The number of oxygenated derivatives of cholesterol, its precursors, and other biologically relevant sterols that exist in biological systems is unknown and may extend substantially beyond the oxysterols currently characterized. Successive oxidation, reduction, hydrolysis, sulfation, glucuronidation, esterification, and conjugation reactions can generate a large chemical space that we refer to as the oxysterolome. However, chemical possibility does not establish endogenous existence, and endogenous existence does not establish biological function. Defining this metabolic space requires a progression from analytical annotation to structural authentication, metabolic reconstruction, and biological validation. Iterative metabolism broadens physicochemical diversity, making analytical coverage method-dependent and requiring complementary approaches for different metabolite classes. Authenticated metabolites should subsequently be connected through precursor–product relationships, enzyme dependence, isotope tracing, metabolic flux, and spatial organization. Biological relevance requires separate evidence linking endogenous exposure and pathway perturbation to molecular mechanisms and phenotypes. Further metabolism can generate, terminate, or redirect biological activity, but these outcomes cannot be predicted from structural complexity. The oxysterolome should therefore be approached not as an expanding catalog of oxygenated sterols, but as an experimentally reconstructed metabolic network integrating molecular identity, pathway connectivity, flux, and biological causality.
Cell-surface gangliosides tune receptor signaling, cell-state transitions, and responses to stress. NEU3 is a mammalian sialidase associated with the plasma membrane and endomembranes that preferentially removes terminal sialic acids from gangliosides. Here, we critically review biochemical studies, cultured-cell experiments, animal models, and observations in human tissues that link NEU3 to myogenesis, hypoxic adaptation, cardioprotection, ganglioside storage disorders, cancer, fibrosis, and intestinal inflammation. Across these settings, NEU3 can alter the local ganglioside environment of receptors and signaling complexes, but the strength and direction of the resulting effects vary with cell type, substrate availability, localization, expression level, and duration of activity. We therefore frame NEU3 as a context-dependent regulator rather than a uniformly beneficial or harmful enzyme. This evidence-weighted model helps reconcile apparently opposing findings while highlighting important uncertainties in membrane topology, extracellular delivery, substrate selection, and pharmacological specificity. Selective inhibitors, tissue-restricted delivery, and biomarker-guided approaches are promising, but clinical translation will require stronger target-engagement data and broader in vivo validation.
