Abstract: Objective To explore the miRNAs that down- regulate calcium-sensing receptor (CaSR) in secondary hyperparathyroidism (SHPT) and their effects on parathyroid hormone (PTH) secretion. Methods Whole transcriptome sequencing was performed for 6 normal parathyroid tissue samples and 11 SHPT parathyroid tissue samples. Based on bioinformatic prediction, we screened out 7 candidate miRNAs that regulate CaSR, among which the most likely miRNA for CaSR regulation was identified by double luciferase test. We detected the differential expression of miR-301a-5p and CaSR mRNA in SHPT and normal parathyroid tissue using qRT-PCR, and analyzed the correlation between their expressions and serum PTH levels of the patients. Western blotting was used to detect the expression of CaSR protein in primary SHPT parathyroid cells transfected with miR-301a-5p mimics or inhibitors, and the level of PTH in the supernatant of the cell culture was determined. Results Among the preliminarily selected 7 miRNAs that potentially regulate CaSR (miR-15a-5p, miR-15b-5p, miR- 16- 5p, miR- 221- 3p, miR- 222- 3p, miR- 301a- 5p and miR- 503- 5p), miR- 301a-5p was significantly upregulated in SHPT compared with normal parathyroid tissue (P<0.05), and its expression appeared to be positively correlated with PTH level, but this correlation was not statistically significant (P>0.05); The expression of CaSR mRNA was significantly downregulated in SHPT (P<0.05), and its expression tended to inversely correlate with the patient's PTH level, but the correlation was not statistically significant (P>0.05). In primary culture of SHPT parathyroid cells, miR-301a-5p overexpression caused a significant decrease of CaSR protein expression (P<0.05), and conversely, inhibition of miR-301a-5p expression increased the expression of CaSR protein (P<0.05). Although miR-301a-5p overexpression did not significantly affect PTH secretion of the cells (P>0.05), inhibition of iR- 301a- 5p expression strongly increased the secretion of PTH (P<0.05). Conclusion MiR- 301a- 5p affects PTH secretion in SHPT possibly by regulating the expression of CaSR.

Key words: secondary hyperparathyroidism; calcium-sensing receptors; parathyroid hormone; miR-301a-5p