Lamin A and lamin C, both products of Lmna, are key components of the nuclear lamina. In the mouse, a deficiency in both lamin A and lamin C leads to slow growth, muscle weakness, and death by 6 weeks of age. Fibroblasts deficient in lamins A and C contain misshapen and structurally weakened nuclei, and emerin is mislocalized away from the nuclear envelope. The physiologic rationale for the existence of the 2 different Lmna products lamin A and lamin C is unclear, although several reports have suggested that lamin A may have particularly important functions, for example in the targeting of emerin and lamin C to the nuclear envelope. Here we report the development of lamin C–only mice (Lmna+/+), which produce lamin C but no lamin A or prelamin A (the precursor to lamin A). Lmna+/+ mice were entirely healthy, and Lmna+/+ cells displayed normal emerin targeting and exhibited only very minimal alterations in nuclear shape and nuclear deformability. Thus, at least in the mouse, prelamin A and lamin A appear to be dispensable. Nevertheless, an accumulation of farnesyl–prelamin A (as occurs with a deficiency in the prelamin A processing enzyme Zmpste24) caused dramatically misshapen nuclei and progeria-like disease phenotypes. The apparent dispensability of prelamin A suggested that lamin A–related progeroid syndromes might be treated with impunity by reducing prelamin A synthesis. Remarkably, the presence of a single LmnaLCO allele eliminated the nuclear shape abnormalities and progeria-like disease phenotypes in Zmpste24–/– mice. Moreover, treating Zmpste24–/– cells with a prelamin A–specific antisense oligonucleotide reduced prelamin A levels and significantly reduced the frequency of misshapen nuclei. These studies suggest a new therapeutic strategy for treating progeria and other lamin A diseases.
Loren G. Fong, Jennifer K. Ng, Jan Lammerding, Timothy A. Vickers, Margarita Meta, Nathan Coté, Bryant Gavino, Xin Qiao, Sandy Y. Chang, Stephanie R. Young, Shao H. Yang, Colin L. Stewart, Richard T. Lee, C. Frank Bennett, Martin O. Bergo, Stephen G. Young