Browsing by Author "Herr, Christian"

MicroRNAs of the miR-34/449 family mediate cell cycle arrest and tumor suppression. Here we show that the expression of microRNA miR-449a, unlike its paralog miR-34a, is highly tissue specific and largely restricted to pulmonary and testicular tissue. MiR-449a levels in the murine lung are particularly high shortly before and after birth, coinciding with terminal differentiation of lung epithelia. Strikingly, miR-449a is upregulated by more than 1,000-fold when epithelial cells from human airways are lifted from a liquid environment to air, allowing them to undergo mucociliary differentiation. The induction of miR-449a occurs in parallel to its host gene CDC20B and the transcription factor FoxJ1. Exposure to tobacco smoke induces a moderate further increase in the levels of miR-449a, and also miR-34a, in differentiated airway epithelia. We propose that miR-449a can serve as an exquisitely sensitive and specific biomarker for the differentiation of bronchial epithelia. Moreover, miR-449a may actively promote mucociliary differentiation through its ability to block cell cycle progression, and it may conribute to a first line of defence against genotoxic stress by its proapoptotic functions.

Airway mucociliary regeneration and function are key players for airway defense and are impaired in chronic obstructive pulmonary disease (COPD). Using transcriptome analysis in COPD-derived bronchial biopsies, we observed a positive correlation between cilia-related genes and microRNA-449 (miR449). In vitro, miR449 was strongly increased during airway epithelial mucociliary differentiation. In vivo, miR449 was upregulated during recovery from chemical or infective insults. miR0449−/− mice (both alleles are deleted) showed impaired ciliated epithelial regeneration after naphthalene and Haemophilus influenzae exposure, accompanied by more intense inflammation and emphysematous manifestations of COPD. The latter occurred spontaneously in aged miR449−/− mice. We identified Aurora kinase A and its effector target HDAC6 as key mediators in miR449-regulated ciliary homeostasis and epithelial regeneration. Aurora kinase A is downregulated upon miR449 overexpression in vitro and upregulated in miR449−/− mouse lungs. Accordingly, imaging studies showed profoundly altered cilia length and morphology accompanied by reduced mucociliary clearance. Pharmacological inhibition of HDAC6 rescued cilia length and coverage in miR449−/− cells, consistent with its tubulin-deacetylating function. Altogether, our study establishes a link between miR449, ciliary dysfunction, and COPD pathogenesis.

Motile multiciliated cells (MCCs) have critical roles in respiratory health and disease and are essential for cleaning inhaled pollutants and pathogens from airways. Despite their significance for human disease, the transcriptional control that governs multiciliogenesis remains poorly understood. Here we identify TP73, a p53 homolog, as governing the program for airway multiciliogenesis. Mice with TP73 deficiency suffer from chronic respiratory tract infections due to profound defects in ciliogenesis and complete loss of mucociliary clearance. Organotypic airway cultures pinpoint TAp73 as necessary and sufficient for basal body docking, axonemal extension, and motility during the differentiation of MCC progenitors. Mechanistically, cross-species genomic analyses and complete ciliary rescue of knockout MCCs identify TAp73 as the conserved central transcriptional integrator of multiciliogenesis. TAp73 directly activates the key regulators FoxJ1, Rfx2, Rfx3, and miR34bc plus nearly 50 structural and functional ciliary genes, some of which are associated with human ciliopathies. Our results position TAp73 as a novel central regulator of MCC differentiation.