X-Message-Number: 27896
Date: Tue, 2 May 2006 19:59:51 -0700 (PDT)
From: Doug Skrecky <>
Subject: mutated lamin A likely key driver of human aging

[Farnesyltransferase inhibitors or lamin A specific oligonucleotides offer
the prospect of effective treatments for Hutchinson-Gilford
progeria. Since the Lamin A defect responsible for this progeria also
plays a role in normal human aging, this raises the interesting
possibility of a significant increase in the normal human lifespan in the
near future. Treatment of those suffering from progeria is expected

Science. 2006 Apr 27; [Epub ahead of print]
Lamin A-Dependent Nuclear Defects in Human Aging.
Scaffidi P, Misteli T.
National Cancer Institute, NIH, Bethesda, MD 20892 USA.
Mutations in the nuclear structural protein lamin A cause the premature
aging syndrome Hutchinson-Gilford Progeria (HGPS). Whether lamin A plays
any role in the normal aging process is unknown. Here we show that the
same molecular mechanism responsible for HGPS is active in healthy
cells. Cell nuclei from old individuals acquire similar defects as HGPS
patient cells including changes in histone modifications and increased
DNA damage. Age-related nuclear defects are caused by sporadic use in
healthy individuals of the same cryptic splice site in lamin A whose
constitutive activation causes HGPS. Inhibition of this splice site
reverses the nuclear defects associated with aging. These observations
implicate lamin A in physiological aging.

J Clin Invest. 2006 Mar;116(3):743-52.
Prelamin A and lamin A appear to be dispensable in the nuclear lamina.
  Lamin A and lamin C, both products of Lmna, are key components of the
nuclear lamina. In the mouse, a deficiency in both lamin A and lamin C
leads to slow growth, muscle weakness, and death by 6 weeks of
age. Fibroblasts deficient in lamins A and C contain misshapen and
structurally weakened nuclei, and emerin is mislocalized away from the
nuclear envelope. The physiologic rationale for the existence of the 2
different Lmna products lamin A and lamin C is unclear, although several
reports have suggested that lamin A may have particularly important
functions, for example in the targeting of emerin and lamin C to the
nuclear envelope. Here we report the development of lamin C-only mice
(Lmna(LCO/LCO)), which produce lamin C but no lamin A or prelamin A (the
precursor to lamin A). Lmna(LCO/LCO) mice were entirely healthy, and
Lmna(LCO/LCO) cells displayed normal emerin targeting and exhibited only
very minimal alterations in nuclear shape and nuclear
deformability. Thus, at least in the mouse, prelamin A and lamin A appear
to be dispensable. Nevertheless, an accumulation of farnesyl-prelamin A
(as occurs with a deficiency in the prelamin A processing enzyme
Zmpste24) caused dramatically misshapen nuclei and progeria-like disease
phenotypes. The apparent dispensability of prelamin A suggested that
lamin A-related progeroid syndromes might be treated with impunity by
reducing prelamin A synthesis. Remarkably, the presence of a single
Lmna(LCO) allele eliminated the nuclear shape abnormalities and
progeria-like disease phenotypes in Zmpste24-/- mice. Moreover, treating
Zmpste24-/- cells with a prelamin A-specific antisense oligonucleotide
reduced prelamin A levels and significantly reduced the frequency of
misshapen nuclei. These studies suggest a new therapeutic strategy for
treating progeria and other lamin A diseases.

Science. 2006 Mar 17;311(5767):1621-3. Epub 2006 Feb 16.
A protein farnesyltransferase inhibitor ameliorates disease in a mouse
model of progeria.
  Progerias are rare genetic diseases characterized by premature
aging. Several progeroid disorders are caused by mutations that lead to
the accumulation of a lipid-modified (farnesylated) form of prelamin A, a
protein that contributes to the structural scaffolding for the cell
nucleus. In progeria, the accumulation of farnesyl-prelamin A disrupts
this scaffolding, leading to misshapen nuclei. Previous studies have
shown that farnesyltransferase inhibitors (FTIs) reverse this cellular
abnormality. We tested the efficacy of an FTI (ABT-100) in
Zmpste24-deficient mice, a mouse model of progeria. The FTI-treated mice
exhibited improved body weight, grip strength, bone integrity, and
percent survival at 20 weeks of age. These results suggest that FTIs may
have beneficial effects in humans with progeria.

[Interesting that nuclear deformation is here associated with
proliferation defects. Some believe this to be the major reason for
escalating age-associated mortality risks from vascular disease.]

Cell Biol Int. 2005 Dec;29(12):1032-7. Epub 2005 Nov 28.
Nuclear deformation characterizes Werner syndrome cells.
  Mutations in the lamin A gene have been shown, among other defects, to
give rise to Hutchinson-Gilford progeria syndrome (HGPS) and to atypical
Werner syndrome (WS), both of which are progeroid disorders. Here, we
have investigated well-characterized WS patient cell strains that are
compound heterozygous for mutations in the WRN gene. As in HGPS and in
atypical WS, we found nuclear deformations to be characteristic of all
cell strains studied. In WS cells centrosome number, assembly of the
nuclear lamina and nuclear pore distribution occurred
normally. Furthermore, nuclear deformations were not associated with a
defect in lamin A expression. We propose that nuclear deformation is a
universal characteristic of progeroid cells and may result from slow cell
cycle progression.

Proc Natl Acad Sci U S A. 2005 Nov 15;102(46):16690-5. Epub 2005 Nov 3.
Age-related changes of nuclear architecture in Caenorhabditis elegans.
  Mutations in lamins cause premature aging syndromes in humans,
including the Hutchinson-Gilford Progeria Syndrome (HGPS) and Atypical
Werner Syndrome. It has been shown that HGPS cells in culture undergo
age-dependent progressive changes in nuclear architecture. However, it is
unknown whether similar changes in nuclear architecture occur during the
normal aging process. We have observed that major changes of nuclear
architecture accompany Caenorhabditis elegans aging. We found that the
nuclear architecture in most nonneuronal cell types undergoes progressive
and stochastic age-dependent alterations, such as changes of nuclear shape
and loss of peripheral heterochromatin. Furthermore, we show that the
rate of these alterations is influenced by the insulin/IGF-1 like
signaling pathway and that reducing the level of lamin and
lamin-associated LEM domain proteins leads to shortening of lifespan. Our
work not only provides evidence for changes of nuclear architecture
during the normal aging process of a multicellular organism, but also
suggests that HGPS is likely a result of acceleration of the normal aging
process. Because the nucleus is vital for many cellular functions, our
studies raise the possibility that the nucleus is a prominent focal point
for regulating aging.

Hum Genet. 2005 Dec;118(3-4):444-50. Epub 2005 Oct 6.
Correction of cellular phenotypes of Hutchinson-Gilford Progeria cells by
RNA interference.
  The great majority of cases of the Hutchinson-Gilford progeroid
syndrome (HGPS) ("Progeria of Childhood'') are caused by a single
nucleotide mutation (1824 C->T) in the LMNA gene which encodes lamin A
and C, nuclear intermediate filaments that are important components of
the nuclear lamina. The resultant mutant protein (Delta50 lamin A) is
thought to act in a dominant fashion. We exploited RNA interference
technology to suppress Delta50 lamin A expression, with the long range
goal of intervening in the pathogenesis of the coronary artery
atherosclerosis that typically leads to the death of HGPS patients. Short
hairpin RNA (shRNA) constructs were designed to target the mutated
pre-spliced or mature LMNA mRNAs, and were expressed in HGPS fibroblasts
carrying the 1824 C->T mutations using lentiviruses. One of the shRNAs
targeted to the mutated mRNA reduced the expression levels of
Delta50 lamin A to 26% or lower. The reduced expression was associated
with amelioration of abnormal nuclear morphology, improvement of
proliferative potential, and reduction in the numbers of senescent
cells. These findings provide a rationale for potential gene therapy.

J Lipid Res. 2005 Dec;46(12):2531-58. Epub 2005 Oct 5.
Prelamin A, Zmpste24, misshapen cell nuclei, and progeria--new evidence
suggesting that protein farnesylation could be important for disease
  Prelamin A undergoes multistep processing to yield lamin A, a
structural protein of the nuclear lamina. Prelamin A terminates with a
CAAX motif, which triggers farnesylation of a C-terminal cysteine (the C
of the CAAX motif), endoproteolytic release of the last three amino acids
(the AAX), and methylation of the newly exposed farnesylcysteine
residue. In addition, prelamin A is cleaved a second time, releasing 15
more residues from the C terminus (including the farnesylcysteine methyl
ester), generating mature lamin A. This second cleavage step is carried
out by an endoplasmic reticulum membrane protease, ZMPSTE24. Interest in
the posttranslational processing of prelamin A has increased with the
recognition that certain progeroid syndromes can be caused by mutations
that lead to an accumulation of farnesyl-prelamin A. Recently, we showed
that a key cellular phenotype of these progeroid disorders, misshapen cell
nuclei, can be ameliorated by inhibitors of protein farnesylation,
suggesting a potential strategy for treating these diseases. In this
article, we review the posttranslational processing of prelamin A,
describe several mouse models for progeroid syndromes, explain the
mutations underlying several human progeroid syndromes, and summarize
recent data showing that misshapen nuclei can be ameliorated by treating
cells with protein farnesyltransferase inhibitors.

Proc Natl Acad Sci U S A. 2005 Oct 4;102(40):14416-21. Epub 2005 Sep 26.
Inhibiting farnesylation reverses the nuclear morphology defect in a HeLa
cell model for Hutchinson-Gilford progeria syndrome.
  Hutchinson-Gilford progeria syndrome (HGPS) is a devastating premature
aging disease resulting from a mutation in the LMNA gene, which encodes
nuclear lamins A and C. Lamin A is synthesized as a precursor (prelamin
A) with a C-terminal CaaX motif that undergoes farnesylation,
endoproteolytic cleavage, and carboxylmethylation. Prelamin A is
subsequently internally cleaved by the zinc metalloprotease Ste24
(Zmpste24) protease, which removes the 15 C-terminal amino acids,
including the CaaX modifications, to yield mature lamin A. HGPS results
from a dominant mutant form of prelamin A (progerin) that has an internal
deletion of 50 aa near the C terminus that includes the Zmpste24 cleavage
site and blocks removal of the CaaX-modified C terminus. Fibroblasts from
HGPS patients have aberrant nuclei with irregular shapes, which we
hypothesize result from the abnormal persistence of the farnesyl and/or
carboxylmethyl CaaX modifications on progerin. If this hypothesis is
correct, inhibition of CaaX modification by mutation or pharmacological
treatment should alleviate the nuclear morphology defect. Consistent with
our hypothesis, we find that expression in HeLa cells of GFP-progerin or
an uncleavable form of prelamin A with a Zmpste24 cleavage site mutation
induces the formation of abnormal nuclei similar to those in HGPS
fibroblasts. Strikingly, inhibition of farnesylation pharmacologically
with the farnesyl transferase inhibitor rac-R115777 or mutationally by
alteration of the CaaX motif dramatically reverses the abnormal nuclear
morphology. These results suggest that farnesyl transferase inhibitors
represent a possible therapeutic option for individuals with HGPS and/or
other laminopathies due to Zmpste24 processing defects.

[Blocking the manufacture of mutated lamin A with a modified
oligonucleotide reverses progeria in the test tube as well.]

Nat Med. 2005 Apr;11(4):440-5. Epub 2005 Mar 6.
Reversal of the cellular phenotype in the premature aging disease
Hutchinson-Gilford progeria syndrome.
  Hutchinson-Gilford progeria syndrome (HGPS) is a childhood premature
aging disease caused by a spontaneous point mutation in lamin A (encoded
by LMNA), one of the major architectural elements of the mammalian cell
nucleus. The HGPS mutation activates an aberrant cryptic splice site in
LMNA pre-mRNA, leading to synthesis of a truncated lamin A protein and
concomitant reduction in wild-type lamin A. Fibroblasts from individuals
with HGPS have severe morphological abnormalities in nuclear envelope
structure. Here we show that the cellular disease phenotype is reversible
in cells from individuals with HGPS. Introduction of wild-type lamin A
protein does not rescue the cellular disease symptoms. The mutant LMNA
mRNA and lamin A protein can be efficiently eliminated by correction of
the aberrant splicing event using a modified oligonucleotide targeted to
the activated cryptic splice site. Upon splicing correction, HGPS
fibroblasts assume normal nuclear morphology, the aberrant nuclear
distribution and cellular levels of lamina-associated proteins are
rescued, defects in heterochromatin-specific histone modifications are
corrected and proper expression of several misregulated genes is
reestablished. Our results establish proof of principle for the
correction of the premature aging phenotype in individuals with HGPS.

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