BRAIN ENDOTHELIAL RESEARCH

The blood-brain barrier (BBB) plays a key role in the maintenance of the homeostasis of the central nervous system (CNS). The morphological basis of the BBB is formed by cerebral endothelial cells lining the capillaries and microvessels of the brain. Cerebral endothelial cells are interconnected by a continuous line of tight and adherens junctions and come into close contact with pericytes and astrocytes.

Due to its complex functions the BBB plays an important role in clinical practice. First, there is increasing evidence that the BBB is involved in the pathomechanism of a large number of CNS diseases like stroke, brain trauma and tumours as well as neurodegenerative disorders. Second, due to the relative impermeability of the barrier, many drugs are unable to reach the CNS in therapeutically relevant concentration, making the BBB one of the major impediments in the treatment of CNS disorders.

By using an in vitro model of the BBB, our research is focused on the elucidation of molecular mechanisms regulating endothelial function under physiological and pathological conditions. Recently we have shown that in different CNS disorders like cerebral ischemia or hemorrhagic shock, complex signalling events are initiated accompanied by changes in the integrity of the junctional complex. Presently we are investigating the signalling mechanisms involved in the regulation of BBB permeability and transmigration of tumour cells through the BBB.

Model system

In order to be able to directly investigate molecular mechanisms regulating BBB function, we use an in vitro model based on the culture of cerebral endothelial cells. The model can be used for basic research and applied research for the study of the interaction of drugs with the BBB and the transport of different drugs through the BBB.

Figure 1: Triple co-culture model of the BBB

Our methods of investigation include Western-blots, phosphorylation analysis, proteomics, real-time PCR, RNA silencing, zymography, immunofluorescence etc.

Signalling in brain endothelial cells under physiological and pathological conditions

The permeability of the BBB is under complex control. This control is mediated by a large number of signalling molecules, many of which are localized to the junctional complex. Our research is focused on the signal transduction pathways in cerebral endothelial cells activated by pathological conditions like oxidative stress, hyperosmosis or the presence of inflammatory mediators. Recently we were able to identify src kinase and the receptor tyrosine kinase Axl as key elements of endothelial signalling.

Figure 2: Axl signalling in brain endothelial cells

Interaction of metastatic tumour cells with the bbb

Brain metastases are clinically diagnosed in the majority of patients having secondary localizations of melanoma. The prognosis for these patients is very poor and treatment can be difficult because of rapid progression of the disease. Since the brain does not have lymphatic vessels, melanoma cells have to transmigrate through the blood-brain barrier in order to reach the brain parenchyma. During this process the tumour cells either must disrupt intercellular junctions or use the transcellular route. We are currently investigating the molecular mechanisms of these phenomena.

Figure 3: A2058 melanoma cells (green) in contact with brain endothelial cells (red: ZO-1 staining).