Westendorf, Jennifer J

Abstract Osteogenesis imperfecta (OI) is a heterogeneous group of inherited connective tissue disorders primarily caused by dominant mutations in COL1A1 or COL1A2 that impair type I procollagen folding and secretion. Misfolded collagen accumulates in the endoplasmic reticulum (ER), triggering ER stress and osteoblast dysfunction and bone fragility. Current pharmacologic therapy focuses on inhibiting bone resorption but has limited efficacy and does not address the underlying biology of the disease. The epigenetic regulator Polycomb-repressive complex 2 (PRC2) has emerged as an important regulator of bone formation. Genetic and pharmacologic disruption of PRC2 enhanced osteogenic differentiation in wild-type cells. Here we demonstrate that inhibition of the PRC2 through targeting its essential component embryonic ectoderm development (EED) enhances osteogenic differentiation, improves bone architecture in male Col1a2+/G610C OI mouse models, modulates the integrated stress response (ISR), and improves ER morphology in OI cells. These findings identify EED inhibition as a novel epigenetic strategy to restore collagen homeostasis and improve skeletal integrity in OI.

The mechanical properties of biological tissues influence their function and can predict degenerative conditions before gross histological or physiological changes are detectable. This is especially true for structural tissues such as articular cartilage, which has a primarily mechanical function that declines after injury and in the early stages of osteoarthritis. While atomic force microscopy (AFM) has been used to test the elastic modulus of articular cartilage before, there is no agreement or consistency in methodologies reported. For murine articular cartilage, methods differ in two major ways: experimental parameter selection and sample preparation. Experimental parameters that affect AFM results include indentation force and cantilever stiffness; these are dependent on the tip, sample, and instrument used. The aim of this project was to optimize these experimental parameters to measure murine articular cartilage elastic modulus by AFM micro-indentation. We first investigated the effects of experimental parameters on a control material, polydimethylsiloxane gel (PDMS), which has an elastic modulus on the same order of magnitude as articular cartilage. Experimental parameters were narrowed on this control material, and then finalized on wildtype C57BL/6J murine articular cartilage samples that were prepared with a novel technique that allows for cryosectioning of epiphyseal segments of articular cartilage and long bones without decalcification. This technique facilitates precise localization of AFM measurements on the murine articular cartilage matrix and eliminates the need to separate cartilage from underlying bone tissues, which can be challenging in murine bones because of their small size. Together, the new sample preparation method and optimized experimental parameters provide a reliable standard operating procedure to measure microscale variations in the elastic modulus of murine articular cartilage.

Abstract The Journal of Bone and Mineral Research (JBMR®), the flagship journal of the American Society for Bone and Mineral Research (ASBMR), enjoys a premiere position in its field and has a global reach. The journal uses a single-blind peer-review process whereby three editors are typically involved in assessing each submission for publication, in addition to external reviewers. Although emphasizing fairness, rigor, and transparency, this process is not immune to the influence of unconscious biases. The gender and geographic diversity of JBMR® authors, editors, and reviewers has increased over the last three decades, but whether such diversity has affected peer-review outcomes is unknown. We analyzed manuscript acceptance rates based on the gender and geographic origin of authors, reviewers, and Associate Editors. The analysis included 1662 original research articles submitted to JBMR® from September 2017 through December 2019. Gender was assigned using probabilities from an online tool and manually validated through internet searches. Predictor variables of manuscript outcome were determined with multivariate logistic regression analysis. The acceptance rate was highest when the first and last authors were of different genders, and lowest when both authors were men. Reviewer gender did not influence the outcome regardless of the genders of the first and last authors. Associate Editors from all geographical regions tended to select reviewers from their same region. The acceptance rate was highest when the Associate Editor was from Europe. Manuscripts with authors from North America and Australia/New Zealand had greater overall odds of acceptance than those from Europe and Asia. Manuscripts reviewed only by Editorial Board (EB) members had a lower acceptance rate than those refereed by non-EB reviewers or a mix of EB and non-EB reviewers. Overall, the geographical origin of authors, reviewers, and editors, as well as reviewers' EB membership may influence manuscript decisions. Yet, the JBMR® peer-review process remains largely free from gender bias. © 2022 American Society for Bone and Mineral Research (ASBMR).

ABSTRACT Endochondral ossification is tightly controlled by a coordinated network of signaling cascades including parathyroid hormone (PTH). Pleckstrin homology (PH) domain and leucine rich repeat phosphatase 1 (Phlpp1) affects endochondral ossification by suppressing chondrocyte proliferation in the growth plate, longitudinal bone growth, and bone mineralization. As such, Phlpp1−/− mice have shorter long bones, thicker growth plates, and proportionally larger growth plate proliferative zones. The goal of this study was to determine how Phlpp1 deficiency affects PTH signaling during bone growth. Transcriptomic analysis revealed greater PTH receptor 1 (Pth1r) expression and enrichment of histone 3 lysine 27 acetylation (H3K27ac) at the Pth1r promoter in Phlpp1-deficient chondrocytes. PTH (1-34) enhanced and PTH (7-34) attenuated cell proliferation, cAMP signaling, cAMP response element-binding protein (CREB) phosphorylation, and cell metabolic activity in Phlpp1-inhibited chondrocytes. To understand the role of Pth1r action in the endochondral phenotypes of Phlpp1-deficient mice, Phlpp1−/− mice were injected with Pth1r ligand PTH (7-34) daily for the first 4 weeks of life. PTH (7-34) reversed the abnormal growth plate and long-bone growth phenotypes of Phlpp1−/− mice but did not rescue deficits in bone mineral density or trabecular number. These results show that elevated Pth1r expression and signaling contributes to increased proliferation in Phlpp1−/− chondrocytes and shorter bones in Phlpp1-deficient mice. Our data reveal a novel molecular relationship between Phlpp1 and Pth1r in chondrocytes during growth plate development and longitudinal bone growth. © 2021 American Society for Bone and Mineral Research (ASBMR).

ABSTRACT The development of high-throughput genotyping technologies and large biobank collections, complemented with rapid methodological advances in statistical genetics, has enabled hypothesis-free genome-wide association studies (GWAS), which have identified hundreds of genetic variants across many loci associated with musculoskeletal conditions. Similarly, basic scientists have valuable molecular cellular and animal data based on musculoskeletal disease that would be enhanced by being able to determine the human translation of their findings. By integrating these large-scale human genomic musculoskeletal datasets with complementary evidence from model organisms, new and existing genetic loci can be statistically fine-mapped to plausibly causal variants, candidate genes, and biological pathways. Genes and pathways identified using this approach can be further prioritized as drug targets, including side-effect profiling and the potential for new indications. To bring together these big data, and to realize the vision of creating a knowledge portal, the International Federation of Musculoskeletal Research Societies (IFMRS) established a working group to collaborate with scientists from the Broad Institute to create the Musculoskeletal Knowledge Portal (MSK-KP)(http://mskkp.org/). The MSK consolidates omics datasets from humans, cellular experiments, and model organisms into a central repository that can be accessed by researchers. The vision of the MSK-KP is to enable better understanding of the biological mechanisms underlying musculoskeletal disease and apply this knowledge to identify and develop new disease interventions. © 2020 American Society for Bone and Mineral Research (ASBMR).