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  Glial and vascular contributions to neurodegenerative diseases
Modelling discontinuous flow patterns on the blood-brain barrier
Adjanie Patabendige1,2, Gregory Lip2,3, Damir Janigro4,5
1Edge Hill University, Ormskirk, UK, 2University of Liverpool, Liverpool, UK, 3Liverpool Heart &
Chest Hospital, Liverpool, UK, 4Flocel Inc, Cleveland, USA, 5Case Western Reserve University, Cleveland, USA
 The blood-brain barrier (BBB) is a protective physiological barrier that is often disrupted during many central nervous system (CNS) diseases. Deterioration in neuroprotective BBB function plays a major role in the pathogenesis of disease since the BBB dynamically responds to many events associated with flow disturbances. Emerging evidence strongly suggest that BBB dysfunction can also lead to secondary neurological damage in non-CNS diseases such as atrial fibrillation (AF) by increasing the risk of developing dementia and worsening stroke outcomes. However, the underlying mechanisms are poorly understood. Although widely used, animal models of AF can only mimic a specific aspect of human AF and are not suitable for direct investigation of AF-induced effects on the BBB. Therefore, alternative, humanised models that can mimic the pathophysiology of cerebral blood flow changes due to abnormal heart rhythm are essential. Here we present current challenges in developing such a model and propose a novel and innovative method to establish a humanised model to determine AF- induced changes on the brain vasculature. The new model has the capacity to accept and translate complex waveform patterns derived from echocardiogram (ECG) recordings from AF patients. It is therefore able to simulate arrhythmia to induce intravascular pressure changes in cerebral blood vessels and provide a platform to determine the effects on the BBB. Once fully established, the humanised model will lead to improved understanding of the role of the BBB during AF and help transform future drug development efforts.
to detect cerebral pH changes on a Bruker 11.7T scanner.
Results: We found breakdown in the BBB permeability to water, indicated by increased permeability surface area product and water extraction fraction in premanifest 5×FAD mice. Moreover, decreased global oxygen extraction fraction, unit-mass CMRO2 and total CMRO2 was manifested in these young 5×FAD mice, together with a relatively intact vascular function and lack of neurodegeneration at this age. In the CrCEST study, the pH value was significantly lower in the hippocampus of 3-month-old 5×FAD mice than that in the age- and gender-matched controls. No cognitive impairment and significant amyloid-β deposition were detectable in the 5×FAD mice at this age. Discussion and Conclusions: Our findings suggest that altered cerebral metabolism and compromised BBB permeability occur prior to brain hypoperfusion and cognitive decline in AD mice. Further validation of these MRI measures in other AD models and human subjects will benefit early diagnosis and facilitate effective therapeutic development for AD.
TDP-43 represses cryptic exons in TFIIH components to regulate epigenetic remodeling at neuronal enhancers
Sarah Hill1, Sahba Seddighi1, Yue Qi1, Wei Wu2, William Nathan2, Dongpeng Wang2, Elsa Callen2, Daniel Ramos1, Joel Reyes1, Caroline Esnault3, Ryan Dale3, Steven Coon3, Mercedes Prudencio4, Leonard Petrucelli4, Zhe Liu5, Jennifer Lippincott-Schwartz5, Andre Nussenzweig2, Michael Ward1
1NINDS/NIH, Bethesda, USA, 2NCI/NIH, Bethesda, USA, 3NICHD/NIH, Bethesda, USA, 4Mayo Clinic, Jacksonville, USA, 5Janelia Research Campus, Ashburn, USA
Cerebral metabolic changes and impaired blood-brain barrier precede amyloid beta deposition in the 5×FAD mouse model Minmin Yao1, Zhiliang Wei2, Ziqin Zhang3, Anna Li4, Ruoxuan Li1, Aaron Kakazu1, Hanzhang Lu2,3, Jiadi Xu2,4, Wenzhen Duan1,5
1Division of Neurobiology, Department of Psychiatry and Behavioral Sciences, Johns Hopkins University School of medicine, Baltimore, USA, 2The Russell H. Morgan Department of Radiology and Radiological Sciences, Johns Hopkins University School of Medicine, Baltimore, USA, 3Department of Biomedical Engineering, Johns Hopkins University, Baltimore, Maryland, USA, Baltimore, USA, 4F.M. Kirby Research Center, Kennedy Krieger Research Institute, Baltimore, USA, 5Solomon H. Snyder Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, USA
 Background: Alzheimer’s disease (AD) is characterized by cerebral amyloid-β accumulation and progressive decline in cognitive function. Altered brain metabolism arise in the predromal AD, suggesting an important metabolic component of early AD pathology. In addition, extant studies suggest that impairment of the blood-brain barrier (BBB) is involved in the pathogenesis of AD. By the time AD is clinically diagnosed, significant neuronal loss has already occurred and becomes irreversible. Therefore, the sensitive biomarkers reflecting early functional changes before neuronal loss are critical for developing effective intervention.
Materials and Methods: 3-month-old 5×FAD mice were examined using following magnetic resonance imaging (MRI) measures, including water extraction with phase-contrast arterial spin tagging (WEPCAST) to assess the BBB integrity, T2 relaxation under spin tagging (TRUST) and phase contrast (PC) to assess cerebral metabolic rate of oxygen (CMRO2), and creatine chemical exchange saturation transfer (CrCEST)
Programmed DNA damage, unlike random toxic DNA damage, occurs at planned sites in the genome and plays essential roles in cellular physiology. In neurons, programmed DNA damage at promoters can activate gene expression in response to synaptic activity. We recently discovered that widespread programmed DNA damage occurs at neuronal enhancers, likely playing key roles through regulating active DNA demethylation. Defects in DNA repair and active DNA demethylation have been observed in neurodegenerative diseases including frontotemporal dementia (FTD), Alzheimer’s disease, and age-related cognitive dysfunction, yet their contribution to neurodegeneration remains unclear. To measure repair of programmed DNA damage in neurons, we performed synthesis-associated repair sequencing (SAR-seq), which detects recurrent DNA repair genome- wide by incorporating a nucleotide analog to capture sites of DNA repair. We used human induced pluripotent stem cell-derived neurons (i3Neurons) and CRISPR interference (CRISPRi) to knock down TDP- 43, a hallmark in FTD and age-related neurodegeneration. In TDP43- knockdown (KD) i3Neurons, we observed substantial reduction of SAR-seq intensity, suggesting that TDP-43 is required for DNA break/ repair in neurons. TDP-43 is a splicing repressor that prevents cryptic exons, repressed intronic sequences, from inclusion into mature RNA transcripts. We performed RNA-seq in TDP-43 KD i3Neurons and found 100s of destabilized transcripts with cryptic exons. We determined that two of the destabilized genes are essential for neuron survival and belong to the TFIIH complex, which regulates transcription. We inhibited TFIIH and observed reduced SAR-seq intensity, suggesting that TFIIH acts upstream of active demethylation. Furthermore, we found that TDP-43 KD i3Neurons display reduced transcription, suggesting that loss of active demethylation and programmed DNA repair upon TDP-43 KD may arise from a loss of transcription. These data are consistent with a model where TDP-43 regulates programmed DNA damage in neurons through splicing repression of TFIIH components and suggests a novel mechanism between TDP-43 and DNA repair.
74 • ISMND 2022

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