salubrinal and Reperfusion-Injury

Growth arrest and DNA damage-inducible protein 34 (GADD34), one of the key effectors of negative feedback loops, is induced by stress and subsequently attempts to restore homeostasis. It plays a critical role in response to DNA damage and endoplasmic reticulum stress. GADD34 has opposing effects on different stimulus-induced cell apoptosis events in many nervous system diseases, but its role in ischemic stroke is unclear. In this study, we evaluated the role of GADD34 and its distribution in a rat cerebral ischemic model. The results showed that GADD34 was increased in the cortex and contributed to brain injury in ischemic rats. Furthermore, treatment with a GADD34 inhibitor reduced the infarct volume, improved functional outcomes, and inhibited neuronal apoptosis in the cortical penumbra after ischemia. The role of GADD34 in ischemic stroke was associated with the dephosphorylation of eukaryotic translation initiation factor 2α (eIF2α) and phosphorylation of p53. In addition, the GADD34 level was increased in plasma exosomes of cerebral ischemic rats. These findings indicate that GADD34 could be a potential therapeutic target and biomarker for ischemic stroke.

Topics: Animals; Antigens, Differentiation; Biomarkers; Cinnamates; Disease Models, Animal; Eukaryotic Initiation Factor-2; Exosomes; Humans; Infarction, Middle Cerebral Artery; Male; Phosphorylation; Proto-Oncogene Proteins; Rats; Reperfusion Injury; Thiourea; Tumor Suppressor Protein p53

Hepatic ischemia-reperfusion (I/R) injury fundamentally influences the performance of aged liver grafts. The significance of mitophagy in the age dependence of sensitivity to I/R injury remains poorly understood. Here, we show that aging aggravated hepatic I/R injury with decreased mitophagy in mice. The enhancement of mitophagy resulted in significant protection against hepatic I/R injury. Parkin, an E3 ubiquitin ligase, was found depleted by I/R in aged livers. In oxygen-glucose deprivation reperfusion (OGD-Rep.)-treated L02 cells, parkin silencing impaired mitophagy and aggravated cell damage through a relative large mitochondrial membrane potential transition. The phosphorylation of the endoplasmic reticulum stress response protein EIF2α, which was also reduced in the aged liver, induced parkin expression both in vivo and vitro. Forty-six hepatic biopsy specimens from liver graft were collected 2 hours after complete revascularization, followed by immunohistochemical analyses. Parkin expression was negatively correlated to donor age and the peak level of aspartate aminotransferase within first week after liver transplantation. Our translational study demonstrates that aging aggravated hepatic I/R injury by impairing the age-dependent mitophagy function via an insufficient parkin expression and identifies a new strategy to evaluate the capacity of an aged liver graft in the process of I/R through the parkin expression.

Topics: Aging; Animals; Autophagy-Related Proteins; Cell Line; Cinnamates; Eukaryotic Initiation Factor-2; Gene Expression Regulation; Gene Silencing; Glucose; Liver; Liver Transplantation; Mice; Mitophagy; Oxygen; Reperfusion Injury; Thiourea; Ubiquitin-Protein Ligases

The endoplasmic reticulum(ER) stress plays a vital role in mediating ischemic neuronal cell death. However, very little is known about the role of ER stress in mediating pathophysiological reactions to acute brain injuries. An attempt was therefore made to assess the role of cerebral ischemia/reperfusion (I/R) induced ER stress and its modulation on outcome of ischemic insult. Focal cerebral ischemia was induced in rats by middle cerebral artery occlusion (MCAO) for 2 h followed by varying time points of reperfusion. The brain loci specific and time-dependent alterations were seen in the expression pattern of molecular markers, i.e., heat-shock protein 70 (HSP70) for cytoplasmic dysfunction, glucose-regulated protein 78 (GRP78), Caspase-12, C/EBP homologous protein/growth arrest and DNA damage-inducible gene 153 (CHOP/GADD153), activating transcription factor 4 (ATF-4), and Processed X-box protein 1 (xbp1) mRNA for ER dysfunction. Further, histological examinations indicated pronounced brain damage, massive neuronal loss, and DNA fragmentation predominantly in the striatum and cortex. The enhanced expression of GRP78, Caspase-12, CHOP/GADD153, ATF4 and processing of xbp1 mRNA in the affected brain regions clearly indicate the critical involvement of ER-mediated cell death/survival mechanisms and also collectively demonstrated the activation of unfolded protein response (UPR). Moreover, Salubrinal, a selective inhibitor of eIF2alpha dephosphorylation was used to counteract ER stress, which significantly increased the phosphorylation of eukaryotic translation initiation factor 2 subunit alpha (eIF2alpha), leading to reduced brain damage after I/R injury. Therefore, inhibition of ER stress following I/R injury may be used as key therapeutic target for neuroprotection.

Topics: Activating Transcription Factor 4; Animals; Brain; Caspase 12; Cinnamates; Disease Models, Animal; Disease Progression; DNA-Binding Proteins; Endoplasmic Reticulum; Functional Laterality; Gene Expression Regulation, Developmental; Heat-Shock Proteins; HSP72 Heat-Shock Proteins; In Situ Nick-End Labeling; Indoles; Infarction, Middle Cerebral Artery; Male; Phosphopyruvate Hydratase; Rats; Rats, Sprague-Dawley; Regulatory Factor X Transcription Factors; Reperfusion Injury; RNA, Messenger; Statistics, Nonparametric; Thiourea; Time Factors; Transcription Factor CHOP; Transcription Factors; X-Box Binding Protein 1