Vascular cells in Hutchinson-Gilford progeria syndrome accumulate a defective protein called progerin, which anchors itself to the nuclear membrane and sets off a cascade of damage. One of the earliest events is the loss of acetylation on histone H4 at lysine 16 (H4K16ac). This mark does more than decorate chromatin: it loosens the connection between neighboring nucleosomes, making the DNA packaging more open, and helps the cell choose the precise route for repairing double-strand breaks, namely homologous recombination. When H4K16ac disappears, chromatin tightens and repair switches to the cruder, error-prone pathway of non-homologous end joining. In earlier work, the authors showed that this mark is sharply reduced in HGPS vascular cells, and now they asked: which enzymes are to blame, and can we "switch them off" to make the cells young again?
The researchers ran a large-scale screen in two cancer cell lines, HeLa and U2OS. Using small interfering RNAs, they switched off, one at a time, the genes of all known candidates: the acetyltransferases KAT5 and KAT8, all eleven deacetylases of the HDAC class, and all seven sirtuins. H4K16ac levels were measured in two ways: quantitative immunofluorescence in individual nuclei and immunoblotting of histones extracted from the cells. The key enzymes were then tested in vascular cells derived from induced pluripotent stem cells of HGPS patients and healthy donors. For pharmacological confirmation, they used a panel of inhibitors with different selectivity: BRD4884 (against HDAC1/2), MI192 (against HDAC2/3), santacruzamate A (claimed to be a selective HDAC2 inhibitor), quisinostat (a broad HDAC inhibitor), and EX527 (a selective SIRT1 inhibitor). Cells were treated with these compounds for 24 hours, after which the team assessed H4K16ac, nuclear morphology, the proliferation marker Ki67, the senescence marker beta-galactosidase, and phosphorylated histone H2AX (γH2AX) as an indicator of DNA double-strand breaks.
In HeLa and U2OS cells, switching off KAT8 lowered H4K16ac by 60-70%, whereas switching off KAT5 had almost no effect. Among the deacetylases, suppressing HDAC2 produced the strongest effect: H4K16ac rose by 42-47%. Suppressing SIRT1 increased the mark by 47-49%, while HDAC1 barely changed it. Overexpressing HDAC2 and SIRT1 reduced H4K16ac to 64-66% of control, confirming their role as "erasers." Pharmacological inhibitors aimed at HDAC2 raised H4K16ac in HeLa: santacruzamate A by 62%, MI192 by 34%, BRD4884 by 22%, while the SIRT1 inhibitor EX527 had no significant effect. In HGPS vascular cells the picture was even more pronounced: santacruzamate A raised H4K16ac by 101%, MI192 by 77%, BRD4884 by 62%, and EX527 by only 15%. Lonafarnib (a farnesyltransferase inhibitor approved for HGPS) on its own increased H4K16ac by 39%, and its combination with HDAC2 inhibitors sustained the highest levels of the mark. Long-term culture showed that HDAC2 inhibitors preserved the cells' ability to divide: at passage 20, the share of Ki67-positive cells was 12% in the vehicle control but 63-75% with BRD4884, MI192, or santacruzamate A, and the combination with lonafarnib reached 84%. The senescence marker beta-galactosidase accumulated much more slowly: a drop of 58-73% compared with control. HDAC2 inhibitors also improved nuclear shape, bringing it closer to that of healthy cells, and reduced the γH2AX signal by 26-50%, pointing to fewer double-strand breaks.
This work is the first to clearly separate the contributions of HDAC2 and SIRT1 to H4K16ac regulation in progeria vascular cells. In fast-dividing cancer lines both enzymes matter, but in HGPS cells HDAC2 turns out to be the main "eraser" of this protective mark. That explains why SIRT1 inhibitors deliver no therapeutic effect and steers efforts toward developing selective HDAC2 inhibitors. The results also link epigenetic regulation to the choice of DNA repair pathway: restoring H4K16ac appears to give cells back their capacity for accurate homologous recombination, reducing the buildup of damage.
The field could move in several directions. First, more selective HDAC2 inhibitors are needed, since the compounds currently used have off-target hits. Second, the effect must be tested in animal models of progeria to gauge the impact on blood vessels and lifespan. Third, the combination with lonafarnib looks promising and needs dose and dosing-schedule optimization. Finally, it is worth studying which genes and pathways are activated when H4K16ac is restored, in order to understand the mechanism of cellular rejuvenation.
The results could shape the development of therapies for progeria and possibly for other diseases linked to accelerated vascular aging. HDAC2 inhibitors are also being considered as candidates for treating Alzheimer's disease, and this work provides additional rationale for studying them.
The immediate steps include testing HDAC2 inhibitors in animal models of progeria, assessing their safety with long-term use, and developing more selective compounds. It will also be necessary to determine which cellular processes besides DNA repair improve when H4K16ac is restored.
In the epigenetics of aging, one question remains open: why do different cells respond differently to the loss of H4K16ac, with the mark falling in some systems and rising in others? This work shows that the key factor may be the balance between acetyltransferases and deacetylases, which depends on cell type and pathological state. For progeria medicine, it is important to understand how to restore that balance specifically in vascular cells without affecting other tissues.
Santacruzamate A, which showed the strongest effect in this work, was first isolated from a marine cyanobacterium and named after Santa Cruz Island, where it was found. Despite debate about its selectivity, it remains a useful tool for studying HDAC2 in cells.
Not published on arXiv. Here are its page, the PDF and the formalization: you can check it yourself, not only read our account.