Pancreatic β cell proliferation by intermittent hypoxia via up-regulation of Reg family genes and HGF gene.
OBJECTIVE
Although accumulating evidence suggests the associations between sleep apnea syndrome (SAS) and type 2 diabetes, the direct effect of intermittent hypoxia (IH) on pancreatic β cell proliferation remains a missing piece of the puzzle.


METHODS
Rat RINm5F β cells, hamster HIT-T15 β cells, and human 1.1B4 β cells were exposed to normoxia (21% O2, 5% CO2, and balance N2), to sustained hypoxia (SH: 1% O2, 5% CO2, and balance N2), or to intermittent hypoxia (IH: 64 cycles of 5 min SH and 10 min normoxia) for 24 h. After the treatment, cellular proliferation and apoptosis were measured by WST-8 assay and TUNEL method, respectively. The expression of regenerating gene (Reg) family, interleukin (IL)-6, and hepatocyte growth factor (HGF) was determined by real-time RT-PCR.


RESULTS
The cellular proliferation of HIT-T15, RINm5F and 1.1B4 cells by IH was significantly increased, whereas apoptosis of these cells was unchanged. Real-time RT-PCR revealed that the mRNA levels of Reg family genes, IL-6, a typical Reg family gene inducer, and HGF, an inhibitor of high-concentration of Reg protein-induced apoptosis, were increased in IH-treated cells. In addition, siRNAs against rat Reg family genes except for PAP I/Reg 2 attenuated IH-induced β cell proliferation.


CONCLUSIONS
IH stress stimulates pancreatic β cell to induce IL-6 gene expression. By the IL-6 stimulation, β cells over-express Reg family genes as well as HGF gene. Reg family proteins stimulate β cell proliferation and HGF inhibits apoptosis of β cells. As a result, β cell numbers are increased by IH.
Second Department of Internal Medicine, Nara Medical University, Kashihara 634-8521, Nara, Japan.
Hiroyo
H
Ota
Asako
A
Itaya-Hironaka
Akiyo
A
Yamauchi
Sumiyo
S
Sakuramoto-Tsuchida
Tomoko
T
Miyaoka
Takanori
T
Fujimura
Hiroki
H
Tsujinaka
Kiyomi
K
Yoshimoto
Kan-Ichi
K
Nakagawara
Shinji
S
Tamaki
Shin
S
Takasawa
Hiroshi
H
Kimura
D000818:Animals; D017209:Apoptosis / Q000235:genetics; D015687:Cell Hypoxia / Q000235:genetics; D049109:Cell Proliferation; D002470:Cell Survival / Q000235:genetics; D002478:Cells, Cultured; D006224:Cricetinae; D017228:Hepatocyte Growth Factor / Q000096:biosynthesis* / Q000235:genetics; D006801:Humans; D050417:Insulin-Secreting Cells / Q000473:pathology*; D015850:Interleukin-6 / Q000096:biosynthesis / Q000235:genetics; D051847:Lithostathine / Q000096:biosynthesis* / Q000235:genetics; D008297:Male; D051381:Rats; D017208:Rats, Wistar; D013997:Time Factors; D015854:Up-Regulation / Q000235:genetics*
C066855:HGF protein, human; D015850:Interleukin-6; D051847:Lithostathine; C497617:REG1A protein, human; D017228:Hepatocyte Growth Factor
Apoptosis; Hepatocyte growth factor; Interleukin-6; Intermittent hypoxia; Pancreatic β cell proliferation; Regenerating gene; Sleep apnea syndrome