Summary / Abstract
The nuclear Lamins are intermediate filament proteins that underlie the nuclear envelope. Lamins assemble
into bundled filaments that strengthen the nucleus and scaffold the genome. The LMNA locus encodes the Lamin
A and C proteins; hundreds of mutations to LMNA have been linked to more than 10 distinct syndromes,
collectively referred to as “laminopathies”. Disease-linked LMNA mutations are found in every domain of these
proteins, and no clear genotype-phenotype correlations exist. LMNA-linked laminopathies primarily afflict the
cardiovascular system, muscle, skin, connective tissue, bone, and fat. A major goal of our research program is
to determine why specific tissues are especially vulnerable to LMNA mutations while the Lamin A/C proteins are
broadly expressed.
In this proposal, we present evidence that modulation of protein lifetime is a major novel axis that regulates
both the function of Lamin A/C and the effects of laminopathy mutations. We have discovered that the lifetime of
the Lamin A/C proteins varies over an order of magnitude across tissues, and these proteins are especially long-
lived in the tissues that are most vulnerable to laminopathies. In the devastating laminopathy Hutchinson-Gilford
progeria syndrome (HGPS), production of a toxic Lamin A isoform called “Progerin” disrupts nuclear function
and causes accelerated aging. We determined that this mutation further slows the turnover of Lamin A in the
diseased cardiovascular system, where it accumulates over time and interferes with the turnover of hundreds of
other proteins. These findings raise key questions that will be addressed by our Aims.
Firstly, while hundreds of mutations to LMNA are linked to human disease, we do not yet know how these
other mutations affect Lamin A/C protein stability and/or aggregation within diseased tissues. We will leverage a
novel in vivo metabolic labeling approach that we developed to probe the effect of another laminopathy mutation
on protein turnover in the LmnaH222P mouse model (Aim 1). Secondly, we do not understand how Lamin A/C
protein lifetime is modulated across tissues or in disease states. Differences in protein folding and/or assembly
state often underlie differences in protein turnover rate, but we know very little about the structure of the Lamin
A/C polymers in the cellular milieu or how variable these are across different tissue contexts. In Aim 2, we will
use functional proteomics to probe the folded state of the Lamin A/C proteins in situ, and we will test the
hypothesis that Lamins sense mechanical information – such as tissue strain – to alter their folded state. Thirdly,
we know that the Lamins perform the important function of scaffolding heterochromatin at the nuclear periphery
into repressive lamina-associated domains (LADs), yet we do not understand the consequences of variable
Lamin A/C folded state on this Lamin function. In Aim 3, we will apply a novel genome binding analysis technique
to map LADs and to define their repressive function within healthy and diseased tissues.
