Emerging and Re-emerging viruses as triggers of human endogenous retrovirus activation: Implications for aging and age-related pathologies

The human genome contains a substantial legacy of ancient retroviral infections known as Human Endogenous Retroviruses (HERVs), composing 8 % of our DNA. In healthy young individuals, these elements are kept dormant by robust epigenetic mechanisms, primarily DNA methylation and repressive H3K9me3 histone marks. However, this epigenetic silencing deteriorates with age, leading to the reactivation of HERVs, particularly the youngest HERV-K subfamily. This report posits that this HERV awakening is not a passive byproduct of aging but an active, transmissible driver of pathology. The reactivation of HERVs leads to the production of retrovirus-like particles (RVLPs) that can induce senescence in healthy neighboring cells, propagating a contagious aging phenomenon. Furthermore, the accumulation of HERV-derived dsRNA and reverse-transcribed DNA triggers chronic innate immune responses through pathways including cGAS-STING and IFIH1-MAVS, fueling the systemic, low-grade inflammation characteristic of inflammaging, catalytically accelerated by exogenous viral infections. Pathogens such as SARS-CoV-2, Epstein-Barr Virus (EBV), and Herpes Simplex Virus (HSV-1) can directly transactivate HERVs via their own viral proteins, overwhelming the already compromised epigenetic controls in an aging host. This mechanistic link between viral triggers and endogenous retroviral activity is strongly implicated in a range of age-related diseases, including neurodegenerative disorders such as Alzheimer's disease and Amyotrophic Lateral Sclerosis (ALS), where the HERV-K envelope protein is directly neurotoxic. It is also linked to autoimmune diseases like Multiple Sclerosis and various cancers. This report synthesizes these findings and identifies a novel mechanistic link between viral activity, chronic inflammation, and the onset of age-related diseases.