Tissue-specific expression and alternative splicing of fibroblast activation protein alpha (FAPα) gene in human stromal cells

BACKGROUND: Activated stromal cells, responsible for tissue repair and restoration of tissue integrity, play an important role in tissue response to damage. The key marker of activated stromal cells is the fibroblast activation protein α (FAPα), which is apparently involved in the regulation of stromal cell functions, especially in the development of fibrosis. However, It is poorly known about tissue differences in expression and possible splice variants of this protein in stromal cells. AIM: The aim is to establish the tissue specificity of FAPα expression, including the synthesis of alternative splicing products, in human stromal cells isolated from various sources. METHODS: The expression of individual sites encoding the functional domains of FAPα in human stromal cells isolated from five tissue sources differing in embryonic origin and reparative reactions to damage (skin, subcutaneous adipose tissue, orbital adipose tissue, lungs, endometrium) was analyzed by real-time polymerase chain reaction. The key profibrotic factor TGFβ was used to activate stromal cells. RESULTS: Low background expression of all RNA sequences encoding functional domains of FAPα responsible for protein configuration or for its enzymatic functions is noted in stromal cells from skin, lungs and adipose tissue. Their expression is significantly increased (2–2.5 times) upon induction of stromal cell activation by TGFβ. In endometrial mesenchymal stromal cell, the expression of these sites is extremely low and comparable to the level of expression in epithelial cells, which indicates the presence of tissue-specific expression of the FAPα gene in stromal cells. In all stromal cell lines, an increase in the relative expression level of the RNA sequence encoding the transmembrane domain of FAPα is observed. CONCLUSION: Thus, the obtained results suggest that the analyzed cell lines either lack alternative FAPα splicing, or manifest themselves with a very low probability when activated in the form of a relative increase in the expression of the gene region encoding the transmembrane domain of FAPα. Most probably, the studied stromal cells synthesize mRNA carrying all the original exons and encoding predominantly the complete FAPα protein, that includes all functional domains.