Parkinson's disease (PD) is increasingly recognized not as a disorder of a single brain region but as a systems-level failure involving both peripheral and central networks. This review summarizes emerging evidence across these domains to propose an innovative integrative model: the vicious triad of PD pathogenesis. The idea suggests that inflammatory signals from the gut, alongside pathologic protein aggregates such as misfolded α-synuclein, may trigger and sustain a central innate immune response. Gut-derived substances are posited to potentially activate the cGAS-STING pathway in the brain, which may instigate chronic interferon-mediated neuroinflammation. This inflammatory condition could, in turn, impair glymphatic clearance by inducing the mislocalization of aquaporin-4 channels on astrocytes. The inability to eliminate cytotoxic waste, such as mitochondrial DNA and α-synuclein clumps, establishes a continual reservoir of damage-associated molecular patterns. These agonists may then enhance cGAS-STING signaling, potentially creating a self-sustaining, closed-loop pathogenic cycle that could mechanistically link gut dysbiosis, neuroinflammation, and glymphatic dysfunction. While each pairwise interaction within this triad is supported by indicative experimental evidence from human, animal, and cellular studies, direct proof of their triadic causation within a single system remains an unresolved issue requiring thorough confirmation. Moving beyond linear or parallel models, this framework reinterprets PD as a dynamic systems disorder fueled by this feed-forward circuit. The triad model explains the disease's chronic progression, the stereotypical spread of pathology, and its clinical heterogeneity. Crucially, this framework necessitates a paradigm shift from monotherapeutic approaches to combinatorial strategies that simultaneously target all three components: the peripheral trigger (gut), the central immune amplifier (cGAS-STING), and the clearance sink (glymphatics). Promising therapies consistent with this concept include microbiota engineering, STING antagonists, astrocyte manipulation, and sleep therapy. A framework for biomarker-driven, individualized clinical studies aimed at testing this notion is delineated. The vicious triad theory presents a framework for significant disease change in PD by integrating the gut-brain axis, neuroinflammation, and waste clearance into a cohesive pathogenic cycle.
