Lecture 2: endothelial cells Flashcards
What is a patrolling neutrophil?
A neutrophil that is searching for infections. It can go against the blood flow while doing this.
In what processes is leukocyte transendothelial migration important?
- Immune surveilance
- Inflammation
- Cancer metastasis
- Immune disease (rheumatoid arthritis)
- Stem cell homing (after transplantation)
- Atherosclerosis
- Etc.
Describe transendothelial migration of a neutrophil in short.
A neutrophil senses an infection in tissue. In the blood stream, neutrophils start rolling → arrest → adhesion to endothelium → crawling → diapedesis or transmigration through endothelium (trans- or paracellular).
What is a way to study endothelial cells and inflammation?
To isolate endothelial cells from a vein of the umbilical cord. By stimulating this tissue by introducing inflammation, it results in specific interaction between the endothelial cells and neutrophils. This results in intravasation of the neutrophils.
During transmigration of neutrophils through endothelial cells, the opening in the endothelium that neutrophils travel through is very narrow. What is the reason for this?
Because this prevents leakage of cellular fluids. Also, this opening won’t be larger then the size of the nucleus (biggest organel of the cell).
What is a very important protein in the cytoskeleton of endothelial cells?
Actin filaments
How is the endothelial actin cytoskeleton regulated (think of how actin is involved in cell spreading/movement)?
Actin is a globular protein in eukaryotic cells. Actin is able to polymerize through the use of ATP. When ATP is bound to actin (ATP-bound actin) it creates an actin oligomer. This elongated actin cytoskeleton can push membranes forward. When ATP is hydrolyzed, ADP-bound actin falls of the oligomer and the oligomer is broken down again. This process makes cells like endothelial cells deformable.
Why are listeria bacteria hard to target?
Bacteria also use or make use of actin polymerisation to invade cells or move around a host cell. The listeria bacteria makes use of our own actin filaments, which makes it really hard to target.
A family of small GTPases regulate the actin cytoskeleton. Name three important small GTPases. Also name their most important function.
RhoA, Rac1 and Cdc42. These GTPases are important in (regulation of) cel migration.
What is the function of the small GTPase RhoA?
RhoA regulates the formation of stress fibers, important in cell-cell or cell-ECM adhesions.
What is the function of the small GTPase Rac1?
Rac1 regulates the formation of lamelli podia, e.g. important for movement like cell migration.
What is the function of the small GTPase Cdc42?
Cdc42 regulates the formation of filopodia, that are able to sense the environment. (Filopodia extend beyond the leading edge of lamellipodia in migrating cells).
How are small GTPases regulated (for this answer take Rho as an example)?
Rho is inactive when GDP is bound to it. When GDP is exchanged for GTP, Rho is in its active state (GTP-bound Rho). When GTP-bound Rho gets dephosphorylated, it will turn back into its inactive state.
Does the location of GTPase activity matter?
Yes. This process cannot be random, because this will lead to no assymetry and no polarity. So you need local activation for directional migration, which is facilitated by chemokines.
What is stem cell homing?
A process whereby stem cells respond to gradients of chemoattractants by migrating up these gradients and lodging within specific tissue areas. This process was initially described for hematopoietic stem cells, which migrate after transplantation from peripheral blood to stem cell niches located in the bone marrow microenvironment.
What will you see if you generate a transgenic Lifeact-GFP knock in mouse and look at e.g. the cremaster muscle from this mouse?
You’ll see that the muscle is lined by endothelium that is lined completely green, which says that the endothelium is filled up with actin filaments.
What will you see if you generate a transgenic Lifeact-GFP knock in mouse and look at e.g. the bone marrow?
You’ll see how many different cells are in the bone marow and also how many cell types are still unknown.
What does this picture of the bone marrow and a vessel display?
That blood cells work their way through the bone marrow and vessel wall to enter the blood stream. This is also how blood platelets arise, when megakaryoctes try to enter the blood stream, pieces of the megakaryocytes are cut of due to the high speed of the blood stream.
How do immune cells breach the vessel wall (think of what molecule is important in this process)?
Endothelial cells are held together by VE-cadherin (CD144). So for invasion of immune cells through the vessel wall, the VE-cadherin connection between endothelial cells needs to be broken down.
What is vessel-on-a-chip technology?
With the help of a specific chip containing a tube, endothelial cells are added that can then line the tube as endothelium. This way a mimic or analog of a physiological vessel is created that offer promise to overcome some of the limitations of conventional in vitro and in vivo models.
