Approaches to develop therapeutics to treat frontotemporal dementia

Benzoxazole-derivatives enhance progranulin expression and reverse the aberrant lysosomal proteome caused by GRN haploinsufficiency

Heterozygous loss-of-function mutations in the GRN gene are a major cause of hereditary frontotemporal dementia. The mechanisms linking frontotemporal dementia pathogenesis to progranulin deficiency are not well understood, and there is currently no treatment. Our strategy to prevent the onset and progression of frontotemporal dementia in patients with GRN mutations is to utilize small molecule positive regulators of GRN expression to boost progranulin levels from the remaining functional GRN allele, thus restoring progranulin levels back to normal within the brain. This work describes a series of blood-brain-barrier-penetrant small molecules which significantly increase progranulin protein levels in human cellular models, correct progranulin protein deficiency in Grn+/- mouse brains, and reverse lysosomal proteome aberrations, a phenotypic hallmark of frontotemporal dementia, more efficiently than the previously described small molecule suberoylanilide hydroxamic acid. These molecules will allow further elucidation of the cellular functions of progranulin and its role in frontotemporal dementia and will also serve as lead structures for further drug development.

Three dimensional and four dimensional live imaging to study mechanisms of progressive neurodegeneration

Neurodegenerative diseases are complex and progressive, posing challenges to their study and understanding. Recent advances in microscopy imaging technologies have enabled the exploration of neurons in three spatial dimensions (3D) over time (4D). When applied to 3D cultures, tissues, or animals, these technologies can provide valuable insights into the dynamic and spatial nature of neurodegenerative diseases. This review focuses on the use of imaging techniques and neurodegenerative disease models to study neurodegeneration in 4D. Imaging techniques such as confocal microscopy, two-photon microscopy, miniscope imaging, light sheet microscopy, and robotic microscopy offer powerful tools to visualize and analyze neuronal changes over time in 3D tissue. Application of these technologies to in vitro models of neurodegeneration such as mouse organotypic culture systems and human organoid models provide versatile platforms to study neurodegeneration in a physiologically relevant context. Additionally, use of 4D imaging in vivo, including in mouse and zebrafish models of neurodegenerative diseases, allows for the investigation of early dysfunction and behavioral changes associated with neurodegeneration. We propose that these studies have the power to overcome the limitations of two-dimensional monolayer neuronal cultures and pave the way for improved understanding of the dynamics of neurodegenerative diseases and the development of effective therapeutic strategies.

Alterations in Lysosomal, Glial and Neurodegenerative Biomarkers in Patients with Sporadic and Genetic Forms of Frontotemporal Dementia

Background

Frontotemporal dementia (FTD) is the most common cause of early-onset dementia with 10-20% of cases caused by mutations in one of three genes: GRN, C9orf72, or MAPT. To effectively develop therapeutics for FTD, the identification and characterization of biomarkers to understand disease pathogenesis and evaluate the impact of specific therapeutic strategies on the target biology as well as the underlying disease pathology are essential. Moreover, tracking the longitudinal changes of these biomarkers throughout disease progression is crucial to discern their correlation with clinical manifestations for potential prognostic usage.

Methods

We conducted a comprehensive investigation of biomarkers indicative of lysosomal biology, glial cell activation, synaptic and neuronal health in cerebrospinal fluid (CSF) and plasma from non-carrier controls, sporadic FTD (symptomatic non-carriers) and symptomatic carriers of mutations in GRN, C9orf72, or MAPT, as well as asymptomatic GRN mutation carriers. We also assessed the longitudinal changes of biomarkers in GRN mutation carriers. Furthermore, we examined biomarker levels in disease impacted brain regions including middle temporal gyrus (MTG) and superior frontal gyrus (SFG) and disease-unaffected inferior occipital gyrus (IOG) from sporadic FTD and symptomatic GRN carriers.

Results

We confirmed glucosylsphingosine (GlcSph), a lysosomal biomarker regulated by progranulin, was elevated in the plasma from GRN mutation carriers, both symptomatic and asymptomatic. GlcSph and other lysosomal biomarkers such as ganglioside GM2 and globoside GB3 were increased in the disease affected SFG and MTG regions from sporadic FTD and symptomatic GRN mutation carriers, but not in the IOG, compared to the same brain regions from controls. The glial biomarkers GFAP in plasma and YKL40 in CSF were elevated in asymptomatic GRN carriers, and all symptomatic groups, except the symptomatic C9orf72 mutation group. YKL40 was also increased in SFG and MTG regions from sporadic FTD and symptomatic GRN mutation carriers. Neuronal injury and degeneration biomarkers NfL in CSF and plasma, and UCHL1 in CSF were elevated in patients with all forms of FTD. Synaptic biomarkers NPTXR, NPTX1/2, and VGF were reduced in CSF from patients with all forms of FTD, with the most pronounced reductions observed in symptomatic MAPT mutation carriers. Furthermore, we demonstrated plasma NfL was significantly positively correlated with disease severity as measured by CDR+NACC FTLD SB in genetic forms of FTD and CSF NPTXR was significantly negatively correlated with CDR+NACC FTLD SB in symptomatic GRN and MAPT mutation carriers.

Conclusions

In conclusion, our comprehensive investigation replicated alterations in biofluid biomarkers indicative of lysosomal function, glial activation, synaptic and neuronal health across sporadic and genetic forms of FTD and unveiled novel insights into the dysregulation of these biomarkers within brain tissues from patients with GRN mutations. The observed correlations between biomarkers and disease severity open promising avenues for prognostic applications and for indicators of drug efficacy in clinical trials. Our data also implicated a complicated relationship between biofluid and tissue biomarker changes and future investigations should delve into the mechanistic underpinnings of these biomarkers, which will serve as a foundation for the development of targeted therapeutics for FTD.

Characterization of Progranulin Gene Mutations in Portuguese Patients with Frontotemporal Dementia

In Portugal, heterozygous loss-of-function mutations in the progranulin (GRN) gene account for approximately half of the genetic mediated forms of frontotemporal dementia (FTD). GRN mutations reported thus far cause FTD through a haploinsufficiency disease mechanism. Herein, we aim to unveil the GRN mutation spectrum, investigated in 257 FTD patients and 19 family members from the central/north region of Portugal using sequencing methods. Seven different pathogenic variants were identified in 46 subjects including 40 patients (16%) and 6 relatives (32%). bvFTD was the most common clinical presentation among the GRN mutation patients, who showed a global pattern of moderate-to-severe frontotemporoparietal deficits in the neuropsychological evaluation. Interestingly, two mutations were novel (p.Thr238Profs*18, p.Leu354Profs*16), and five were previously described, although three of them only in the Portuguese population, suggesting a population-specific GRN mutational spectrum. The subjects harboring a GRN mutation showed a significant reduction in serum PGRN levels, supporting the pathogenic nature of these variants. This work broadens the mutation spectrum of GRN and the identification of the underlying GRN mutations provided an accurate genetic counselling and allowed the enrolment of subjects with GRN mutations (both asymptomatic and symptomatic) in ongoing clinical trials, which is essential to test new drugs for the disease.

Comparison of Design Fluency Test Results among Patients with Parkinson's Disease, Frontotemporal Dementia, and the Control Group

Background:

Design Fluency Test (DFT) is a nonverbal frame-free, nonstructured assessment of executive function (EF). Since previous studies evaluating EF in Parkinson's disease (PD) have mainly used verbal assessments for EF, this study aims to evaluate the pattern of executive domains in PD using DFT and to compare it with behavioral variant frontotemporal dementia (FTD) as a prototype for executive dysfunction and also with normal controls (NCs).

Materials and Methods:

Twenty-eight patients with PD, 27 with FTD, and 27 NCs were included in the study in Ayatollah Kashani Neuropsychiatry Clinic affiliated to Isfahan University of Medical Sciences from September 2019 to February 2020. All participants were assessed via semi-structured neuropsychiatric interview, questionnaire for demographic profile (age, handedness, gender, education, and marital status), duration of illness, comorbid medical condition, comorbid psychiatric illnesses and medications, DFT, Short Parkinson's Evaluation Scale, Frontal Assessment Battery, Judgment of Line Orientation, and Neuropsychiatry Unit Cognitive Assessment Tool.

Results:

Fixed condition novelty score was significantly different between FTD and PD (P < 0.001), FTD and control (P < 0.001), and also between PD and control (P = 0.001). When free and fixed condition novelty scores were considered to predict diagnostic attribution, multinomial logistic regression revealed that odds ratio for free condition novelty score was 0.705 (P = 0.005, 95% confidence interval [CI] = 0.553–0.899) and 0.494 (P = 0.001, 95% CI = 0.328–0.744) in PD and FTD, respectively. The odds ratio for fixed condition novelty score was 0.772 (P = 0.011, 95% CI = 0.632–0.942) and 0.449 (P = 0.00, 95% CI = 0.292–0.691).

Conclusion:

DFT subscores can be helpful in diagnosis and differentiation between FTD and PD.

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.

Anti-sortilin1 Antibody Up-Regulates Progranulin via Sortilin1 Down-Regulation

Progranulin (PGRN) haploinsufficiency associated with loss-of-function mutations in the granulin gene causes frontotemporal dementia (FTD). This suggests that increasing PGRN levels could have promising therapeutic implications for patients carrying GRN mutations. In this study, we explored the therapeutic potential of sortilin1 (SORT1), a clearance receptor of PGRN, by generating and characterizing monoclonal antibodies against SORT1. Anti-SORT1 monoclonal antibodies were generated by immunizing Sort1 knockout mice with SORT1 protein. The antibodies were classified into 7 epitope bins based on their competitive binding to the SORT1 protein and further defined by epitope bin-dependent characteristics, including SORT1-PGRN blocking, SORT1 down-regulation, and binding to human and mouse SORT1. We identified a positive correlation between PGRN up-regulation and SORT1 down-regulation. Furthermore, we also characterized K1-67 antibody via SORT1 down-regulation and binding to mouse SORT1 in vivo and confirmed that K1-67 significantly up-regulated PGRN levels in plasma and brain interstitial fluid of mice. These data indicate that SORT1 down-regulation is a key mechanism in increasing PGRN levels via anti-SORT1 antibodies and suggest that SORT1 is a potential target to correct PGRN reduction, such as that in patients with FTD caused by GRN mutation.