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

Table 1 Condensed evidence-and-gap map for the GrpE-like 1-phosphatase and tensin homolog-induced kinase 1-mitophagy axis in osteoarthritis

Evidence layer	Source/model	Key readouts	Bottom-line message	Strength	Key gap/next step
In silico nomination	Public OA cartilage transcriptomes (GSE169077; GSE114007)	DEG/prioritization; pathway enrichment; immune deconvolution	GRPEL1 emerges as a mitochondria/MQC-associated candidate with disease/immune association tags	Associative	Validate across additional cohorts/platforms; control for cell-composition confounding
Human association	Human OA vs controls (biofluids/tissue) + clinical indices	GRPEL1 level vs CRP/IL-6/TNF-α; KL grade	Lower GRPEL1 associates with higher inflammatory burden and worse radiographic severity	Correlative (cross-sectional)	Independent validation cohort; analytic validation of protein assays (IHC/ELISA) and clinically usable thresholds
Product definition	SMSC-Exos ± GRPEL1 engineering	EV identity markers; particle metrics; GRPEL1 enrichment	Engineering plausibly alters cargo and strengthens biological activity	Enabling (not MoA proof)	Quantify GRPEL1 per dose/particle; define release specs and batch comparability
In vitro efficacy	IL-1β-challenged chondrocytes	Proliferation/migration; ECM markers; oxidative injury; ΔΨm	GRPEL1-Exos improve injury phenotypes and ECM balance	Functional	Distinguish pleiotropy vs mitophagy dependence; add flux-aware mitophagy readouts
Mechanistic anchoring	Co-IP + pathway perturbation	GRPEL1-PINK1 association; PINK1 loss-of-function attenuates benefit	Supports a PINK1-dependent linkage rather than generic anti-inflammatory effects	Causal-supporting	Event-level tags (e.g., pS65-Ub; Parkin recruitment) + mitophagy flux confirmation
In vivo outcome	DMM rat OA; intra-articular dosing	OARSI/ICRS; histology; ECM IHC; mitophagy-associated tissue signals	Structural benefit with cargo dependence is shown preclinically	Strong preclinical coherence	Joint PK/retention; repeated-dose safety; large-animal bridging; PD-to-regimen linkage and patient endotype

OA: Osteoarthritis; DEG: Differentially expressed gene(s); GRPEL1: GrpE-like 1; MQC: Mitochondrial quality control; CRP: C-reactive protein; IL-1β: Interleukin-1 beta; IL-6: Interleukin-6; TNF-α: Tumor necrosis factor-alpha; KL: Kellgren-Lawrence; IHC: Immunohistochemistry; ELISA: Enzyme-linked immunosorbent assay; SMSC-Exos: Synovial mesenchymal stem cell-derived exosomes; EV: Extracellular vesicle(s); MoA: Mechanism of action; ECM: Extracellular matrix; ΔΨm: Mitochondrial membrane potential; Exos: Exosomes; Co-IP: Co-immunoprecipitation; PINK1: Phosphatase and tensin homolog-induced kinase 1; pS65-Ub: Phospho-Ser65 ubiquitin; DMM: Destabilization of the medial meniscus; OARSI: Osteoarthritis Research Society International; ICRS: International Cartilage Repair Society; PK: Pharmacokinetics; PD: Pharmacodynamics.