Using mouse models to dissect the roles of ZMPSTE24 and prelamin A in accelerated aging

PROJECT SUMMARY Accelerated aging disorders can provide critical insights into aspects of physiological aging. A subset of accelerated aging disorders, including Hutchinson-Gilford progeria syndrome (HGPS) and mandibuloacral dysplasia type B (MAD-B), are characterized by accumulation of farnesylated prelamin A or its variants. Normally, farnesylated prelamin A is processed to mature lamin A – an intermediate filament protein of the nuclear lamina – by a proteolytic cleavage near the carboxyl-terminus catalyzed by the zinc metalloproteinase ZMPSTE24. Defects in this processing resulting from mutations in either LMNA encoding prelamin A or ZMPSTE24 respectively cause HGPS and MAD-B. Some studies have even implicated farnesylated prelamin A or its variants in physiological aging. However, much remains to be learned about the underlying pathogenic mechanisms of how prelamin A mediates accelerated and possibly physiological aging. We have generated a mouse with a point mutation that changes the leucine just downstream from the ZMPSTE24 cleavage site in prelamin A to an arginine. LmnaL648R/L648R mice express permanently farnesylated prelamin A, with a single amino acid substitution at residue 648, and no mature lamin A. However, in contrast to Zmpste24-/- mice that have severe progeroid phenotypes and significantly shortened lifespans, LmnaL648R/L648R mice have more mild and later onset progeroid features and near-normal longevity. This finding leads to two alterative hypotheses we will test in this R03 small research project: 1) that ZMPSTE24 has functions related to accelerated aging independent of prelamin A processing or 2) that a single amino acid substitution in prelamin A renders it less “toxic” than the wild-type protein with regards to accelerated aging phenotypes. The single Specific Aim is to determine if deletion of Zmpste24 shortens the lifespan and worsen the progeroid phenotypes of LmnaL648R/L648R mice. To test this hypothesis, we will cross Lmna+/L648R and Zmpste24+/- mice to generate LmnaL648R/L648R;Zmpste24-/- mice. These mice will express L648R prelamin A and have no active ZMPSTE24. If they are similar to Zmpste24-/- mice, with a more severe progeroid phenotype and shorter lifespan than LmnaL648R/L648R mice, it will indicate that ZMPSTE24 has other critical functions in aging. If these “double mutant” mice have a longer lifespan and less severe progeroid phenotypes than Zmpste24-/- mice, it will indicate that a single amino acid substitution in farnesylated prelamin A reduces its ability to induce accelerated aging. Data that supports one of these alternative hypotheses will lead to future projects on either 1) a role of ZMPSTE24 in accelerated aging separate from that of prelamin A processing or 2) specific functions of the region around leucine 648 in prelamin A in generating accelerated aging phenotypes.