Increased Cathepsin S activity associated with decreased protease inhibitory capacity contributes to altered tear proteins in Sj\xf6gren\u2019s Syndrome patients

Maria C Edman,Martin Heur,William Stohl,Neha Teekappanavar,Chongiin Kim,Arunava Sarma,Sarah F Hamm-Alvarez,Zhen Meng,Wendy J Mack,Simranjit Singh,Stratos Christianakis,Alice Y Kim,Luke Naman,Alexander F Chen,Daniel G Arkfeld,Mercy Bechtold,Srikanth R Janga,Elizabeth Ortiz,Sara Madrigal

doi:10.1038/s41598-018-29411-9

Abstract

Cathepsin S (CTSS) activity is elevated in Sjögren’s Syndrome (SS) patient tears. Here we tested whether protease inhibition and cystatin C (Cys C) levels are reduced in SS tears, which could lead to enhanced CTSS-driven degradation of tear proteins. CTSS activity against Cys C, LF and sIgA was tested in SS or healthy control tears. Tears from 156 female subjects (33, SS; 33, rheumatoid arthritis; 31, other autoimmune diseases; 35, non-autoimmune dry eye (DE); 24, healthy controls) were analyzed for CTSS activity and Cys C, LF, and sIgA levels. Cys C and LF showed enhanced degradation in SS tears supplemented with recombinant CTSS, but not supplemented healthy control tears. CTSS activity was significantly increased, while Cys C, LF and sIgA levels were significantly decreased, in SS tears compared to other groups. While tear CTSS activity remained the strongest discriminator of SS in autoimmune populations, combining LF and CTSS improved discrimination of SS beyond CTSS in DE patients. Reductions in Cys C and other endogenous proteases may enhance CTSS activity in SS tears. Tear CTSS activity is reconfirmed as a putative biomarker of SS in an independent patient cohort while combined LF and CTSS measurements may distinguish SS from DE patients.

Highlights

Cathepsin S (CTSS) activity is elevated in Sjögren’s Syndrome (SS) patient tears
We demonstrate that CTSS, at activity levels found in tears of SS patients but not in tears of healthy controls, promotes degradation of two other abundant tear proteins, lactoferrin (LF) and secretory IgA, both of which play fundamental roles in ocular defense against pathogens[19,20,21]
Immunofluorescence analysis of cystatin C (Cys C) confirmed its weaker expression in NOD mouse lacrimal glands (LG) (Fig. 1C), there was no difference in its gene expression (Fig. 1D), suggesting that the difference in its abundance could be due to increased degradation and/or decreased translation

Summary

Introduction

Cathepsin S (CTSS) activity is elevated in Sjögren’s Syndrome (SS) patient tears. Here we tested whether protease inhibition and cystatin C (Cys C) levels are reduced in SS tears, which could lead to enhanced CTSS-driven degradation of tear proteins. Tears from 156 female subjects (33, SS; 33, rheumatoid arthritis; 31, other autoimmune diseases; 35, non-autoimmune dry eye (DE); 24, healthy controls) were analyzed for CTSS activity and Cys C, LF, and sIgA levels. CTSS is an intriguing protein with functions linked to inflammation including regulation of major histocompatibility complex class II-mediated antigen presentation[6,7]. It has important functions in extracellular matrix degradation[8] and activation of the protease activated receptor 29 which mediates inflammatory pain[10,11], triggering cytokine production and itchiness[12]. Proteoglygan 4/lubricin, a glycoprotein important for lubrication and smooth movement of the eyelids, is degraded by tear CTSS14

Methods

Results

Conclusion