Defective postnatal endochondral bone development by chondrocyte-specific targeted expression of parathyroid hormone type 2 receptor

The Chinese Medicinal Formulation Guzhi Zengsheng Zhitongwan Modulates Chondrocyte Structure, Dynamics, and Metabolism by Controlling Multiple Functional Proteins

Traditional Chinese medicine is one of the oldest medical systems in the world and has its unique principles and theories in the prevention and treatment of human diseases, which are achieved through the interactions of different types of materia medica in the form of Chinese medicinal formulations. GZZSZTW, a classical and effective Chinese medicinal formulation, was designed and created by professor Bailing Liu who is the only national medical master professor in the clinical research field of traditional Chinese medicine and skeletal diseases. GZZSZTW has been widely used in clinical settings for several decades for the treatment of joint diseases. However, the underlying molecular mechanisms are still largely unknown. In the present study, we performed quantitative proteomic analysis to investigate the effects of GZZSZTW on mouse primary chondrocytes using state-of-the-art iTRAQ technology. We demonstrated that the Chinese medicinal formulation GZZSZTW modulates chondrocyte structure, dynamics, and metabolism by controlling multiple functional proteins that are involved in the cellular processes of DNA replication and transcription, protein synthesis and degradation, cytoskeleton dynamics, and signal transduction. Thus, this study has expanded the current knowledge of the molecular mechanism of GZZSZTW treatment on chondrocytes. It has also shed new light on possible strategies to further prevent and treat cartilage-related diseases using traditional Chinese medicinal formulations.

Parathyroid hormone resistance syndromes - Inactivating PTH/PTHrP signaling disorders (iPPSDs)

Metabolic disorders caused by impairments of the Gsα/cAMP/PKA pathway affecting the signaling of PTH/PTHrP lead to features caused by non-responsiveness of target organs, in turn leading to manifestations similar to the deficiency of the hormone itself. Pseudohypoparathyroidism (PHP) and related disorders derive from a defect of the α subunit of the stimulatory G protein (Gsα) or of downstream effectors of the same pathway, such as the PKA regulatory subunit 1A and the phosphodiesterase type 4D. The increasing knowledge on these diseases made the actual classification of PHP outdated as it does not include related conditions such as acrodysostosis (ACRDYS) or progressive osseous heteroplasia (POH), so that a new nomenclature and classification has been recently proposed grouping these disorders under the term "inactivating PTH/PTHrP signaling disorder" (iPPSD). This review will focus on the pathophysiology, clinical and molecular aspects of these rare, heterogeneous but closely related diseases.

The Parathyroid Hormone Second Receptor PTH2R and its Ligand Tuberoinfundibular Peptide of 39 Residues TIP39 Regulate Intracellular Calcium and Influence Keratinocyte Differentiation

Genes related to the parathyroid hormone (PTH) influence cutaneous immune defense and development, but the full functions of the PTH family in cutaneous biology remain incompletely understood. In this study, we examined the expression and potential functions of the PTH second receptor (PTH2R) and its ligand, the tuberoinfundibular peptide of 39 residues (TIP39), in the skin. TIP39 and PTH2R mRNA and protein were detectable in both human and mouse skin, and in cultured keratinocytes and adipocytes. TIP39 was observed in the basal layer of human skin, whereas PTH2R was detected in the spinous to granular layer. The subcellular localization of TIP39 in keratinocytes changed during calcium-induced differentiation and shifted to colocalize with PTH2R at the membrane. The addition of recombinant TIP39 to normal human keratinocytes in culture induced an increase in intercellular calcium and triggered aspects of terminal differentiation including decreased keratin-14 and increased involucrin expression. Consistent with these observations, PTH2R(-/-) mice were observed to have increased epidermal thickness. In summary, identification of TIP39 and its receptor in the epidermis reveals an additional PTH family member that is expressed in the skin and may influence keratinocyte function.

Breakpoint mapping by whole genome sequencing identifies PTH2R gene disruption in a patient with midline craniosynostosis and a de novo balanced chromosomal rearrangement

BACKGROUND

Craniosynostosis (CRS) is a premature closure of calvarial sutures caused by gene mutation or environmental factors or interaction between the two. Only a small proportion of non-syndromic CRS (NSC) patients have a known genetic cause, and thus, it would be meaningful to search for a causative gene disruption for the development NSC. We applied a whole genome sequencing approach on a 15-month-old boy with sagittal and metopic synostosis to identify a gene responsible for the development of the disease.

METHODS AND RESULTS

Conventional chromosome study revealed a complex paracentric inversion involving 2q14.3 and 2q34. Array comparative genomic hybridisation did not show any copy number variation. Multicolour banding analysis was carried out and the breakpoints were refined to 2q14 and 2q34. An intronic break of the PTH2R gene was detected by whole genome sequencing and fluorescence in situ hybridisation analysis confirmed disruption of PTH2R.

CONCLUSIONS

We report PTH2R as a gene that is disrupted in NSC. The disruption of the PTH2R gene may cause uncontrolled proliferation and differentiation of chondrocytes, which in turn results in premature closure of sutures. This addition of PTH2R to the list of genes associated with NSC expands our understanding of the development of NSC.

Deletion of the PH-domain and Leucine-rich Repeat Protein Phosphatase 1 (Phlpp1) Increases Fibroblast Growth Factor (Fgf) 18 Expression and Promotes Chondrocyte Proliferation

Endochondral ossification orchestrates formation of the vertebrate skeleton and is often induced during disease and repair processes of the musculoskeletal system. Here we show that the protein phosphatase Phlpp1 regulates endochondral ossification. Phlpp1 null mice exhibit decreased bone mass and notable changes in the growth plate, including increased BrdU incorporation and matrix production. Phosphorylation of known Phlpp1 substrates, Akt2, PKC, and p70 S6 kinase, were enhanced in ex vivo cultured Phlpp1(-/-) chondrocytes. Furthermore, Phlpp1 deficiency diminished FoxO1 levels leading to increased expression of Fgf18, Mek/Erk activity, and chondrocyte metabolic activity. Phlpp inhibitors also increased matrix content, Fgf18 production and Erk1/2 phosphorylation. Chemical inhibition of Fgfr-signaling abrogated elevated Erk1/2 phosphorylation and metabolic activity in Phlpp1-null cultures. These results demonstrate that Phlpp1 controls chondrogenesis via multiple mechanisms and that Phlpp1 inhibition could be a strategy to promote cartilage regeneration and repair.

PFOA and PFOS are associated with reduced expression of the parathyroid hormone 2 receptor (PTH2R) gene in women

Little is known about interactions between environmental and genetic risk factors for osteoarthritis (OA). Genetic factors include variation or mutation in genes involved in parathyroid hormone signalling. Exposure to the endocrine disrupting chemicals perfluoro-octanoic acid (PFOA) or perfluorooctane sulfonate (PFOS) have been suggested as potential environmental contributors, although evidence to support this association is conflicting. Here we test the hypothesis that PFOA and PFOS may alter the mRNA expression of genes in the parathyroid signalling cascade to provide evidence on possible pathways between these chemicals and OA. We measured the relationship between PFOA or PFOS serum levels and the in vivo expression of the Parathyroid hormone 1 and 2 genes (PTH, PTH2), Parathyroid hormone 1 and 2 receptor genes (PTH1R, PTH2R) and the parathyroid hormone-like (PTHLH) gene in peripheral blood from a cross-sectional population study designed to assess the potential health effects of these chemicals. We used multivariate linear regression models and found that PFOA or PFOS was inversely correlated with parathyroid hormone 2 receptor (PTH2R) expression (coefficients=-0.43 and -0.32, p=p=0.017 and 0.006 for PFOA and PFOS respectively) in 189 female subjects. The levels of PTH2 transcripts encoding the ligand of PTH2r, were also found to be lower in women with OA (median 2.08) compared with controls (median 3.41, p=0.046). As the parathyroid signalling cascade is a known candidate for osteoarthritis risk and our findings raise the possibility that exposure to these chemicals may contribute to the pathogenesis of OA in some individuals.