Characterization of a human in vitro blood-brain barrier model to study the effects of systemic aging on responses to Alzheimer's disease effectors - Project Summary/Abstract: Aging is the strongest risk factor for Alzheimer’s disease (AD), yet the molecular
mechanisms that relate healthy aging and AD are understudied. One feature of aging is an increased level of
chronic, low-grade inflammation which results in increased concentrations of circulating inflammatory
molecules in blood. Further, blood from aged rodents can cause CNS dysfunctions and exacerbate responses
to injury in young mice, indicating that factors in blood contribute to CNS dysfunction with aging. The blood-
brain barrier (BBB) is an important interface between brain and blood and is thus a probable mediator of aged
blood’s effects on the brain. The BBB is also adversely affected with aging and in AD; in both conditions data
suggest that the BBB becomes leaky, and develops deficiencies in transporters, such as those for glucose and
amyloid beta (Aβ). The net effect of these age-associated BBB dysfunctions includes entry of potentially
harmful circulating molecules into the brain, reduced nutrient availability, and Aβ accumulation in the CNS.
However, it is unknown whether factors in aged blood could contribute to age-associated BBB dysfunctions
that may increase vulnerability to AD.
Our project aims to address the hypothesis that the systemic aging milieu, modeled by application of serum
from aged human donors, alters BBB functions (Aim 1) and exacerbates responses of the BBB to pro-
inflammatory stimuli and Aβ oligomers (Aim 2) when compared with serum from young human donors. To test
this hypothesis, we will use a recently developed in vitro model of the human BBB that is derived from induced
pluripotent stem cells (iPSCs). iPSC-derived brain endothelial-like cells (iBECs) develop hallmark features of
the in vivo BBB such as high transendothelial resistance (TEER), and so are suitable for use to assess BBB
disruption and transporter deficiencies in response to stimuli on the brain or blood-facing side. We will
determine in Aim 1 whether application of young vs. old human serum affects iBEC leakiness, which is proxied
by TEER and permeability to large and small inert tracers. We will also test whether aged serum alters
glucose and Aβ transport across iBECs, and whether the efflux transporter P-glycoprotein (Pgp) is functionally
impaired. In Aim 2, we will test whether exposure to aged human serum exacerbates BBB responses to
treatments with pro-inflammatory cytokines or Aβ, which models neuroinflammation and Aβ accumulation in
AD. We will also measure serum levels of a large panel of proteins implicated in aging and inflammation and
assess their associations with measures of BBB dysfunction from both aims. Successful completion of this
project could identify possible candidates in blood that may cause different aspects of BBB dysfunction with
aging, and would highlight the utility of iBECs as a model for studying mechanisms by which aging contributes
to AD-associated CNS dysfunction through the BBB.
