m(en)TOR(ing) differentiating T helper cells

The Gut-Immune-Brain Axis in Autism Spectrum Disorders; A Focus on Amino Acids

Autism spectrum disorder (ASD) is a range of neurodevelopmental conditions that affect communication and social behavior. Besides social deficits, systemic inflammation, gastrointestinal immune-related problems, and changes in the gut microbiota composition are characteristic for people with ASD. Animal models showed that these characteristics can induce ASD-associated behavior, suggesting an intimate relationship between the microbiota, gut, immune system and the brain in ASD. Multiple factors can contribute to the development of ASD, but mutations leading to enhanced activation of the mammalian target of rapamycin (mTOR) are reported frequently. Hyperactivation of mTOR leads to deficits in the communication between neurons in the brain and to immune impairments. Hence, mTOR might be a critical factor linking the gut-brain-immune axis in ASD. Pharmacological inhibition of mTOR is shown to improve ASD-associated behavior and immune functions, however, the clinical use is limited due to severe side reactions. Interestingly, studies have shown that mTOR activation can also be modified by nutritional stimuli, in particular by amino acids. Moreover, specific amino acids are demonstrated to inhibit inflammation, improve gut barrier function and to modify the microbiota composition. In this review we will discuss the gut-brain-immune axis in ASD and explore the potential of amino acids as a treatment option for ASD, either via modification of mTOR activity, the immune system or the gut microbiota composition.

Interleukin-6 upregulates Th17 response via mTOR/STAT3 pathway in acute-on-chronic hepatitis B liver failure

BACKGROUND

Interleukin (IL)-17-producing CD4(+) T cells (Th17) have been shown to play crucial roles in the pathogenesis of hepatitis B virus (HBV)-associated acute-on-chronic liver failure (ACLF). However, the mechanism underlying the enhanced Th17 responses in these patients remains elusive. In this study, the relevance of the IL-6/signal transducer and activator of transcription 3 (STAT3)/mammalian target of rapamycin (mTOR)/Th17 loop in HBV-associated ACLF was investigated.

METHODS

Eight patients with HBV-associated ACLF, eight asymptomatic chronic HBV carriers and eight healthy controls were enrolled in our study. The frequency of peripheral Th17 cells was determined by flow cytometry. IL-17 and IL-6 mRNA levels in peripheral blood mononuclear cells were quantified using quantitative real-time reverse polymerase chain reaction. The activation of STAT3 was seen upon stimulation with IL-6. Rapamycin, an mTOR inhibitor, was used for analysis of the suppressive effect on the Th17 response in vitro.

RESULTS

The percentage of peripheral Th17 cells significantly increased in ACLF patients. CD4(+) T cells from ACLF patients produced higher levels of IL-17 and IL-6 upon stimulation in vitro. Activation of STAT3 in response to IL-6 was elevated in ACLF patients. The IL-6-induced upregulation of IL-17 production by CD4(+) T cells could be reversed by an mTOR inhibitor through decreasing STAT3 activation.

CONCLUSIONS

STAT3 activation upon IL-6 stimulation contributed to the enhanced Th17 response in HBV-associated ACLF patients and mTOR regulated STAT3 phosphorylation. mTOR can be a novel target to suppress Th17-mediated liver injury in HBV-associated ACLF patients.

Type I and III interferon production in response to RNA viruses

The biology of RNA viruses is closely linked to the type I and type III interferon (IFN) response of the host. These viruses display a range of molecular patterns that may be detected by host cells resulting in the induction of IFNs. Consequently, there are many examples of mechanisms employed by RNA viruses to block or delay IFN induction and reduce the expression of IFN-stimulated genes (ISGs), a necessary step in the virus lifecycle because of the capacity of IFNs to block virus replication. Efficient transmission of viruses depends, in part, on maintaining a balance between virus replication and host survival; specialized host cells, such as plasmacytoid dendritic cells, can sense viral molecular patterns and produce IFNs to help maintain this balance. There are now many examples of RNA viruses inducing type I and type III IFNs, and although these IFNs act through different receptors, in many systems studied, they induce a similar spectrum of genes. However, there may be a difference in the temporal expression pattern, with more prolonged expression of ISGs in response to type III IFN compared with type I IFN. There are also examples of synergy between type I and type III IFNs to induce antiviral responses. Clearly, it is important to understand the different roles of these IFNs in the antiviral response in vivo. One of the most striking differences between these 2 IFN systems is the distribution of the receptors: type I IFN receptors are expressed on most cells, yet type III receptor expression is restricted primarily to epithelial cells but has also been demonstrated on other cells, including dendritic cells. There is increasing evidence that type III IFNs are a key control mechanism against RNA viruses that infect respiratory and enteric epithelia.

Paradoxical effects of rapamycin on experimental house dust mite-induced asthma

The mammalian target of rapamycin (mTOR) modulates immune responses and cellular proliferation. The objective of this study was to assess whether inhibition of mTOR with rapamycin modifies disease severity in two experimental murine models of house dust mite (HDM)-induced asthma. In an induction model, rapamycin was administered to BALB/c mice coincident with nasal HDM challenges for 3 weeks. In a treatment model, nasal HDM challenges were performed for 6 weeks and rapamycin treatment was administered during weeks 4 through 6. In the induction model, rapamycin significantly attenuated airway inflammation, airway hyperreactivity (AHR) and goblet cell hyperplasia. In contrast, treatment of established HDM-induced asthma with rapamycin exacerbated AHR and airway inflammation, whereas goblet cell hyperplasia was not modified. Phosphorylation of the S6 ribosomal protein, which is downstream of mTORC1, was increased after 3 weeks, but not 6 weeks of HDM-challenge. Rapamycin reduced S6 phosphorylation in HDM-challenged mice in both the induction and treatment models. Thus, the paradoxical effects of rapamycin on asthma severity paralleled the activation of mTOR signaling. Lastly, mediastinal lymph node re-stimulation experiments showed that treatment of rapamycin-naive T cells with ex vivo rapamycin decreased antigen-specific Th2 cytokine production, whereas prior exposure to in vivo rapamycin rendered T cells refractory to the suppressive effects of ex vivo rapamycin. We conclude that rapamycin had paradoxical effects on the pathogenesis of experimental HDM-induced asthma. Thus, consistent with the context-dependent effects of rapamycin on inflammation, the timing of mTOR inhibition may be an important determinant of efficacy and toxicity in HDM-induced asthma.