Novel variations in the adiponectin gene (ADIPOQ) may affect distribution of oligomeric complexes.

Adiponectin is an obesity related protein that mediates the risk of type 2 diabetes in obese individuals with its anti-inflammatory and insulin-sensitizing properties. To date, five functional variations have been identified in the adiponectin gene. However, these variations are rare, and fail to fully explain adiponectin variability, suggesting unidentified causal variations exist. Thus, our objective was to identify novel, potentially functional amino acid-changing variations in ADIPOQ exonic regions and relate them to oligomeric forms of adiponectin in serum. We sequenced ADIPOQ exons in 30 adolescents chosen from a school-based cohort based on serum adiponectin and insulin levels. Four coding region changes were identified: a methionine initiation skip (MIS), P32L, R55C, and Y111H, of which R55C and Y111H have been previously identified. Individuals with the novel variations and R55C had low levels of adiponectin and decreased adiponectin oligomerization compared to adolescents with similar body mass index and insulin levels. Further, bioinformatic analysis predicted putative functionality of these variations. In our study, Y111H was unrelated to total circulating adiponectin or adiponectin oligomerization. Given the disruption of adiponectin oligomerization in the individuals with MIS, P32L, and R55C coding changes, these variations may lead to increased metabolic disease risk and warrant further examination in larger cohorts.

Adiponectin is present in human milk and is associated with maternal factors.

BACKGROUND: Previous studies have shown that human milk has a role in the gastrointestinal, neural, and immune development of neonates. If present in milk, adiponectin would be a promising candidate for influencing infant development, given its metabolic functions. OBJECTIVES: Our objectives were to determine whether adiponectin is present in human milk and to characterize maternal factors associated with potential variation in milk adiponectin concentrations. DESIGN: We quantified adiponectin concentrations in human milk samples from donors to the Cincinnati Children's Research Human Milk Bank and randomly selected participants in a cohort study in Mexico City funded by the National Institutes of Health. Using cross-sectional and longitudinal data, we examined milk adiponectin concentrations in relation to lactation duration, maternal body mass index (BMI; in kg/m(2)), and ethnicity. RESULTS: Adiponectin was detected in human skim milk (range: 4.2-87.9 ng/mL). In cross-sectional and longitudinal analyses, duration of lactation was negatively associated with milk adiponectin concentrations (beta = -0.059 +/- 0.024 and -0.059 +/- 0.007, respectively; P < 0.02 for both). Maternal postpregnancy BMI was positively associated with milk adiponectin concentrations (beta = 0.08 +/- 0.02, P < 0.0001; longitudinal analysis). Mexican mothers had lower median milk adiponectin concentrations at 1 mo than did the non-Hispanic white subjects from Cincinnati (11.5 and 19.8 ng/mL; P = 0.003). CONCLUSIONS: Adiponectin is present in human milk and its concentrations are associated with duration of lactation, maternal adiposity, and ethnicity. Given the importance of adiponectin in inflammation, insulin sensitivity, and fatty acid metabolism, future studies should examine milk adiponectin's role in infant metabolic development.

Targeted expression of a protease-resistant IGFBP-4 mutant in smooth muscle of transgenic mice results in IGFBP-4 stabilization and smooth muscle hypotrophy.

The insulin-like growth factor-binding protein 4 (IGFBP-4), the most abundant IGF-binding protein produced by rodent smooth muscle cells (SMC), is degraded by specific protease(s) potentially releasing IGF-I for local bioactivity. IGFBP-4 protease(s) recognizes basic residues within the midregion of the molecule. We constructed a mutant IGFBP-4 with the cleavage domain substitution 119-KHMAKVRDRSKMK-133 to 119-AAMAAVADASAMA-133. Myc-tagged native and IGFBP-4.7A retained equivalent IGF-I binding affinity. Whereas native IGFBP-4 was cleaved by SMC-conditioned medium, IGFBP-4.7A was completely resistant to proteolysis. To explore the function of the protease-resistant IGFBP-4 in vivo, expression of the mutant and native proteins was targeted to SMC of transgenic mice by means of a smooth muscle alpha-actin promoter. Transgene expression was confined to SMC-rich tissues in all lines. Bladder and aortic immunoreactive IGFBP-4/transgene mRNA ratios in SMP8-BP4.7A mice were increased by 2- to 4-fold relative to SMP8-BP4 mice, indicating that the IGFBP-4.7A protein was stabilized in vivo. SMP8-BP4.7A mice had lower aortic, bladder, and stomach weight and intestinal length relative to SMP8-BP4 counterparts matched for protein expression by Western blotting. Thus, IGFBP-4.7A results in greater growth inhibition than equivalent levels of native IGFBP-4 in vivo, demonstrating a role for IGFBP-4 proteolysis in the regulation of IGF-I action.