lysosomes and proteasomes

christian de duve

discovered lysosomes through a biomedical approacg using velocity sedimentation and density gradient centrifugation

christian de duve’s lysosome discovery

1. took whole cells and homogenized in sucrose

2. centrifuged a pellet which he was able to characterize

3. found mitochondria present in pellet due to respiratory activity

4. detected proteolytic activity due to the presence of lysosomes

lysosomes typically contain

40-60 hydrolytic enzymes that can break down

marker enzyme used to define lysosomes

acid phosphatase

is a single membrane bound organelle stains positice for acid phosphatase

then the organelle is a lysosome

PH that lysosomal enzymes work best at

4.5 to 5.0

• if the lysosome leaks into the cytosol at a pH of about 7, the enzymes become less active and wont immediately destroy the cell

heterophagy

eating others— digesting materials brought in from outside the cell

autophagy

eating self— the degradation and reneweal of the cells own aged organelles

Rudolph virchow

responsible for intially finding cells inside other cells. he saw a RBC inside a WBC and thought that WBCs gave birth to RBCs. — proved to be phagocytosis

Ellie metchnikoff

responsible for phagocytosis

• believed that phagocytosis is responsible for aging since he thought that grey hairs came from phagocytes engulfing hair pigment

metchnikoff

known for introducing the concept fo probiotics, gerontology, and most importantly the cellular basis of immuniity

role of acrosome in sperm

it is a specialized, highy differentiated lysosome at the tipf of the sperm. it contains enzyemes that break down the egg’s outer membrane to allow fertilization

mysathenia gravis

droopy eyelids

• a neuromusclar disease that stems from both heterophagy and autophagy

WBCs have FC receptors which means

they can endocytose bacterium — a critical part of endocytosis

curare 1960

a drug given to patients with MG. those who took this drug were extremely sensitive to the drug.

• eserine drugs were helpful

curare blocks

acetylcholine receptos on the neuromuscular junction by blocking pores

eserine

extends the half life of the acetylcholine making the active concentration of the acetylcholine higherin the synaptic’ cleft

• blocks acetylcholine esterase which is an enzyme that breaks acetyl choline into two parts

mysathenia gravis patients

have fewer acetylcholine receptors present that bind 3H-alpha bungarotoxin

• this was proven by doing ultra structural radiography which counted raidoactive squiggles

experiement used to understand M.G

injecting purified acetylcholine receptors from a torpedo ray into mice which caused M.G like symptoms

• allowed us to determine that MG is an autoimmune disease due to fewer receptors in the post synaptic neuromuscular junction

vyvgart (newer)

a drug designed to treat MG by increasing the degradation rate of all circulating antibodies in the blood which also includes the anti-nicotinic acteylcholine receptors that are the basis of MG

• patients are acteylcholine antibody receptor positive

acetylcholine receptors

membrane proteins that bind the neurotransmitter acetylcholine, initiating signals for muscle contraction, autonomic nervous system activity, and brain functions like memory and arousa

anti-nicotinic acteylcholine receptors

autoantibodies that destroy and target nicotinic acetylcholine receptors at the neuromuscuslar junction, causing musclar weakness

autophagy

the ability for the lysosome to engluf itself

mitochondria has a half life of

5 to 6 days

peroxisome has a half life of

1 to 2 days

autophagocytosis may be the cause of

cancer

autophagosome (RER) and LC3

important to autophagy

• binds and fuses with lysosomes

cisplatin

a common chemotherapy drug that binds to nuclear DNA in cancer and other cells and prevents repair triggering apoptosis

bafilomycin A

poisons the proton pump, into the lysosome, and maintains the acidic environment

chloroquine

increases the internal pH from 4.5 to 7, inactivating the enzymes

silicosis (miners disease)

silica particles are inhaled and taken up by lung macrophages.

• the silica punctures the lysosome membrae. causing enzymes to leak out and kill the cell, leading to inelastic collage depositis in the lungs

chloroquine myopathy

a unique case where patients are injected with chloroquine which allowed the lysosomes in the muscles to work

lysosomes

membrane bound organelles containng hydrolytic enzymes that act as the cells waste disposal, recycling center, and defense system

chlorquine retinopathy

can cause irreversible blindness that contines to progress even after not using chloroquine

Genzyme

a company , formed in 1981, that is famous for making the decision to develop enzyme replacement therapies to treat lysosomal diseases

• discovers ways to treat the 50 to 70 inherited lysosomal storage diseases

tay-sachs 1

deficient enzyme: hexoaminidase A

hurlers disease 1

deficient enzyme: alpha L- iduronidase

hurlers disease 2

causes lysosomes to become bigger in size and accumulate in cells due to the accumulation of glycosaminoglycans (complex sugars)

• when co-cultured with other cells, they appear to become normal again — an example of being in a conditioned medium or co-culture experiements

tay -sachs 2

causes an accumulation of gangllioside GM2 due to them being unable to be broken down in the lysosome

• primarly affects brain/meural tissue beacsue of the high concentration of gangliosides in neural tissue

i cell disease 1

deficient enzyme : N-acetylglucosaminylphosphotransferase

i cell disease observation A

there are lysosomes with few lysosomal enzymes

conclusion: either lysosome enzymes arent synthesized at all or there are problems with the M6P address tag that is added in the CIS GOLGI

i cell disease

a rare, inherited metabolic disorder where cells cannot properly sort and transort enzy,es to their correct location which leads to a buildup of undigested materials (mucolipids and mucopolysaccharides) in the lysosome

optimization

FC receptors allowing immune cells to recognize and zip up around pathogens

• fc receptors on a phagocyte bind to antibody-coated particles (like bacteria) and then pull the particle inside the cell.

yoshinori ohsumi

received a nobel prie for discovering autophagy mechanisms

LC3

a key protein in the autophagy pathway, responsible for degrading and recycling cellular components

aldurazyme

medication used to treat hurler syndrome

i cell disease observation B

i cells have lots of lysosomal enzymes outside the cell

i cell disease observation C

i cells can endocytose normal lysosomal enzymes

gaucher disease

a rare inherited disorder caused by a deficiency in the enzyme GLUCOCEREBROSIDASE

gaucher disease leads to

the buildup of a fatty substance in organs like the spleen, liver, bones, and sometimes the brain

• causes spleen enlargement and bone deformations

cerezyme

the first enzyme replacement therapy to treat type 1 gauchers disease

popme disease

a rare genetic disorder that causes progressive muscle weakness and heart failure. leads to the accumulation of glycogen in lysosomes

popme disease deficient enzyme

acid alpha glucosidase GAA

myozyme

treats pompe disease

glycogen can be broken

down into glucose in the lysosome

glycogen can be transported to the lysosome

GAA breaks it down into glucose, and then the glucose is pumped out of the lysosome into the cytoplasm where it is used in glycolysis

proteasomes

very large macromolecular machines or particles that influence the cell cycle, apoptosis, and are involved in the final stage in the unfolding protein response system

the ubiquitation of target proteins

is a key event of proteasomes since it is required for proteasome degradation.

proteasome inhibitor effects

• increasese ER stress

• trigger apoptosis

• turn off cell survival pathways

• affect mitochondrial function

• influence epigenetic changes

• influence DNA repair

proteasome inhibitors used routinely in clinical settings

bortezomib

• carfilzomib

• izazomib

Why are cancer cells more sensitive to proteasome inhibitors than normal cells?

Cancer cells overproduce normal proteins + generate mutated proteins → cancer cells rely heavily on proteasomes to protect them from proteotoxicity

proteotoxicity

cellular damage or dysfunction caused by misfolded or aggregated proteins