Expression of α-smooth muscle (α-SM) actin during corneal stromal wound healing

Department of Ophthalmology, University of Texas, Southwestern Medical Center at Dallas 75235-9057, USA.
Investigative Ophthalmology &amp Visual Science (Impact Factor: 3.4). 05/1995; 36(5):809-19.
Source: PubMed


The purpose of this study was to correlate the temporal expression of alpha-smooth muscle specific actin (alpha-SM actin), a molecular marker for myofibroblast transformation, with corneal wound contraction.
After full-thickness, central corneal injury in rabbit eyes, the anterior width of the wound (wound gape) was measured in the same animals using in vivo confocal microscopy. In addition, animals were sacrificed at various times after injury for the determination of alpha-SM actin expression by immunofluorescent microscopy using a mouse monoclonal antibody specific for human alpha-actin. Antibody specificity was confirmed by Western blot analysis of normal and wound fibroblasts. Expression of alpha-SM actin also was related spatially to f-actin and the wound margin by co-localization with phalloidin and DTAF (5([4,6-dichlorotriazin-2yl]amino)fluorescein), a fluorescent marker bound to the wound margin.
Wound contraction was most evident from days 7 to 42, when wound gape progressively decreased from 574 +/- 120 microns to 250 +/- 61 microns. Thereafter, the wound remained stable to day 84 (304 +/- 58 microns). Expression of alpha-SM actin directly correlated with wound contraction--appearing across the wound at day 7, the full thickness of the wound at day 14, and the posterior wound at day 28. alpha-SM actin was localized exclusively to phalloidin-stained, f-actin microfilament bundles or stress fibers within wound healing fibroblasts, and the disappearance of alpha-SM actin correlated with the concomitant disappearance of stress fibers at days 28 to 42. Staining of the wound margin with DTAF confirmed that the expression of alpha-SM actin was limited to fibroblasts within the wound.
The expression of alpha-SM actin was directly correlated to corneal wound contraction, appearing at the initiation of and disappearing at the completion of the contraction process. Furthermore, the exclusive expression of alpha-SM actin by fibroblasts present only within the wound suggests that local environmental factors unique to the wound may play an important role in myofibroblast transformation.

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    • "However, the low amount of ECM produced by these cells contains keratocan and lumican (Sundarraj et al. 1998). The cytoplasm of these cells contains α-smooth muscle actin (α-SMA) (Jester et al. 1995), a protein implicated in wound contraction and considered as a myofibroblast marker. According to these observations, it has been suggested that these Bhypercellular cells^ observed earlier during wound healing are in fact Bhypercellular myofibroblasts^ (Hassell and Birk 2010), a kind of myofibroblasts that produce a low amount of ECM. "
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    • "In the current study, the proportion of a-SMA-positive cells (myofibroblasts) observed in the spheres at 4, 7 and 14 days post-injury was less than the peak observed at 24 h; this observation is consistent with that demonstrated in physiological wound healing (Jester et al., 1995). Dissipation of local signalling molecules, myofibroblast apoptosis and phenotype reversion may underlie this process (Maltseva et al., 2001; Wilson et al., 2001; Ramos et al., 2006). "
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    • "These activated keratocytes proliferate to repopulate the region of stromal injury in which keratocytes have disappeared due to apoptosis (Helena et al. 1998; Wilson 2002). At 1–2 weeks after injury myofibroblasts, mostly differentiating from bone marrowderived cells (Barbosa et al. 2010; Wilson 2012), and less transparent than keratocytes (Jester et al. 1999; Piatigorsky 2000) can be detected (Jester et al. 1995). Myofibroblasts deposit large amounts of ECM (Klingberg et al. 2013) that contributes to stromal opacity (Wilson 2012) and their contraction is associated with wound closure, compaction of matrix (Tomasek et al. 2002; Gabbiani 2003) and activation of latent TGF-β (Wipff et al. 2007). "
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