Differences between the Glycosylation Patterns of Haptoglobin Isolated from Skin Scales and Plasma of Psoriatic Patients

Abstract

Improved diagnosis of psoriasis, by new biomarkers, is required for evaluating the progression rate of the disease and the response to treatment. Haptoglobin (Hpt), a glycoprotein secreted by hepatocytes and other types of cells including keratinocytes, was found with glycan changes in psoriasis and other diseases. We previously reported that Hpt isolated from plasma of psoriatic patients is more fucosylated than Hpt of healthy subjects. The aim of this study was to compare the glycosylation pattern of Hpt isolated from skin scales or plasma of patients with psoriasis with that of Hpt from cornified epidermal layer or plasma of healthy subjects. High performance liquid chromatography analysis of the glycans isolated from the protein backbone revealed that glycan patterns from skin and plasma of patients were similar, and mostly displayed quantitative rather than qualitative differences from normal pattern. Biotin-labeled lectins were used to evaluate quantitative differences in the glycoforms of Hpt from plasma and psoriatic skin scales. Hpt from skin and plasma of patients showed more fucosylated and branched glycans than Hpt from plasma of healthy subjects. Tryptic glycopeptides of Hpt were also analyzed by mass spectrometry, and a decreased amount of sialylated glycan chains was found in glycopeptides of skin Hpt, as compared with Hpt from plasma. High levels of glycans with fucosylated and tetra-antennary chains were detected on the peptide NLFLNHSENATAK from Hpt of psoriatic patients. Our data demonstrate that specific changes in glycan structures of Hpt, such as enhanced glycan branching and fucose content, are associated with psoriasis, and that differences between circulating and skin Hpt do exist. A lower extent of glycan fucosylation and branching was found in Hpt from plasma of patients in disease remission. Altered glycoforms might reflect changes of Hpt function in the skin, and could be used as markers of the disease.

Acute phase proteins as promising biomarkers: Perspectives and limitations for human and veterinary medicine

“…Hpt is differentially fucosylated by different cancer cell lines, similar to the predominantly circulating Hpt homologs . Moreover, in psoriasis plasma, Hpt glycoforms have been identified that are very similar to glycoforms isolated from psoriatic skin samples . In accordance with these results, we could identify not one but several altered species of Hpt in psoriatic serum, differing in molecular weight and isoelectric point and in the direction of alteration .…”

Understanding the role of haptoglobin in psoriasis: effects of ultraviolet B

“…In addition, in a previous study, we found that Hp in patients with psoriasis had specific and more abundant glycans compared with Hp from healthy controls, which might be associated with disease activity . In the current study, we assessed the specific changes in Hp glycan structures associated with psoriasis, and the differences between circulating and cutaneous Hp …”

“…In addition, Hp has been reported to be a potent T‐cell immunosuppressor . We previously investigated the role of Hp in the pathogenesis of psoriasis, and found that this protein displays some structural modifications potentially associated with protein function in the disease . In addition, in a previous study, we found that Hp in patients with psoriasis had specific and more abundant glycans compared with Hp from healthy controls, which might be associated with disease activity .…”

The intricacy of biomarker complexity–the identification of a genuine proteomic biomarker is more complicated than believed

“…Translated into the terms of preclinical searches for proteomic biomarker, the protein altered in disease and identified by mass spectrometry very probably applies only to part of the total number of all proteoforms related to the peptides identified. This is shown impressively and discussed, for example, for splice variants , for glycoforms of apo‐lipoproteins , and of acute phase proteins . Such variants can be detected after pre‐fractionation of proteins with intact mass and by lysine counts , by pI‐variants , and by western blots .…”