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Low-dose repeated lipopolysaccharide pre-challenge followed by chronic mild stress (LPS/CMS) protocol has been introduced as a rodent model of depression combining the roles of immune activation and chronic psychological stress. However, the impact of this paradigm on cognitive functioning has not been investigated hitherto. Methods This study evaluated LPS/CMS-induced cognitive effects and the role of glycogen synthase kinase-3β (GSK-3β) activation with subsequent neuroinflammation and pathological tau deposition in the pathogenesis of these effects using lithium (Li) as a tool for GSK-3 inhibition. Results LPS pre-challenge reduced CMS-induced neuroinflammation, depressive-like behavior and cognitive inflexibility. It also improved spatial learning but increased GSK-3β expression and exaggerated hyperphosphorylated tau accumulation in hippocampus and prefrontal cortex. Li ameliorated CMS and LPS/CMS-induced depressive and cognitive deficits, reduced GSK-3β over-expression and tau hyperphosphorylation, impeded neuroinflammation and enhanced neuronal survival. Conclusion This study draws attention to LPS/CMS-triggered cognitive changes and highlights how prior low-dose immune challenge could develop an adaptive capacity to buffer inflammatory damage and maintain the cognitive abilities necessary to withstand threats. This work also underscores the favorable effect of Li (as a GSK-3β inhibitor) in impeding exaggerated tauopathy and neuroinflammation, rescuing neuronal survival and preserving cognitive functions. Yet, further in-depth studies utilizing different low-dose LPS challenge schedules are needed to elucidate the complex interactions between immune activation and chronic stress exposure.

Accumulating evidence indicates the role of microglial activation and sustained neuroinflammation in the pathogenesis of cognitive dysfunction, a common feature associated with depressive disorders. It also indicates the role of Wnt/β-catenin pathway in regulation of microglia-mediated neuroinflammation. Amisulpride exhibits antidepressant and pro-cognitive activities in several clinical and experimental studies. Hitherto, the direct effects of amisulpride on Wnt/β-catenin signaling and microglial activity have not been thoroughly studied. This study aimed at investigating the effects of chronic amisulpride treatment on Wnt/β-catenin signaling and pro-inflammatory microglial activation and its role in alleviation of depressive-like behavior and cognitive deficits elicited by unpredictable chronic mild stress (UCMS). The effects of amisulpride (3 mg/kg/day) were investigated on behavioral/cognitive deficits, expression of Wnt/β-catenin pathway and microglial activation in the prefrontal cortex (PFC) of UCMS-exposed male Wistar rats. UCMS induced depressive-like behavior with impairment of performance in novel object recognition test and attentional set-shifting task. These behavioral deficits were associated with decreased total β-catenin and increased pro-inflammatory microglial activation. Amisulpride improved UCMS-induced behavioral/cognitive deficits, ameliorated Wnt/β-catenin signaling dysregulation and pro-inflammatory microglial activation. This work highlights the antidepressant and pro-cognitive effects of amisulpride in UCMS-exposed rats that could be mediated by modulation of Wnt/β-catenin pathway activity and amelioration of pro-inflammatory microglial activation in the prefrontal cortex. This could provide new insights into the putative mechanisms behind the antidepressant and pro-cognitive effects exerted by amisulpride.

Microglial in vivo production of pro-inflammatory cytokines is central to the pathogenesis of multiple neurological disorders including depression, with a rising role of Wnt/β-catenin signaling as potential regulator of microglia-mediated neuro-inflammation. This study aimed at investigating the hippocampal expression of the Wnt/ß-catenin pathway in chronic mild stress (CMS)-exposed rats and the effects of Lithium (Li) on the expression of this pathway as a method to identify a plausible link between exposure to chronic stress, microglial activation, and neuroinflammation. METHODS: The effect of chronic administration of Li was investigated on behavioral changes, hippocampal expression of Wnt-DVL-GSK3β-β-catenin signaling pathway, and microglial activation in CMS-exposed male Wistar rats RESULTS: CMS induced a depressive-like behavior associated with increased pro-inflammatory microglial activation and reduced hippocampal expression of the Wnt/β-catenin signaling pathway. Chronic Li treatment ameliorated stress induced-behavioral changes, reduced microglial activation and enhanced the hippocampal expression of Wnt/β-catenin signaling pathway. CONCLUSION: This work highlights that Li-induced inhibition of GSK-3β with subsequent accumulation of β-catenin could impede pro-inflammatory microglia activation which is a key pathological hallmark associated with depression. Wnt/β-catenin signaling represents a promising therapeutic target, not only for alleviation of depression, but also for a wide array of neurological disorders.

Neurodegeneration in Alzheimer's disease (AD) correlates with dysfunction of signaling mediated by Galphaq/11. Nondissociable angiotensin II AT2 receptor oligomers are linked to the impaired Galphaq/11-stimulated signaling of AD patients and transgenic mice with AD-like symptoms. To further analyze the role of AT2 receptor oligomers, we induced the formation of AT2 oligomers in an in vitro cell system. Similarly as in vivo, sequential oxidative and transglutaminase-dependent cross-linking steps triggered the formation of AT2 oligomers in vitro. Elevated reactive oxygen species mediated oxidative cross-linking of AT2 monomers to dimers involving tyrosine residues located at putative interreceptor contact sites of the cytoplasmic loop connecting transmembrane helices III/IV. Cross-linked AT2 dimers were subsequently a substrate of activated transglutaminase-2, which targeted the carboxyl terminus of AT2 dimers, as assessed by truncated and chimeric AT2 receptors, respectively. AT2 oligomers acted as dominant negative receptors in vitro by mediating Galphaq/11 protein sequestration and Galphaq/11 protein arrest. The formation of AT2 oligomers and G-protein dysfunction could be suppressed in vitro and in vivo by an AT2 receptor mutant. Inhibition of AT2 oligomerization upon stereotactic expression of the AT2 receptor mutant revealed that Galphaq/11-sequestering AT2 oligomers enhanced the development of neurodegenerative symptoms in the hippocampus of transgenic mice with AD-like pathology. Thus, AT2 oligomers inducing Galphaq/11 arrest are causally involved in inducing symptoms of neurodegeneration.

Reactive oxygen species (ROS) is a significant feature of atherosclerosis but the impact of ROS on atherogenesis is not clear since antioxidants such as vitamin E have little effect on atherosclerosis development in vivo. To investigate the role of ROS in atherosclerosis, we used ApoE-deficient mice, and compared the treatment effect of the antioxidant vitamin E with that of the angiotensin-converting enzyme (ACE) inhibitor, captopril, because angiotensin II is a major source of ROS in the vasculature. Dihydroethidium (DHE) staining demonstrated that vitamin E and captopril both prevented the atherosclerosis-induced increase in aortic superoxide content. In contrast, seven months of vitamin E treatment retarded the development of atherosclerotic lesions by only 45.8 ± 11.5% whereas captopril reduced the aortic plaque area by 88.1 ± 7.5%. To discriminate between vitamin E-sensitive and -insensitive effects of ACE inhibition, we performed whole genome microarray gene expression profiling. Gene ontology (GO) and immunohistology analyses showed that vitamin E and captopril prevented atherosclerosis-related changes of aortic intima and media genes. However, vitamin E did not reduce the expression of probe sets detecting the aortic recruitment of pro-inflammatory immune cells while immune cell-specific genes were normalized by captopril treatment. Moreover, vitamin E did not prevent the atherosclerosis-dependent down-regulation of perivascular nerve-specific genes, which were preserved in captopril-treated aortas. Taken together, our study detected antioxidant vitamin E-like effects of angiotensin II inhibition in atherosclerosis treatment regarding preservation of aortic intima and media genes. Additional vitamin E-insensitive effects targeting atherosclerosis-enhancing aortic immune cell recruitment and perivascular nerve degeneration could account for the stronger anti-atherogenic activity of ACE inhibition compared to vitamin E. ISSN:1664-042X

Progressive neurodegeneration and decline of cognitive functions are major hallmarks of Alzheimer disease (AD). Neurodegeneration in AD correlates with dysfunction of diverse signal transduction mechanisms, such as the G-protein-stimulated phosphoinositide hydrolysis mediated by Galphaq/11. We report here that impaired Galphaq/11-stimulated signaling in brains of AD patients and mice correlated with the appearance of cross-linked oligomeric angiotensin II AT2 receptors sequestering Galphaq/11. Amyloid beta (Abeta) was causal to AT2 oligomerization, because cerebral microinjection of Abeta triggered AT2 oligomerization in the hippocampus of mice in a dose-dependent manner. Abeta induced AT2 oligomerization by a two-step process of oxidative and transglutaminase-dependent cross-linking. The induction of AT2 oligomers in a transgenic mouse model with AD-like symptoms was associated with Galphaq/11 dysfunction and enhanced neurodegeneration. Vice versa, stereotactic inhibition of AT2 oligomers by RNA interference prevented the impairment of Galphaq/11 and delayed Tau phosphorylation. Thus, Abeta induces the formation of cross-linked AT2 oligomers that contribute to the dysfunction of Galphaq/11 in an animal model of Alzheimer disease.