  A critical barrier in the nephrology field is the lack of appropriate in
vitro renal tubule models that allow manipulation of various mechanical
factors, facilitating studies of disease pathophysiology and drug discovery.
Here we report development of a novel in vitro assay system comprised of a
renal tubule within an elasto-plastic extracellular matrix microenvironment.
This in vitro tubule mimetic device consists of a container with two,
pipette-accessible ports, filament-deposition (3D-) printed into 35 mm cell
culture dishes. The container is filled with a hydrogel, such as a collagen I
or fibrin gel, while a narrow masking tube is threaded through the ports.
Following gelation, the masking material is pulled out leaving a tunnel within
the gel. Seeding of the tunnels with M1 or MDCK renal epithelial cells through
the side ports results in a monolayer with apical-basal polarity, such that
laminin and fibronectin are present on the basal surface, while primary cilia
project from the apical side of cells into the tubular lumen. The device is
optically accessible, and can be live-imaged by phase contrast or
epifluorescence microscopy. The lumen of the epithelial-lined tube can be
connected through the side ports to a circulatory flow. We demonstrate that
kidney epithelial cells are able to adjust the diameter of the model tubule by
myosin-II dependent contractility. Furthermore, cells of the tubule are also
able to remodel the surrounding hydrogel leading to budding from the main
tubule. We propose that this versatile in vitro model system can be developed
into a future pre-clinical tool to study pathophysiology of kidney diseases and
identify therapeutic compounds.
