Pickles, Sarah

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.

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.

Functional loss of TDP-43, an RNA binding protein genetically and pathologically linked to amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD), leads to the inclusion of cryptic exons in hundreds of transcripts during disease. Cryptic exons can promote the degradation of affected transcripts, deleteriously altering cellular function through loss-of-function mechanisms. Here, we show that mRNA transcripts harboring cryptic exons generated de novo proteins in TDP-43–depleted human iPSC–derived neurons in vitro, and de novo peptides were found in cerebrospinal fluid (CSF) samples from patients with ALS or FTD. Using coordinated transcriptomic and proteomic studies of TDP-43–depleted human iPSC–derived neurons, we identified 65 peptides that mapped to 12 cryptic exons. Cryptic exons identified in TDP-43–depleted human iPSC–derived neurons were predictive of cryptic exons expressed in postmortem brain tissue from patients with TDP-43 proteinopathy. These cryptic exons produced transcript variants that generated de novo proteins. We found that the inclusion of cryptic peptide sequences in proteins altered their interactions with other proteins, thereby likely altering their function. Last, we showed that 18 de novo peptides across 13 genes were present in CSF samples from patients with ALS/FTD spectrum disorders. The demonstration of cryptic exon translation suggests new mechanisms for ALS/FTD pathophysiology downstream of TDP-43 dysfunction and may provide a potential strategy to assay TDP-43 function in patient CSF.

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