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.