CRFR1Mediates Expression Of IGFs And IGFBPs In Rat Liver Under Hypoxia

Background and ObjectiveThe insulin-like growth factor (IGF) family system includes two ligands (IGF-I and IGF-II), their cell surface receptors (IGF-IR and IGF-IIR), and six high affinity binding proteins (IGFBP1-6). The IGF family has important biological function in the regulation of cell proliferation, survival, differentiation and transference. Many studies have indicated, the IGF family plays important role in hypoxia-ischemic damage. The corticotrophin-releasing factor (CRF) functions as the primary regulator of the neuro-endocrine and physiological function responses to hypoxia stress. Both IGF and CRF can protect cell injury by hypoxia. It has important significance for understanding the body’s adaption to hypoxia to research whether CRF can regulate the expression of IGF family gene under hypoxia.Our laboratory used low pressure cabin to simulate plateau hypoxia and to determine the relative variation of the IGF family mRNA in the body level. And in the cell level, we study the relative variation of the IGF family mRNA in the BRL-3A cell line challenged with CRF. The purpose of this experiment is to study the effect of hypoxia on IGF family gene expression in rat liver, to analysis the cell injury induced by hypoxia and the anti-apoptosis and protection of IGF-I from cell injury under hypoxia. Rat normal hepatic cell (BRL-3A) was used to study the IGF protection from cell injury challenged with CRF. We also used CRFRl antagonist to study whether CRF involved in IGF family regulation under hypoxia.Research Design and MethodsAnimal hypoxia model:SD rats were exposed to hypoxia5km (10.8%O2,54.02kPa) for8h,24h,5d and10d. CRFR1antagonist (cpl54,526,30mg/kg) was injected before exposed to hypoxia. The mRNA and protein of IGF-I, IGF-II, IGFBPl, IGFBP2and IGFBP3in liver were tested.Cell culture:rat normal hepatic cell (BRL-3A) was challenged with CRF (1nM and10nM) for24h, mRNA of IGF-I, IGF-II, IGFBP1, IGFBP2and IGFBP3were tested.Quantitative Real Time PCR was used to test the gene expression of IGF family, ELISA and Western-blot were used to test the protein level of IGF family.Results1. Hypoxia changed the gene expression and protein level of IGFs and IGFBPs in rat liver. Hypoxia5km8h and24h increased IGF-I, IGF-II mRNA and IGF-I protein expression in liver, and hypoxia5km5d and10d decreased IGF-I, IGF-II mRNA and IGF-I protein expression in liver. Hypoxia significantly increased IGFBP1mRNA and protein expression, and hypoxia5km5d and10d decreased IGFBP2and IGFBP3mRNA and protein expression in rat liver.2. CRF (1nM and10nM) changed IGF-I and IGFBPs mRNA expression in BRL-3A cell line. Challenge with1nM and10nM CRF both significantly increased IGF-I, IGFBP1and IGFBP2mRNA expression, and decreased IGFBP3mRNA expression, but did not change IGF-II mRNA expression.3. CRF involved in the regulation of IGF family genes through CRFR1under hypoxia. CRFR1antagonist can block the increased IGF-I and IGFBP1mRNA induced by hypoxia.ConclusionsAcute hypoxia increased rat hepatic IGF-I, IGF-II mRNA and IGF-I protein expression, while mild hypoxia decreased IGF-I, IGF-II mRNA and IGF-I protein expression. And hypoxia changed the expression of IGFBP1, IGFBP2and IGFBP3mRNA and protein concurrently. This different model of IGF family genes expression suggested that hypoxia activated IGF-I to inhibit apoptosis under hypoxia challenge, and implied the complicated regulation mechanism of IGF family.The different effects of CRF on IGF-I, IGF-II, IGFBP1, IGFBP2and IGFBP3mRNA expression in BRL-3A cell line suggested that CRF involved in the regulation of IGF family. And the regulation maybe carried out through CRFR1.