Endurance Training Increases Leptin Expression in the Retroperitoneal Adipose Tissue of Rats Fed with a High-Sugar Diet

Karina Barbosa de Queiroz 0 1 2 Juliana Bohnen Guimara es 0 1 2 Ca ndido Celso Coimbra 0 1 2 Gisele Vieira Rodovalho 0 1 2 Cla udia Martins Carneiro 0 1 2 Elsio Alberto Evangelista 0 1 2 Renata Guerra-Sa 0 1 2 0 C. M. Carneiro Laborato rio de Imunopatologia, Departamento de Ciencias Biologicas , NUPEB, ICEB, Universidade Federal de Ouro Preto , Ouro Preto, MG, Brazil 1 J. B. Guimaraes C. C. Coimbra G. V. Rodovalho Departamento de Fisiologia e Biofsica, Universidade Federal de Minas Gerais , Belo Horizonte, MG, Brazil 2 Present Address: K. B. de Queiroz E. A. Evangelista R. Guerra-Sa (&) Laborato rio de Bioqumica e Biologia Molecular, Departamento de Ciencias Biologicas , NUPEB, ICEB2, Universidade Federal de Ouro Preto , Room 045 Morro do Cruzeiro Campus, Ouro Preto, MG 35400-000, Brazil The presence of leptin receptors in white adipose tissue (WAT) suggests a type of peripheral control during the development of obesity and other metabolic disorders. Both diet composition and exercise influence serum leptin; however, the effect of their combination on long-term WAT leptin metabolism is unknown. In this study, rats fed with standard or high-sugar diets (HSD) were simultaneously subjected to running training for 4and 8-week periods, and the retroperitoneal WAT (rWAT) was evaluated for adipocyte cell size, lipid and catecholamine content, Lep, OB-Rb and Ucp2 mRNA transcription levels, and circulating leptin and non-esterified fatty acids (NEFA). The HSD groups displayed a higher adiposity index and rWAT weight, Lep mRNA and protein upregulation, and a period-dependent effect on OB-Rb mRNA expression. Exercise decreased serum leptin and upregulated the OB-Rb mRNA levels. However, in rats fed with an HSD, the increase in OB-Rb mRNA and reduction in catecholamine levels resulted in a high level of adiposity and hyperleptinemia. The combination of training and an HSD decreases the NEFA levels and upregulating the Ucp2 mRNA expression in the 4-week period, while downregulating the Ucp2 mRNA expression in the 8-week period without changing the NEFA levels. Our results suggest that an HSD induces an increase in leptin expression in rWAT, while reducing adipocytes via leptin-mediated lipolysis after an 8-week period. In exercised rats fed an HSD, TAG synthesis and storage overlaps with lipolysis, promoting fat store development and Lep mRNA and plasma protein upregulation in adult rats. - Abbreviations HSD High-sugar diet RGD Rat genome database OB-Rb Leptin receptor rWAT Retroperitoneal white adipose tissue S-HSD Sedentary-high-sugar diet S-STD Sedentary-standard diet qRT-PCR Quantitative reverse transcription polymerase chain reaction T-HSD Trained-high-sugar diet T-STD Trained-standard diet Ucp2 Uncoupling protein 2 Leptin, a cytokine mainly produced by white adipose tissue (WAT), is a 16 kDa protein that acts directly on hypothalamus, regulating energy homeostasis and adiposity by reducing food intake and increasing energy expenditure [1]. The hormone acts via transmembrane receptors (OB-R) expressed in the central nervous system and peripheral tissues [2]. There are six leptin-receptor isoforms known (OB-Ra, OB-Rb, OB-Rc, OB-Rd, OB-Re and OB-Rf), which are divided into three classes: long, short and soluble [3, 4]. The long spliced OB-Rb variant mediates the effects of leptin via the JAK-STAT signaling pathway [5, 6], and the soluble OB-Re isoform acts as a leptin-linked circulating protein that modulates the steady state of the hormone by preventing its degradation and clearance [3, 7]. The leptin actions in the nuclei hypothalamic has been exclusively related to its ability to regulate food intake, body weight, adiposity and insulin sensitivity [1, 8]. However, the presence of leptin receptors in others tissues (for instance, adipose tissue and skeletal muscle), suggests that leptin has peripheral actions. Experimental studies have suggested that leptin can impair insulin signaling in skeletal muscle and adipocytes, changing the lipid synthesis and degradation ratio [1, 9, 10]. Thus, the dysregulation of leptin actions, e.g., changes in leptin receptor expression in adipose tissue, may influence obesity and other metabolic disorders development, such as insulin resistance and type II diabetes [1, 11]. Circulating leptin is correlated with adipose tissue mass, but may decrease in a short-term fasting, and increase after refeeding [1214], despite a minimal change in adipose pads, suggesting that recent changes in energy balance have a major influence on leptin levels [15]. Furthermore, dietary macronutrient content may affect leptin concentration [13]. It was observed that leptin responses to macronutrient composition in a different way, suggesting an increase in leptin levels after a carbohydrate meals intake [16], with changes in leptin mRNA expression [17]. With changes in energy expenditure, exercise fuels flux, and systemic hormone concentration contributes to leptin regulation [15]. However, the effects of physical training on the regulation of leptin are conflicting. Although some authors found no change in hormone levels with exercise training, it is well established that chronic exercise results in a change in leptin levels [18, 19]. The pathways involved may be related to alterations in the long form of the leptin receptor OB-Rb [20] at the central level. Zhao et al. [21] demonstrated that endurance exercise during a 9-week period activates the same signaling pathways induced by leptin in the rat hypothalamus, suggesting a mimetic effect of training in relation to the hormone in the hypothalamic region, resulting in a reduction in serum leptin after exercise. However, there are no reports concerning the effects of exercise on adipocyte leptin receptors. Adipose tissue lipolysis can be extracellular, a process which is mediated by lipoprotein lipase (LPL), or intracellular, a process which is mediated by catecholamine [22], and some studies have suggested that the sympathetic nervous system is the primary physiological regulator for leptin synthesis in this tissue [23]. There are studies reporting that the exercise-induced oxidation of energy substrates, such as glucose and fatty acids, changes the leptin concentration, suggesting that the reduction in hormone levels is due to changes in availability or nutrient flux [24, 25]. As mentioned above, both diet composition and exercise influence serum leptin; however, there are no data on their combined long-term effects on leptin metabolism in WAT. Indeed, leptin functions in the WAT has been essential for modulating adipocyte metabolic functions [10], upregulating fat oxidation [26] and decreasing lipogenesis [27]. Some authors consider the leptin paracrine actions to be important for the metabolic system of the entire body [1]. The knowledge of the factors that contribute with leptin receptor expression in WAT as well as understanding the effect of diet macronutrient composition and exercise training on leptin (...truncated)