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Coordinate IGF-I and IGFBP5 gene expression in perinatal rat brain after hypoxia-ischemia
W H Lee1, G M Wang, L B Seaman
1Department of Pediatrics, Indiana University School of Medicine, Indianapolis, USA.
Insights
Insulin-like growth factor I (IGF-I) and its related proteins are vital for brain development. Cerebral hypoxia-ischemia significantly disrupts their gene expression, potentially causing neuronal damage during critical growth periods in rats.
Area of Science:
- Neuroscience
- Developmental Biology
- Molecular Biology
Background:
- Insulin-like growth factor I (IGF-I) is crucial for postnatal brain development, particularly during the critical first 21 days.
- Cerebral hypoxic-ischemic insults in the perinatal period can lead to severe, permanent brain damage.
Purpose of the Study:
- To investigate the gene expression regulation of the IGF-I system following hypoxic-ischemic insults in immature rats.
- To understand the immediate and delayed transcriptional responses of IGF-I, its receptor, and binding proteins (IGFBPs) to metabolic stress.
Main Methods:
- Gene expression analysis of IGF-I, type I IGF receptor, IGFBP2, and IGFBP5.
- Study conducted in immature rats subjected to cerebral hypoxia-ischemia.
- Analysis performed at 1, 24, and 72 hours post-insult.
Main Results:
- Within 1 hour of recovery, mRNA levels of all IGF system components decreased ipsilaterally.
- This suppression was most pronounced at 24 hours, especially in vulnerable brain regions like the thalamus and hippocampus.
- By 72 hours, IGF-I and IGFBP5 gene expression was reactivated in astrocytes, while IGFBP2 and receptor levels remained suppressed.
Conclusions:
- The IGF system's transcriptional levels are highly sensitive to metabolic disturbances like hypoxia-ischemia during critical brain growth periods.
- The initial decrease in IGF-I gene expression may contribute to neuronal death and myelinogenesis vulnerability.
- Reactive astrocytes play a role in reactivating specific IGF components post-insult.
Abstract:
Insulin-like growth factor I (IGF-I) is an anabolic pleiotrophic factor essential for postnatal rat brain development, especially during the first 21 days, the "critical growth period." Cerebral hypoxic-ischemic insults occurring during the perinatal period can result in neuronal necrosis and permanent brain damage. To understand the regulation of the action of IGF-I in response to such a metabolic insult, we investigated the gene expression of IGF-I, type I IGF receptor, IGF binding protein (IGFBP)2, and IGFBP5 during the first 72 h after hypoxia-ischemia in the immature rat. At 1 h of recovery, messenger RNA (mRNA) levels of all IGF system components were decreased throughout the hemisphere ipsilateral to the carotid artery ligation. This decrease is more pronounced at 24 h of recovery, especially in areas vulnerable to hypoxic-ischemic injury, such as the thalamus and hippocampus. At 72 h of recovery, although IGFBP2 and type 1 IGF receptor mRNA levels remain suppressed, gene expression of both IGF-I and IGFBP5 was activated in reactive astrocytes.Therefore, during the critical growth period in rats, the transcriptional levels of all IGF system components are extremely sensitive to metabolic perturbations associated with cerebral hypoxia-ischemia. The immediate decrease in IGF-I gene expression may be partially responsible for the impending neuronal death and selective vulnerability of myelinogenesis during the perinatal period.