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Method Article
Maintaining blood-brain barrier coverage is key for the homeostasis of the central nervous system. This protocol describes in vitro techniques to delineate the fundamental and pathological processes that modulate blood-brain barrier coverage.
Blood-brain barrier (BBB) coverage plays a central role in the homeostasis of the central nervous system (CNS). The BBB is dynamically maintained by astrocytes, pericytes and brain endothelial cells (BECs). Here, we detail methods to assess BBB coverage using single cultures of immortalized human BECs, single cultures of primary mouse BECs, and a humanized triple culture model (BECs, astrocytes and pericytes) of the BBB. To highlight the applicability of the assays to disease states, we describe the effect of oligomeric amyloid-β (oAβ), which is an important contributor to Alzheimer's disease (AD) progression, on BBB coverage. Further, we utilize the epidermal growth factor (EGF) to illuminate the drug screening potential of the techniques. Our results show that single and triple cultured BECs form meshwork-like structures under basal conditions, and that oAβ disrupts this cell meshwork formation and degenerates the preformed mesh structures, but EGF blocks this disruption. Thus, the techniques described are important for dissecting fundamental and disease-relevant processes that modulate BBB coverage.
The blood-brain barrier (BBB) of cerebral capillaries is the largest interface of blood-to-brain contact and plays a central role in the homeostasis of the central nervous system (CNS)1,2. Dynamic processes at the BBB prevent the uptake of unwanted molecules from the blood, remove waste products from the CNS, supply essential nutrients and signaling molecules to the CNS, and modulate neuroinflammation1,2,3,4,5. BBB damage is prevalent during aging and several neurodegenerative disorders including Alzheimer's disease (AD), multiple sclerosis and stroke1,2,3,4,5,6. Therefore, BBB dysfunction may play a key role in neurodegenerative disorders, including as a therapeutic target.
Maintaining vessel coverage is important for the homeostatic functions of the BBB. However, in vivo and in vitro data conflict on whether the processes involved in neurodegenerative disorders cause higher or lower BBB coverage6,7,8,9,10,11,12,13, particularly in AD. Therefore, there is a strong rationale for the development of in vitro models using relevant cell types to assess and more comprehensively understand the dynamics of BBB coverage. Cerebral capillaries are composed of astrocytes, pericytes and brain endothelial cells (BECs)3. All cell types contribute to the function of the BBB through structural support and via the secretion of effector molecules such as angiogenic growth factors, cytokines and chemokines that act in paracrine- and autocrine-like fashion. However, the major effector cells of the BBB are BECs3. In general, the cell culture techniques for assessing BBB function are permeability assays performed on cells grown on filter inserts, or assessing levels of key BEC proteins, both after the addition of stressors14,15,16. Although important, these assays do not focus on the cerebrovascular coverage.
Here, our previous methods17 are detailed to assess BEC coverage and meshwork-like structures using single cultures of immortalized human BECs, single cultures of primary mouse BECs, and a humanized triple culture model (BECs, astrocytes and pericytes) of the BBB. The goal was to demonstrate the detrimental effect of oAβ, which is considered an important contributor to AD progression, on BEC coverage. The protective effect of the epidermal growth factor (EGF) highlights the potential of the technique as a therapeutic screening tool. The technique has several broad applications for basic and applied research including: 1) delineating the role of specific pathways on angiogenesis and vessel coverage, 2) evaluating the effects of disease and aging-relevant factors on angiogenesis and vessel coverage, and 3) identifying pharmacological targets.
All experiments follow the University of Illinois, Chicago Institutional Animal Care and Use Committee protocols.
1. General Preparation
NOTE: The brain microvascular endothelial cell line (hCMEC/D3) is an extensively characterized immortalized human BEC line14,15,16,18,19. Culture the hCMEC/D3 cells on tissue culture flasks coated with collagen Type I (calf skin, 1:20 dilution of 0.1% solution in Hank's Balanced Salt Solution (HBSS) containing Ca2+ and Mg2+) in basal Endothelial Growth Basal Medium (EBM-2) containing 2-5% Fetal Bovine Serum (FBS), 10% ascorbic acid, 10% gentamicin sulphate, 25% hydrocortisone and 1/4 of the total volume of the supplied growth factor supplements per 500 mL of media [vascular endothelium growth factor (VEGF), epidermal growth factor (EGF), insulin-like growth factor 1 (IGF-1) and human basic fibroblastic growth factor (bFGF), see Table of Materials].
NOTE: EBM-2 medium with FBS and growth factors is referred to as "EBM-2 complete". EBM-2 without FBS and supplements is referred to as "EBM-2 basal". At full confluence, the hCMEC/D3 cells are ~1 x 105 cells/cm2.
2. Meshwork-like Formation and Disruption Assays
3. Quantification
In single cultures, both the hCMEC/D3 cells (Figure 3A) and the primary mouse BECs (Figure 3B) form meshwork-like structures throughout the well. The structures are characterized by a meshwork of interlinked nodes (Figure 3). In all the paradigms described (Figure 1), the meshwork-like structures are similar after 24 h in the control groups, forming ~20 meshwork-like str...
The methods described can be utilized to address several fundamental biological questions surrounding cerebrovascular coverage24. Specifically, they can identify which receptors and signaling pathways play a role in angiogenesis, vessel coverage in cancer tissue, and peripheral endothelial cells relevant to the brain. Examples include angiogenic growth factor receptors, nitric oxide, mitogen activated protein kinase signaling and calcium signaling25,
The authors have nothing to disclose.
Leon Tai is funded by University of Illinois Chicago start-up funds.
Name | Company | Catalog Number | Comments |
hCMEC/D3 cells | Milipore | SCC066 | |
EBM-2 basal media | Lonza | CC-3156 | |
Collagen Type 1 | ThermoFisher | A1064401 | |
HBSS, calcium, magnesium, no phenol red | ThermoFisher | 14025092 | |
HBSS, no calcium, no magnesium, no phenol red | ThermoFisher | 14175095 | |
Trypsin-EDTA (0.25%) | ThermoFisher | 25200056 | |
Final concentrations of the SingleQuot growth factor supplements for EBM2 media | Lonza | CC-4147 | |
5% FBS | Lonza | CC-4147 | |
10% Ascorbic acid | Lonza | CC-4147 | |
10% Gentamycin sulphate | Lonza | CC-4147 | |
25% Hydrocortisone | Lonza | CC-4147 | |
1/4 volume of the supplied growth factors: fibroblast growth factor, epidermal growth factor, insulin-like growth factor, vascular endothelial growth factor | Lonza | CC-4147 | |
Puromycin hydrochloride | VWR | 80503-312 | |
MEM-HEPES | Thermo Scientific | 12360-038 | |
Papain cell dissociation system (papain and DNase1) | Worthington Biochemical | LK003150 | |
Human pericytes | Sciencell | 1200 | |
Pericyte basal media | Sciencell | 1201 | |
Pericyte growth supplement | Sciencell | 1252 | |
Human Astrocytes | Sciencell | 1800 | |
Astrocyte media | Sciencell | 1801 | |
Astrocyte growth supplement | Sciencell | 1852 | |
Basement membrane (Matrigel Growth Factor Reduced) | Corning | 356231 | |
Angiogenesis m-plates (96-well) | ibidi | 89646 | |
Human Epidermal growth factor | Shenendoah Biotechnology | 100-26 | |
CellTracker green | ThermoFisher | C7025 | |
CellTracker orange | ThermoFisher | C34551 | |
CellTracker blue | ThermoFisher | C2110 | |
Poly-l-lysine | Sciencell | 0403 | |
10% Neutral Buffered Formalin | Sigma-Aldrich | HT5012-60ML | |
C57BL mice | Jackson Laboratory | na | |
PCR tube strips | GeneMate | T-3014-2 | |
Zeiss stereo discover v.8 dissecting microscope | Zeiss | na |
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