Signalling Molecules and Cellular Locations in Cardiac Pathophysiology (Dr Murdoch) Flashcards
List the three primary causes of heart failure (and what causes them)
1) Pressure overload: Aortic stenosis and hypertension (hypertension is most common). Heart must pump out blood at a higher pressure
2) Volume overload: Aortic or mitral valve regurgitation. Volume stress due to valve malfunction causes heart to dilate
3) Contractile dysfunction: Ischaemic heart disease. Blockage of coronary artery by atherosclerosis
List three normal times the heart hypertrophies
1) Postnatal growth: From foetal development to fully grown
2) Exercise
3) Pregnancy
List three abnormal times the heart hypertrophies
1) MI
2) Cardiomyopathy
3) Sarcomeric gene mutation
Describe the difference between physiological and pathological hypertrophy of the heart
Physiological: Normal or enhanced function, no fibrosis, normal gene expression and proportional to chamber enlargement
Pathological: Can be cardiac dysfunction, fibrosis, myocyte necrosis and apoptosis, heart failure and increased mortality
What happens to the volume and pressure in dilated hearts
The volume increases but the pressure decreases
What happens to the volume and pressure in concentric hypertrophied hearts
The volume decreases and the pressure increases
Describe the four ways in which the heart can remodel and how they relate to fetal genes/fibrosis/cellular dysfunction.
1) Physiological hypertrophy: No fetal genes, fibrosis or cellular dysfunction
2) Concentric hypertrophy: Some fetal genes, fibrosis +++ and with or without cellular dysfunction
3) Eccentric hypertrophy: Some fetal genes, with or without fibrosis and with or without cellular dysfunction
4) Heart failure: Fetal genes +, fibrosis ++ and cellular dysfunction ++
Describe three different mouse models of cardiac hypertrophy
Pressure overload: Angiotensin 2 infusion
Pressure overload: Minimally invasive but a transverse aortic constriction
Physiological hypertrophy: Exercise
LV hypertrophy is described as a combination of what four things
1) Bigger hearts: Physiological and pathological
2) Fibrosis, myocyte loss. Increase in pathologica;
3) Reduced ejection fraction: Reduced cardiac function in pathological
4) Fetal genes: Different changes in gene expression in physiological and pathological
Switching to which type of myosin decreases the ATPase activity of the contractile apparatus, which decreases contractility
Beta myosin heavy chain
Down regulation of what reduced the amount of calcium stored in the sarcoplasmic reticulum
SERCA
How does signalling essentially work
Ligand -> intracellular signalling -> transcriptional regulation -> response
How do g-protein coupled receptors stimulate the release of calcium
via IP3
What molecules regulates pathological hypertrophy and which regulates physiological
AngII= Pathological and IGF-1 regulates physiological
List the initiating stimulus, cell membrane molecules, signalling pathways, cellular responses and cardiac function in pathological hypertrophy
1) Initiating stimulus: Cardiomyopathy or disease
2) Cell membrane: Ang II, ET-1, NE
3) Signalling pathways: MAPK, calmodulin, protein kinase C, calcineurin
4) Cellular responses: Protein synthesis, gene expression, increased cell size, fetal gene expression, fibrosis and cell death
5) Cardiac function: Decreased
List the initiating stimulus, cell membrane molecules, signalling pathways, cellular responses and cardiac function in physiological hypertrophy
1) Initiating stimulus: Postnatal growth and exercise training
2) Cell membrane:Growth factors (IGF-1) and RTK
3) Signalling pathways: PI3K -> AKT
4) Cellular response: Gene expression, protein synthesis and increased cell size
5) Cardiac function: Normal
What happens to mice that express more active and less active PI3K
More = Larger hearts Less = Smaller hearts
Does calcineurin/NFAT coupling participates in pathological or physiological hypertrophy??
Just pathological
List the calcineurin/NFAT pathway that leads to hypertrophy
1) Increased gene transcription
2) Calcineurin is a calcium activated phosphate
3) This directly binds to and dephosphorylates NFAT (nuclear factor of activated T cells) transcription factors in the cytoplasm
4) Allowing NFAT translocation to the nucleus and subsequent hypertrophic gene expression
What antagonised NFAT translocation
Phosphorylation via indicated kinases
What inhibits calcineurin enzymatic activity
Cyclosporin A and overexpression of modulatory calcineurininteracting protein (MCIP) overexpression
Decribe the process of chromatin (genetic material) remodelling
1) HDACs-GSK3beta
2) HDAC promote the condensation of chromatin and the inactivation of transcription
3) Class II HDACs have been implicated in cardiac hypertrophy
4) Calcineurin or pressure overload was associated with enhanced serine phosphorylation of HDAC
What to HDAC5 null mice hearts show
Increased hypertrophy due to activated calcineurin (3 x normal size by 4 weeks of age) and increased expression of fetal cardiac genes
How to HDAC inhibtors reduce cardiac hypertrophy
Suppressing autophagy
Examples of biochemical stress signals
Internal stretch sensors, integrins, LIM-domain protein MLP
What is melusin
A protein binding to the integrin beta 1 cytoplasm domain and specifically expressed in striated muscle tissue where it localizes at costameres in proximity of the Z line along with integrins and vinculin
What is melusin required for
For the adaptive hypertrophic response to biochemical stimuli but not biochemical stimuli (such as G-protein-coupled receptor)
Is heart size and cardiac function angiogenesis dependent/independent
Angiogenesis dependent
How does the heart grow during embryonic development
Via proliferation and hypertrophy of cardiac myocytes (this is the re-use of embryonic transcription factors)
What happens to angiogenesis in HF and how?
Reduced angiogenesis due to p53
What are ROS
Highly reactive metabolites of molecular oxygen that are inevtiable by-products of the reduction of oxygen in the mitochondrial resp chain
Give examples of ROS
1) Superoxide anion
2) Hydrogen peroxide
3) Hydroxl radical
4) Peroxynitrite (formed from nitrous oxide and superoxide anion)
What are major sources of ROS in the cell and have multiple ROS-generating enzymes implicated in cardiac disease
NADPH oxidases
Give info on Nox2 and Nox4 NADPH oxidases
- Nox2 and Nox4 NADPH oxidases:
- Nox2 needs to become activated
- Nox4 constitutively active
- Nox 2 produces superoxide
- Nox4 produces hydrogen peroxide
- They are both highly expressed in endothelial cells
- There are low levels of ROS involved in redox signalling
Where is NOX2 located
Sacrolemmal and t-tubule membranes and it sensitizes near the ryan
What does stretch do to NOX2
Activates it to produce ROS which trigger calcium sparks in myocytes (which increases contractility)
What can stop stretch induced increase in spark frequency
NAC (antioxidant) or DPI (blocks NADPH oxidase). This shows stretch induced calcium spark is dependent on ROS as there is chemical inhibition. This is all positively inotropic.
Describe glutathione
- An antioxidant
- Is a cellular reducing agent
- Tripeptide
- Used by a variety of enzymes as a reducing agent in antioxidant defence, when it becomes oxidised to GSSG
- Can also form disulphides with proteins
Write about cysteine
Something about ROS signal through modifications of cysteine oxidative post-translational modifications
Describe how oxidative stress impact HF
- Oxidative stress in HF reduces free thiol content in ryanodine receptors (cysteines have been oxidised)
- RyR opens more in heart failure or on application of oxidising agent (DTDP)
- Reversed by a reducing agent (DTT)
- This RyR activation by oxidation/HF decreases calcium transients reversed by anti-oxidant
- A leaky RyR empties the sarcoplasmic reticulum of calcium and directly reduces performance
What do oxidising agents inhibit
L-type calcium channels
What do free radicals inhibit
Free radicals inhibit L-type calcium channels relevant for reperfusion injury
What do ROS do to voltage gated sodium channels
Delay inactivation of the voltage gated sodium channels. This leads to a longer depolarizing current -> longer AP -> arrhythmogenic. Also leads to Na overload
What does caffeine do to SR calcium content
Increases it
Where is the peroxynitrite-induced glutathionylation on the sodium pump
Beta sodium pump (not catalytic alpha subunit)
What blocks glutathionylation of sodium pump beta subunt
Superoxide dismutase
Describe the effects of ROS on cardiac ion transporters
1) ROS activate the RyR, but paradoxically this reduces Ca transient because it empties the SR of calcium
2) Inhibition of the L-type calcium channel by ROS reduces the calcium transient by reducing trigger calcium
3) ROS prolong the cardiac AP by decreasing the inactivation of voltage gated sodium channels
4) SERCA is inhibited by some ROS but activated by others
5) NCX is activated ROS leading to excess calcium removal
6) Sodium pump is inhibited by ROS leading to sodium overload
What induces substrate phosphorulation by PKA
Hydrogen peroxide. H202 also increases contractility in single cells
Name the sites of PKA action in control of cardiac output
1) Voltage gated calcium channels. Function is to trigger calcium plateau phase of action potential, activated by depolarisation, phosphorylated by PKA, increases trigger calcium, increases calcium induced calcium release
2) RyR: Calcium induced calcium release from the SR and is activated by PKA
3) SERCA: Removes calcium at the end of the beat and is indirectly activated by phospholamban (phosphlamban phosphorylation increases calcium reuptake by SERCA and increases the size of the calcium store creating larger calcium transients.
4) Sodium pump: Phospholemman (PLM) indirectly. PLM phosphorylation activates pump and increases sodium efflux
5) Troponin I: Is a part of the thin filament troponin complex. Acts to inhibit actin myosin interaction. TnI is phosphorylated by PKA and this reduces affinity of TnC for calcium causing a minor reduction in contraction which accelerates relaxation
