Proteinase 3 Interferes With C1q-Mediated Clearance of Apoptotic Cells.

Pascale Tacnet-Delorme,Véronique Witko-Sarsat,Simon Chatfield,Julie Gabillet,Philippe Frachet,Nathalie Thieblemont

doi:10.3389/fimmu.2018.00818

Abstract

Proteinase 3 (PR3) is the autoantigen in granulomatosis with polyangiitis, an autoimmune necrotizing vasculitis associated with anti-neutrophil cytoplasmic antibodies (ANCAs). Moreover, PR3 is a serine protease whose membrane expression can potentiate inflammatory diseases such as ANCA-associated vasculitis and rheumatoid arthritis. During apoptosis, PR3 is co-externalized with phosphatidylserine (PS) and is known to modulate the clearance of apoptotic cells through a calreticulin (CRT)-dependent mechanism. The complement protein C1q is one mediator of efferocytosis, the clearance of altered self-cells, particularly apoptotic cells. Since PR3 and C1q are both involved in the clearance of apoptotic cells and immune response modulation and share certain common ligands (i.e., CRT and PS), we examined their possible interaction. We demonstrated that C1q binding was increased on apoptotic rat basophilic leukemia (RBL) cells that expressed PR3, and we demonstrated the direct interaction between purified C1q and PR3 molecules as shown by surface plasmon resonance. To better understand the functional consequence of this partnership, we tested C1q-dependent phagocytosis of the RBL cell line expressing PR3 and showed that PR3 impaired C1q enhancement of apoptotic cell uptake. These findings shed new light on the respective roles of C1q and PR3 in the elimination of apoptotic cells and suggest a novel potential axis to explore in autoimmune diseases characterized by a defect in apoptotic cell clearance and in the resolution of inflammation.

Highlights

Proteinase 3 (PR3) is a neutrophil-derived serine protease located together with its homologs, human neutrophil elastase, and cathepsin G, in azurophilic granules as reviewed in Martin and Witko-Sarsat [1]
It has been proposed that PR3 can modulate apoptotic cell clearance [7] through a mechanism linked to the ability of PR3 to associate with calreticulin (CRT), a protein involved in apoptotic cell recognition and an important “eat-me” signal [8]
As it has been shown that PR3 expression on the neutrophil population is non-homogenous and is characterized by important interindividual variability, further experiments were conducted using the previously established rat basophilic leukemia (RBL) cell line that expresses PR3 at the cell surface during apoptosis [7]

Summary

Introduction

Proteinase 3 (PR3) is a neutrophil-derived serine protease located together with its homologs, human neutrophil elastase, and cathepsin G, in azurophilic granules as reviewed in Martin and Witko-Sarsat [1]. One particular feature of PR3 is its affinity for membranes leading to its surface expression on viable and apoptotic neutrophils [2]. PR3 and C1q Interaction Modulates Efferocytosis and apoptosis, membrane expression of PR3 increases, and soluble PR3 is released into the extracellular environment during degranulation [4]. PR3 is a pro-inflammatory factor whose membrane expression can potentiate chronic inflammatory diseases such as anti-neutrophil cytoplasmic antibodies (ANCAs) systemic vasculitis (AAV) and rheumatoid arthritis [5]. PR3 is co-externalized with phosphatidylserine (PS) via its association with phospholipid scramblase 1 [4]. It has been proposed that PR3 can modulate apoptotic cell clearance [7] through a mechanism linked to the ability of PR3 to associate with calreticulin (CRT), a protein involved in apoptotic cell recognition and an important “eat-me” signal [8]

Methods

Results

Conclusion