Effects of insulin on transcriptional response and permeability in an in vitro model of human blood‐brain barrier

Abstract

Alzheimer's disease (AD) is the most prevalent form of dementia worldwide and is an emerging global epidemic. Active and passive immune therapies targeting beta amyloid (Aβ) have shown very limited evidence in human studies of clinical benefits from these approaches. Epidemiological studies have shown that subjects with type 2 diabetes (T2D) are at higher risk of developing AD. However, whether and how these two conditions are causally linked is unknown. With the purpose of confirming the relationship between T2D and AD, this study specifically focused on effects of insulin in an in vitro model of the human blood-brain barrier (BBB) and on potential mechanisms of action in the treatment of AD. By using a series of assays to establish a BBB model, we demonstrated that insulin treatment alone could induce the increase of brain endothelial barrier properties. The transcriptional response of hCMEC/D3 cells to activation with different concentrations of insulin was determined by RT-PCR, and expression levels of genes involved in the control of barrier permeability, including inter-brain endothelial junctions, integrin-focal adhesions complexes, and transporter system, were found to be altered by the treatment. Notably, the influence of insulin on expression of the ATP-binding cassette (ABC) transporter which contributes to the clearance of Aβ was investigated. Insulin up-regulated adherens junction and tight junction transmembrane proteins, as well as the ABC transporter. By treatment with insulin, the models have major advantages: it is fast, it has low cost, it is fit for considerable samples, and its conditions are under control.

Effect of Insulin Receptor-Knockdown on the Expression Levels of Blood–Brain Barrier Functional Proteins in Human Brain Microvascular Endothelial Cells

“…High-insulin and high-glucose treatments weakened tight junctions in human BCECs in vitro [16]. The mRNA levels of the ABCB1/ MDR1, which is a major BBB efflux transporter, was also suppressed by high-insulin treatment in cultured human BMECs [17]. High-fat diet (HFD)-fed mice show increased serum insulin levels, while the expression levels of transporters (Slc2a1/Glut1 and Abcb1a/Mdr1a) and tight junction proteins (claudin-5 and occludin) decrease in the isolated brain microvessels of HFD-fed mice [18].…”

Toward the Decipherment of Molecular Interactions in the Diabetic Brain

“…Increased BBB permeability has been reported in experimental diabetic animal models [ 78 ]. Insulin also impacts various transporters in the BBB, as the receptor for advanced glycation end products, low-density lipoprotein receptor-related protein 1, ATP-binding cassette transporter family members, and those regulating the efflux of β-amyloid peptide out of the cerebral tissue, suggesting its implication in the development of Alzheimer’s pathology [ 79 , 80 ]. In AD patients, reduced insulin levels in the brain and cerebrospinal fluid (CSF), despite elevated plasma insulin levels, insinuate impaired transport of insulin across the BBB [ 81 ].…”