Anti-Inflammatory Action of Keratinocyte-Derived Vaspin: Relevance for the Pathogenesis of Psoriasis.

Impaired cross talk between keratinocytes (KCs) and immune cells is believed to contribute to the pathogenesis of chronic inflammatory skin diseases, such as psoriasis. We have previously identified KCs as a rich source of the serpin protease inhibitor vaspin (serpinA12), originally described as an adipokine in adipose tissue. Herein, we studied whether dysregulated vaspin expression in KCs contributes to the pathogenesis of psoriasis. We found vaspin expression to be closely associated to epidermal differentiation, with low levels in proliferating KCs and high levels in differentiated cells. Consistently, in human psoriasis and in a mouse model of a psoriasis-like skin inflammation, epidermal vaspin expression was significantly down-regulated. Down-regulation of vaspin in KCs resulted in decreased expression of differentiation-associated genes and up-regulation of interferon-inducible and inflammation-associated psoriasis signature genes. Vaspin was also shown to modulate the communication between KCs and inflammatory cells under co-culture conditions. A decrease in vaspin expression in KCs stimulated the secretion of tumor necrosis factor-α, IL-1ß, IL-6, IL-8, and monocyte chemoattractant protein-1 by co-cultured dendritic cells, macrophages, monocytes, and neutrophils. Consequently, the application of vaspin inhibited myeloid cell infiltration in a mouse model of a psoriasis-like skin inflammation. In conclusion, vaspin expression by maturing KCs modulates cutaneous immune responses and may be involved in the pathogenesis of psoriasis.

Crystal structure of cleaved vaspin (serpinA12).

The adipokine vaspin (serpinA12) is mainly expressed in white adipose tissue and exhibits various beneficial effects on obesity-related processes. Kallikrein 7 is the only known target protease of vaspin and is inhibited by the classical serpin inhibitory mechanism involving a cleavage of the reactive center loop between P1 (M378) and P1' (E379). Here, we present the X-ray structure of vaspin, cleaved between M378 and E379. We provide a comprehensive analysis of differences between the uncleaved and cleaved forms in the shutter, breach, and hinge regions with relation to common molecular features underlying the serpin inhibitory mode. Furthermore, we point out differences towards other serpins and provide novel data underlining the remarkable stability of vaspin. We speculate that the previously reported FKGx1Wx2x3 motif in the breach region may play a decisive role in determining the reactive center loop configuration in the native vaspin state and might contribute to the high thermostability of vaspin. Thus, this structure may provide a basis for future mutational studies.

A unique serpin P1' glutamate and a conserved ß-sheet C arginine are key residues for activity, protease recognition and stability of serpinA12 (vaspin).

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 ß-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 ß-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.

Vaspin inhibits kallikrein 7 by serpin mechanism.

The molecular target of the adipokine vaspin (visceral adipose tissue-derived serpin; serpinA12) and its mode of action are unknown. Here, we provide the vaspin crystal structure and identify human kallikrein 7 (hK7) as a first protease target of vaspin inhibited by classical serpin mechanism with high specificity in vitro. We detect vaspin-hK7 complexes in human plasma and find co-expression of both proteins in murine pancreatic ß-cells. We further demonstrate that hK7 cleaves human insulin in the A- and B-chain. Vaspin treatment of isolated pancreatic islets leads to increased insulin concentration in the media upon glucose stimulation without influencing insulin secretion. By application of vaspin and generated inactive mutants, we find the significantly improved glucose tolerance in C57BL/6NTac and db/db mice treated with recombinant vaspin fully dependent on the vaspin serpin activity and not related to vaspin-mediated changes in insulin sensitivity as determined by euglycemic-hyperinsulinemic clamp studies. Improved glucose metabolism could be mediated by increased insulin plasma concentrations 150 min after a glucose challenge in db/db mice, supporting the hypothesis that vaspin may inhibit insulin degradation by hK7 in the circulation. In conclusion, we demonstrate the inhibitory serpin nature and the first protease target of the adipose tissue-derived serpin vaspin, and our findings suggest hK7 inhibition by vaspin as an underlying physiological mechanism for its compensatory actions on obesity-induced insulin resistance.

Proteolytic activation of prochemerin by kallikrein 7 breaks an ionic linkage and results in C-terminal rearrangement.

The excessive accumulation of adipose tissue in obesity is associated with multiple inflammatory dermatological diseases. Chemerin, a chemoattractant adipokine, dependent on proteolytical activation, is highly expressed in skin. Different proteases have been reported to activate prochemerin, but none is inherently expressed in human skin. In the present study, we identified a tissue-specific protease and investigated the underlying mechanism of activation at the molecular level. We characterized human KLK7 (kallikrein 7) as a prochemerin processing protease in vitro converting prochemerin into active chemerinF(156). The activating truncation by the protease might trigger a structural rearrangement leading to an increased affinity of chemerin to CMKLR1 (chemokine-like receptor 1). Molecular modelling and experimental data suggest an underlying ionic interaction in prochemerin C-terminal domains. These findings provide a general molecular basis for the necessity of C-terminal processing of prochemerin. Moreover, immunohistochemistry was used to investigate prochemerin, KLK7 and the recently identified KLK7 inhibitor vaspin expression in human skin biopsies, and distinct co-localization in psoriatic biopsies was observed. On the basis of these results, it is hypothesized that KLK7 activity may contribute to the development of psoriatic lesions as a consequence of excessive chemerin activation and impaired protease activity regulation by vaspin. Therefore this interaction represents an interesting target for psoriasis therapy and treatment of other obesity-related diseases.

Chemerin and vaspin: possible targets to treat obesity?

Obesity is one of the main human epidemics today. The increase in fat accumulation, which is associated with obesity, may significantly change the expression of several bioactive molecules known as adipokines. These adipokines interact not only with adipose tissue, but also with metabolically relevant organs such as liver and muscle. Understanding the molecular basics of potential novel targets might help to improve the therapeutic treatment of people who suffer from obesity. Herein we summarize the state of the art of two novel adipokines and their impaired or protective action in obesity: chemerin and vaspin. Their expression patterns, signal transduction activity, and resulting functions within the human body are introduced. We also discuss various possibilities to target these adipokines, which may represent promising new targets for the treatment of obesity by small and synthetic compounds.