Bidirectional Modulation of Adipogenesis by the Secreted Protein Ccdc80/DRO1/URB

Abstract

Adipocyte-secreted proteins play important roles in metabolic regulation through autocrine, paracrine, and endocrine mechanisms. Using transcriptional profiling, we identified coiled-coil domain containing 80 (Ccdc80; also known as DRO1 and URB) as a novel secreted protein highly expressed in white adipose tissue. In 3T3-L1 cells Ccdc80 is expressed and secreted in a biphasic manner with high levels in postconfluent preadipocytes and terminally differentiated adipocytes. To determine whether Ccdc80 regulates adipocyte differentiation, Ccdc80 expression was manipulated using both knockdown and overexpression approaches. Small hairpin RNA-mediated silencing of Ccdc80 in 3T3-L1 cells inhibits adipocyte differentiation. This phenotype was partially reversed by treating the knockdown cells with Ccdc80-containing conditioned medium from differentiated 3T3-L1 cells. Molecular studies indicate that Ccdc80 is required for the full inhibition of T-cell factor-mediated transcriptional activity, down-regulation of Wnt/␤-catenin target genes during clonal expansion, and the subsequent induction of C/EBP␣ and peroxisome proliferator-activated receptor ␥. Surprisingly, overexpression of Ccdc80 in 3T3-L1 cells also inhibits adipocyte differentiation without affecting the repression of the Wnt/␤-catenin signaling pathway. Taken together, these data suggest that Ccdc80 plays dual roles in adipogenesis by mechanisms that involve at least in part down-regulation of Wnt/␤-catenin signaling and induction of C/EBP␣ and peroxisome proliferator-activated receptor ␥.The metabolic abnormalities associated with obesity underlie the development of insulin resistance and type 2 diabetes (1, 2). The emergence of white adipose tissue as an endocrine organ has refined our understanding of the mechanisms by which adipocytes can affect whole-body energy homeostasis (3). Adipose cells not only serve as lipid storage sites but can also secrete various autocrine, paracrine, and/or endocrine mediators referred to as adipocyte-secreted proteins or adipokines. These secreted proteins can have profound effects on energy balance and insulin sensitivity and are affected by hormonal changes, nutritional status, inflammatory mediators, and/or pharmacological treatments (4, 5). Understanding the full set of secreted proteins present in adipocytes and their regulation and activities might help reveal novel molecular links between obesity and metabolic disorders and potential therapeutic opportunities.Commitment of mesenchymal progenitor cells to the adipocyte lineage involves a complex transcriptional cascade that culminates in the induction of the basic leucine-region zipper proteins C/EBP␣, 2 C/EBP␤, and C/EBP␦, the Krüppel-like transcription factor KLF5, and the nuclear receptor PPAR␥ (6 -8). In the mouse 3T3-L1 cell line (9, 10) initiation of this cascade requires the stimulation of growth-arrested fibroblastlike cells with adipogenic inducers forcing the cells to re-enter the cell cycle allowing transcription of early adipogenic genes (11,12). This clona...

Adipose Tissue and Serum CCDC80 in Obesity and Its Association with Related Metabolic Disease

“…The human CCDC80 gene is predominantly expressed in WAT (7,8), but its protein pattern of expression in adipose depots and regulation by obesity have ( Figure 2C). Therefore, CCDC80 expression is transiently downregulated during early stages of adipocyte differentiation and reaches a maximum in mature adipocytes.…”

“…Rodent (6) and human (10) CCDC80 bear a signal peptide, suggesting that the protein is either expressed on the extracellular surface or secreted. Indeed, secretion of the protein has been demonstrated from primary cultured human adipocytes (7) and differentiated 3T3L1 adipocytes (8). The aim of this study was to investigate the regulation of CCDC80 in human adipose tissue in obesity, and to assess the relationship between circulating CCDC80 and markers of obesity-related metabolic derangements and diseases.…”

“…Overall, these results suggest for the first time that CCDC80 may be a component of the obesity-altered secretome in VAT and could act as an adipokine whose circulant levels are linked to glucose tolerance derangements and related to inflammationassociated chronic complications. Online address: http://www.molmed.org doi: 10.2119/molmed.2017.00067 that involve Wnt/β-catenin signaling, C/EBPα and PPARγ (8).…”

“…Contrastingly, CCDC80 downregulation was detected in white adipose tissue (WAT) in other obese mouse models, including ob/ob, KKAy and diet-induced obesity (7). CCDC80 is widely expressed in normal tissues, and particularly in preadipocytes and adipocytes of both primary cultured human cells (7) and mouse 3T3L1 cells (7,8), while it is transiently downregulated during differentiation (7,8). In mature adipocytes, CCDC80 expression is repressed by insulin, tumor necrosis factor-a, H 2 O 2 and hypoxia (7), and by dexamethasone and 3-isobutyl-1-methylxanthine (IBMX) in confluent preadipocytes (8).…”

“…CCDC80 is widely expressed in normal tissues, and particularly in preadipocytes and adipocytes of both primary cultured human cells (7) and mouse 3T3L1 cells (7,8), while it is transiently downregulated during differentiation (7,8). In mature adipocytes, CCDC80 expression is repressed by insulin, tumor necrosis factor-a, H 2 O 2 and hypoxia (7), and by dexamethasone and 3-isobutyl-1-methylxanthine (IBMX) in confluent preadipocytes (8). CCDC80 has been shown to play a dual role in adipogenesis in vitro through mechanisms for the development of obesity-related disorders such as insulin resistance (3), cardiovascular disease (4) and liver steatosis (5).…”