Gene silencing by double-stranded RNA, denoted RNA interference, represents a new paradigm for rational drug design1. However, the transformative therapeutic potential of short interfering RNA (siRNA) has been stymied by a key obstacle—safe delivery to specified target cells in vivo2. Macrophages are particularly attractive targets for RNA interference therapy because they promote pathogenic inflammatory responses in diseases such as rheumatoid arthritis, atherosclerosis, inflammatory bowel disease and diabetes3. Here we report the engineering of β1,3-d-glucan-encapsulated siRNA particles (GeRPs) as efficient oral delivery vehicles that potently silence genes in mouse macrophages in vitro and in vivo. Oral gavage of mice with GeRPs containing as little as 20 µg kg−1 siRNA directed against tumour necrosis factor α (Tnf-α)depleted its messenger RNA in macrophages recovered from the peritoneum, spleen, liver and lung, and lowered serum Tnf-α levels. Screening with GeRPs for inflammation genes revealed that the mitogen-activated protein kinase kinase kinase kinase 4 (Map4k4) is a previously unknown mediator of cytokine expression. Importantly, silencing Map4k4 in macrophages in vivo protected mice from lipopolysaccharide-induced lethality by inhibiting Tnf-α and interleukin-1β production. This technology defines a new strategy for oral delivery of siRNA to attenuate inflammatory responses in human disease.

Excessive consumption of sweets is a risk factor for metabolic syndrome. A major chemical feature of sweets is fructose. Despite strong ties between fructose and disease, the metabolic fate of fructose in mammals remains incompletely understood. Here we use isotope tracing and mass spectrometry to track the fate of glucose and fructose carbons in vivo, finding that dietary fructose is cleared by the small intestine. Clearance requires the fructose-phosphorylating enzyme ketohexokinase. Low doses of fructose are ∼90% cleared by the intestine, with only trace fructose but extensive fructose-derived glucose, lactate, and glycerate found in the portal blood. High doses of fructose (≥1 g/kg) overwhelm intestinal fructose absorption and clearance, resulting in fructose reaching both the liver and colonic microbiota. Intestinal fructose clearance is augmented both by prior exposure to fructose and by feeding. We propose that the small intestine shields the liver from otherwise toxic fructose exposure.

Summary The C. elegans insulin/IGF-1 signaling (IIS) cascade plays a central role in the regulation of lifespan, dauer diapause, metabolism and stress response. The major regulatory control of IIS is through phosphorylation of its components by serine/threonine-specific protein kinases. In a RNAi screen for serine/threonine protein phosphatases that counter-balance the effect of the kinases in the IIS pathway, we identified pptr-1, a B56 regulatory subunit of the PP2A holoenzyme. Modulation of pptr-1 affects phenotypes associated with the IIS pathway including lifespan, dauer, stress resistance and fat storage. We show that PPTR-1 functions by regulating worm AKT-1 phosphorylation at Thr 350. With striking conservation, mammalian B56β regulates Akt phosphorylation at Thr 308 in 3T3-L1 adipocytes. In C. elegans, this modulation ultimately leads to changes in subcellular localization and transcriptional activity of the forkhead transcription factor DAF-16. This study reveals a conserved role for the B56 regulatory subunit in modulating insulin signaling through AKT dephosphorylation and thereby has widespread implications in cancer and diabetes research.

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Phagocytic macrophages and dendritic cells are desirable targets for potential RNAi (RNA interference) therapeutics because they often mediate pathogenic inflammation and autoimmune responses. We recently engineered a complex 5 component glucan-based encapsulation system for siRNA (small interfering RNA) delivery to phagocytes. In experiments designed to simplify this original formulation, we discovered that the amphipathic peptide Endo-Porter forms stable nanocomplexes with siRNA that can mediate potent gene silencing in multiple cell types. In order to restrict such gene silencing to phagocytes, a method was developed to entrap siRNA-Endo-Porter complexes in glucan shells of 2-4 μm diameter in the absence of other components. The resulting glucan particles containing fluorescently labelled siRNA were readily internalized by macrophages, but not other cell types, and released the labelled siRNA into the macrophage cytoplasm. Intraperitoneal administration of such glucan particles containing siRNA-Endo-Porter complexes to mice caused gene silencing specifically in macrophages that internalized the particles. These results from the present study indicate that specific targeting to phagocytes is mediated by the glucan, whereas Endo-Porter peptide serves both to anchor siRNA within glucan particles and to catalyse escape of siRNA from phagosomes. Thus we have developed a simplified siRNA delivery system that effectively and specifically targets phagocytes in culture or in intact mice.

Tumor necrosis factor ␣ (TNF␣) is a cytokine secreted by macrophages and adipocytes that contributes to the low grade inflammation and insulin resistance observed in obesity. TNF␣ signaling decreases peroxisome proliferator-activated receptor ␥ and glucose transporter isoform 4 (GLUT4) expression in adipocytes, impairing insulin action, and this is mediated in part by the yeast Ste20 protein kinase ortholog Map4k4. Here we show that Map4k4 expression is selectively up-regulated by TNF␣, whereas the expression of the protein kinases JNK1/2, ERK1/2, p38 stress-activated protein kinase, and mitogen-activated protein kinase kinases 4/7 shows little or no response. Furthermore, the cytokines interleukin 1␤ (IL-1␤) and IL-6 as well as lipopolysaccharide fail to increase Map4k4 mRNA levels in cultured adipocytes under conditions where TNF␣ elicits a 3-fold effect. Using agonistic and antagonistic antibodies and small interfering RNA (siRNA) against TNF␣ receptor 1 (TNFR1) and TNF␣ receptor 2 (TNFR2), we show that TNFR1, but not TNFR2, mediates the increase in Map4k4 expression. TNFR1, but not TNFR2, also mediates a potent effect of TNF␣ on the phosphorylation of JNK1/2 and p38 stress-activated protein kinase and their downstream transcription factor substrates c-Jun and activating transcription factor 2 (ATF2). siRNA-based depletion of c-Jun and ATF2 attenuated TNF␣ action on Map4k4 mRNA expression. Consistent with this concept, the phosphorylation of ATF2 along with the expression and phosphorylation of c-Jun by TNF␣ signaling was more robust and prolonged compared with that of IL-1␤, which failed to modulate Map4k4. These data reveal that TNF␣ selectively stimulates the expression of a key component of its own signaling pathway, Map4k4, through a TNFR1-dependent mechanism that targets the transcription factors c-Jun and ATF2.

RNA interference (RNAi) is a robust gene silencing mechanism that degrades mRNAs complementary to the antisense strands of double-stranded, short interfering RNAs (siRNAs). As a therapeutic strategy, RNAi has an advantage over small-molecule drugs, as virtually all genes are susceptible to targeting by siRNA molecules. This advantage is, however, counterbalanced by the daunting challenge of achieving safe, effective delivery of oligonucleotides to specific tissues in vivo. Lipid-based carriers of siRNA therapeutics can now target the liver in metabolic diseases and are being assessed in clinical trials for the treatment of hypercholesterolemia. For this indication, a chemically modified oligonucleotide that targets endogenous small RNA modulators of gene expression (microRNAs) is also under investigation in clinical trials. Emerging 'self-delivery' siRNAs that are covalently linked to lipophilic moieties show promise for the future development of therapies. Besides the liver, inflammation of the adipose tissue in patients with obesity and type 2 diabetes mellitus may be an attractive target for siRNA therapeutics. Administration of siRNAs encapsulated within glucan microspheres can silence genes in inflammatory phagocytic cells, as can certain lipid-based carriers of siRNA. New technologies that combine siRNA molecules with antibodies or other targeting molecules also appear encouraging. Although still at an early stage, the emergence of RNAi-based therapeutics has the potential to markedly influence our clinical future.

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