Proteomic Profiling of Tears in Blau Syndrome Patients in Identification of Potential Disease Biomarkers

Abstract

Blau syndrome (BS) is a rare autoinflammatory granulomatosis characterized by granulomatous arthritis, uveitis, and dermatitis. Ocular complications are particularly severe in BS, significantly contributing to morbidity. This study aims to identify potential biomarkers for BS ocular degeneration through proteomic profiling of tear samples from affected patients. Seven subjects from the same family, including four carriers of the BS-associated NOD2 mutation (p.E383K), were recruited alongside healthy controls. Tear samples were collected using Schirmer strips and analyzed via mass spectrometry. A total of 387 proteins were identified, with significant differences in protein expression between BS patients, healthy familial subjects, and healthy controls. Key findings include the overexpression of alpha-2-macroglobulin (A2M) and immunoglobulin heavy constant gamma 4 (IGHG4) in BS patients. Bioinformatic analysis revealed that differentially expressed proteins are involved in acute-phase response, extracellular exosome formation, and protein binding. Notably, neutrophils' azurophilic granule components, as azurocidin (AZU1), myeloperoxidases (MPO), and defensins (DEFA3), were highly expressed in the most severely affected subject, suggesting a potential role of neutrophils in BS ocular severity. These proteins might be promising biomarkers for ocular involvement in BS, facilitating early detection and tailored treatment strategies.

Keywords: Blau syndrome; autoinflammatory disease; biomarkers; proteomics; tear fluids; uveitis.

Figure 1

Ophthalmological evaluation of both left and right eyes of BS patients I1 and II1 with abnormal features.

Figure 2

Volcano plots of differentially abundant proteins between BS-affected patients and unaffected familial subjects (plot A) or BS-patients and healthy controls (plot B). Positive values (on the right of each plot) on x-axis indicate higher expression, while negative values on the left suggest decreased expression. Significant data points above the p-value threshold (red dotted line) are considered statistically significant and highlighted in red. The green dotted lines bound the minimal fold-change for the most-differentially-expressed genes.

Figure 3

Volcano plots of differentially abundant proteins between I1 and II1 (plot A), I1 and III1-2 (plot C), and II1 and III1-2 (plot B). Positive values (on the right of each plot) on x-axis indicate higher expression, while negative values on the left suggest decreased expression. Significant data points above the p-value threshold (red dotted line) are considered statistically significant and highlighted in red. The green dotted lines bound the minimal fold change for the most-differentially-expressed genes.

Figure 4

STRING network analysis of the proteins identified as significantly different between BS-affected patients and unaffected familial subjects. Lines connecting the different nodes represent functional and/or physical interactions.

Figure 5

STRING network analysis of the proteins identified as significantly different between BS-affected patients and healthy controls. Lines connecting the different nodes represent functional and/or physical interactions.

Figure 6

Representation of the familial transmission of BS in the patient group considered in the study. The p.E383K mutation in the NACHT domain of NOD2 gene is present in patients I1, II1, III1, and III2, confirmed by genetic analysis. Family tree modified from [2].