Attenuation of glucose-induced insulin secretion by intermittent hypoxia via down-regulation of CD38

Aims: Sleep apnea syndrome (SAS) is characterized by recurrent episodes of oxygen desaturation during sleep, the development of daytime sleepiness, and deterioration in the quality of life. Accumulating evidence suggests the association of intermittent hypoxia (IH), a hallmark of SAS, and type 2 diabetes independently on body mass index and waist circumference. In addition to insulin resistance, the progression to type 2 diabetes is dependent on the impairment of glucose-induced insulin secretion (GIS) from pancreatic beta-cells. However, the direct effects of IH on GIS are elusive. Main methods: HIT-T15 hamster beta-cells and isolated rat islets were exposed to 64 cycles/24 h of IH (5 min hypoxia/10 min normoxia) or normoxia for 24 h. Changes of GIS and gene expression in IH-treated beta-cells were analyzed by ELISA and real-time RT-PCR, respectively. Key findings: After IH treatment, GIS both from IH-treated HIT-T15 cells and isolated rat islets were significantly attenuated. The level of insulin mRNA was unchanged by IH. The mRNA levels of glucose transporter 2 (Glut2), glucokinase (GK), sulfonylurea receptor1 (SUR1), and L-type Ca2+ channel1.2 (Cav1.2) in IH-treated-islets were similar to those in normoxia-treated islets. In contrast, the mRNA level of CD38 in IH-treated islets was significantly lower than that in normoxia-treated islets. The reporter gene assay revealed that the transcription of CD38 was attenuated by IH, and the transfection of CD38 expression vector recovered the attenuation of GIS by IH. Significance: These results indicate that IH stress directly attenuates GIS from beta-cells via the down-regulation of CD38. (c) 2011 Elsevier Inc. All rights reserved.