Abstract
BackgroundCerebrovascular complications involving endothelial dysfunction at the blood-brain barrier (BBB) are central to the pathogenesis of diabetes-related CNS disorders. However, clinical and experimental studies have reported contrasting evidence in relation to the effects of hyperglycemia on BBB permeability and function. Similarly the effect of hypoglycemia on BBB integrity is not well understood. Therefore, we assessed the differential impact of hypo and hyperglycemic conditions on BBB integrity and endothelial function in vitro using hCMEC/D3, a well characterized human brain microvascular endothelial cell line.MethodsParallel monolayers of hCMEC/D3 were exposed to normal, hypo- or hyperglycemic media, containing 5.5, 2.2 or 35 mM D-glucose, respectively. Following 3-24h exposure, the expression and distribution of BBB tight junction (ZO-1 and claudin-5) adherence junction (VE-cadherin) proteins, and glucose transporters as well as inflammatory (VCAM-1) and oxidative stress (Nrf-2) markers were analyzed by immunofluorescence and western blotting. Endothelial release of growth factors and pro-inflammatory cytokines were determined by ELISA. Further, the impact of altered glycemia on BBB permeability was assessed in hCMEC/D3 – astrocyte co-cultures on Transwell supports using fluorescent dextrans (4–70 kDa).ResultsCompared to controls, exposure to hypoglycemia (3 and 24h) down-regulated the expression of claudin-5 and disrupted the ZO-1 localization at cell-cell contacts, while hyperglycemia marginally reduced claudin-5 expression without affecting ZO-1 distribution. Permeability to dextrans (4-10 kDa) and VEGF release at 24h were significantly increased by hypo- and hyperglycemia, although 70 kDa dextran permeability was increased only under hypoglycemic conditions. The expression of SGLT-1 was up-regulated at 24h hypoglycemic exposure while only a modest increase of GLUT-1 expression was observed. In addition, the expression of Nrf-2 and release of interleukin-6 and PDGF-BB, were down-regulated by hypoglycemia (but not hyperglycemia), while both conditions induced a marginal and transient increase in VCAM-1 expression from 3 to 24h, including a significant increase in VE-cadherin expression at 3 h following hyperglycemia.ConclusionsIn summary, our findings demonstrate a potential impairment of BBB integrity and function by hypo or hyperglycemia, through altered expression/distribution of TJ proteins and nutrient transporters. In addition, hypoglycemic exposure severely affects the expression of oxidative and inflammatory stress markers of BBB endothelium.
Highlights
The blood-brain barrier (BBB), a dynamic interface between systemic circulation and brain, precisely regulates the Central nervous system (CNS) microenvironment [1]
Analysis of the results clearly indicate a lack of cytotoxic effect of either hypo or hyperglycemia on hCMEC/D3 under the tested exposure conditions (3 and 24 h - see Figure 1A) hypoglycemia did induce slight increase in lactate dehydrogenase (LDH) release at both time points when compared to controls
These data were supported by phase contrast microscopy analysis of hCMEC/D3 cell cultures showing complete and fully confluent cell monolayers devoid of morphological alterations and/or empty spots indicative of cell injury and death
Summary
The blood-brain barrier (BBB), a dynamic interface between systemic circulation and brain, precisely regulates the CNS microenvironment [1]. Increasing evidence indicts BBB dysfunction as a major cerebrovascular complication in diabetes mellitus that underlies the pathogenesis of a host of CNS disorders [7,8]. Both hypoglycemia and diabetes-dependent chronic hyperglycemia have profound impact on cerebrovasculature in terms of endothelial dysfunction, increased vascular permeability, and altered gene expression, leading to potential neuronal injuries. Disparate evidence from clinical and experimental studies has been reported in relation to the effects of hyperglycemia on BBB glucose transporters (mainly GLUT-1) expression and nutrient transport. Cerebrovascular complications involving endothelial dysfunction at the blood-brain barrier (BBB) are central to the pathogenesis of diabetes-related CNS disorders. We assessed the differential impact of hypo and hyperglycemic conditions on BBB integrity and endothelial function in vitro using hCMEC/D3, a well characterized human brain microvascular endothelial cell line
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
