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Thymus-associated parathyroid hormone has two cellular origins with distinct endocrine and immunological functions.

TitleThymus-associated parathyroid hormone has two cellular origins with distinct endocrine and immunological functions.
Publication TypeJournal Article
Year of Publication2010
AuthorsLiu Z, Farley A, Chen L, Kirby BJ, Kovacs CS, C Blackburn C, Manley NR
JournalPLoS Genet
Volume6
Issue12
Paginatione1001251
Date Published2010
ISSN1553-7404
KeywordsAnimals, Female, Humans, Male, Mice, Mice, Inbred C57BL, Mice, Knockout, Nuclear Proteins, Organogenesis, Parathyroid Glands, Parathyroid Hormone, Thymus Gland, Transcription Factors
Abstract

In mammals, parathyroid hormone (PTH) is a key regulator of extracellular calcium and inorganic phosphorus homeostasis. Although the parathyroid glands were thought to be the only source of PTH, extra-parathyroid PTH production in the thymus, which shares a common origin with parathyroids during organogenesis, has been proposed to provide an auxiliary source of PTH, resulting in a higher than expected survival rate for aparathyroid Gcm2⁻/⁻ mutants. However, the developmental ontogeny and cellular identity of these "thymic" PTH-expressing cells is unknown. We found that the lethality of aparathyroid Gcm2⁻/⁻ mutants was affected by genetic background without relation to serum PTH levels, suggesting a need to reconsider the physiological function of thymic PTH. We identified two sources of extra-parathyroid PTH in wild-type mice. Incomplete separation of the parathyroid and thymus organs during organogenesis resulted in misplaced, isolated parathyroid cells that were often attached to the thymus; this was the major source of thymic PTH in normal mice. Analysis of thymus and parathyroid organogenesis in human embryos showed a broadly similar result, indicating that these results may provide insight into human parathyroid development. In addition, medullary thymic epithelial cells (mTECs) express PTH in a Gcm2-independent manner that requires TEC differentiation and is consistent with expression as a self-antigen for negative selection. Genetic or surgical removal of the thymus indicated that thymus-derived PTH in Gcm2⁻/⁻ mutants did not provide auxiliary endocrine function. Our data show conclusively that the thymus does not serve as an auxiliary source of either serum PTH or parathyroid function. We further show that the normal process of parathyroid organogenesis in both mice and humans leads to the generation of multiple small parathyroid clusters in addition to the main parathyroid glands, that are the likely source of physiologically relevant "thymic PTH."

DOI10.1371/journal.pgen.1001251
Alternate JournalPLoS Genet.
PubMed ID21203493
PubMed Central IDPMC3009658
Grant ListR01HD035920 / HD / NICHD NIH HHS / United States
R21AI075244 / AI / NIAID NIH HHS / United States
/ / Medical Research Council / United Kingdom