Senescence is a stable cell cycle arrest that is either tumor suppressive or tumor promoting depending on context. Epigenetic changes such as histone methylation are known to affect both induction and suppression of senescence by altering expression of genes that regulate the cell cycle and the senescence-associated secretory phenotype. A conserved group of proteins containing a Jumonji C (JmjC) domain alter chromatin state, and therefore gene expression, by demethylating histones. Here, we will discuss what is currently known about JmjC demethylases in induction of senescence and how these enzymes suppress senescence to contribute to tumorigenesis.

Epigenetic changes are changes in gene expression that do not involve alterations to the basic DNA sequence. These changes lead to establishing a so-called epigenetic code that dictates which and when genes are activated, thus orchestrating gene regulation and playing a central role in development, health, and disease. The brain, being for the most formed by cells that do not undergo a renewal process through life, is highly prone to the risk of alterations leading to neuronal death and neurodegenerative disorders, mainly at late age. Here we review the main epigenetic modifications that have been described in the brain, with particular attention to those related to the onset of developmental anomalies or neurodegenerative conditions and/or occurring in old age. DNA methylation and several types of histone modifications (acetylation, methylation, phosphorylation, ubiquitination, sumoylation, lactylation, and crotonylation) are major players in these processes. They are directly or indirectly involved in the onset of neurodegeneration in Alzheimer’s or Parkinson’s disease. Therefore, this review briefly describes the role of these epigenetic changes in the mechanisms of brain development, maturation, and aging and some of the most important factors dynamically regulating or contributing to these changes such as oxidative stress, inflammation, and mitochondrial dysfunction.

Excessive extracellular histones can damage cells despite their importance in DNA structure and gene regulation. We previously showed the harmful effect of histone 3.3 (H3.3) and its acetylated form (AcH3.3) in chronic obstructive pulmonary disease (COPD), but further research is needed to understand the in vivo underlying mechanisms. To investigate this, we administered a single dose of recombinant histones via intra-tracheal instillation in C57BL/6 mice and analyzed the outcomes after 48 hours. Both rH3.3 and rAcH3.3 effectively reached the bronchial and alveolar space. Lung histology revealed severe immune cell infiltration, rupture, damage, and thickening of many alveolar walls. Micro-CT scans showed macroscopic structure changes with a decreased tissue volume to total volume ratio. The administration of rH3.3 and rAcH3.3 induced lung apoptotic activity, as indicated by increased levels of cleavage caspase 3 and 9. Moreover, elevated plasma levels of pro-inflammatory cell mediators, including TNF-alpha, IL-6, MCP-3, and CXCL-1, were observed. The pathological changes and pro-inflammatory cytokine response were more pronounced in animals treated with rAcH3.3, which also exhibited leukocytosis and lymphocytosis. These findings emphasize the crucial role of extracellular H3.3 acetylation in inducing cytotoxicity and a robust, acute inflammatory response similar to what occurs in the lungs of COPD patients.