Can lineage-specific markers be identified to characterize mesenchyme-derived cell populations in the human airways?

Abstract

Mesenchyme-derived cells in the airway wall including airway smooth muscle cells, fibroblasts, and myofibroblasts are known to play important roles in airway remodeling. The lack of specific phenotypical markers makes it difficult to define these cell populations in primary cultures. Most relevant studies to date have used animal airway tissues, vascular tissues, or transformed cell lines with only limited studies attempting to phenotypically characterize human airway mesenchymal cells. The objectives of this study were to evaluate reported markers and identify novel markers to define these cell types. We could not identify any specific marker to define these cell populations in vitro that permitted unequivocal identification using immunocytochemistry. However, characteristic filamentous alpha-smooth muscle actin distribution was observed in a significant ( approximately 25%) proportion of human airway smooth muscle cells, whereas this was not observed in airway fibroblasts. A significantly higher proportion of airway fibroblasts expressed alpha(1)- and alpha(2)-integrin receptors compared with human airway smooth muscle cells as assessed by fluorescence activated cell sorting. Global gene expression profiling identified aldo-keto reductase 1C3 (AKR1C3) and cathepsin K as being novel markers to define airway smooth muscle cells, whereas integrin-alpha(8) (ITGA8) and thromboxane synthase 1 (TBXAS1) were identified as novel airway fibroblast-specific markers, and these findings were validated by RT-PCR. Ex vivo studies in human airway tissue sections identified high-molecular weight caldesmon and alpha-smooth muscle actin as being expressed in smooth muscle bundles, whereas ITGA8 and TBXAS1 were absent from these.

The a“MAZE”ing World of Lung-Specific Transgenic Mice

“…There is still much disagreement over the numbers of different lung mesenchymal cell types and their best markers [136]. The challenge of the available mesenchymal mouse strains is that they are not lung-specific and that many of their expression patterns are highly variable depending on the integration of the transgene.…”

The building blocks of mammalian lung development

“…There is still no general consensus around the number of different differentiated mesenchymal cell types in the adult lung, or the molecular markers which can be used to distinguish between them. Indeed, a recent study of adult human lung mesenchymal cells suggests that no single molecular marker yet identified is specific for an individual mesenchymal cell type (Singh et al, 2010). This makes identification of the mesenchymal progenitor cells difficult, although progress has been made.…”

Clonally expanded human airway smooth muscle cells exhibit morphological and functional heterogeneity

“…The expression profile of these characteristic markers revealed some qualitative differences (see Table 1) with counter-intuitively, the slow-growing populations demonstrating increased levels of FSP and decreased levels of α- smooth muscle actin when compared with the fast-growing populations. We also investigated the expression of the novel mesenchymal cell markers identified in our previous work [11] in these clonal populations. Aldo-keto reductase 1 C3 (AKR1C3) expression could not be observed at detectable levels in either the fast- or slow-growing clonal cell populations (figure not shown).…”

“…Cells were cultured and immunostained using published methods [11]. Primary antibodies and concentrations used were: α-smooth muscle actin, 0.4 μg/ml; fibroblast surface protein, 0.4 μg/ml; aldo-keto reductase 1 (AKR1C3), 11 μg/ml (Sigma-Aldrich, Poole, UK); cathepsin K, 2.5 μg/ml (Abcam, Cambridge, UK); thromboxane synthase, 8 μg/ml (Proteintech, Manchester, UK); α8 integrin, 1 μg/ml (Insight Biotechnology, Wembley, UK).…”

“…Given the phenotypic heterogeneity which ASM cells can exhibit in vitro [11], we aimed to investigate the clonal origin of populations of cells in ASM in order to determine whether single cells were capable of clonal expansion and also to define how different resulting clones might be from each other and their parental cell in terms of morphology and function. Functional differences were investigated by assessing pro-relaxant and pro-contractile second messenger signaling pathways, namely β 2 -adrenoceptor-mediated cyclic AMP formation and bradykinin B1 and histamine H1 receptor-mediated inositol phosphate production respectively.…”