Overexpression of the Flii gene increases dermal–epidermal blistering in an autoimmune ColVII mouse model of epidermolysis bullosa acquisita

Abstract

Epidermolysis bullosa (EB) is a severe genetic skin fragility syndrome characterized by blister formation. The molecular basis of EB is still largely unknown and wound healing in patients suffering from EB remains a major challenge to their survival. Our previous studies have identified the actin remodelling protein Flightless I (Flii) as an important mediator of wound repair. Here we identify Flii as a novel target involved in skin blistering. Flii expression was significantly elevated in 30 patients with EB, most prominently in patients with recessive dystrophic EB (RDEB) who have defects in production of type VII collagen (ColVII). Using an autoimmune ColVII murine model of EB acquisita (EBA) and an immunocompetent-ColVII-hypomorphic genetic mouse model of RDEB together with murine Flii alleles, we investigated the contribution of Flii to EB. Overexpression of Flii produced severe blistering post-induction of EBA, while decreased Flii reduced blister severity, elevated integrin expression, and improved ColVII production. Flii(+/-) blistered skin showed reduced α-SMA, TGF-β1, and Smad 2/3 expression, suggesting that decreasing Flii may affect fibrosis. In support of this, Flii-deficient fibroblasts from EBA mice were less able to contract collagen gels in vitro; however, addition of TGF-β1 restored collagen contraction, suggesting an interplay between Flii and TGF-β1. Elevated Flii gene and protein expression was further observed in the blisters of ColVII hypomorphic mice, a murine model of RDEB, suggesting that reducing Flii in blistered skin could be a potential new approach for treating patients with EB.

Topically Applied Flightless I Neutralizing Antibodies Improve Healing of Blistered Skin in a Murine Model of Epidermolysis Bullosa Acquisita

“…Having a unique structure to other members of the gelsolin family of actin-remodeling proteins, Flii has the ability to transduce the cell signaling events into cytoskeleton remodeling and therefore link different signaling pathways with the actin cytoskeleton. Flii is increased in blisters of EB patients, and its upregulation correlates with the severity of blistering seen in mouse models of recessive dystrophic epidermolysis bullosa and EBA (Kopecki et al, 2011a). We have also described the increased dermal-epidermal separation and altered TGF-b1/Smad signaling and collagen-mediated contraction and fibrosis associated with increased levels of Flii gene (Kopecki et al, 2011a).…”

“…Flii is increased in blisters of EB patients, and its upregulation correlates with the severity of blistering seen in mouse models of recessive dystrophic epidermolysis bullosa and EBA (Kopecki et al, 2011a). We have also described the increased dermal-epidermal separation and altered TGF-b1/Smad signaling and collagen-mediated contraction and fibrosis associated with increased levels of Flii gene (Kopecki et al, 2011a). Neutralizing the extracellular Flii activity via intradermal injection of monoclonal Fliineutralizing antibodies (FnAbs) accelerates wound reepithelialization and improves the macroscopic appearance of early scars in porcine models of wound healing (Jackson et al, 2012).…”

“…The actin-remodeling protein flightless I (Flii) has an important role in mediating cellular adhesion, hemidesmosome structure, and collagen deposition (Kopecki et al, 2009(Kopecki et al, , 2011a, with key roles in development, wound healing, and tissue regeneration (Campbell et al, 2002;Lin et al, 2011;Waters et al, 2011). Flii L-rich repeat domain also allows for interaction with numerous proteins (Fong and de Couet, 1999;Kopecki et al, 2009Kopecki et al, , 2011b and regulation of cellular functions, including migration and proliferation (Cowin et al, 2007), transcriptional regulation (Archer et al, 2004), focal adhesion turnover (Kopecki et al, 2011b), toll-like receptor signaling (Dai et al, 2009), inflammation, cytokine production (Li et al, 2008), and cell division (Deng et al, 2007).…”

Collagen VII plays a dual role in wound healing

“…Flii is upregulated in wounds (50) and in Col7a1-hypomorphic skin (51), and its overexpression slows healing of skin wounds by altering both re-epithelialization and wound contraction (50). In addition, Flii overexpression stimulates TGF-β1 production (51). However, it is important to note that the primary cause of the reduced wound healing of COL7A1-deficient skin lies in loss of COL7A1 and perturbed signaling by the microenvironment; aberrant Flii expression is one consequence of the faulty matrix.…”

Pathogenesis of Epidermolysis Bullosa Acquisita

“…Similar fi ndings were observed in experimental EBA, where induction of disease led to an increased cutaneous Flii expression. In line, reduced Flii expression in Flii +/− mice signifi cantly impaired the induction of experimental EBA [ 60 ]. The events leading to tissue injury in EBA are summarized in Fig.…”