Hypoxia Induced Ribosomal RNA Fragmentation Mediated by RNase L

Ischemic injury contributes to a range of global pathologies. Ischemia/Reperfusion Injury (IRI) is a paradoxical phenomenon that involves an initial restriction of blood flow followed by a sudden restoration of perfusion. This type of injury takes place in conditions such as myocardial infarction, acute kidney disease, and ischemic stroke and often leads to cellular death. Additionally, IRI exacerbates post-surgical outcomes and plays a role in graft dysfunction and transplant rejection. Despite efforts to develop therapies targeting known IRI pathways, clinical trials have largely been unsuccessful, underscoring the need for alternative mechanisms and biomarkers associated with IRI-induced apoptosis. Reactive oxygen species (ROS) generated during IRI-induced apoptosis inflict damage on proteins, lipids, and nucleic acids, including ribosomal RNA (rRNA), which is vital for ribosome function. Our cell culture studies uncovered distinct rRNA fragmentation patterns under oxidative stress and metal homeostasis defects, which differ from those observed in hypoxia/reoxygenation scenarios. This indicates that a unique mechanism is involved in IRI-induced apoptosis. One potential contributor to these rRNA alterations is ribonuclease activity. RNase-L, an interferon-associated ribonuclease, is upregulated during low-oxygen states and may be responsible for rRNA cleavage in hypoxia/reoxygenation conditions. Northern blot analysis revealed specific rRNA cleavages in wild-type (WT) A549 cells that were absent in RNase-L knockout (KO) A549 cells. Furthermore, WT cells exhibited significant morphological changes following hypoxia, while KO cells remained indistinguishable from control samples. These findings suggest a link between RNase-L and the unique rRNA cleavages observed during IRI-induced apoptosis. Further investigation into IRI-specific rRNA alterations, including fragmentation patterns and nucleotide modifications, could yield valuable insights into ischemic pathology. If validated, rRNA changes may serve as biomarkers for IRI, which can be used to enhance diagnostic capabilities and guide therapeutic development.