ADAM17 Transactivates EGFR Signaling during Embryonic Eyelid Closure

Abstract

PURPOSE. During mammalian embryonic eyelid closure ADAM17 has been proposed to play a role as a transactivator of epidermal growth factor receptor (EGFR) signaling by shedding membrane bound EGFR ligands. However, ADAM17 also sheds numerous other ligands, thus implicating ADAM17 in additional molecular pathways. The goal of this study was to experimentally establish the role of ADAM17 and determine ADAM17-mediated pathways essential for the embryonic eyelid closure.METHODS. Wild-type (WT) and woe mice, carrying a hypomorphic mutation in Adam17, were evaluated using H&E and scanning electron microscopy. Expressions of ADAM17, EGFR, and the phosphorylated form EGFR-P were evaluated using immunohistochemistry. BrdU and TUNEL assays were used to evaluate cell proliferation and apoptosis, respectively. In vitro scratch assays of primary cultures were used to evaluate cell migration. Clinical and histologic analyses established if the hypermorphic Egfr Dsk5 allele can rescue the woe embryonic eyelid closure.RESULTS. woe mice exhibited a failure to develop the leading edge of the eyelid and consequently failure of the embryonic eyelid closure. Expression of ADAM17 was identified in the eyelid epithelium in the cells of the leading edge. ADAM17 is essential for epithelial cell migration, but does not play a role in proliferation and apoptosis. EGFR was expressed in both WT and woe eyelid epithelium, but the phosphorylated EGFR-P form was detected only in WT. The Egfr Dsk5 allele rescued woe eyelid closure defects, but also rescued woe anterior segment defects and the absence of meibomian glands.CONCLUSIONS. We provide in vivo genetic evidence that the role of ADAM17 during embryonic eyelid closure is to transactivate EGFR signaling. (Invest Ophthalmol Vis Sci.

A biosensor for the activity of the “sheddase” TACE (ADAM17) reveals novel and cell type–specific mechanisms of TACE activation

“…Mouse embryonic fibroblasts (MEFs) have been used in previous research to study TACE dependent cellular responses, where TACE mediates cleavage of EGFR1 ligands (4). MEF cells stably expressing TSen respond to PMA stimulation with TACE activation in a similar manner to both HeLa-TSen and 293T-TSen cells (Figs 1E, 1B and S1B, respectively).…”

“…The Tumor Necrosis Factor-α Converting Enzyme (TACE), encoded by the adam17 gene, is a trans-membrane protease that has been implicated in numerous physiological processes, including inflammation (1, 2), wound healing (3), development (4), and cancer progression (5, 6). In these diverse processes, TACE plays a common role as an extracellular sheddase that cleaves the pro-/transmembrane form of a wide variety of ligands and receptors (6).…”

Embryologic and Fetal Development of the Human Eyelid

“…This could be an evolutionary response to protect adults against microbial invasion if the skin barrier is broken, whereas the sealed environment of the embryo does not require such protection against infection. 50 The mechanism of re-epithelialization itself may be different, and several other factors may help explain this discrepancy. Embryonic eyelids fuse by first advancing filopdia and lamellipodia, which reach out and interdigitate with the opposite eyelid followed by closure of the gap in a sweeping purse-string like manner by forming a homogenous cable of contractile actin.…”

“…In adults, on the other hand, the skin heals by filopodial and lamellipodial crawling of cells only without involvement of the actin cytoskeleton. 35,50,56 Different collagens and keratins are involved, and signaling pathways are also differentially expressed in adult wound healing versus embryonic eyelid fusion, or even fetal wound healing, which also appears to be a relatively scarless process. 56,57 Finally, while macrophages are actively involved in the adult wound healing process to clear cellular debris and release growth factors like TGFβ1, which appears to be instrumental in mediating a tissue-mediated fibrotic response, embryonic eyelid fusion seems to be a “macrophageless” process.…”

“…Some of the cytokines and growth factors expressed by those 7 signaling pathways may be differentially or solely expressed in the leading edge cells or in the inner edge cells during eyelid fusion, in the mesenchyme, or in the cornea, and some may even be over-expressed in the upper eyelid more than the lower eyelid. 23,49,50 It seems plausible to state that eyelid embryogenesis is “orchestrated by highly compartmentalized and spatially segregated developmental signals,” 48 but exactly how they interact in vivo is not yet fully understood. 46 …”