Endocrine Abstracts

Multiple endocrine neoplasia type 1 (MEN1) is characterized by the combined occurrence of parathyroid, pancreatic islet and anterior pituitary tumours. Over 95% of MEN1 patients will have developed a manifestation of MEN1 by the age of forty years, and in >85% of patients, parathyroid tumours are the first to occur. In a previously reported Men1 knockout mouse model, parathyroid tumours occurred in less than 50% of Men1 heterozygous (Men1^+/−) mice by the old age of eighteen months (upper life expectancy twenty-two months). This suggests that the parathyroid proliferation rate may be low and in order to assess this we used continuous long-term in vivo 5-bromo-2-deoxyuridine (BrdU) labelling. BrdU is recognised to be the most reliable marker of cell proliferation as it allows the substitution of an endogenous DNA base, thymidine, with the BrdU analogue, ensuring specific labelling during S-phase of only the dividing cells. Mice were kept in accordance with UK Home Office welfare guidelines and project licence restrictions. Drinking water containing BrdU at 1mg/ml was given to eighteen month old wild-type (Men1^+/+) and Men1^+/− littermates for two weeks. Parathyroid sections were immunofluorescently labelled for calcium-sensing receptor, BrdU and with DAPI, and parathyroid glands from each of six animals per genotype were analyzed to determine the percent of BrdU-positive cells. The mean (±S.E.M.) proliferation rate of parathyroid cells in Men1^+/− mice was significantly higher than that in Men1^+/+ mice (0.49% (±0.12) versus 0.08% (±0.02), P<0.016). Thus, our studies have demonstrated a six fold increase of the in vivo proliferation rate in parathyroids of Men1^+/− mice, and this opens the way to assess the effectiveness of new therapies, such as allosteric modulators of the calcium-sensing receptor, in the treatment of parathyroid tumours.