The Vesicular Intersection Layer: A Framework for Cross-Kingdom Extracellular Vesicle Signaling That May Connect Gut Dysbiosis to Skeletal Muscle Wasting in Colorectal Cancer Cachexia

Colorectal cancer (CRC) cachexia is a multifactorial, treatment-limiting syndrome characterized by progressive loss of skeletal muscle with or without loss of fat mass, accompanied by systemic inflammation, anorexia, metabolic dysregulation, and impaired treatment tolerance. Despite decades of work, cachexia remains clinically underdiagnosed and therapeutically underserved, in part because canonical models treat tumor-derived factors and host inflammatory mediators as a largely 'host-only' network. In parallel, CRC is strongly linked to intestinal dysbiosis, barrier disruption, and microbial translocation. Extracellular vesicles (EVs)-host small EVs, tumor-derived EVs, and bacterial extracellular vesicles (including outer membrane vesicles)-may provide a mechanistically plausible, information-dense route by which these domains could be coupled. Here, we synthesize emerging evidence suggesting that cross-kingdom EV signaling may operate as a vesicular ecosystem spanning gut lumen, mucosa, circulation, and peripheral organs. We propose the "vesicular intersection layer" as a unifying framework for how heterogeneous EV cargos converge on shared host decoding hubs (e.g., pattern-recognition receptors and stress-response pathways) to potentially contribute to muscle catabolism. We critically evaluate what is known-and what remains unproven-about EV biogenesis, trafficking, and causal mechanisms in CRC cachexia, highlight methodological constraints in microbial EV isolation and attribution, and outline minimum evidentiary standards for cross-kingdom claims. Finally, we translate the framework into actionable hypotheses for EV-informed endotyping, biomarker development (including stool EV assays), and therapeutic strategies targeting shared signaling nodes (e.g., TLR4-p38) and endocrine mediators that are predominantly soluble but may be fractionally vesicle-associated (e.g., GDF15). By reframing CRC cachexia as an emergent property of tumor-host-microbiota vesicular communication, this review provides a roadmap for mechanistic studies and clinically tractable interventions.