Targeted overexpression of OGFr in epithelium of transgenic mice suppresses cell proliferation and impairs full-thickness wound closure

Abstract

The opioid growth factor (OGF) and its receptor, OGFr, play a regulatory role in cell proliferation, and maintain homeostasis through a tonically active negative feedback mechanism. To directly evaluate the repercussion of increased OGFr expression and consequent gain-of-function in epithelium, bovine keratin 5 promoter elements were used to direct the expression of OGFr to skin in a tetracycline-regulated manner. Three founder lines overexpressing OGFr (OGFrTG/K5-tTA) were established. Evidence for increased OGFr in the epithelium included a three-fold increase in OGFr binding activity, as well as significant increases in OGFr protein, as monitored by semiquantitative immunohistochemistry. DNA synthesis in target epithelium, including cornea, tongue, and skin of transgenic mice was decreased 41% to 80% from wild-type littermates; the liver, a nonepithelial organ, was not altered. Decreased DNA synthesis in corneal epithelium induced by transgenic expression of OGFr was further reduced by treatment with exogenous OGF but reversed by exposure to the opioid antagonist, naloxone. The number of cell layers in both epidermis and cornea of OGFrTG/K5-tTA animals was reduced nearly 45% from wild-type mice. Full-thickness wounds in mice overexpressing OGFr healed 37% to 75% slower than wild-type littermates. These data demonstrate for the first time that stable genetic amplification of OGFr downregulates homeostatic cell proliferation, as well as pathophysiological processes with respect to wound repair. These mice also can serve as a valuable model to dissect the mechanism of OGF-OGFr action and may be important in understanding the etiology, pathogenesis, and treatment of epithelium-related diseases.

Role of neuropeptides, neurotrophins, and neurohormones in skin wound healing

“…McLaughlin et al. showed a decrease in the number of cell layers in the epidermis in transgenic mice overexpressing OGFR which impaired full‐thickness wound closure . To further analyze the role of OGF in skin wound healing, the group of Bigliardi used an in vivo model of mice KO for DOR.…”

“…To further analyze the role of OGF in skin wound healing, the group of Bigliardi used an in vivo model of mice KO for DOR. They noted that the loss of DOR induced a faster increase in the epidermal thickness compared with WT mice during the wound healing process; this epidermal hypertrophy was correlated with an increased expression of markers of skin proliferation, differentiation, reepithelialization and dermal repair in KO mice vs. WT . In the two cases, i.e., the overexpresssion or absence of DOR, skin wound healing was delayed.…”

Opioid Antagonists Enhance Diabetic Wound Closure: A New Therapy

“…Several endogenous opioids (enkephalins, endorphins, dynorphins, endomorphins) and classical (μ/MOR/Oprm1, δ/DOR/Oprd1, κ/KOR/Oprk1) opioid receptors, as well as the nuclear-associated, non-classical OGFr are present and functioning in skin [19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38]. Enkephalins such as [Met 5 ] and [Leu 5 ]-enkephalin and the synthetic d-Ala-d-Leu-enkephalin have been reported to inhibit cell differentiation dose-dependently in human keratinocytes in vitro, while β-endorphin had no effect [38].…”

“…A regulatory pathway that mediates homeostasis of cellular proliferation is the opioid growth factor (OGF) [20,24,26,29].…”

“…In the last two decades, research has demonstrated that endogenous opioids serve to mediate fundamental cellular processes associated with proliferation, tissue organization, cell migration, adhesion, and cell survival [19][20][21][22][23][24][25][26][27][28][29]. In particular, the OGF-OGFr axis has been shown to be present and functioning as a modulator of proliferation of epithelial tissues, with OGF repressing DNA synthesis in corneal epithelium [26], palm skin [29], and cancers of ectodermal origin [40].…”