Keratinocyte-Targeted Overexpression of the Glucocorticoid Receptor Delays Cutaneous Wound Healing

Abstract

Delayed wound healing is one of the most common secondary adverse effects associated to the therapeutic use of glucocorticoid (GC) analogs, which act through the ligand-dependent transcription factor GC-receptor (GR). GR function is exerted through DNA-binding-dependent and –independent mechanisms, classically referred to as transactivation (TA) and transrepression (TR). Currently both TA and TR are thought to contribute to the therapeutical effects mediated by GR; however their relative contribution to unwanted side effects such as delayed wound healing is unknown. We evaluated skin wound healing in transgenic mice with keratinocyte-restricted expression of either wild type GR or a mutant GR that is TA-defective but efficient in TR (K5-GR and K5-GR-TR mice, respectively). Our data show that at days (d) 4 and 8 following wounding, healing in K5-GR mice was delayed relative to WT, with reduced recruitment of granulocytes and macrophages and diminished TNF-α and IL-1β expression. TGF-β1 and Kgf expression was repressed in K5-GR skin whereas TGF-β3 was up-regulated. The re-epithelialization rate was reduced in K5-GR relative to WT, as was formation of granulation tissue. In contrast, K5-GR-TR mice showed delays in healing at d4 but re-established the skin breach at d8 concomitant with decreased repression of pro-inflammatory cytokines and growth factors relative to K5-GR mice. Keratinocytes from both transgenic mice closed in vitro wounds slower relative to WT, consistent with the in vivo defects in cell migration. Overall, the delay in the early stages of wound healing in both transgenic models is similar to that elicited by systemic treatment with dexamethasone. Wound responses in the transgenic keratinocytes correlated with reduced ERK activity both in vivo and in vitro. We conclude that the TR function of GR is sufficient for negatively regulating early stages of wound closure, while TA by GR is required for delaying later stages of healing.

Glucocorticoid receptor signaling in health and disease

“…In particular, anti-proliferative effects of the GR in keratinocytes were shown to be regulated by transrepression. However, both GR transrepression and transactivation were found to negatively delay wound healing of keratinocytes [98]. In addition, GR was found to regulate eyelid development [97].…”

Epidermal Mineralocorticoid Receptor Plays Beneficial and Adverse Effects in Skin and Mediates Glucocorticoid Responses

“…For cutaneous wounding assays, full-thickness wounds (n ¼ 4 wound per mouse) were performed (6 mm, Biopsy punch, Stiefel, Brentford, UK) in female MR EKO and CO littermates (n ¼ at least 7 mice per genotype), and wound areas were recorded daily, as described (Sanchis et al, 2012). Mice were killed 7 days after wounding.…”

Glucocorticoid Receptor Signaling in Skin Barrier Function

“…These animals showed normal healing by day 8, concomitant with decreased repression of proinflammatory cytokines and growth factors relative to K5-GR mice. In wound healing experiments with both transgenic mouse models, keratinocyte proliferation was inhibited correlating with reduced ERK activity, in vitro and in vivo, and collagen deposition was reduced to a similar extent [91]. These data suggest that the early stages of wound closure are negatively regulated by GR independently of transcription, while GR transcriptional actions are necessary for delaying later stages of healing.…”

“…The use of K5-GR and K5-GR-TR mice allowed us to demonstrate that keratinocyte-targeted GR overexpression delayed skin wound healing [91]. This delay resulted from reducing the inflammatory response and decreasing keratinocyte migration in vitro and in vivo, consistent with the impaired skin healing observed with GC treatment [91]. While in K5-GR mice, cutaneous healing was delayed at days 4 and 8 after wounding, there was only a delay at day 4 in K5-GR-TR mice.…”