Endocrine Abstracts

Introduction: Hypoxia-inducible factors (HIF) are the key transcription factor induced by hypoxic condition, which regulate expression of specific target genes including angiogenic factors, erythropoietin, glucose transporters, and glycolytic enzymes. Recently, many studies connected to intracellular calcium levels and regulation of HIF-1α protein level. Calbindin-D_9k is a cytosolic calcium-binding protein and compensate with other calcium transporter protein for maintenance of cellular calcium level. It is expressed in primarily duodenum for absorption of calcium and in kidney for resorption of calcium. The objective of this study is to investigate interaction between HIF-1α and calbindin-D_9k.

Materials and methods: 8–10 weeks old C57BL/6 mice and calbindin-D_9K knockout mice were exposed to hypoxia (12±2% O2) for 3 weeks in closed polycarbonate chamber with nitrogen supply to remove the oxygen vs the normoxic groups. Calbindin-D_9k-transfected ACHN cells were cultured in normobaric hypoxia (1% O2), with match control in normoxic conditions. Expression of HIF-1α and glucose transporter 1 (GLUT1, a downstream gene of HIF-1α) were analyzed in mRNA or protein level.

Results: Protein level of HIF-1α was increased in calbindin-D_9K knockout mice compared with that of control in normoxic condition. However, increased protein level of HIF-1α of calbindin-D_9k knockout mice was reduced in hypoxic condition. mRNA levels of GLUT1 showed similar pattern with HIF-1α expression. In comparison to in vivo experiment, expression of HIF-1α and GLUT1 in mRNA and protein levels corresponded to that of Calbindin-D_9k knockout mice.

Conclusions: These results suggest that calbindin-D_9k can regulate expression of HIF-1α in protein level.