The function of NOX4 (NADPH oxidase 4, ENSG00000086991) is as follows. NADPH oxidase that catalyzes predominantly the reduction of oxygen to H2O2 (PubMed:14966267, PubMed:15356101, PubMed:15927447, PubMed:21343298, PubMed:25062272). Can also catalyze to a smaller extent, the reduction of oxygen to superoxide (PubMed:10869423, PubMed:11032835, PubMed:15155719, PubMed:15572675, PubMed:15927447, PubMed:16019190, PubMed:16179589, PubMed:16230378, PubMed:16324151, PubMed:25062272). May function as an oxygen sensor regulating the KCNK3/TASK-1 potassium channel and HIF1A activity (PubMed:16019190). May regulate insulin signaling cascade (PubMed:14966267). May play a role in apoptosis, bone resorption and lipolysaccharide-mediated activation of NFKB (PubMed:15356101, PubMed:15572675). May produce superoxide in the nucleus and play a role in regulating gene expression upon cell stimulation (PubMed:16324151). Promotes ferroptosis, reactive oxygen species production and reduced glutathione (GSH) levels by activating NLRP3 inflammasome activation and cytokine release (PubMed:39909992). {ECO:0000269|PubMed:10869423, ECO:0000269|PubMed:11032835, ECO:0000269|PubMed:14966267, ECO:0000269|PubMed:15155719, ECO:0000269|PubMed:15356101, ECO:0000269|PubMed:15572675, ECO:0000269|PubMed:15927447, ECO:0000269|PubMed:16019190, ECO:0000269|PubMed:16179589, ECO:0000269|PubMed:16230378, ECO:0000269|PubMed:16324151, ECO:0000269|PubMed:21343298, ECO:0000269|PubMed:25062272, ECO:0000269|PubMed:39909992}. [Isoform 4]: NADPH oxidase that catalyzes the generation of superoxide from molecular oxygen utilizing NADPH as an electron donor (PubMed:15721269, PubMed:23393389). Involved in redox signaling in vascular cells (PubMed:23393389). Modulates the nuclear activation of ERK1/2 and the ELK1 transcription factor, and is capable of inducing nuclear DNA damage (PubMed:23393389). {ECO:0000269|PubMed:15721269, ECO:0000269|PubMed:23393389}. [Isoform 3]: Lacks superoxide-generating NADPH oxidase activity. .