The TSC-mTOR signaling pathway regulates the innate inflammatory response.

The innate inflammatory immune response must be tightly controlled to avoid damage to the host. Here, we showed that the tuberous sclerosis complex-mammalian target of rapamycin (TSC-mTOR) pathway regulated inflammatory responses after bacterial stimulation in monocytes, macrophages, and primary dendritic cells. Inhibition of mTOR by rapamycin promoted production of proinflammatory cytokines via the transcription factor NF-kappaB but blocked the release of interleukin-10 via the transcription factor STAT3. Conversely, deletion of TSC2, the key negative regulator of mTOR, diminished NF-kappaB but enhanced STAT3 activity and reversed this proinflammatory cytokine shift. Rapamycin-hyperactivated monocytes displayed a strong T helper 1 (Th1) cell- and Th17 cell-polarizing potency. Inhibition of mTOR in vivo regulated the inflammatory response and protected genetically susceptible mice against lethal Listeria monocytogenes infection. These data identify the TSC2-mTOR pathway as a key regulator of innate immune homeostasis with broad clinical implications for infectious and autoimmune diseases, vaccination, cancer, and transplantation.

Tyk2 and signal transducer and activator of transcription 1 contribute to intestinal I/R injury.

Previously, we have shown that the Jak-signal transducer and activator of transcription signaling constituents Tyk2 and STAT1 play a role in the development of multiple organ failure during endotoxin shock. Here, we report that Tyk2 and STAT1 contribute to death caused by intestinal I/R injury. Tyk2- and STAT1-deficient mice showed increased survival to I/R because their intestines were protected from gross histomorphological tissue destruction and neutrophil infiltration. On the molecular level, the reduced ischemia induced inflammatory response in mutant versus wild-type mice was accompanied by an impaired up-regulation of the adhesion molecules P-selectin and intercellular adhesion molecule 1 and of the matrix metalloproteinases (MMPs) MMP-2, MMP-9, and MMP-14 in the reperfused intestine. In conclusion, this study demonstrates for the first time that Tyk2 or STAT1 promote intestinal I/R-induced shock based on a deregulated local inflammatory response and a destruction of the gut intestinal barrier.

Mechanisms of vasodilatation induced by nitrite instillation in intestinal lumen: possible role of hemoglobin.

It has been shown that nitrite can be reduced to nitric oxide (NO) in intestine and a number of other tissues and released into the blood to form nitrosylhemoglobin (NO-Hb), existing in an equilibrium with S-nitrosohemoglobin. The latter has been suggested to be an NO transporter to distant organs. The aim of this study was to define the pathway of nitrite reduction to form NO in intestinal wall and to estimate whether this pathway has an effect on peripheral circulation. We have shown that in rat intestine at pH 7.0 70% of nitrite is converted to NO in mitochondria. At pH 6.0, nonenzymatic nitrite reduction becomes as efficient as the mitochondrial pathway. To prove whether the NO formed from nitrite in intestine can induce vasodilatation, sodium nitrite was instilled into intestinal lumen and the concentration of NO formed and diffused into the blood was followed by measuring of NO-Hb complex formation. We found that the concentration of NO-Hb gradually increases with the increase of nitrite concentration in intestinal lumen. However, it was not always accompanied by a decrease in systemic blood pressure. Blood pressure dropped down only after NO-Hb reached a threshold concentration of approximately 10 microM. These data show that NO-Hb cannot provide enough NO for vasodilatation if the concentration of NO bound to Hb is < 10 microM. The exact mechanism underlying vasodilatation observed when the concentration of NO-bound Hb was > 10 microM is, however, not clear yet and requires further studies.