Granule Leakage Induces Cell-Intrinsic, Granzyme B-Mediated Apoptosis in Mast Cells

Sabrina Sofia Burgener; Melanie Brügger; Nathan Georges François Leborgne; Sophia Sollberger; Paola Basilico; Thomas Kaufmann; Phillip Ian Bird; Charaf Benarafa

doi:10.3389/fcell.2021.630166

Granule Leakage Induces Cell-Intrinsic, Granzyme B-Mediated Apoptosis in Mast Cells

Front Cell Dev Biol. 2021 Nov 8:9:630166. doi: 10.3389/fcell.2021.630166. eCollection 2021.

Authors

Sabrina Sofia Burgener^{1

2}, Melanie Brügger^{1

2

3}, Nathan Georges François Leborgne^{1

2}, Sophia Sollberger^{1

2}, Paola Basilico^{3

4}, Thomas Kaufmann⁵, Phillip Ian Bird⁶, Charaf Benarafa^{1

2}

Affiliations

¹ Institute of Virology and Immunology (IVI), Mittelhäusern, Switzerland.
² Department of Infectious Diseases and Pathobiology, Vetsuisse Faculty, University of Bern, Bern, Switzerland.
³ Graduate School for Cellular and Biomedical Science, University of Bern, Bern, Switzerland.
⁴ Theodor Kocher Institute, Department of Preclinical Medicine, Faculty of Medicine, University of Bern, Bern, Switzerland.
⁵ Institute of Pharmacology, Department of Preclinical Medicine, Faculty of Medicine, University of Bern, Bern, Switzerland.
⁶ Department of Biochemistry and Molecular Biology, Monash Biomedicine Discovery Institute, Monash University, Clayton, VIC, Australia.

Abstract

Mast cells are multifunctional immune cells scattered in tissues near blood vessels and mucosal surfaces where they mediate important reactions against parasites and contribute to the pathogenesis of allergic reactions. Serine proteases released from secretory granules upon mast cell activation contribute to these functions by modulating cytokine activity, platelet activation and proteolytic neutralization of toxins. The forced release of granule proteases into the cytosol of mast cells to induce cell suicide has recently been proposed as a therapeutic approach to reduce mast cell numbers in allergic diseases, but the molecular pathways involved in granule-mediated mast cell suicide are incompletely defined. To identify intrinsic granule proteases that can cause mast cell death, we used mice deficient in cytosolic serine protease inhibitors and their respective target proteases. We found that deficiency in Serpinb1a, Serpinb6a, and Serpinb9a or in their target proteases did not alter the kinetics of apoptosis induced by growth factor deprivation in vitro or the number of peritoneal mast cells in vivo. The serine protease cathepsin G induced marginal cell death upon mast cell granule permeabilization only when its inhibitors Serpinb1a or Serpinb6a were deleted. In contrast, the serine protease granzyme B was essential for driving apoptosis in mast cells. On granule permeabilization, granzyme B was required for caspase-3 processing and cell death. Moreover, cytosolic granzyme B inhibitor Serpinb9a prevented caspase-3 processing and mast cell death in a granzyme B-dependent manner. Together, our findings demonstrate that cytosolic serpins provide an inhibitory shield preventing granule protease-induced mast cell apoptosis, and that the granzyme B-Serpinb9a-caspase-3 axis is critical in mast cell survival and could be targeted in the context of allergic diseases.

Keywords: cell death; granzyme B; lysosomal peptidases; lysosomal permeabilization; mast cells; serine protease; serpins.