Why do traumatic brain injury survivors exhibit an increased risk of Alzheimer's disease? Researchers here observe a specific set of changes in the vasculature of the injured brain that appear to accelerate deposition of amyloid-β, an outcome supportive of the amyloid cascade hypothesis for the development of Alzheimer's disease. Despite the inability of amyloid-β clearance to much affect patient outcomes in the later stages of Alzheimer's disease, it remains the case that many lines of evidence support amyloid-β aggregation as the foundational pathology that initially causes Alzheimer's disease.
Traumatic brain injury (TBI) often leads to impaired regulation of cerebral blood flow, which may be caused by pathological changes of the vascular smooth muscle cells (VSMCs) in the arterial wall. Moreover, these cerebrovascular changes may contribute to the development of various neurodegenerative disorders such as Alzheimer's-like pathologies that include amyloid beta aggregation. Despite its importance, the pathophysiological mechanisms responsible for VSMC dysfunction after TBI have rarely been evaluated.
Here, we show that acute human TBI resulted in early pathological changes in leptomeningeal arteries, closely associated with a decrease in VSMC markers such as NOTCH3 and alpha smooth muscle actin (α-SMA). These changes coincided with increased aggregation of variable-length amyloid peptides including Aβ1-40/42, Aβ1-16, and β-secretase-derived fragment (βCTF) (C99) caused by altered processing of amyloid precursor protein (APP) in VSMCs. The aggregation of Aβ1-40/42 peptides were also observed in the leptomeningeal arteries of young TBI patients.
These pathological changes also included higher β-secretase (BACE1) in the leptomeningeal arteries, plausibly caused by hypoxia and oxidative stress as shown using human VSMCs in vitro. Importantly, BACE1 inhibition not only restored NOTCH3 signalling but also normalized ADAM10 levels in vitro. Furthermore, we found reduced ADAM10 activity and decreased NOTCH3, along with increased βCTF (C99) levels in mice subjected to an experimental model of TBI. This study provides evidence of early post-injury changes in VSMCs of leptomeningeal arteries that can contribute to vascular dysfunction and exacerbate secondary injury mechanisms following TBI.
Link: https://doi.org/10.1007/s00401-025-02848-9
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