Autophagy, a conserved pathway that delivers intracellular materials into lysosomes for degradation, is involved in development, aging, and a variety of diseases. Accumulating evidence demonstrates that autophagy plays a protective role against infectious diseases by diminishing intracellular pathogens, including bacteria, viruses, and parasites. However, the mechanism by which autophagy regulates innate immunity remains largely unknown. Here, we show that autophagy is involved in host defense against a pathogenic bacterium Pseudomonas aeruginosa in the metazoan Caenorhabditis elegans. P. aeruginosa infection induces autophagy via a conserved extracellular signal-regulated kinase (ERK). Intriguingly, impairment of autophagy does not influence the intestinal accumulation of P. aeruginosa, but instead induces intestinal necrosis. Inhibition of necrosis results in the survival of autophagy-deficient worms after P. aeruginosa infection. These findings reveal a previously unidentified role for autophagy in protection against necrosis triggered by pathogenic bacteria in C. elegans and implicate that such a function of autophagy may be conserved through the inflammatory response in diverse organisms.A utophagy, a well-conserved lysosomal pathway that involves the degradation of cytoplasmic components, plays important roles in a broad diversity of the biological processes, ranging from development, senescence, and lifespan extension, to cancer (1, 2). In addition, autophagy has a prominent role in resistance to bacterial, viral, and protozoan infection in metazoan organisms (3-6). Autophagy is unique in its capacity to sequester invading bacteria, and target these pathogens for lysosomal degradation, thus providing a mechanism for the elimination of intracellular microorganisms. For example, after the pathogenic bacterium Streptococcus pyogenes (group A Streptococcus) enters human epithelial cells, the bacterium in the cytoplasm is sequestered in autophagosome-like compartments and degraded upon fusion with lysosomes. In contrast, Streptococcus exits freely into the cytoplasm of autophagy-deficient Atg5 −/− cells that lack autophagic ability (3). In phagocytic cells, such as macrophages, Mycobacterium tuberculosis resides intracellularly in the phagosome and blocks phagolysosome biogenesis (4). Induction of autophagy by physiological or pharmacological factors promotes mycobacterial colocalization with the autophagosomes and results in a decreased viability of intracellular mycobacteria (4, 7). In addition to pathogen clearance, accumulating evidence suggests that autophagy is associated with other aspects of immunity and inflammation (8-11). For instance, lack of autophagy in macrophages results in the accumulation of dysfunctional mitochondria, which, in turn, promotes secretion of proinflammatory factors IL-1β and IL-18 (8, 10), suggesting that autophagy regulates inflammation responses by suppressing the secretion of immune mediators.The genetically tractable model host Caenorhabditis elegans provides a useful tool ...

Octopamine acts as a metabolic sensor that links environmental nutrient signals to energy homeostasis in C. elegans.

contributed equally to this work.Abbreviations: 3′-UTR, 3′-untranslated region; CHOP, CCAAT/enhancer-binding protein homologous protein; ER, endoplasmic reticulum; HFD, high fat diet; miRNA, microRNA; NAFLD, non-alcoholic fatty liver disease; qRT-PCR, quantitative real-time PCR; SERCA2b, sarco(endo)plasmic reticulum Ca 2+ -ATPase 2b. AbstractBackground & Aims: Insulin resistance is strongly associated with non-alcoholic fatty liver disease, a chronic, obesity-related liver disease. Increased endoplasmic reticulum (ER) stress plays an important role in the development of insulin resistance. In this study, we investigated the roles of miRNAs in regulating ER stress in the liver of rats with obesity. Methods:We used miRNA microarray to determine the miRNA expression profiles in the liver of rats fed with a high fat diet (HFD). We used prediction algorithms and luciferase reporter assay to identify the target gene of miRNAs. To overexpress the miRNA miR-30b or inhibit miR-30b rats were injected with lentivirus particles containing PGLV3-miR-30b or PGLV3-miR-30b antimiR through tail vein. Hepatic steatosis was measured using transient elastography in human subjects. Results:Our data showed that miR-30b was markedly up-regulated in the liver of HFD-treated rats. Bioinformatic and in vitro and in vivo studies led us to identify sarco(endo)plasmic reticulum Ca 2+ -ATPase 2b (SERCA2b), as a novel target of miR-30b. Overexpression of miR-30b induced ER stress and insulin resistance in rats fed with normal diet, whereas inhibition of miR-30b by miR-30b antimiR suppressed ER stress and insulin resistance in HFD-treated rats. Finally, our data demonstrated that there was a positive correlation between serum miR-30b levels and hepatic steatosis or homoeostasis model assessment of insulin resistance (HOMA-IR) in human subjects. Conclusions:Our findings suggest that miR-30b represents not only a potential target for the treatment of insulin resistance, but also a non-invasive disease biomarker of NAFLD. K E Y W O R D S endoplasmic reticulum stress, insulin resistance, microRNA, NAFLD | 1505 DAI et Al.

The unfolded protein response (UPR), which is activated by perturbations of the endoplasmic reticulum homeostasis, has been shown to play an important role in innate immunity and inflammation. However, little is known about the molecular mechanisms underlying activation of the UPR during immune responses. Using small RNA deep sequencing and reverse genetic analysis, we show that the microRNA mir-233 is required for activation of the UPR in Caenorhabditis elegans exposed to Pseudomonas aeruginosa PA14. P. aeruginosa infection up-regulates the expression of mir-233 in a p38 MAPK-dependent manner. Quantitative proteomic analysis identifies SCA-1, a C. elegans homologue of the sarco/endoplasmic reticulum Ca2+-ATPase, as a target of mir-233. During P. aeruginosa PA14 infection, mir-233 represses the protein levels of SCA-1, which in turn leads to activation of the UPR. Whereas mir-233 mutants are more sensitive to P. aeruginosa infection, knockdown of sca-1 leads to enhanced resistance to the killing by P. aeruginosa. Our study indicates that microRNA-dependent pathways may have an impact on innate immunity by activating the UPR.

Animals often experience periods of nutrient deprivation; however, the molecular mechanisms by which animals survive starvation remain largely unknown. In the nematode Caenorhabditis elegans, the nuclear receptor DAF-12 acts as a dietary and environmental sensor to orchestrate diverse aspects of development, metabolism, and reproduction. Recently, we have reported that DAF-12 together with co-repressor DIN-1S is required for starvation tolerance by promoting fat mobilization. In this report, we found that genetic inactivation of the DAF-12 signaling promoted the production of reactive oxygen species (ROS) during starvation. ROS mediated systemic necrosis, thereby inducing organismal death. The DAF-12/DIN-1S complex up-regulated the expression of antioxidant genes during starvation. The antioxidant enzyme GST-4 in turn suppressed ROS formation, thereby conferring worm survival. Our findings highlight the importance of antioxidant response in starvation tolerance and provide a novel insight into multiple organisms survive and adapt to periods of nutrient deprivation.