The blood–brain barrier (BBB), which is comprised of brain capillary endothelial cells, plays a pivotal role in the transport of drugs from the blood to the brain. Therefore, an analysis of proteins in the endothelial cells, such as transporters and tight junction proteins, which contribute to BBB function, is important for the development of therapeutics for the treatment of brain diseases. However, gene transfection into the vascular endothelial cells of the BBB is fraught with difficulties, even in vitro. We report herein on the development of lipid nanoparticles (LNPs), in which mRNA is encapsulated in a nano-sized capsule composed of a pH-activated and reductive environment-responsive lipid-like material (ssPalm). We evaluated the efficiency of mRNA delivery into non-polarized human brain capillary endothelial cells, hCMEC/D3 cells. The ssPalm LNPs permitted marker genes (GFP) to be transferred into nearly 100% of the cells, with low toxicity in higher concentration. A proteomic analysis indicated that the ssPalm-LNP had less effect on global cell signaling pathways than a Lipofectamine MessengerMAX/GFP-encoding mRNA complex (LFN), a commercially available transfection reagent, even at higher mRNA concentrations.

Vascular endothelial cells (ECs) exposed to fluid shear stress (FSS) become elongated and aligned to the direction of flow. However, the process of morphological change in individual cells is different depending of their initial shape. Rac1 and RhoA, members of the family of Rho GTPases, play important roles in cellular morphological changes but are thought to be activated differently in the process. Here, we measured changes in Rac1 and RhoA activities with a focus on the effect of cell orientation when exposed to FSS. In ECs initially oriented parallel to the direction of flow, RhoA and Rac1 were activated primarily in the upstream and the downstream regions of cells, respectively, accompanied by the formation of lamellipodia in the direction of flow. On the other hand, in cells oriented perpendicular to the direction of flow, FSS caused RhoA activation in the upstream region but did not change Rac1 activity. Furthermore, treatment with cytochalasin D inhibited the localization of Rac1 activation and suppressed RhoA activation by FSS. These results indicate that cell orientation affects the local activation of Rac1 and RhoA when induced by forces transmitted through the actin cytoskeleton under a FSS condition.

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