Search

The human spinal column is a dynamic, segmented, bony, and cartilaginous structure that protects the neurologic system and simultaneously provides balance and flexibility. Children with developmental disorders that affect the patterning or shape of the spine can be at risk of neurologic and other physiologic dysfunctions. The most common developmental disorder of the spine is scoliosis, a lateral deformity in the shape of the spinal column. Scoliosis may be part of the clinical spectrum that is observed in many developmental disorders, but typically presents as an isolated symptom in otherwise healthy adolescent children. Adolescent idiopathic scoliosis (AIS) has defied understanding in part due to its genetic complexity. Breakthroughs have come from recent genome-wide association studies (GWAS) and next generation sequencing (NGS) of human AIS cohorts, as well as investigations of animal models. These studies have identified genetic associations with determinants of cartilage biogenesis and development of the intervertebral disc (IVD). Current evidence suggests that a fraction of AIS cases may arise from variation in factors involved in the structural integrity and homeostasis of the cartilaginous extracellular matrix (ECM). Here, we review the development of the spine and spinal cartilages, the composition of the cartilage ECM, the so-called "matrisome" and its functions, and the players involved in the genetic architecture of AIS. We also propose a molecular model by which the cartilage matrisome of the IVD contributes to AIS susceptibility.

Adolescent idiopathic scoliosis (AIS) is the most common musculoskeletal disorder of childhood development. The genetic architecture of AIS is complex, and the great majority of risk factors are undiscovered. To identify new AIS susceptibility loci, we conducted the first genome-wide meta-analysis of AIS genome-wide association studies, including 7956 cases and 88 459 controls from 3 ancestral groups. Three novel loci that surpassed genome-wide significance were uncovered in intragenic regions of the CDH13 (P-value_rs4513093 = 1.7E-15), ABO (P-value_ rs687621 = 7.3E-10) and SOX6 (P-value_rs1455114 = 2.98E-08) genes. Restricting the analysis to females improved the associations at multiple loci, most notably with variants within CDH13 despite the reduction in sample size. Genome-wide gene-functional enrichment analysis identified significant perturbation of pathways involving cartilage and connective tissue development. Expression of both SOX6 and CDH13 was detected in cartilage chondrocytes and chromatin immunoprecipitation sequencing experiments in that tissue revealed multiple HeK27ac-positive peaks overlapping associated loci. Our results further define the genetic architecture of AIS and highlight the importance of vertebral cartilage development in its pathogenesis.

Introduction: It may take decades to develop cardiovascular dysfunction following exposure to high doses of ionizing radiation from medical therapy or from nuclear accidents. Since astronauts may be exposed continually to a complex space radiation environment unlike that experienced on Earth, it is unresolved whether there is a risk to cardiovascular health during long-term space exploration missions. Previously, we have described that mice exposed to a single dose of simplified Galactic Cosmic Ray (GCR5-ion) develop cardiovascular dysfunction by 12 months post-radiation. Methods: To investigate the biological basis of this dysfunction, here we performed a quantitative mass spectrometry-based proteomics analysis of heart tissue (proteome and phosphoproteome) and plasma (proteome only) from these mice at 8 months post-radiation. Results: Differentially expressed proteins (DEPs) for irradiated versus sham irradiated samples (fold-change ≥1.2 and an adjusted p-value of ≤0.05) were identified for each proteomics data set. For the heart proteome, there were 87 significant DEPs (11 upregulated and 76 downregulated); for the heart phosphoproteome, there were 60 significant differentially phosphorylated peptides (17 upregulated and 43 downregulated); and for the plasma proteome, there was only one upregulated protein. A Gene Set Enrichment Analysis (GSEA) technique that assesses canonical pathways from BIOCARTA, KEGG, PID, REACTOME, and WikiPathways revealed significant perturbation in pathways in each data set. For the heart proteome, 166 pathways were significantly altered (36 upregulated and 130 downregulated); for the plasma proteome, there were 73 pathways significantly altered (25 upregulated and 48 downregulated); and for the phosphoproteome, there were 223 pathways significantly affected at 0.1 adjusted p-value cutoff. Pathways related to inflammation were the most highly perturbed in the heart and plasma. In line with sustained inflammation, neutrophil extracellular traps (NETs) were demonstrated to be increased in GCR5-ion irradiated hearts at 12-month post irradiation. NETs play a fundamental role in combating bacterial pathogens, modulating inflammatory responses, inflicting damage on healthy tissues, and escalating vascular thrombosis. Discussion: These findings suggest that a single exposure to GCR5-ion results in long-lasting changes in the proteome and that these proteomic changes can potentiate acute and chronic health issues for astronauts, such as what we have previously described with late cardiac dysfunction in these mice. [ABSTRACT FROM AUTHOR]

Neurofibromatosis type 1 (NF1) is a tumor predisposition syndrome caused by heterozygous NF1 gene mutations. Patients with NF1 present with pleiotropic somatic secondary manifestations, including development of bone pseudarthrosis after fracture. Somatic NF1 gene mutations were reproducibly identified in patient‐derived pseudarthrosis specimens, suggesting a local mosaic cell population including somatic pathologic cells. The somatic cellular pathogenesis of NF1 pseudarthroses remains unclear, though defects in osteogenesis have been posited. Here, we applied time‐series single‐cell RNA‐sequencing (scRNA‐seq) to patient‐matched control and pseudarthrosis‐derived primary bone stromal cells (BSCs). We show that osteogenic specification to an osteoblast progenitor cell population was evident for control bone‐derived cells and haploinsufficient pseudarthrosis‐derived cells. Similar results were observed for somatic patient fracture‐derived NF1−/− cells; however, expression of genetic pathways associated with skeletal mineralization were significantly reduced in NF1−/− cells compared with fracture‐derived NF1+/− cells. In mice, we show that Nf1 expressed in bone marrow osteoprogenitors is required for the maintenance of the adult skeleton. Results from our study implicate impaired Clec11a‐Itga11‐Wnt signaling in the pathogenesis of NF1‐associated skeletal disease. © 2022 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR). [ABSTRACT FROM AUTHOR]

The neurofibromatosis type 1 (NF1) RASopathy is associated with persistent fibrotic nonunions (pseudarthrosis) in human and mouse skeletal tissue. Here, we performed spatial transcriptomics to define the molecular signatures occurring during normal endochondral healing following fracture in mice. Within the control fracture callus, we observed spatially restricted activation of morphogenetic pathways, such as TGF-β, WNT, and BMP. To investigate the molecular mechanisms contributing to Nf1-deficient delayed fracture healing, we performed spatial transcriptomic analysis on a Postn-cre;Nf1fl/- (Nf1Postn) fracture callus. Transcriptional analyses, subsequently confirmed through phospho-SMAD1/5/8 immunohistochemistry, demonstrated a lack of BMP pathway induction in Nf1Postn mice. To gain further insight into the human condition, we performed spatial transcriptomic analysis of fracture pseudarthrosis tissue from a patient with NF1. Analyses detected increased MAPK signaling at the fibrocartilaginous-osseus junction. Similar to that in the Nf1Postn fracture, BMP pathway activation was absent within the pseudarthrosis tissue. Our results demonstrate the feasibility of delineating the molecular and tissue-specific heterogeneity inherent in complex regenerative processes, such as fracture healing, and reconstructing phase transitions representing endochondral bone formation in vivo. Furthermore, our results provide in situ molecular evidence of impaired BMP signaling underlying NF1 pseudarthrosis, potentially informing the clinical relevance of off-label BMP2 as a therapeutic intervention.

Talipes equinovarus (clubfoot, TEV) is a congenital rotational foot deformity occurring in 1 per 1000 births with increased prevalence in males compared with females. The genetic etiology of isolated clubfoot (iTEV) remains unclear. Using a genome-wide association study, we identified a locus within FSTL5, encoding follistatin-like 5, significantly associated with iTEV. FSTL5 is an uncharacterized gene whose potential role in embryonic and postnatal development was previously unstudied. Utilizing multiple model systems, we found that Fstl5 was expressed during later stages of embryonic hindlimb development, and, in mice, expression was restricted to the condensing cartilage anlage destined to form the limb skeleton. In the postnatal growth plate, Fstl5 was specifically expressed in prehypertrophic chondrocytes. As Fstl5 knockout rats displayed no gross malformations, we engineered a conditional transgenic mouse line (Fstl5LSL) to overexpress Fstl5 in skeletal osteochondroprogenitors. We observed that hindlimbs were slightly shorter and that bone mineral density was reduced in adult male, but not female, Prrx1-cre;Fstl5LSL mice compared with control. No overt clubfoot-like deformity was observed in Prrx1-cre;Fstl5LSL mice, suggesting FSTL5 may function in other cell types to contribute to iTEV pathogenesis. Interrogating published mouse embryonic single-cell expression data showed that Fstl5 was expressed in cell lineage subclusters whose transcriptomes were associated with neural system development. Moreover, our results suggest that lineage-specific expression of the Fstl genes correlates with their divergent roles as modulators of transforming growth factor beta and bone morphogenetic protein signaling. Results from this study associate FSTL5 with iTEV and suggest a potential sexually dimorphic role for Fstl5 in vivo., (© The Author(s) 2020. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.)