This resubmitted proposal for funding is the result of 2 years of ARRA R01 funding that generated novel data demonstrating a critical role for the parathyroid cell-specific transcription factor Gcm2 (glial cell missing 2) after early embryologica development of the parathyroid glands as well how this protein functions in mature parathyroid glands to control function and survival of parathyroid cells. The long-term goal is use knowledge of the role of Gcm2 to develop novel strategies for medical treatment of patients with hyperparathyroidism. The objective in this application is to identify the extent to which depletion of Gcm2 leads to reduced survival of parathyroid cells in genetically engineered mouse models. The central hypothesis is that expression of Gcm2 in the parathyroid is necessary throughout life to maintain parathyroid cell mass, and that lack of Gcm2 will induce parathyroid cell death. We propose to use mouse models that we have developed to genetically delete the Gcm2 gene conditionally, in a temporally controlled manner, to identify the genes that regulate expression of Gcm2 as well as those that are controlled by Gcm2 action, and to uncover the effect of loss of Gcm2 on mature parathyroid cells. Mice with conditional Gcm2 alleles will also allow us to determine the extent to which ablation of Gcm2 late in life can "rescue" mice that have parathyroid disorders that replicate human hyperparathyroidism. Guided by strong preliminary data, this hypothesis will be tested by pursuing two specific aims: 1) determine the role of Sonic hedgehog signaling function and other transcription factor pathway on transcription of the GCM2 gene. Based on our preliminary data, we expect Sonic hedgehog plays a major role in repressing expression of Gcm2 in non-parathyroid cells;and 2) determine the effect of conditional deletion of Gcm2 on the transcriptosome of normal parathyroid glands and on function and size of hyperfunctioning mouse parathyroid glands. We expect that deletion of Gcm2 in normal parathyroid glands will reveal genes that are regulated by Gcm2 and will result in parathyroid atrophy. Moreover, using well-established murine models of primary hyperparathyroidism, we expect that timed deletion of Gcm2 in hyperplastic or adenomatous parathyroid glands will result in decreased survival of parathyroid cells and regression of hyperparathyroidism. The reagents and mouse models are in hand, and the techniques have been established as feasible in the applicants'labs. The approach is innovative because it utilizes novel mouse models, applies new techniques such as enhanced yeast 1-hybrid screening to uncover genes that regulate Gcm2 expression, and uses RNA-seq to develop a comprehensive catalog of the Gcm2-dependent transcriptosome. The proposed research is significant because it is expected to advance our understanding of parathyroid cell biology, and ultimately, to identify molecular targets that will allow development of new medical treatments for primary and tertiary hyperparathyroidism in humans.
The proposed research is relevant to public health because the discovery of new mechanisms that control the growth and function of the parathyroid glands is ultimately expected to increase understanding of the pathogenesis of developmental abnormalities that cause hypoparathyroidism and the acquired defects that cause hyperparathyroidism. We now know that the regulatory protein Gcm2 is essential for development and function of the parathyroid glands, and that parathyroid tumors overexpress this same protein. Hence, this research project is relevant to the NIH mission as the proposed experiments will extend our knowledge of the role of Gcm2 in parathyroid cell biology and lead to strategies to develop novel medical treatments for patients with parathyroid disorders.
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