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Published on: June 2, 2015
Neuronal K(ATP) channels mediate hypoxic preconditioning and reduce subsequent neonatal hypoxic-ischemic brain injury
Hong-Shuo Sun1, Baofeng Xu2, Wenliang Chen2
1Department of Surgery, Faculty of Medicine, University of Toronto, Toronto, Ontario M5S 1A8, Canada; Department of Physiology, Faculty of Medicine, University of Toronto, Toronto, Ontario M5S 1A8, Canada; Department of Pharmacology & Toxicology, Faculty of Medicine, University of Toronto, Toronto, Ontario M5S 1A8, Canada; Institute of Medical Science, Faculty of Medicine, University of Toronto, Toronto, Ontario M5S 1A8, Canada.
Insights
Hypoxic preconditioning protects neonatal brains from injury by activating K(ATP) channels. This study shows K(ATP) channel openers could treat hypoxic-ischemic encephalopathy in newborns.
Area of Science:
- Neuroscience
- Neonatal Medicine
- Cellular Physiology
Background:
- Neonatal hypoxic-ischemic brain injury and encephalopathy cause significant neurological damage in children.
- Hypoxic preconditioning (HPC) offers neuroprotection against cerebral ischemia, but the role of neuronal K(ATP) channels in this process remains unclear.
- Understanding the mechanisms of HPC is crucial for developing effective treatments for neonatal brain injury.
Purpose of the Study:
- To investigate the role of neuronal K(ATP) channels in hypoxic preconditioning (HPC)-mediated neuroprotection against hypoxia-ischemia (HI) induced brain injury in neonatal mice.
- To determine if K(ATP) channel modulators can influence neuroprotection or neurodegeneration in this model.
- To elucidate the molecular pathways involved in HPC-induced neuroprotection.
Main Methods:
- Utilized a neonatal mouse model of hypoxic-ischemic (HI) brain injury.
- Assessed infarct volume using 2,3,5-triphenyltetrazolium chloride (TTC) staining.
- Quantified apoptotic cells via TUNEL staining and evaluated protein levels using Western blots.
- Measured K(ATP) channel activity using patch-clamp recordings and assessed functional recovery through behavioral tests.
Main Results:
- HPC significantly reduced infarct volume, decreased apoptotic cell death, and improved neurobehavioral outcomes in neonatal mice following HI.
- Pharmacological manipulation of K(ATP) channels demonstrated their critical role: blockers (tolbutamide) abolished HPC's neuroprotection, while openers (diazoxide) mimicked it.
- HPC upregulated Kir6.2, enhanced K(ATP) channel activity, restored PKC and pAkt levels, and reduced caspase-3 expression, effects inhibited by tolbutamide.
Conclusions:
- Neuronal K(ATP) channels are integral to the neuroprotective effects of hypoxic preconditioning in neonatal hypoxic-ischemic brain injury.
- K(ATP) channel openers represent a promising therapeutic strategy for treating neonatal hypoxic-ischemic brain injury and encephalopathy.
Abstract:
Neonatal hypoxic-ischemic brain injury and its related illness hypoxic-ischemic encephalopathy (HIE) are major causes of nervous system damage and neurological morbidity in children. Hypoxic preconditioning (HPC) is known to be neuroprotective in cerebral ischemic brain injury. K(ATP) channels are involved in ischemic preconditioning in the heart; however the involvement of neuronal K(ATP) channels in HPC in the brain has not been fully investigated. In this study, we investigated the role of HPC in hypoxia-ischemia (HI)-induced brain injury in postnatal seven-day-old (P7) CD1 mouse pups. Specifically, TTC (2,3,5-triphenyltetrazolium chloride) staining was used to assess the infarct volume, TUNEL (Terminal deoxynucleotidyl transferase mediated dUTP nick end-labeling) to detect apoptotic cells, Western blots to evaluate protein level, and patch-clamp recordings to measure K(ATP) channel current activities. Behavioral tests were performed to assess the functional recovery after hypoxic-ischemic insults. We found that hypoxic preconditioning reduced infarct volume, decreased the number of TUNEL-positive cells, and improved neurobehavioral functional recovery in neonatal mice following hypoxic-ischemic insults. Pre-treatment with a K(ATP) channel blocker, tolbutamide, inhibited hypoxic preconditioning-induced neuroprotection and augmented neurodegeneration following hypoxic-ischemic injury. Pre-treatment with a K(ATP) channel opener, diazoxide, reduced infarct volume and mimicked hypoxic preconditioning-induced neuroprotection. Hypoxic preconditioning induced upregulation of the protein level of the Kir6.2 isoform and enhanced current activities of K(ATP) channels. Hypoxic preconditioning restored the HI-reduced PKC and pAkt levels, and reduced caspase-3 level, while tolbutamide inhibited the effects of hypoxic preconditioning. We conclude that K(ATP) channels are involved in hypoxic preconditioning-induced neuroprotection in neonatal hypoxic-ischemic brain injury. K(ATP) channel openers may therefore have therapeutic effects in neonatal hypoxic-ischemic brain injury.
