Obestatin as a regulator of adipocyte metabolism and adipogenesis

Abstract

The role of obestatin, a 23-amino-acid peptide encoded by the ghrelin gene, on the control of the metabolism of pre-adipocyte and adipocytes as well as on adipogenesis was determined. For in vitro assays, pre-adipocyte and adipocyte 3T3-L1 cells were used to assess the obestatin effect on cell metabolism and adipogenesis based on the regulation of the key enzymatic nodes, Akt and AMPK and their downstream targets. For in vivo assays, white adipose tissue (WAT) was obtained from male rats under continuous subcutaneous infusion of obestatin. Obestatin activated Akt and its downstream targets, GSK3α/β, mTOR and S6K1, in 3T3-L1 adipocyte cells. Simultaneously, obestatin inactivated AMPK in this cell model. In keeping with this, ACC phosphorylation was also decreased. This fact was confirmed in vivo in white adipose tissue (omental, subcutaneous and gonadal) obtained from male rats under continuous sc infusion of obestatin (24 and 72 hrs). The relevance of obestatin as regulator of adipocyte metabolism was supported by AS160 phosphorylation, GLUT4 translocation and augment of glucose uptake in 3T3-L1 adipocyte cells. In contrast, obestatin failed to modify translocation of fatty acid transporters, FATP1, FATP4 and FAT/CD36, to plasma membrane. Obestatin treatment in combination with IBMX and DEX showed to regulate the expression of C/EBPα, C/EBPβ, C/EBPδ and PPARγ promoting adipogenesis. Remarkable, preproghrelin expression, and thus obestatin expression, increased during adipogenesis being sustained throughout terminal differentiation. Neutralization of endogenous obestatin secreted by 3T3-L1 cells by anti-obestatin antibody decreased adipocyte differentiation. Furthermore, knockdown experiments by preproghrelin siRNA supported that obestatin contributes to adipogenesis. In summary, obestatin promotes adipogenesis in an autocrine/paracrine manner, being a regulator of adipocyte metabolism. These data point to a putative role in the pathogenesis of metabolic syndrome.

Ghrelin Gene Products in Acute and Chronic Inflammation

“…Successive works, however, did not support these assertions (Bassil et al 2007;Chartrel et al 2007;Lauwers et al 2006), and the biological role of obestatin is still debated (Lacquaniti et al 2011). Nevertheless, obestatin has several biological activities, including protective effects on the cardiovascular system (Agnew et al 2012;Alloatti et al 2010;Aragno et al 2012), promotion of adipocytes survival, differentiation, and metabolism Gurriarán-Rodríguez et al 2011;Miegueu et al 2011;Pruszynska-Oszmalek et al 2013), induction of myoblasts differentiation and promotion of skeletal muscle regeneration (Gurriarán-Rodríguez et al 2012), inhibition of pancreatic b-cell and islets apoptosis, stimulation of glucose-stimulated insulin secretion in both normal and diabetic animal models, and enhancement of functional bcell generation from pancreatic precursor cells (Baragli et al 2013;Granata et al 2008Granata et al , 2010. Notably by an evolutionary point of view, while ghrelin is mainly involved in food intake, obestatin has an inhibitory effect on water drinking by acting on mechanisms involved in the thirst (Samson et al 2007) and decreases vasopressin concentration in plasma (Samson et al 2008).…”

The Obestatin/GPR39 System Is Up-regulated by Muscle Injury and Functions as an Autocrine Regenerative System

“…2A). The individual autocrine role of obestatin was tested using a neutralizing obestatin antibody (Ab) (30). L6E9 cells were maintained in GM, DM, anti-obestatin Ab (5 g/l) in DM, obestatin ϩ antiobestatin Ab (1:1, w/w) in DM, or preimmune IgG (5 g/l) in DM during a 6-day differentiation period in which DM plus reactive were replaced every 24 h. As shown in Fig.…”

“…Male rats received a 72-h continuous subcutaneous infusion of obestatin (300 nmol/kg of body weight/24 h) (30), and dissected gastrocnemius and soleus tissues were processed for immunoblot analysis. Levels of Pax-7, Myf5, MyoD, myogenin, Myf6, and MHC were up-regulated in gastrocnemius and soleus muscle tissues from obestatin-treated rats when compared with control tissues (Fig.…”

“…This dual activity is determined by the cell type-specific context in which differential activation of signaling pathways provides an important switching function that determines the cell fate in the differentiation process (26 -28). Recent works from our laboratory have uncovered that insulin, through IGF1R, triggers the expression of obestatin during adipocyte differentiation as a key target for preadipocyte commitment to the adipocyte lineage (29,30). Obestatin, a 23-amino acid peptide derived from a polypeptide called preproghrelin, precursor of ghrelin, was originally isolated from the stomach.…”

“…It was reported to be the ligand for the orphan receptor GPR39, which belongs to the family of the ghrelin and motilin receptors (32). The autocrine role on adipogenesis was further supported by the effect of exogenous obestatin on the expression of master regulators of the adipocyte fate and, consequently, lipid accumulation (30). This action appears to be related to Akt activation and its downstream targets, mammalian target of rapamycin (mTOR) and S6K1.…”