Adipose tissue derived factors in obesity, inflammation & energy homeostasis

Obesity is the foremost contributory factor in the progression to type 2 diabetes mellitus (T2DM). Moreover, chronic inflammation, through activation of innate immunity is proposed to link obesity, insulin resistance and T2DM. Adipose tissue, traditionally considered a storage compartment for triglycerides, also functions as an active endocrine organ. Adipocyte-secreted products, termed adipokines, may link obesity-associated inflammation and insulin resistance. Adipokines exert multiple effects on insulin sensitisation, glucose homeostasis, inflammatory processes or central systems mediating energy expenditure. This thesis principally examined two adipokines; resistin and adiponectin. Resistin and components of innate immunity were assessed in human obesity. In-vitro analysis established that resistin was expressed and secreted by human adipocytes. Furthermore, key factors in the innate immune pathway were highly expressed in obese and T2DM adipose tissue. This thesis further explored the pro-inflammatory actions of resistin in adipocytes. Resistin stimulated the secretion of inflammatory cytokines from adipocytes and, the expression of key intermediates of the innate immune and insulin signalling pathways. Clinical studies entailed examination of resistin as a marker of inflammation in childhood obesity. Serum analysis revealed gender-differences in resistin levels in obese children. Furthermore, bacterial endotoxin correlated with several markers of inflammation and cardiovascular disease; suggesting endotoxin as a contributor to inflammation in childhood obesity. This thesis subsequently examined another adipokine, adiponectin; considered to have a `ying-and-yang' relationship with resistin. Studies explored a central role for adiponectin in energy homeostasis. Gelfiltration liquid chromatography established that the adiponectin trimer was predominant in human cerebrospinal fluid. Such identification of trimeric adiponectin in vivo implicates the pharmacologically generated globular adiponectin in central regulation of energy expenditure. In conclusion, resistin may serve as a pathogenic pro-inflammatory factor, exacerbating inflammation within adipose tissue; potentially contributing to the progression of obesity-driven T2DM. Alternatively, adiponectin may have favourable central actions, influencing energy expenditure through its basic trimeric form. Collectively, this thesis suggests that resistin and adiponectin, with a range of opposing properties, may substantially affect whole-body metabolism.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

The in vitro effects of resistin on the innate immune signaling pathway in isolated human subcutaneous adipocytes

Context: Obesity-associated inflammation is a contributory factor in the pathogenesis of type 2 diabetes mellitus (T2DM); the mechanisms underlying the progression to T2DM are unclear. The adipokine resistin has demonstrated pro-inflammatory properties in relation to obesity and T2DM. Objective: To characterize resistin expression in human obesity and address the role of resistin in the innate immune pathway. Furthermore, examine the influence of lipopolysaccharide, recombinant human resistin (rhResistin), insulin and rosiglitazone in human adipocytes. Finally, analyze the effect of rhResistin on the expression of components of the NF-κB pathway and insulin signaling cascade. Methods: Abdominal subcutaneous adipose tissue was obtained from patients undergoing elective liposuction surgery (n = 35, aged: 36-49 yr; BMI: 26.5 ± 5.9 kg/m2). Isolated adipocytes were cultured with rhResistin (10-50 ng/ml). The level of cytokine secretion from isolated adipocytes was examined by ELISA. The effect of rhResistin on protein expression of components of the innate immune pathway was examined by Western blot. Results: In-vitro studies demonstrated that antigenic stimuli increase resistin secretion (P < 0.001) from isolated adipocytes. Pro-inflammatory cytokine levels were increased in response to rhResistin (P < 0.001); this was attenuated by rosiglitazone (P < 0.01). When examining components of the innate immune pathway, rhResistin stimulated Toll-like receptor-2 protein expression. Similarly, mediators of the insulin signaling pathway, phosphospecific JNK1 and JNK2, were upregulated in response to rhResistin. Conclusion: Resistin may participate in more than one mechanism to influence pro-inflammatory cytokine release from human adipocytes; potentially via the integration of NF-κB and JNK signaling pathways

Cyclin D1 Restrains Oncogene-Induced Autophagy by Regulating the AMPK-LKB1 Signaling Axis.

Autophagy activated after DNA damage or other stresses mitigates cellular damage by removing damaged proteins, lipids, and organelles. Activation of the master metabolic kinase AMPK enhances autophagy. Here we report that cyclin D1 restrains autophagy by modulating the activation of AMPK. In cell models of human breast cancer or in a cyclin D1-deficient model, we observed a cyclin D1-mediated reduction in AMPK activation. Mechanistic investigations showed that cyclin D1 inhibited mitochondrial function, promoted glycolysis, and reduced activation of AMPK (pT172), possibly through a mechanism that involves cyclin D1-Cdk4/Cdk6 phosphorylation of LKB1. Our findings suggest how AMPK activation by cyclin D1 may couple cell proliferation to energy homeostasis

Dichotomous effects of VEGF-A on adipose tissue dysfunction

Obese fat pads are frequently undervascularized and hypoxic, leading to increased fibrosis, inflammation, and ultimately insulin resistance. We hypothesized that VEGF-A-induced stimulation of angiogenesis enables sustained and sufficient oxygen and nutrient exchange during fat mass expansion, thereby improving adipose tissue function. Using a doxycycline (Dox)-inducible adipocyte-specific VEGF-A overexpression model, we demonstrate that the local up-regulation of VEGF-A in adipocytes improves vascularization and causes a "browning" of white adipose tissue (AT), with massive up-regulation of UCP1 and PGC1 alpha. This is associated with an increase in energy expenditure and resistance to high fat diet-mediated metabolic insults. Similarly, inhibition of VEGF-A-induced activation of VEGFR2 during the early phase of high fat diet-induced weight gain, causes aggravated systemic insulin resistance. However, the same VEGF-A-VEGFR2 blockade in ob/ob mice leads to a reduced body-weight gain, an improvement in insulin sensitivity, a decrease in inflammatory factors, and increased incidence of adipocyte death. The consequences of modulation of angiogenic activity are therefore context dependent. Proangiogenic activity during adipose tissue expansion is beneficial, associated with potent protective effects on metabolism, whereas antiangiogenic action in the context of preexisting adipose tissue dysfunction leads to improvements in metabolism, an effect likely mediated by the ablation of dysfunctional proinflammatory adipocytes.National Institutes of HealthNational Institutes of Health [R01-DK55758, RC1DK086629, P01DK088761

Epoxygenase inactivation exacerbates diet and aging-associated metabolic dysfunction resulting from impaired adipogenesis

• Cyp2j4 deletion in rats offers a simplified genetic landscape as opposed to the mice locus, which is under significant allelic expansion. • Under different metabolic stresses (aging, cafeteria diet), Cyp2j4−/− rats show an accelerated adipogenesis, which progress towards adipocyte dysfunction. • Adipocyte dysfunction in Cyp2j4−/− rats under cafeteria diet (CAF) is characterised by down-regulation of white adipose tissue (WAT) PPARγ and C/EBPα, adipocyte hypertrophy and extracellular matrix remodeling. • Cyp2j4−/− rats treated with CAF display exacerbated weight gain, insulin resistance, hepatic lipid accumulation and dysregulated gluconeogenesis. • Cyp2j4−/− rats display alternative arachidonic acid pathway usage in their adipose tissue upon CAF and aging

Properties and functions of adipose tissue macrophages in obesity

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/146625/1/imm13002.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/146625/2/imm13002_am.pd

Genomic and Epigenomic Responses to Chronic Stress Involve miRNA-Mediated Programming

Stress represents a critical influence on motor system function and has been shown to impair movement performance. We hypothesized that stress-induced motor impairments are due to brain-specific changes in miRNA and protein-encoding gene expression. Here we show a causal link between stress-induced motor impairment and associated genetic and epigenetic responses in relevant central motor areas in a rat model. Exposure to two weeks of mild restraint stress altered the expression of 39 genes and nine miRNAs in the cerebellum. In line with persistent behavioural impairments, some changes in gene and miRNA expression were resistant to recovery from stress. Interestingly, stress up-regulated the expression of Adipoq and prolactin receptor mRNAs in the cerebellum. Stress also altered the expression of Prlr, miR-186, and miR-709 in hippocampus and prefrontal cortex. In addition, our findings demonstrate that miR-186 targets the gene Eps15. Furthermore, we found an age-dependent increase in EphrinB3 and GabaA4 receptors. These data show that even mild stress results in substantial genomic and epigenomic changes involving miRNA expression and associated gene targets in the motor system. These findings suggest a central role of miRNA-regulated gene expression in the stress response and in associated neurological function