Perinuclear damage from nuclear envelope deterioration elicits stress responses that contribute toLMNAcardiomyopathy

Abstract

Mutations in the LMNA gene encoding nuclear lamins A/C cause a diverse array of tissue-selective diseases, with the heart being the most commonly affected organ. Despite progress in understanding the molecular perturbations emanating from LMNA mutations, an integrative understanding of the pathogenesis leading to cardiac dysfunction remains elusive. Using a novel cell-type specific Lmna deletion mouse model capable of translatome profiling, we found that cardiomyocyte-specific Lmna deletion in adult mice led to rapid cardiomyopathy with pathological remodeling. Prior to the onset of cardiac dysfunction, lamin A/C-depleted cardiomyocytes displayed nuclear envelope deterioration, golgi dilation/fragmentation, and CREB3-mediated golgi stress activation. Translatome profiling identified upregulation of Med25, a transcriptional co-factor that can selectively dampen UPR axes. Autophagy is disrupted in the hearts of these mice, which can be recapitulated by disrupting the golgi or inducing nuclear damage by increased matrix stiffness. Systemic administration of pharmacological modulators of autophagy or ER stress significantly improved the cardiac function. These studies support a hypothesis wherein stress responses emanating from the perinuclear space contribute to the development of LMNA cardiomyopathy.

Med25 Limits Master Regulators That Govern Adipogenesis

“…We recently described a novel cre recombinase driver line referred to as CM-CreTRAP mice [ 14 ]. It is a bi-cistronic transgenic line wherein tamoxifen (Tam)-inducible Cre recombinase (CreERT2) and EGFP-L10a fusion protein are co-expressed under the control of a CM-specific promoter, myosin heavy chain 6 ( Myh6 ) promoter.…”

“…EGFP-L10a is a fusion of enhanced green fluorescent protein and ribosomal protein L10a, a component of the 60S ribosomal protein, which allows tagging of polysomes for immunoaffinity purification of translating mRNA termed Translating Ribosome Affinity Purification (TRAP) [ 25 ]. These mice develop molecular and histological changes by 2 weeks post Tam administration and a severe decline in cardiac function and pathological fibrosis by 4 weeks [ 14 ]. Following 100 mg/kg Tam administration at 12 weeks of age for 5 consecutive days followed by 2 days rest to delete Lmna specifically in CMs, we assessed lipid accumulation by oil-red-O staining at the indicated time points ( Figure 1 A and Supplementary Figure S1 ).…”

“…We previously showed that there is a gradual elevation of Med25 protein expression that reaches its peak by 2 weeks post Tam in hearts of CM- Lmna -deleted mice [ 14 ]. To determine whether a similar elevation of Med25 protein expression occurs in the human disease, we performed immunoblot analyses on myocardial tissue from human patients and compared them to age-/sex-matched controls ( Figure 1 F).…”

“…We recently showed in a novel tamoxifen-inducible CM-specific Lmna deletion model that fulminant cardiomyopathy and pathological fibrosis develops within 4 weeks post cessation of tamoxifen administration [ 14 ]. Coincident with the incipient phase of the disease, in which subtle histological and molecular changes are evident without impacting myocardial pump function, we discovered the upregulation of Med25 protein in a translating mRNA screen [ 14 ].…”

“…We recently showed in a novel tamoxifen-inducible CM-specific Lmna deletion model that fulminant cardiomyopathy and pathological fibrosis develops within 4 weeks post cessation of tamoxifen administration [ 14 ]. Coincident with the incipient phase of the disease, in which subtle histological and molecular changes are evident without impacting myocardial pump function, we discovered the upregulation of Med25 protein in a translating mRNA screen [ 14 ]. Med25 is a member of the Mediator complex, an evolutionarily conserved multi-subunit complex that integrates cellular signals and relays to the basal Pol II transcriptional machinery to generate an appropriate transcriptional response.…”