Hypoxia causes triglyceride accumulation via HIF-1-mediated stimulation of lipin 1 expression

Adaptation to hypoxia involves the hypoxia-inducible transcription factors HIFs and requires reprogramming of cellular metabolism that is essential during both physiological and pathological processes. In contrast to the established role of HIF-1 in glucose metabolism, the involvement of HIFs and the molecular mechanisms concerning the effects of hypoxia on lipid metabolism are poorly characterized. Here, we report that exposure of human cells to hypoxia causes triglyceride and lipid droplet accumulation. This is accompanied by induction of lipin 1, a phosphatidate phosphatase isoform that catalyzes the penultimate step in triglyceride biosynthesis, while lipin 2 remains unaffected. Hypoxic up-regulation of lipin 1 expression involves predominantly HIF-1, which binds to a single distal hypoxia-responsive element in the lipin 1 gene promoter and causes its activation under low oxygen conditions. Hypoxic triglyceride or lipid droplet accumulation can be blocked by siRNA-mediated silencing of lipin 1 expression or kaempferol-mediated inhibition of HIF-1. We conclude that direct control of lipin 1 transcription by HIF-1 is an important regulatory feature of lipid metabolism and its adaptation to hypoxia.