Quantitative In-Depth Analysis of the Mouse Mast Cell Transcriptome Reveals Organ-Specific Mast Cell Heterogeneity

Abstract

Mast cells (MCs) are primarily resident hematopoietic tissue cells that are localized at external and internal surfaces of the body where they act in the first line of defense. MCs are found in all studied vertebrates and have also been identified in tunicates, an early chordate. To obtain a detailed insight into the biology of MCs, here we analyzed the transcriptome of MCs from different mouse organs by RNA-seq and PCR-based transcriptomics. We show that MCs at different tissue locations differ substantially in their levels of transcripts coding for the most abundant MC granule proteins, even within the connective tissue type, or mucosal MC niches. We also demonstrate that transcript levels for the major granule proteins, including the various MC-restricted proteases and the heparin core protein, can be several orders of magnitude higher than those coding for various surface receptors and enzymes involved in protease activation, as well as enzymes involved in the synthesis of heparin, histamine, leukotrienes, and prostaglandins. Interestingly, our analyses revealed an almost complete absence in MCs of transcripts coding for cytokines at baseline conditions, indicating that cytokines are primarily produced by activated MCs. Bone marrow-derived MCs (BMMCs) are often used as equivalents of tissue MCs. Here, we show that these cells differ substantially from tissue MCs with regard to their transcriptome. Notably, they showed a transcriptome indicative of relatively immature cells, both with respect to the expression of granule proteases and of various enzymes involved in the processing/synthesis of granule compounds, indicating that care should be taken when extrapolating findings from BMMCs to the in vivo function of tissue-resident MCs. Furthermore, the latter finding indicates that the development of fully mature tissue-resident MCs requires a cytokine milieu beyond what is needed for in vitro differentiation of BMMCs. Altogether, this study provides a comprehensive quantitative view of the transcriptome profile of MCs resident at different tissue locations that builds nicely on previous studies of both the mouse and human transcriptome, and form a solid base for future evolutionary studies of the role of MCs in vertebrate immunity.

The Chymase Mouse Mast Cell Protease-4 Regulates Intestinal Cytokine Expression in Mature Adult Mice Infected with Giardia intestinalis

“…In contrast, the lack of chymase/mMCP-4 significantly reduced the infiltration of mast cells in the inflamed joint in a collagen-induced arthritis model [54], and in a model of bleomycin-induced lung inflammation, the mast cell numbers were increased in the mMCP-4 −/− mice [55]. In the mouse small intestine, the submucosal mast cell counts is normally very low (<1 mast cell per 100 villi) [56], and the low numbers of submucosal mast cells are confirmed by the low numbers of mast cell protease transcriptional reads ( [44] and Lars Hellman, personal communication). During infections with Giardia and other intestinal parasites, submucosal mast cell counts increase ( [23][24][25]57,58] and current study).…”

“…The chymase mMCP-4 is only significantly expressed by the connective tissue mast cells (CTMCs) (see reference [44] and Immgen.org), and the knockout of mMCP-4 did not affect the storage and expression of other mast cell proteases [45]. This stands in contrast to the knockout of mMCP-5, which affected the storage and activity of carboxypeptidase A3 [46] and vice versa, the knockout of CPA3 affected the storage and activity of mMCP-5 [47].…”

Protease profile of normal and neoplastic mast cells in the human bone marrow

“…About 5% of the genome encodes information on human MC proteases, and the protease mRNA content is comparable to the content of housekeeping genes transcripts. This re ects the high content of proteases in the cytoplasm of MC 7,15,[35][36][37][38][39] .…”

“…[3][4][5] . A special characteristic of the biology of MCs is the high presence of proteases in comparison with other immunocompetent cells 6,7 .…”

Novel Insight into the in vivo Function of Mast Cell Chymase: Lessons from Knockouts and Inhibitors

“…Chymases belong to the large family of serine proteases, and their expression is essentially unique to mast cells [11-13]. Mast cells can express high levels of chymase-encoding mRNA, previous findings having revealed that up to 2.5% of the total mRNA pool in mast cells can code for chymases [13, 14]. Notably, chymase expression in mast cells is constitutive and in most cases not affected to any major extent by mast cell activation [10].…”