Telomerase and the consequence of telomere dysfunction

AAAS Annual meeting

February 19th 2010

Carol Greider

Daniel Nathans Professor & Director Department of Molecular

Biology and Genetics

Johns Hopkins UniversitySchool of Medicine

Telomeres and Telomerase: Bridging Science and Society

Curiosity driven research establishes

fundamental knowledge that fuels

practical applications.

Telomeres are the ends of chromosomes

Protect ends Maintain length

Tetrahymena thermophila: single celled animal with 40,000 chromosomes

Elizabeth Blackburn & Joe Gall (1978): Defined telomere sequence as tandem repeats of TTGGGG

Replication

Replication

Replication

TTGGGG

Nature July 1984

Maintain linearplasmid in yeast

Telomere MarkerOri

Remove right telomereAdd yeast genomic DNAYeast telomeres stabilizeslinear plasmid

Tetrahymena and yeast: conservation of telomere function & telomere elongation

Telomerase activityidentified

Replication

Telomerase allows telomere length equilibrium maintenance

Telomerase

TR

TERT

Why does telomerase matter?

Cancer Tissue renewal

It is required for cells that must divide many times

Nature May 1990

Telomere shortening in cellular senescence

Vaziri et al. AJHG (1995)

Telomeres shorten with age

Telomerase is Telomerase is limiting in cellslimiting in cells

Using laboratory mice to probe telomere function

Telomerase knockout mouse

mTR+/ - mTR+/ -

mTR+/ + mTR+/ - mTR- / - G1 G1

G2 G2

G3 G3

G4 G4

G5 G5

G6 G6

Cell deathorSenescence

Blasco et al. Cell 1997

Quantitative analysis of telomere length

Telomeres shorten progressively in telomerase-null mice

mTR+/ - mTR+/ -

mTR- / - (G1) G1

G2 G2

G3 G3

G4 G4

G5 G5

G6

Blasco et al. Cell 1997

Loss of telomere sequence leads to loss of telomere function

WT KO-G2

KO-G4 KO-G6

The consequences of short telomeres

mTR+/ - mTR+/ -

mTR+/ + mTR+/ - mTR- / - G1 G1

G2 G2

G3 G3

G4 G4

G5 G5

G6 G6

Cell deathorSenescence

Telomere shortening leads to cell death

Cell Death

Replication

Replication

Replication

Short telomeres limit cell growth

Cancer Tissue renewal

Nature 2001

• Skin and nail problems– Skin hyperpigmentation– Rashes– Abnormal nail growth

Dyskeratosis congentia causes bone marrow failure

• Mortality–Bone marrow failureBone marrow failure–Cancer–other?

TERT mutations cause autosomal dominant inheritance of dyskeratosis congentia

Armanios et al. PNAS (2005)

Genetic anticipation.

Affected people are heterozygous for hTR or hTERT mutations.

Dominant negative or haploinsufficiency?

Hopkins Family 1

I 1 2

1 2

1 2 3 4

3 4 5 6 7II

III

?

Cast/Ei mice have short telomeres similar to humans

Hemann & Greider NAR 2000

Bred mTR null allele onto Cast/Ei background

Progressive telomere shortening during mTR+/- breeding

HG5

mTR+/ - mTR+/ -

HG1 HG1

HG2 HG2

HG3 HG3

HG4 HG4

Short telomeres in CAST/EiJ mTR+/- mice

Hao et al. Cell 2005

Telomerase is Telomerase is limiting in cellslimiting in cells

Telomere shortening at each mTR+/- generation affects survival of offspring

HG5 KO(G5)WT5*

mTR+/ - mTR+/ -

HG1 HG1

HG2 HG2

HG3 HG3

HG4 HG4

Decreased survival of mTR-/- from later generation heterozygous crosses

Inheritance of short telomeres decreases survival.Resembles genetic anticipation in dyskeratosis congenita.

0 100 200 300 4000

25

50

75

100KO from HG3 parents

KO from HG6 parents

WT

KO from HG8 parents

Days

Percent survival

Armanios et al. AJHG 2009

Telomere shortening during mTR+/- breeding affects wildtype offspring

HG5 KO(G5)WT5*

mTR+/ - mTR+/ -

HG1 HG1

HG2 HG2

HG3 HG3

HG4 HG4

Short telomeres in Wt5* mice

HG4 HG4

KO HG5 WT5*

Hao et al. Cell 2005

Corrected Spleen Weight

0

1

2

3

4

5

6

7

wt (n=6) wt8*1 (n=7) ko (n=9)

Short telomeres cause phenotypes in Wt* mice

TESTIS APOPTOSIS SPLEEN WEIGHT

Genetic disease in the absence of telomerase mutation (Occult genetic disease)

Wt* mice reestablish telomere equilibrium after several generations

Armanios et al. AJHG 2009

mTR+/ - HG4 mTR+/ - HG4

mTR+/ + WT5*1 mTR+/ +WT5*1

mTR+/ +WT5*2 mTR+/ +WT5*2

mTR+/ +WT5*3 mTR+/ +WT5*3

mTR+/ +WT5*4 mTR+/ +WT5*4

Telomerase is limiting in cellsTelomerase is limiting in cells

Reestablishment of telomere length equilibrium rescues testes phenotype

Armanios et al. AJHG (2009)

Telomere shortening implicated in several diseases

Hopkins Family 1

I 1 2

1 2

1 2 3 4

3 4 5 6 7II

III

?

NEJM 357 p1317 (2007)

Short telomeres in lung disease

Many diseases seen in families with insufficient telomerase share features of age-related disease

Syndromes of telomere shortening:the tip of the iceberg

Wide distribution of telomere length in the human population

Valdes et al, 2005 Lancet (2005)

Bridging Science and Society: Understanding of telomeres came from curiosity about chromosome maintenance

Summary and implications

Telomeres are required for chromosome end protection.

Telomerase is essential for telomere maintenance.

Telomere shortening leads to cell death or senescence after many cell divisions.

Short telomeres limit tissue renewal.

Telomere length may predict onset of certain age related diseases.

Fundamental discoveries lead to clinical applications

Greider Lab

Carla Connely

Telomere length regulation

Margaret Strong

Response to telomere dysfunction

Vinny Raganathan

Sofia Vidal-Cardenas

Collaborators

Baktiar KarimDavid Huso

Nini Guo

Jonathan Alder

Mary Armanios

Erin Parry

Tammy Morrish

Oncology

Pathology

New discoveries come from unlikely places

Telomere length predicts mortality rate

Cawthon et al. Lancet (2005)