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
cytochrome P-450?
- cytochrome P-450: breaks down toxins in the body, detoxification
- barbituates and ethanol will induce cytochrome P-450, this is how people develop resistance to their medications
- results in hypertrophy of ER
- P-450 can result in toxic products: ROS from oxidative metabolisms
- creates toxic metabolites
physiologic hyperplasia vs. pathologic hyperplasia?
physiologic:
- hormonal stimulation (i.e. breast development with estrogen, ACTH)
- compensatory (partial hepectomy, nephrectomy)
Pathologic:
- hormonal stimulation (gigantism, prostatic)
- increased fn. demand (bone marrow in chronic blood loss and infections, secondary hyperparathyroidism)
- persistent cell injury (lichen simplex chronicus)
- infectious agents (papillomaviruses have viral genes for growth factors)
What occurs with liver partial hepatectomy? what is the mechanism?
- it is not regeneration
- called “compensatory hyperplasia” (hepatocytes proliferate)
Mechanism:
- growth factor driven proliferation of mature cells
- increased output of new cells from stem cells (backup hyperplasia mechanism)
Stem cells of liver = oval cells: generate lineage only in situations in which hepatocyte proliferation is blocked or delayed
What is seen in endometrial menstrual cycle?
- proliferative phase = hyperplasia
- secretory phase = hypertrophy
- menstrual phase = atrophy and necrosis
- look at slide #45, the histology of the menstrual cycle- must identify these for the exam!!!
what does retinoic acid/ vitamin A do?
- this is a hormone, because it can regulate gene txn through retinoid receptors: retinoic acid regulates gene transcription through retinoid receptors (Vitamin A)
- can get squamous metaplasia with deficiency or excess
- behaves as a steroid hormone, because can diffuse directly into the cytoplasm of the cell
- ex. Acutane
- vitamin A deficiency: major consequence in the eye is in the production of keratinizing metaplasia of specialized epithelial surfaces, results in problems with cornea
squamous metaplasia
Know SLIDE 50
- the most common example of metaplasia is that of columnar to squamous epithelium
- often protective
- double edged sword:
- in bronchi decreased cilia results in increased mucus. This can lead to malignant transformation
Periductal mastitis
- squamous metaplasia that happens to 90% of smokers within the breast ducts
- ductal epithelium goes from glandular to squamous epithelium
- initiated by keratin trapped after metaplasia
- results in duct rupture, and strong inflammatory response to keratin
- fistulas occur if disease is recurrent
Barrets esophagus
- glandular metaplasia
- physiologic sphincter does not function well and acid moves into esophagus.
- results in heartburn, and digestion of squamous mucosa.
- cells at base result in reprogramming towards gastric or intestinal mucosa
- will see goblet cells in esophagus (those are only seen in intestine normally), will also see a glandular mucosa
- glandular cells are being chronically irritated, will result in increased replication, will result in glandular cancer (adino carcinomas)
- need to be able to recognize these pictures on slide 52
what is the sequential development of biochemical and morphologic changes in cell injury?
(reversible cell injury)= decrease in cell function
(irreversible cell injury)
- see biochemical changes, leading to cell death (not enough ATP)
- see injury with ultrastructural changes (electromicroscope level, seen injury on mitochondria)
- light microscopic changes (see histological changes)
- gross morphologic changes (can see problem with the naked eye)
ex. takes 12-24 hours until you can see MI problems. at least 6 hours before you can see MI on histological slide
oncosis
cell death with swelling (associated with necrosis)
- he doesn’t like this word
what are three results of irreversible injury?
- necrosis: see inflammation
- apoptosis: no inflammation
- autophagy: no inflammation
what are causes to cell death?
- decreased ATP
- damaged mitochondria: proapoptotic messengers released from mitochondria
- entry of Ca2+: caused by hole in lysozomes or cytoplasmic membranes, stimulates digestive enzymes in cells
- increased ROS: have free electrons that will cause damage to DNA, lipids, and proteins
- membrane damage: plasma membrane is damaged resulting in loss of cellular components, if lysosomal membrane is ruptured, it will cause enzymatic digestion of cellular components.
- protein misfolding and DNA damage: results in activation of pro-apoptotic proteins
what happens with mitochondrial damage?
- decreased ox phos
- decreased ATP
- decreased Na+/K+ pump, sodium will go up in cell, K+ will go down in cell (will see hyperkalemia in blood), results in increased ER swelling, cellular swelling and loss of microvilli blebs
- increased anaerobic glycolysis: decreased glycogen, increased lactic acid, and decreased pH. results in clumping of nuclear chromatin
- detachment of ribosomes, results in decreased protein synth, and lipid deposition
damage of plasma membrane
- cell will most likely die
- influx of Ca2+, activates phospholipases, cell membrane damage and dysfunction, results in more Ca2+ influx
- Ca2+ also activates proteases, ATPases, which will result in increased mitochondria damage
what does mitochondria release due to damage?
cytochrome C is released, results in cellular apoptosis
megamitochondria
- seen with alcoholic liver disease, aging and other disorders.
- the hepatocytes of alcoholics will have this
what are species of free radicals?
- hydroxyl radical (most damaging) OH*
- hydrogen peroxide H2O2
- superoxide O2*