The roles of mTORC1 in parathyroid gland function in chronic kidney disease-induced secondary hyperparathyroidism: Evidence from male genetic mouse models and clinical data

Abstract

Secondary hyperparathyroidism (SHP) associated with chronic kidney disease (CKD) contributes to morbidity and mortality, yet the related parathyroid signaling pathways are not fully understood. Previous studies have indicated that the parathyroid mTORC1 pathway is activated in both experimental CKD and hypocalcemia-induced SHP. Furthermore, mice with parathyroid-specific mTOR deficiency (PT-mTOR^−/−) exhibit disrupted parathyroid glands, but maintain normal serum PTH levels. Conversely, PT-Tsc1^−/− mice, with mTORC1 hyperactivation, have enlarged glands and high serum PTH and calcium levels. We now uncover links between mTORC1 function, parathyroid gland morphology, and the response to CKD. Despite impaired gland structure, PT-mTOR^−/− mice increased serum PTH to levels similar to controls in response to CKD, but not to acute kidney injury (AKI), highlighting the adaptability of their parathyroid glands to chronic but not acute stimulation. PT-Tsc1^−/− mice, with enlarged glands also exhibited a CKD-induced rise in serum PTH comparable to controls, but with a reduced magnitude, suggesting compromised secretion capacity. Parathyroid glands from PT-Tsc1^−/− mice displayed sustained high PTH secretion in culture, with no further increase when exposed to calcium-depleted media, unlike control glands. Complementing these findings, human data from 106 healthcare organizations demonstrated that drug-induced mTORC1 inhibition is associated with reduced serum PTH and a lower incidence of SHP in kidney transplant recipients. Collectively, our findings underscore the complex interplay between mTORC1 signaling and gland structure in the pathogenesis of SHP.