Investigating the Role of TDP-43 Microvasculopathy on Neurovascular unit Function in the Setting of COVID-19 and Alzheimer’s Disease and Related Dementias
Authors: Mathew Smita , Gopal Pallavi 
Published: May 2024

Dysfunction of the blood-brain-barrier and the neurovascular unit, comprised of brain endothelial cells, pericytes, neurons, and glia, has been strongly implicated in the neurological manifestations of SARS-CoV-2 and vascular contributions to cognitive impairment and dementia (VCID) in Alzheimer’s disease (AD). A challenging unanswered question is whether the cognitive and neuropsychiatric disturbances of post-acute neurological sequelae of SARS-CoV-2 (Neuro-PASC) or long COVID are potentially linked to the development of AD. The RNA/DNA-binding protein TDP-43 (transactive response DNA-binding protein of 43 kDa) has been implicated in the pathogenesis of several viral infections and is cleaved by the main SARS-CoV-2 protease Nsp5, leading to neurotoxic TDP-43 fragments in mammalian cells. Aggregates composed of phosphorylated, ubiquitinated TDP-43 are also frequently present in AD. While TDP-43 microvasculopathy has been described in a subset of ADRD cases, its impact on blood-brain barrier integrity and neurovascular unit function is unknown. In this study, we investigated whether TDP-43 microvasculopathy is observed in AD and COVID-19 patient brains. We hypothesized that perivascular TDP-43 induces neurovascular unit dysfunction through cell autonomous and non-autonomous effects of pathologic TDP-43 deposition in astrocytic endfeet processes. To test this, hippocampus and dorsolateral prefrontal cortex (dlPFC) from human AD brains (Braak IV-VI; CERAD definite) and cognitively normal age- and sex-matched controls, with and without comorbid COVID-19, were selected from autopsy cases conducted at Yale between 2014-2018 (non-COVID), and COVID-positive cases conducted between April 2020-present; (n=10-12 per group). Our data from COVID-19 and ADRD human brain samples show a distinctive profile of phosphorylated TDP-43 (pTDP-43) and Tau expression compared to COVID-19 negative AD and control brains. Immunofluorescence analysis of hippocampus and cerebral cortex showed perivascular deposits of pTDP-43 found as threads or aggregates in close proximity to capillaries and vascular basal lamina, labeled with type IV collagen. We also observe a subset of pTDP-43 that colocalizes with neuronal tau, suggesting involvement of multiple neurovascular unit cells. Our data also revealed CD31 (platelet endothelial cell adhesion molecule-1, PECAM-1) positive cells in the microvessels colocalize with pTDP-43. Interestingly, colocalization of PECAM-1 and pTDP-43 positive cells in the perivascular zone suggests transendothelial migration. Atypical pTDP-43 accumulation was also noted in astrocytic endfeet, and astrocytic hypertrophy was identified. Furthermore the blood-brain barrier may be breached, detected by a downregulation or change in the expression and distribution of Claudin-5 in the blood vessels where pTDP-43 is present. Breakdown of these tight junction proteins has been strongly implicated in the neurological manifestations of SARS-CoV-2 and vascular contributions to cognitive impairment and dementia (VCID) in AD. These findings raise the possibility that perivascular pTDP-43 aggregates impair endothelial, neuronal, and/or astrocytic functions in the neurovascular unit, disrupt blood-brain-barrier, and potentially suggest a novel role for TDP-43 induced microvasculopathy in ADRD and COVID-19. This research and the Center for Human Brain Discovery is supported through philanthropic funds and NIH/NINDS R01NS122907 (to PPG). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.