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.

SUMMARY Adipose tissue (AT) of obese mice and humans accumulates immune cells, which secrete cytokines that can promote insulin resistance. AT macrophages (ATMs) are thought to originate from bone marrow-derived monocytes, which infiltrate the tissue from the circulation. Here we show that a major fraction of macrophages unexpectedly undergo cell division locally within AT, as detected by Ki67 expression and 5-ethynyl-2′-deoxyuridine incorporation. Macrophages within the visceral AT (VAT), but not those in other tissues, including liver and spleen, displayed increased proliferation in obesity. Importantly, depletion of blood monocytes had no impact on ATM content, while their proliferation in situ continued. Treatment with monocyte chemotactic protein 1 (MCP-1) induced macrophage cell division in AT explants, while MCP-1 deficiency in vivo decreased ATM proliferation. These results reveal that proliferation in situ driven by MCP-1 is an important process by which macrophages accumulate in the VAT in obesity, in addition to blood monocyte recruitment.

that is activated and on the cellular model analysed. In addition, the duration of the stimulus can also affect the cellular response. A wide panel of different stimuli are capable to activate the MAPK pathways, but a good correlation has been found between the types of stimulus and the function assigned to the pathway. Schematically, ERK is preferentially activated by mitogens such as the serum or growth factors and, accordingly, this pathway is an important regulator of cell cycle and cell proliferation. p38 and JNK are more responsive to various stress stimuli from UV to cytokines and they have been involved in apoptosis and/or in the response to cellular stresses. Because they have been extensively studied (see for reviews [2] [3]), these general aspects will not be detailed in this review, except for their specific relevance towards adipogenesis.Regarding the process of differentiation, the role of MAPKs is extremely complex and depends on multiple parameters. The complexity is due, firstly, to the biological process itself, which, most of the time, involves different successive steps. Furthermore, each of these steps can be modulated by MAPKs leading, sometimes, to opposite effects. Probably because this complexity renders experimental models extremely sensitive, most of the tools used for Because of its essential role in cell proliferation and the fact that adipogenic stimuli, such as insulin, activate the ERK pathway, the role of this pathway in normal and pathological adipogenesis has been intensively investigated the last decade. Indeed, obesity is due to the hypertrophy of adipocytes and to the recruitment of new adipocytes from precursor cells, two processes largely dependent on regulation of adipocyte differentiation. In addition, obesity is associated with insulin resistance both in experimental models and in humans, and the role of adipose tissue and, consequently, of adipocyte differentiation is important in this pathology. Although the implication of MAPKs in insulin resistance is largely documented, our review does not discuss this aspect in details because Gual et al. review it in this series.Although much of the knowledge originates from analysis of preadipocyte cell lines, such as 3T3-L1 or 3T3-F442A, various cellular models are now available; they are summarized in figure 2.

Type 2 diabetes mellitus (T2DM) progresses from compensated insulin resistance to beta ceil failure resulting in uncompensated hyperglycemia, a process replicated in the Zucker diabetic fatty (ZDF) rat. The Nlrp3 inflammasome has been implicated in obesity-induced insulin resistance and beta cell failure. Endocannabinoids contribute to insuiin resistance through activation of peripheral CB1 receptors (CB1Rs) and also promote beta cell failure. Here we show that beta cell failure in adult ZDF rats is not associated with CB1R signaling in beta ceils, but rather in M1 macrophages infiltrating into pancreatic islets, and that this leads to activation of the Nlrp3-ASC inflammasome in the macrophages. These effects are replicated in vitro by incubating wild-type human or rodent macrophages, but not macrophages from CB1R-deficient [Cnr1−/−) or Nlrp3−/− mice, with the endocannabinoid anandamide. Peripheral CB1R blockade, in vivo depletion of macrophages or macrophage-specific knockdown of CB1R reverses or prevents these changes and restores normoglycemia and glucose-induced insulin secretion. These findings implicate endocannabinoids and inflammasome activation in beta cell failure and identify macrophage-expressed CB1R as a therapeutic target in T2DM.