Senescence Flashcards
aging is?
the inevitable time-dependent decline in physiological organ function that eventually leads to death
changes in life expectancy throughout human history
-changes in the environment, nutrition, and medical care –> can extend expected survival age
-the average age expectancy continues to increase
-the area under the curves has dramatically increased
the ______ lifespan appears to be unchanged?
maximum
central nervous system effects from aging
extreme shrinkage of the cerebral cortex
severely enlarged ventricles
shrinkage of hippocampus : learning and memory
respiratory system effects from aging
-clogged and deformed alveoli
(fewer and large)
timeline of ageing research
caloric restriction enhances lifespan in mice and rats (1930s)
The 1950s - medewar accumulation theory, Williams antagonistic pleiotropy
1960s- Hayflick limit
1990s- senescence observed in human aging
2000s- SASP identified: senescence-associated sensitive phenotype
, first senolytics clinical trial
9 hallmarks of aging, grouped into 3 categories
- the primary causes of cellular damage
-genomic instability
-telomere attrition
-epigenetic alteration
-loss of proteostasis - compensatory or antagonistic responses to the damages
-cellular senescence
-mitochondrial dysfunction
-deregulated nutrient sensing - the consequences of aging cues: hallmarks group 1-2
responsible for the functional decline associated with aging
-stem cell exhaustion
-altered intercellular communication
Alexis Carrel
studied phenomenon of senescence or aging
“on the permanent life of tissue outside of the organism”
-tissue from embryonic chicken heart, the cultures were supplied with nutrients regularly
-tissue were maintained for over 20 years– this is longer than a chicken’s normal lifespan
“all cells continued to grow indefinitely”- this was widely accepted in the 20th century
an image of a thirty-day-old culture of connective tissue. in the center there was debris of old plasma, around it is a ring of concentric layers of very active new tissue
primary cells
cells obtained from original tissue that have been cultivated in vitro for the first time
cell strains
cells were derived from animal tissue, sub-cultivated more than once in vitro (diploid)
cell lines
immortal cells that have been grown in vitro for extended periods of time (years) (heteroploid)
cultured normal human cells have a limited capacity to divide
-around 40-60 doubling before entering a senescence phase
cell alteration
phase 1: or primary culture: the beginning of culture. cells are isolated from the original tissue
-this phase terminates with the formation of the first confluent sheet
phase 2: the luxuriant growth period where cells are continuously proliferating
-cells in this phase are termed “cell strains”
- an alteration may occur at any time giving rise to a “cell line” -whose potential life is infinite
phase 3: the period where cell replication rate slows, a phenomenon named “senescence”
-cell strains enter phase 3 and are lost after a finite period of time
primary causes of cellular damage
genomic instability, telomere attrition, epigenetic alteration, loss of proteostasis
compensatory or antagonistic responses
cellular senescence or ageing
eukaryotic cell
10 to 100 um
-can see the nucleus
-condensed chromatin
-an extension of nuclear envelope
cytoplasm: fluid within the cell that surrounds the organelles
building blocks of life
DNA, RNA, and protein
liquid-liquid phase separation (LLPS)
-underlies the formation of membrane-less organelles (MLOs)
-LLPS leads to a conversion of homogenous solution into a dense phase and a dilute phase
-intrinsically disordered proteins (IDP’s) containing, LCDs, PLDs (PrLDs) etc bind to multivalent polymers such as RNA and DNA as well as proteins
-MLOs function to concentrate proteins, and nucleic acids, and regulate gene expression
nucleolus and paraspeckles are nuclear MLOS
stress granules (SGs), RNA transport granules, and P-bodies are cytoplasmic MLO’s
Paraspeckle is involved in?
gene expression regulation, RNA processing
stress granule is involved in?
translational regulation, antiviral defense, response to stresses, store some mRNA and proteins
Nucleolus is involved in?
ribosome biogenesis
cajal body is involved in?
pre-mRNA and pre-rRNA processing
the p body is involved in?
post-transcriptional modification, response to stress
nuclear pore complex?
nuclear import and export, tumor, immune
cellular senescence
- well-established driver of aging and age-related diseases
- refers to the irreversible growth arrest that occurs when cells become exposed to a variety of stressors
cell growth
the increase in size (mass accumulation)
cell division:
the division of a mother cell into 2 daughter cells (cytokinesis)
cell proliferation
the process of generating an increased number of cells through cell division
eukaryotic cell division cycle
interphase: duplication of its entire cellular contents
M phase: creation of genetically identical cells
two main events
1. DNA replication (S phase)
2. segregation of the DNA (cytokinesis)
check points
G1 and G2 phases: commit to enter the next cycle
M phase: mitotic exit
A snapshot of dividing cells
HEK293 is a human embyronic kidney cell line
-invitro cell culture model for tauopathies (e.g. Alzheimer’s)
immunocytochemistry
lamin b1: protein of nuclear lamina which is a meshwork of proteins inside the inner layer of the NE
Hoechst 33342 (nuclei) a blue fluorescent dye for DNA stains
HEK293 expressing Dox:
GFP-tau (isoform 0N4R) is a microtubule binding protein
progression of the cell cycle
CDK: cyclin-dependent kinase in inactivated form
cyc: cyclin binding to CDK- promotes entry into the cell cycle
p16, p21, p27 : CDK inhibitors
E2F: transcription factor
RB, tumor supressor retinoblastoma in active form
cell division cycle withdrawal
- Quiescent cells
- terminally differentiated cells
- senescent cells
Quiescence
cell cycle: reversible arrest
macromolecular damage: no
signaling: p27kipi dependant
secretion: no
differentiation
cell cycle: genetically irreversible arrest
macromolcular damage: no
secretion: yes/no
senescence
generally irreversible arrest
macromolecular damage: yes
secretion: yes
paracrine/autocrine signaling
genomic dna damage an telomere shortening
persistent DDR signaling -> cellular senescence and altered stemness and differentiation -> inflammation and fibrosis
all considered aging
-impair stem cells properties and alter its differentiation
mutation types
point, DNA amplification and chromosomal rearrangement
substitution: change the code of the single triplet
insertion: changes the genetic code of all triplets following
deletion: changes genetic code of all triplets following
a individual cell can suffer up to ________ DNA changes per day?
one million
mutations and chromosome aberrations can lead to?
cancer, ageing, inborn disease
inhibition of _______ leads to apoptosis (cell death)
transcription, replication, chromosome segregation
homologous recombination
simultaneous action of large numbers of molecules (multiple protein complex)
cohesins
facilitate the identification of homologous sequence from the sister chromatid
RAD51
exchange the ssdNA with the same sequence from dsDNA
end joining (alternative)
simply links ends of DSB together (KU70/80)
-associated with gain or loss of a few nucleotides
DNA replication and associated proteins at the replication fork
topoisomerase: removes
helicase: unwinds
SSBs: coat
ligase: seals
pol E: synthesize
telomere
short nucleotide sequences found at the end of linear chromosomes
telomerase (TERT gene) : a reverse-transcriptase
telomerase binds to the 3’ end of the telomere sequence, along with an RNA template
telomerase catalyzes the addition of bases restoring the telomere length
DNA polymerase extends and seals the DNA strands
proliferating tissues
telomeres are shortened, when critically short, they trigger a DDR
post mitotic tissues
telomere dysfunction can be driven by irreparable DD within telomeres
persistent DDR (DNA damage response) activation
senescent phenotype
1) arrested proliferation and 2) SASP activation
inhibition of DNA damage repair at telomeres
-accumulation of DD at telomeres –> DDR–> cell cycle arrest or senescence or senescence like phenotype
post mitotic tissues
cardiomyocyte, adipocyte, neuron, osteocyte
how stem cells age?
stem-cell number and self-renewal do not necessarily decline with aging, but function does decline
young stem cells -> many progenitors-> many effectors
after physiological ageing, mutagen exposure or forced regeneration
old cells-> less progenitors -> less effectors
fates of damaged stem cells
stem cell-> RAF mutation, p53 loss (mutations or tumor suppressors) -> transformation->cancer
stem cell-> telomere dysfunction->senescence -> regenerative failure, SA-SP
stem cell-> unrepaired DSBs-> apoptosis-> tissue dysfunction and failure
stem cell-> y chromosome or 5q- loss, Tert gene -> dysfunction -> tissue dysfunction and failure (e,g. Myelodysplasia (MDS))
