Lecture 9 - The cardiac fibroblast

Question 1

What cells is the heart made from?

Answer 1

1/3 cardiomyocytes
2/3 non-myocytes
- majority fibroblasts 
-endothelial cells
-SMC
-pericytes
-neuronal cells
-inflammatory cells

Question 2

What happens to the Constitution of cells after an MI

Answer 2

neutrophils / monocytes infiltrate the area

Question 3

what happens to the constitution of cells after cardiac fibrosis

Answer 3

-number of cardiac fibroblasts / myofibroblasts increases

Question 4

what connects myocytes and fibroblasts together?

Answer 4

gap junctions

- allows movement of cytoplasmic contents and transmission of electrical impulses

Question 5

Role of connexin-43 in showing the relationship between myocytes and fibroblasts

Answer 5

connexin-43 = protein in gap junctions
-found at myocyte edges where myocytes meet
fibroblasts
-staining between cells suggests their connection

Question 6

what can proliferation of fibroblasts cause?

Answer 6

laying down of excess collagen can interfere with electrical activity and cause arrhythmia

Question 7

How can capillaries signal fibroblasts?

Answer 7

through releasing cytokines and growth factors

Question 8

how do fibroblasts regulate their own cellular function?

Answer 8

through release of bioactive molecules in an autocrine and paracrine manner

Question 9

how are fibroblasts associated with the ECM

Answer 9

physically associated through specific receptors –> DDR2 and integrins

Question 10

what are the first two stages of an MI?

Answer 10

1. cell death –> oxygen / glucose depletion
2. acute inflammatory response
   - inflammtory cells arrive –> chemoreceptors / cytokines

Question 11

Explain the formation of granulation tissue post-MI

Answer 11

1. fibroblasts converted to myofibroblast
2. myofibroblast and macrophage accumulation
3. ECM degradation
4. neovascularisation

Question 12

explain the maturation phase post-MI

Answer 12

1. scar formation –>ECM deposition

2. scar contraction –> myofibroblasts

Question 13

explain the last two stages of Post-MI

Answer 13

1. resolution of inflammatory response
   - anti-inflammatory cytokines
   - myofibroblast apoptosis
2. long term
   - fibrosis –>adverse remodelling –> HF

Question 14

where do cardiac fibroblasts come from

Answer 14

distinct lineage from cardiomyocytes and other sources of fibroblasts
-Derived from epicardial epithelial cells by epithelial-mesenchymal
transformation

Question 15

list fibroblast markers

Answer 15

Vimentin, DDR2, PDGFRA, (FSP/S100A4)

Question 16

list myofibroblast markers

Answer 16

Vimentin, DDR2, PDGFRA, (FSP/S100A4)

a-SMA (but not SM-MHC)

Question 17

what phenotype do cardiac fibroblasts have in culture

Answer 17

myofibroblast phenotype

Question 18

what happens to cardiac fibroblasts in cardiac remodelling

Answer 18

• highly proliferative
• migrate to different areas such as the infarct zone
• undergo modulation to myofibroblasts

Question 19

what is the active phenotype of myofibroblasts characterised by?

Answer 19

• increased expression of contractile proteins ( alpha smooth muscle / actin ) / focal adhesion proteins / extracellular matrix proteins
• this allows them to physically contract around wound edges

Question 20

how do fibroblasts interact with the ECM?

Answer 20

modulators of ECM

• through expression of ECM proteins
• regulating production of ECM-degrading proteases such as matrix metalloproteinases (MMPs), and their natural inhibitors TIMPs

Question 21

what can cardiac fibroblasts secrete?

Answer 21

synthesise high levels of proinflammatory (e.g. IL-1, IL-6, IL-8, TNF) and profibrotic cytokines (e.g. TGF-beta, CTGF) and growth factors (e.g. PDGF and VEGF) - stimulators of angiogenesis.

Question 22

Role of CF in cardiac remodelling?

Answer 22

• proliferation
• matrix synthesis
• cytokine and growth factor secretion
• migration
• myofibroblast differentiation
• matrix degradation

Question 23

What are the essential roles of CF? beneficial

Answer 23

1. maintenance of normal cardiac structure and function
2. supporting adaptive and structural changes in heart structure
3. repair of heart –> scar formation and healing after MI
4. preventing cardiac rupture

Question 24

What are the detrimental roles of CF?

Answer 24

1. Fibrosis
   - excessive and sustained proliferation and ECM deposition
2. Arrhythmia
   - disturbance and blockage electrical conduction

Question 25

what stimuli cause the conversion of CF to myofibroblast?

Answer 25

- mechanical tension - TGF-B - FN-EDA / collagen VI

Question 26

what are increased in expression in myofibroblasts compared to CF?

Answer 26

1. contractile proteins --> a-SMA / vimentin 2. focal adhesion proteins --> tensin / integrins 3. cell surface receptors -->TBRII / AT1R 4. ECM proteins --> collagen I / III

Question 27

what characteristics does myofibroblasts have compared to CF?

Answer 27

increased tensile characteristics | contraction of ECM

Question 28

what happens to the number of myofibroblasts after an MI? and how is this measured?

Answer 28

high number of a-SMA positve myofibroblasts

Question 29

What is the effect of TGF-B on CF?

Answer 29

increased a-SMA expression organisation into filaments increased ability to contract collagen gels Nieuwenhoven FA et al

Question 30

where do myofibroblasts originate from?

Answer 30

- significant proportion from the fibroblasts in the heart - endothelial / epithelial cells through EndMT / EMT - resident SMC

Question 31

what is pro-fibrotic in terms of ECM?

Answer 31

production of ECM leads to fibrosis 1. ECM synthesis - collagens / laminins / GAGs / fibronectin 2. Inhibition of ECM degradation - TIMPs ( reduce action of MMPs)

Question 32

what is anti-fibrotic in terms of ECM?

Answer 32

reduction in ECM 1. ECM degradation - MMPs / ADAMS / ADAMTS - break down structural proteins in ECM

Question 33

What are MMPs

Answer 33

- family > 25 Zn dependent proteases - degrade all elements of ECM - mostly secreted from cells - low expression but can be induced - secreted as inactive zymogens - inhibited by TIMPs

Question 34

what are signals that regulate the expression and activity of MMPs?

Answer 34

Increase activity generally by inflammatory signals --> cytokines / ROS Decreased activity by profibrotic signals

Question 35

what do CF's release?

Answer 35

- growth factors and cytokines - produce molecules that have opposing effects - depend on the signals released from the surroundings - they release --> inflammatory / anti-inflammatory / fibrotic / anti-fibrotic / apoptoic / mitogenic / angiogenic / anti-angiogenic

Question 36

What does IL-1 do in cultured CF tissue?

Answer 36

``` - similar gene expression to post-MI Stimulates 1.pro-inflammatory cytokines/chemokines/ adhesion proteins 2.angiogenesis 3. cell migration 4.ECM degradation Inhibits 1. ECM production 2. myofibroblast differentiation ```

Question 37

what is the purpose of CF targetted therapy ?

Answer 37

ensure cardiac repair but prevent adverse remodelling and fibrosis

Question 38

what are potential CF therapies?

Answer 38

-direct reprogramming -genetic therapies miR-21

Question 39

what cardiovascular drugs target CF?

Answer 39

ACEi Beta blockers statins

Question 40

how do ACEi and ARBs effect CF?

Answer 40

reduce adverse remodelling AT-II stimulates CF proliferation AT II increases matrix synthesis/ proliferation /myofibroblast differentiation

Question 41

How do Beta blockers effect CF?

Answer 41

reduce adverse cardiac remodelling -beta agonists increase the proliferation of CF in cultures -beta blockers reduced CF proliferation Turner NA & Porter KE

Question 42

how do statins effect CF?

Answer 42

``` reduce adverse cardiac remodelling inhibit HMG-CoA reductase reduce proliferation of cardiac fibroblasts reduce MMP secretion prevent cardiacmyocyte hypertrophy ```