cPKCγ-Modulated Autophagy Contributes to Ischemic Preconditioning-Induced Neuroprotection in Mice with Ischemic Stroke via mTOR-ULK1 Pathway

Neuron-specific conventional protein kinase C (cPKC)γ mediates cerebral hypoxic preconditioning (HPC). In parallel, autophagy plays a prosurvival role in ischemic preconditioning (IPC) against ischemic stroke. However, the effect of cPKCγ on autophagy in IPC still remains to be addressed. In this study, adult and postnatal 1-day-old C57BL/6 J wild-type (cPKCγ+/+) and knockout (cPKCγ-/-) mice were used to establish in vivo and in vitro IPC models. The results showed that IPC pretreatment alleviated neuronal damage caused by lethal ischemia, which could be suppressed by autophagy inhibitor 3-MA or bafilomycin A1. Meanwhile, cPKCγ knockout blocked IPC-induced neuroprotection, accompanied by significant increase of LC3-I to LC3-II conversion and Beclin 1 protein level, and a significant decrease in p62 protein level. Immunofluorescent staining results showed a decrease of LC3 puncta numbers in IPC-treated cPKCγ+/+ neurons with fatal ischemia, which was reversed in cPKCγ-/- neurons. In addition, cPKCγ-modulated phosphorylation of mTOR at Ser 2448 and ULK1 at Ser 555, rather than p-Thr-172 AMPK, was detected in IPC-pretreated neurons upon lethal ischemic exposure. The present data demonstrated that cPKCγ-modulated autophagy via the mTOR-ULK1 pathway likely modulated IPC-induced neuroprotection.

Hepatic Ischemic Preconditioning Alleviates Ischemia-Reperfusion Injury by Decreasing TIM4 Expression

Ischemia-reperfusion injury (IRI) of the liver is a primary cause of post-liver-surgery complications and ischemic preconditioning (IPC) has been verified to protect against ischemia-reperfusion injury. TIM-4 activation plays an important role in macrophage mediated hepatic IRI. This study aimed to determine whether IPC protects against hepatic IRI through inhibiting TIM-4 activation. In this study, a model of warm liver ischemia (90 min) and reperfusion for 6 h was used. Mice were subjected to ischemia-reperfusion injury with or without ischemic preconditioning and TIM4 blocking antibody. Western blot was determined to detect the expression of TIM4 protein and mitochondrial apoptosis-related protein expression. Liver function was evaluated using the level of alanine transaminase (ALT) and aspartate transaminase (AST), cell apoptosis and pathological examination. We found that compared with the control group, ischemic preconditioning reduced IRI by decreasing hepatocyte apoptosis, ALT, AST, CD68 and CD3 positive cells, tissue myeloperoxidase activity(MPO), and downregulating TIM-4 expression. TIM4 blocking could reduce CD68 and CD3 positive cells in liver. Furthermore, activated monocytes transfusion significantly abolished the protect effect of IPC with increased hepatocyte apoptosis, ALT, AST, CD68 and CD3 positive cells while TIM-4 knockdown monocytes lost this effect. These results suggested that IPC protects against hepatic IRI by downregulating TIM-4 and indicated TIM-4 would be a novel therapeutic target to minimize IRI.

Ischemic Preconditioning in the Intensive Care Unit

OPINION STATEMENT

Preconditioning is the premise that controlled preemptive exposure to sub-lethal doses of a stressor and can condition an organism or organ to later withstand a lethal dose. This process relies on marshaling endogenous survival resources that have evolved as part of an organism's evolutionary struggle to overcome at times harsh environmental conditions. This preconditioning response occurs through activation of myriad complex mechanisms that run the gamut from alterations in gene expression to the de novo synthesis and post-translational modification of proteins, and it may occur across exposure to a wide variety of stressors (i.e., ischemia, hypoxia, hypothermia, drugs). This review will focus on preconditioning in relation to an ischemic stressor (ischemic preconditioning) and how this process may be harnessed as a protective method to ameliorate targeted acute neurologic diseases especially. There has been considerable eagerness to translate ischemic preconditioning to the bedside, and to that end there have been recent trials examining its efficacy in various clinical settings. However, some of these trials have reached diverging conclusions with a protective effect seen in studies targeting acute kidney injury solely while no benefit was seen in larger trials targeting combined endpoints including cardio-, neuro-, and renoprotection in a cohort of patients undergoing cardiac surgery. While an extensive body of pre-clinical research offers ischemic preconditioning as a robust and highly faithful protective phenomenon, its clinical utility remains unproven. This current state may be due to persisting gaps in our understanding of how best to harness its power. This review will provide an overview of the biological mechanisms proposed to underlie ischemic preconditioning, explore initial disease targets, examine the challenges we must overcome to optimally engage this system, and report findings of recent clinical trials.