(656e) Soluble Amyloid-β Aggregates Modify Expression of Claudin-3 In a Model of the Blood-Brain Barrier

A compromised blood-brain barrier (BBB) can cause neurological damage either directly, as in the case of hemorrhagic stroke, or indirectly by increasing the concentrations of blood plasma proteins in the brain parenchyma.  These plasma proteins are associated with amyloid plaques that are believed to promote the pathogenesis of Alzheimer’s disease (AD).  Although AD diagnosis requires evidence of parenchymal plaques, cerebrovascular plaque deposits that result in cerebral amyloid angiopathy (CAA) present in 90% of AD patients.  The cerebrovascular deposits characteristic of CAA and neuritic plaques—hallmarks of AD—are composed of fibrillar amyloid-β protein (Aβ).  Monomeric Aβ self-assembles to create soluble aggregates, which serve as nucleation sites for further growth into fibrillar plaques. 

Claudin-3 (Cldn3) is an extracellular tight junction protein that is required for proper function of the BBB, particularly its ability to restrict the movement of plasma proteins into the parenchyma.  The current study measures Cldn3 in an in vitro BBB model to investigate the vascular mechanisms of AD pathology.  To better understand Aβ induced dysregulation in the BBB, we challenged monolayers of human brain microvascular endothelial cells (HBMVEC) with isolated Aβ monomers and soluble aggregates.  By using Cldn3 as a marker of BBB integrity, proper function was assessed qualitatively with confocal microscopy and quantitatively with Western blot assays.  

Preparations of Aβ aggregates, but not monomer, induced delocalization of Cldn3 from cell-cell junctions and reduced the total cellular content of Cldn3.  Recent evidence has suggested vascular damage may precede the neurological pathology of AD.  Without Cldn3 available for tight junction formation, HBMVECs can no longer properly maintain separation between blood and brain.  Aβ induced dysregulation of Cldn3 expression supports the idea that damage to the vasculature is the first step in the development of AD pathology and precedes the formation of neuritic plaques.