Block B Lecture 3 - Ageing Flashcards
What are 5 properties of aged cells?
Examples Include:
Slow division
Change in cellular metabolism (decrease basal rate and slowing of all chemical reactions)
Change in cellular function
Inability to carry out apoptosis
Decreased sensitivity of all receptors
Reduced ability to withstand ROS
DNA Instability (Note - may lead to a cancerous growth forming)
(Slide 3)
What are 3 signs that we are programmed to die?
The Hayflick limit of cell division
Telomere shortening
Insulin/IGF-1 signalling via FOXO transcription factor deficits occurring with age
Reduced immunity over time
(Slide 4)
How did Leonard Hayflick prove the existence of the Hayflick Limit?
- He isolated and cultured fibroblasts cells from human tissue, an placed them in a culture vessel with a nutrient medium
- Cells then divide and form a confluent layer on vessel surface
- He then discarded half of the cells, allowing the remainder of them to grow back to confluency - this is known as a passage
- Passages are repeated
- Cell replication is observed to slow, and eventually it stops after about 50 (+ or - 10) passages.
- Cells have reached the Hayflick limit and undergone replicative senescence
(Slide 5)
What is a confluent layer?
It means that cells have grown to cover the entire surface of the culture dish
(Slide 5)
What is the function of telomeres?
To protect the ends of chromosomes from damage
(Slide 6)
What repeated nucelotide sequence do telomeres contain?
TTAGGG
(Slide 6)
What happens to telomeres as cells divide?
The gradually shorten, until eventually cell division stops once they run out
(Slide 6)
What kind of protein is telomerase?
A ribonucleoprotein (a protein containing both RNA and protein molecules)
(Slide 7)
What are the 2 main components of telomerase?
Telomerase reverse transcriptase (hTERT) protein and the hTR RNA (aka TERC) component
(Slide 7)
What are the functions of the telomerase reverse transcriptase (hTERT) protein and the hTR RNA component contained in telomerase?
the hTERT protein contains the catalytic component whereas the hTR RNA component provides the template for telomere synthesis
(Slide 7)
What does telomerase do?
It adds the telomere repeats (TTAGGG) onto the ends of chromosomes
(Slide 7)
What differentiated cells usually don’t express telomerase?
Differentiated somatic cells
(Slide 7)
Is telomerase expressed in stem cells?
Yes
(Slide 7)
How are cancer cells able to divide uncontrollably and infinitely?
As telomerase becomes reactivated in these cells, allowing it to add to the ends of telomeres and divide without limit
(Slide 7)
What are 2 issues with trying to reverse ageing with telomerase?
It may lead to an increased risk of tumours
It may not even work! E.g mouse tissue has active telomerase but mice aren’t immortal
(Slide 8)
What are 5 signs that we die because “we are worn out”?
Answers Include:
The Wear-and-tear theory
Metabolic “rate-of-living” aka “burn-out”
Nutrients / Diet
Mitochondrial dysfunction
Free radical generation
Oxidative Stress / accumulated cellular and DNA damage
(Slide 9)
What does the “Rate-of-living” theory state?
“The duration of life varies inversely as the rate of energy expenditure increases” - in other words the length of life depends on the rate of living.
(Slide 10)
What is an example of an experiment which backs up the “rate-of-living” theory?
- Drosophila flies were kept in confinement under different temperatures
- Flies kept in higher temperatures were observed to have a shorter lifespan
- It was theorised that this is because a higher temperature increases the metabolic rate of the flies
^ “the length of life depends on the rate of living”
(Slide 10)
What is the free radical / superoxide theory of ageing?
Free radicals are by-products of mitochondrial respiration, with excessive ROS or RNS eventually leading to the damage of cellular components, such as DNA, proteins and lipids
(Slide 11)
What are 2 examples of oxygen free radicals?
Answers Include:
Superoxide
Hydroxyl
Peroxyl
Alkoxyl
Hydroperoxyl
(Slide 11)
What organism is used as a model of aging?
Drosophila flies
(Slide 13)
What is the mechanism that results in an decreased essential amino acid consumption and what is it mediated by?
Its mediated by TOR signalling, if there isn’t an adequate amount of nutrients then autophagy (consumption of the body’s own tissue as a metabolic process occurring in starvation and certain diseases) increases, and cell growth and protein synthesis decreases leading to an extended life
(Slide 12)
What happens when you connect the circulatory systems of old and a young mouse together?
The heart size of the old mouse decreases whereas the heart size of the young mouse increases
Note: debated whether this is de-aging or just rejuvenation of stem cell niche
(Slide 15)
What are 3 causative factors for aging?
Growth Differentiation Factor 11
CCL11
Oxytocin
(Slide 17)
What is Werner’s syndrome?
“Adult progeria” - manifests in older age.
First sign is the lack of growth spurt at puberty - patients are shorter and weigh less than than the general population. It’s a progressive disease from the 30s.
Death usually occurs in the 40ths - heart disease is a major contributor
(Slide 19)
What kind of disease is Werner’s syndrome?
Autosomal recessive disease
(Slide 19)
What gene does Werner’s syndrome affect?
The WRN gene
(Slide 21)
What does the absence of the WRN protein lead to?
Abnormalities in DNA repair, replication and telomere maintenance
(Slide 21)
What are 4 examples of WRN gene mutations and what do they lead to?
Nonsense mutations -> Changes the amino acid to a stop codon
Insertion and / or deletion -> Leading to a frameshift and subsequent termination
Substitution of splice junction -> Causing skipping exon and frameshift
One case of a missense mutation causing a change in codon -> Protein stability affected
Most mutation generate truncated (shortened) WRN protein lacking NLS found at the C terminal portion
(Slide 22)
What are 3 characteristics of Werner’s Syndrome cells?
Answers Include:
Cells derived from WS patients display accelerated ageing characteristics
Premature replicative senescence in culture: 20 rather than a 40-60 Hayflick limit
Prolonged S phase during cell cycle
Accumulate toxic DNA intermediates that lead to DNA damage and apoptotic responses
Increased chromosomal instability
Apoptotic response reduced
(Slide 23)
What are 2 characteristics of Werner’s Syndrome telomeres?
Telomere maintenance is an issue
Erosion rate is similar to normal cells!
Telomere erosion is not uniform - meaning that some telomeres may shorten faster than others
Werner’s syndrome cells may be more sensitive to the presence of a few dysfunctional telomeres, with just one possibly being sufficient to signal to a cell that it is time to enter replicative senescence
(Slide 23)
How can Werner’s syndrome lead to an increased cancer risk?
The WRN protein can bind to the C-terminus of the p53 in vivo
Werner’s syndrome fibroblasts display reduced p53-mediated apoptotic response
Cancer incidence increases due to failure to suppress genomic instability
(Slide 24)
What are 3 differences between Werner’s syndrome and “real” aging?
No increases tendency to neurodegeneration
In men, no prostate problems
No changes in the immune system
(Slide 26)
What is Hutchinson-Gilford Syndrome also known as?
Progeria
(Slide 27)
Is Hutchinson-Gilford syndrome autosomally dominant or recessive?
It can be both depending on what mutation it is
(Slide 27)
What are 5 symptoms of Hutchinson-Gilford syndrome?
First signs appear in the 1st year of life
Dwarfism
Lack of hair
Disproportionally large head
“Pinched” facial features
Lipodystrophy (almost complete absence of subcutaneous fat)
Incomplete extension at the knees and elbows indicating stiffness of joints
Coronary artery disease
Senile appearance
Patient’s hair starts turning grey by age 10
Individuals often die in their teens, usually of heart disease
(Slide 28)
What are 3 differences between Hutchinson-Gilford syndrome and real aging?
Males don’t develop prostate problems
No increased risk of cancer or cataracts
Rapid development of atherosclerosis (high blood pressure is very rare though)
Diabetes is very rare
Patients don’t get Alzheimer’s disease or suffer mental degeneration / dementia
(Slide 29)
Mutations in what gene cause Hutchinson-Gilford syndrome?
Its caused by mutations in the lamin A gene (LMNA)
(Slide 30)
What are lamins structural protein components of?
The nuclear lamina
(Slide 30)
How can a mutation in the lamin A gene lead to Hutchinson-Gilford syndrome?
- Most cases are caused by a mutation of a C -> T
- This results in a silent gly-gly change at codon 608 in exon 11
- This activates a cryptic splice site within exon 11 of the lamin A gene
- Protein product has a 50 amino acid deletion near the C-terminus
- This results in an aberrant (not acceptable standard) protein called progerin
(Slide 30)
What are 4 functions of lamin?
Answers Include:
Involvement in Mitosis
DNA synthesis and repair
RNA transcription and processing
Apoptosis
Organisation of chromatin structure
Regulation of gene expression
(Slide 31)
Does the progerin gene a gain or loss of function mutated protein?
Gain of function
(Slide 31)
What are 3 ways in which Hutchinnson-Gilford syndrome cells experience cell dysfunction?
They have a reduced lifespan in culture
They experience irregular nuclear phenotypes such as “blebbing of the nuclear envelope”
They have altered chromatin organisation
Reduced telomere length
Chronic DNA-damage response
(Slide 33)
What effects does hTERT (telomerase) have on Hutchinson-Gilford syndrome cells?
It extends cell lifespan by preventing cells from entering senescence and it reduces DNA-damage / proliferative defects associated with progerin
(Slide 33)
