Local NF-κB Activation Promotes Parathyroid Hormone Synthesis and Secretion in Uremic Patients

Abstract

Secondary hyperparathyroidism (SHPT) in uremic patients is characterized by parathyroid gland (PTG) hyperplasia and parathyroid hormone (PTH) elevation. Previously, we demonstrated that NF-κB activation contributed to parathyroid cell proliferation in rats with chronic kidney disease. Although vitamin D inhibits inflammation and ameliorates SHPT, the contribution of vitamin D deficiency to SHPT via local NF-κB activation remains to be clarified. PTGs collected from 10 uremic patients with advanced SHPT were used to test the expressions of vitamin D receptor (VDR), NF-κB, and proliferating cell nuclear antigen (PCNA). Freshly excised PTG tissues were incubated for 24 hours in vitro with VDR activator (VDRA) calcitriol or NF-κB inhibitor pyrrolidine thiocarbamate (PDTC). Chromatin immunoprecipitation (ChIP) and luciferase reporter assays were performed to investigate the regulation of PTH transcription by NF-κB. We found higher levels of activated NF-κB and lower expression of VDR in nodular hyperplastic PTGs than in diffuse hyperplasia. In cultured PTG tissues, treatment with VDRA or PDTC inhibited NF-κB activation and PCNA expression, and downregulated preproPTH mRNA and intact PTH levels. ChIP assays demonstrated the presence of NF-κB binding sites in PTH promoter. Furthermore, in luciferase reporter assays, addition of exogenous p65 significantly increased PTH luciferase activity by 2.4-fold (P < 0.01), while mutation of NF-κB binding site at position -908 of the PTH promoter suppressed p65-induced PTH reporter activity (P < 0.01). In summary, local NF-κB activation contributes to SHPT and mediates the transcriptional activation of PTH directly in uremic patients. Vitamin D deficiency may be involved in SHPT via the activation of NF-κB pathway.

Keywords: nuclear factor-κB; parathyroid hormone; secondary hyperparathyroidism; vitamin D receptor activator.