Browsing by Author "Hamilton, Douglas W."

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    Periostin and matrix stiffness combine to regulate myofibroblast differentiation and fibronectin synthesis during palatal healing
    (Elsevier, 2020) Nikoloudaki, Georgia; Snider, Paige; Simmons, Olga; Conway, Simon J.; Hamilton, Douglas W.; Pediatrics, School of Medicine
    Although the matricellular protein periostin is prominently upregulated in skin and gingival healing, it plays contrasting roles in myofibroblast differentiation and matrix synthesis respectively. Palatal healing is associated with scarring that can alter or restrict maxilla growth, but the expression pattern and contribution of periostin in palatal healing is unknown. Using periostin-knockout (Postn-/-) and wild-type (WT) mice, the contribution of periostin to palatal healing was investigated through 1.5 mm full-thickness excisional wounds in the hard palate. In WT mice, periostin was upregulated 6 days post-wounding, with mRNA levels peaking at day 12. Genetic deletion of periostin significantly reduced wound closure rates compared to WT mice. Absence of periostin reduced mRNA levels of pivotal genes in wound repair, including α-SMA/acta2, fibronectin and βigh3. Recruitment of fibroblasts and inflammatory cells, as visualized by immunofluorescent staining for fibroblast specific factor-1, vimentin, and macrophages markers Arginase-1 and iNOS was also impaired in Postn-/-, but not WT mice. Palatal fibroblasts isolated from the hard palate of mice were cultured on collagen gels and prefabricated silicon substrates with varying stiffness. Postn-/- fibroblasts showed a significantly reduced ability to contract a collagen gel, which was rescued by the exogenous addition of recombinant periostin. As the stiffness increased, Postn-/- fibroblasts increasingly differentiated into myofibroblasts, but not to the same degree as the WT. Pharmacological inhibition of Rac rescued the deficient myofibroblastic phenotype of Postn-/- cells. Low stiffness substrates (0.2 kPa) resulted in upregulation of fibronectin in WT cells, an effect which was significantly reduced in Postn-/- cells. Quantification of immunostaining for vinculin and integrinβ1 adhesions revealed that Periostin is required for the formation of focal and fibrillar adhesions in mPFBs. Our results suggest that periostin modulates myofibroblast differentiation and contraction via integrinβ1/RhoA pathway, and fibronectin synthesis in an ECM stiffness dependent manner in palatal healing.
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    Periostin as a Multifunctional Modulator of the Wound Healing Response
    (Springer, 2016-09) Walker, John T.; McLeod, Karrington; Kim, Shawna; Conway, Simon J.; Hamilton, Douglas W.; Pediatrics, School of Medicine
    During tissue healing, dynamic and temporal alterations occur in the structure and composition of the extracellular matrix (ECM) that are required for effective repair to occur. Matricellular proteins (MPs) are a group of diverse non-structural ECM components, which bind cell surface receptors mediating interactions between the cell and its microenviroment, effectively regulating adhesion, migration, proliferation, signaling and cell phenotype. Periostin (Postn), a pro-fibrogenic secreted glycoprotein, was defined as a MP based on its expression pattern and regulatory roles during development, healing and in disease processes. Postn consists of a typical signal sequence, an EMI domain responsible for binding to fibronectin, four tandem fasciclin-like domains that are responsible for integrin binding and a C-terminal region where multiple splice variants originate. This review will focus specifically on the role of Postn in wound healing and remodeling, an area of intense research in the last 10 years particularly related to skin healing as well as in myocardium post infarction. Postn interacts with cells through various integrin pairs and is an essential downstream effector of TGF-β superfamily signaling. As will be discussed, across different tissues, Postn is associated with pro-fibrogenic process, specifically, the transition of fibroblasts to myofibroblasts, collagen fibrillogenesis and ECM synthesis. Although the complexity of Postn as a modulator of cell behavior in tissue healing is only beginning to be elucidated, its expression is clearly a defining event in moving wound healing through the proliferative and remodeling phases.