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Growth of the musculoskeletal system requires precise coordination between bone, muscle, and tendon during development. Insufficient elongation of the muscle-tendon unit relative to bone growth results in joint contracture, a condition characterized by reduction or complete loss of joint range of motion. Here we establish a novel murine model of joint contracture by targeting Smad4 for deletion in the tendon cell lineage using Scleraxis-Cre (ScxCre). Smad4 ScxCre mutants develop a joint contracture shortly after birth. The contracture is stochastic in direction and increases in severity with age. Smad4 ScxCre mutant tendons exhibited a stable reduction in cellularity and a progressive reduction in extracellular matrix volume. Collagen fibril diameters were reduced in the Smad4 ScxCre mutants, suggesting a role for Smad4 signaling in the regulation of matrix accumulation. Although ScxCre also has sporadic activity in both cartilage and muscle, we demonstrate an essential role for Smad4 loss in tendons for the development of joint contractures. Disrupting the canonical TGFβ-pathway in Smad2;3 ScxCre mutants did not result in joint contractures. Conversely, disrupting the BMP pathway by targeting BMP receptors (Alk3 ScxCre /Alk6 null ) recapitulated many features of the Smad4 ScxCre contracture phenotype, suggesting that joint contracture in Smad4 ScxCre mutants is caused by disruption of BMP signaling. Overall, these results establish a model of murine postnatal joint contracture and a role for BMP signaling in tendon elongation and extracellular matrix accumulation., (Copyright © 2020 Elsevier Inc. All rights reserved.)

Syndecan-1 is a transmembrane proteoglycan expressed prominently by lung epithelium and has pleiotropic functions such as regulating cell migration, proliferation, and survival. Loss of syndecan-1 expression by lung cancer cells is associated with higher-grade cancers and worse clinical prognosis. We evaluated the effects of syndecan-1 in various cell-based and animal models of lung cancer and found that lung tumorigenesis was moderated by syndecan-1. We also demonstrate that syndecan-1 (or lack thereof) alters the miRNA cargo carried within exosomes exported from lung cancer cells. Analysis of the changes in miRNA expression identified a distinct shift toward augmented procancer signaling consistent with the changes found in lung adenocarcinoma. Collectively, our work identifies syndecan-1 as an important factor in lung cancer cells that shapes the tumor microenvironment through alterations in miRNA packaging within exosomes., (Copyright © 2018 American Society for Investigative Pathology. Published by Elsevier Inc. All rights reserved.)

Rationale: Syndecan-1 is a cell surface heparan sulfate proteoglycan primarily expressed in the lung epithelium. Because the influenza virus is tropic to the airway epithelium, we investigated the role of syndecan-1 in influenza infection., Objectives: To determine the mechanism by which syndecan-1 regulates the lung mucosal response to influenza infection., Methods: Wild-type (WT) and Sdc1(-/-) mice were infected with a H1N1 virus (PR8) as an experimental model of influenza infection. Human and murine airway epithelial cell cultures were also infected with PR8 to study the mechanism by which syndecan-1 regulates the inflammatory response., Measurement and Main Results: We found worsened outcomes and lung injury in Sdc1(-/-) mice compared with WT mice after influenza infection. Our data demonstrated that syndecan-1 suppresses bronchial epithelial apoptosis during influenza infection to limit widespread lung inflammation. Furthermore, we determined that syndecan-1 attenuated apoptosis by crosstalking with c-Met to potentiate its cytoprotective signals in airway epithelial cells during influenza infection., Conclusions: Our work shows that cell-associated syndecan-1 has an important role in regulating lung injury. Our findings demonstrate a novel mechanism in which cell membrane-associated syndecan-1 regulates the innate immune response to influenza infection by facilitating cytoprotective signals through c-Met signaling to limit bronchial epithelial apoptosis, thereby attenuating lung injury and inflammation.

Matrix metalloproteinase-7 (MMP7) expression is quickly up-regulated after injury, and functions to regulate wound repair and various mucosal immune processes. We evaluated the global transcriptional response of airway epithelial cells from wild-type and Mmp7-null mice cultured at an air-liquid interface. The analysis of differentially expressed genes between genotypes after injury revealed an enrichment of functional categories associated with inflammation, cilia, and differentiation. Because these analyses suggested that MMP7 regulated ciliated cell formation, we evaluated the recovery of the airway epithelium in wild-type and Mmp7-null mice in vivo after naphthalene injury, which revealed augmented ciliated cell formation in the absence of MMP7. Moreover, in vitro studies evaluating cell differentiation in air-liquid interface cultures also showed faster ciliated cell production under Mmp7-null conditions compared with wild-type conditions. These studies identified a new role for MMP7 in attenuating ciliated cell differentiation during wound repair.

After injury, residual epithelial cells coordinate contextual clues from cell-cell and cell-matrix interactions to polarize and migrate over the wound bed. Protrusion formation, cell body translocation and rear retraction is a repetitive process that allows the cell to move across the substratum. Fundamental to this process is the assembly and disassembly of focal adhesions that facilitate cell adhesion and protrusion formation. Here, we identified syndecan-1 as a regulator of focal adhesion disassembly in migrating lung epithelial cells. Syndecan-1 altered the dynamic exchange of adhesion complex proteins, which in turn regulates migration speed. Moreover, we provide evidence that syndecan-1 controls this entire process through Rap1. Thus, syndecan-1 restrains migration in lung epithelium by activating Rap1 to slow focal adhesion disassembly.

Syndecan-1 is a cell surface proteoglycan that can organize co-receptors into a multimeric complex to transduce intracellular signals. The syndecan-1 core protein has multiple domains that confer distinct cell- and tissue-specific functions. Indeed, the extracellular, transmembrane, and cytoplasmic domains have all been found to regulate specific cellular processes. Our previous work demonstrated that syndecan-1 controls lung epithelial migration and adhesion. Here, we identified the necessary domains of the syndecan-1 core protein that modulate its function in lung epithelial repair. We found that the syndecan-1 transmembrane domain has a regulatory function in controlling focal adhesion disassembly, which in turn controls cell migration speed. In contrast, the extracellular domain facilitates cell adhesion through affinity modulation of α(2)β(1) integrin. These findings highlight the fact that syndecan-1 is a multidimensional cell surface receptor that has several regulatory domains to control various biological processes. In particular, the lung epithelium requires the syndecan-1 transmembrane domain to govern cell migration and is independent from its ability to control cell adhesion via the extracellular domain.