Degradation of Lung Protective Angiotensin Converting Enzyme-2 by Meconium in Human Alveolar Epithelial Cells: A Potential Pathogenic Mechanism in Meconium Aspiration Syndrome
Pancreatic digestive enzymes present in meconium might be responsible for meconium-induced lung injury. The local Renin Angiotensin System plays an important role in lung injury and inflammation. Particularly, angiotensin converting enzyme-2 (ACE-2) has been identified as a protective lung enzyme against the insult. ACE-2 converts pro-apoptotic Angiotensin II to anti-apoptotic Angiotensin 1–7. However, the effect of meconium on ACE-2 has never been studied before.
To study the effect of meconium on ACE-2, and whether inhibition of proteolytic enzymes present in the meconium reverses its effects on ACE-2.
Alveolar epithelial A549 cells were exposed to F-12 medium, 2.5% meconium, meconium + a protease inhibitor cocktail (PIc) and PIc alone for 16 h. At the end of incubation, apoptosis was measured with a nuclear fragmentation assay and cell lysates were collected for ACE-2 immunoblotting and enzyme activity.
Meconium caused a fourfold increase in apoptotic nuclei (p < 0.001). The pro-apoptotic effect of meconium can be reversed by PIc. Meconium reduced ACE-2 enzyme activity by cleaving ACE-2 into a fragment detected at ~ 37 kDa by immunoblot. PIc prevented the degradation of ACE-2 and restored 50% of ACE-2 activity (p < 0.05).
These data suggest that meconium causes degradation of lung protective ACE-2 by proteolytic enzymes present in meconium, since the effects of meconium can be reversed by PIc.
KeywordsMeconium aspiration syndrome Angiotensin-converting enzyme 2 Renin-angiotensin system Neonatal lung injury
We thank Dr. Amal T. Abdul-Hafez for helping in designing and executing the experiments. We also thank Sparrow Hospital (Lansing, MI) Newborn Unit nursing staff for helping in collecting the meconium for the study.
This work was supported by a grant from the Fellowship Research Fund of Sparrow Hospital, Lansing, MI (to C.G).
Compliance with Ethical Standards
Conflict of interest
The authors declare that they have no conflict of interest.
The study protocol was approved by the Sparrow Hospital and Michigan State University institutional review board.
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