We previously showed that leucine deprivation decreases abdominal fat mass largely by increasing energy expenditure, as demonstrated by increased lipolysis in white adipose tissue (WAT) and uncoupling protein 1 (UCP1) expression in brown adipose tissue (BAT). The goal of the present study was to investigate the possible involvement of central nervous system (CNS) in this regulation and elucidate underlying molecular mechanisms. For this purpose, levels of genes and proteins related to lipolysis in WAT and UCP1 expression in BAT were analyzed in wild-type mice after intracerebroventricular administration of leucine or corticotrophin-releasing hormone antibodies, or in mice deleted for three β-adrenergic receptors, after being maintained on a leucine-deficient diet for 7 d. Here, we show that intracerebroventricular administration of leucine significantly attenuates abdominal fat loss and blocks activation of hormone sensitive lipase in WAT and induction of UCP1 in BAT in leucine-deprived mice. Furthermore, we provide evidence that leucine deprivation stimulates fat loss by increasing expression of corticotrophin-releasing hormone in the hypothalamus via activation of stimulatory G protein/cAMP/protein kinase A/cAMP response element-binding protein pathway. Finally, we show that the effect of leucine deprivation on fat loss is mediated by activation of the sympathetic nervous system. These results suggest that CNS plays an important role in regulating fat loss under leucine deprivation and thereby provide novel and important insights concerning the importance of CNS leucine in the regulation of energy homeostasis.

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It is well established that the central nervous system (CNS), especially the hypothalamus, plays an important role in regulating energy homeostasis and lipid metabolism. We have previously shown that hypothalamic corticotropin-releasing hormone (CRH) is critical for stimulating fat loss in response to dietary leucine deprivation. The molecular mechanisms underlying the CNS regulation of leucine deprivation–stimulated fat loss are, however, still largely unknown. Here, we used intracerebroventricular injection of adenoviral vectors to identify a novel role for hypothalamic p70 S6 kinase 1 (S6K1), a major downstream effector of the kinase mammalian target of rapamycin, in leucine deprivation stimulation of energy expenditure. Furthermore, we show that the effect of hypothalamic S6K1 is mediated by modulation of Crh expression in a melanocortin-4 receptor–dependent manner. Taken together, our studies provide a new perspective for understanding the regulation of energy expenditure by the CNS and the importance of cross-talk between nutritional control and regulation of endocrine signals.

Substrate stiffness is known to impact characteristics including cell differentiation, proliferation, migration and apoptosis. Hydrogels are polymeric materials distinguished by high water content and diverse physical properties. Gradient stiffness hydrogels are designed by the need to develop biologically friendly materials as extracellular matrix (ECM) alternatives to replace the separated and narrow-ranged hydrogel substrates. Important new discoveries in cell behaviors have been realized with model gradient stiffness hydrogel systems from the two-dimensional (2D) to three-dimensional (3D) scale. Basic and clinical applications for gradient stiffness hydrogels in tissue engineering and regenerative medicine continue to drive the development of stiffness and structure varied hydrogels. Given the importance of gradient stiffness hydrogels in basic research and biomedical applications, there is a clear need for systems for gradient stiffness hydrogel design strategies and their applications. This review will highlight past work in the field of gradient stiffness hydrogels fabrication methods, mechanical property test, applications as well as areas for future study. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 1799-1812, 2017.

Recent studies have revealed that the central nervous system, particularly the hypothalamus, is critical for regulating insulin sensitivity in peripheral tissues. The aim of our current study is to investigate the possible involvement of hypothalamic activating transcription factor 4 (ATF4) in the regulation of insulin sensitivity in the liver. Here, we show that overexpression of ATF4 in the hypothalamus resulting from intracerebroventricular injection of adenovirus expressing ATF4 induces hepatic insulin resistance in mice and that inhibition of hypothalamic ATF4 by intracerebroventricular adenovirus expressing a dominant-negative ATF4 variant has the opposite effect. We also show that hypothalamic ATF4-induced insulin resistance is significantly blocked by selective hepatic vagotomy or by inhibiting activity of the mammalian target of rapamycin (mTOR) downstream target S6K1. Finally, we show that inhibition of hypothalamic ATF4 reverses hepatic insulin resistance induced by acute brain endoplasmic reticulum (ER) stress. Taken together, our study describes a novel central pathway regulating hepatic insulin sensitivity that is mediated by hypothalamic ATF4/mTOR/S6K1 signaling and the vagus nerve and demonstrates an important role for hypothalamic ATF4 in brain ER stress–induced hepatic insulin resistance. These results may lead to the identification of novel therapeutic targets for treating insulin resistance and associated metabolic diseases.

Although numerous functions of extracellular signalregulated kinase 1/2 (ERK1/2) are identified, a direct effect of ERK1/2 on liver steatosis has not been reported. Here, we show that ERK1/2 activity is compromised in livers of leptin receptor-deficient (db/db) mice. Adenovirusmediated activation of mitogen-activated protein kinase kinase 1 (MEK1), the upstream regulator of ERK1/2, significantly ameliorated liver steatosis in db/db mice, increased expression of genes related to fatty acid b-oxidation and triglyceride (TG) export and increased serum b-hydroxybutyrate (3-HB) levels. Opposite effects were observed in adenovirus-mediated ERK1/2 knockdown C57/B6J wild-type mice. Furthermore, autophagy and autophagy-related protein 7 (ATG7) expression were decreased or increased by ERK1/2 knockdown or activation, respectively, in primary hepatocytes and liver. Blockade of autophagy by the autophagy inhibitor chloroquine or adenovirus-mediated ATG7 knockdown reversed the ameliorated liver steatosis in recombinant adenoviruses construct expressing rat constitutively active MEK1 Ad-CA MEK1 db/db mice, decreased expression of genes related to fatty acid b-oxidation and TG export, and decreased serum 3-HB levels. Finally, ERK1/2 regulated ATG7 expression in a p38-dependent pathway. Taken together, these results identify a novel beneficial role for ERK1/2 in liver steatosis via promoting ATG7-dependent autophagy, which provides new insights into the mechanisms underlying liver steatosis and important hints for targeting ERK1/2 in treating liver steatosis.Nonalcoholic fatty liver disease involves a serious pathological change in liver (1). The initial stage of nonalcoholic fatty liver disease is liver steatosis, characterized by the excess deposition of triglyceride (TG) and/or cholesterol (TC) in liver (2). If uncontrolled, liver steatosis will progress to life-threatening diseases, such as liver cirrhosis and dysfunction (3). Abnormal hepatic lipid accumulation results from increased uptake of fatty acid/augmented de novo lipogenesis and/or decreased b-oxidation/impaired TG export (4).Autophagy, a cellular process that degrades intracellular organelles and proteins (5), has recently been demonstrated to regulate lipid metabolism (6,7). Lipid droplets are sequestered by autophagosome with the coordination of autophagy-related genes (ATGs). Autophagosome is then fused with lysosome (8) for the degradation of lipid droplets into free fatty acids (FFAs). FFAs are then degraded by mitochondrial b-oxidation to produce ATP or are reesterified into TG for storage (9). Impaired autophagy decreases hepatic fatty acid b-oxidation (FAO) and TG export and results in liver steatosis in mice (7,10), and fatty liver is ameliorated when hepatic autophagy is stimulated by certain compounds (11,12) or some signaling pathways (13) in various animal models.The mitogen-activated protein kinase-extracellular signalregulated kinase (MEK-ERK) signaling pathway is involved in a wide variety of cellular processes (14-16). Several lines of evidence, ...

Insulin resistance is one of the major contributing factors in the development of metabolic diseases. The mechanisms responsible for insulin resistance, however, remain poorly understood. Although numerous functions of the prolactin receptor (PRLR) have been identified, a direct effect on insulin sensitivity has not been previously described. The aim of our current study is to investigate this possibility and elucidate underlying mechanisms. Here we show that insulin sensitivity is improved or impaired in mice injected with adenovirus that overexpress or knock down PRLR expression, respectively. Similar observations were obtained in in vitro studies. In addition, we discovered that the signal transducer and activator of transcription-5 pathway are required for regulating insulin sensitivity by PRLR. Moreover, we observed that PRLR expression is decreased or increased under insulin-resistant (db/db mice) or insulin-sensitive (leucine deprivation) conditions, respectively, and found that altering PRLR expression significantly reverses insulin sensitivity under both conditions. Finally, we found that PRLR expression levels are increased under leucine deprivation via a general control nonderepressible 2/mammalian target of rapamycin/ribosomal protein S6 kinase-1–dependent pathway. These results demonstrate a novel function for hepatic PRLR in the regulation of insulin sensitivity and provide important insights concerning the nutritional regulation of PRLR expression.

Under ultrasonic irradiation, organic fluorescence nanoparticles have been prepared by a reprecipitation method. Compared with single organic fluorophores, these nanoparticles are brighter, more stable against photobleaching and more water-soluble. They also have high room-temperature fluorescence quantum yields (∼20%) and a long fluorescence lifetime (∼0.2 µs). Based on the fluorescence quenching of nanoparticles by chromium(VI), a method for the selective determination of chromium(VI) without the separation of chromium(III) in water was developed. Under the optimal conditions, the linear range of the calibration curve was 7.0 × 10 -6 -1.0 × 10 -4 mol L -1 . The detection limit was 2.8 × 10 -6 mol L -1 . The method is characterized by a short reaction time, stable fluorescence signals, simplicity and high selectivity. The present assay has been applied to the selective quantification of Cr(VI) in wastewater with satisfactory results.