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  • To determine the post translation

    2023-02-01

    To determine the post-translation modifications in chicken adiponectin, we isolated adiponectin from chicken adipose tissue by immunoprecipitation. Chicken adiponectin was then subjected to tryptic digestion and UPLC/MS/MS. The collagenous domain of chicken adiponectin was found to possess certain ddr1 receptor that are likely to aid in multimerization (Fig. 2). For instance, there were twice as many lysine residues (8 versus 4) compared to human or mouse adiponectin in the collagenous domain. Mutations in some or all of the lysine residues in the collagenous domain of mouse adiponectin leads to a progressive loss of multimerization (Richards et al., 2006, Wang et al., 2006), suggesting that a greater number of lysine residues are likely to favor multimerization. In addition, five lysine residues (three conserved and two non-conserved; Fig. 2) contained a glucosylgalactosyl hydroxyl moiety, a post-translational modification that is likely to aid in multimerization of chicken adiponectin. Similar to chicken adiponectin, all four lysine residues in the collagenous domain of mammalian adiponectin are modified as glucosylgalactosyl hydroxylysine, and such post-translational modifications were found to be essential for improving stability of the HMW adiponectin isoform and for conferring certain biological activities (Peake et al., 2007, Richards et al., 2006, Wang et al., 2002, Wang et al., 2004, Wang et al., 2006). Further studies are required to determine how the oligomers of chicken adiponectin are assembled into multimers and held stably in the circulation as a predominant HMW isoform.
    Plasma adiponectin levels in chickens Following production and verification of an anti-chicken adiponectin antibody, we developed a chicken-specific enzyme-linked immunosorbent assay (EIA) and sought to determine the levels of adiponectin in chicken plasma (Hendricks et al., 2009). We found that the adiponectin levels are in the range of 4–10μg/ml in broiler chicken plasma. Such high levels of adiponectin (1.9–17μg/ml) have similarly been reported in human serum (Arita et al., 1999). We found that a 48h fast did not affect plasma adiponectin levels in chickens, suggesting that circulating adiponectin levels are resistant to metabolic changes in response to fasting. Plasma adiponectin levels were lower in 8-week-old chickens when their body weight and abdominal fat pad mass increased by 2- and 1.5-fold, respectively, compared to 4-week-old broiler chickens (Hendricks et al., 2009). Changes associated with age or rapid growth may have also led to the lower levels of circulating adiponectin in the older chickens.
    Adiponectin receptors Adiponectin signals through two receptors, designated as AdipoR1 and AdipoR2 (Yamauchi et al., 2003). We cloned the genes encoding chicken AdipoR1 and AdipoR2 (GenBank Accession Nos. DQ072275, DQ072276, (Ramachandran et al., 2007). The chicken AdipoR1 cDNA and AdipoR2 cDNA sequences were only 68% homologous to each other, similar to the homology of mammalian AdipoR1 and AdipoR2 cDNA sequences (Yamauchi et al., 2003). The chicken AdipoR1 cDNA, however, was found to be 80–83% homologous to human, mouse, rat, or pig AdipoR1 cDNA, while the deduced protein sequence was 91% similar to mammalian AdipoR1. Similarly, the chicken AdipoR2 cDNA was 76–78% homologous to human, mouse, or pig AdipoR2 cDNA, while the deduced protein sequence was 82% similar to mammalian AdipoR2 (Ramachandran et al., 2007). A significant homology between avian and mammalian AdipoR1 and AdipoR2 sequences may suggest that both genes are evolutionarily conserved and may have important biological functions. Using a hydrophobicity plot analysis, the amino acid sequence of chicken AdipoR1 and AdipoR2 have been predicted to form seven transmembrane domains (Ramachandran et al., 2007). AdipoR1 has been reported to have greater binding affinity to the globular domain of adiponectin while AdipoR2 binds to both the globular and full length adiponectin with intermediate affinity (Yamauchi et al., 2003). While chicken adiponectin contains putative globular and collagenous domains (Hendricks et al., 2009, Maddineni et al., 2005), the relative affinities of the chicken AdipoR1 and AdipoR2 to adiponectin remain to be determined.