The key role of smooth muscle cells in AAA

Question 1

Name characteristics of an aortic aneurysm.

Answer 1

• Weakening and dilation of the aortic wall
• Asymptomatic and unable to predict
• 5000 hospital admissions yearly in the Netherlands

Question 2

Name characteristics of a ruptured aortic aneurysm.

Answer 2

• Surgical emergency
• Associated with mortality of up to 80%
• Terminal disease state of the aortic wall

Question 3

What is the problem with current treatment options of an aortic aneurysm?

Answer 3

It is invasive and has a high reintervention rate.

Question 4

What two options of treatment are there for (aortic) aneurysms?

Answer 4

• Open repair (open surgery and graft placement)
• Endovascular repair (placement of stent graft via blood vessels/arteries)

Question 5

Name a reason why the only available treatment option for AAA is invasive surgery?

Answer 5

Because the pathophysiology/molecular mechanism is unknown and therefore, no pharmacological therapy is available.

Question 6

Smooth muscle cells (SMCs) play an important role in AAA. What function do SMCs have?

Answer 6

Responsible for:
- contraction (vasoconstriction and vasodilation)
- structural support to other wall components
- production of extracellular matrix

Question 7

How would smooth muscle cell (SMC) dysfunction play a critical rol in the development and progression of aortic aneurysms?

Answer 7

Since SMCs are responsible for contraction and ECM production, if there are defect in the SMCs there are also defect in SMC contractibility and ECM production. This causes weakening of the aortic wall, which can play a crucial role in the development of an aortic aneurysm.

Question 8

Mutations in MYH11, TGFβR1, TGFβR2, MYLK and ACTA2 account for at least 23% of the familial thoracic aortic aneurysms and aortic dissections. What do most of these mutations have in common?

Answer 8

That they encode for SMC contractile proteins

Question 9

How to study the effects of these SMC mutations before patients undergo surgery?

Answer 9

By using (skin) fibroblasts and inducing them into SMCs.
(SMC-like cells express SMC specific genes and proteins, so we can investigate the effects of the mutations before the patients need surgery. This can be used to find new biomarkers.)

Question 10

How can you investigate SMC function?

Answer 10

To study the function of SMCs, you need SMCs of aneurysm patients (during surgery).
Note: there is also a ‘live’ biobang of the Amsterdam UMC where patient speficic SMC, fibroblasts, perivescular fat, urine and blood are stored.

Question 11

Name a method that can be used to answer the following questions:
- Is there a difference in contraction of SMC derived from AAA patients compared to contraction of SMC derived from healthy controls?
- If so, what is the underlying mechanism of these
differences?

Answer 11

By using Electric Cell-substrate Impedance Sensing (ECIS) measures impedance value based on electrode coverage. Here, the SMCs are grown on the surface of small and planar gold-film electrodes, deposited on a petri dish. The alternating current impedance of the cell-covered electrode is then measured at one or several frequencies as a function of time. Upon stimulation with ionomycin (Ca2+ ionophore inducing influx of Ca2+), SMC go from their relaxed state to their contracted state, which reduces the impedance value.

Question 12

Electric cell-substrate impedance sensing (ECIS) for SMCs was used to answer the following question:
- Is there a difference in contraction of SMC derived from AAA patients compared to contraction of SMC derived from healthy controls?

Answer this question.

Answer 12

SMC contraction is more variable in AAA-SMC than in control SMC.

Question 13

So based on the previous question, we have established a difference in the contraction of SMC derived from AAA patients compared to contraction of SMC derived from healthy controls.
- What is the underlying mechanism of affected SMC contractility and how is this involved in AAA development and progression?

Answer 13

A lot of genes involved in SMC contraction have an altered expression pattern compared to control. Besides this, AAA-SMC can be subdivided based on the contraction and gene expression.

Question 14

The fact that gene expression is altered in AAA-SMCs is not sufficient to make a conclusion about the pathophysiology of AAA.
What else can be used to explain the altered SMC contraction in AAA?

Answer 14

Studying (phospho)proteomics (protein level instead of gene level) in order to identify proteins and pathways involved in the altered SMC contraction in AAA.

Question 15

What has been found in the research of (phospho)proteomics that could explain the altered SMC contraction in AAA?

Answer 15

• 4 proteins were found to be correlated to SMC contraction.
• These proteins were involved in: cell-cell and cell-matrix interaction, energy production, calcium homeostasis, cytoskeleton organization.

Question 16

What is the extracellular matrix (ECM)?

Answer 16

A large network of proteins and other molecules that surround, support, and give structure to cells and tissues in the body.

Question 17

What enzyme is responsible for the degradation of the ECM?

Answer 17

Matrix metalloproteinases (MMPs)

Question 18

Is there a relation between ECM degradation and AAA?

Answer 18

Yes, ECM degradation is a cause and part of AAA pathology. ECM degradation results in vascular SMC detachment from the ECM, which results in SMC apoptosis, phenotypic switch and reduced contrability.

Question 19

A 3D structure of the aorta (the media and intima) is recreated, where SMC growth is followed over time. What was found in this experiment when control was compared to AAA?

Answer 19

That control SMC produced more fibrillin-1 compared to AAA SMC. Fibrillin-1 is a structural ECM protein.

Question 20

What should be a future aim for the diagnosis, treatment and follow-up of AAA?

Answer 20

By understanding SMC function, so that the following things can be done:
- slow down aneurysm growth
- prevent rupture
- identify potential new therapeutic targets