Heterogeneity in the Rat Brain Vasculature Revealed by Quantitative Confocal Analysis of Endothelial Barrier Antigen and P-Glycoprotein Expression

Abstract

While phenotypic endothelial heterogeneity is well documented in peripheral organs, it is only now being explored in the brain. We used confocal imaging of thick sections of rat brain to qualitatively and quantitatively examine the expression of two key markers of the blood-brain barrier (BBB) in the rat, P-glycoprotein (P-gp), and endothelial barrier antigen (EBA). We found that these markers were not uniformly distributed throughout the whole vasculature of the cortex and hippocampus. P-glycoprotein displayed a gradient of expression from an almost undetectable level in large penetrating arterioles to a high and uniform level in capillaries and venules. While EBA was lacking in all cerebral arterioles, regardless of their size, its expression varied greatly among endothelial cells in capillaries and venules, yielding a striking mosaic pattern. A detailed quantitative analysis of the distribution of these markers at the single cell level in capillaries is provided. These results challenge the view of a uniform BBB and suggest that regulatory mechanisms might differentially modulate BBB features not only among arterioles/capillaries/venules but also at the single cell level within the capillaries. Hypotheses are made regarding the underlying mechanisms and physiopathological consequences of this heterogeneity.

Vascular Neural Network Phenotypic Transformation After Traumatic Injury: Potential Role in Long-Term Sequelae

“…On a similar note, it has been reported that some transporters, such as P-gp, are also differentially expressed in large vessels as compared with capillaries [36–39]. In fact, P-gp expression gradually increases in rat brain vasculature from a low level in the largest arterioles (20 to 50 μm) to a high level in capillary beds and venules [39]. In addition to variation along the vasculature, there are regional differences in the level of transporters in capillary beds that could depend on brain synaptic activity.…”

“…Few studies have evaluated the rate of transcytosis or the organization of junctional complexes, and the expression of some enzymes such as Na+/K+ ATPase differ among arterioles, capillaries, and venules [35]. On a similar note, it has been reported that some transporters, such as P-gp, are also differentially expressed in large vessels as compared with capillaries [36–39]. In fact, P-gp expression gradually increases in rat brain vasculature from a low level in the largest arterioles (20 to 50 μm) to a high level in capillary beds and venules [39].…”

In Vitro Models of CNS Barriers

“…Pioneering studies have recently been published, establishing the feasibility of the method and scope for miniaturization (Booth and Kim 2012 ;Griep et al 2013 ;Prabhakarpandian et al 2013 ), so far with BBB cell-line models RBE4, bEND3 and hCMEC/D3. Many questions could be addressed in such systems, including the contribution of differential fl ow rates/shear stress to the observed heterogeneity of endothelial cytoarchitecture and function in different segments of the vasculature (Ge et al 2005 ;Macdonald et al 2010 ;Saubaméa et al 2012 ;Paul et al 2013 ;cf Ballermann et al 1998 ). Given the complexity of the microfl uidics chambers these are not likely to be suitable for high-throughput permeability assays at least in the short term, but meanwhile the generation of detailed mechanistic information is likely to be the most valuable output.…”

A research update on the potential roles of aquaporin 4 in neuroinflammation

“…Similarly, Fukuda et al [38] observed that siAQP4 treatment after TBI resulted in a decrease in AQP4 associated with less BBB disruption, less edema, and better behavioral outcomes compared to the control group at up to 2 months post-injury. In cryo-injury models [39], AQP4-knockout mice presented increased microglia and reduced astrogliosis compared to WT. In this model, a decrease in the lesion volume and in neuronal loss in AQP4-knockout mice compared to WT was reported at 1 day after injury, whereas the opposite result was reported at 7 and 14 days.…”