The PRC2 Functional Switch: A Unified Mechanistic Framework for Non-Linear Stress Adaptation and Epigenetic Memory

Current paradigms in stress research largely rely on the concept of Hans Selye’s stress theory (1936) and Allostatic Load by Bruce McEwen and Eliot Stellar in 1993, viewing stress as a cumulative, linear physiological fluctuation. However, these models fail to explain a fundamental biological observation: the abrupt, often irreversible transition from resilience to persistent pathological states such as PTSD or neurodegeneration. We propose the Epigenetic Homeostasis Theory (EHT), which recasts stress not as a continuous response, but as a non-linear epigenetic phase transition. We argue that the regulatory architecture of the genome possesses an inherent stability threshold T(c). When environmental perturbations exceed this threshold, the system undergoes a discrete state transition, mediated by a functional switch in the Polycomb Repressive Complex 2 (PRC2) machinery. This transition establishes a new, stable epigenetic attractor that encodes long-term stress memory – a “lock” that persists long after the initial stressor has dissipated.