Pathogenic and Experimental Lamin A Mutants

The nuclear lamina is a filamentous protein meshwork that underlies the inner nuclear membrane (INM), providing structural integrity to the nucleus and serving as a crucial hub for a multitude of nuclear processes.1 The primary components of this structure are the nuclear lamins, which are Type V intermediate filament proteins.1 Mutations in the genes encoding these proteins, particularly the

LMNA gene, give rise to a remarkably diverse and often devastating group of human diseases collectively known as laminopathies.2 These disorders exhibit striking tissue specificity, affecting tissues such as striated muscle, adipose tissue, peripheral nerve, and bone, or causing systemic syndromes of accelerated aging.5 The perplexing question of how mutations in a ubiquitously expressed gene can lead to such a wide array of tissue-restricted phenotypes has driven intense research for over two decades. This review provides a comprehensive and critical analysis of a panel of specific lamin A mutants, alongside wild-type and deletion constructs, to synthesize the current understanding of their molecular mechanisms, associated phenotypes, and their profound implications for the process of cellular and organismal aging.

The remarkable diversity of laminopathy phenotypes is intimately linked to the location of the causative mutation within the lamin A protein. Different domains of the protein are responsible for distinct functions, such as filament assembly, chromatin binding, and interaction with signaling partners. By organizing the analysis of specific mutants according to their position, clear patterns emerge that connect genotype to molecular mechanism and ultimately to clinical phenotype.

Mutations in the N-terminal head and the adjacent Coil 1A/1B segments of the rod domain often disrupt the fundamental process of lamin polymerization and filament stability. This region is critical for the head-to-tail assembly of lamin dimers into protofilaments, and perturbations here can have profound effects on the integrity of the entire lamina network.

The study of constructs that result in the partial or complete absence of the lamin A/C proteins provides a crucial baseline for understanding the consequences of lamin A/C loss-of-function. These models, referred to here under the general term "Delta NLA," help to dissect the protein's essential roles and provide context for the dominant-negative or gain-of-function effects of many point mutants.

A complete loss of A-type lamins, achieved through genetic knockout (Lmna-/- mice) or RNAi-mediated knockdown, results in a severe, multi-system phenotype that underscores the essential nature of these proteins in differentiated cells.

The extensive research into LMNA mutations has painted a complex picture where the location of a mutation dictates its primary molecular defect, which in turn drives a cascade of cellular events leading to a specific, and often tissue-restricted, clinical phenotype. Synthesizing the data from individual mutants allows for the identification of overarching principles of laminopathy pathogenesis and highlights key areas for future investigation.

The relationship between a specific LMNA variant and its resulting disease is not always straightforward, with variable penetrance and expressivity even within families carrying the same mutation. However, broad correlations have emerged that link mutations in specific protein domains to distinct classes of molecular defects and clinical outcomes. The following table summarizes the key findings for the reviewed variants.