ABSTRACT
Mutations in LMNA, the gene encoding the nuclear membrane proteins, lamins A and C, produce cardiac and muscle disease. In the heart, these autosomal dominant LMNA mutations lead to cardiomyopathy frequently associated with cardiac conduction system disease. Herein, we describe a patient with the R374H missense variant in nesprin-1alpha, a protein that binds lamin A/C. This individual developed dilated cardiomyopathy requiring cardiac transplantation. Fibroblasts from this individual had increased expression of nesprin-1alpha and lamins A and C, indicating changes in the nuclear membrane complex. We characterized mice lacking the carboxy-terminus of nesprin-1 since this model expresses nesprin-1 without its carboxy-terminal KASH domain. These Delta/DeltaKASH mice have a normally assembled but dysfunctional nuclear membrane complex and provide a model for nesprin-1 mutations. We found that Delta/DeltaKASH mice develop cardiomyopathy with associated cardiac conduction system disease. Older mutant animals were found to have elongated P wave duration, elevated atrial and ventricular effective refractory periods indicating conduction defects in the myocardium, and reduced fractional shortening. Cardiomyocyte nuclei were found to be elongated with reduced heterochromatin in the Delta/DeltaKASH hearts. These findings mirror what has been described from lamin A/C gene mutations and reinforce the importance of an intact nuclear membrane complex for a normally functioning heart.
Subject(s)
Cardiomyopathies/genetics , Cardiomyopathies/metabolism , Mutation , Nerve Tissue Proteins/genetics , Nerve Tissue Proteins/physiology , Nuclear Proteins/genetics , Nuclear Proteins/physiology , Animals , Cell Nucleus/metabolism , Cytoskeletal Proteins , Echocardiography/methods , Fibroblasts/metabolism , Heterochromatin/metabolism , Humans , Laminin/genetics , Mice , Mutation, Missense , Myocytes, Cardiac/cytology , Nuclear Envelope/metabolismABSTRACT
Otitis media is an extremely common pediatric inflammation of the middle ear that often causes pain and diminishes hearing. Vulnerability to otitis media is due to eustachian tube dysfunction as well as other poorly understood factors, including genetic susceptibility. As EYA4 mutations cause sensorineural hearing loss in humans, we produced and characterized Eya4-deficient (Eya4(-/-)) mice, which had severe hearing deficits. In addition, all Eya4(-/-) mice developed otitis media with effusion. Anatomic studies revealed abnormal middle ear cavity and eustachian tube dysmorphology; thus, Eya4 regulation is critical for the development and function of these structures. We suggest that some human otitis media susceptibility reflects underlying genetic predisposition in genes like EYA4 that regulate middle ear and eustachian tube anatomy.
Subject(s)
Ear, Middle/abnormalities , Eustachian Tube/abnormalities , Genetic Predisposition to Disease , Hearing Loss, Sensorineural/genetics , Otitis Media with Effusion/genetics , Trans-Activators/genetics , Animals , Disease Models, Animal , Mice , Mice, Mutant Strains , MutationABSTRACT
We identified a human mutation that causes dilated cardiomyopathy and heart failure preceded by sensorineural hearing loss (SNHL). Unlike previously described mutations causing dilated cardiomyopathy that affect structural proteins, this mutation deletes 4,846 bp of the human transcriptional coactivator gene EYA4. To elucidate the roles of eya4 in heart function, we studied zebrafish embryos injected with antisense morpholino oligonucleotides. Attenuated eya4 transcript levels produced morphologic and hemodynamic features of heart failure. To determine why previously described mutated EYA4 alleles cause SNHL without heart disease, we examined biochemical interactions of mutant Eya4 peptides. Eya4 peptides associated with SNHL, but not the shortened 193-amino acid peptide associated with dilated cardiomyopathy and SNHL, bound wild-type Eya4 and associated with Six proteins. These data define unrecognized and crucial roles for Eya4-Six-mediated transcriptional regulation in normal heart function.
