Michael Hendzel

Significance: Hutchinson-Gilford Progeria Syndrome (HGPS) is a devastating premature aging disorder caused by accumulation of the toxic protein progerin. This groundbreaking study reveals that HDAC2 (histone deacetylase 2) plays a central role in progerin toxicity. Progerin directly interacts with HDAC2, hijacking it to disrupt normal chromatin structure and gene regulation.

Most remarkably, we demonstrated that pharmacological inhibition of HDAC2 rescues multiple cellular defects in progeria cells, including restoration of normal nuclear morphology, reduction of DNA damage, and normalization of heterochromatin markers. This work identifies HDAC2 as a promising therapeutic target and provides proof-of-concept that small molecule inhibitors could potentially treat this currently incurable disease. The findings also have broader implications for understanding normal aging processes, as progerin accumulates at low levels during physiological aging.

Significance: Cardiovascular disease is the leading cause of death in Hutchinson-Gilford Progeria Syndrome (HGPS), yet the molecular mechanisms underlying vascular pathology have remained poorly understood. This comprehensive study reveals that vascular smooth muscle cells (VSMCs) from progeria patients undergo profound epigenetic changes that drive premature cellular senescence.

Using patient-derived cells and sophisticated imaging techniques including super-resolution microscopy, we discovered that progerin expression leads to loss of key heterochromatin marks (H4K16ac) and chromatin architectural proteins (MOF), resulting in accelerated senescence and impaired VSMC function. Remarkably, these epigenetic defects mirror those observed during normal vascular aging, but occur at a dramatically accelerated rate in progeria. This work establishes progeria as a powerful model for understanding physiological vascular aging and identifies specific epigenetic pathways as potential therapeutic targets for both progeria and age-related cardiovascular disease.

Significance: Understanding the ultrastructural organization of the cell nucleus has been limited by the inability to simultaneously visualize multiple molecular components at nanometer resolution. This technical tour de force presents a novel correlative imaging approach that combines super-resolution fluorescence microscopy with multi-color electron microscopy (EM) to achieve unprecedented visualization of nuclear architecture.

Using energy-filtered transmission electron microscopy (EFTEM) with elemental mapping, we developed a method to simultaneously detect multiple markers in the same sample, revealing the precise spatial relationships between chromatin, DNA repair factors, and nuclear bodies at the nanoscale. This approach enabled us to discover that DNA repair factors are not randomly distributed but are organized into distinct sub-compartments within repair foci. These findings challenge existing models of nuclear organization and provide a powerful new tool for investigating the structural basis of genome function. The methodology has broad applications for studying any nuclear process where spatial organization is critical.

Significance: DNA double-strand breaks (DSBs) are among the most dangerous forms of DNA damage, and cells respond by recruiting hundreds of repair proteins to damaged sites, forming microscopically visible "repair foci." However, how these proteins are organized within foci and how this organization influences repair pathway choice has been unclear.

Using advanced super-resolution microscopy and quantitative image analysis, we discovered that repair foci are not homogeneous structures but contain distinct sub-compartments where different repair proteins are spatially segregated. Specifically, we found that 53BP1, a key regulator of repair pathway choice, forms a core domain surrounded by regions enriched in factors promoting homologous recombination. This spatial organization creates distinct microenvironments that influence which repair pathway is ultimately employed. Understanding this sub-compartmentalization provides crucial insights into how cells make the critical decision between error-prone and error-free repair mechanisms, with important implications for cancer susceptibility and therapy resistance.

Significance: Heterochromatin is the densely packed, transcriptionally silent portion of the genome that was long thought to be relatively inaccessible to cellular machinery. This poses a significant challenge: how do DNA repair proteins access and repair damage within these highly compacted regions? This study addresses this fundamental question.

Using a combination of laser micro-irradiation to induce localized DNA damage and live-cell imaging with fluorescently tagged repair factors, we discovered that heterochromatin undergoes dynamic, transient changes in compaction that allow repair protein access. Remarkably, different repair factors exhibit distinct kinetics of heterochromatin penetration, with some accessing damaged sites almost immediately while others show delayed recruitment. We identified specific histone modifications and chromatin remodeling complexes that regulate this accessibility. These findings reveal that heterochromatin is far more dynamic than previously appreciated and provide mechanistic insights into how cells balance genome protection with the need to maintain chromatin organization. This work has important implications for understanding mutation patterns in cancer genomes.