Mitochondria–Lysosome Quality Flux in Aging Mesenchymal Stem/Stromal Cells: Quality-Control Bottlenecks and Therapeutic Opportunities for Regenerative Decline

Aging mesenchymal stem/stromal cells (MSCs) lose regenerative capacity as redox imbalance, mitochondrial damage, defective organelle quality control and chronic inflammation converge. Yet these processes are commonly considered in isolation, obscuring whether damaged mitochondrial cargo reaches lysosomes and is ultimately degraded. Here, we define mitochondria–lysosome quality flux (MLQF) as an author-proposed, evidence-graded framework that tracks mitochondrial damage from recognition and sorting through lysosomal delivery to terminal lysosomal degradation in aging MSCs. The framework explicitly separates delivery to an acidic compartment from completed degradation and distinguishes direct MSC evidence from cross-model mechanisms and candidate pathways. MSC studies most strongly support macroautophagy-dependent mitophagy, particularly when assessed using dynamic flux reporters. By contrast, mitochondria-derived vesicles and microautophagy-like or piecemeal routes remain incompletely validated in MSCs. Studies in non-MSC systems further show that mitochondria–lysosome contact sites can support lysosomal acidification, although their contribution to natural MSC aging remains unresolved. By locating rate-limiting defects across this continuum, MLQF provides a testable basis for linking incomplete mitochondrial clearance to inflammatory signaling, lineage drift and regenerative decline, and for selecting bottleneck-matched interventions.