Ischemic injury is a primary cause of distal flap necrosis. Previous studies have shown that Flufenamic acid (FFA) can reduce inflammation, decrease oxidative stress (OS), and promote angiogenesis, suggesting its potential role in protecting flaps from ischemic damage. This study investigated the effects and mechanisms of FFA in enhancing the survival of ischemic flaps.

The viability of ischemic flaps was evaluated using laser doppler blood flow (LDBF) and survival rates. We examined levels of pyroptosis, OS, transcription factor E3 (TFE3)-induced autophagy, and elements of the AMPK-TRPML1-Calcineurin pathway through western blotting (WB), immunofluorescence, molecular docking, cellular thermal shift assay (CETSA) and surface plasmon resonance.

The findings suggest that FFA significantly enhances the viability of ischemic flaps. The improvement in flap survival associated with FFA can be attributed to increased autophagy, diminished OS, and the suppression of pyroptosis. Notably, the promotion of autophagy flux and an augmented resistance to OS are instrumental in curbing pyroptosis in these flaps. Activation of TFE3 by FFA promoted autophagy and diminished oxidative damage. The therapeutic effects of FFA were negated when TFE3 levels were decreased using adeno-associated virus (AAV)-TFE3shRNA. Additionally, FFA modified TFE3 activity through the AMPK-TRPML1-Calcineurin pathway.

FFA promotes ischemic flap survival via induction of autophagy and suppression of OS by activation of the AMPK-TRPML1-Calcineurin-TFE3 signaling pathway. These findings could have therapeutic implications.

Ensuring the survival of the distal end of a random flap during hypoperfusion (ischaemia) is difficult in clinical practice. Effective prevention of programmed cell death is a potential strategy for inhibiting ischaemic flap necrosis. The activation of stimulator of interferon genes (STING) pathway promotes inflammation and leads to cell death. The epidermal growth factor family member neuregulin-1 (NRG1) reduces cell death by activating the protein kinase B (AKT) signalling pathway. Moreover, AKT signalling negatively regulates STING activity. We aimed to verify the efficacy of NRG1 injection in protecting against flap necrosis. Additionally, we investigated whether NRG1 effectively enhances ischemic flap survival by inhibiting pyroptosis and necroptosis through STING suppression.

A random-pattern skin flap model was generated on the backs of C57BL/6 mice. The skin flap survival area was determined. The blood supply and vascular network of the flap was assessed by laser Doppler blood flow analysis. Cluster of differentiation 34 immunohistochemistry (IHC) and haematoxylin and eosin (H&E) staining of the flap sections revealed microvessels. Transcriptome sequencing analysis revealed the mechanism by which NRG1 promotes the survival of ischaemic flaps. The levels of angiogenesis, oxidative stress, necroptosis, pyroptosis and indicators associated with signalling pathways in flaps were examined by IHC, immunofluorescence and Western blotting. Packaging adeno-associated virus (AAV) was used to activate STING in flaps.

NRG1 promoted the survival of ischaemic flaps. An increased subcutaneous vascular network and neovascularization were found in ischaemic flaps after the application of NRG1. Transcriptomic gene ontology enrichment analysis and protein level detection indicated that necroptosis, pyroptosis and STING activity were reduced in the NRG1 group. The phosphorylation of AKT and forkhead box O3a (FOXO3a) were increased after NRG1 treatment. The increased expression of STING in flaps induced by AAV reversed the therapeutic effect of NRG1. The ability of NRG1 to phosphorylate AKT-FOXO3a, inhibit STING and promote flap survival was abolished after the application of the AKT inhibitor MK2206.

NRG1 inhibits pyroptosis and necroptosis by activating the AKT-FOXO3a signalling pathway to suppress STING activation and promote ischaemic flap survival.