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Abstract
Introduction: The nuclear lamina is a mesh network of intermediate filament proteins that line the inner nuclear membrane. It consists of nuclear lamins A, B and C, which play a role in maintaining the integrity of the nuclear envelope, as well as in DNA replication and repair, and in transcription. Mutations in Lamin A and/or defects in the processing of its precursor – prelamin A – are responsible for rare genetic disorders known as laminopathies. The most severe of these, Hutchison Gilford Progeria syndrome (HGPS), causes premature ageing in children who die from accelerated cardiovascular events. Prelamin A has also been shown to accumulate in normal ageing, particularly in aged vascular smooth muscle cells (VSMCs) in vitro and in vivo, due, in part, to downregulation of Zmpste24, the enzyme responsible for the final processing step of prelamin A into mature lamin A.
Aims This study aimed to understand the effects of prelamin A accumulation in VSMCs in vivo by determining its effects on vessel structure and function and relating these to VSMC phenotypic change using a SMC-specific Zmpste24 knockout (KO) mouse model.
Methods SMC-specific Zmpste24 KO mouse model was generated using the Cre-loxP system and validated by measuring Zmpste24 mRNA expression and prelamin A accumulation in the aorta. We performed echocardiography and blood pressure measurements using the tail cuff method to assess the cardiovascular phenotype of the mouse model. Additionally, we performed histology, western blot, qPCR, microarray and extracellular matrix proteomics to determine the effect of prelamin A in vessel structure and VSMC function.
Results Zmpste24 mRNA was significantly decreased and prelamin A was detected in the aorta of Zmpste24 KO mice which also had reduced survival rates and showed significant weight loss at 6 months prior to early death. KO mice exhibited aortic root dilatation, aortic regurgitation and impaired cardiac function shown by decreased ejection fraction. Furthermore, KO mice displayed increased systolic blood pressure. Histologically, aortic sections from KO mice showed increased deposition of extracellular matrix (ECM) glycosaminoglycans, DNA damage and VSMC loss – all hallmarks of vascular ageing in adults. DNA microarray and ECM proteomics, was used to elucidate the mechanisms involved in driving vascular ageing and identified potential defects in the transforming growth factor beta (TGF-β) and connective tissue growth factor (CTGF) signalling pathways.
Conclusion This mouse model can be used to identify and test novel therapeutic pathways that may be able to protect, delay or reverse the process of vascular decline seen in ageing.