The intestinal intermediate filament network responds to and protects against microbial insults and toxins

Abstract

The enrichment of intermediate filaments in the apical cytoplasm of intestinal cells is evolutionary conserved forming a sheath that is anchored to apical junctions and positioned below the microvillar brush border suggestive of a protective intracellular barrier function. To test this, we used C. elegans, whose intestinal cells are endowed with a particularly dense intermediate filament-rich layer that is referred to as the endotube. We find alterations in endotube structure and intermediate filament expression upon infection with nematicidal Bacillus thuringiensis or treatment with its major pore-forming toxin crystal protein Cry5B. Endotube impairment due to defined genetic mutations of intermediate filaments and their regulators results in increased Cry5B sensitivity as evidenced by elevated larval arrest, prolonged time of larval development and reduced survival. Phenotype severity reflects the severity of endotube alterations and correlates with reduced rescue upon toxin removal. The results provide in vivo evidence for a major protective role of a properly configured intermediate filament network as an intracellular barrier in intestinal cells. This notion is further supported by increased sensitivity of endotube mutants to oxidative and osmotic stress.