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The blood-brain barrier (BBB) is indispensable for the maintenance of brain homeostasis and proper neuronal functioning. Dysfunction of the BBB significantly contributes to the pathogenesis of neuroinflammatory and neurodegenerative diseases like stroke, multiple sclerosis (MS), and Alzheimer's disease (AD). The neuroinflammatory environment that characterizes these disorders propagates chronic impaired function of the BBB, processes that will be discussed in this review. Limiting dysfunction of the BBB may be an attractive target for treatment of neurological disorders. To date, no current treatments are directly targeting the function of the BBB. In this review, we will specifically discuss the potential protective role of nuclear liver X receptors (LXRs) as a promising therapeutic target to reverse or prevent BBB impairment in neurological diseases. This work was supported by grants from the ZonMw Memorabel program (NMdW; project nr 733050105) and from the Dutch MS Research Foundation (AK; grant MS-09-358d)

Need for novel models of the NVU Chapter 1, the general introduction, describes the need for novel in vitro models of the human brain and its vasculature. Morphogens and the blood-brain barrier In chapter 2, a review is performed of various morphogens involved in development, maintenance, and disease of the neurovascular unit. These morphogens regulate adherens junctions (AJs) and tight junctions (TJs) that hold the endothelial cells together and support proper transport of a myriad of molecules from the periphery into the brain. As neurological diseases are becoming more prevalent and dysfunction of the NVU is observed in most of them, increased knowledge on the morphogens that govern healthy neurovascular function is essential and may lead to new therapies. 3D networks of neurons and glia In chapter 3, a three-dimensional model of the human brain is presented. Induced pluripotent stem-cell (iPSC) derived networks of neurons and astrocytes are cultured in a microfluidic platform, the OrganoPlate. Cultures rapidly formed 3D neuronal-glial networks that remained viable over several weeks. Immunostaining revealed presence of astrocytes and glutamatergic, GABAergic, and dopaminergic neurons. Using a fluorescent calcium-imaging assay, networks were shown to exhibit spontaneous neuronal activity, which was modulated using compounds that inhibit or promote neuronal firing. Antibody transcytosis across a BBB on-a-chip Chapter 4 focuses on the development of the brain’s vascular component. The OrganoPlate platform was used to grow blood vessels using immortalized human brain endothelial cells. Immortalized human astrocytes and pericytes were added to the culture, to model the NVU. The model developed here showed expression of relevant junctional markers, which are essential for barrier formation. Barrier function was confirmed using a 20 kDa fluorescent dye, which was shown to be retained within the brain endothelial vessel. The model was applied to study receptor mediated transcytosis, an attractive route to target large therapeutic molecules into the brain. Microfluidic neurovascular unit to study stroke Chapter 5 combines the work presented in the previous chapters and presents a model of the NVU comprising brain microvascular endothelial cells in direct contact with astrocyte end-feet and in co-culture with neurons. The NVU model was used to mimic ischemic stroke by stopping medium perfusion, omitting glucose, and creating a hypoxic environment. The resulting ischemic NVU model displayed several key features of stroke, including impaired BBB function, reduced mitochondrial potential, and reduced adenosine triphosphate (ATP) levels. This model holds potential to assess novel drug candidates for the treatment of ischemic stroke. Conclusion and future directions of the research The work in this thesis describes the development of microfluidic models of the neurovascular unit. Compared to traditional models, these new models show increased complexity through co-culture of different cell types, cell-matrix interactions, and fluid perfusion. In addition, the compatibility of the microfluidic platform makes these NVU models the first to be compatible with drug testing. Future work may focus on the role of immune cells – resident and circulating – in NVU health and disease. Additional cell types can be added to further increase complexity where needed. It is important to note that the NVU is a very complex structure and that it is unlikely that one model can capture all its functions. Fit-for-purpose models offer a feasible compromise between physiological relevance and ease of use and thus pose the future of NVU modeling: as simple as possible, as complex as needed.

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promotiedatum: 2-4-2015 � prom-id: 11958

promotiedatum: 16-9-2013 � prom-id: 10937

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promotiedatum: 23-9-2013 � prom-id: 10639