HIF

HIF prolyl-hydroxylases (PHDs/EGLNs) are oxygen-dependent 2-oxoglutarate dioxygenases that function as the principal cellular oxygen sensors by hydroxylating HIF-α subunits and promoting their proteasomal degradation under normoxic conditions^[1][2][3]. Mechanistically, decreased oxygen availability suppresses PHD activity, resulting in HIF-α stabilization, nuclear accumulation, and transcriptional activation of genes involved in oxygen homeostasis, metabolism, angiogenesis, and erythropoietic responses^[1][2][4][5]. The PHD-HIF axis therefore constitutes a central hypoxia-signaling pathway that coordinates adaptive cellular responses to oxygen limitation and contributes to physiological and pathological processes including cancer, ischemia, tissue repair, and hypoxia-associated diseases^[2][4][5][6]. Among the three major isoforms, PHD2 (EGLN1) is widely recognized as the dominant regulator of HIF-1α stability and the key oxygen sensor controlling basal HIF activity, whereas PHD1 and PHD3 display distinct regulatory functions and tissue-specific contributions^[7][8][9]. Experimental studies demonstrated that silencing PHD2, but not PHD1 or PHD3, markedly impairs oxygen-dependent HIF-1α degradation, highlighting the unique role of PHD2 in HIF regulation^[7]. PHD isoforms also exhibit differential expression patterns and feedback regulation by HIF signaling, supporting nonredundant functions within hypoxia-responsive networks^[8][9]. For experimental applications, pharmacological PHD inhibitors stabilize HIF-1α and are widely used to model hypoxic signaling, while selective inhibition of PHD activity provides a practical approach for investigating oxygen sensing, HIF-dependent transcriptional programs, and disease-relevant adaptive responses^[10][11].