Molecular mechanisms of vaspin action: from adipose tissue to skin and bone, from blood vessels to the brain

Visceral adipose tissue derived serine protease inhibitor (vaspin) or SERPINA12 according to the serpin nomenclature was identified together with other genes and gene products that  were specifically expressed or overexpressed in the intra abdominal or visceral adipose tissue  (AT) of the Otsuka Long-Evans Tokushima fatty rat. These rats spontaneously develop visceral  obesity, insulin resistance, hyperinsulinemia and ‐glycemia, as well as hypertension and thus represent a well suited animal model of obesity and related metabolic disorders such as type  2 diabetes.  The follow-up study reporting the cloning, expression and functional characterization of  vaspin suggested the great and promising potential of this molecule to counteract obesity induced insulin resistance and inflammation and has since initiated over 300 publications, clinical and experimental, that have contributed to uncover the multifaceted functions and molecular mechanisms of vaspin action not only in the adipose, but in many different cells, tissues and organs. This review will give an update on mechanistic and structural aspects of vaspin with a focus on its serpin function, the physiology and regulation of vaspin expression, and will summarize the latest on vaspin function in various tissues such as the different adipose tissue depots as well as the vasculature, skin, bone and the brain

Identification of CXCL11 as part of chemokine network controlling skeletal muscle development

The chemokine, CXCL12, and its receptors, CXCR4 and CXCR7, play pivotal roles during development and maintenance of limb muscles. CXCR7 additionally binds CXCL11, which uses CXCR3 as its prime receptor. Based on this cross-talk, we investigate whether CXCL11 would likewise affect development and/or function of skeletal muscles. Western blotting and immunolabelling demonstrated the developmentally restricted expression of CXCL11 in rat limb muscles, which was contrasted by the continuous expression of its receptors in proliferating and differentiating C2C12 cells as well as in late embryonic to adult rat limb muscle fibres. Consistent with a prime role in muscle formation, functional studies identified CXCL11 as a potent chemoattractant for undifferentiated C2C12 cells and further showed that CXCL11 does neither affect myoblast proliferation and differentiation nor metabolic/catabolic pathways in formed myotubes. The use of selective receptor antagonists unravelled complementary effects of CXCL11 and CXCL12 on C2C12 cell migration, which either require CXCR3/CXCR7 or CXCR4, respectively. Our findings provide new insights into the chemokine network controlling skeletal muscle development and function and, thus, might provide a base for future therapies of muscular diseases

Vaspin suppresses cytokine-induced inflammation in 3T3-L1 adipocytes via inhibition of NFκB pathway

Vaspin expression is increased in white adipose tissue (WAT) of diet-induced obese mice and rats and is supposed to compensate HFD-induced inflammatory processes and insulin resistance in adipose tissue by counteracting pro-inflammatory gene expression in obesity. Multiple studies have also demonstrated strong anti-inflammatory effects in vascular and skin cells. Here, we used vaspin treated 3T3-L1 murine adipocytes as well as 3T3-L1 cells with stable vaspin expression to investigate the effect of exogenous and endogenous vaspin on inflammatory processes and insulin signaling in adipocytes. Our stably transfected cells secreted significant amounts of vaspin which was in the physiological range of ∼0.5 ng/ml in cell supernatants. Adipocyte differentiation was not affected by vaspin as expression of adipogenic marker genes as well as lipid accumulation after full differentiation was similar to control cells. We found that IL-1β induced expression and secretion of pro-inflammatory cytokines, such as IL-6, MCP1 and TNFα was significantly blunted in vaspin expressing 3T3-L1 cells. Treatment of 3T3-L1 cells with exogenous vaspin resulted in reduced cytokine-induced activation of the intracellular and pro-inflammatory NFκB signaling cascades (IKKα/β, IκB and NFκB). Moreover, endogenous vaspin positively affected insulin signaling by increasing insulin-stimulated phosphorylation of the key mediator protein kinase B (AKT). Together, we demonstrate anti-inflammatory effects of vaspin in 3T3-L1 adipocytes as well as increased insulin signaling by endogenous expression or exogenous treatment. The results provide evidence for potent anti-inflammatory action of vaspin not only in vascular cells but also in adipose tissue

Brown adipose tissue (BAT) specific vaspin expression is increased after obesogenic diets and cold exposure and linked to acute changes in DNA-methylation

Objective: Several studies have demonstrated anti-diabetic and anti-obesogenic properties of visceral adipose tissue-derived serine protease inhibitor (vaspin) and so evoked its potential use for treatment of obesity-related diseases. The aim of the study was to unravel physiological regulators of vaspin expression and secretion with a particular focus on its role in brown adipose tissue (BAT) biology. Methods: We analyzed the effects of obesogenic diets and cold exposure on vaspin expression in liver and white and brown adipose tissue (AT) and plasma levels. Vaspin expression was analyzed in isolated white and brown adipocytes during adipogenesis and in response to adrenergic stimuli. DNA-methylation within the vaspin promoter was analyzed to investigate acute epigenetic changes after cold-exposure in BAT. Results: Our results demonstrate a strong induction of vaspin mRNA and protein expression specifically in BAT of both cold-exposed and high-fat (HF) or high-sugar (HS) fed mice. While obesogenic diets also upregulated hepatic vaspin mRNA levels, cold exposure tended to increase vaspin gene expression of inguinal white adipose tissue (iWAT) depots. Concomitantly, vaspin plasma levels were decreased upon obesogenic or thermogenic triggers. Vaspin expression was increased during adipogenesis but unaffected by sympathetic activation in brown adipocytes. Analysis of vaspin promoter methylation in AT revealed lowest methylation levels in BAT, which were acutely reduced after cold exposure. Conclusions: Our data demonstrate a novel BAT-specific regulation of vaspin gene expression upon physiological stimuli in vivo with acute epigenetic changes that may contribute to cold-induced expression in BAT. We conclude that these findings indicate functional relevance and potentially beneficial effects of vaspin in BAT function. Keywords: Brown adipose tissue, Browning, Cold exposure, DNA methylation, High-fat diet, High-sucrose diet, SerpinA12, Thermogenesis, UCP1, Vaspi

Ablation of kallikrein 7 (KLK7) in adipose tissue ameliorates metabolic consequences of high fat diet-induced obesity by counteracting adipose tissue inflammation in vivo

Vaspin is an adipokine which improves glucose metabolism and insulin sensitivity in obesity. Kallikrein 7 (KLK7) is the first known protease target inhibited by vaspin and a potential target for the treatment of metabolic disorders. Here, we tested the hypothesis that inhibition of KLK7 in adipose tissue may beneficially affect glucose metabolism and adipose tissue function. Therefore, we have inactivated the Klk7 gene in adipose tissue using conditional gene-targeting strategies in mice. Klk7-deficient mice (ATKlk7 −/−) exhibited less weight gain, predominant expansion of subcutaneous adipose tissue and improved whole body insulin sensitivity under a high fat diet (HFD). ATKlk7 −/− mice displayed higher energy expenditure and food intake, most likely due to altered adipokine secretion including lower circulating leptin. Pro-inflammatory cytokine expression was significantly reduced in combination with an increased percentage of alternatively activated (anti-inflammatory) M2 macrophages in epigonadal adipose tissue of ATKlk7 −/−. Taken together, by attenuating adipose tissue inflammation, altering adipokine secretion and epigonadal adipose tissue expansion, Klk7 deficiency in adipose tissue partially ameliorates the adverse effects of HFD-induced obesity. In summary, we provide first evidence for a previously unrecognized role of KLK7 in adipose tissue with effects on whole body energy expenditure and insulin sensitivity