Table 2. Evidence from the literature supports all three mechanisms.

Myofibroblast	Proliferation	Migration
Shimazaki 2008: Postn−/− mice had an increased incidence of ventricular rupture following myocardial infarction due to reduced α-SMA positive cells and impaired collagen formation.6	Ben 2011: Transfection of pancreatic cancer cell lines (BxPC-3 and Panc-1) with a periostin expression vector (Ad5-PN) promoted anchorage-independent growth.33	Shimazaki 2008: Recombinant periostin (ΔbΔe splice variant) enhanced chemotaxis of cardiac fibroblasts from Postn−/− mice. This increase was attenuated by an anti-periostin antibody.6
Erkan 2007: Addition of rhPN to pancreatic stellate cells resulted in increased expression of α-SMA, collagen 1, fibronectin, TGFβ1 and periostin. Silencing periostin decreased α-SMA expression.34	Erkan 2007: Under serum deprivation, rhPN stimulated growth of Panc1, SU86.86, and T3M3 (pancreatic cancer cell lines).34	Ben 2011: Cells (BxPC-3 or Panc-1) infected with Ad5-PN migrated and invaded faster than controls in transwell assays.33
Vi 2009: Fibroblasts isolated from Dupuytren disease (DD) overexpressed periostin and had an increased ability to contract a collagen matrix, which was further enhanced by addition of rhPN. DD cells in 3D culture induced α-SMA in response to rhPN.18	Vi 2009: Growth on rhPN coated plates resulted in an increase in proliferation of palmar fascia fibroblasts.18
Sidhu 2010: Transfection of bronchial epithelial cells (BEAS2B) with a rhPN expression vector resulted in increased α-SMA protein and mRNA.23	Liu 2011: Periostin-silenced gastric cancer cells exhibited reduced cell proliferation.35	Liu 2011: Periostin-silenced gastric cancer cells exhibited reduced invasion using a Boyden chamber invasion assay.35
Bozyk 2012: Hyperoxia exposure increased α-SMA positive myofibroblasts in the lungs of Postn+/+, but not Postn−/−, mice.36 Bozyk 2012: Periostin treatment increased α-SMA expression in neonatal lung mesenchymal stromal cells.36	Bozyk 2012: Periostin induced human mesenchymal stromal cell DNA synthesis in the presence of TGF-β1.36
Hakuno 2010: High fat diet-induced α-SMA in cardiac valve complexes is attenuated in Postn−/− mice.22	Kuhn 2007: rhPN induced proliferation of neonatal cardiomyocytes in a PI3K/Akt dependent manner. Injecting rhPN into the myocardium induced DNA synthesis and division of nearby differentiated cardiomyocytes.37	Hakuno 2010: Conditioned media from periostin transfected cells increased migration of human coronary artery endothelial cells.22
Yoshida 2011: Silencing of periostin splice variant III attenuated TGF-β2 induced α-SMA production in primary human retinal pigment epithelial cells.28	Zhu 2011: Neutralizing monoclonal antibody to periostin inhibited anchorage-independent growth of the periostin-expressing ovarian cancer cell line A2780.38	Zhu 2011: Neutralizing monoclonal antibody to periostin inhibited periostin-induced cancer cell migration and invasion.38
Jackson-Boeters 2009: Periostin expression coincides with 〈-SMA expression within the granulation tissue of excisional wounds of mice.10	Liu 2010: Inhibition of periostin expression via RNA interference suppressed proliferation of a human osteosarcoma cell line (U2OS).39	Liu 2010: Inhibition of periostin gene expression via RNA interference suppressed migration and invasion of U2OS cells in transwell assays.39
Lindner 2005: Acquisition of a smooth muscle cell phenotype (α-SMA expression) correlated with acquisition of periostin expression both in vitro and in vivo.8	Yan 2006: Mice that received periostin-producing 293T cells at the mammalian fat pad tissue had significantly larger local tumors than did mice receiving control cells.40	Lindner 2005: Periostin overexpressing C3H10T1/2 cells had greater migratory response to serum, which was attenuated by a periostin-blocking antibody.8
Hong 2010: Periostin overexpressing A549 cells expressed higher levels of vimentin mRNA.41	Hong 2010: Periostin overexpressing A549 cells displayed increased proliferation.41	Hong 2010: Periostin overexpressing A549 cells migrated and closed scratch wounds at an increased rate.41
Kikuchi 2008: Close approximation of periostin immunoreactivity to α-SMA positive cells (periocryptal fibroblast) in normal colonic mucosa. Decreased periostin immunoreactivity preceded a decrease of α-SMA positive cells.42	Kikuchi 2008: Ki-67-positive epithelial cells were significantly decreased in the colonic crypts of Postn−/− mice.42	Yan 2006: Using transwell assays, significantly more periostin-expressing 293T cells migrated into the membrane relative to control cells.40

A brief summary of the literature surrounding periostin shows that there is support for each proposed mechanism. Cell-type and tissue specific effects of periostin certainly cloud the issue. To confidently say which mechanism(s) is most important in skin repair we must focus our attention on the in vivo evidence for context specific clues.