Tong, Jimei

Progranulin (PGRN) deficiency is a common hallmark in frontotemporal dementia (FTD) patients with granulin ( GRN ) mutations (FTD- GRN ). Previous studies by our group and others have observed that reduced PGRN perturbs lysosomal function and microglial activation, which is believed to accelerate neurodegeneration in FTD- GRN patients. Lysosomal function is intrinsically linked to lipid metabolism, and evidence suggests that GRN deficiency can alter lipid profiles in the brain. Unfortunately, studies to date have focused on whole brain or cortical extracts, limiting our ability to assess cell type-dependent changes in lipid metabolism under disease conditions. Here, we employed lipidomic analysis specifically within the pontine microglia of Grn knock-out (KO) mice, a cell population that was previously linked to disease phenotypes in this model. We observed a significant reduction in the endolysosomal lipid bis(monoacylglycero)phosphate (BMP) and the lipid metabolite phosphatidylethanolamine (PE); these microglial-specific lipid alterations mirror previous whole-brain findings, suggesting that similar changes may occur across multiple cell types in the brain. We also detected a significant increase in the myelin-composing factor galactosylceramide (GalCer), which may reflect an aberrant accumulation of myelin debris within microglia that arises due to defective lysosomal clearance. Notably, lipid perturbations were exacerbated with age within Grn KO microglia, suggesting that changes in lipid metabolism are both age- and genotype-dependent in this model. Together, our results support our hypothesis that PGRN acts as a master regulator of critical microglial processes – including lysosomal function, lipid metabolism, and the regulation of myelination – in an age-dependent manner.

Abstract Background Some cases of Alzheimer's Disease (AD) and Frontotemporal Dementia (FTD) feature the mislocalization of the normally nuclear TAR DNA binding protein (TDP‐43) to the cytoplasm where it is incorporated into inclusions in affected brain regions. TDP‐43 plays a crucial role in the suppression of cryptic exons in the mature RNA of many targets in both AD and FTD. One such target, Stathmin‐2 (STMN2), is misspliced in the absence of TDP‐43 leading to a reduction of STMN2 RNA and protein while the levels of the cryptic splice variant is increased. Cryptic exons are not conserved across species, meaning previous Tdp‐43 models did not capture Stmn2 processing defects and Stmn2 loss of function (LOF). We hypothesize that STMN2 LOF contributes to cognitive phenotypes observed in AD and FTD. Method We have generated a novel mouse that more accurately models human disease mechanisms by expressing short‐hairpin (shRNA) via adeno associated virus in the central nervous system of a recently described humanized Stmn2 mouse model in which Stmn2 splicing is dependent on Tdp‐43. In this mouse we will simultaneously model Tdp‐43 loss of function and aberrant Stmn2 splicing. Result Our preliminary experiments demonstrate that humanized Stmn2 mice expressing shRNA against Tardbp have a reduction of Tardbp RNA and TDP‐43 protein compared to mice expressing a non‐targeting shRNA. Tdp‐43 knock‐down is accompanied by cryptic splicing of endogenous mouse targets, Sortilin 1 and Translin . As anticipated, we also detected cryptic Stmn2 splicing, suggesting that correct Stmn2 splicing is dependent on Tdp‐43 in this model. We will further characterize motor and cognitive functions in addition to neurodegeneration and gliosis in these animals. Conclusion We anticipate this novel model, and our subsequent studies will identify relevant disease mechanisms and provide an invaluable tool with which to investigate therapies for AD and FTD.

Amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) are fatal neurodegenerative diseases that share clinical and pathological features, as well as genetic causes. A G4C2 repeat expansion in chromosome 9 open reading frame 72 (C9orf72) is the most common genetic cause of ALS and FTD, collectively referred to as c9ALS/FTD. Assembly modulation is a new therapeutic approach which appears to target allosteric sites on aberrant forms of multi-protein complexes and restore them to the healthy state. Recent findings demonstrate that tetrahydroisoquinolone (THIQ)-based protein assembly modulators can ameliorate ALS/FTD-associated phenotypes in cellular and animal models. In the present study, we investigated the effects of PAV-615, a novel and advanced THIQ-based modulator, in a c9ALS/FTD mouse model expressing 149 G4C2 repeat expansions (referred to as 149R mouse model). Specifically, PAV-615 was administered to 5-month-old 149R mice via intraperitoneal injection for one month. Motor function was evaluated using the hang wire test, while anxiety-like behavior and hyperactivity were assessed using the open-field test. Pathological markers, including dipeptide repeat (DPR) proteins, phosphorylated TAR DNA-binding protein 43 (pTDP-43) and ataxin 2-positive stress granules, were quantified by Meso Scale Discovery and immunohistochemistry assays. Compared with vehicle-treated controls, PAV-615 significantly improved motor performance and modestly reduced anxiety-like behavior and hyperactivity in 149R mice. Moreover, PAV-615 treatment significantly decreased cortical DPR, pTDP-43 and ataxin 2-positive stress granule burdens. These results support assembly modulation as a promising therapeutic approach treatment of ALS/FTD.

Abstract Background Perry syndrome (PS) is a rare and fatal hereditary autosomal dominant neurodegenerative disorder caused by mutations in dynactin ( DCTN1 ). PS brains accumulate inclusions positive for ubiquitin, transactive‐response DNA‐binding protein of 43 kDa (TDP‐43), and to a lesser extent dynactin. Objectives Little is known regarding the contributions of TDP‐43, an RNA binding protein that represses cryptic exon inclusion, in PS. Therefore, we sought to identify the degree of TDP‐43 dysfunction in two regions of PS brains. Methods We evaluated the levels of insoluble pTDP‐43 and TDP‐43‐regulated cryptic RNAs and protein in the caudate nucleus and substantia nigra of 7 PS cases, 12 cases of frontotemporal lobar degeneration (FTLD) with TDP‐43 pathology, and 11 cognitively healthy controls without TDP‐43 pathology. Results Insoluble pTDP‐43 protein levels were detected in PS brains to a similar extent in the caudate nucleus and substantia nigra but lower than those in FTLD brains. The caudate nucleus of PS showed accumulation of eight TDP‐43‐regulated cryptic RNAs ( ACTL6B , CAMK2B , STMN2 , UNC13A , KCNQ2 , ATG4B , GPSM2 , and HDGFL2 ) and cryptic protein (HDGFL2) characteristic of FTLD. Conversely, only one cryptic target, UNC13A , reached significance in the substantia nigra despite similar pTDP‐43 levels. Conclusion We detected TDP‐43 cryptic RNAs and protein in PS caudate nucleus. Given the importance of cryptic exon biology in the development of biomarkers, and the identification of novel targets for therapeutic intervention, it is imperative we understand the consequences of TDP‐43 dysfunction across different brain regions and determine the targets that are specific and common to TDP‐43 proteinopathies. © 2025 The Author(s). Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Frontotemporal dementia and amyotrophic lateral sclerosis (FTD-ALS) are associated with both a repeat expansion in the C9orf72 gene and mutations in the TANK-binding kinase 1 ( TBK1 ) gene. We found that TBK1 is phosphorylated in response to C9orf72 poly(Gly-Ala) [poly(GA)] aggregation and sequestered into inclusions, which leads to a loss of TBK1 activity and contributes to neurodegeneration. When we reduced TBK1 activity using a TBK1-R228H (Arg 228 →His) mutation in mice, poly(GA)-induced phenotypes were exacerbated. These phenotypes included an increase in TAR DNA binding protein 43 (TDP-43) pathology and the accumulation of defective endosomes in poly(GA)-positive neurons. Inhibiting the endosomal pathway induced TDP-43 aggregation, which highlights the importance of this pathway and TBK1 activity in pathogenesis. This interplay between C9orf72 , TBK1 , and TDP-43 connects three different facets of FTD-ALS into one coherent pathway.

G 4 C 2 repeat–derived poly(GR) plays a key role in mediating TDP-43 mislocalization and aggregation in vitro and in vivo.

How dipeptide repeats cause pathology A repeat expansion in the chromosome 9 open reading frame 72 ( C9orf72 ) gene is the most common known cause of two neurodegenerative diseases: frontotemporal dementia and amyotrophic lateral sclerosis. This expansion leads to the abnormal production of proteins of repeating dipeptides, but their contribution to disease pathogenesis remains unclear. Zhang et al. engineered a mouse model to study the consequences of one of these dipeptides—prolinearginine dipeptide repeat protein, poly(PR)—in the brain. They found that poly(PR) caused neuron loss as well as motor and memory impairments. These detrimental effects resulted from poly(PR)-induced perturbation of heterochromatin function, a tightly packed form of DNA that represses gene expression. Science , this issue p. eaav2606

Poly(GP) proteins are a promising pharmacodynamic marker for developing and testing therapeutics for treating C9ORF72 -associated amyotrophic lateral sclerosis.

Inclusions of TAR DNA-binding protein-43 (TDP-43), a nuclear protein that regulates transcription and RNA splicing, are the defining histopathological feature of frontotemporal lobar degeneration with ubiquitin-positive inclusions (FTLD-Us) and sporadic and familial forms of amyotrophic lateral sclerosis (ALS). In ALS and FTLD-U, aggregated, ubiquitinated, and N-terminally truncated TDP-43 can be isolated from brain tissue rich in neuronal and glial cytoplasmic inclusions. The loss of TDP-43 function resulting from inappropriate cleavage, translocation from the nucleus, or its sequestration into inclusions could play important roles in neurodegeneration. However, it is not known whether TDP-43 fragments directly mediate toxicity and, more specifically, whether their abnormal aggregation is a cause or consequence of pathogenesis. We report that the ectopic expression of a ≈25-kDa TDP-43 fragment corresponding to the C-terminal truncation product of caspase-cleaved TDP-43 leads to the formation of toxic, insoluble, and ubiquitin- and phospho-positive cytoplasmic inclusions within cells. The 25-kDa C-terminal fragment is more prone to phosphorylation at S409/S410 than full-length TDP-43, but phosphorylation at these sites is not required for inclusion formation or toxicity. Although this fragment shows no biological activity, its exogenous expression neither inhibits the function nor causes the sequestration of full-length nuclear TDP-43, suggesting that the 25-kDa fragment can induce cell death through a toxic gain-of-function. Finally, by generating a conformation-dependent antibody that detects C-terminal fragments, we show that this toxic cleavage product is specific for pathologic inclusions in human TDP-43 proteinopathies.