Blood-Brain barrier

Question 1

Founder’s of the concept of BBB:

Answer 1

• 1885 Paul Ehrlich
• 1900 Max Lewandowsky Bield & Kraus
• 1913 Edwin Goldmann

Question 2

Functions of the BBB

Answer 2

1. Maintenance of CNS homeostasis
2. Protection from extracellular environment
3. Supply of nutrients via transport systems
4. Direct inflammatory cells

Question 3

Where is the BBB absent?

Answer 3

No BBB in autonomic NS controlling endocrine glands, Circumventricular organs (e.g. pineal gland -> melatonin secretion into blood)

Question 4

What does a neurovascular unit consist of?

Answer 4

1. Endothelial cells
2. Pericytes
3. Basement membrane
4. Astrocytes
5. Neurons
6. Microglia

Question 5

EC characteristics in the brain:

Answer 5

1. Higher mitochondrial content
2. Junctions instead of fenestrae 3. Minimal pinocytosis / transendothelial transport
3. Negative surface charge
4. Continuous basement membrane

Question 6

Endothelial transport through the BBB

Answer 6

… …

Question 7

Control of BBB integrity - EC to BM:

Answer 7

CAMs
- selectins
- immunoglobulins
- integrins
(dynamic control; focal adhesion complex assembly / disassembly via kinases and Rho GTPases)

Question 8

Control of BBB integrity - EC-EC

Answer 8

Cytoskeleton:
- Actin-rich adhesion belt (complex of F-actin-cytosolic-membrane proteins-EC matrix forming tight and adherens junctions)
Dynamic (dis)assembly of stress fibers (actin-℗-myosin)

Intermediate filament- vimentin-vascular endothelial- cadherin (adherens junction) affected by histamine

Microtubules = assembly focal adhesion, contraction, transendothelial leukocyte migration

Question 9

Steps in BBB signalling:

Answer 9

1. Tethering & rolling
2. Activation
3. Arrest
4. Diapedesis

Question 10

Pericytes and their action

Answer 10

(vascular smooth cells, mural cells, myofibroblasts)

• structural support
• maintenance of junctions
• remodeling of the vascular system

EC proliferation, migration, differentiation
control blood flow and junctional permeability
α-smooth muscle actin
synthesize basement membrane (proteoglycans)

Pericytes are contractile cells that wrap around the endothelial cells of capillaries and venules throughout the body.[1] Also known as Rouget cells or mural cells, pericytes are embedded in basement membrane where they communicate with endothelial cells of the body’s smallest blood vessels by means of both direct physical contact and paracrine signaling.[2] In the brain, pericytes help sustain the blood–brain barrier as well as several other homeostatic and hemostatic functions of the brain.[3] These cells are also a key component of the neurovascular unit, which includes endothelial cells, astrocytes, and neurons.[4] Pericytes regulate capillary blood flow, the clearance and phagocytosis of cellular debris, and the permeability of the blood–brain barrier. Pericytes stabilize and monitor the maturation of endothelial cells by means of direct communication between the cell membrane as well as through paracrine signaling.[5] A deficiency of pericytes in the central nervous system can cause the blood–brain barrier to break down.[3]

Question 11

Properties of the Basement membrane

Answer 11

Extracellular matrix (30-40 nm)

1. Structural proteins (collagen, elastin)
2. Specialized proteins (fibronectin, laminin) anchor EC via integrin binding - intracellular signalling
3. Proteoglycans

Question 12

Astrocytes & neurons in the BBB

Answer 12

Astrocytes promote proteoglycan synthesis and tight junctional proteins (ZO-1, occludin)
Metabolic requirements of neurons
- expression of enzymes in EC
- BBB function
Not directly involved in physical BBB properties

Question 13

Features of extracellular junctions

Answer 13

Function :
Seals lateral plasma membrane diffusion
Limits paracellular permeability
Signalling:
cell  TJ regulate assembly / function
TJ  cell regulate gene expression
Structure >40 proteins

Question 14

Intracellular junctions - AJ

Answer 14

Function
- EC-EC adhesion contact inhibition during vascular growth and remodeling initiation of cell polarity regulate paracellular permeability
Structure
- Adhesion belt

Question 15

Intracellular signalling pathways that regulate junctions

Answer 15

Calcium
Phosphorylation (kinases)
G-proteins
Endothelial NO synthase
Wnt/β-catenin (gene transcription)

Question 16

Study approaches to the BBB

Answer 16

• in vivo (reliable, but expensive & limited applicability in humans) (app: brain metabolism, disruption assessment, tarnsport, neurological disease & progression, drug biodistribution)
• ex vivo (+ living tissue, autopsy controls, whole organs & systems, applicable in humans; - rare human living samples, acute experiments, artificial environment) (app: neurological/infectious disease; homeostasis, hypoxia, permeability, protein efflux, gene therapy)
• in vitro (+simplified model, human cells, co-cultures; - no microenvironment, difficult to reproduce) (app:permeability, transporter properties, toxicity evaluation, differences in phenotype)
• in silico (+ cheap, no animals; - prediction-based, conformation of molecules may lead to false results)(app: permeability, transporter properties, toxicity evaluation)