Abstract
Nesprins-1 and -2 are multi-isomeric scaffolding proteins. They are highly expressed in skeletal and cardiac muscle, and together with SUN (Sad1p/UNC84)-domain containing proteins and lamin A/C, forming the LInker of Nucleoskeleton and Cytoskeleton (LINC) complex at the nuclear envelope (NE). Mutations in nesprin-1/-2 have previously been identified in patients with autosomal dominant Emery–Dreifuss muscular dystrophy (EDMD) as well as dilated cardiomyopathy (DCM).In my study, three novel rare variants (R8272Q, S8381C, N8406K) in the C-terminus of the SYNE-1 (nesprin-1) gene were identified in 7 DCM patients by mutation screening. These mutants caused nuclear morphology defects, reduced lamin A/C and SUN2 staining at the NE and disrupted binding between nesprin-1/lamin/SUN. Nesprin-1 mutations were also associated with augmented activation of the ERK pathway in vitro and in hearts in vivo. During C2C12 myoblast differentiation, nesprin-1 protein levels increased concomitantly with kinesin light chain (KLC-1/2). GST pull-down assay showed that nesprin-1 and KCL-1/2 bind at the NE. Expression of nesprin-1 mutants in C2C12 cells caused defects in myoblast differentiation and fusion associated with dysregulation of myogenic regulatory factors and disruption of the nesprin-1 and KLC-1/2 interaction. Furthermore, expression of nesprin-1α2 WT and mutants in zebrafish embryos caused heart developmental and conduction defects that varied in severity. In addition, a novel cardiac specific dominant negative nesprin-2 KASH (Klarsicht/ANC-1/Syne-1 homology) transgenic (Tg) mouse model was generated. Data showed overexpression of KASH domain caused disruption of NE-LINC complex and induced a hypertrophic response with activated fetal gene re-expression in Tg mice at the basal line, which was exacerbated when subjected to pathological hemodynamic stress.
These findings support roles for nesprin-1/-2 in nuclear organisation and myogenesis, which may uncover a novel mechanism whereby disruption of the NE-LINC complex may contribute to the pathogenesis of DCM.
| Date of Award | 2018 |
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| Original language | English |
| Awarding Institution |
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| Supervisor | Qiuping Zhang (Supervisor) & Cathy Shanahan (Supervisor) |