Chronic hypoxemia induces mitochondrial respiratory complex gene expression in the fetal sheep brain

James K Moon; Kendall M Lawrence; Mallory L Hunt; Marcus G Davey; Alan W Flake; Daniel J Licht; Jonathan M Chen; Todd J Kilbaugh; J William Gaynor; Daniel P Beiting

doi:10.1016/j.xjon.2022.04.040

Chronic hypoxemia induces mitochondrial respiratory complex gene expression in the fetal sheep brain

JTCVS Open. 2022 May 5:10:342-349. doi: 10.1016/j.xjon.2022.04.040. eCollection 2022 Jun.

Authors

James K Moon^{1

2}, Kendall M Lawrence³, Mallory L Hunt^{1

4}, Marcus G Davey¹, Alan W Flake¹, Daniel J Licht⁵, Jonathan M Chen³, Todd J Kilbaugh⁶, J William Gaynor⁴, Daniel P Beiting⁷

Affiliations

¹ Department of Surgery, The Center for Fetal Research, Children's Hospital of Philadelphia, Philadelphia, Pa.
² Department of General Surgery, Mount Sinai Hospital, New York, NY.
³ Division of Cardiothoracic Surgery, Children's Hospital of Philadelphia, Philadelphia, Pa.
⁴ Division of Cardiovascular Surgery, Hospital of the University of Pennsylvania, Philadelphia, Pa.
⁵ Division of Neurology, Children's Hospital of Philadelphia, Philadelphia, Pa.
⁶ Division of Anesthesia and Critical Care Medicine, Children's Hospital of Philadelphia, Philadelphia, Pa.
⁷ Department of Pathobiology, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, Pa.

Abstract

Objective: The molecular pathways underlying hypoxemia-induced alterations in neurodevelopment of infants with congenital heart disease have not been delineated. We used transcriptome analysis to investigate differential gene expression induced by hypoxemia in an ovine artificial-womb model.

Methods: Mid-gestation fetal sheep (median [interquartile range] 109 [107-112] days' gestation) were cannulated via the umbilical vessels, attached to a pumpless, low-resistance oxygenator circuit, and incubated in a sterile, fluid environment for 22 [21-23] days. Fetuses were maintained with an oxygen delivery of 20-25 mL/kg/min (normoxemia, n = 3) or 14-16 mL/kg/min (hypoxemia, n = 4). Transcriptional profiling by RNA sequencing was carried out on left frontal brains and hypoxemia-regulated genes were identified by differential gene expression analysis.

Results: A total of 228 genes whose expression was up or down regulated by ≥1.5-fold (false discovery rate ≤0.05) were identified. The majority of these genes were induced in hypoxemic animals compared to normoxemic controls, and functional enrichment analysis identified respiratory electron transport as a pathway strongly upregulated in the brain during chronic hypoxemia. Further examination of hypoxemia-induced genes showed robust induction of all 7 subunits of the mitochondrial NADH:ubiquinone oxidoreductase (complex I). Other hypoxemia-induced genes included cytochrome B, a component of complex III, and ATP6, ATP8, both of which are components of complex V.

Conclusions: Chronic fetal hypoxemia leads to upregulation of multiple mitochondrial respiratory complex genes critical for energy production and reactive oxygen species generation, including complex I. These data provide valuable insight into potential pathways involved in chronic hypoxemia-induced neuropathology and offers potential therapeutic targets for fetal neuroprotection in fetuses with congenital heart defects.

Keywords: ATP, adenosine triphosphate; CHD; CHD, congenital heart disease; DO2, oxygen delivery; EXTEND, EXTrauterine Environment for Neonatal Development; FFPE, formalin-fixed, paraffin-embedded; ROS, reactive oxygen species; anatomy; animal model; assessment; brain; congenital heart disease; fetal surgery/research; function; hypoxia/reoxygenation; imaging; injury.