ß-carotene regulates cancer stemness in colon cancer in vivo and in vitro.

BACKGROUND/OBJECTIVES: Colorectal cancer (CRC) is the third most common cancer worldwide and has a high recurrence rate, which is associated with cancer stem cells (CSCs). ß-carotene (BC) possesses antioxidant activity and several anticancer mechanisms. However, no investigation has examined its effect on colon cancer stemness. MATERIALS/METHODS: CD133+CD44+ HCT116 and CD133+CD44+ HT-29 cells were isolated and analyzed their self-renewal capacity by clonogenic and sphere formation assays. Expressions of several CSCs markers and Wnt/ß-catenin signaling were examined. In addition, CD133+CD44+ HCT116 cells were subcutaneously injected in xenograft mice and analyzed the effect of BC on tumor formation, tumor volume, and CSCs markers in tumors. RESULTS: BC inhibited self-renewal capacity and CSC markers, including CD44, CD133, ALDH1A1, NOTCH1, Sox2, and ß-catenin in vitro. The effects of BC on CSC markers were confirmed in primary cells isolated from human CRC tumors. BC supplementation decreased the number and size of tumors and delayed the tumor-onset time in xenograft mice injected with CD133+CD44+ HCT116 cells. The inhibitory effect of BC on CSC markers and the Wnt/ß-catenin signaling pathway in tumors was confirmed in vivo as well. CONCLUSIONS: These results suggest that BC may be a potential therapeutic agent for colon cancer by targeting colon CSCs.

Neohesperidin Dihydrochalcone and Neohesperidin Dihydrochalcone-O-Glycoside Attenuate Subcutaneous Fat and Lipid Accumulation by Regulating PI3K/AKT/mTOR Pathway In Vivo and In Vitro.

Neohesperidin dihydrochalcone (NHDC), a semi-natural compound from bitter orange, is an intense sweetener. The anti-obesity effects of NHDC and its glycosidic compound, NHDC-O-glycoside (GNHDC), were investigated. C57BLKS/J db/db mice were supplemented with NHDC or GNHDC (100 mg/kg b.w.) for 4 weeks. Body weight gain, subcutaneous tissues, and total adipose tissues (sum of perirenal, visceral, epididymal, and subcutaneous adipose tissue) were decreased in the NHDC and GNHDC groups. Fatty acid uptake, lipogenesis, and adipogenesis-related genes were decreased, whereas ß-oxidation and fat browning-related genes were up-regulated in the sweetener groups. Furthermore, both sweeteners suppressed the level of triacylglycerol accumulation, lipogenesis, adipogenesis, and proinflammatory cytokines in the 3T3-L1 cells. The PI3K/AKT/mTOR pathway was also down-regulated, and AMP-acttvated protein kinase (AMPK) was phosphorylated in the treatment groups. These results suggest that NHDC and GNHDC inhibited subcutaneous fat and lipid accumulation by regulating the PI3K/AKT/mTOR pathway and AMPK-related lipogenesis and fat browning.

Skeletal Muscle Tissue Trib3 Links Obesity with Insulin Resistance by Autophagic Degradation of AKT2.

BACKGROUND/AIMS: Obesity is a serious health risk factor strongly associated with insulin resistance and type 2 diabetes; however, the underlying mechanisms associating obesity with insulin resistance remain unknown. In this study, we explored the physiological role of Trib3 in regulating glucose metabolism in skeletal muscle tissues in a Trib3 transgenic mice model. METHODS: Glucose metabolism in transgenic mice overexpressing Trib3 specifically in the skeletal muscle was examined by glucose/insulin tolerance test, metabolic cage studies, and glucose uptake assay. The effect of Trib3 overexpression on AKT phosphorylation and AKT protein turnover were assessed by RT-PCR and immunoblot analysis. Subcellular distribution of Trib3 and AKT1/2 was determined by microscopic analysis, co-immunoprecipitation experiments, and limited-detergent extraction of subcellular organelles. Ubiquitin assay was performed and ATG7 deficient cell line was employed to address the mechanisms of Trib3-dependent AKT protein homeostasis. RESULTS: We found that Trib3 expression in skeletal muscle is elevated in obese conditions, and transgenic mice that overexpressed Trib3, specifically in skeletal muscle tissues, displayed impaired glucose homeostasis by suppressing insulin-stimulated glucose uptake. Disruption of insulin signaling in skeletal muscle Trib3 transgenic mice may occur due to the specific downregulation of AKT2 but not AKT1. Autophagy regulated AKT2 protein turnover, and Trib3 overexpression stimulated autophagic degradation of AKT2 by promoting AKT2 ubiquitination. CONCLUSION: Because diet-induced obesity upregulates Trib3 and downregulates AKT2 in skeletal muscle tissues, Trib3 may play a key role in establishing an association between obesity and insulin resistance by regulating AKT2 protein homeostasis.

NEDD4L limits cAMP signaling through ubiquitination of CREB-regulated transcription coactivator 3.

The transcription factor cAMP-responsive element-binding protein (CREB) is involved in a variety of physiologic processes. Although its activity appears to be largely correlated with its phosphorylation status, cAMP-mediated dephosphorylation and the subsequent nuclear migration of the CREB-regulated transcription factors (CRTCs) are required to stimulate CREB transcriptional activity. Among the 3 identified mammalian homologs of CRTCs, CRTC3 has been shown to be expressed predominantly in adipose tissues in response to catecholamine signals that regulate lipid metabolism. Here, we show that prolonged cAMP signaling down-regulates CRTC3 in a proteasome-dependent manner and that neural precursor cell-expressed developmentally down-regulated gene 4-like (NEDD4L), a specific ubiquitin ligase for CRTC3, is responsible for this process. By recognizing the PY motif of CRTC3, NEDD4L interacts with CRTC3 and promotes its polyubiquitination. Interaction between NEDD4L and CRTC3 is further boosted by cAMP signaling, and this enhanced interaction appears to be dependent on the cAMP-mediated phosphorylation of NEDD4L at the Ser448 site. Furthermore, we show that food withdrawal stimulates NEDD4L phosphorylation in mice, which then show a decrease of adipose tissue CRTC3 protein levels. Together, these results suggest that NEDD4L plays a key role in the feedback regulation of cAMP signaling by limiting CRTC3 protein levels.-Kim, Y.-H., Yoo, H., Hong, A.-R., Kwon, M., Kang, S.-W., Kim, K., Song, Y. NEDD4L limits cAMP signaling through ubiquitination of CREB-regulated transcription coactivator 3.

Selective effect of phosphatidylcholine on the lysis of adipocytes.

Obesity, a serious health risk factor, is often associated with depression and negatively affects many aspects of life. Injection of a formula comprising phosphatidylcholine (PPC) and deoxycholate (DC) has emerged as an alternative to liposuction in the reduction of local fat deposits. However, the formula component mainly responsible for this effect and the mechanism behind the actions of the components with respect to fat reduction are unknown. Here, we investigate the specific effects of PPC and DC on adipocyte viability. When exposed to PPC or DC, 3T3L1 preadipocytes and differentiated adipocytes showed dose dependent decrease in cell viability. Interestingly, while DC mediated cell death was non-specific to both preadipocytes and adipocytes, PPC specifically induced a decrease in mature adipocyte viability, but had less effect on preadipocytes. Injection of PPC and DC into inguinal fat pads caused reduction in size. PPC injections preferentially decreased gene expression in mature adipocytes, while a strong inflammatory response was elicited by DC injection. In line with the decreased adipocyte viability, exposure of differentiated adipocytes to PPC resulted in triglyceride release, with a minimal effect on free fatty acids release, suggesting that its fat-reducing effect mediated mainly through the induction of adipocyte cell death rather than lipolysis. Taken together, it appears that PPC specifically affects adipocytes, and has less effect on preadipocyte viability. It can therefore be a promising agent to selectively reduce adipose tissue mass.

Impaired macrophage autophagy induces systemic insulin resistance in obesity.

Obesity-induced insulin resistance and diabetes are significantly associated with infiltrates of inflammatory cells in adipose tissue. Previous studies recognized the involvement of autophagy in the regulation of metabolism in multiple tissues, including ß-cells, hepatocytes, myocytes, and adipocytes. However, despite the importance of macrophages in obesity-induced insulin resistance, the role of macrophage autophagy in regulating insulin sensitivity is seldom addressed. In the present study, we show that macrophage autophagy is important for the regulation of systemic insulin sensitivity. We found that macrophage autophagy is downregulated by both acute and chronic inflammatory stimuli, and blockade of autophagy significantly increased accumulation of reactive oxygen species (ROS) in macrophages. Macrophage-specific Atg7 knockout mice displayed a shift in the proportion to pro-inflammatory M1 macrophages and impairment of insulin sensitivity and glucose homeostasis under high-fat diet conditions. Furthermore, inhibition of ROS in macrophages with antioxidant recovered adipocyte insulin sensitivity. Our results provide evidence of the underlying mechanism of how macrophage autophagy regulates inflammation and insulin sensitivity. We anticipate our findings will serve as a basis for development of therapeutics for inflammatory diseases, including diabetes.