Copper-Free Click Chemistry Enables High-Fidelity Engineering of Mitochondria-Targeted Brain-Derived Exosomes

Mitochondrial dysfunction is a hallmark of neurodegenerative and neuroinflammatory disorders, including hypertension and cardiovascular disease, yet strategies for safe and precise mitochondrial-targeted delivery remain limited. Here, we establish strain-promoted azide-alkyne cycloaddition (SPAAC) as a biocompatible, high-fidelity chemical platform for engineering mitochondria-targeted brain-derived exosomes (BR-EVs). Copper-free click conjugation of a mitochondrial-targeting ligand (e.g. Cy5-DBCO) under mild aqueous conditions preserved vesicle morphology (30-150 nm core; 120-200 nm hydrodynamic), proteomic composition, and uptake dynamics. Time-course imaging and fluorescence recovery after photobleaching (FRAP) revealed unaltered endocytic kinetics, >75 % mitochondrial colocalization, and intact organelle architecture. In vivo neuroinflammation and biodistribution analyses demonstrated immunological neutrality, strong central nervous system retention, and minimal peripheral dispersion following intracerebroventricular administration. Proteomic profiling of unlabeled Sprague-Dawley (SD) and hypertensive Dahl salt-sensitive (DSS) BR-EVs uncovered hypertension-driven enrichment of oxidative and complement pathways correlating with mitochondrial fragmentation and reactive oxygen species generation in neuronal cultures. These findings establish SPAAC-mediated ligand conjugation as a biocompatible and chemically precise approach for generating mitochondria-targeted exosomes that preserve exosomal identity, biodistribution, and signaling fidelity-advancing a foundational platform for organelle-specific delivery and mechanistic imaging in the central nervous system.