Search

Author(s): Devram S. Ghorpade [1]; Lale Ozcan (corresponding author) [1]; Ze Zheng [1]; Sarah M. Nicoloro [2]; Yuefei Shen [2]; Emily Chen [3, 4]; Matthias Blher [5]; Michael P. Czech [...]

Gene silencing by double-stranded RNA, denoted RNA interference, represents a new paradigm for rational drug design (1). However, the transformative therapeutic potential of short interfering RNA (siRNA) has been stymied by a key obstacle--safe delivery to specified target cells in vivo (2). 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 diabetes (3). Here we report the engineering of β 1,3-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.sup.-1] siRNA directed against tumournecrosis 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 mitogenactivated 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., To accomplish oral delivery of siRNA to macrophages in mice, we targeted M cells in intestinal wall Peyer's patches (Supplementary Fig. 1) to transfer micrometre-sized β 1,3-D-glucan particles to the [...]

PPAR[gamma] activators such as rosiglitazone (RSG) stimulate adipocyte differentiation and increase subcutaneous adipose tissue mass. However, in addition to preadipocyte differentiation, adipose tissue expansion requires neovascularization to support increased adipocyte numbers. Paradoxically, endothelial cell growth and differentiation is potently inhibited by RSG in vitro, raising the question of how this drug can induce an increase in adipose tissue mass while inhibiting angiogenesis. We find that adipose tissue from mice treated with RSG have increased capillary density. To determine whether adipose tissue angiogenesis was stimulated by RSG, we developed a novel assay to study angiogenic sprout formation ex vivo. Angiogenic sprout formation from equally sized adipose tissue fragments, but not from aorta rings, was greatly increased by obesity and by TZD treatment in vivo. To define the mechanism involved in RSG-stimulated angiogenesis in adipose tissue, the expression of proangiogenic factors by adipocytes was examined. Expression of VEGFA and VEGFB, as well as of the angiopoietin-like factor-4 (ANGPTL4), was stimulated by in vivo treatment with RSG. To define the potential role of these factors, we analyzed their effects on endothelial cell growth and differentiation in vitro. We found that ANG L4 stimulates endothelial cell growth and tubule formation, albeit more weakly than VEGF. However, ANGPTL4 mitigates the growth inhibitory actions of RSG on endothelial cells in the presence or absence of VEGF. Thus, the interplay between VEGF and ANGPTL4 could lead to a net expansion of the adipose tissue capillary network, required for adipose tissue growth, in response to PPAR[gamma], activators. neovascularization; endothelial cell; insulin resistance; diabetes; adipokines

Author(s): Avirup Bose; Adilson Guilherme; Stacey I. Robida; Sarah M. C. Nicoloro; Qiong L. Zhou; Zhen Y. Jiang; Darcy P. Pomerleau; Michael P. Czech (corresponding author) Insulin stimulates glucose uptake [...]

The insulin-regulated glucose transporter GLUT4 is a key modulator of whole body glucose homeostasis, and its selective loss in adipose tissue or skeletal muscle causes insulin resistance and diabetes. Here we report an RNA interference-based screen of protein kinases expressed in adipocytes and identify four negative regulators of insulin-responsive glucose transport: the protein kinases PCTAIRE-1 (PCTK1), PFTAIRE-1 (PFTK1), 1κB kinase a, and MAP4K4/NIK. lntegrin-linked protein kinase was identified as a positive regulator of this process. We characterized one of these hits, MAP4K4/NIK, and found that it is unique among mitogen- activated protein (MAP) kinases expressed in cultured adipocytes in attenuating hexose transport. Remarkably, MAP4K4/NIK suppresses expression of the adipogenic transcription factors C/EBPα, C/EBPβ, and PPARγ and of GLUT4 itself in these cells. RNA interference-mediated depletion of MAP4K4/NIK early in differentiation enhances adipogenesis and triglyceride deposition, and even in fully differentiated adipocytes its loss up-regulates GLUT4. Conversely, conditions that inhibit adipogenesis such as TNF-α treatment or depletion of PPARγ markedly up-regulate MAP4K4/ NIK expression in cultured adipocytes. Furthermore, TNF-α signaling to down-regulate GLUT4 is impaired in the absence of MAP4K4/NIK, indicating that MAP4K4 expression is required for optimal TNF-α action. These results reveal a MAP4K4/NIK-dependent signaling pathway that potently inhibits PPARγ-responsive gene expression, adipogenesis, and insulin-stimulated glucose transport. [ABSTRACT FROM AUTHOR]

RNA-guided, engineered nucleases derived from the prokaryotic adaptive immune system CRISPR-Cas represent a powerful platform for gene deletion and editing. When used as a therapeutic approach, direct delivery of Cas9 protein and singleguide RNA (sgRNA) could circumvent the safety issues associated with plasmid delivery and therefore represents an attractive tool for precision genome engineering. Gene deletion or editing in adipose tissue to enhance its energy expenditure, fatty acid oxidation, and secretion of bioactive factors through a "browning" process presents a potential therapeutic strategy to alleviate metabolic disease. Here, we developed "CRISPR-delivery particles," denoted CriPs, composed of nano-size complexes of Cas9 protein and sgRNA that are coated with an amphipathic peptide called Endo-Porter that mediates entry into cells. Efficient CRISPR-Cas9-mediated gene deletion of ectopically expressed GFP by CriPs was achieved in multiple cell types, including a macrophage cell line, primary macrophages, and primary pre-adipocytes. Significant GFP loss was also observed in peritoneal exudate cells with minimum systemic toxicity in GFP-expressing mice following intraperitoneal injection of CriPs containing Gfp-targeting sgRNA. Furthermore, disruption of a nuclear co-repressor of catabolism, the Nrip1 gene, in white adipocytes by CriPs enhanced adipocyte browning with a marked increase of uncoupling protein 1 (UCP1) expression. Of note, the CriP-mediated Nrip1 deletion did not produce detectable off-target effects. We conclude that CriPs offer an effective Cas9 and sgRNA delivery system for ablating targeted gene products in cultured cells and in vivo, providing a potential therapeutic strategy for metabolic disease. [ABSTRACT FROM AUTHOR]

Adipocyte function is crucial for the control of whole body energy homeostasis. Pathway analysis of differentiating 3T3-L1 adipocytes reveals that major metabolic pathways induced during differentiation involve mitochondrial function. However, it is not clear why differentiated white adipocytes require enhanced respiratory chain activity relative to pre-adipocytes. To address this question, we used small interference RNA to interfere with the induction of the transcription factor Tfam, which is highly induced between days 2 and 4 of differentiation and is crucial for replication of mitochondrial DNA. Interference with Tfam resulted in cells with decreased respiratory chain capacity, reflected by decreased basal oxygen consumption, and decreased mitochondrial ATP synthesis, but no difference in many other adipocyte functions or expression levels of adipose-specific genes. However, insulin-stimulated GLUT4 translocation to the cell surface and subsequent glucose transport are impaired in Tfam knockdown cells. Paradoxically, insulin- stimulated Akt phosphorylation is significantly enhanced in these cells. These studies reveal independent links between mitochondrial function, insulin signaling, and glucose transport, in which impaired respiratory chain activity enhances insulin signaling to Akt phosphorylation, but impairs GLUT4 translocation. These results indicate that mitochondrial respiratory chain dysfunction in adipocytes can cause impaired insulin responsiveness of GLUT4 translocation by a mechanism downstream of the Akt protein kinase. [ABSTRACT FROM AUTHOR]

Proinflammatory pathways in adipose tissue macrophages (ATMs) can impair glucose tolerance in obesity, but ATMs may also be beneficial as repositories for excess lipid that adipocytes are unable to store. To test this hypothesis, we selectively targeted visceral ATMs in obese mice with siRNA against lipoprotein lipase (LPL), leaving macrophages within other organs unaffected. Selective silencing of ATM LPL decreased foam cell formation in visceral adipose tissue of obese mice, consistent with a reduced supply of fatty acids from VLDL hydrolysis. Unexpectedly, silencing LPL also decreased the expression of genes involved in fatty acid uptake (CD36) and esterification in ATMs. This deficit in fatty acid uptake capacity was associated with increased circulating serum free fatty acids. Importantly, ATM LPL silencing also caused a marked increase in circulating fatty acid-binding protein-4, an adipocyte-derived lipid chaperone previously reported to induce liver insulin resistance and glucose intolerance. Consistent with this concept, obese mice with LPL-depleted ATMs exhibited higher hepatic glucose production from pyruvate and glucose intolerance. Silencing CD36 in ATMs also promoted glucose intolerance. Taken together, the data indicate that LPL secreted by ATMs enhances their ability to sequester excess lipid in obese mice, promoting systemic glucose tolerance., (Copyright © 2014 the American Physiological Society.)

Insulin stimulates glucose uptake in muscle and adipose cells by mobilizing intracellular membrane vesicles containing GLUT4 glucose transporter proteins to the plasma membrane. Here we show in live cultured adipocytes that intracellular membranes containing GLUT4-yellow fluorescent protein (YFP) move along tubulin-cyan fluorescent protein-labeled microtubules in response to insulin by a mechanism that is insensitive to the phosphatidylinositol 3 (PI3)-kinase inhibitor wortmannin. Insulin increased by several fold the observed frequencies, but not velocities, of long-range movements of GLUT4-YFP on microtubules, both away from and towards the perinuclear region. Genomics screens show conventional kinesin KIF5B is highly expressed in adipocytes and this kinesin is partially co-localized with perinuclear GLUT4. Dominant-negative mutants of conventional kinesin light chain blocked outward GLUT4 vesicle movements and translocation of exofacial Myc-tagged GLUT4-green fluorescent protein to the plasma membrane in response to insulin. These data reveal that insulin signaling targets the engagement or initiates the movement of GLUT4-containing membranes on microtubules via conventional kinesin through a PI3-kinase-independent mechanism. This insulin signaling pathway regulating KIF5B function appears to be required for GLUT4 translocation to the plasma membrane.