Hypoxia-Inducible Factor-1 Regulates High Phosphate-Induced Vascular Calcification via Type III Sodium-Dependent Phosphate Cotransporter 1

Vascular calcification (VC) has a high incidence in patients with chronic kidney disease, which is a worldwide public health problem and presents a heavy burden to society. Hypoxia-inducible factor (HIF)-1 alpha, the active subunit of HIF-1, has been reported to play a vital role in high phosphate-induced VC. However, the underlying mechanism is still undetermined, and effective treatment is unavailable. In the present study, human aortic smooth muscle cells (HASMCs) were cultured under normal or high phosphate media conditions. HIF-1 alpha small interfering RNA and overexpression plasmids were employed to regulate HIF-1 alpha expression. Phosphonoformic acid was employed to restrain the function of type III sodium-dependent phosphate cotransporter 1 (Pit-1). The expression levels of HIF-1 alpha, Pit-1, runt-related transcription factor 2 (Runx2), and smooth muscle 22 alpha (SM22 alpha) were evaluated, and the calcium contents were also examined. Cell growth was assessed using an MTT assay. High phosphate stimulation caused an upregulation in HIF-1 alpha and Pit-1 expression levels and induced calcium depositions in HASMCs. Upregulation of Runx2 expression accompanied by downregulation of SM22 alpha expression was observed in the high phosphate group. Following the suppression of HIF-1 alpha expression, there was a concomitant attenuation in Pit-1 expression, calcium deposition, the alteration of phenotypic transition marker genes, and vice versa. The most serious calcium deposition was noted in HASMCs cultured under high phosphate conditions which were pretreated with a HIF-1 alpha overexpression plasmid. However, when the biological functions of Pit-1 were restrained, the putative serious calcium deposition was not formed even in HASMCs transfected with a HIF-1 alpha overexpression plasmid. The findings confirmed that HIF-1 alpha regulated Pit-1 expression and exerted its pro-calcifying effect through Pit-1, which identified HIF-1 alpha and Pit-1 as therapeutic targets for high phosphate-induced VC.