Mitochondria as programmable redox rheostats: Advancing from transplantation to bioengineered organelle therapeutics.

Mitochondria are the primary arbiters of cellular redox homeostasis, bioenergetic flux, and programmed cell death. Their dysfunction, characterized by excessive reactive oxygen species (ROS) production, impaired oxidative phosphorylation (OXPHOS), and collapsed membrane potential, is a hallmark of diverse pathologies, including ischemia-reperfusion injury, neurodegeneration, and metabolic syndrome. Over the last decade, mitochondrial transplantation has emerged as a radical therapeutic paradigm for restoring metabolic competence via the exogenous delivery of intact organelles. While early evidence confirms that internalized mitochondria can rescue bioenergetic deficits and suppress apoptotic signaling, the transition to clinical practice is hindered by poor targeting specificity, low delivery kinetics, and post-isolation functional decay. This review highlights a pivotal shift toward mitochondrial engineering, where the organelle is no longer viewed as a static payload but as a programmable therapeutic unit. By integrating principles from synthetic biology, nanomedicine, and biomaterials, researchers are now modifying mitochondria to enhance their ROS-scavenging capacity, stability in the extracellular milieu, and cell-specific uptake. We critically evaluate emerging strategies for organelle modification, including surface functionalization, genetic modulation, and advanced delivery platforms like fusogenic capsules and photothermal nanoblades. Finally, we discuss the redox-dependent mechanisms underlying therapeutic efficacy and the translational hurdles essential for evolving mitochondrial engineering into a precise, scalable clinical reality.