Primary and secondary hyperparathyroidism present different expressions of calcium-sensing receptor

BACKGROUND: Decreased calcium-sensing receptor (CaSR) has been observed in hyperparathyroidism (HPT) without a known mechanism. The purpose of this study was to evaluate the expression of CaSR in primary (PHPT) and secondary (SHPT) subtypes. METHODS: Immunohistochemical (IHC) staining and quantitative real-time PCR (qRT-PCR) assay were used to measure the differences in expression of CaSR protein and gene in PHPT and SHPT human samples, compared to matched controls. RESULTS: CaSR protein was differentially downregulated in SHPT and PHPT compared to normal parathyroid tissues (2.42 ± 0.5 vs. 3.2 ± 0.62, P < 0.05; 1.8 ± 0.83 vs. 3.2 ± 0.62, P < 0.05, respectively). Furthermore, SHPT tissues exhibited significantly higher levels of CaSR mRNA (0.29 ± 0.23 vs. 0.01 ± 0.12, P < 0.05) and protein (2.42 ± 0.5 vs. 1.8 ± 0.83, P < 0.05) than those in PHPT tissue samples. CONCLUSION: Depressed CaSR expression was a critical pathological hallmark of HPT. We found a differential decline of CaSR, in terms of both mRNA and protein levels, in PHPT and SHPT human samples. We think that CaSR dysregulation occurred at the very beginning of disease onset in PHPT, while a similar pathological scenario appeared at the later stage of SHPT. Future studies should be directed to dissect the mechanistic involvement of CaSR in PHPT and SHPT in order to bring treatment precisions in HPT management.