Ncl liquid-liquid phase separation and SUMOylation mediate the stabilization of HIF-1α expression and promote pyroptosis in ischemic hindlimb

Liquid-liquid phase separation (LLPS) has emerged as a flexible intracellular compartment that modulates various pathological processes. Hypoxia-inducible factor-1α (HIF-1α) has been shown to play an essential role in inflammation after ischemic injury. However, the mechanisms underlying HIF-1α-induced inflammation in ischemic diseases have not been defined. This study found that HIF-1α mediated the progression of ischemia-induced muscle injury. After ischemic injury, SUMO1 is upregulated and rapidly activates NLRP3 inflammasome through the upregulation of HIF-1α, leading to enhanced inflammation and pyroptosis. Co-IP revealed an interaction between SUMO1 and HIF-1α and SUMOylation of HIF-1α at K477. Moreover, we demonstrated the important role of dynamic phase separation of Nucleolin (Ncl) in regulating HIF-1α mRNA stability through fluorescence recovery after photobleach (FRAP) analysis. The stability of HIF-1α is regulated by Ncl liquid-liquid phase separation and SUMOylation in ischemia-induced hindlimb injury. HIF-1α can promote the expression of NLRP3 and other inflammation-related molecules, leading to pyroptosis, suggesting that Ncl/LLPS/HIF-1α or SUMO1/HIF-1α pathway may be a new target for the treatment of inflammation in ischemic diseases. Although previous studies have found that HIF-1α is able to promote the expression of target genes after hypoxia, and these genes are used to maintain the stability of the intracellular environment to adapt to hypoxia. We found that HIF-1α is involved in the activation process of NLRP3 inflammasomes after hind limb ischemia, which enriches our understanding of the biological role of HIF-1α.