Anyone wants to study cell biology

1. Cell Ageing
Dr. Gauri Haval
A.G. College,
Pune

2. • Cells are the fundamental structures comprising
our bodies.
• Cellular decline, cell senescence results in ageing
of an organism.
• Cellular Senescence
• What is it?
• What causes it?
• Why is it important

3. Ageing
Demography
Ageing-related
disease
cardiovascular
disease, Alzheimer’s,
cancer, diabetes, etc
Evolution
theory
Biochemistry
Genetics Cell biology
Bioethics
Endocrinology
Comparative
biology
Regenerative
medicine
stem cells
Demography
Ageing-related
disease
cardiovascular
disease, Alzheimer’s,
cancer, diabetes, etc
Evolution
theory
Biochemistry
Genetics Cell biology
Bioethics
Endocrinology
Comparative
biology
Regenerative
medicine
stem cells

4. Comparative biology: How does ageing and longevity vary between species?
Are there non ageing organisms?
Urticina felina (Dahlia anemone) Non ageing
110 years
59 years
Maximum lifespans in mammals
3 years
Pinus longaeva (Bristlecone pine) ~5000 years

5. • Molecular biology/ biochemistry: What is
the basis of ageing and longevity?
• Cell biology: How does cellular
senescence contribute to ageing and
cancer? How are telomeres important?
• Immunology: Why does the immune
system fail in ageing? How does this
impact health in later life?

6. Cellular Theories
The Hayflick Limit (1961)
Pre-1961: “All metazoan cells are potentially
immortal. Ageing not cell autonomous”
Is replicative senescence the cause of ageing?
Leonard Hayflick
Fibroblasts: connective tissue cells, e.g. from skin
•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
Hayflick and Moorhead (1961)

7. • Hayflick worked on fibroblast cells. but this
phenomenon was observed in other cells too.
• The ageing cells show different morphology
• They are –bigger, have diverse morphotypes
• Enzyme β galactosidase has an abnormal
behavior. This enzyme is active at pH 4 in normal
cells. In ageing cells it is active at pH 6.
• Lysosomes increase in size and number.
• Mutations are observed in mitochondrial DNA.
• Decreased ability to express heat shock proteins
• Expression level of several genes changes
• Increased activity of metalloproteinase which
degrade extracellular matrix

8. • Telomers are non-coding regions at the tip of
chromosomes which show shortening in
ageing cells.
• Decline in the ability to respond to stress,
increasing homeostatic imbalance.
• CNS show most dramatic changes in protein
degradation
• Decline in immune function thus susceptibility
to infections, autoimmunity and cancer
increases.
• Post translational processes are affected.

9. EPITHELIUM
Basement Membrane
STROMA
Senescent
Epithelial Cell
Senescent Fibroblast
EPITHELIUM
Basement Membrane
STROMA
YOUNG TISSUE
OLD TISSUE
Degradative enzymes,
Inflammatory cytokines, etc.
AGING ?
BM + PreS Fb BM + Sen Fb
Pre-S Fb Sen Fb
b-casein
E-cadherin

10. Theories for cellular ageing
The free radical theory of ageing
Denham Harman (1956)
“A free radical is any species capable of independent existence
(hence the term ‘free’) that contains one or more unpaired
electron”
Barry Halliwell & John Gutteridge
O2 + e- -> O2
.-
Superoxide

11. Somatic Mutation theory
• The somatic mutation theory of aging points that the
accumulation of mutations in the genetic material of
somatic cells as a function of time results in a decrease
in cellular function. In particular, the accumulation of
random mutations inactivates genes that are important
for the functioning of the somatic cells of various organ
systems of the adult, which results in a decrease in
organ function. When the organ function decreases
below a critical level, death occurs. A significant
amount of research has shown that somatic mutations
play an important role in aging and a number of age
related pathologies. In this review, we explore evidence
for increases in somatic nuclear mutation burden with
age and the consequences for aging, cancer, and
neurodegeneration.

12. • During their lifetime, aging cells accumulate DNA
mutations and unrepaired lesions, progressively
shortened telomeres, defective mitochondria,
heterochromatic silencing, misfolded or
carbonylated proteins, and oxidized lipids to
name a few.
• When the balance between DNA damage and
repair is altered, it could enhance the frequency
of age-associated diseases. This suggests that the
accuracy of DNA synthetic processes is critical for
the maintenance of both the nuclear and
mitochondrial genomes and is necessary to
minimize the deleterious effects of aging.

13. Telomere loss theory
• In many human somatic tissues, a decline in cellular division
capacity with age appears to be linked to the fact that the
telomeres, which protect the ends of chromosomes, get
progressively shorter as cells divide. This is due to the absence of
the enzyme telomerase, which is normally expressed only in germ
cells (in testis and ovary) and in certain adult stem cells. Some have
suggested that in dividing somatic cells telomeres act as an intrinsic
“division counter,” perhaps to protect us against runaway cell
division as happens in cancer but causing aging as the price for this
protection (Campisi, 2005). While the loss of telomeric DNA is
commonly attributed to the so-called “end replication” —the
inability of the normal DNA copying machinery to copy right to the
very end of the strand in the absence of telomerase—it has been
found that stress, especially oxidative stress, has an even bigger
effect on the rate of telomere loss (von Zglinicki, 2002), telomere
shortening being greatly accelerated (or slowed) in cells with
increased (or reduced) levels of stress.

14. Clonal selection theory
• Clonal selection theory is a scientific
theory in immunology that explains the functions of cells of
the immune system (lymphocytes) in response to
specific antigens invading the body. The concept was
introduced by Australian doctor Frank Macfarlane Burnet in
1957, in an attempt to explain the great diversity
of antibodies formed during initiation of the immune
response. How the human immune system responds
to infection and how certain types of B and T lymphocytes are
selected for destruction of specific antigens.
• The theory states that in a pre-existing group of lymphocytes
(specifically B cells), a specific antigen activates (i.e. selects)
only its counter-specific cell, which then induces that
particular cell to multiply, producing identical clones for
antibody production. This activation occurs in secondary
lymphoid organs such as the spleen and the lymph nodes

15. • He explained immunological memory as the cloning of
two types of lymphocyte. One clone acts immediately
to combat infection whilst the other is longer lasting,
remaining in the immune system for a long time and
causing immunity to that antigen.
• When an antigen enters the blood or tissue fluids it is
assumed that it will attach to the surface of any
lymphocyte carrying reactive sites that correspond to
one of its antigenic determinants. Then the cell is
activated and undergoes proliferation to produce a
variety of descendants. In this way, preferential
proliferation is initiated of all those clones whose
reactive sites correspond to the antigenic determinants
on the antigens present in the body. The descendants
are capable of active liberation of soluble antibody and
lymphocytes, the same functions as the parental forms

16. Cell Death
• Cell death is the event of a biological cell ceasing
to carry out its functions. This may be the result
of the natural process of old cells dying and being
replaced by new ones, or may result from such
factors as disease, localized injury, or the death of
the organism of which the cells are
part. Apoptosis or Type I cell-death,
and autophagy or Type II cell-death are both
forms of programmed cell death, while necrosis is
a non-physiological process that occurs as a result
of infection or injury.[

17. • How do cells die?
• Cells can die because they are damaged, but most cells die by killing
themselves.
• There are several distinct ways in which a cell can die. Some occur by an
organised, ‘programmed’ process. Some cell death processes leave no
trace of the dead cell, whereas others activate the immune system with
substances from the dead cell.
• Apoptosis: is a form of cell death that prevents immune activation.
Apoptotic cells have a particular microscopic appearance. The cell
activates proteins called caspases that are normally dormant. These
caspases dismantle the cell from within. The apoptotic cell breaks into
small packages that can be engulfed by other cells. This prevents the cell
contents leaking out of the dying cell and allows the components to be
recycled.
• Necrosis: occurs when a cell dies due to lack of a blood supply, or due to a
toxin. The cells’ contents can leak out and damage neighbouring cells, and
may also trigger inflammation.

18. • Necroptosis: is similar in appearance to necrosis, in
that the dying cell’s contents can leak out. However,
like apoptosis, necroptosis is a programmed suicide
process triggered by specific proteins in the dying cell.
• Pyroptosis: is a form of cell death that occurs in some
cells infected with certain viruses or bacteria. A cell
dying by pyroptosis releases molecules, called
cytokines, that alert neighbouring cells to the infection.
This triggers inflammation, a protective response that
restricts the spread of the viruses and bacteria.

19. • Necrotic cell death
• Necrosis is cell death where a cell has been badly
damaged through external forces such as trauma or
infection and occurs in several different forms. In
necrosis, a cell undergoes swelling, followed by
uncontrolled rupture of the cell membrane with cell
contents being expelled. These cell contents often then
go on to cause inflammation in nearby cells.[14] A form
of programmed necrosis, called necroptosis, has been
recognized as an alternative form of programmed cell
death. It is hypothesized that necroptosis can serve as
a cell-death backup to apoptosis when the apoptosis
signaling is blocked by endogenous or exogenous
factors such as viruses or mutations. Necroptotic
pathways are associated with death receptors such as
the tumor necrosis factor receptor

20. • Necrosis is recognized by