Hepoxilin A3 protects β-cells from apoptosis in contrast to its precursor, 12-hydroperoxyeicosatetraenoic acid

Pancreatic β-cells have a deficit of scavenging enzymes such as catalase (Cat) and glutathione peroxidase (GPx) and therefore are susceptible to oxidative stress and apoptosis. Our previous work showed that, in the absence of cytosolic GPx in insulinoma RINm5F cells, an intrinsic activity of 12 lipoxygenase (12(S)-LOX) converts 12S-hydroperoxyeicosatetraenoic acid (12(S)-HpETE) to the bioactive epoxide hepoxilin A3 (HXA3). The aim of the present study was to investigate the effect of HXA3 on apoptosis as compared to its precursor 12(S)-HpETE and shed light upon the underlying pathways. In contrast to 12(S)-HpETE, which induced apoptosis via the extrinsic pathway, we found HXA3 not only to prevent it but also to promote cell proliferation. In particular, HXA3 suppressed the pro-apoptotic BAX and upregulated the anti-apoptotic Bcl-2. Moreover, HXA3 induced the anti-apoptotic 12(S)-LOX by recruiting heat shock protein 90 (HSP90), another anti-apoptotic protein. Finally, a co-chaperone protein of HSP90, protein phosphatase 5 (PP5), was upregulated by HXA3, which counteracted oxidative stress-induced apoptosis by dephosphorylating and thus inactivating apoptosis signal-regulating kinase 1 (ASK1). Taken together, these findings suggest that HXA3 protects insulinoma cells from oxidative stress and, via multiple signaling pathways, prevents them from undergoing apoptosis.

Research highlights
► 12(S)-HpETE induces apoptosis of RINm5F cells by activating the extrinsic pathway.
► HXA3 protects RINm5F cells against apoptosis and promotes cell survival.
► HXA3 protects RINm5F cells from apoptosis by promoting Bcl-2 and downregulating Bax.
► HXA3 induces 12(S)-LOX transcription via HSP90 upregulation.
► HXA3 induces PP5 that subsequently inactivates ASK1 and inhibits apoptosis.