Human SERPINA12 ELISA Matched Antibody Pair

Aims/Introduction Vaspin is linked to obesity and its metabolic abnormalities. However, the role of vaspin serum levels in diabetic retinopathy (DR) is unknown. In the present study, we investigated the association between serum levels of vaspin and both DR and vision-threatening DR. Materials and Methods This was a cross-sectional single-center observational study from December 2018 to September 2019. We evaluated circulating serum levels of vaspin in 372 participants with type 2 diabetes. DR was screened through detailed ocular examination. DR patients were also divided two groups: vision-threatening DR and non-vision-threatening DR. The relationship between vaspin and DR was investigated by univariate and multivariate logistic regression analyses, and the results are shown as odds ratios with 95% confidence intervals. Results The vaspin serum levels of 372 patients were obtained, with a median value of 1.50 ng/mL (interquartile range 0.94-2.18 ng/mL). The median age of those patients was 53 years (interquartile range 44-62 years), and 44.4% were women. Patients with DR and VDTR had significantly increased vaspin serum levels (P P < 0.001). A multivariable regression model found that patients with high levels of vaspin were approximately 1.85-fold (odds ratio for per unit increase 1.85, 95% confidence interval 1.43-2.55;P < 0.001) more likely to experience DR, and 3.76-fold (odds ratio for per unit increase 3.76, 95% confidence interval 2.05-6.55;P < 0.001) more likely to experience VTDR. The predictive value of vaspin was stronger in women than in men. Conclusion Higher vaspin serum levels were associated with an increased risk of DR and VDTR in patients with type 2 diabetes, which showed that vaspin is an important indicator factor for DR.

SerpinA12 (vaspin) is thought to be mainly expressed in adipose tissue and has multiple beneficial effects on metabolic, inflammatory and atherogenic processes related to obesity. KLK7 (kallikrein 7) is the only known protease target of vaspin to date and is inhibited with a moderate inhibition rate. In the crystal structure, the cleavage site (P1-P1') of the vaspin reactive centre loop is fairly rigid compared with the flexible residues before P2, possibly supported by an ionic interaction of P1' glutamate (Glu(379)) with an arginine residue (Arg(302)) of the beta-sheet C. A P1' glutamate seems highly unusual and unfavourable for the protease KLK7. We characterized vaspin mutants to investigate the roles of these two residues in protease inhibition and recognition by vaspin. Reactive centre loop mutations changing the P1' residue or altering the reactive centre loop conformation significantly increased inhibition parameters, whereas removal of the positive charge within beta-sheet C impeded the serpin-protease interaction. Arg(302) is a crucial contact to enable vaspin recognition by KLK7 and it supports moderate inhibition of the serpin despite the presence of the detrimental P1' Glu(379), which clearly represents a major limiting factor for vaspin-inhibitory activity. We also show that the vaspin-inhibition rate for KLK7 can be modestly increased by heparin and demonstrate that vaspin is a heparin-binding serpin. Noteworthily, we observed vaspin as a remarkably thermostable serpin and found that Glu(379) and Arg(302) influence heat-induced polymerization. These structural and functional results reveal the mechanistic basis of how reactive centre loop sequence and exosite interaction in vaspin enable KLK7 recognition and regulate protease inhibition as well as stability of this adipose tissue-derived serpin.