes. We suggest a diagnostic algorithm to help in identifying potential genetic cases of CBS in order to improve the diagnostic accuracy and to better understand the still poorly defined underlying pathogenetic process.