Analysis of human lung mast cells by single cell RNA sequencing

Abstract

Mast cells are tissue-resident cells playing major roles in homeostasis and disease conditions. Lung mast cells are particularly important in airway inflammatory diseases such as asthma. Human mast cells are classically divided into the subsets MCT and MCTC, where MCT express the mast cell protease tryptase and MCTC in addition express chymase, carboxypeptidase A3 (CPA3) and cathepsin G. Apart from the disctintion of the MCT and MCTC subsets, little is known about the heterogeniety of human lung mast cells and a deep analysis of their heterogeniety has previously not been performed. We therefore performed single cell RNA sequencing on sorted human lung mast cells using SmartSeq2. The mast cells showed high expression of classical mast cell markers. The expression of several individual genes varied considerably among the cells, however, no subpopulations were detected by unbiased clustering. Variable genes included the protease-encoding transcripts CMA1 (chymase) and CTSG (cathepsin G). Human lung mast cells are predominantly of the MCT subset and consistent with this, the expression of CMA1 was only detectable in a small proportion of the cells, and correlated moderately to CTSG. However, in contrast to established data for the protein, CPA3 mRNA was high in all cells and the correlation of CPA3 to CMA1 was weak.

Detection of Mast Cells in Human Superficial Fascia

“…Further studies should add some controls with normal BMI range, to avoid alterations of the superficial fascia tissue of obese patients; however, we decided to not consider the possibility to collect samples from cadavers because mast cells can degranulate during the conservation methods. Furthermore, future studies will shed light on the content of the granules of mast cells; a further analysis will be fundamental for the classification of these mast cells into the two classical subsets, tryptase-positive and chymase-positive [40]. This characterization will permit a better comprehension of their role and function and of the activated pathways in the superficial fascial tissue.…”