Cellular Responses 4/23 Flashcards
what causes cellular aging?
- telomere shortening (replicative senescence)
- environmental insults (free radicals –> damage to proteins and organelles)
- DNA repair defects (causes accumulation of DNA defects and damage)
- abnormal growth factor signaling
Sirtuins
- appears to prevent aging in cells
- may reduce aging progress via insulin sensitization and prevention of apoptosis
- reduce oxidative stress and free radical prevention
- low calorie diets can increase sirtuin levels
ex. Resveratrol is found in red wines, and induces formations of sirtuins through Sirt1
role of telomeres
- Telomeres function in replicative senescence of cells. Germ cells retain a higher telomere length than stem cells, than normal somatic cells. If the telomere gets too short, the cell loses its ability to replicate.
- Telomerase directs RNA template dependent DNA synthesis in which nucleotides are added to one strand at the end of chromosomes
- (telomerase does not operate in normal somatic cells, but is active in cancer cells)
Atrophy
Decrease in cell number and/or size of tissue and/or organ
Hypertrophy
Cell increases in size
Cellular changes:
- cytoplasm increased, more ribosomes, more protein
- nucleolus is enlarged (this is where protein is made)
Hyperplasia
Cells increase in number
Cellular changes:
- nucleus enlarged but less basophilic (i.e. chromatin is dispersed because it is undergoing txn and replication)
- increased DNA txn
Metaplasia
- conversion of one differentiated (mature) cell type into another
- ex: cigarette smoking: results in squamous metaplasia of ciliated columnar epithelium within bronchioles
- ex. chronic irritation of endocervix, results in squamous metaplasia of endocervical glandular epithelium
- ex. chronic reflux esophagitis: squamous epithelial changes to stomach or intestinal epithelium, gastric glandular metaplasia
note if cell has been terminally differentiated (i.e. the top layer of epithelium) it will die and not change. however the stem cells and less differentiated reserve cells at the base of the epithelium will be reprogrammed to produce a new cell type
What are the causes of pathologic atrophy?
- decreased workload/use (cast)
- denervation
- decreased blood supply - ischemia
- decreased O2 - hypoxia
- nutrition (marasmus, cachexia, kwashikorkor)
- loss of endocrine stimulation (endometrium, breast, ovary)
- pressure (tumor, decubitus ulcers)
- inflammatory/immunologic
- senility (senile osteoporosis)
ubiquitin-proteasome protein breakdown pathway
- this is a primary mechanism of atrophy
- allows for accelerated proteolysis in catabolic conditions
- proteins are ubiquitinated, and then proteasomes will come and will break down the protein
- may be accompanied by autophagy –> resulting in residual bodies
ex. lipofuscin
lipofuscin
- golden brown residual body, left over after breakdown via the ubiquitin-proteasome breakdown pathway
- remains in the cell, called “aging pigment”
- atrophy with lots of lipofuscin = brown atrophy (seen in atrophy organs)
What are residual bodies?
- left over particles resulting from autophagy, that are indigestible
- ex. lipofuscin
What is seen with marasmus?
- calorie deficient state, but protein levels are normal
- thin child, uses its own fats and proteins for energy - a form of atrophy
- seen normal hair, old man appearance, thin limbs with little muscle or fat, very underweight
What is seen with kwashiorkor?
- deficiency is purely in proteins, the fat content in these children is normal. protein levels are low.
- swelling of legs (oedema), sparse hair, moon face, little interest in surroundings, flaky appearance of skin, swollen abdomen, thin muscles, fat present
- fluid shifts (due to lack of proteins in blood), to cause edema
- this is the worse off disease compared to marasmus
What is seen with extracellular tissue atrophy due to immobilized limbs?
immobilized limbs:
- loss of proteoglycans in articular cartilage
- decreased strength of ligaments
- osteopenia = loss of bone mass
is atrophy reversible?
- if energy is kept from cell and it dies, it will result in complete atrophy and irreversible death
- starvation induced fat atrophy can result in complete regeneration
- motor denervation of skeletal muscle (return of function if repaired in 3-5 weeks, useless to repair after 20-24 months)
how do you get hypertrophy/hyperplasia?
- increased functional demands (i.e. physiologic hypertrophy during exercise)
- pathology
- compensation
- excessive nutrition
- increased blood flow
- endocrine stimulation
- mechanical factors
what happens in the heart and skeletal muscle in response to increased functional demands?
- pure hypertrophy WITHOUT hyperplasia
- this occurs in the heart and skeletal mm.
- may be physiologic or pathologic
- increased RNA and DNA in nucleus, increased amount of cytoplasm
what happens in kidney with increased fn. demands?
hypertrophy AND hyperplasia
what happens in striated mm. in response to increased fn. demand?
- Endurance mm - increased number and volume of mitochondria
- Resistance mm- hypertrophy of contractile elements and
increased capillary network
what happens to smooth mm with increased fn. demand?
- hypertorphy and hyperplasia
- * smooth muscle polyploidy (increased number of DNA)*
what happens with cardiac remodeling? biochemical pathways? what gene expressions will change in response to increased stress?
- hypertrophy ONLY
Two main biochemical pathways:
- phosophinositide3-kinase/AKT pathway (exercise induced, will make more proteins)
- Growth factors or vasoactive amines will cause GPCR cascades (this is more pathological)
Things that may occur:
- switch of contractile protein to fetal forms (ex. alpha heavy chain myosin replaced with Beta heavy chain myosin, which is more energetically economical)
- early development genes re-expressed (i.e. increased ANF, results in increased sodium excretion in kidney, results in decreased intravascular volume and pressure)
what are signals to myocardial hypertrophy?
- increased mechanical stress, will stimulate genes to be turned on
- agonists (i.e. alpha adrenergic hormones and ANG)
- Growth factors
these things will all increase mechanical performance and decrease workload
look at myocardial hypertrophy slides
slide 38
is cardiac hypertrophy reversible?
- yes, portions of it.
- mm. mass and RNA can return to normal
- DNA does not change, results in increased nuclear size (doesn’t return to normal size)
- see fibrosis (scarring) does not change, results in decreased compliance