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Acute O2 sensing through HIF2α-dependent expression of atypical cytochrome oxidase subunits in arterial chemoreceptors

HIF2α-mediated gene expression enables the carotid body to respond to acute hypoxia. Breathing faster with HIF2α In response to hypoxia, glomus cells in the carotid body trigger an increase in ventilation. At the molecular level, hypoxia slows down the electron transport chain in mitochondria, resulting in the accumulation of ROS and NADH, which ultimately activate glomus cells. HIF2α is a hypoxia-induced transcription factor that is highly abundant in glomus cells. Moreno-Domínguez et al. found that HIF2α was necessary for acute responses to hypoxia (see the Focus by Bishop and Ratcliffe). HIF2α mediated the expression of three atypical electron transport chain subunits that were necessary for a rapid buildup of ROS and NADH under hypoxic conditions in glomus cells. Similar to mice deficient in HIF2α in glomus cells, mice that lacked at least one of these atypical electron transport chain subunits in glomus cells also failed to increase ventilation in response to hypoxia. The authors propose that HIF2α target gene expression may set a tissue’s acute O2-sensing ability. Acute cardiorespiratory responses to O2 deficiency are essential for physiological homeostasis. The prototypical acute O2-sensing organ is the carotid body, which contains glomus cells expressing K+ channels whose inhibition by hypoxia leads to transmitter release and activation of nerve fibers terminating in the brainstem respiratory center. The mechanism by which changes in O2 tension modulate ion channels has remained elusive. Glomus cells express genes encoding HIF2α (Epas1) and atypical mitochondrial subunits at high levels, and mitochondrial NADH and reactive oxygen species (ROS) accumulation during hypoxia provides the signal that regulates ion channels. We report that inactivation of Epas1 in adult mice resulted in selective abolition of glomus cell responsiveness to acute hypoxia and the hypoxic ventilatory response. Epas1 deficiency led to the decreased expression of atypical mitochondrial subunits in the carotid body, and genetic deletion of Cox4i2 mimicked the defective hypoxic responses of Epas1-null mice. These findings provide a mechanistic explanation for the acute O2 regulation of breathing, reveal an unanticipated role of HIF2α, and link acute and chronic adaptive responses to hypoxia.