Globale Expressionsprofile Pneumokokken-infizierter Bronchialepithelzellen - Einfluss der miRNA-3135b und des Nicotinamidstoffwechselweges auf die bakterielle Replikation

Streptococcus pneumoniae, the pneumococcus, is a gram‐positive bacterium that colonizes the human nasopharynx as a commensal, in most cases asymptomatically, but can also cause severe diseases, including sepsis or meningitis. Pneumococci are major pathogens of human pneumonia, causing millions of death each year worldwide. Furthermore, co‐infections with Influenza A viruses can worsen the disease. Increasing abundance of antibiotics resistance makes treatment more and more difficult. The epithelial cells of the human respiratory tract are the first line of defense against the infection. However, many aspects of the interaction between epithelial cells and S. pneumoniae have not been fully elucidated yet. To analyze this interaction in detail, an expression profile of mRNAs, proteins and miRNAs of infected bronchial epithelial cells has been created. In addition, a co‐infection model in human ex vivo lung tissue was investigated for comparison. Pathway analysis of the infected epithelial cells revealed an up‐regulation of cell cycle associated molecules at 16 h post infection. Linking of the data with the miRNA profile revealed mainly known interaction partners. However, treatment‐dependent expression patterns of miRNAs have been detected, which revealed miRNAs specifically induced by S. pneumoniae, but not isolated TLR2‐ligation, such as miRNA‐3135b. Overexpression of miRNA‐3135b resulted in a significant reduction in pneumococcal load, suggesting involvement of a defense mechanism of epithelial cells. In addition, RNA sequencing after miRNA‐3135b overexpression revealed various putative target mRNAs, whose functions are currently only partially known. It is currently still under investigation if miRNA‐3135b is a bona fide miRNA or a t‐RNA‐derived fragment (tRF). Furthermore, functional analyses of regulated mRNAs and proteins indicated involvement of the nicotinamide metabolism. In epithelial cells, depletion of NAMPT, the key enzyme of this pathway, resulted in a reduced replication of S. pneumoniae. Moreover, the addition of nicotinamide mononucleotide (NMN) caused an increased rate of bacterial replication. This suggests NMN might be an important nutrient source of pneumococci. The data from this work extends the understanding of the interaction of human epithelial cells and pneumococci, and might be useful for the identification of alternative or adjuvant therapeutic strategies.