Cartilage rings contribute to the proper embryonic tracheal epithelial differentiation, metabolism and expression of inflammatory genes. Mus musculus

The signaling crosstalk between the tracheal mesenchyme and epithelium has not been researched extensively leaving a substantial gap of knowledge in the mechanisms dictating embryonic development of the proximal airways by the adjacent mesenchyme. Recently, we have reported that embryos lacking mesenchymal expression of Sox9 did not develop tracheal cartilage rings and showed aberrant differentiation of the tracheal epithelium. Herein, we propose that tracheal cartilage provides local inductive signals responsible for the proper differentiation, metabolism, and inflammatory status regulation of the tracheal epithelium. The tracheal epithelium of mesenchyme-specific Sox9D/D mutants showed altered mRNA expression of various epithelial markers such as Pb1fa1, Sftpb, Scgb1a1, and Tff-1. In vitro tracheal epithelial cell cultures confirmed that tracheal chondrocytes secrete factors that inhibit club cell differentiation. Whole gene expression profiling and ingenuity pathway analysis showed that the TNF-a, IFN-g and TGF-b signaling pathways were significantly altered in the Sox9 mutant trachea. Tnf-a and Ifn-g interfered with the differentiation of tracheal epithelial progenitor cells into mature epithelial cell types in vitro. Meanwhile, mesenchymal knockout of Tgf-b1 in vivo resulted in altered differentiation of the tracheal epithelium. Finally, mitochondrial enzymes involved in fat and glycogen metabolism Cox8b and Cox7a1 were strongly up-regulated in the Sox9 mutant trachea, with consequently increased number and size of glycogen storage vacuoles. Our results support an a role for tracheal cartilage in the modulation of the differentiation and metabolism, and the expression of inflammatory related genes in the tracheal epithelium by feeding into the TNF-a, IFN-g and TGF-b signaling pathways. Overall design: E18.5 lung tracheas were used. RNA was extracted from a pool of three tracheas to get sufficient good quality RNA for expression analysis. Three mutant trachea pools and 3 control tracheal pools were used. The total of 9 mutants and 9 control embryonic tracheas were collected by 7 different pregnant females and randomly pooled together right before extracting the total RNA.