KIN 406 Midterm 2 Flashcards
How much exercise can someone with McArdle’s Disease tolerate?
Very low-low intensity exercise can be tolerated, however, under high intensity situations, muscle fatigue occurs within a few seconds-minutes after ATp-PCr stores and blood glucose are depleted
Does muscle fatigue in McArdle’s disease come along with lactate accumulation?
NO, because glycoylsis is fully activated due to the inability to utilize glycogen.
What are the painful muscle contractures in McArdle’s disease caused from?
Resemble rigor mortis. Fatigue and contractures are a result of ATP depletion—myosin fails to detach from actin. Fatigue and contractures are confounded by decreased Ca2+ pump activity due to a fall in ATP content in critical intracellular compartments (SR-glycogenolytic complex). Damage may also occur since elevated Ca2+ can lead to caspase activation (proteolytic enzyme) and signal apoptosis.
What is the role of the SR-glycogenolytic complex?
It provides compartmentalized ATP supply to the SERCA pump, so that myosin ATPase doesn’t use all the ATP in the cell for itself
What are mitochondrial myopathies?
Includes disorders which show defects in mitochondrial function.
What type of exercise capacity do individuals with mitochondrial myopathies have?
Very limited because they cannot make ATP aerobically or the ability is severely limited. Even mild activity is associated with breathlessness and severe metabolic acidosis becuase they use more glyocolysis. Very pronounced when performing longer duration exercise. THere is normal glycolytic function for ATP production since large increases in lactate occur
Amount of individuals mtiochondrial myopathies affect?
1:8000 individuals
What type of DNA do mitochondria have?
Both nuclear DNA and mitochondrial DNA
Where are the gene mutations and deletions in people with mitochondrial myopathies?
In NDNA and mtDNA
Most studies and most common mitochondrial myopathies effect what?
Electron Transport Chain
How are the mitochondria abnormal in mitochondrial myopathies?
Pateients with defects in Complex I have abnirmal mitochondria proliferation, and mitochondria accumulate around the edge of the fibers and appear red with trichrome stain (“ragged red fibers”). Frequency ranges from 1-40%.
What structures do patients with mitochondrial myopathies show?
Paracrystallin inclusions which are composed of mt creatine kinase
Why do the mitochondria proliferate and paracrystalline structures accumulate during mitochondrial myopathies?
To compensate for energy deficiency
What mtCK do?
Makes creatine phosphate and ships into the cytosol
What does cystolic CK do?
Takes phosphate group from creatine phosphate and transfers it to an ADP to make ATP
What do fat metabolism disorders affect?
Usually have a dysfunction or deficiency in carntine or carnitine palmitoyl transferase (CPT) enzymes
What are the symptoms of a fat metabolism disorder?
Patients lacking carnitine and/or CPT develop muscle weakness, pain and damage during exercise (ATP depletion, acidosis, elevated Ca2+)
Why are symptoms of a fat metabolism disorder more evident during prolonged, submax exercise?
The glycogen and blood glucose stores become depleted, and then all that is left is fat for energy. However, fat cannot be utilized as a fuel source, so the person fatiguges/
What do biopsies of fat metabolism disorder patients show?
Large fat droplets…which under severe conditions may also disrupt myofibril architecture
What is COPD?
Disease of the lungs that makes breathing difficult. Chronic bronchitis and emphasema. Exposure to an initiating factor (mainly cigarette smoke) causes enlargement of the mucus glands and an increase in the mucus-secreting goblet cells. Ciliated epithelium that lines the airway become damages leading to decreased mucus transport, leading to an increased likelihood of respiratory infections
Damage from COPD causes what?
An inflammatory response (infiltrating neutrophils, macrophages, lymphocytes), and release of inflammatory mediators (TNF-alpha, IL-8, elastases)
How does COPD relate to skeletal muscle?
It is associated with exercise intolerance, which is expected, but patients with atrophy fatigue occur much sooner. Loss of muscle mass is a major co-morbidity of COPD and a powerful predictor of mortality.
What fibre type is preferentially atrophied and lost in COPD?
Type I
What does COPD do to the oxidative capacity of muscle fibres, and MLC?
Reduces it…decreases in SDH, CS, capillary density, and decreased myoglobin (25% lower)…shift towards MLC fast form and in most extreme cases, MHC, too
Consequences of the muscle brought on my COPD?
- decreased muscle strength due to atrophy 2. decreased muscular endurance and increased fatigability (atrophy and decrease in Type I) 3. Lower resting ATP, PCr, and glycogen concentrations 4. Accelerated PCr and ATP depletion, glycogen breakdown, and lactate accumulation during exercise becaue the lack of O2 to produce ATP aerobically
How are VO2 and muscle wasting related in COPD?
People with muscle wasting have a lower VO2 than people with normal BMI, suggesting that muscle wasting in addition to COPD causes a drop in VO2
What phenotype does fibers become more like in COPD?
A fast phenotype
What is CHF?
Chronic heart failure/congestive heart failure. Caused by any number of conditions (CAD, hypertension, MI). Condition of the heart where functional or structural changes impair the ability of the heart to fill with or pump sufficient blood to body. Can have an impact on peripheral tissues since distribution of nutrients, growth factors, and O2 from blood can be altered.
What are the consequences of CHF on muscle?
1) muscle atrophy of both Type I and II fibers (greater in Type I) 2) Decreased Type I and increased Type I and increased Type II percentage (preferential loss of Type I fibers and fiber type switching Type I –> Type II). 3) inc. intracellular lipid droplets and some fibrosis 4. decreased capillary density 5. decreased mitochondria volume and size 5. decreased Kreb’s cycle enzymes (SDH, CS) 6) Lower resting ATP, PCr, and glycogen concentrations 7) Decreased muscle strength, mass, faster onset of fatigue 8) Increased exercise tolerance and decreased VO2 max 9) Accelerated PCr and ATP depletion, glycogen breakdown, and lactate accumulation during exercise (lack of O2 for aerobic metabolism)
Preferential loss and atrophy of fibers in CHF?
Preferntial loss of Type I fibers and fiber type switching Type I –> Type II, increases fatigability and decreases capillary density in hypertensive animals and humans
Direct and indirect mechanism of COPD and CHF?
Direct: both lead to exercise intolerance, which leads to a reduced health status Indirect: both cause hypoxia, oxidative, nutritional stress, systemic inflammation, medication, and disuse, causing limb and respiratory muscle alterations, leading to exercise intolerance, which reduces health statis
What are the 6 most important mechanisms that play the biggest role in the skeletal muscle dysfunction and atrophy observed during aging and disease?
- Decreased satellite cell number and function 2. Mitochondrial dysfunction and accumulation of mt DNA mutations 3. Increased free radical generation and oxidative stress 4. Increased apoptosis nad cell death and autophagy and protein degradation 5. Systemic and local inflammation
Imbalances in cell proliferation and death can result in?
Undesired tissue growth or atrophy. The cell cycle is integral in controlling cell proliferation and tissue turnover.
What are steroids?
Growth factors (testosterone, estrogen, and cortisol) that penetrate the cell membrane and act on steroid receptors directly effecting genomic regulatory mechanisms
How do polypeptide GFs work?
Cannot penetrate the membrane and instead act on membrane receptors to activate kinases, which leads to activation of certain transcription factors (IGF-I, IL-2)
What do growth factors do?
Stimulate the cell to enter the cell cycle (proliferate) but small amounts are needed to inhibit the cell from dying
Which of the following would lead to a mitochondrial myopathy? a) PFK deficiency b) carnitine deficiency c) creatine kinase deficiency d) a and b e) a,b,c
b) carnitine deficiency
Muscles of individuals with COPD show similar phenotypes to people with?
Inactivty atrophic myopathy and CHF
What are the 5 phases of the cell cycle?
Go, G1, S, G2, and M
What is G0?
A non-proliferation state where the cell is quiescent, waiting for GF to activate it
What are G1 and G2?
Gap phases; cellular components such as RNA, protein and enzymes are synthesized and accumulated to be used in subsequent phases
What is S phase?
Synthesis phase where DNA replication occurs
What are the G and S phases grouped as?
Interphase
What is mitosis?
Involves the division of nuclear and cellular components.
6 subphases of mitosis?
- Prophase: chromosal material condenses to form compact mitotic chromosomes 2. Prometaphase: chromosomes become organized and move towards spindle equator 3. Metaphase: chromosomes line up on equator 4. Anaphase: chromosomes move towards opposite poles and cell begins to split 5. Telophase: chromosomes cluster at opposite poles and new nuclear membrane is formed 6. Cytokinesis: formation of 2 genetically identical daughter cells
What causes the transition from G0 to G1?
Growth stimulation from hormones or GFs
What happens to G1 cells deprived of sufficient growth factor?
Can exit into G0
How ling is growth stimulation needed during G1?
Only during the first 2/3
What is the restriction point?
The point where growth stimulation is required (early G1) and an irreversible commitment for the cell to undergo one cell division (late G1-M)
What are checkpoints, and where are they found?
Are safeguards to ensure the evensts of the previous stage have been completed correctly and are found at the G1 to S, and G2 to M phase
What progresses the cell cycle and its specific stages?
Cyclins and cyclin dependent kinases
What are cdk’s?
Normally inactive but become activated when they become associated with cylcins (active cyclin-cdk complex). Collectively, these complexes phosphorylate proteins which stimulate gene expression of transcription factors and other critical cell cycle components
What are cdk’s regulated by?
Their expression level (depending on the phase of the cell cycle), but also by the expression of cdk inhibitors (p21, p27) and tumor suppressors genes (p53)
What is the Hayflick limit?
The finite number of cellular divisions a cell can undergo
How is DNA copied?
With the aid of a RNA primer and DNA polymerase
How does DNA polymerase add nucleotides?
5’ –> 3’ direction upstream of the primer. DNA polymerase cannot add nucleotides to the new 5’ end.
What are telomeres?
DNA structures which form “caps” on the end of the chromosome that consist of 1000-1700 base pair double stranded sequence followed by a single strand overhang that protrudes the 3’ end. Serve to protect the end of the chromosome from degradation.
What is the purpose of telomeres?
Serve to protect the end of the chromosome from degradation and as a means to compensate for chromosome shortening during replication. Instead of the chromosome becoming shorter with every replication, the telomere does by 50 base pairs every time
What is telomerase and what does it do?
A telomere specific enzyme that is important to telomere maintenance, and is a reverse transcriptase that adds base pairs to the telomere to allow replication to continue without shortening the telomere all the way to the chromosome
How can replication capacity of a cell be predicted?
Telomere length…varies between cell tpyes and from one chromosome to another
What type of cells have shorter telomeres? Longer?
Cells that proliferate faster and more often (leukocytes) have shorter telomere lengths than cells that replicate slower (skin fibroblasts)
What is telomerase activity like in adult cells?
Very low or absent. Cessation of a cell to prolierate is indicative of cellular senescence and aging
Why don’t skeletal muscle cells undergo the cell cycle?
The shape and fucntion of skeletal muscle fibers give it a high degree of specialization, but this comes at a cost of losing the ability to proliferate
How doe muscle cells repair and adapt?
Adding new nuclei to the existing fiber via satellite cells
What are myonuclei like in adult mammalian skeletal muscle?
Very stable with very little turnover of myonuclei. Estimated that no more that 1-2% of the myonucleo are replaced every week in healthy individuals
Where does the source of myonuclei for mmuscle regeneration come from?
Expansion of satellite cells and myogenic stem cells
Are muscle datellite cells myoblasts?
Muscle satellite cells in adults are distinct from the myoblast population during embryonic and fetal development
What are satellite cells?
Undifferentiated mononuclear cells.
Where are satellite cells located?
Between the plasma membrane and basement membrane.
Compared to myonuclie, satellite cells have…
a high nuclear to cytoplasm ratio, decreased organelle content, and smaller nuclear size
Morphological difference between satellite cells and myonuclei?
Smaller size, chromatin composition is different (compact and unorganized because cell is not dividing), and less cytoplasmic portion
How can satellite cells be identified besides from locatioN/
Pax7 appears to be specific to satellite cells since it is not epxressed in other cell types including differentiated myotubes. Skeletal umscle from Pax7-/- mice are absent of satellite cells and muscle regeneration is greatly reduced
ARe there more myocnuclei or satellite cells?
More myonuclei
Is the same satellite cell marker found the entire cell cylce?
No, depends on what stages of development the cell is in
What do Pax7-/- mice show?
Much smaller overall size and much smaller muscles…shows that at some point after fibre formation and grouping, Pax7 is needed for muscle growth.
What do Pax7-/- mice lack?
Do not express other markers found in satellite cells including Desmin and c-Met
When are satellite cells present in limb muscle?
18 days after the primary fiber has been formed (after weeks 7-9 of gestation)
What happens to the relative number or percentage of satellite cells in all muscle fibers after birth?
Falls rapidly…at birth, SC account for approx 32% of muscle nuclie, 5% at 2 months, and less than 2-3% in adults. This trend continues as we age though the change is much slower
Which fiber type has more satellite cells?
Type I
Why do Type I fibers have more satellite cells?
1) Since slow muscle (i.e. soleus) is used to a greater extent there may be more “wear and tear” compared to fast 2) Nuclei number (not including satellitecells) is greater in slow fibers, therefore, may need more satellite cells to replace nuclei 3) Satellite cells have also been found to be more abundant in close proximity to capillaries which would give these cells access to a transport system and growth factors
What activates satellite cells?
Disease, exercise and damage
What determines the time course and the magnitude of the response of satellite cells?
The severity of the injury
Upon injury/damage, what happens to satellite cells?
Become actiavted, enter the cell cycle, and proliferate. These cells will undergo a number of cycles of proliferation to form a pool of muscle precursor cells
Once satellite cells have expanded and exit the cell cycle, what happens?
They mugrate to the specific muscle site, terminally differneitate, and fuse to the myofiber. Satellite cell activation is not restricted to the site of damage as damage at one end of a fiber can activate cells of the entire fiber.
7 satellite cells can give rise to?
> 100 new myofibers containing >25000 differentiated myonuclie…have a high proliferative potential and ability to provide new genetic matieral
2 divisions satellite cells can undergo?
Plana and apical-basal division
Planar division?
Division on a vertical plane with cells remaining in contact with the basal lamina and sarcolemma…typically will generate two identical “self” cells (satellite cells with proliferative potential)…symmetric division
Apical-basal division?
Division on a horizontal plane with one cell maintaining contact with the basal lamina and the other losing contact…typically will generate one cell committed to becoming a myotube and one “self” cell with proliferative potential (satellite cell)…asymmetric division
How many of the satellite cells that divide will differentiate and form myotubes or be incorporated into existing fibers?
~80%, the remaining 20% grow very slowly and are reserve cells that become quiescent
Is the regenerative capacity of stem cells unlimited?
NO!
In order for the cell cycle to begin, a cell requires…
growth factor stimulation (which then inc. the expression of cyclin-cdk complexes, increases the expression of cell-cycle specific transcription factors, increased levels of 2nd messenger kinases)
Which of the following would be a cdk-inhibitor? a) p53 b) p21 c) CDK-2 d) cyclin E e) all the above
b) p21
The process of muscle regeneration and satellite cell expansion requires….
the influence of growth factors in a concentration and time dependant manner
How long after injury do satellite cells become activated?
6 hours
After activation, how long do satellite cells proliferate for?
2-3 days in response to various growth factors
What produces growth factors for the satellite cells?
Autocrine, paracrine, and endocrine sources
Main satellite cell growth factors?
Insulin-like growth factor I and II, hepatocyte growth factor, fibroblast growth factor, leukemia inhibitory factor. Other factos such as NO, testosterone, IL-6, platelet derived growth factor, endothelial derived growth factor also play a role in satellite cell activity.
What do satellite cell growth factors do to the satellite cell?
Activation, chemotaxis, proliferation, and differentiation.
Before activation, do satellite cells express markers such as MyoD, Myogenin, Myf5, Desmin, and MHC?
No, these markers are assicated with myogenic potential and terminal differentiation…cells are quiescent
Following activation/proliferation how is satellite cell morpholically changed?
1) Satellite cells swell and develop cytoplasmic processes which extend at the poles of the cell (cell flattens out so it can fuse to a myofiber) 2) There is a decrease in heterochromatin, an increase in cytoplasmic to nuclear ratio, and in increase in organelle content
During satellite cell activation what molecules are upregulated, and what do they do in terms of promoting attachment?
Neural cell adhesion molecule, vascular cell adhesion molecule, and M-cadherin are upregulated. These adhesion molecules aid in satellite cell migration to sites of injury/damage by promoting attachment of satellite cells to the membrane of the myofiber.
When growth factor levels are high so is the expression of cyclin-cdk complexes, what does this promote?
Promotes proliferation and inhibits differentiation
What is upregulated in the early stages of satellite cell proliferation?
Cyclin D and MyoD in response to growth factors
As the levels of cylin D-cdk4 and cyclinE-cdk2 increase in satellite cell prolferation, what happens to levels of myoD and Myf5?
Decrease in levels of myoD and increases in Myf5…this up and down pattern allows the celll cycle to progress
WHen is Ofxo1 activated, and what does it do?
Activated under low growth factor conditions. Foxo1 works by activating the cdk inhibitor p21. p21 inhibits cyclin E-cdk2 and prevents the cell cycle progress through G1. The cell remains quiescent and doesn’t express MyoD and Myf5.
What does IGF-I do for satellite cell activation and proliferation?
Growth factors (like IGF-I) bind to their receptors and activate the mitogen activated protein kinase (MAPK), which inhibits Foxo1. Inhibition of Foxo1, relieves the inhibition of cycline-cdk2 by p21 and allows the cell cycle and proliferation to progress. IFG-1/growth factors also upregualtes MyoD and Myf5, which allow the cell cycle and proliferation to occur.
How long after injury do satellite cells begin to withdraw from the cell cycle and wither self renew or differentiate?
4-5 days
What is differentiation characterized by?
A downregulation of Pax7 (no longer a satellite cell), cell cycle exit, terminal differentiation. Many of the cyclins and cdk’s that regulate proliferation and cell cycle are down regulated during differentiation.
What causes the dowwnregulation of cyclins and cdk’s that regulate proliferation and the cell cycle during satellite cell differentiation?
1) change in growth factor levels and type 2) changes in intracellular factors that regulate proliferation and differentiation
p21 inhibits cyclin-dependenat kinases, primarily by binding to…
cdk2, cdk4, and cdk6. Other factors including p15, p16, p18, p19, p27, and p57 act in a similar manner to p21 in the muscle.
