Orexin-A exerts neuroprotective effect in experimental intracerebral hemorrhage by suppressing autophagy via OXR1-mediated ERK/mTOR signaling pathway

Abstract

BackgroundOrexin-A (OXA) is a polypeptide produced in the hypothalamus, which binds to specific receptors and exerts multiple physiological effects. Autophagy plays a vital role in early brain injury (EBI) after intracerebral hemorrhage (ICH). However, the relationship between OXA and autophagy after ICH has not been confirmed.MethodsIn this study, the protective role of OXA was investigated in a model of hemin-induced injury in PC12 cells and blood-injection ICH model in rats, and its potential molecular mechanism was clarified. Neurobehavioral tests, brain water content, and pathologic morphology were assessed after ICH. Cell survival rate was determined using Cell Counting Kit-8 (CCK-8), while apoptosis was detected using flow cytometry. The autophagy protein LC3 that was originally identified as microtubule-associated protein 1 light 3 was evaluated by immunohistochemistry. The ultrastructural changes of cells following ICH were observed by transmission electron microscopy. Western blotting was performed to determine the expression levels of LC3, p62/SQSTM1 (p62), phosphorylated extracellular signal-regulated kinase 1/2 (p-ERK1/2), total extracellular signal-regulated kinase 1/2 (t-ERK1/2), mammalian target of rapamycin (mTOR), and phosphorylated mammalian target of rapamycin (p-mTOR).ResultsOXA treatment significantly improved neurofunctional outcomes, reduced brain edema, and alleviated neuronal apoptosis. OXA administration upregulated p-mTOR and p62, while it downregulated p-ERK1/2 and LC3; this effect was reversed by the orexin receptor 1 (OXR1) antagonist SB-334867.ConclusionsThis study demonstrates that OXA suppresses autophagy via the OXR1-mediated ERK/mTOR signaling pathway to exert neuroprotective effects, and it might provide a novel therapeutic approach in patients suffering from ICH.

Orexin-A alleviates ferroptosis by activating the Nrf2/HO-1 signaling pathway in traumatic brain injury

“…Previous research by our group found that non-invasive nerve-regulation technology can induce the increase of OXA in the cortex of TBI rats, reduce neuroinflammation, and play a neuroprotective role. What’s more, research revealed OXA can diminish neuronal damage via autophagy and apoptosis inhibition [ 15 , 31 – 33 ]. However, the relation of OXA to ferroptosis with TBI conditions was not confirmed.…”

Mechanisms and therapeutic targets of mitophagy after intracerebral hemorrhage

“…Orexin-A inhibits the ERK/mTOR signaling pathway to reduce thrombin-mediated autophagy by upregulating LC3B-II/LC3B and downregulating p62. Combined with Oxidation Resistance 1, it prevents heme-induced PC12 cell damage and protects against neuronal apoptosis [ 102 ].…”

“… [ 47 , 59 ] HIF-1α/VEGF downregulation Neuron ICH Patients high-flow oxygen 8 L/min, 1 h each time for 6 cycles daily Normobaric Oxygen Therapy NBO therapy increases brain metabolic rate, attenuated cerebral edema, reduced local brain cell acidosis, and protected the BBB(Brain Barriers) [ [96] , [97] , [98] , [99] ] ICH Rats 1 h after ICH(90 % concentrations in a single 6 h session daily) NBO therapy suppresses HIF-1 activity and alleviates cerebral edema. Autophagy Damaged or superfluous organelle ERK/mTOR/p62/LC3 downregulation Neuron ICH Rats – Orexin-A Inhibition of autophagy to attenuate secondary brain injury and protect against inflammation [ 102 ] Glutamate/calcium-related cascades downregulation Neuron, astrocyte ICH Rats 2h after ICH Alpha-asarone Inhibition of autophagy to ameliorate short- and long-term neurological impairments, bodyweight loss, and learning and memory ability, and alleviate neuronal damage, brain edema, and BBB dysfunction via enhancing the expression of GABA [ 94 ] AMPK/mTOR downregulation Neuron ICH Rats – Lovastatin Inhibition of autophagy to mitigate cognitive impairment, enhance their spatial learning and memory abilities, reduce oxidative stress response and inflammatory factors which induce nervous system damage, lesion area, and brain water content after ICH [ 104 ] …”

Therapeutic effects of orexin-A in sepsis-associated encephalopathy in mice

“…A large number of previous studies have shown that an imbalance in OXA is associated with Parkinson’s disease [ 22 ], Alzheimer’s disease [ 23 ], and other neurological disorders. Animal studies have further shown that OXA reduces neuroinflammation [ 24 , 25 ], inhibits the endothelial cell inflammation induced by oxidized low-density lipoproteins in endothelial cells [ 26 ], and inhibits neuronal apoptosis [ 27 ]. Thus, OXA may be a potential therapeutic drug for central nervous system cognitive disorders.…”