The Matrikine Tenascin-C Protects Multipotential Stromal Cells/Mesenchymal Stem Cells from Death Cytokines Such as FasL

Abstract

Multipotential stromal cells/mesenchymal stem cells (MSCs) are attractive candidates for regenerative therapy due to the ability of these cells to differentiate and positively influence neighboring cells. However, on implantation for wound reconstruction, these cells are lost as they are challenged by nonspecific inflammation signals generated in the wound environment and in response to any implanted foreign body. We have previously shown that sustained and surface-restricted epidermal growth factor receptor (EGFR) signaling by a tethered form of its prototypal ligand EGF enhances survival of MSC in the presence of death cytokines such as FasL, serum deprivation, and low oxygen in vitro. This was proposed to be due to the plasma membrane restriction of EGFR signaling. Interestingly, during wound repair, an extracellular matrix (ECM) component Tenascin-C (TNC) containing EGF-like repeats (EGFL) and fibronectin-like repeats (FNL) is upregulated. A few of the 14 EGFL on each of the 6 arms, especially the 14th, bind as low-affinity/high-avidity ligands to EGFR causing sustained surface-restricted EGFR signaling. We queried whether signaling by this physiologically relevant EGFR matrikine also protects MSCs from FasLinduced death. MSCs grown on TNC and Collagen I (as TNC by itself is antiadhesive) displayed a survival advantage in the presence of FasL. TNC neither sequestered nor neutralized FasL; rather, the effects of survival were via cell signaling. This survival was dependent on TNC activating EGFR and downstream pathways of Erk and Akt through EGFL; to a much lesser extent, the FNL of TNC also contributed to survival. Taken together, these results suggest that providing MSCs with a nonimmunogenic naturally occurring ECM moiety such as TNC enhances their survival in the presence of death factors, and this advantage occurs via signaling through EGFR primarily and integrins only to a minor extent. This matrix component is proposed to supplement MSC delivery on the scaffolds to provide a survival advantage against death upon in vivo implantation.

Tenascin-C: Form versus function

“…Interactions of tenascin-C with growth factors and growth factor receptors. For studies on EGF-L repeats, [198][199][200] 201 and FBG. 202 Vascular endothelial growth factor (VEGF), phosphatidylinositoL-glycan biosynthesis class F protein (PIGF), bone morphogenetic protein (BMP), neurotrophin (NT), brain-derived neurotrophic factor (BDNF), nerve growth factor (NGF), insulin-like growth factor (IGF), insulin-like growth factor -binding protein (IGF-BP), connective tissue growth factor (CTGF), heparin-binding EGF-like growth factor (HB-EGF), hepatocyte growth factor (HGF), chicken acidic leucine-rich EGFlike domain containing brain protein (CALEB)…”

Tenascin-C Signaling in melanoma

“…3 Each TNC subunit is comprised of a N-terminal rod-like assembly domain, a domain consisting of 14.5 epidermal growth factor-like (EGFL) repeats of 30-50 amino acids in length for each repeat, a domain composed of up to 17 fibronectin type III-like (FNIII) repeats, and a carboxyl terminus homologous to fibrinogen [4][5][6][7] ( Fig. 1).…”

“…6,26 As TNC EGFL domains resemble a physiological correlate of EGF, TNC may also protect stem cells from apoptosis. 6 Thus, the presence of TNC can serve 2 functions in melanoma progression. First, it can promote migration and invasion through the dermis.…”

“…6 This would be beneficial at the metastatic site where tumor cells face an ectopic microenvironment that lacks the normal trophic factors and that the mere onset of invasion triggers a non-specific foreign body response of death promoting cytokines. 46 This is consistent with the upregulation of TNC throughout metastatic nodules, 47,48 though this may represent persistent expression by the invasive cells that attained the distant site rather than an adaptive expression to promote tumorigenic behaviors in the metastatic site.…”

“…These behaviors relate in large part to the EGFL of TNC signaling via the EGFR in a unique manner to promote both motility and survival rather than proliferation. 6,18,22 Still, while the findings both in human melanoma biopsies and from the laboratory experiments are highly suggestive, an experimental demonstration supporting this hypothesis is still lacking. Thus, future efforts should focus on isolating such behaviors in ex vivo organotypic microphysiological systems and animal models.…”