Impaired Ventilatory Responses to Hypoxia in Mice Deficient in Endothelin-Converting-Enzyme-1

Abstract

Endothelin-converting-enzyme (ECE-1) catalyzes the proteolytic activation of big endothelin-1 to mature endothelin-1. Most homozygous ECE-1Ϫ/Ϫ embryos die in utero and show severe craniofacial, enteric, and cardiac malformations precluding ventilatory function assessment. In contrast, heterozygous ECE-1ϩ/Ϫ embryos develop normally. Their respiratory function at birth has not been studied. Taking into account previous respiratory investigations in mice with endothelin-1 gene disruption, we hypothesized that ECE-1-deficient mice may have impaired ventilatory control. We analyzed ventilatory responses to hypercapnia (8% CO 2 ) and hypoxia (10% O 2 ) in newborn and adult mice heterozygous for ECE-1 deficiency (ECE-1ϩ/Ϫ) and in their wild-type littermates (ECE-1ϩ/ϩ). Ventilation, breath duration, and tidal volume were measured using whole-body plethysmography. Ventilatory responses to hypoxia were significantly weaker in ECE-1ϩ/Ϫ than in ECE-1ϩ/ϩ newborn mice (percentage ventilation increase: 1 Ϯ 25% versus 33 Ϯ 29%, p ϭ 0.010). Baseline breathing variables and ventilatory responses to hypercapnia were normal in the ECE-1ϩ/Ϫ newborn mice. No differences were observed between adult ECE-1ϩ/Ϫ and ECE-1ϩ/ϩ mice. We conclude that ECE-1 is required for normal ventilatory response to hypoxia at birth. Abbreviations CCHS, congenital central hypoventilation syndrome ECE-1, endothelin-converting-enzyme-1 ET-1, endothelin-1 GDNF, glial-cell-line-derived neurotrophic factor HSCR, Hirschsprung's disease NTS, nucleus tractus solitarius RET, rearranged during transfection TTOT, breath duration VE, ventilation VT, tidal volume ECE-1 catalyzes the proteolytic activation of big ET-1 to mature ET-1 (1, 2). Targeted ECE-1 gene disruption, which has recently been achieved in mice, has important effects on embryonic development and autonomic functions (3). Among homozygous ECE-1Ϫ/Ϫ embryos, most die in utero (about 75% in a C57BL/6 -129SvEv hybrid background) and all exhibit craniofacial, enteric, and cardiac malformations (3) that preclude valid ventilatory function assessment. In contrast, heterozygous ECE-1ϩ/Ϫ newborns are apparently healthy and develop normally. In a recent study, the differences in respiratory function between adult heterozygous ECE-1ϩ/Ϫ and wild-type ECE-1ϩ/ϩ adult mice were found to be not significant (4). Newborn mice were not studied. In the present study, we tested the ventilatory responses to chemical stimuli in heterozygous ECE-1ϩ/Ϫ newborn mice, and we reexamined the normality of adult heterozygous ECE-1ϩ/Ϫ mice in a larger sample of mice than previously done (4).Our working hypothesis was based on previous data showing that ET-1 is required for normal ventilatory control. First, in anesthetized rats, topical applications of ET-1 in the chemosensitive area of the ventral medulla oblongata and other areas involved in respiratory control cause changes in phrenic nerve activity (2). Specifically, applications of ET-1 in regions extending between the caudal end of the trapezoid body and the rootlets of the XIIth ...

Respiratory Adaptations to Lung Morphological Defects in Adult Mice Lacking Hoxa5 Gene Function

“…These data indicate that the acute frequency response is a transient overshoot that may reflect an increased sensitivity of Hoxa5 -/-mice to hypoxia. The absence of a tidal volume increase during hypoxia in wild-type mice is consistent with previous reports (30,39,40). The significant tidal volume increase observed in Hoxa5 -/-mice does not reflect an inability to further increase breathing frequency since mutant mice exposed to hypercapnia breathe at a much faster rate.…”

Sudden Infant Death Syndrome: Case-Control Frequency Differences at Genes Pertinent to Early Autonomic Nervous System Embryologic Development

“…This is of particular interest because of the relationship of RET to Hirschsprung disease and to CCHS and because of the RET knock-out model with a depressed ventilatory response to inhaled carbon dioxide with decreased frequency and tidal volume (42). The knock-out models for ECE1 (43) and TLX3 (45) also include impaired breathing and/or early death in the mouse phenotype, with suggestion of a central respiratory deficit. On the basis of these interesting and suggestive findings, further research is necessary to understand better the role of these and other genes in the SIDS phenotype and in explaining the ethnic disparity in SIDS.…”

“…Therefore, in the current study, we examined bone morphogenic protein-2(BMP2) (24,26,27), mammalian achaete-scute homolog-1 (MASH1) (28 -30), PHOX2a (31)(32)(33)(34)(35), rearranged during transfection factor (RET) (36 -42), endothelin converting enzyme-1 (ECE1) (24,43), endothelin-1 (EDN1) (44), T cell leukemia homeobox protein (TLX3) (24,(45)(46)(47), and engrailed-1 (EN1) (48,49) genes by sequence analysis in a cohort of infants who succumbed to SIDS. We also screened the SIDS cohort for the CCHS-associated polyalanine repeat mutation in PHOX2b.…”

Neural control of breathing: insights from genetic mouse models

“…Null mutant newborn mice lacking Edn1 (a potent vasoconstrictor peptide) and the endothelin receptor a (Ednra) had blunted ventilatory responses to hypoxia (15,45). Furthermore, heterozygous mutant newborn mice lacking endothelin-converting-enzyme 1 (Ece1) allele exhibited abnormal hyperpneic ventilatory responses to hypoxia (71). Responses to hypoxia were blunted in null mutant newborn mice lacking Nurr1, a gene involved in dopamine transmission and expressed in the carotid bodies and nucleus of the solitary tract (56).…”