MOUSE MODEL OF
WERNER SYNDROME
Table 1. Summary of phenotypes observed in the Wrn+/+
Terc-/- and Wrn-/- Terc-/- mouse models
HUMAN WS
MOUSE MODELS
Wrn-/- Terc-/-
Long
telomeres
Wrn+/+ Terc-/-
Control*
Wrn-/- Terc-/-
Short
telomeres
Osteoporosis
Cataracts
Type II diabetes
Skin defects
Hypogonadism
Atherosclerosis
Genome instability
Mesenchymal tumours
No
No
No
No
No
No
No
+
No
No
No
++
++
No
+++
+
++++
++++
++++
++++
++++
No
++++
++++
*Telomerase null animals display a subset of aging phenotypes but do
not display many of the symptoms associated with human aging.
1. Telomere biology differences
2. Telomerase activity
3. Redundant function of murine WRN
4. Inter-individual differences
10-15kb 40-80kb
ACCCAC 3’ 5’
somatic cell
telomerase
ACCCAC 3’ 5’
ACCCAC3’ 5’
telomerase
somatic
cell
WRN
Other RecQ
helicases
WRN
Other RecQ helicases
WS
fibroblast
Normal
fibroblast
Chromosomal
fusions and
non-reciprocal
chromosomal
translocations
mTerc
deletion
� Mutation rate
Premature loss
of proliferative
capacity
Wrn-/-
NO aging phenotype
Premature aging phenotype
Wrn-/- Terc-/-
DNA damage
response
Premature
replicative
senescence
Sister
telomere
loss (STL) Dysfunctional telomere
Normal telomere
Lagging
Leading
5’
5’
5’ 5’
5’
5’
5’
5’
3’
3’
3’
3’
3’
3’ 3’
3’ 3’
FISH analysis of WS cells.
Telomeres were hybridized with a
TRITC-[TTAGGG]4 probe and are
shown in the red channel. Arrows
indicate missing telomeric staining
from single sister chromatids.
WS patient
Slow growth rates
Premature senescence
Genome instability
Telomere dysfunction
S
G1
G2
M telomeres
STALLED
REPLICATION FORK
G
G
WRN-/-
Lagging
Lagging
Leading
Leading
5’
5’
3’
TELOMERE DYSFUNCTION CONTRIBUTES TO WS PATHOLOGY
WRN – TRF1/2 and POT1
POT1
D-loop
T-loop
WRN
Uncapping/
recapping
POT1
ROS ROS
TR
F1
TR
F2
Repair of
oxidative
damage
WRN
TR
F1
TR
F2
POT1
TR
F2
TR
F1
loopNHEJ
WRN – Ku and DNA-PKcs
Telomere
T loop
D loop
Shelterin Shelte
DNA
replication
Apoptosis
DNA repair
Transcription
Recombination
Telomere ends
WRN
Ku
DNA-
PKcs
DSB
End
recognition
Processing
Ligation
WRN INTERACTS WITH RESIDENT TELOMERIC PROTEINS
Werner Syndrome (WS) is a rare genetic disorder that mimics
the characteristics of normal human aging. Since aging is likely
caused by numerous genetic and environmental factors acting
simultaneously, it is very difficult to dissect the roles of individual
genes in this process. In order to simplify such complexity, the
goal of this review is focused on the relationship between three
key components: aging, telomeres and the enzyme telomerase, taking Werner syndrome as a model of human aging.
WERNER SYNDROME AS A MODEL OF AGING:
THE ROLE OF WRN AT TELOMERES AND THE IMPACT OF TELOMERASE
Anna Esteve Garcia. Facultat de Biociències. Curs acadèmic 2013-2014. Universitat Autònoma de Barcelona (Catalunya, Espanya)
WRN
TR
F1
TR
F2
TR
F1
TR
F2
TR
F1
TR
F2
TR
F1
TR
F2
TR
F1
TR
F2
T
RF
1
TR
F2
TR
F1
TR
F2
TR
F1
TR
F2
TR
F1
TR
F2
Both shortened telomeres
and a lack of telomerase
are required, at least in
mice, for WS disease
manifestation.
FUTURE APPROACHES
Increased
telomerase
expression
WS aging
associated
phenotypes
INCREASED
HEALTHSPAN
WS fibroblasts
WS fibroblasts
DIFFERENT STUDIES EXEMPLIFY THIS INTERDEPENDENT FUNCTION BETWEEN WRN AND TELOMERASE:
STL rescued Sister telomere
signal
G strand C strand
Expression of
exogenous
TERT or WRN
WS
patient DNA induced lesions reversion
4NQO
WS fibroblasts
Sensitivity reversed
Colony forming
capacity
High sensitivity
Colony forming
capacity loss
Premature aging protection
Restoration
of telomere
function in
WS iPSCs WS
fibroblasts
WS
iPSCs
WS fibroblasts WS fibroblasts
Helicase-deficient
WRN WRN
WS
phenotypes
WRN preserves the
genome integrity of WS
fibroblasts, protecting
telomeres erosion
BOTH WRN AND TELOMERASE RESCUE DEFICIENCIES IN WS FIBROBLASTS
Extension of
telomeres
TERT
mTERT
TELOMERE
DYSFUNCTION
GENOME
INSTABILITY
? CHROMOSOME
FUSIONS
ST
L
replic
ation
fusio
n
ST
L
replic
atio
n
replic
ation
bre
akag
e
bre
akag
e
fusio
n
Fusion with telomeric
DNA at fusion site
Fusion without telomeric
DNA at fusion site
Telomere loss
(STL)
Unprotected
telomere ends
Controls cells WS cells
BOTH CONTROL
AND WS CELLS
WITH
CHROMOSOMAL
ABERRATIONS
DNA at fusion si
DRUG INTERVENTION IN PREVENTING ACCELERATED
AGING IN WS
Telomere dysfunction &
chromosomal aberration
Decreased cellular
lifespan of WS
fibroblasts
SENESCENCE
Activation
of p38
WRN gene
mutation
Oxidative
stress
ACCELERATED
PREMATURE
AGING
PREVENTION
Because of their G-rich nature,
telomeres are fraught with
potential obstacles to DNA
replication that block replication
forks. WRN is capable of
unwinding such structures,
preventing collapse in telomere
forks. In its absence, telomeric
signals are only detected at a
single chromatid, phenotype
termed sister telomere loss
(STL).
WRN participates in several important DNA metabolic pathways. These include
DNA repair, replication, recombination and telomere maintenance. WRN plays a
role at telomeres as it interactions with other resident telomeric proteins.
Elevated stress response
correlates with the activation
of the stress-associated
mitogen-activated protein
kinase (MAPK) p38.
Activation of p38 stabilizes
p21 and promotes entry into
cellular senescence.
SB203580 is a drug that
targets p38 activity. This drug
treatment extends the
replicative lifespan of WS
fibroblasts in vitro.
Detected
by FISH
? ?
?
WERNER SYNDROME AS A MODEL OF HUMAN AGING Main features Molecular level Bilateral cataracts
Greying hair and hair loss
Short stature
Scleroderma-like skin
Atherosclerosis
Ischemic heart disease
Osteoporosis
Type II diabetes mellitus
Hypogonadism
Cancer predisposition
(sarcomas)
Bloom Syndrome
Cockayne Syndrome
Xeroderma Pigmentosum
Rothmund-Thomson Syndromes
Hutchinson-Guilford Progeria Syndrome
WERNER
SYNDROME
geri Synd
Progeroid aging
syndromes
cr.8
WRN
Human RecQ helicase family
Exonuclease and helicase activities
Multiple
functions
Normal human
aging
New potent and
selective inhibitors
WRN
WRN loss induces the wide range of premature aging phenotypes seen in Werner Syndrome.
The key event, caused by WRN mutations, is the dysfunction of telomeres. Thus, the cascade started by
telomere dysfunction explains the majority of the WS pathological phenotypes.
Telomerase phenotypes recruitment as well as the WS mouse model generation reinforce this hypothesis.
The SB203580 drug treatment may lead to novel therapies involving MAPK.
