Deleterious assembly of mutant p.S143P lamin A/C causes ER stress in familial dilated cardiomyopathy

Abstract

Mutation of the LMNA gene, encoding nuclear lamin A/C, is a common cause of familial dilated cardiomyopathy (DCM). Among Finnish DCM patients, the founder mutation c.427T>C (p.S143P) is the most frequently reported genetic variant. Here we show that p.S143P lamin A/C is more nucleoplasmic and soluble than wild type lamin A/C and accumulates into large intranuclear aggregates in a fraction of cultured patient fibroblasts as well as in cells ectopically expressing either FLAG- or GFP-tagged p.S143P lamin A. In fluorescence loss in photobleaching (FLIP) experiments, non-aggregated EGFP-tagged p.S143P lamin A is significantly more dynamic. In in vitro association studies p.S143P lamin A failed to form appropriate filament structures but instead assembled into disorganized aggregates similar to those observed in patient cell nuclei. A whole genome expression analysis revealed an elevated unfolded protein response (UPR) in p.S143P lamin A/C expressing cells. Additional endoplasmic reticulum (ER) stress induced by tunicamycin reduced the viability of mutant lamin expressing cells further. In summary, p.S143P lamin A/C affects normal lamina structure and influences the cellular stress response, homeostasis and viability.

The nuclear envelope: LINCing tissue mechanics to genome regulation in cardiac and skeletal muscle

“…Disease-causing mutations likely affect such properties. In one study, the LMNA-S143P mutant, which causes familial DCM, led to lamin A proteins being more mobile and less tightly bound to the lamin network than wild-type (WT) proteins [21]. Lamin staining and confocal microscopy of DCM patient tissue showed that in the S143P mutant, lamins were mislocalized to the nucleoplasm.…”

Imbalance of ER and Mitochondria Interactions: Prelude to Cardiac Ageing and Disease?

“…Accumulating evidence indicates that ER stress and mitochondrial stress play important roles in cardiomyopathy [78][79][80], of which approximately 50% is inherited [81]. Elevated expression of the ER stress markers GRP78, eIF2α, and XBP1 and increased activation of the UPR ER is observed in patients with the p.S143P mutation in the intermediate filament gene lamin A/C, the most frequently reported genetic variant in inherited dilated cardiomyopathy (DCM) [82]. Enhanced mitochondrial oxidative stress and mitochondrial dysfunction were observed in the heart of cats with hypertrophic cardiomyopathy (HCM) [83].…”

The clinical outcome of LMNA missense mutations can be associated with the amount of mutated protein in the nuclear envelope

“…A recent study of a missense mutation suggested that mutant lamin protein may accumulate and form intra-nuclear aggregates and thereby exhibit a dominant negative effect. 11 In the current study, we report the disease expression associated with a LMNA-p.Arg216Cys variant in a large family with 36 mutation carriers. The phenotype was remarkable since most of the affected mutation carriers had a late onset of disease manifestations and a favourable prognosis.…”

“…It has been suggested that haploinsufficiency is the disease mechanism in patients carrying truncating LMNA mutations, while LMNA missense mutations have been proposed to act through a dominant negative pathway . A recent study of a missense mutation suggested that mutant lamin protein may accumulate and form intra‐nuclear aggregates and thereby exhibit a dominant negative effect …”