lecture 3 biochemistry (week 2) Flashcards
what are the properties of aged cells?
slower division
change in cellular metabolism (decreased basal metabolic rate and slowing of all chemical reactions)
change in cellular function (production of non-physiological proteins, cytokines, growth factors, etc.)
inability to carry out apoptosis
decreased sensitivity of all receptors
reduced ability to withstand ROS
DNA instability, which may result in cancerous growth
why do we die in evolutionary terms?
we shouldn’t live after reproduction/raising offspring, because of competition with our own
what is hayflick limit of cell division?
isolate cells from human tissue, place in culture vessel with nutrient medium
cells divide and form confluent layer on vessel surface
discard half the cells, allow remainder to grow to confluency = one passage
continue to passage the cells
cell replication slows and stops after 50 ± 10 passages –> cells have reached the Hayflick limit and undergone replicative senescence
is replicative senescence the cause of ageing?
describe telomere ageing
repetitive DNA sequences at the ends of all human chromosomes
protect the ends of chromosomes from damage
they contain thousands of repeats of the six-nucleotide sequence TTAGGG
as cells divide there is a gradual shortening of the telomers
what is telomerase?
ribonucleoprotein, with two main components: the telomerase reverse transcriptase (hTERT) protein containing the catalytic component; and the hTR RNA (also called TERC) component, providing the template for telomeres synthesis.
telomerase adds the telomere repeats to the ends of chromosomes
most differentiated somatic cells do not express this enzyme
expressed in stem cells and some cancer cells
can ageing be reversed with telomerase?
may lead to increased risk of tumours
most mouse tissues have an active telomerase; however, mice are not immortal!
viral delivery of hTERT to mice causes telomere expansion and increases health span
this mouse model was already genetically resistant to cancer
worked better on old mice
mice with hyper-long telomeres show less metabolic ageing and longer lifespans
what is the link between nutrients/diet and ageing?
essential amino acid reduction in food increases lifespan in yeast, flies, and mice
mediated by TOR signalling (target of rapamycin, a kinase)
autophagy increases, cell growth and protein synthesis decrease extended life
rapamycin has been shown to increase lifespan
what observations were made in drosophila ageing?
median lifespan of 50 days
max of 90 days
gene mutants affect longevity
caloric restriction increases health span
what is GDF 11
growth differentiation factor 11 –> reverses age related cardiac hypertrophy
describe the fusion of old and young mices’ circulatory system
circulatory systems fused together
Heterochronic pair= old-young
isochronic pail= old-old or young-young
parabiosis mimics GDF11
heterochronic parabiosis leads to lack of the cEBP-a-Brm complex forming allowing more neurogenesis and angiogenesis
what are the progeroid syndromes?
diseases of premature ageing
hutchinson-gilford progeria syndrome – mutation in LMNA3-5 genes, growth retardation evident in first year of birth, skin atrophy, alopecia, osteolysis, cardiovascular complications
werner’s syndrome – mutation in WRN12 gene, symptoms appear in early teenage years, cataract development, atherosclerosis, skin atrophy, osteoporosis
describe werner’s syndrome
affects 1 in 1,000,000
1 in 40,000 in japan
also called adult progeria because it manifests in older age
first clinical sign = lack of growth spurt at puberty
short stature - 13cm shorter and 20kg lighter than average
progressive from 30s
death in 40s, heart disease
autosomal recessive
what are the genetics in the werner syndrome?
gene affected: WRN:
RecQL2 helicase protein
3’-5’ exonuclease
3’-5’ helicase activity
absence of WRN protein leads to abnormalities in DNA repair, replication and telomere maintenance
nonsense mutations –> changes the amino acid to a stop codon
insertion and/or deletion –> leading to a frameshift and subsequent termination
substitution at splice junction –> causing skipping of exons and frameshift
one case of missense mutation causing a change in codon –> protein stability affected
most mutations generate truncated WRN protein lacking NLS, found at the C terminal portion.
characteristics of the WRN cells
accelerated ageing
premature replicative senescence
20 rather than 60 hayflick limit
prolonged S phase during cycle
accumulate toxic DNA intermediates that lead to DNA damage and apoptotic responses
increased cancer risk as genomic instability is not suppressed because of reduced apoptosis –> p53 apoptotic pathway disrupted
characteristics of the WRN telomers
maintenance is an issue
on average WS cells erode at similar rate to normal
erosion is not uniform
WS cells may be sensitive to the presence for a few dysfunctional telomeres
one dysfunctional telomere may be sufficient to signals to cell that it is time to enter replicative senescence
what was observed in the WS animal model?
mice did not display obvious premature ageing or spontaneous cancer predisposition
murine Wrn might be functionally redundant, with other helicases may be compensating
combination of Wrn and Terc (telomerase RNA component) mutations DOES show progeria-like phenotype
differences between werner’s and real ageing
no increased tendency to neurodegeneration…but is that a ‘time’ issue
in men, no prostate problems
no changes in the immune system
describe hutchinson-gilford syndrome
1 in 8,000,000
autosomal dominant and autosomal recessive
slow growth, dwarfism
lack of hair
disproportionately 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.
generally a senile appearance
by age 10 patients hair start turning grey
Individuals often die in their teens typically of heart disease
differences between hutchinson-gilford syndrome and real ageing
males don’t develop prostate problems
no increased risk of cancer or cataracts
rapid development of atherosclerosis but high
blood pressure is very rare
diabetes is very rare
they don’t get alzheimer’s disease or suffer mental degeneration/dementia
hutchinson-gilford syndrome gene
caused by mutations in the lamin A gene (LMNA)
lamins are structural protein components of the nuclear lamina
a protein network underlying the inner nuclear membrane that determines nuclear shape and size.
lamins constitute a class of intermediate filament.
many cases caused by a single base substitution –> C to T transition
silent gly to gly change at codon 608 in exon 11
activates a cryptic splice site within exon 11
protein product has 50 amino acid deletion near c terminus
progerin produced
cell dysfunction in Hutchinson-Gilford syndrome
reduced lifespan in culture
irregular nuclear phenotypes such as
‘blebbing’ of the nuclear envelope
altered chromatin organization
reduced telomere length
Chronic DNA-damage response
hTERT (telomerase) extends HGPS cellular lifespan by preventing entry into senescence
hTERT also rescues DNA-damage/proliferative defects associated with progerin
