Icon Legend

This session is not in your schedule.

This session is in your schedule. Click again to remove it.

Cellular and Molecular Bioengineering

Cellular and Molecular Bioengineering - Poster Session E

Poster I3 - TDP-43 depletion accelerates tauopathy driven brain atrophy by increasing neuronal sensitivity to caspase 3-mediated tau cleavage in a mouse model of Multiple Etiology Dementia

Saturday, October 26, 2024

10:00 AM - 11:00 AM EST

Location: Exhibit Hall E, F & G

Presenting Author(s)

Margarita Tsapatsis

Undergraduate
Johns Hopkins University
Baltimore, Maryland, United States

Co-Author(s)

MB

Meghraj Baghel

Post Doctoral Fellow
Johns Hopkins University School of Medicine, United States
Grace Burns, BS

Graduate Student
Johns Hopkins University School of Medicine, United States
AM

Aswathy Mallika

Post Doctoral Fellow
Johns Hopkins University School of Medicine, United States
AC

Anna Cruz

Graduate Student
Johns Hopkins University School of Medicine, United States
Tianyu Cao, md (he/him/his)

Post Doctoral Fellow
Johns Hopkins University School of Medicine
Baltimore, Maryland, United States
Xiaoke K. Chen, MSE (she/her/hers)

Graduate Student
Johns Hopkins University
Baltimore, Maryland, United States
Id

Isabel de la rosa

Undergraduate
Johns Hopkins University, United States
SM

Shaelyn Marx

Research Technician
Johns Hopkins University, United States
YY

Yingzhi Ye

Graduate Student
Johns Hopkins University School of Medicine, United States
SS

Shuying Sun

Associate Professor
Johns Hopkins University School of Medicine, United States
TL

Tong Li

Assistant Professor
Johns Hopkins University School of Medicine, United States

Primary Investigator(s)

PW

Philip Wong

Professor
Johns Hopkins University School of Medicine, United States

Introduction: Alzheimer’s disease (AD), the fifth leading cause of death in individuals over the age of 65 in the United States, is the most common age-related dementia, marked by a progressive loss of synapses and eventually neurons. Two characteristic features of AD pathology are neuritic plaques and neurofibrillary tangles. While substantial evidence supports a linear progression in familial AD, where excessive amyloid-β triggers tau aggregation and subsequent neurodegeneration, the etiology of sporadic late-onset AD is thought to be multifactorial. Recent research indicates that up to 75% of cases of AD and AD-Related Dementia (ADRD) present with non-canonical pathologies, such as TAR DNA/RNA binding protein (TDP-43) pathology, which can be found in 40-60% of ADRD cases and is strongly associated with increased neurodegeneration and cognitive decline. Furthermore, TDP-43 pathology is also observed in certain tauopathies, including frontotemporal lobar dementia (FTLD), primary age-related tauopathy (PART), corticobasal degeneration (CBD), and progressive supranuclear palsy (PSP). Consequently, the presence and interaction of these pathological factors likely contribute to more severe neurodegeneration and accelerated cognitive decline.

Materials and

Methods: The conditional knockout mouse model of TDP-43 was used by generating CaMKIIα-CreER;Tardbpf/f (TDP-43 KO) mice with loxP sites flanking Tardbp exon 3, creating a tamoxifen-induced recombination in excitatory forebrain neurons in adult mice. These mice were bred with the tTA;Tau4R (Tau4R) line generated previously and a cohort of tTA;Tau4R;CaMKIIα-CreER;Tardbpf/f (Tau4R;TDP-43 KO) mice on a C57BL/6J background, as well as littermate controls. Animals were genotyped at weaning, and mice were subsequently housed with one littermate of each genotype (5 mice/cage) when possible. Oral administration of tamoxifen citrate through diet was done in all animals for a 4 week period, beginning at 12 months of age. Studies in transgenic Tau4R;TDP-43 KO mice and littermate controls were carried out in brain tissue dissected out from 19 or 25 month old mice. For the AAV-PhP.eB-hTau4R/GFP injection model, we deleted TDP-43 at 11 months of age through the administration of tamoxifen feed. Mice were returned to normal feed for recovery for 2 weeks and then stereotaxic surgery was performed. Unilateral injections were performed using a syringe containing AAV-PhP.eB-hTauRD or GFP as a control. Multiple staining techniques were used upon sacrifice. Immunofluorescence staining was performed using antiserum against cleaved caspase 3 while immunohistochemistry staining used antiserum against NeuN, TDP-43 N-terminus, phosphorylated S422 tau, Tau4R cleaved caspase 3, and cleaved tau.

Results, Conclusions, and Discussions: The loss of TDP-43 splicing repression observed in presymptomatic ALS-FTD individuals suggests that this early loss could promote the pathological conversion of tau, accelerating neuronal loss. Our study reveals that the loss of TDP-43 repression of cryptic exons in forebrain neurons is necessary for exacerbating tauopathy-related brain atrophy by making vulnerable neurons more susceptible to caspase 3-dependent cleavage of endogenous tau, thereby promoting tauopathy. Using a mouse model, specifically CaMKII-CreER;Tardbpf/f mice expressing a four-repeat microtubule-binding domain of human tau, we demonstrated that the amount of tau seed correlates positively with levels of caspase 3-cleaved tau. In human models, we show that TDP-43 loss in iPSC-derived cortical neurons leads to the early inclusion of cryptic exons and subsequent caspase 3-mediated tau endoproteolysis. We found that the vulnerability of hippocampal neurons to TDP-43 depletion is contingent upon the level of caspase 3-cleaved tau, with the CA2/3 region being the most vulnerable, followed by the dentate gyrus and CA1 being the least. These findings strongly support the idea that TDP-43 loss exacerbates tauopathy-related brain atrophy by increasing neuronal sensitivity to caspase 3-mediated tau endoproteolysis, leading to greater neurodegeneration in disorders with both tau and TDP-43 pathologies. The need for a model system that accurately represents these co-pathologies is critical, given that they account for over 75% of all cases of ADRD. Recent FDA-approved drugs targeting only β-amyloidosis have highlighted this issue, as many participants did not respond due to the lack of focus on tau, α-synuclein, or TDP-43. Our research provides new mechanistic insights and therapeutic targets for human tauopathies with co-pathologies of TDP-43 and introduces a novel MED model to clarify disease mechanisms, identify therapeutic targets, and validate treatment strategies for these complex dementias.

Baghel M, Burns G, Tsapatsis M, et al. Depletion of TDP-43 exacerbates tauopathy-dependent brain atrophy by sensitizing vulnerable neurons to caspase 3-mediated endoproteolysis of tau in a mouse model of Multiple Etiology Dementia, bioRxiv, doi: 10.1101/2024.06.26.600814

Acknowledgements (Optional): Thanks to T. Melnikova and B. Kim for technical support