The Johns Hopkins University
How Tight Junctions Form Selective Barriers
Tight junctions have the instrumental task of being paracellular gatekeepers between all epithelial and endothelial cells throughout the body. Thus, they are critical for maintaining organ microenvironments and forming protective barriers. Naturally, tight junctions are prime points for pathogen entry, and dysregulation, depending on the tissue, leads to cancers, neurodegeneration, visual impairment, gastrointestinal distress, and breathing impairment.
The tight junction barriers are paracellular channels defined by strands of transmembrane claudin polymers contributed by each cell at the junction. Claudins are anchored in the tight junction by cytosolic scaffolding proteins and other transmembrane factors. It is proposed that over 40 unique proteins contribute to the overall assembly, architecture, and function of tight junctions. Despite the wealth of knowledge on the role of tight junctions in human physiology, many key mechanistic questions remain: How do paracellular channels function? How do the components assemble into a tight junction? What is the overall tight junction architecture? How do pathogens exploit tight junction components for entry?
These questions are fundamental barriers in understanding the major barrier forming structures in all our organs, as well as an obstacle in therapeutic and diagnostic design. We are addressing these critical questions by using a combination of biochemical and biophysical techniques. We will determine the molecular mechanism of tight junction function at paracellular channels, elucidate the basis of tight junction assembly, and develop the atomistic basis tight junction architecture. We will uncover tight junctions in unprecedented detail using single-particle cryo-electron microscopy, cryo-electron tomography, molecular modelling, fluorescent imaging, fluorescence-based size exclusion chromatography, and single molecule pulldown.
In short, these approaches will allow us to understand tight junction biology in unprecedented detail. Our research will allow us to understand the building blocks of the major epithelial and endothelial barriers in our bodies and provide new foundations for in silico design of therapeutics, antivirals, and diagnostics.