From Parallel Programming to Bidirectional Crosstalk: The Brain–Kidney Axis in Cardiovascular–Kidney–Metabolic Syndrome

Cardiovascular-kidney-metabolic (CKM) syndrome is a systemic, interdependent disorder arising from the convergence of metabolic dysfunction, chronic kidney disease, and cardiovascular pathology. Anchored in the Developmental Origins of Health and Disease (DOHaD) framework, this review advances a "parallel hit" model, primarily based on evidence from experimental animal studies, particularly rodent models, posited that early-life environmental insults concurrently program structural and functional vulnerabilities in both renal and central nervous system hubs. These early perturbations prime susceptibility long before clinical manifestations emerge. CKM progression is conceptualized as a two-stage trajectory, with an initial phase of parallel programming affecting kidney and brain development, followed by a transition to maladaptive bidirectional crosstalk. In the later phase, heightened efferent sympathetic outflow and aberrant afferent renal signaling-potentiated by uremic toxin accumulation, neuroinflammation, and blood-brain barrier disruption-drive a self-perpetuating cycle that accelerates cardiorenal and metabolic injury. Key integrative mechanisms, including oxidative stress, chronic low-grade inflammation, mitochondrial dysfunction, and gut microbiota dysbiosis, serve as convergent pathways linking early-life exposures to adult CKM phenotypes. These pathways not only sustain disease progression but also represent actionable therapeutic targets. Importantly, this framework underscores the translational potential of early-life "reprogramming" strategies. Interventions such as precision nutrition, antioxidant supplementation, microbiota-directed therapies (including prebiotics, probiotics, and postbiotics), and mechanism-based pharmacotherapies may mitigate or reverse maladaptive programming. However, much of the current mechanistic evidence remains preclinical, and further human studies are needed to validate these pathways and therapeutic approaches. Collectively, this dual-hub paradigm reframes CKM syndrome as a life-course continuum rather than a late-stage comorbidity cluster, emphasizing the necessity of early, mechanism-driven interventions to stabilize the brain-kidney axis and improve long-term cardiovascular-kidney-metabolic outcomes.