PTHrP targets salt-inducible kinases, HDAC4 and HDAC5, to repress chondrocyte hypertrophy in the growth plate.

Hypertrophy of chondrocytes is a crucial step in the endochondral bone formation process that drives bone lengthening and the transition to endochondral bone formation. Both Parathyroid hormone-related protein (PTHrP) and Histone deacetylase 4 (HDAC4) inhibit chondrocyte hypertrophy. Use of multiple mouse genetics models reveals how PTHrP and HDAC4 participate in a pathway that regulates chondrocyte hypertrophy.

Secondary ossification center induces and protects growth plate structure.

Growth plate and articular cartilage constitute a single anatomical entity early in development but later separate into two distinct structures by the secondary ossification center (SOC). The reason for such separation remains unknown. We found that evolutionarily SOC appears in animals conquering the land - amniotes.

Salt-inducible kinases dictate parathyroid hormone 1 receptor action in bone development and remodeling.

The parathyroid hormone 1 receptor (PTH1R) mediates the biologic actions of parathyroid hormone (PTH) and parathyroid hormone-related protein (PTHrP). Here, we showed that salt-inducible kinases (SIKs) are key kinases that control the skeletal actions downstream of PTH1R and that this GPCR, when activated, inhibited cellular SIK activity. Sik gene deletion led to phenotypic changes that were remarkably similar to models of increased PTH1R signaling.

PTHrP targets HDAC4 and HDAC5 to repress chondrocyte hypertrophy.

During endochondral bone formation, chondrocyte hypertrophy represents a crucial turning point from chondrocyte differentiation to bone formation. Both parathyroid hormone-related protein (PTHrP) and histone deacetylase 4 (HDAC4) inhibit chondrocyte hypertrophy. Using multiple mouse genetics models, we demonstrate in vivo that HDAC4 is required for the effects of PTHrP on chondrocyte differentiation.

SIKs control osteocyte responses to parathyroid hormone.

Parathyroid hormone (PTH) activates receptors on osteocytes to orchestrate bone formation and resorption. Here we show that PTH inhibition of SOST (sclerostin), a WNT antagonist, requires HDAC4 and HDAC5, whereas PTH stimulation of RANKL, a stimulator of bone resorption, requires CRTC2. Salt inducible kinases (SIKs) control subcellular localization of HDAC4/5 and CRTC2.

Parathyroid hormone receptor signalling in osterix-expressing mesenchymal progenitors is essential for tooth root formation.

Dental root formation is a dynamic process in which mesenchymal cells migrate toward the site of the future root, differentiate and secrete dentin and cementum. However, the identities of dental mesenchymal progenitors are largely unknown. Here we show that cells expressing osterix are mesenchymal progenitors contributing to all relevant cell types during morphogenesis.

Bone Is a Major Target of PTH/PTHrP Receptor Signaling in Regulation of Fetal Blood Calcium Homeostasis.

The blood calcium concentration during fetal life is tightly regulated within a narrow range by highly interactive homeostatic mechanisms that include transport of calcium across the placenta and fluxes in and out of bone; the mechanisms of this regulation are poorly understood. Our findings that endochondral bone-specific PTH/PTHrP receptor (PPR) knockout (KO) mice showed significant reduction of fetal blood calcium concentration compared with that of control littermates at embryonic day 18.5 led us to focus on bone as a possibly major determinant of fetal calcium homeostasis.

MicroRNA-140 Provides Robustness to the Regulation of Hypertrophic Chondrocyte Differentiation by the PTHrP-HDAC4 Pathway.

Growth plate chondrocytes go through multiple differentiation steps and eventually become hypertrophic chondrocytes. The parathyroid hormone (PTH)-related peptide (PTHrP) signaling pathway plays a central role in regulation of hypertrophic differentiation, at least in part, through enhancing activity of histone deacetylase 4 (HDAC4), a negative regulator of MEF2 transcription factors that drive hypertrophy. We have previously shown that loss of the chondrocyte-specific microRNA (miRNA), miR-140, alters chondrocyte differentiation including mild acceleration of hypertrophic differentiation.

HDAC5 controls MEF2C-driven sclerostin expression in osteocytes.

Osteocytes secrete paracrine factors that regulate the balance between bone formation and destruction. Among these molecules, sclerostin (encoded by the gene SOST) inhibits osteoblastic bone formation and is an osteoporosis drug target. The molecular mechanisms underlying SOST expression remain largely unexplored.

The transcriptional cofactor Lbh regulates angiogenesis and endochondral bone formation during fetal bone development.

Lbh is thought to act as a transcriptional cofactor and is highly conserved among species. Here we show that Lbh is expressed in chondrocytes, cells of the perichondrium, and the primary spongiosa in fetal growth plates of mice and chickens. Lbh overexpression in chick wings, using the RCAS-retroviral vector strategy, results in shortened skeletal elements and delayed hypertrophic chondrocyte maturation and bone formation.

A new ubiquitin ligase involved in p57KIP2 proteolysis regulates osteoblast cell differentiation.

Transforming growth factor-beta1 (TGF-beta1) has many physiological functions and inhibits the differentiation of osteoblasts. Previously, we reported that TGF-beta1 stimulation induces the degradation of p57(KIP2) in osteoblasts. p57(KIP2) proteolysis depends on the ubiquitin-proteasome pathway and SMAD-mediated transcription; however, the molecular mechanism underlying p57(KIP2) degradation has been largely unknown.

p57Kip2 regulates actin dynamics by binding and translocating LIM-kinase 1 to the nucleus.

p57Kip2 is the only cyclin-dependent kinase (Cdk) inhibitor shown to be essential for mouse embryogenesis. The fact suggests that p57 has a specific role that cannot be compensated by other Cdk inhibitors. LIM-kinase 1 (LIMK-1) is a downstream effector of the Rho family of GTPases that phosphorylates and inactivates an actin depolymerization factor, cofilin, to induce the formation of actin fiber.

Vitamin D-dependent recruitment of DNA-PK to the chromatinized negative vitamin D response element in the PTHrP gene is required for gene repression by vitamin D.

The mechanism of transcriptional repression by nuclear hormone receptors, especially in the presence of the ligands, is largely unknown. We previously reported that 1,25-dihydroxyvitamin D(3) (1,25 vitamin D3) inhibited expression of the parathyroid hormone-related polypeptide (PTHrP) gene through the interaction between the liganded monomeric vitamin D receptor (VDR) and the negative DNA element in the PTHrP gene (nVDRE(RP)). In this study, we employed chromatin immunoprecipitation (ChIP) assay and confirmed that 1,25 vitamin D3 recruited DNA-dependent protein kinase (DNA-PKcs) to the chromatinized nVDRE(RP).

Smad-mediated transcription is required for transforming growth factor-beta 1-induced p57(Kip2) proteolysis in osteoblastic cells.

Cyclin-dependent kinase inhibitory proteins (CKIs) are negative regulators of the cell cycle. Of all CKIs, only p57(Kip2) plays an essential role(s) that other CKIs cannot compensate for in embryonic development. Recently, we found that p57(Kip2) is degraded through the ubiquitin-proteasome pathway in osteoblastic cells stimulated to proliferation by transforming growth factor (TGF)-beta1 (Urano, T.

A new SUMO-1-specific protease, SUSP1, that is highly expressed in reproductive organs.

A full-length cDNA encoding a SUMO-1-specific protease, named SUSP1, was identified and cloned for the first time from the human brain. Nucleotide sequence analysis of the cDNA containing an open reading frame of 3336 base pairs revealed that the protease consists of 1112 amino acids with a calculated molecular mass of 126,116 Da. Like yeast Ulp1, SUSP1 is a cysteine protease containing the well conserved His/Asp/Cys catalytic triad.

Hyperosmolarity-induced gene stimulation is mediated by the negative calcium responsive element.

The negative calcium responsive elements of the parathyroid hormone gene bind to a specific set of nuclear proteins in an extracellular calcium (Ca2+e)-dependent manner. We have found that one of the negative calcium responsive elements, named oligo B, is found in the 5'-flanking region of such vasoactive genes as the vasopressin and atrial natriuretic polypeptide genes. Furthermore, the oligo B-like sequence in the former gene is conserved throughout evolution.

Evaluation of laser Doppler flowmetry in renal transplantation.

Renal grafts are presently evaluated based on the surgeon's observation of the organ microcirculation. Effectiveness of organ microcirculation has traditionally been accomplished through evaluation of the appearance of the graft. Laser doppler flowmetry (LDF) has been suggested as a possible means to determine graft effectiveness.

[The clinical significance of albuminuria in renal transplantation].

Urinary excretion of albumin was measured after renal transplantation in 37 patients who received cyclosporine quadrotherapy (cyclosporine A, azathioprine, prednisolone and antilymphocytoglobulin). In 26 patients with a favorable clinical course, daily urinary albumin level increased significantly on the first operative day. Subsequently, it decreased gradually, and remained at about 40mg/day after 3 weeks.