Simultaneous expression analysis of vitamin D receptor, calcium-sensing receptor, cyclin D1, and PTH in symptomatic primary hyperparathyroidism in Asian Indians

Abstract

Background: To explore underlying molecular mechanisms in the pathogenesis of symptomatic sporadic primary hyperparathyroidism (PHPT). Materials and methods: Forty-one parathyroid adenomas from patients with symptomatic PHPT and ten normal parathyroid glands either from patients with PHPT (nZ3) or from euthyroid patients without PHPT during thyroid surgery (nZ7) were analyzed for vitamin D receptor (VDR), calcium-sensing receptor (CASR), cyclin D1 (CD1), and parathyroid hormone (PTH) expressions. The protein expressions were assessed semiquantitatively by immunohistochemistry, based on percentage of positive cells and staining intensity, and confirmed by quantitative real-time PCR. Results: Immunohistochemistry revealed significant reductions in VDR (both nuclear and cytoplasmic) and CASR expressions and significant increases in CD1 and PTH expressions in adenomatous compared with normal parathyroid tissue. Consistent with immunohistochemistry findings, both VDR and CASR mRNAs were reduced by 0.36-and 0.45-fold change (P!0.001) and CD1 and PTH mRNAs were increased by 9.4-and 17.4-fold change respectively (P!0.001) in adenomatous parathyroid tissue. PTH mRNA correlated with plasma PTH (rZ0.864; P!0.001), but not with adenoma weight, while CD1 mRNA correlated with adenoma weight (rZ0.715; P!0.001). There were no correlations between VDR and CASR mRNA levels and serum Ca, plasma intact PTH, or 25-hydroxyvitamin D levels. In addition, there was no relationship between the decreases in VDR and CASR mRNA expressions and the increases in PTH and CD1 mRNA expressions. Conclusions: The expression of both VDR and CASR are reduced in symptomatic PHPT in Asian Indians. In addition, CD1 expression was greatly increased and correlated with adenoma weight, implying a potential role for CD1 in adenoma growth and differential clinical expression of PHPT.

Diffuse PTH expression in parathyroid tumors argues against important functional tumor subclones

“…The level of downregulation was unrelated to patient serum calcium, PTH or 25(OH)D 3 levels. Carling and coworkers reported a correlation between tumor VDR levels and patient serum calcium, but neither this study nor Varshney and coworkers could confirm these findings (32, 36, 37, 38). In our study samples, tumors whose PTH mRNA levels were lower than adjacent normal rim were significantly larger than tumors with equivalent levels.…”

“…We found that a majority of parathyroid tumors had generally lower levels of PTH mRNA than the corresponding normal rim. Previously, studies have found both lower and higher PTH mRNA expression in parathyroid tumors as compared with normal parathyroids (28, 29, 30, 31, 32). Similar to other studies, we did not observe a relationship between PTH IHC or PTH CISH and serum calcium and serum PTH levels (33, 34).…”

“…The rationale behind these discrepancies may be due to differences in the study populations, including the degree of vitamin D insufficiency. Specifically, the impact of vitamin D insufficiency may be limited in primary hyperparathyroidism diagnosed at an early stage (18, 19, 20, 21, 32, 40, 41). Indeed, our semi-quantitative immunohistochemistry may be too crude to accurately quantify the tumor PTH levels for weaker statistical relationships.…”

Parathyroid Growth

“…109 In parathyroid adenomas there is significant underexpression of the 110,111 and protein, [112][113][114] which is likely the proximate cause of the increase in set point. 108,114 No mutations in the CaSR gene have been found, 115,116 but CaSR expression appears to be significantly reduced in almost every cell, 117 so it could have been the initial abnormality in the founder cell. No abnormal methylation of the CaSR gene has been found in parathyroid adenomas 118 but other epigenetic changes 90 have not been studied.…”

Primary hyperparathyroidism: epidemiology, clinical features, diagnostic tools and current management

“…In the first case newborns presented with hypotonia, poor feeding, constipation and respiratory distress: it is usually due to a homozygous mutation of calcium sensing receptor gene. 25 Familial hypocalciuric hypercalcemia is generally a benign disorder caused by heterozygous inactivating mutation of calcium sensing receptor gene: the patients presented with elevated serum calcium and PTH levels but not complication of primary hyperparathyroidism. 26 The expression of the VDR gene (vitamin D receptor) and the CASR gene (calcium sensing receptor) may play an important role in the development of PHPT caused by parathyroid adenomas: recent studies have explored the underlying molecular mechanism in the pathogenesis of sporadic symptomatic primary hyperparathyroidism implying a potential role in adenoma growth and differential clinical expression.…”