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First published online 11 January 2006
doi: 10.1242/dev.02237
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1 Department of Anatomy and Cell Biology, C. S. Mott Center for Human Growth and
Development, Wayne State University School of Medicine, Detroit, MI,
USA.
2 Department of Obstetrics and Gynecology, C. S. Mott Center for Human Growth
and Development, Wayne State University School of Medicine, Detroit, MI,
USA.
3 Perinatology Research Branch, National Institute of Child Health and Human
Development, NIH, DHHS, Bethesda, MD, USA.
4 Departments of Obstetrics and Gynecology, and Physiology and Biophysics,
University of Illinois School of Medicine, Chicago, IL, USA.
* Author for correspondence (e-mail: d.armant{at}wayne.edu)
Accepted 5 December 2005
Heparin-binding EGF-like growth factor (HBEGF), which is expressed in the
placenta during normal pregnancy, is downregulated in pre-eclampsia, a human
pregnancy disorder associated with poor trophoblast differentiation and
survival. This growth factor protects against apoptosis during stress,
suggesting a role in trophoblast survival in the relatively low O2
(
2%) environment of the first trimester conceptus. Using a
well-characterized human first trimester cytotrophoblast cell line, we found
that a 4-hour exposure to 2% O2 upregulates HBEGF synthesis and
secretion independently of an increase in its mRNA. Five other expressed
members of the EGF family are largely unaffected. At 2% O2,
signaling via HER1 or HER4, known HBEGF receptors, is required for both HBEGF
upregulation and protection against apoptosis. This positive-feedback loop is
dependent on metalloproteinase-mediated cleavage and shedding of the HBEGF
ectodomain. The restoration of trophoblast survival by the addition of soluble
HBEGF in cultures exposed to low O2 and metalloproteinase inhibitor
suggests that the effects of HBEGF are mediated by autocrine/paracrine, rather
than juxtacrine, signaling. Our results provide evidence that a
post-transcriptional mechanism induced in trophoblasts by low O2
rapidly amplifies HBEGF signaling to inhibit apoptosis. These findings have a
high clinical significance, as the downregulation of HBEGF in pre-eclampsia is
likely to be a contributing factor leading to the demise of trophoblasts.
Key words: Trophoblast, Placenta, Oxygen, HBEGF (HB-EGF), Metalloproteinases, Apoptosis, Human, Pregnancy
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