Therapeutic targeting of ADAM8 with isoacteoside mitigates myocardial infarction injury via OPA1-mediated mitochondrial fusion dynamics

Background Mitochondrial dysfunction is a central driver of myocardial injury following myocardial infarction (MI). Our previous work demonstrated that macrophage-specific knockout of a disintegrin and metalloproteinase 8 (ADAM8), a membrane-anchored metalloproteinase upregulated post-MI, markedly improved cardiac function, yet no small-molecule inhibitor has been identified and the downstream mitochondrial mechanisms remain undefined. Objective To identify an ADAM8 small-molecule inhibitor and elucidate its cardioprotective mechanisms with a focus on OPA1-mediated mitochondrial fusion dynamics. Methods High-throughput structure-based virtual screening and molecular docking targeted the catalytic domain of human ADAM8. Binding affinity of the lead compound, isoacteoside, was determined by surface plasmon resonance (SPR). Cardioprotective effects were evaluated in a murine MI model and an in vitro hypoxia/reoxygenation (H/R) model. Cardiac function was assessed by echocardiography; mitochondrial ultrastructure was visualised by transmission electron microscopy (TEM) and fluorescent probes; OPA1 cleavage was quantified by immunoblotting. Transcriptomic and metabolomic profiles were integrated via multi-omics analysis. Results (1) SPR confirmed that isoacteoside binds ADAM8 with high affinity (KD=0.938 μM). (2) Isoacteoside-treated MI mice showed reduced infarct size and attenuated myocardial fibrosis, with left ventricular ejection fraction and fractional shortening markedly preserved on echocardiography, recapitulating the cardioprotective phenotype of macrophage-specific ADAM8 knockout. (3) TEM revealed that isoacteoside reversed the extensive mitochondrial fragmentation and ruptured cristae seen in vehicle groups, restoring elongated, interconnected mitochondria with tightly stacked lamellar cristae; fluorescent probes confirmed restoration of mitochondrial membrane potential. (4) Mechanistically, ischaemic stress induced ADAM8 to cleave long-OPA1 (L-OPA1) to short-OPA1 (S-OPA1) on the inner mitochondrial membrane. This reduction in the L-OPA1/S-OPA1 ratio abolished inner membrane fusion capacity. Isoacteoside blocked this cleavage, restoring the L-OPA1 pool, GTPase-driven inner membrane tethering activity, and mitochondrial fusion competence. (5) Multi-omics analyses revealed upregulation of purine transporters Slc43a3 and Aqp9, replenishing the mitochondrial GTP pool for OPA1-dependent fusion, alongside enhanced cardiolipin biosynthesis, consolidating the lipid scaffold essential for OPA1-mediated inner membrane curvature and tubular network formation. Conclusion Isoacteoside is a novel ADAM8 inhibitor that protects against ischaemic cardiac injury by blocking ADAM8-mediated L-OPA1 cleavage and providing sustained metabolic support for OPA1-dependent mitochondrial fusion, highlighting ADAM8 inhibition as a promising translational strategy for MI therapy.Schematic diagram