The ability to ensure continous availability of energy despite highly variable supplies in the environment is a major determinant of the survival of all species. In higher organisms, including mammals, the capacity to efficiently store excess energy as triglycerides in adipocytes, from which stored energy could be rapidly released for use at other sites, was developed. To orchestrate the processes of energy storage and release, highly integrated systems operating on several physiological levels have evolved. The adipocyte is no longer considered a passive bystander, because fat cells actively secrete many members of the cytokine family, such as leptin, tumor necrosis factor-α, and interleukin-6, among other cytokine signals, which influence peripheral fuel storage, mobilization, and combustion, as well as energy homeostasis. The existence of a network of adipose tissue signaling pathways, arranged in a hierarchical fashion, constitutes a metabolic repertoire that enables the organism to adapt to a wide range of different metabolic challenges, such as starvation, stress, infection, and short periods of gross energy excess.

Objective: Glycerol constitutes an important metabolite for the control of lipid accumulation and glucose homeostasis. The impact of obesity and obesity-associated type 2 diabetes as well as the potential regulatory role of insulin and leptin on aquaglyceroporins (AQP) 3, 7, and 9 were analyzed. Research Design and Methods: The tissue distribution and expression of AQP in biopsies of omental and sc adipose tissue as well as liver were analyzed in lean and obese Caucasian volunteers (n = 63). The effect of insulin (1, 10, and 100 nmol/liter) and leptin (0.1, 1, and 10 nmol/liter) on the expression of the glycerol channels was determined in vitro in human omental adipocytes and HepG2 hepatocytes. The translocation of AQP in response to insulin and isoproterenol was analyzed by immunocytochemistry. Results: In addition to the well-known expression of AQP7 in adipose tissue, AQP3 and AQP9 were also expressed in both omental and sc adipose tissue. Obese type 2 diabetes patients showed higher expression of AQP in visceral adipose tissue and lower expression of AQP7 in sc adipose tissue and hepatic AQP9. The staining of AQP9 in the plasma membrane of adipocytes was reinforced by insulin, whereas isoproterenol induced the translocation of AQP3 and AQP7 from the lipid droplets to the plasma membrane. Insulin up-regulated all AQP, whereas leptin up-regulated AQP3 and down-regulated AQP7 and AQP9 in adipocytes and hepatocytes. These effects were abrogated by both the phosphatidylinositol 3-kinase inhibitor wortmannin and the mammalian target of rapamycin inhibitor rapamycin. Conclusions: Our findings show, for the first time, that insulin and leptin regulate the AQP through the phosphatidylinositol 3-kinase/Akt/mammalian target of rapamycin pathway in human visceral adipocytes and hepatocytes. AQP3 and AQP7 may facilitate glycerol efflux from adipose tissue while reducing the glycerol influx into hepatocytes via AQP9 to prevent the excessive lipid accumulation and the subsequent aggravation of hyperglycemia in human obesity.

Osteopontin (OPN) is a multifunctional extracellular matrix (ECM) protein involved in multiple physiological processes. OPN expression is dramatically increased in visceral adipose tissue in obesity and the lack of OPN protects against the development of insulin resistance and inflammation in mice. We sought to unravel the potential mechanisms involved in the beneficial effects of the absence of OPN. We analyzed the effect of the lack of OPN in the development of obesity and hepatic steatosis induced by a high-fat diet (HFD) using OPN-KO mice. OPN expression was upregulated in epididymal white adipose tissue (EWAT) and liver in wild type (WT) mice with HFD. OPN-KO mice had higher insulin sensitivity, lower body weight and fat mass with reduced adipose tissue ECM remodeling and reduced adipocyte size than WT mice under a HFD. Reduced MMP2 and MMP9 activity was involved in the decreased ECM remodeling. Crown-like structure number in EWAT as well as F4/80-positive cells and Emr1 expression in EWAT and liver increased with HFD, while OPN-deficiency blunted the increase. Moreover, our data show for the first time that OPN-KO under a HFD mice display reduced fibrosis in adipose tissue and liver, as well as reduced oxidative stress in adipose tissue. Gene expression of collagens Col1a1, Col6a1 and Col6a3 in EWAT and liver, as well as the profibrotic cytokine Tgfb1 in EWAT were increased with HFD, while OPN-deficiency prevented this increase. OPN deficiency prevented hepatic steatosis via reduction in the expression of molecules involved in the onset of fat accumulation such as Pparg, Srebf1, Fasn, Mogat1, Dgat2 and Cidec. Furthermore, OPN-KO mice exhibited higher body temperature and improved BAT function. The present data reveal novel mechanisms of OPN in the development of obesity, pointing out the inhibition of OPN as a promising target for the treatment of obesity and fatty liver.

Orexins, hypothalamic neuropeptides initially involved in the control of food intake and sleep-wake cycle, have recently emerged as pleiotropic regulators of different biological systems, including the reproductive axis. Besides central actions, peripheral expression and functions of orexins have been reported, and prepro-orexin and orexin type-1 receptor mRNAs have been detected in the testis. However, the pattern of expression and biological actions of orexin in the male gonad remain mostly unexplored. In this study, we report analyses on testicular prepro-orexin mRNA expression and orexin-A immunoreactivity in different experimental settings, and on direct effects of orexin-A on seminiferous tubule functions. Expression of prepro-orexin mRNA was demonstrated in the rat testis at different stages of postnatal development, with negligible levels at early juvenile period and maximum values in adulthood. Likewise, orexin-A immunoreactivity was demonstrated along postnatal maturation, with strong peptide signal in Leydig cells and spermatocytes at specific stages of meiosis. Testicular expression of prepro-orexin mRNA appeared hormonally regulated; its levels decreased after hypophysectomy and increased after gonadotropin replacement and ghrelin stimulation. Finally, orexin-A suppressed the expression of key Sertoli cell genes, such as Müllerian-inhibiting substance and stem cell factor, and inhibited DNA synthesis in specific stages of the seminiferous epithelium. In conclusion, we provide evidence for the regulated expression of orexin in the rat testis and its potential involvement in the control of seminiferous tubule functions. Together with our recent results on the expression of orexin type-1 receptor in the rat testis, our data further document a novel testicular site of action of orexins in the control of male reproductive axis.

Objectives: Treatment of human brucellosis demands antibiotic targeting into the mononuclear-phagocytic system. The aim of this work was to prepare and characterize particulate carriers containing gentamicin and to study their interactions with phagocytic cells and bactericidal activity against intracellular Brucella melitensis. Methods: Different poly(lactide-co-glycolide) (PLGA) polymers with free carboxylic end-group were used to formulate micro- and nanoparticles containing gentamicin, by a water-oil-water solvent-evaporation technique. PLGA 502H and 75:25H microparticles were selected because they showed the highest gentamicin loadings as well as good physico-chemical properties and sustained release in vitro. Results: Gentamicin-containing microspheres of both polymers were successfully phagocytosed by infected THP-1 human monocytes, and immunocytochemistry studies revealed that the antibiotic reached Brucella-specific compartments. A dose of 30 μg of encapsulated gentamicin was able to reduce intracellular Brucella infection by 2.2 log. Conclusions: Altogether, these results suggest that 502H and 75:25H microspheres are suitable carriers for gentamicin targeting inside human macrophages and thus for brucellosis treatment.