Abstract 20645: Lamin A/C Aggregation is a Major Factor Underlying Skeletal and Cardiac Muscle Laminopathies
Background: LMNA encodes lamin A/C, which are comprised of an N-terminal head domain, a central rod consisting of four coiled-coil domains (CCD 1A, 1B, 2A, and 2B) and a C-terminal immunoglobulin-like (Ig-like) domain. These intermediate filament proteins form the nuclear lamina and play a critical role in nuclear shape, transcriptional regulation, chromatin organization and other functions. Nearly two hundred missense mutations have been linked to numerous diseases affecting: 1) cardiac muscle (e.g. dilated cardiomyopathy), 2) skeletal muscle (e.g. Emery-Dreifuss muscular dystrophy), 3) adipose tissue (e.g. Dunnigan-type familiar partial lipodystrophy) or 4) multiple tissues (e.g. progeria). While significant advances have been made in understanding the molecular mechanisms behind laminopathies, it remains unclear how mutations spanning this single protein can lead to such diverse, tissue specific effects.
Results: Using a GFP tagged Lamin A construct, we systematically characterized nuclear aggregation of Lamin A mutations over-expressed in HEK cells for each CCD and the Ig-like domain. Of 145 mutations characterized, 79 (55%) showed increased aggregation throughout the nucleus compared to WT with marked differences between diseases where 65/82 (79%) of skeletal muscle, 19/50 (38%) of cardiac muscle, 4/17 (23%) of lipodystrophy and 0/17 (0%) of premature aging mutations exhibited increased aggregation compared to WT. By domain, 45-57% of CCD 1A, 1B, 2B and Ig-like domain mutations showed increased aggregation, while 92% of CCD 2A mutations showed increased aggregation. Finally, using a recombinant Ig-like domain solubility assay in E.coli as a proxy for misfolding, we tested 44 mutations and found that 26 (59%) had decreased solubility. By disease, 22/29 (76%) of skeletal muscle, 2/12 (17%) of cardiac, 2/10 (20%) of lipodystrophy and 0/2 (0%) of progeria mutations showed decreased solubility, which correlated with aggregation.
Conclusions: This study identifies Lamin A aggregation and Ig-like domain misfolding as major mechanisms underlying laminopathies but to different degrees (i.e. skeletal > cardiac > lipodystrophy), which has important implications for developing therapeutic strategies.
Author Disclosures: C.L. Anderson: None. T.C. Routes: None. T.J. Kamp: None.
- © 2016 by American Heart Association, Inc.