Abstract Body: Cardiac fibrosis is a major determinant of adverse remodeling after ischemia-reperfusion (I/R) injury. This process is driven by the activation of resident fibroblasts into extracellular matrix-secreting myofibroblasts, regulated by a signaling network including TGF-β and proinflammatory cytokines. A potential modulator of this landscape is the plasma membrane-associated sialidase Neu3, an enzyme that influences cellular responsiveness by desialylating surface glycoconjugates. Neu3 activity has been linked to fibrotic progression in the liver and lungs, where its inhibition by the compound 2-acetylpyridine (2-AP) effectively attenuates tissue scarring. However, its specific role in the myocardium remains unclear.
Mice subjected to transient LAD occlusion were treated with 2-AP (1 mg/kg) for 14 days. Echocardiographic analysis revealed that the reduction in ejection fraction and fractional shortening was approximately 50% lower in treated mice than in controls, indicating partial preservation of cardiac function. Histological analysis demonstrated a 70% reduction in extracellular matrix deposition in the infarcted myocardium of treated mice compared with controls. Despite these promising in vivo outcomes, enzymatic assays on cardiac fibroblasts showed that 2-AP failed to inhibit Neu3 sialidase activity. To elucidate the specific involvement of this enzyme, human cardiac fibroblasts were stimulated with TGF-β and treated with either a highly selective Neu3 inhibitor (LR332) or an inducible system for Neu3 overexpression. Contrary to the initial hypothesis, specific inhibition via LR332 failed to attenuate fibroblast activation. However, Neu3 upregulation suppressed the pro-fibrotic phenotype, reducing α-smooth muscle actin (α-SMA) expression by about 30% and collagen I expression by about 25%. Thus, while 2-AP exerts cardioprotective and anti-fibrotic effects in vivo, its mechanism appears independent of Neu3 inhibition. Unexpectedly, Neu3 upregulation limits fibroblast activation, suggesting that Neu3 may represent a novel modulator of cardiac fibrosis and a potential target to limit adverse cardiac remodeling.