Keratin expression in discoid lupus erythematosus

Discovery of Novel Circulating Immune Complexes in Lupus Nephritis Using Immunoproteomics

Objective

The goal is to discover novel circulating immune complexes (ICx) in the serum of lupus nephritis (LN) as potential biomarkers.

Methods

Protein A/G magnetic beads or C1q-coated plates were used to capture ICx in the serum of LN, followed by the identification of immunoglobulin-binding proteins using liquid chromatography and tandem mass spectrometry (LC-MS/MS). Bioinformatic approaches and single-cell RNA sequencing (scRNA Seq) databases were used to select potential candidate ICx markers in LN. The selected ICx markers were further validated using ELISA.

Results

A total of 300 immunoglobulin-binding proteins were discovered in the screening, among which 77 proteins were detectable only in LN samples. Bioinformatics-assisted selection allowed us to further identify 10 potential immunoglobulin-binding proteins, which form ICx as potential biomarkers in LN. In a validation cohort of 62 LN patients and 21 healthy controls (HC), we found that prolyl 3-hydroxylase 1 (P3H1), phosphatase and actin regulator 4 (PHACTR4), and regulator of G-protein signaling 12 (RGS12) ICx exhibited discriminative capability in distinguishing LN from HC, with an area under the curve (AUC) values of 0.82, 0.99, and 0.90, respectively. Furthermore, a biomarker panel comprising CD14, CD34, cystatin A, myocyte enhancer factor 2C (MEF2C), RGS12, and ubiquitin C (UBC) ICx could distinguish active LN from inactive LN with an AUC value of 0.85, which is comparable to or better than pathological parameters such as renal activity index (AI) and renal chronicity index (CI).

Conclusion

Immunoproteomics-based discovery studies have enabled us to identify circulating immune complexes as potential biomarkers of LN.

Comparative proteomics analysis of cytokeratin and involucrin expression in lesions from patients with systemic lupus erythematosus

To get a better understanding of the abnormal differentiation or maturation of keratinocytes, we studied the expression and distribution of cytokeratin and involucrin in lesions from systemic lupus erythematosus patients. Two groups of 10 specimens each from systemic lupus erythematosus and normal controls were analyzed by two-dimensional gel electrophoresis, mass spectrometric protein identification, Western blotting and immunohistochemistry. Our results showed that keratin 1 (K1)/K10 together with the new synthesis of K6/K16 were down-regulated and that K5/K14, K2e and involucrin were up-regulated. We found that involucrin was strongly stained in lower epidermal cell layers while K1/10 was weakly stained, particularly when compared with staining in normal epidermis. Additionally, we found that the expression of involucrin was increased. These results imply an aberrant early and terminal differentiation stage in the epidermis of systemic lupus erythematosus, which may be associated with inflammatory cytokines released during the wound healing response of lesion.