S-nitrosation in endothelium: different outcomes of NRF2 and GSNOR loss

Cardiovascular diseases are a major global health burden, and that is largely caused by premature aging of endothelial cells (ECs). Therefore, understanding of molecular mechanisms of EC aging is central to establishing novel therapeutic approaches. We have previously found that cells devoid of the transcription factor NRF2 are prematurely aged and identified numerous concomitant phenomena, among them extensive S-nitrosation (SNO) and increased expression of innate immunity regulators. As both could be putative reasons for the premature senescence, we aimed to establish their causative role. We found that the premature senescence of NRF2-deficient ECs is related to an overactivation of cGAS/STING pathway, a canonical modulator of innate immune response. To address the significance of abundant SNO, we used the model of S-nitrosoglutathione reductase (GSNOR), and we found that its deletion does not result in the induction of senescence or cGAS/STING activation. This supports a divergent outcome of increased SNO on EC phenotype. In the quest for a conducive mechanism, we characterized GSNOR-deficient ECs. We evidenced presence of atypical DNA cytoplasmic inclusions, abnormal structure and permeability of the nuclear envelope, along with changes in the actin cytoskeleton architecture. Interestingly, we found that the cytoplasmic DNA is not retained within ECs, but it is released out of the cell in an autophagy-dependent manner. Molecularly, we found that macrophage inhibitory factor (MIF) is an essential driver of this secretion. In sum, we have shown that premature senescence of NRF2-deficient ECs is triggered by overactivation of STING. In parallel, we have identified the pivotal role of GSNOR in ECs. This study advances the understanding of the mechanisms of premature senescence of ECs and points out at a cellular context-dependent outcome of enhanced SNO in ECs.