GrpE-like 1-engineered synovial mesenchymal stromal cell exosomes: Mechanistic and translational priorities in osteoarthritis

Figure 2 Integrated mechanism-to-translation schematic for GrpE-like 1-engineered synovial mesenchymal stem cell-derived exosomes targeting phosphatase and tensin homolog-induced kinase 1-dependent mitophagy in osteoarthritis. A left-to-right workflow summarizes the proposed therapeutic logic. Osteoarthritis-relevant inflammatory stress (interleukin-1β/tumor necrosis factor-alpha) and oxidative pressure (ROS) precipitate chondrocyte mitochondrial injury, characterized by decreased mitochondrial membrane potential (ΔΨm) and ATP production with increased mitochondrial ROS. Synovial mesenchymal stem cell-derived exosomes engineered to carry GrpE-like 1 are delivered intra-articularly and internalized by chondrocytes. GrpE-like 1 associates with phosphatase and tensin homolog-induced kinase 1 at the outer mitochondrial membrane, promoting phosphatase and tensin homolog-induced kinase 1 signaling (phospho-Ser65 ubiquitin), Parkin recruitment, and LC3-positive autophagosome formation followed by lysosomal degradation, thereby activating mitophagy. Enhanced mitochondrial renewal (mitochondrial ROS↓, ΔΨm↑, ATP↑) is linked to restoration of extracellular matrix homeostasis (collagen type II alpha 1/aggrecan↑; matrix metalloproteinase-13/A disintegrin and metalloproteinase with thrombospondin motifs 5↓) and improved cartilage integrity. The bottom ribbon highlights the minimal translational priorities required to move from proof-of-concept to an actionable disease-modifying osteoarthritis drug pathway: Flux validation, chemistry, manufacturing, and controls and mechanism-linked potency, and intra-articular pharmacokinetics/pharmacodynamics with endotype-aware stratification. OA: Osteoarthritis; IL-1β: Interleukin-1β; TNF-α: Tumor necrosis factor-alpha; ROS: Reactive oxygen species; ΔΨm: Mitochondrial membrane potential; mtROS: Mitochondrial reactive oxygen species; SMSC: Synovial mesenchymal stem cell; GRPEL1: GrpE-like 1; PINK1: Phosphatase and tensin homolog-induced kinase 1; pS65-Ub: Phospho-Ser65 ubiquitin; OMM: Outer mitochondrial membrane; ECM: Extracellular matrix; COL2A1: Collagen type II alpha 1; MMP-13: Matrix metalloproteinase-13; ADAMTS5: A disintegrin and metalloproteinase with thrombospondin motifs 5; CMC: Chemistry, manufacturing, and controls; IA: Intra-articular; PK/PD: Pharmacokinetics/pharmacodynamics.