Effects of temperature on ventilatory response to hypercapnia in newborn mice heterozygous for transcription factor Phox2b

Abstract

Congenital central hypoventilation syndrome (CCHS) is a rare disease with variable severity, generally present from birth and chiefly characterized by impaired chemosensitivity to hypercapnia. The main cause of CCHS is a mutation in the PHOX2B gene, which encodes a transcription factor involved in the development of autonomic medullary reflex pathways. Temperature regulation is abnormal in many patients with CCHS. Here, we examined whether ambient temperature influenced CO2sensitivity in a mouse model of CCHS. A weak response to CO2at thermoneutrality (32°C) was noted previously in 2-day-old mice with an invalidated Phox2b allele ( Phox2b+/−), compared with wild-type littermates. We exposed Phox2b+/− pups to 8% CO2at three ambient temperatures (TAs): 29°C, 32°C, and 35°C. We measured breathing variables and heart rate (HR) noninvasively using a novel whole body flow plethysmograph equipped with contact electrodes. Body temperature and baseline breathing increased similarly with TA in mutant and wild-type pups. The hypercapnic ventilatory response increased linearly with TA in both groups, while remaining smaller in mutant than in wild-type pups at all TAs. The differences between the absolute increases in ventilation in mutant and wild-type pups become more pronounced as temperature increased above 29°C. The ventilatory abnormalities in mutant pups were not associated with significant impairments of heart rate control. In both mutant and wild-type pups, baseline HR increased with TA. In conclusion, TA strongly influenced the hypercapnic ventilatory response in Phox2b+/− mutant mice. These findings suggest that abnormal temperature regulation may contribute to the severity of respiratory impairments in CCHS patients.