Age-related effects of ethanol consumption on triiodothyronine and retinoic acid nuclear receptors, neurogranin and neuromodulin expression levels in mouse brain

Dietary methionine restriction improves gut microbiota composition and prevents cognitive impairment in D-galactose-induced aging mice

Dietary methionine restriction (MR) has been shown to delay aging and ameliorate age-related cognitive impairments. We hypothesized that changes in the gut microbiota may mediate these effects. To test this hypothesis, ICR mice subcutaneously injected with 150 mg kg^-1 day^-1D-galactose were fed a normal (0.86% methionine) or an MR (0.17% methionine) diet for 2 months. Multiple behavioral experiments were performed, and the gut microbiota composition, metabolite profiles related to short-chain fatty acids (SCFAs) in the feces, and indicators related to the redox and inflammatory states in the hippocampus were further analyzed. Our results indicated that MR alleviated cognitive impairment (including non-spatial memory deficits, working memory deficits, and hippocampus-dependent spatial memory deficits) and anxiety-like behavior in D-Gal-induced aging mice. Furthermore, MR increased the abundance of putative SCFA-producing bacteria such as Lachnospiraceae, Turicibacter, Roseburia, Ruminococcaceae_UCG-014, Intestinimonas, Rikenellaceae, Tyzzerella, and H₂S-producing bacteria such as Desulfovibrio in feces. Moreover, MR reversed and normalized the levels of intestinal SCFAs (acetate, propionate, and butyrate) and important intermediate metabolites of the SCFAs (pyruvate, lactate, malate, fumarate, and succinate), abolished aging-induced oxidative stress and inflammatory responses, increased the levels of H₂S in the plasma and hippocampus, and selectively modulated the expression of multiple learning- and memory-related genes in the hippocampus. These findings suggest that MR improved the gut microbiota composition and SCFA production and alleviated oxidative stress and inflammatory responses in the hippocampus, which might prevent cognitive impairment in D-galactose-induced aging mice.

Neurogranin Expression Is Regulated by Synaptic Activity and Promotes Synaptogenesis in Cultured Hippocampal Neurons

Neurogranin (Ng) is a calmodulin (CaM)-binding protein that is phosphorylated by protein kinase C (PKC) and is highly enriched in the dendrites and spines of telencephalic neurons. It is proposed to be involved in regulating CaM availability in the post-synaptic environment to modulate the efficiency of excitatory synaptic transmission. There is a close relationship between Ng and cognitive performance; its expression peaks in the forebrain coinciding with maximum synaptogenic activity, and it is reduced in several conditions of impaired cognition. We studied the expression of Ng in cultured hippocampal neurons and found that both protein and mRNA levels were about 10% of that found in the adult hippocampus. Long-term blockade of NMDA receptors substantially decreased Ng expression. On the other hand, treatments that enhanced synaptic activity such as long-term bicuculline treatment or co-culture with glial cells or cholesterol increased Ng expression. Chemical long-term potentiation (cLTP) induced an initial drop of Ng, with a minimum after 15 min followed by a slow recovery during the next 2-4 h. This effect was most evident in the synaptosome-enriched fraction, thus suggesting local synthesis in dendrites. Lentiviral expression of Ng led to increased density of both excitatory and inhibitory synapses in the second and third weeks of culture. These results indicate that Ng expression is regulated by synaptic activity and that Ng promotes the synaptogenesis process. Given its relationship with cognitive function, we propose targeting of Ng expression as a promising strategy to prevent or alleviate the cognitive deficits associated with aging and neuropathological conditions.

Retinoic acid protects from experimental cerebral infarction by upregulating GAP-43 expression

The aim of this study was to investigate whether exogenous retinoic acid (RA) can upregulate the mRNA and protein expression of growth-associated protein 43 (GAP-43), thereby promoting brain functional recovery in a rat distal middle cerebral artery occlusion (MCAO) model of ischemia. A total of 216 male Sprague Dawley rats weighing 300–320 g were divided into 3 groups: sham-operated group, MCAO+vehicle group and MCAO+RA group. Focal cortical infarction was induced with a distal MCAO model. The expression of GAP-43 mRNA and protein in the ipsilateral perifocal region was assessed using qPCR and immunocytochemistry at 1, 3, 7, 14, 21, and 28 days after distal MCAO. In addition, an intraperitoneal injection of RA was given 12 h before MCAO and continued every day until the animal was sacrificed. Following ischemia, the expression of GAP-43 first increased considerably and then decreased. Administration of RA reduced infarction volume, promoted neurological functional recovery and upregulated expression of GAP-43. Administration of RA can ameliorate neuronal damage and promote nerve regeneration by upregulating the expression of GAP-43 in the perifocal region after distal MCAO.

EPA/DHA and Vitamin A Supplementation Improves Spatial Memory and Alleviates the Age-related Decrease in Hippocampal RXRγ and Kinase Expression in Rats

Studies suggest that eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), and vitamin A are critical to delay aged-related cognitive decline. These nutrients regulate gene expression in the brain by binding to nuclear receptors such as the retinoid X receptors (RXRs) and the retinoic acid receptors (RARs). Moreover, EPA/DHA and retinoids activate notably kinase signaling pathways such as AKT or MAPK, which includes ERK1/2. This suggests that these nutrients may modulate brain function in a similar way. Therefore, we investigated in middle-aged rats the behavioral and molecular effects of supplementations with EPA/DHA and vitamin A alone or combined. 18-month-old rats exhibited reference and working memory deficits in the Morris water maze, associated with a decrease in serum vitamin A and hippocampal EPA/DHA contents. RARα, RXRβ, and RXRγ mRNA expression and CAMKII, AKT, ERK1/2 expression were decreased in the hippocampus of middle-aged rats. A combined EPA/DHA and vitamin A supplementation had a beneficial additive effect on reference memory but not in working memory in middle-aged rats, associated with an alleviation of the age-related decrease in RXRγ, CAMKII, AKT, and ERK1 expression in the hippocampus. This study provides a new combined nutritional strategy to delay brain aging.

Effects of ethanol on physiological retinoic acid levels

All-trans-retinoic acid (atRA) serves essential functions during embryogenesis and throughout postnatal vertebrate life. Insufficient or excess atRA causes teratogenic and/or toxic effects in the developing embryo: interference with atRA biosynthesis or signaling likely underlies some forms of cancer. Many symptoms of vitamin A (atRA precursor) deficiency and/or toxicity overlap with those of another pleiotropic agent--ethanol. These overlapping symptoms have prompted research to understand whether interference with atRA biosynthesis and/or action may explain (in part) pathology associated with excess ethanol consumption. Ethanol affects many aspects of retinoid metabolism and mechanisms of action site specifically, but no robust data support inhibition of vitamin A metabolism, resulting in decreased atRA in vivo during normal vitamin A nutriture. Actually, ethanol either has no effect on or increases atRA at select sites. Despite this realization, insight into whether interactions between ethanol and retinoids represent cause versus effect requires additional research.

Type 1 equilibrative nucleoside transporter regulates ethanol drinking through accumbal N-methyl-D-aspartate receptor signaling

BACKGROUND

Mice lacking type 1 equilibrative nucleoside transporter (ENT1(-/-)) exhibit increased ethanol-preferring behavior compared with wild-type littermates. This phenotype of ENT1(-/-) mice appears to be correlated with increased glutamate levels in the nucleus accumbens (NAc). However, little is known about the downstream consequences of increased glutamate signaling in the NAc.

METHODS

To investigate the significance of the deletion of ENT1 and its effect on glutamate signaling in the NAc, we employed microdialysis and iTRAQ proteomics. We validated altered proteins using Western blot analysis. We then examined the pharmacological effects of the inhibition of the N-methyl-D-aspartate (NMDA) glutamate receptor and protein kinase Cγ (PKCγ) on alcohol drinking in wild-type mice. In addition, we investigated in vivo cyclic adenosine monophosphate response element binding activity using cyclic adenosine monophosphate response element-β-galactosidase mice in an ENT1(-/-) background.

RESULTS

We identified that NMDA glutamate receptor-mediated downregulation of intracellular PKCγ-neurogranin-calcium-calmodulin dependent protein kinase type II signaling is correlated with reduced cyclic adenosine monophosphate response element binding activity in ENT1(-/-) mice. Inhibition of PKCγ promotes ethanol drinking in wild-type mice to levels similar to those of ENT1(-/-) mice. In contrast, an NMDA glutamate receptor antagonist reduces ethanol drinking of ENT1(-/-) mice.

CONCLUSIONS

These findings demonstrate that the genetic deletion or pharmacological inhibition of ENT1 regulates NMDA glutamate receptor-mediated signaling in the NAc, which provides a molecular basis that underlies the ethanol-preferring behavior of ENT1(-/-) mice.

Thyroid hormone receptor alpha plays an essential role in the normalisation of adult-onset hypothyroidism-related hypoexpression of synaptic plasticity target genes in striatum

Thyroid hormone (TH) deficiency leads to molecular changes resulting in behavioural deficits. TH action is mediated by two types of nuclear receptors (TRs), TRalpha and TRbeta, which control target gene transcription. The relative contributions of the two TR products in mediating adult TH responses are poorly understood. As TRalpha1 transcripts are widely distributed in the brain, they presumably mediate most of the TH effects. This report examines the role and specific functions of T3 receptor isoforms on regulation of striatal synaptic plasticity indicators using adult hypothyroid mutant mice that fail to express single or multiple TR gene products. We then evaluated the effect of this hypothyroidism, with or without subsequent administration of T3, on T3 nuclear receptor (TRalpha1, TRbeta) and synaptic plasticity gene expression in TRalpha(0/0), TRbeta(-/-) and wild-type 129/SV mice. Hypothyroid wild-type mice exhibited reduced TRbeta, RC3, CaMKII and Rhes expression. The mRNA levels of Rhes and CaMKII were the same in all three hypothyroid substrains. By contrast, hypothyroid TRbeta(-/-) mice had higher RC3 mRNA levels than wild-type. T3 administration restored TRbeta, RC3 and CaMKII levels in hypothyroid wild-type mice, without significant Rhes upregulation. T3 administration normalised expression of all genes studied in hypothyroid TRbeta(-/-) but not TRalpha(0/0) mice. Thus, TRalpha apparently plays an essential role in restoring the expression of the TH-regulated genes potentially involved in striatal synaptic plasticity.

T3 administration in adult hypothyroid mice modulates expression of proteins involved in striatal synaptic plasticity and improves motor behavior

Adult-onset hypothyroidism is associated with neurological changes such as cognitive dysfunction and impaired learning, which may be related to alterations of synaptic plasticity. We investigate the consequence of adult-onset hypothyroidism on thyroid-mediated transcription events in striatal synaptic plasticity, and the effect of triiodothyronine (T3) replacement. We used hypothyroid mice, treated with propylthiouracil (PTU) and methimazole (MMI), with or without subsequent administration of T3. We evaluated the amount of T3 nuclear receptors (TRalpha1, TRbeta) and striatal plasticity indicators: neurogranin (RC3), Ras homolog enriched in striatum (Rhes), Ca2+/calmodulin-dependent protein kinase (CaMKII), and dopamine- and cAMP-regulated phosphoprotein (DARPP-32). In addition, we assessed hypothyroid mice motor behavior as related to striatum synaptic functions. Hypothyroid mice exhibited significantly reduced TRbeta, RC3 and Rhes expression. T3 administration reversed the expression of TRbeta, RC3, and up-regulated CaMKII levels as well as motor behavior, and decreased DARPP-32 protein phosphorylation. We suggest that thyroid hormone modulation had a major impact on striatal synaptic plasticity of adult mice which produced in turn motor behavior modifications.

Retinoid hyposignaling contributes to aging-related decline in hippocampal function in short-term/working memory organization and long-term declarative memory encoding in mice

An increasing body of evidence indicates that the vitamin A metabolite retinoic acid (RA) plays a role in adult brain plasticity by activating gene transcription through nuclear receptors. Our previous studies in mice have shown that a moderate downregulation of retinoid-mediated transcription contributed to aging-related deficits in hippocampal long-term potentiation and long-term declarative memory (LTDM). Here, knock-out, pharmacological, and nutritional approaches were used in a series of radial-arm maze experiments with mice to further assess the hypothesis that retinoid-mediated nuclear events are causally involved in preferential degradation of hippocampal function in aging. Molecular and behavioral findings confirmed our hypothesis. First, a lifelong vitamin A supplementation, like short-term RA administration, was shown to counteract the aging-related hippocampal (but not striatal) hypoexpression of a plasticity-related retinoid target-gene, GAP43 (reverse transcription-PCR analyses, experiment 1), as well as short-term/working memory (STWM) deterioration seen particularly in organization demanding trials (STWM task, experiment 2). Second, using a two-stage paradigm of LTDM, we demonstrated that the vitamin A supplementation normalized memory encoding-induced recruitment of (hippocampo-prefrontal) declarative memory circuits, without affecting (striatal) procedural memory system activity in aged mice (Fos neuroimaging, experiment 3A) and alleviated their LTDM impairment (experiment 3B). Finally, we showed that (knock-out, experiment 4) RA receptor beta and retinoid X receptor gamma, known to be involved in STWM (Wietrzych et al., 2005), are also required for LTDM. Hence, aging-related retinoid signaling hypoexpression disrupts hippocampal cellular properties critically required for STWM organization and LTDM formation, and nutritional vitamin A supplementation represents a preventive strategy. These findings are discussed within current neurobiological perspectives questioning the historical consensus on STWM and LTDM system partition.

Beneficial effects of nicotinamide on alcohol-induced liver injury in senescence-accelerated mice

The deleterious effects of ethanol in senescence-accelerated prone 8 mice (SAMP8) and the protective role of nicotinamide (NAM) against ethanol-induced liver injury were examined. The mice were orally administered 2 g ethanol/kg BW and 200 mg or 500 mg NAM/kg BW three times/week for 10 weeks. Results showed that ethanol elevated activity of alanine aminotransferase (ALT) significantly. Ethanol also enhanced the formation of malondialdehyde (MDA) and protein carbonyls in the liver, whereas ethanol treatment resulted in significantly lower activity of hepatic glutathione peroxidase (GPx), catalase and superoxide dismutase (SOD). Hematoxylin and eosin staining indicated moderate to severe fatty infiltration but not fibrosis. Administration of high NAM (500 mg/kg BW) led to markedly decreased levels of hepatic MDA, protein carbonyls, fatty infiltration and the activity of ALT, and increased activity of GPx, catalase and SOD in the ethanol-fed group. Thus, using SAMP8 as animal model for ethanol-induced liver injury in the aged mice, this study demonstrates that NAM is effective in protecting such damage.