The Importance of Endoplasmic Reticulum Stress as a Novel Antidepressant Drug Target and Its Potential Impact on CNS Disorders.

Many central nervous system (CNS) diseases, including major depressive disorder (MDD), are underpinned by the unfolded protein response (UPR) activated under endoplasmic reticulum (ER) stress. New, more efficient, therapeutic options for MDD are needed to avoid adverse effects and drug resistance. Therefore, the aim of the work was to determine whether UPR signalling pathway activation in astrocytes may serve as a novel target for antidepressant drugs. Among the tested antidepressants (escitalopram, amitriptyline, S-ketamine and R-ketamine), only S-ketamine, and to a lesser extent R-ketamine, induced the expression of most ER stress-responsive genes in astrocytes. Furthermore, cell viability and apoptosis measuring assays showed that (R-)S-ketamine did not affect cell survival under ER stress. Under normal conditions, S-ketamine played the key role in increasing the release of brain-derived neurotrophic factor (BDNF), indicating that the drug has a complex mechanism of action in astrocytes, which may contribute to its therapeutic effects. Our findings are the first to shed light on the relationship between old astrocyte specifically induced substance (OASIS) stabilized by ER stress and (R-)S-ketamine; however, the possible involvement of OASIS in the mechanism of therapeutic ketamine action requires further study.

Cytokines use different intracellular mechanisms to upregulate the membrane expression of CX3CR1 in human monocytes.

Membrane expression of fractalkine (CX3CL1)-receptor (CX3CR1) is relevant in monocytes (Mo) because CX3CR1-CX3CL1 interactions might participate on both, homeostatic and pathologic conditions. We have previously demonstrated that CX3CR1 levels are decreased during culture and when Mo are differentiated into dendritic cells, but enhanced when differentiated into macrophages. Regarding soluble factors, lipopolysaccharide (LPS) accelerated the loss of CX3CR1, while interleukin (IL)-10 and Interferon-gamma (IFN-γ) prevented it. However, the comprehensive knowledge about the intracellular pathways that underlay the level of CX3CR1 expression in Mo is still incomplete. In the current work, we studied the effect of anti-inflammatory cytokines (IL-4, IL-13, IL-10), alone or together with IFN- γ on CX3CR1 expression. We found that only IL-10 and IFN-γ separately were able to prevent CX3CR1 down-modulation during culture of human Mo. Besides, Mo incubated with IL-10 plus IFN-γ showed the highest CX3CR1 expression by cell, suggesting cooperation between two different mechanism used by both cytokines. By studying intracellular mechanisms triggered by IL-10 and IFN-γ, we demonstrated that they specifically induced PI3K-dependent serine-phosphorylation of signal transducer and activator of transcription (STAT)3 or STAT1, respectively. Moreover, chemical inhibitors of STAT1 or STAT3 abrogated IFN-γ or IL-10 effects on CX3CR1 expression. Strikingly, only IL-10 increased CX3CR1 mRNA level, as consequence of augmenting mRNA stability. CX3CR1 mRNA increase was PI3K-dependent, supporting the causal link between the action of IL-10 at the CX3CR1 transcript and CX3CR1 protein level on Mo. Thus, both cytokines up-regulate CX3CR1 expression on human Mo by different intracellular mechanisms.

Differential expression of the fractalkine chemokine receptor (CX3CR1) in human monocytes during differentiation.

Circulating monocytes (Mos) may continuously repopulate macrophage (MAC) or dendritic cell (DC) populations to maintain homeostasis. MACs and DCs are specialized cells that play different and complementary immunological functions. Accordingly, they present distinct migratory properties. Specifically, whereas MACs largely remain in tissues, DCs are capable of migrating from peripheral tissues to lymphoid organs. The aim of this work was to analyze the expression of the fractalkine receptor (CX3CR1) during the monocytic differentiation process. Freshly isolated Mos express high levels of both CX3CR1 mRNA and protein. During the Mo differentiation process, CX3CR1 is downregulated in both DCs and MACs. However, MACs showed significantly higher CX3CR1 expression levels than did DC. We also observed an antagonistic CX3CR1 regulation by interferon (IFN)-γ and interleukin (IL)-4 during MAC activation through the classical and alternative MAC pathways, respectively. IFN-γ inhibited the loss of CX3CR1, but IL-4 induced it. Additionally, we demonstrated an association between CX3CR1 expression and apoptosis prevention by soluble fractalkine (sCX3CL1) in Mos, DCs and MACs. This is the first report demonstrating sequential and differential CX3CR1 modulation during Mo differentiation. Most importantly, we demonstrated a functional link between CX3CR1 expression and cell survival in the presence of sCX3CL1.

Oral administration of Shiga toxin-producing Escherichia coli induces intestinal and systemic specific immune response in mice.

Hemolytic uremic syndrome (HUS) is the major complication of gastrointestinal infections with enterohemorrhagic Escherichia coli (EHEC) and is mediated by the production of Shiga toxins (Stx). Although it has been previously reported that not only HUS patients but healthy children have anti-Stx antibodies, very little is known about how these infections impact on mucosal immune system to generate a specific immune response. This work aimed to evaluate the immune responses elicited after a single oral dose of EHEC in a mouse model of HUS at weaning. We found sequential activation of T and B lymphocytes together with an increased percentage of IgA-bearing B cells in Peyer's patches and mesenteric lymph nodes. We also found fecal anti-EHEC IgA and serum anti-Stx2 IgG in EHEC-inoculated mice. Besides, these mice were partially protected against an intravenous challenge with Stx2. These data demonstrate that one episode of EHEC infection is enough to induce activation in the gut-associated lymphoid tissue, especially the B cell compartment, and lead to the production of specific IgA in mucosal tissue and the generation of systemic protection against Stx2 in a percentage of intragastrically inoculated mice. These data also support the epidemiologic observation that a second episode of HUS is very rare.