Abstract
BACKGROUND: HIV-associated neurocognitive impairment (HAND) is a common complication of HIV-1 infection, which can be exacerbated by exposure to cigarette smoke (CS). Tight junction proteins (TJPs) of the blood-brain barrier (BBB) play a crucial role in maintaining BBB integrity and preventing the entry of circulating toxic factors, including those resulting from HIV-1 infection, into the central nervous system. Both CS exposure and HIV-1 infection can independently disrupt TJPs and compromise BBB integrity; however, the combined or individual effects of these factors on BBB TJPs remain poorly understood. METHODS: An in vitro BBB comprised of Sprague-Dawley rat brain microvascular endothelial cell (RBMVEC) transwell cultures was exposed to wild-type (WT) and HIV-1 transgenic (TG) rat sera, alone or in combination with cigarette smoke extract (CSE) and analyzed for trans-endothelial electrical resistance (TEER) and paracellular permeability to 10 kDa fluorescein isothiocyanate (FITC)-dextran. Immunofluorescence staining was performed to assess the effects of treatment on the cellular localization and expression of the TJPs, "zonula occludens-1 (ZO-1) and claudin-5. RESULTS: Pretreatment TEER measures were significantly higher for cultures treated with WT serum alone compared to those treated with TG serum or with CSE. Compared to pretreatment, TEER measures were significantly reduced by treatment with WT serum alone, CSE alone, WT serum + CSE, and TG serum + CSE. TG serum alone or TG serum + CSE resulted in statistically significant increased permeability compared to WT serum. All treatments decreased TJP staining intensity, and, in some cases, altered TJP localization. These effects were most prominent following incubation with either CSE alone, TG serum alone, or TG serum + CSE. CONCLUSIONS: CSE and TG serum induced separate and additive toxic effects on BBB function and integrity, which may underlie mechanisms that are associated with more severe HAND among HIV+ cigarette smokers.