ABSTRACT
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)-1α, 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-1α small interfering RNA and overexpression plasmids were employed to regulate HIF-1α expression. Phosphonoformic acid was employed to restrain the function of type III sodium-dependent phosphate cotransporter 1 (Pit-1). The expression levels of HIF-1α, Pit-1, runt-related transcription factor 2 (Runx2), and smooth muscle 22 alpha (SM22α) 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-1α and Pit-1 expression levels and induced calcium depositions in HASMCs. Upregulation of Runx2 expression accompanied by downregulation of SM22α expression was observed in the high phosphate group. Following the suppression of HIF-1α 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-1α 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-1α overexpression plasmid. The findings confirmed that HIF-1α regulated Pit-1 expression and exerted its pro-calcifying effect through Pit-1, which identified HIF-1α and Pit-1 as therapeutic targets for high phosphate-induced VC.
ABSTRACT
Vascular calcification (VC) is highly prevalent in chronic kidney disease (CKD), especially in patients with end stage renal disease and is strongly associated with cardiovascular morbidity and mortality. Clinical observations have demonstrated that hyperphosphatemia and hyperglycemia can accelerate VC. Spironolactone (SPL) has been proven to improve cardiovascular outcomes in clinical trials and its protective effect on VC has been reported recently; however, the underlying mechanisms are not completely understood and require further investigation. Furthermore, the current CKD rat models that are used to research VC do not match well with the clinical characteristics of CKD patients. Aortic rings were obtained from male SpragueDawley rats, then cultured in different media with varying phosphorus and glucose concentrations to investigate the effects and the possible mechanisms, as well as the effective serum concentrations of SPL, on VC and type III sodiumdependent phosphate cotransporter1 (Pit1) expression. SPL dosedependently alleviated VC by suppressing the phenotypic transition of vascular smooth muscle cell (VSMCs) through downregulation of Pit1 in a high phosphorus medium and even in a high phosphorus combined with high glucose medium. The combined effects of hyperglycemia and hyperphosphatemia on the calcification of aortic rings ex vivo were demonstrated. In conclusion to the best of our knowledge, this article is the first report on the effective serum concentrations of SPL capable of protecting VSMCs from calcification and provides the first experimental evidence for the combined effects of hyperglycemia and hyperphosphatemia on VC of aortic rings. Additionally, the Pit1 protein level may be a novel index for evaluating the magnitude of VC in CKD patients.
