Wei-Wei Hou

Endoplasmic reticulum stress induced by tunicamycin and thapsigargin protects against transient ischemic brain injury: Involvement of PARK2-dependent mitophagy.

Transient cerebral ischemia leads to endoplasmic reticulum (ER) stress. However, the contributions of ER stress to cerebral ischemia are not clear. To address this issue, the ER stress activators tunicamycin (TM) and thapsigargin (TG) were administered to transient middle cerebral artery occluded (tMCAO) mice and oxygen-glucose deprivation-reperfusion (OGD-Rep.)-treated neurons. Both TM and TG showed significant protection against ischemia-induced brain injury, as revealed by reduced brain infarct volume and increased glucose uptake rate in ischemic tissue. In OGD-Rep.-treated neurons, 4-PBA, the ER stress releasing mechanism, counteracted the neuronal protection of TM and TG, which also supports a protective role of ER stress in transient brain ischemia. Knocking down the ER stress sensor Eif2s1, which is further activated by TM and TG, reduced the OGD-Rep.-induced neuronal cell death. In addition, both TM and TG prevented PARK2 loss, promoted its recruitment to mitochondria, and activated mitophagy during reperfusion after ischemia. The neuroprotection of TM and TG was reversed by autophagy inhibition (3-methyladenine and Atg7 knockdown) as well as Park2 silencing. The neuroprotection was also diminished in Park2+/− mice. Moreover, Eif2s1 and downstream Atf4 silencing reduced PARK2 expression, impaired mitophagy induction, and counteracted the neuroprotection. Taken together, the present investigation demonstrates that the ER stress induced by TM and TG protects against the transient ischemic brain injury. The PARK2-mediated mitophagy may be underlying the protection of ER stress. These findings may provide a new strategy to rescue ischemic brains by inducing mitophagy through ER stress activation.

Protective Effect of Carnosine on Subcortical Ischemic Vascular Dementia in Mice

Recently, we found carnosine protects against N‐Methyl‐D‐Aspartate (NMDA) induced excitotoxicity through a histaminergic pathway. The aim of this study was to determine whether the carnosine‐histidine‐histamine pathway also played a protective role in subcortical ischemic vascular dementia (SIVD).

Histamine H3 receptors aggravate cerebral ischaemic injury by histamine-independent mechanisms

The role of the histamine H3 receptor (H3R) in cerebral ischaemia/reperfusion (I/R) injury remains unknown. Here we show that H3R expression is upregulated after I/R in two mouse models. H3R antagonists and H3R knockout attenuate I/R injury, which is reversed by an H3R-selective agonist. Interestingly, H1R and H2R antagonists, a histidine decarboxylase (HDC) inhibitor and HDC knockout all fail to compromise the protection by H3R blockade. H3R blockade inhibits mTOR phosphorylation and reinforces autophagy. The neuroprotection by H3R antagonism is reversed by 3-methyladenine and siRNA for Atg7, and is diminished in Atg5−/− mouse embryonic fibroblasts. Furthermore, the peptide Tat-H3RCT414-436, which blocks CLIC4 binding with H3Rs, or siRNA for CLIC4, further increases I/R-induced autophagy and protects against I/R injury. Therefore, H3R promotes I/R injury while its antagonism protects against ischaemic injury via histamine-independent mechanisms that involve suppressing H3R/CLIC4 binding-activated autophagy, suggesting that H3R inhibition is a therapeutic target for cerebral ischaemia.

Wide therapeutic time-window of low-frequency stimulation at the subiculum for temporal lobe epilepsy treatment in rats

Low-frequency stimulation (LFS) has been considered as an option for the treatment of intractable epilepsy. However, previous data showed that LFS of certain brain regions only exerts its effect within a very narrow therapeutic time window, which lasts from seconds to tens of seconds, thus restricting its clinical application. The present study was designed to determine whether there exists a target with a wider therapeutic window for LFS treatment. Therefore, evoked seizures in the rat were induced by amygdala kindling and spontaneous seizures were induced by pilocarpine. The effects of different modes of LFS at the subiculum on the progression and severity of evoked seizures and the frequency of spontaneous seizure were evaluated. We found that (i) LFS at 1Hz delivered to the subiculum before and immediately after the kindling stimulations, or after the cessation of afterdischarge (afterdischarge duration, ADD) decreased the seizure stages and shortened the ADD both in seizure acquisition and expression in amygdaloid-kindled seizures. In addition, even LFS delivered after duration of double the ADD prolonged the kindling progression. (ii) LFS delivered at 1Hz, but not 0.5, 3 or 130Hz, immediately after the cessation of kindling stimulations retarded the progression of kindling seizures. (iii) Pilocarpine-induced spontaneous seizures were completely inhibited by 1Hz LFS. Thus, these results demonstrated that LFS of the subiculum has a wide therapeutic time-window for temporal lobe epilepsy treatment in rats, suggesting that the subiculum may be a promising and suitable target for clinical application.

A Novel Neuroprotective Strategy for Ischemic Stroke: Transient Mild Acidosis Treatment by CO2 Inhalation at Reperfusion

Acidosis is one of the key components in cerebral ischemic postconditioning that has emerged recently as an endogenous strategy for neuroprotection. We set out to test whether acidosis treatment at reperfusion can protect against cerebral ischemia/reperfusion injury. Adult male C57BL/6 J mice were subjected to 60-minute middle cerebral arterial occlusion followed by 24-hour reperfusion. Acidosis treatment by inhaling 10%, 20%, or 30% CO2 for 5 or 10 minutes at 5, 50, or 100 minutes after reperfusion was applied. Our results showed that inhaling 20% CO2 for 5 minutes at 5 minutes after reperfusion-induced optimal neuroprotection, as revealed by reduced infarct volume. Attenuating brain acidosis with NaHCO3 significantly compromised the acidosis or ischemic postconditioning-induced neuroprotection. Consistently, both acidosis-treated primary cultured cortical neurons and acute corticostriatal slices were more resistant to oxygen–glucose deprivation/reperfusion insult. In addition, acidosis inhibited ischemia/reperfusion-induced apoptosis, caspase-3 expression, cytochrome c release to cytoplasm, and mitochondrial permeability transition pore (mPTP) opening. The neuroprotection of acidosis was inhibited by the mPTP opener atractyloside both in vivo and in vitro. Taken together, these findings indicate that transient mild acidosis treatment at reperfusion protects against cerebral ischemia/reperfusion injury. This neuroprotection is likely achieved, at least partly, by inhibiting mPTP opening and mitochondria-dependent apoptosis.

Modulation of astrocytic glutamine synthetase expression and cell viability by histamine in cultured cortical astrocytes exposed to OGD insults

Histamine, a neurotransmitter or neuromodulator has been demonstrated to be neuroprotective in cerebral ischemia. However, few reports concern its function on astrocytes during cerebral ischemia. The purpose of this study was to investigate the effects of histamine on astrocytic cell damage and glutamate signaling, especially on glutamine synthetase (GS) expression in primary cultured cortical astrocytes exposed to oxygen-glucose deprivation (OGD) insult. OGD for 6h caused a severe damage of astrocytic mitochondrial function, and decreased GS expression and then increased the extracellular glutamate level. Pretreatment with histamine significantly prevented the cell damage and rescued the expression of GS in a concentration-dependent manner. The protective effect of histamine on astrocytic cell damage could be partly reversed either by H1 receptor antagonist pyrilamine or H2 receptor antagonist cimetidine. However, the regulatory effect of histamine on GS expression was antagonized only by pyrilamine. In addition, bisindolylmaleimide II, a broad-spectrum inhibitor of PKC, reversed the regulatory action of histamine on GS expression. These results indicate that histamine can effectively protect against OGD-induced cell damage in astrocytes through H1 and H2 receptors, and its regulatory effect on astrocytic GS expression may be due to the activation of H1 receptor and PKC pathway. Histamine may be an endogenous protective factor and calls for its further study as a regulator of astrocyte function during ischemic stroke.

Effects of histamine on spontaneous neuropathic pain induced by peripheral axotomy

The present study was designed to investigate the effects of histamine on spontaneous neuropathic pain (NP) induced by peripheral axotomy. Rats and mice were subjected to complete transection of the left sciatic and saphenous nerves to induce spontaneous NP (the neuroma model). Rats were then treated with drugs once daily for 30 days (histidine and loratadine, i.p.) or 21 days (histamine, i.c.v.). Autotomy behavior was scored daily until day 50 post-operation (PO). On days 14 to 21 PO, some rats in the control group were subjected to single-fiber recording. Autotomy behavior was also monitored daily in histidine decarboxylase (the key enzyme for histamine synthesis) knockout (HDC-/-) and wild-type mice for 42 days. We found that both histidine (500 mg/kg) (a precursor of histamine that increases histamine levels in the tissues) and histamine (50 μg/5 μL) significantly suppressed autotomy behavior in rats. HDC-/- mice lacking endogenous histamine showed higher levels of autotomy than the wild-type. In addition, the analgesic effect of histidine was not antagonized by loratadine (a peripherally-acting H1 receptor antagonist), while loratadine alone significantly suppressed autotomy. Electrophysiological recording showed that ectopic spontaneous discharges from the neuroma were blocked by systemic diphenhydramine (an H1 receptor antagonist). Our results suggest that histamine plays an important role in spontaneous NP. It is likely that histamine in the central nervous system is analgesic, while in the periphery, via H1 receptors, it is algesic. This study justifies the avoidance of a histamine-rich diet and the use of peripherally-acting H1 receptor antagonists as well as agents that improve histamine action in the central nervous system in patients with spontaneous NP.

Histamine upregulates Nav1.8 expression in primary afferent neurons via H2 receptors: involvement in neuropathic pain.

The upregulation of Nav1.8 in primary afferents plays a critical role in the development and persistence of neuropathic pain. The mechanisms underlying the upregulation are not fully understood.

Histamine Modulation of Acute Nociception Involves Regulation of Nav1.8 in Primary Afferent Neurons in Mice

To explore the role of histamine in acute pain perception and its possible mechanisms.

Blocking GluN2B subunits reverses the enhanced seizure susceptibility after prolonged febrile seizures with a wide therapeutic time-window.

Febrile seizures (FSs), the most common type of convulsive events in infants, are closely associated with temporal lobe epilepsy (TLE) in adulthood. It is urgent to investigate how FSs promote epileptogenesis and find the potential therapeutic targets. In the present study, we showed that the phosphorylation of GluN2B Tyr1472 gradually reached peak level at 24h after prolonged FSs and remained elevated during 7days thereafter. IL-1β treatment alone, which in previous study mimicked the effect of prolonged FSs on adult seizure susceptibility, increased GluN2B Tyr1472 phosphorylation. Both IL-1 receptor antagonist (IL-1Ra) and IL-1R1 deletion were sufficient to reverse the prolonged FSs induced hyper-phosphorylation of GluN2B Tyr1472. GluN2B antagonist ifenprodil showed a wide therapeutic time-window (3days) to reverse the enhanced seizure susceptibility after prolonged FSs or IL-1β treatment. Our study demonstrated that GluN2B phosphorylation at Tyr1472 site mediated by the transient increase of IL-1β was involved in the enhanced adult seizure susceptibility after prolonged FSs, implicating GluN2B-containing NMDAR is a new potential drug target with a wide therapeutic time window to prevent epileptogenesis in patients with infantile FSs.