A genomic comparison of in vivo and in vitro brain microvascular endothelial cells

The blood-brain barrier (BBB) is composed of uniquely differentiated brain microvascular endothelial cells (BMEC). Often, it is of interest to replicate these attributes in the form of an in vitro model, and such models are widely used in the research community. However, the BMEC used to create in vitro BBB models de-differentiate in culture and lose many specialized characteristics. These changes are poorly understood at a molecular level, and little is known regarding the consequences of removing BMEC from their local in vivo microenvironment. To address these issues, suppression subtractive hybridization (SSH) was used to identify 25 gene transcripts that were differentially expressed between in vivo and in vitro BMEC. Genes affected included those involved in angiogenesis, transport and neurogenesis, and real-time quantitative polymerase chain reaction (qPCR) verified transcripts were primarily and significantly downregulated. Since this quantitative gene panel represented those BMEC characteristics lost upon culture, we used it to assess how culture manipulation, specifically BMEC purification and barrier induction by hydrocortisone, influenced the quality of in vitro models. Puromycin purification of BMEC elicited minimal differences compared with untreated BMEC, as assessed by qPCR. In contrast, qPCR-based gene panel analysis after induction with hydrocortisone indicated a modest shift of 10 of the 23 genes toward a more 'in vivo-like' gene expression profile, which correlated with improved barrier phenotype. Genomic analysis of BMEC de-differentiation in culture has thus yielded a functionally diverse set of genes useful for comparing the in vitro and in vivo BBB.