Lecture 9 - The cardiac fibroblast Flashcards
What cells is the heart made from?
1/3 cardiomyocytes 2/3 non-myocytes - majority fibroblasts -endothelial cells -SMC -pericytes -neuronal cells -inflammatory cells
What happens to the Constitution of cells after an MI
neutrophils / monocytes infiltrate the area
what happens to the constitution of cells after cardiac fibrosis
-number of cardiac fibroblasts / myofibroblasts increases
what connects myocytes and fibroblasts together?
gap junctions
- allows movement of cytoplasmic contents and transmission of electrical impulses
Role of connexin-43 in showing the relationship between myocytes and fibroblasts
connexin-43 = protein in gap junctions
-found at myocyte edges where myocytes meet
fibroblasts
-staining between cells suggests their connection
what can proliferation of fibroblasts cause?
laying down of excess collagen can interfere with electrical activity and cause arrhythmia
How can capillaries signal fibroblasts?
through releasing cytokines and growth factors
how do fibroblasts regulate their own cellular function?
through release of bioactive molecules in an autocrine and paracrine manner
how are fibroblasts associated with the ECM
physically associated through specific receptors –> DDR2 and integrins
what are the first two stages of an MI?
- cell death –> oxygen / glucose depletion
- acute inflammatory response
- inflammtory cells arrive –> chemoreceptors / cytokines
Explain the formation of granulation tissue post-MI
- fibroblasts converted to myofibroblast
- myofibroblast and macrophage accumulation
- ECM degradation
- neovascularisation
explain the maturation phase post-MI
- scar formation –>ECM deposition
2. scar contraction –> myofibroblasts
explain the last two stages of Post-MI
- resolution of inflammatory response
- anti-inflammatory cytokines
- myofibroblast apoptosis - long term
- fibrosis –>adverse remodelling –> HF
where do cardiac fibroblasts come from
distinct lineage from cardiomyocytes and other sources of fibroblasts
-Derived from epicardial epithelial cells by epithelial-mesenchymal
transformation
list fibroblast markers
Vimentin, DDR2, PDGFRA, (FSP/S100A4)
list myofibroblast markers
Vimentin, DDR2, PDGFRA, (FSP/S100A4)
a-SMA (but not SM-MHC)
what phenotype do cardiac fibroblasts have in culture
myofibroblast phenotype
what happens to cardiac fibroblasts in cardiac remodelling
- highly proliferative
- migrate to different areas such as the infarct zone
- undergo modulation to myofibroblasts
what is the active phenotype of myofibroblasts characterised by?
- increased expression of contractile proteins ( alpha smooth muscle / actin ) / focal adhesion proteins / extracellular matrix proteins
- this allows them to physically contract around wound edges
how do fibroblasts interact with the ECM?
modulators of ECM
- through expression of ECM proteins
- regulating production of ECM-degrading proteases such as matrix metalloproteinases (MMPs), and their natural inhibitors TIMPs
what can cardiac fibroblasts secrete?
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.
Role of CF in cardiac remodelling?
- proliferation
- matrix synthesis
- cytokine and growth factor secretion
- migration
- myofibroblast differentiation
- matrix degradation
What are the essential roles of CF? beneficial
- maintenance of normal cardiac structure and function
- supporting adaptive and structural changes in heart structure
- repair of heart –> scar formation and healing after MI
- preventing cardiac rupture
What are the detrimental roles of CF?
- Fibrosis
- excessive and sustained proliferation and ECM deposition - Arrhythmia
- disturbance and blockage electrical conduction
what stimuli cause the conversion of CF to myofibroblast?
- mechanical tension
- TGF-B
- FN-EDA / collagen VI
what are increased in expression in myofibroblasts compared to CF?
- contractile proteins –> a-SMA / vimentin
- focal adhesion proteins –> tensin / integrins
- cell surface receptors –>TBRII / AT1R
- ECM proteins –> collagen I / III
what characteristics does myofibroblasts have compared to CF?
increased tensile characteristics
contraction of ECM
what happens to the number of myofibroblasts after an MI? and how is this measured?
high number of a-SMA positve myofibroblasts
What is the effect of TGF-B on CF?
increased a-SMA expression
organisation into filaments
increased ability to contract collagen gels
Nieuwenhoven FA et al
where do myofibroblasts originate from?
- significant proportion from the fibroblasts in the heart
- endothelial / epithelial cells through EndMT / EMT
- resident SMC
what is pro-fibrotic in terms of ECM?
production of ECM leads to fibrosis
- ECM synthesis
- collagens / laminins / GAGs / fibronectin - Inhibition of ECM degradation
- TIMPs ( reduce action of MMPs)
what is anti-fibrotic in terms of ECM?
reduction in ECM
- ECM degradation
- MMPs / ADAMS / ADAMTS
- break down structural proteins in ECM
What are MMPs
- 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
what are signals that regulate the expression and activity of MMPs?
Increase activity generally by inflammatory signals –> cytokines / ROS
Decreased activity by profibrotic signals
what do CF’s release?
- 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
What does IL-1 do in cultured CF tissue?
- 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
what is the purpose of CF targetted therapy ?
ensure cardiac repair but prevent adverse remodelling and fibrosis
what are potential CF therapies?
-direct reprogramming
-genetic therapies
miR-21
what cardiovascular drugs target CF?
ACEi
Beta blockers
statins
how do ACEi and ARBs effect CF?
reduce adverse remodelling
AT-II stimulates CF proliferation
AT II increases matrix synthesis/ proliferation /myofibroblast differentiation
How do Beta blockers effect CF?
reduce adverse cardiac remodelling
-beta agonists increase the proliferation of CF in cultures
-beta blockers reduced CF proliferation
Turner NA & Porter KE
how do statins effect CF?
reduce adverse cardiac remodelling inhibit HMG-CoA reductase reduce proliferation of cardiac fibroblasts reduce MMP secretion prevent cardiacmyocyte hypertrophy
