The GABAB positive allosteric modulators CGP7930 and GS39783 stimulate ERK1/2 signalling in cells lacking functional GABAB receptors

Analysis of the functional role and mRNA expression of GABA B R in the nucleus accumbens of cocaine-addicted rats

BACKGROUND

Drug addiction is a social and medical problem that must be urgently addressed. The nucleus accumbens (NAc) is closely related to addiction-related learning memory, and γ-aminobutyric acid type B receptor (GABA B R) is a potential target for the treatment of drug addiction. However, the role of GABA B R activity levels in the NAc in cocaine addiction is unclear.

METHODS

In this study, we established an animal model of cocaine dependence, modulated the level of GABA B R activity, applied a conditioned place preference assay (CPP) to assess the role of the NAc in reconsolidation of addiction memory, evaluated learning and memory functions by behavioral experiments, examined the expression of GB1, GB2, cyclic adenosine monophosphate response element binding protein (CREB), p-CREB, protein kinase A (PKA), protein kinase (ERK), and Brain-derived neurotrophic factor (BDNF) in the NAc by molecular biology experiments, and screened differentially significantly expressed genes by transcriptome sequencing.

RESULTS

Our study showed that the GABA B receptor agonist baclofen (BLF) had a significant effect on locomotor distance in rats, promoted an increase in GABA levels and significantly inhibited the PKA and ERK1/2/CREB/BDNF signaling pathways. Moreover, transcriptome sequencing showed that GABA B R antagonist intervention identified a total of 21 upregulated mRNAs and 21 downregulated mRNAs. The differentially expressed (DE) mRNA genes were mainly enriched in tyrosine metabolism; however, further study is needed.

CONCLUSION

GABA B R activity in the NAc is involved in the regulation of cocaine addiction and may play an important role through key mRNA pathways.

CGP7930 - An allosteric modulator of GABABRs, GABAARs and inwardly-rectifying potassium channels

Type-A and -B GABA receptors (GABAARs/GABABRs) control brain function and behaviour by fine tuning neurotransmission. Over-time these receptors have become important therapeutic targets for treating neurodevelopmental and neuropsychiatric disorders. Several positive allosteric modulators (PAMs) of GABARs have reached the clinic and selective targeting of receptor subtypes is crucial. For GABABRs, CGP7930 is a widely used PAM for in vivo studies, but its full pharmacological profile has not yet been established. Here, we reveal that CGP7930 has multiple effects not only on GABABRs but also GABAARs, which for the latter involves potentiation of GABA currents, direct receptor activation, and also inhibition. Furthermore, at higher concentrations, CGP7930 also blocks G protein-coupled inwardly-rectifying K+ (GIRK) channels diminishing GABABR signalling in HEK 293 cells. In male and female rat hippocampal neuron cultures, CGP7930 allosteric effects on GABAARs caused prolonged rise and decay times and reduced the frequency of inhibitory postsynaptic currents and potentiated GABAAR-mediated tonic inhibition. Additional comparison between predominant synaptic- and extrasynaptic-isoforms of GABAAR indicated no evident subtype selectivity for CGP7930. In conclusion, our study of CGP7930 modulation of GABAARs, GABABRs and GIRK channels, indicates this compound is unsuitable for use as a specific GABABR PAM.

Development of tolerance upon repeated administration with the GABAB receptor positive allosteric modulator, COR659, on alcohol drinking in rodents

Background: Recent work has demonstrated that acute administration of the novel positive allosteric modulator of the GABAB receptor, COR659, reduces several alcohol-related behaviors in rodents.Objective: To assess whether COR659 continues to lessen alcohol intake after repeated administration, a fundamental feature of drugs with therapeutic potential.Methods: Male C57BL/6J mice (n = 40) were exposed to daily 2-hour drinking sessions (20% (v/v) alcohol) under the 1-bottle "drinking in the dark" protocol and male Sardinian alcohol-preferring rats (n = 40) were exposed to daily 1-hour drinking sessions under the 2-bottle "alcohol (10%, v/v) vs water" choice regimen. COR659 (0, 10, 20, and 40 mg/kg in the mouse experiment; 0, 5, 10, and 20 mg/kg in the rat experiment) was administered intraperitoneally before 7 consecutive drinking sessions.Results: Alcohol intake in vehicle-treated mice and rats averaged 2.5-3.0 and 1.5-1.6 g/kg/session, respectively, indicative of high basal levels. In both experiments, treatment with COR659 resulted in an initial, dose-related suppression of alcohol intake (up to 70-80% compared to vehicle treatment; P < .0005 and P < .0001 in mouse and rat experiments, respectively). The magnitude of the reducing effect of COR659 on alcohol drinking diminished progressively, until vanishing over the subsequent 2-4 drinking sessions.Conclusion: COR659 effectively reduced alcohol intake in two different rodent models of excessive alcohol drinking. However, tolerance to the anti-alcohol effects of COR659 developed rapidly. If theoretically transposed to humans, these data would represent a possible limitation to the clinical use of COR659.

Sirt7 associates with ELK1 to participate in hyperglycemia memory and diabetic nephropathy via modulation of DAPK3 expression and endothelial inflammation

Diabetic nephropathy (DN) is one of the most serious complications of advanced diabetes, and increases patient mortality. Recently, epigenetics-mediated hyperglycemic memory in pathological process of DN has received attention. The purpose of this study was to determine the underlying mechanism by which sirt7 modulates hyperglycemic memory in DN. In glomerular endothelial cells (GECs) cultured in high glucose and glomeruli of DN patients and rats, an increase in p65 phosphorylation and endothelial adhesion molecule levels persisted after glucose normalization but was reversed by glucose normalization associated with death-associated protein kinase-3 (DAPK3) knockout or DAPK3 inhibitor. High glucose-mediated decrease in sirt7, the deacetylase modulating H3K18-acetylation (H3K18ac), was sustained after normoglycemia. Sirt7 overexpression accompanied by glucose normalization suppressed DAPK3 expression and inflammation in GECs. Moreover, sh-sirt7-induced inflammation was inhibited by si-DAPK3. Furthermore, sirt7 and H3K18ac were located at the DAPK3 promoter region. ELK1 was found to combine with sirt7. si-ELK1 supplemented with normoglycemia inhibited high glucose-induced DAPK3 expression and inflammation in GECs. ELK1 overexpression-mediated inflammation was inhibited by si-DAPK3. In addition, ELK1 and sirt7 were located at the same promoter region of DAPK3. ELK1 overexpression enhanced DAPK3 promoter activity, which disappeared after specific binding site mutation. In vivo, sirt7 overexpression decreased inflammation and improved renal function during insulin treatment of DN rats, whereas insulin alone did not work. Our data demonstrated high glucose-mediated mutual inhibition between sirt7 and ELK1 induced DAPK3 transcription and inflammation despite normoglycemia in GECs, thus forming a vicious cycle and participating in the occurrence of hyperglycemic memory in DN.

The SETD8/ELK1/bach1 complex regulates hyperglycaemia-mediated EndMT in diabetic nephropathy

Background

Diabetic nephropathy (DN), the most common microvascular complication in patients with diabetes, induces kidney failure. Previous research showed that endothelial-to-mesenchymal transition (EndMT) of human glomerular endothelial cells (HGECs) is involved in the progression of DN. Moreover, SET domain-containing protein 8 (SETD8), ETS-domain containing protein (ELK1) and BTB and CNC homology 1 (bach1) all participate in endothelial injury. In this study, we hypothesize that the SETD8/ELK1/bach1 functional axis is involved in mediating EndMT in diabetic nephropathy.

Methods

Immunohistochemistry, Western blotting and qPCR were performed to determine the protein and mRNA levels of genes in HGECs and the kidney tissues of participants and rats. Immunofluorescence, Co-IP and GST pulldown assays were performed to verify the direct interaction between SETD8 and ELK1. ChIP and dual-luciferase assays were performed to determine the transcriptional regulation of bach1 and Snail. AVV-SETD8 injection in rat kidney was used to verify the potential protective effect of SETD8 on DN.

Results

Our current study showed that hyperglycaemia triggered EndMT by increasing Snail expression both in vitro and in vivo. Moreover, high glucose increased bach1 expression in HGECs, positively regulating Snail and EndMT. As a transcription factor, ELK1 was augmented and participated in hyperglycaemia-induced EndMT via modulation of bach1 expression. Moreover, ELK1 was found to associate with SETD8. Furthermore, SETD8 negatively regulated EndMT by cooperating with bach1 to regulate Snail transcription. Furthermore, histone H4-Lys-20 monomethylation (H4K20me1), which is downstream of SETD8, was accompanied by ELK1 localization at the same promoter region of bach1. ELK1 overexpression enhanced bach1 promoter activity, which disappeared after specific binding site deletion. Mutual inhibition between ELK1 and SETD8 was found in HGECs. In vivo, SETD8 overexpression decreased ELK1 and bach1 expression, as well as EndMT. Moreover, SETD8 overexpression improved the renal function of rats with DN.

Conclusions

SETD8 cooperates with ELK1 to regulate bach1 transcription, thus participating in the progression of DN. In addition, SETD8 interacts with bach1 to modulate Snail transcription, thus inducing EndMT in DN. SETD8 plays a core role in the SETD8/ELK1/bach1 functional axis, which participates in hyperglycaemia-mediated EndMT in DN, and SETD8 may be a potential therapeutic target for DN.

Trial registration ChiCTR, ChiCTR2000029425. 2020/1/31, http://www.chictr.org.cn/showproj.aspx?proj=48548

Supplementary Information

The online version contains supplementary material available at 10.1186/s12967-022-03352-4.

Central and peripheral emetic loci contribute to vomiting evoked by the Akt inhibitor MK-2206 in the least shrew model of emesis

Akt (protein kinase B) signaling is frequently activated in diverse cancers. Akt inhibitors such as perifosine and MK-2206 have been evaluated as potential cancer chemotherapeutics. Although both drugs are generally well tolerated, among their most common side-effects vomiting is a major concern. Here we investigated whether these Akt inhibitors evoke emesis in the least shrew model of vomiting. Indeed, both perifosine and MK-2206 induced vomiting with maximal efficacies of 90% at 50 mg/kg (i.p.) and 100% at 10 mg/kg (i.p.), respectively. MK-2206 (10 mg/kg, i.p.) increased c-Fos immunoreactivity both centrally in the shrew brainstem dorsal vagal complex (DVC) emetic nuclei, and peripherally in the jejunum. MK-2206 also evoked phosphorylation of extracellular signal-regulated kinase 1/2 (ERK1/2) in both the DVC emetic nuclei and the enteric nervous system in the jejunum. The ERK1/2 inhibitor U0126 suppressed MK-2206-induced emesis dose-dependently. We then evaluated the suppressive efficacy of diverse antiemetics against MK-2206-evoked vomiting including antagonists/inhibitors of the: L-type Ca2+ channel (nifedipine at 2.5 mg/kg, subcutaneously (s.c.)); glycogen synthase kinase 3 (GSK-3) (AR-A014418 at 10 mg/kg and SB216763 at 0.25 mg/kg, i.p.); 5-hydroxytryptamine 5-HT3 receptor (palonosetron at 0.5 mg/kg, s.c.); substance P neurokinin NK1 receptor (netupitant at 10 mg/kg, i.p.) and dopamine D2/3 receptor (sulpride at 8 mg/kg, s.c.). All tested antagonists/blockers attenuated emetic parameters to varying degrees. In sum, this is the first study to demonstrate how pharmacological inhibition of Akt evokes vomiting via both central and peripheral mechanisms, a process which involves multiple emetic receptors.

ETS-domain containing protein (Elk1) suppression protects cortical neurons against oxygen-glucose deprivation injury

ETS-domain containing protein (Elk1), which is a transcription factor, is reported to be closely related to the apoptosis of primary neurons and could be activated by hypoxia in human microvascular endothelial cells. In this study, we aimed to investigate the role of Elk1 in cortical neurons under oxygen-glucose deprivation (OGD) conditions. The OGD model of cortical neurons was established the anoxia/hypoglycemia-induced injury and the in vivo model was established by middle cerebral artery occlusion (MCAO). Elk1 mRNA and protein expression was significantly up-regulated in neurons exposed to OGD for 24 h, and mRNA expression was also markedly increased in cerebral cortex of rats with MCAO after 10 days. The knockdown of Elk1 in neurons without OGD obviously constrained Fra-1 and promoted Nrf2 expression. Also, Elk1 inhibition suppressed neuronal apoptosis, caspase-3 activity, LDH leakage, and MDA and SOD contents, while it increased cell viability in the neurons with OGD. The overexpression of Fra-1 showed a reverse effect on caspase-3 activity, cell viability and SOD contents in neurons under OGD conditions compared with Elk1 knockdown. Thus, Elk1 inhibition has a protective effect on neurons against OGD-induced injury.

Glutamate as a potential "survival factor" in an in vitro model of neuronal hypoxia/reoxygenation injury: leading role of the Na+/Ca2+ exchanger

In brain ischemia, reduction in oxygen and substrates affects mitochondrial respiratory chain and aerobic metabolism, culminating in ATP production impairment, ionic imbalance, and cell death. The restoration of blood flow and reoxygenation are frequently associated with exacerbation of tissue injury, giving rise to ischemia/reperfusion (I/R) injury. In this setting, the imbalance of brain bioenergetics induces important metabolic adaptations, including utilization of alternative energy sources, such as glutamate. Although glutamate has long been considered as a neurotoxin, it can also be used as intermediary metabolite for ATP synthesis, and both the Na⁺/Ca²⁺ exchanger (NCX) and the Na⁺-dependent excitatory amino-acid transporters (EAATs) are essential in this pathway. Here we analyzed the role of NCX in the potential of glutamate to improve metabolism and survival of neuronal cells subjected to hypoxia/reoxygenation (H/R). In SH-SY5Y neuroblastoma cells differentiated into a neuron-like state, H/R produced a significant cell damage, a decrease in ATP cellular content, and intracellular Ca²⁺ alterations. Exposure to glutamate at the onset of the reoxygenation phase attenuated H/R-induced cell damage and evoked a significant raise in intracellular ATP levels. Furthermore, we found that in H/R cells NCX reverse-mode activity was reduced, and that glutamate limited such reduction. All the effects induced by glutamate supplementation were lost when cells were transfected with small interfering RNA against NCX1 and EAAT3, suggesting the need of a specific functional interplay between these proteins for glutamate-induced protection. Collectively, our results revealed the potential beneficial effect of glutamate in an in vitro model of H/R injury and focused on the essential role exerted by NCX1. Although preliminary, these findings could be a starting point to further investigate in in vivo systems such protective effect in ischemic settings, shedding a new light on the classical view of glutamate as detrimental factor.