Endocrine Abstracts

Introduction: Two major assay systems have been used for evaluation of parathyroid hormone (PTH) secretion. Whole PTH (wPTH) recognizes full-length 84 amino acid residues [PTH(1–84)], and Intact PTH (iPTH) recognizes NH2-truncated forms, such as PTH(7–84), in addition to PTH(1–84). Patients with chronic renal failure have increased amount of PTH(7–84) in circulations, so that the ratio of wPTH/iPTH indicates 0.7 or below usually. On the other hand, chromogranin-A (ChgA) is known to be a major protein costored and cosecreted with PTH in parathyroid glands. So, a role of ChgA in the process of biosynthesis of PTHs in cultured parathyroid cells was studied by using RNA interference (RNAi).

Method and result: RNAi was performed for 24 h to suppress the expression of ChgA in parathyroid cells. We observed that 50 nM of siRNA suppressed both values of wPTH and iPTH moderately, and importantly, they kept being almost equal for two weeks. Representatively, the mean values and S.D. of secreted wPTH and iPTH from cells transfected with siRNA for ChgA were 466.3±48.0 ng and 477.0±18.4 ng, respectively (wPTH/iPTH=0.98), whereas those of cells transfected with a negative control siRNA were 602.0±168.9 ng and 860.0±191.8 ng, respectively (wPTH/iPTH=0.70). The result indicates that almost no truncated PTH(7–84) was produced in cells of ChgA suppression.

Conclusion: It is suggested that ChgA plays a role in production of truncated forms of PTH. Parathyroid cell culture system with suppression of CgA is useful to examine processes of PTH biosynthesis.

Declaration of interest: The authors declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research project.

Funding: This research did not receive any specific grant from any funding agency in the public, commercial or not-for-profit sector.