Glutamine Supplementation Ameliorates Chronic Stress-induced Reductions in Glutamate and Glutamine Transporters in the Mouse Prefrontal Cortex.

Chronic immobilization stress (CIS) induces low levels of glutamate (Glu) and glutamine (Gln) and hypoactive glutamatergic signaling in the mouse prefrontal cortex (PFC), which is closely related to the Glu-Gln cycle. A Gln-supplemented diet ameliorates CIS-induced deleterious changes. Here, we investigated the effects of CIS and Gln supplementation on Glu-Gln cycle-related proteins to characterize the underlying mechanisms. Using the CIS-induced depression mouse model, we examined the expression of 11 proteins involved in the Glu-Gln cycle in the PFC. CIS decreased levels of glutamate transporter 1 (GLT1) and sodium-coupled neutral amino acid transporter (SNAT) 1, SANT2, SNAT3, and SNAT5. Gln supplementation did not affect the non-stressed group but significantly increased GLT1 and SNATs of the stressed group. By immunohistochemical analysis, we confirmed that SNAT1 and SNAT2 were decreased in neurons and GLT1, SNAT3, and SNAT5 were decreased in astrocytes in the medial PFC of the stressed group, but Gln-supplemented diet ameliorated these decrements. Collectively, these results suggest that CIS may cause depressive-like behaviors by decreasing Glu and Gln transportation in the PFC and that a Gln-supplemented diet could prevent the deleterious effects of CIS.

Glutamine has antidepressive effects through increments of glutamate and glutamine levels and glutamatergic activity in the medial prefrontal cortex.

Emerging evidence has shown the low levels of glutamate (Glu) and glutamine (Gln) and the hypoactivity in the cortex of patients with depression. The hypoactivity is closely related with low frequency of glutamatergic signaling that is affected by the levels of Glu and Gln. Thus, we hypothesized that there might be a causality among low levels of Glu and Gln, hypoactive glutamatergic neurotransmissions, and depressive behaviors. Here, we found low Glu and Gln levels and low frequency of spontaneous excitatory postsynaptic current (sEPSC) of glutamatergic neurons in the medial prefrontal cortex (mPFC) of chronic immobilization stress (CIS)-induced depressed mice. The depressed mice also showed hypoactive Gln synthetase (GS). Inhibition of GS by methionine sulfoximine (MSO) decreased Glu and Gln levels and increased depressive behaviors with low frequency of sEPSC in the mPFC, indicating that Glu and Gln decrements cause hypoactive glutamatergic neurotransmissions and depressive behaviors. Both Glu and Gln could increase sEPSC of glutamatergic neurons in the mPFC on slice patch, but only Gln overcame MSO to increase sEPSC, suggesting that exogenous Gln would recover CIS-induced low frequency of sEPSC caused by hypoactive GS and act as an antidepressant. Expectedly, Gln supplementation showed antidepressant effects against CIS; it increased glutamatergic neurotransmissions with Glu and Gln increment in the mPFC and attenuated depressive behaviors. Moreover, selective glutamatergic activation in the mPFC by optogenetics decreased depressive behavior. In conclusion, depressive behaviors evoked by chronic stress were due to hypoactive glutamatergic neurons in the mPFC caused by low levels of Glu and Gln, and exogenous Gln can be used as an alternative antidepressant to increase glutamatergic neurotransmission.

Aralia elata (Miq) Seem Extract Decreases O-GlcNAc Transferase Expression and Retinal Cell Death in Diabetic Mice.

Aralia elata (Miq) Seem (AES) is a medicinal plant used in traditional Chinese and Korean medicine for the treatment of several diseases, including diabetes. This study aimed to investigate the neuroprotective effect of AES extract against high glucose-induced retinal injury in diabetic mice. AES extract (20 and 100 mg/kg body weight) was orally administered to control mice or mice with streptozotocin-induced diabetes. Protein levels of O-linked ß-N-acetylglucosamine (O-GlcNAc) transferase (OGT), carbohydrate-responsive element-binding protein (ChREBP), sterol regulatory element-binding protein (SREBP)-1, thioredoxin-interacting protein (TXNIP), fatty acid synthase (FAS), and acetyl CoA carboxylase (ACC) were analyzed by western blotting. Colocalization of terminal deoxynucleotide transferase-mediated dUTP nicked-end labeling (TUNEL)-positive ganglion cells and OGT, ChREBP, or TXNIP were monitored using double immunofluorescence analysis. Interaction between ChREBP and OGT was assessed using coimmunoprecipitation analysis. AES extract protected the retinas from neuronal injury and decreased levels of OGT, ChREBP, TXNIP, SREBP-1, FAS, and ACC in the diabetic retinas. AES extract reduced colocalization of TUNEL-positive ganglion cells and OGT, ChREBP, or TXNIP in the diabetic retinas. Coimmunoprecipitation analysis indicated that AES extract reduced interaction between ChREBP and OGT and attenuated ganglion cell death in diabetic retinas. Moreover, the ChREBP that colocalized with OGT or the TUNEL signal was significantly decreased in diabetic mice treated with AES extract. These findings show that AES extract can alleviate OGT-, ChREBP-, TXNIP-, or SREBP-1-related retinal injury in diabetic retinopathy.

Aralia elata prevents neuronal death by downregulating tonicity response element binding protein in diabetic retinopathy.

BACKGROUND/AIMS: The present study addresses the role of tonicity response element binding protein (TonEBP) in retinal ganglion cell (RGC) death in diabetic retinopathy and the impact of Aralia elata extract on the TonEBP/RGC interaction. METHODS: Diabetes was induced in C57BL/6 mice by intraperitoneal injection of streptozotocin (STZ). Control mice received phosphate-buffered saline. After five injections of STZ or saline buffer, A. elata extract was administered by daily oral tube feeding for 7 weeks. All mice were killed at 2 months after the last injection of STZ or saline and the extent of cell death together with the protein expression levels of TonEBP, aldose reductase (AR) and nuclear factor-kappa B (NF-κB) were examined. RESULTS: Terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL)-positive signals were colocalized with TonEBP-immunoreactive RGCs. The apoptotic cell death of RGCs and the expression levels of TonEBP, AR and NF-κB were significantly increased in the retinas of diabetic mice compared with controls at 2 months after the induction of diabetes. However, these changes were effectively blocked by the administration of A. elata extract. CONCLUSIONS: These results indicate that A. elata prevents diabetes-induced RGC apoptosis and downregulates TonEBP expression. Therefore, A. elata extract may have therapeutic potential to prevent diabetes-induced retinal neurodegeneration in diabetic retinopathy.

The GABAB receptor associates with regulators of G-protein signaling 4 protein in the mouse prefrontal cortex and hypothalamus.

Regulators of G-protein signaling (RGS) proteins regulate certain G-protein-coupled receptor (GPCR)-mediated signaling pathways. The GABA(B) receptor (GABA(B)R) is a GPCR that plays a role in the stress response. Previous studies indicate that acute immobilization stress (AIS) decreases RGS4 in the prefrontal cortex (PFC) and hypothalamus (HY) and suggest the possibility of a signal complex composed of RGS4 and GABA(B)R. Therefore, in the present study, we tested whether RGS4 associates with GABA(B)R in these brain regions. We found the co-localization of RGS4 and GABA(B)R subtypes in the PFC and HY using double immunohistochemistry and confirmed a direct association between GABA(B2)R and RGS4 proteins using co-immunoprecipitation. Furthermore, we found that AIS decreased the amount of RGS4 bound to GABA(B2)R and the number of double-positive cells. These results indicate that GABA(B)R forms a signal complex with RGS4 and suggests that RGS4 is a regulator of GABA(B)R.

Resveratrol attenuates obesity-associated peripheral and central inflammation and improves memory deficit in mice fed a high-fat diet.

Obesity-induced diabetes is associated with chronic inflammation and is considered a risk factor for neurodegeneration. We tested the hypothesis that an AMP-activated protein kinase activator, resveratrol (RES), which is known to exert potent anti-inflammatory effects, would attenuate peripheral and central inflammation and improve memory deficit in mice fed a high-fat diet (HFD). C57BL/6J mice were fed an HFD or an HFD supplemented with RES for 20 weeks. Metabolic parameters in serum were evaluated, and Western blot analysis and immunohistochemistry in peripheral organs and brain were completed. We used the Morris water maze test to study the role of RES on memory function in HFD-treated mice. RES treatment reduced hepatic steatosis, macrophage infiltration, and insulin resistance in HFD-fed mice. In the hippocampus of HFD-fed mice, the protein levels of tumor necrosis factor-α and Iba-1 expression were reduced by RES treatment. Choline acetyltransferase was increased, and the phosphorylation of tau was decreased in the hippocampus of HFD-fed mice upon RES treatment. In particular, we found that RES significantly improved memory deficit in HFD-fed mice. These findings indicate that RES reverses obesity-related peripheral and central inflammation and metabolic derangements and improves memory deficit in HFD-fed diabetic mice.

Sequential induction of heme oxygenase-1 and manganese superoxide dismutase protects cultured astrocytes against nitric oxide.

Nitric oxide (NO) is a widely recognized mediator of physiological and pathophysiological signal transmission. In an attempt to better understand the molecular actions of NO in astrocytes, stress protein expression in response to NO donor sodium nitroprusside was investigated. Heme oxygenase-1 (HO-1) has been identified as an inducer of manganese superoxide dismutase (MnSOD), playing a cytoprotective role under the condition of nitrosative stress. We present evidence that the sequential induction of HO-1 and MnSOD protects astrocytes from NO toxicity: (1) both HO-1 and MnSOD expression were induced by NO; (2) NO-mediated increase in MnSOD activity was partly abolished by HO-1 inhibitor Zn(II) protoporphyrin IX (ZnPP); (3) pretreatment of astrocytes with a nontoxic dose of NO protected the cells against the later treatment with a toxic dose of NO; (4) inhibition of HO-1 by ZnPP sensitized astrocytes to the nontoxic dose of NO resulting in a marked cytotoxicity; and (5) adenovirus-mediated overexpression of MnSOD protected astrocytes from the NO toxicity. The molecular action of NO in astrocytes appears to be dose-dependent. While a high dose of NO exerts cytotoxicity leading to the tissue damage in the central nervous system, a low dose of NO may act as an important signaling molecule in astrocytes with concurrent induction of cytoprotective proteins such as HO-1 and MnSOD.

Prepubertal chronic ethanol administration alters TTF-1 and Oct-2 expression in the hypothalamus of female rats.

We found that prolonged administration of ethanol (3 g/kg i.p. at 08:00, once per day) to young female rats starting on postnatal day 24 caused delayed puberty. We further found that prolonged ethanol administration changed the typical hypothalamic expression patterns of TTF-1 and Oct-2 and reduced GnRH mRNA expression. We suggest that these changes may cause the ethanol-induced disturbances in the regulation of GnRH in the hypothalamus and may be responsible for the ethanol-induced reduction in GnRH and LH associated with delayed puberty.

Flavonoid wogonin from medicinal herb is neuroprotective by inhibiting inflammatory activation of microglia.

Wogonin (5,7-dihydroxy-8-methoxyflavone), a flavonoid originated from the root of a medicinal herb Scutellaria baicalensis Georgi, has been previously shown to have anti-inflammatory activities in various cell types including macrophages. In this work, we have found that wogonin is a potent neuroprotector from natural source. Wogonin inhibited inflammatory activation of cultured brain microglia by diminishing lipopolysaccharide-induced tumor necrosis factor-alpha (TNF-alpha), interleukin-1beta, and nitric oxide (NO) production. Wogonin inhibited NO production by suppressing inducible NO synthase (iNOS) induction and NF-kappaB activation in microglia. Inhibition of inflammatory activation of microglia by wogonin led to the reduction in microglial cytotoxicity toward cocultured PC12 cells, supporting a neuroprotective role for wogonin in vitro. The neuroprotective effect of wogonin was further demonstrated in vivo using two experimental brain injury models; transient global ischemia by four-vessel occlusion and excitotoxic injury by systemic kainate injection. In both animal models, wogonin conferred neuroprotection by attenuating the death of hippocampal neurons, and the neuroprotective effect was associated with inhibition of the inflammatory activation of microglia. Hippocampal induction of inflammatory mediators such as iNOS and TNF-alpha was reduced by wogonin in the global ischemia model, and microglial activation was markedly down-regulated by wogonin in the kainate injection model as judged by microglia-specific isolectin B4 staining. Taken together, our results indicate that wogonin exerts its neuroprotective effect by inhibiting microglial activation, which is a critical component of pathogenic inflammatory responses in neurodegenerative diseases. The current study emphasizes the importance of medicinal herbs and their constituents as an invaluable source for the development of novel neuroprotective drugs.

Flavonoid baicalein attenuates activation-induced cell death of brain microglia.

Baicalein (5,6,7-trihydroxyflavone), a flavonoid originated from the root of Chinese medicinal herb Scutellaria baicalensis, has been shown to exert anti-inflammatory and antioxidant effects, and it is a well known inhibitor of 12-lipoxygenase. We have previously reported that neuroglia undergo nitric oxide (NO)-dependent and NO-independent apoptosis upon inflammatory activation. In the current work, we asked how anti-inflammatory baicalein influences autoregulatory apoptosis of activated microglia and their NO production. Baicalein attenuated NO production and apoptosis of lipopolysaccharide (LPS)-activated, but not interferon-gamma-activated, BV-2 mouse microglial cells as well as rat primary microglia cultures. The inhibition of NO production by baicalein was due to the suppression of inducible NO synthase induction. Moreover, baicalein inhibited LPS-induced nuclear factor-kappaB (NF-kappaB) activity in BV-2 cells without affecting caspase-11 activation, interferon regulatory factor-1 induction, or signal transducer and activator of transcription-1 phosphorylation. Transfection of BV-2 cells with a p65 subunit of NF-kappaB abolished the apoptosis-attenuating effects of baicalein, indicating that the inhibition of NF-kappaB is a major mechanism of action. Baicalein, however, did not significantly affect NO donor-mediated cytotoxicity, and the apoptosis-attenuating effects of baicalein were independent of 12-lipoxygenase inhibition. Based on our previous findings that activation-induced cell death (AICD) of microglia occurs through two separate pathways (NO-dependent pathway and caspase-11-dependent pathway), our current results suggest that baicalein selectively inhibits the NO-dependent apoptotic pathway of activated microglia by suppressing cytotoxic NO production. Also, the AICD-inhibiting effects of baicalein were specific for the inflammatory stimulus that activated microglia.