Mild hypothermia protects neurons against oxygen glucose deprivation via poly (ADP-ribose) signaling

Resveratrol Preconditioning Downregulates PARP1 Protein to Alleviate PARP1-Mediated Cell Death Following Cerebral Ischemia

Stroke remains a leading cause of mortality; however, available therapeutics are limited. The study of ischemic tolerance, in paradigms such as resveratrol preconditioning (RPC), provides promise for the development of novel prophylactic therapies. The heavily oxidative environment following stroke promotes poly-ADP-ribose polymerase 1 (PARP1)-overactivation and parthanatos, both of which are major contributors to neuronal injury. In this study, we tested the hypothesis that RPC instills ischemic tolerance through decreasing PARP1 overexpression and parthanatos following in vitro and in vivo cerebral ischemia. To test this hypothesis, we utilized rat primary neuronal cultures (PNCs) and middle cerebral artery occlusion (MCAO) in the rat as in vitro and in vivo models, respectively. RPC was administered 2 days preceding ischemic insults. RPC protected PNCs against oxygen and glucose deprivation (OGD)-induced neuronal loss, as well as increases in total PARP1 protein, implying protection against PARP1-overactivation. Twelve hours following OGD, we observed reductions in NAD+/NADH as well as an increase in AIF nuclear translocation, but RPC ameliorated NAD+/NADH loss and blocked AIF nuclear translocation. MCAO in the rat induced AIF nuclear translocation in the ischemic penumbra after 24 h, which was ameliorated with RPC. We tested the hypothesis that RPC's neuroprotection was instilled through long-term downregulation of nuclear PARP1 protein. RPC downregulated nuclear PARP1 protein for at least 6 days in PNCs, likely contributing to RPC's ischemic tolerance. This study describes a novel mechanism by which RPC instills prophylaxis against ischemia-induced PARP1 overexpression and parthanatos, through a long-term reduction of nuclear PARP1 protein.

LOX-1 mediates inflammatory activation of microglial cells through the p38-MAPK/NF-κB pathways under hypoxic-ischemic conditions

BACKGROUND

Microglial cells play an important role in the immune system in the brain. Activated microglial cells are not only injurious but also neuroprotective. We confirmed marked lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1) expression in microglial cells in pathological lesions in the neonatal hypoxic-ischemic encephalopathy (nHIE) model brain. LOX-1 is known to be an activator of cytokines and chemokines through intracellular pathways. Here, we investigated a novel role of LOX-1 and the molecular mechanism of LOX-1 gene transcription microglial cells under hypoxic and ischemic conditions.

METHODS

We isolated primary rat microglial cells from 3-day-old rat brains and confirmed that the isolated cells showed more than 98% Iba-1 positivity with immunocytochemistry. We treated primary rat microglial cells with oxygen glucose deprivation (OGD) as an in vitro model of nHIE. Then, we evaluated the expression levels of LOX-1, cytokines and chemokines in cells treated with or without siRNA and inhibitors compared with those of cells that did not receive OGD-treatment. To confirm transcription factor binding to the OLR-1 gene promoter under the OGD conditions, we performed a luciferase reporter assay and chromatin immunoprecipitation assay. In addition, we analyzed reactive oxygen species and cell viability.

RESULTS

We found that defects in oxygen and nutrition induced LOX-1 expression and led to the production of inflammatory mediators, such as the cytokines IL-1β, IL-6 and TNF-α; the chemokines CCL2, CCL5 and CCL3; and reactive oxygen/nitrogen species. Then, the LOX-1 signal transduction pathway was blocked by inhibitors, LOX-1 siRNA, the p38-MAPK inhibitor SB203580 and the NF-κB inhibitor BAY11-7082 suppressed the production of inflammatory mediators. We found that NF-κB and HIF-1α bind to the promoter region of the OLR-1 gene. Based on the results of the luciferase reporter assay, NF-κB has strong transcriptional activity. Moreover, we demonstrated that LOX-1 in microglial cells was autonomously overexpressed by positive feedback of the intracellular LOX-1 pathway.

CONCLUSION

The hypoxic/ischemic conditions of microglial cells induced LOX-1 expression and activated the immune system. LOX-1 and its related molecules or chemicals may be major therapeutic candidates. Video abstract.

Sevoflurane Post-Conditioning Ameliorates Neuronal Deficits and Axon Demyelination After Neonatal Hypoxic Ischemic Brain Injury: Role of Microglia/Macrophage

Microglia/macrophages have been identified to be highly polarized after ischemia. Interestingly, the polarization of these microglia/macrophages varies immensely under differing disease conditions. Post-conditioning using sevoflurane, a volatile anesthetic, could provide long-term neuroprotection to neonatal rats after hypoxic-ischemic brain injury (HIBI). Thus, the current study aimed at investigating the effects of sevoflurane post-conditioning (SPC) on microglia/macrophage polarization after HIBI induction in neonatal rats. Additionally, we aimed at identifying the underpinning mechanisms specifically related to autophagy and lysosomal protease enzyme, cathepsin B. To develop a HIBI model, 7-day-old Sprague-Dawley rats underwent left common carotid artery ligation followed by 2 h of hypoxia. The role of microglia/macrophages in the neuroprotection conferred by SPC was examined by left-side intra-cerebroventricular injection with adenovirus vector carrying catB-GFP or rapamycin. The number of interleukin (IL)-1β+ cells, cathepsin B+ cells, light chain 3B positive (LC3B+) cells among ionized calcium binding adaptor molecule 1(Iba1+)cells to investigate microglia polarization, neuronal apoptosis to assess neuronal death in the acute phase were tested at 24 h after HIBI. Behavioral tests including suspension test, Morris water maze tests were performed to investigate the long-term effects of SPC, at 21 to 34 days post HIBI. Nissl staining and myelin basic protein (MBP) immunostaining to assess the long-term neuronal and myelin damage were performed at 34 days after HIBI. Based on the obtained results post HIBI, we observed the cells that were positive for IL-1β, cathepsin B, and LC3B among Iba1 positive cell population in the hippocampus were significantly decreased after SPC treatment. SPC significantly attenuated the HIBI-induced increase in neuronal apoptosis, improved long-term cognitive function, and attenuated HI-induced decrease of Nissl-positive cells and MBP expression. However, these trends were reversed by injection of adenovirus vector carrying catB-GFP and rapamycin. SPC attenuated microglia polarization towards neurotoxic phenotypes, alleviates neuronal death and axon demyelination after HIBI in neonatal rats by regulating microglia autophagy and cathepsin B expression, and therefore provided long-term cognitive, learning and memory protection.

Neuroprotective Effects of Diabetes Drugs for the Treatment of Neonatal Hypoxia-Ischemia Encephalopathy

The perinatal period represents a time of great vulnerability for the developing brain. A variety of injuries can result in death or devastating injury causing profound neurocognitive deficits. Hypoxic-ischemic neonatal encephalopathy (HIE) remains the leading cause of brain injury in term infants during the perinatal period with limited options available to aid in recovery. It can result in long-term devastating consequences with neurologic complications varying from mild behavioral deficits to severe seizure, intellectual disability, and/or cerebral palsy in the newborn. Despite medical advances, the only viable option is therapeutic hypothermia which is classified as the gold standard but is not used, or may not be as effective in preterm cases, infection-associated cases or low resource settings. Therefore, alternatives or adjunct therapies are urgently needed. Ongoing research continues to advance our understanding of the mechanisms contributing to perinatal brain injury and identify new targets and treatments. Drugs used for the treatment of patients with type 2 diabetes mellitus (T2DM) have demonstrated neuroprotective properties and therapeutic efficacy from neurological sequelae following HIE insults in preclinical models, both alone, or in combination with induced hypothermia. In this short review, we have focused on recent findings on the use of diabetes drugs that provide a neuroprotective effect using in vitro and in vivo models of HIE that could be considered for clinical translation as a promising treatment.

Neuroprotective Role of Hypothermia in Hypoxic-ischemic Brain Injury: Combined Therapies using Estrogen

Hypoxic-ischemic brain injury is a complex network of factors, which is mainly characterized by a decrease in levels of oxygen concentration and blood flow, which lead to an inefficient supply of nutrients to the brain. Hypoxic-ischemic brain injury can be found in perinatal asphyxia and ischemic-stroke, which represent one of the main causes of mortality and morbidity in children and adults worldwide. Therefore, knowledge of underlying mechanisms triggering these insults may help establish neuroprotective treatments. Selective Estrogen Receptor Modulators and Selective Tissue Estrogenic Activity Regulators exert several neuroprotective effects, including a decrease of reactive oxygen species, maintenance of cell viability, mitochondrial survival, among others. However, these strategies represent a traditional approach of targeting a single factor of pathology without satisfactory results. Hence, combined therapies, such as the administration of therapeutic hypothermia with a complementary neuroprotective agent, constitute a promising alternative. In this sense, the present review summarizes the underlying mechanisms of hypoxic-ischemic brain injury and compiles several neuroprotective strategies, including Selective Estrogen Receptor Modulators and Selective Tissue Estrogenic Activity Regulators, which represent putative agents for combined therapies with therapeutic hypothermia.