Remodelin Nuclear Defects: Deregulation of A-type lamin proteins leads to disorganization of chromatin structure and misshapen nuclei, which are believed to underlie the pathologies of various human diseases, including the premature aging disorder Hutchinson Gilford progeria syndrome (HGPS) and various cancers. Larrieu et al. (p. 527 ) developed a small molecule, Remodelin, that not only improved nuclear shape defects of human lamin A/C–depleted cells, HGPS cells, and aged normal cells, but also decreased the levels of a DNA damage marker and improved global cellular fitness.

Hutchinson-Gilford Progeria Syndrome (HGPS) is a rare, but devastating genetic disease characterized by segmental premature aging, with cardiovascular disease being the main cause of death. Cells from HGPS patients accumulate progerin, a permanently farnesylated, toxic form of Lamin A, disrupting the nuclear shape and chromatin organization, leading to DNA-damage accumulation and senescence. Therapeutic approaches targeting farnesylation or aiming to reduce progerin levels have provided only partial health improvements. Recently, we identified Remodelin, a small-molecule agent that leads to amelioration of HGPS cellular defects through inhibition of the enzyme N-acetyltransferase 10 (NAT10). Here, we show the preclinical data demonstrating that targeting NAT10 in vivo, either via chemical inhibition or genetic depletion, significantly enhances the healthspan in a Lmna ^G609G HGPS mouse model. Collectively, the data provided here highlights NAT10 as a potential therapeutic target for HGPS.

Hutchinson-Gilford progeria syndrome (HGPS) is an incurable premature aging disease. Identifying deregulated biological processes in HGPS might thus help define novel therapeutic strategies. Fibroblasts from HGPS patients display defects in nucleocytoplasmic shuttling of the GTP-bound form of the small GTPase Ran (RanGTP), which leads to abnormal transport of proteins into the nucleus. We report that microtubule stabilization in HGPS cells sequestered the nonclassical nuclear import protein Transportin-1 (TNPO1) in the cytoplasm, thus affecting the nuclear localization of its cargo, including the nuclear pore protein NUP153. Consequently, nuclear Ran, nuclear anchorage of the nucleoporin TPR, and chromatin organization were disrupted, deregulating gene expression and inducing senescence. Inhibiting N-acetyltransferase 10 (NAT10) ameliorated HGPS phenotypes by rebalancing the nuclear to cytoplasmic ratio of TNPO1. This restored nuclear pore complex integrity and nuclear Ran localization, thereby correcting HGPS cellular phenotypes. We observed a similar mechanism in cells from healthy aged individuals. This study identifies a nuclear import pathway affected in aging and underscores the potential for NAT10 inhibition as a possible therapeutic strategy for HGPS and perhaps also for pathologies associated with normal aging.

Any given cell type has an associated “normal” nuclear morphology, which is important to maintain proper cellular functioning and safeguard genomic integrity. Deviations from this can be indicative of diseases such as cancer or premature aging syndrome. To accurately assess nuclear abnormalities, it is important to use quantitative measures of nuclear morphology. Here, we give an overview of several nuclear abnormalities, including micronuclei, nuclear envelope invaginations, blebs and ruptures, and review the current methods used for image-based quantification of these abnormalities. We discuss several parameters that can be used to quantify nuclear shape and compare their outputs using example images. In addition, we present new pipelines for quantitative analysis of nuclear blebs and invaginations. Quantitative analyses of nuclear aberrations and shape will be important in a wide range of applications, from assessments of cancer cell anomalies to studies of nucleus deformability under mechanical or other types of stress.

The nuclear lamina is essential for the proper structure and organization of the nucleus. Deregulation of A-type lamins can compromise genomic stability, alter chromatin organization and cause premature vascular aging. Here, we show that accumulation of the lamin A precursor, prelamin A, inhibits 53BP1 recruitment to sites of DNA damage and increases basal levels of DNA damage in aged vascular smooth muscle cells. We identify that this genome instability arises through defective nuclear import of 53BP1 as a consequence of abnormal topological arrangement of nucleoporin NUP153. We show for the first time that this nucleoporin is important for the nuclear localization of Ran and that the deregulated Ran gradient is likely to be compromising the nuclear import of 53BP1. Importantly, many of the defects associated with prelamin A expression were significantly reduced upon treatment with Remodelin, a small molecule recently reported to reverse deficiencies associated with abnormal nuclear lamina.

The mechanistic target of rapamycin complex 1 (mTORC1) is a master regulator of cell growth, metabolism and autophagy. Multiple pathways modulate mTORC1 in response to nutrients. Here we describe that nucleus–cytoplasmic shuttling of p300/EP300 regulates mTORC1 activity in response to amino acid or glucose levels. Depletion of these nutrients causes cytoplasm-to-nucleus relocalization of p300 that decreases acetylation of the mTORC1 component raptor, thereby reducing mTORC1 activity and activating autophagy. This is mediated by AMP-activated protein kinase-dependent phosphorylation of p300 at serine 89. Nutrient addition to starved cells results in protein phosphatase 2A-dependent dephosphorylation of nuclear p300, enabling its CRM1-dependent export to the cytoplasm to mediate mTORC1 reactivation. p300 shuttling regulates mTORC1 in most cell types and occurs in response to altered nutrients in diverse mouse tissues. Interestingly, p300 cytoplasm–nucleus shuttling is altered in cells from patients with Hutchinson–Gilford progeria syndrome. p300 mislocalization by the disease-causing protein, progerin, activates mTORC1 and inhibits autophagy, phenotypes that are normalized by modulating p300 shuttling. These results reveal how nutrients regulate mTORC1, a cytoplasmic complex, by shuttling its positive regulator p300 in and out of the nucleus, and how this pathway is misregulated in Hutchinson–Gilford progeria syndrome, causing mTORC1 hyperactivation and defective autophagy.