Biology subjects

Kilav-Levin, R.

Publications and source records attributed to Kilav-Levin, R..

2 recordsLinked to original sources

bioRxiv2023

Maintaining intact parathyroid glands throughout life requires Dicer and microRNA-mediated mTORC1 signaling

Secondary hyperparathyroidism (SHP) frequently accompanies chronic kidney disease (CKD), contributing to morbidity and mortality in patients. Our previous findings demonstrated that PT-Dicer-/- mice, with parathyroid specific deletion of Dicer and consequently microRNA, maintained normal serum PTH levels but failed to increase serum PTH in response to the major inducers of PTH secretion, hypocalcemia and CKD. Additionally, we elucidated a critical role of mTORC1 in CKD-induced SHP. We now explored the roles of Dicer and mTORC1 in parathyroid development and function. Despite sustaining normal serum PTH levels, PT-Dicer-/- mice displayed apoptotic loss of intact parathyroid glands postnatally, which were replaced by scattered cell clusters, and reduced mTORC1 activity. PT-mTORC1-/- mice exhibited the absence of intact parathyroid glands, while retaining normal serum PTH levels, mirroring the characteristics of PT-Dicer-/- mice. Conversely, PT-Tsc1-/-mice with hyperactivated mTORC1 exhibited enlarged glands and elevated serum PTH and calcium levels. Significantly, PT-Dicer-/-;Tsc1-/- double knockout mice demonstrated a reversal of the aparathyroidism of PT-Dicer-/- mice, preserving intact parathyroid glands and reinstating CKD-induced SHP. Lastly, data collected from a network of 106 healthcare organizations demonstrated that drug-induced mTOR inhibition is associated with reduced elevation of serum PTH levels in kidney transplant recipients. The latter findings offer physiological validation for our observations in genetically modified mouse models, highlighting the central role of mTORC1 signaling in CKD-SHP. Altogether, our results indicate that mTOR operates downstream of Dicer and miRNA. Consequently, Dicer, miRNA and mTORC1 collectively play a crucial role in maintaining the postnatal integrity and function of the parathyroid glands.

developmental biology↗

bioRxiv2021

Chronic kidney disease alters Pin1 phosphorylation and parathyroid hormone mRNA binding proteins leading to secondary hyperparathyroidism

Parathyroid hormone (PTH) regulates calcium metabolism and bone strength. Chronic kidney disease leads to secondary hyperparathyroidism (SHP) which increases morbidity and mortality. In experimental SHP, the increased PTH gene expression is due to enhanced PTH mRNA stability, mediated by changes in its interaction with stabilizing AUF1 and destabilizing KSRP. Pin1 isomerizes target proteins and leads to KSRP dephosphorylation. In SHP, Pin1 isomerase activity is decreased and phosphorylated KSRP fails to bind PTH mRNA, resulting in high PTH mRNA stability and levels. However, the up- and down-stream mechanisms by which kidney failure stimulates the parathyroid remain elusive. We now reveal a pathway where kidney failure induces parathyroid Pin1 phosphorylation, linking Pin1, KSRP and PTH mRNA stability as key players for the high PTH expression in SHP. We identified by mass-spectrometry, changes in rat parathyroid proteome and phosphoproteome profiles induced by impaired renal function, including KSRP phosphorylation at Pin1 target sites. Furthermore, both acute and chronic kidney failure led to parathyroid-specific Pin1 Ser16 and Ser71 phosphorylation, which disrupts Pin1 activity. Accordingly, pharmacologic Pin1 inhibition, that mimics the decreased Pin1 activity in SHP, increased PTH expression ex-vivo in parathyroid organ cultures and in transfected cells, through the PTH mRNA protein-interacting element and KSRP phosphorylation at potential Pin1-binding motifs. Therefore, kidney failure leads to loss of parathyroid Pin1 activity by inducing Pin1 phosphorylation. This predisposes parathyroids to increase PTH production through impaired PTH mRNA decay that is dependent on KSRP phosphorylation. Pin1 and KSRP phosphorylation and the Pin1-KSRP-PTH mRNA axis thus drive SHP.

molecular biology↗