Human proximal tubule cells form functional microtissues.

The epithelial cells lining the proximal tubules of the kidney mediate complex transport processes and are particularly vulnerable to drug toxicity. Drug toxicity studies are classically based on two-dimensional cultures of immortalized proximal tubular cells. Such immortalized cells are dedifferentiated, and lose transport properties (including saturable endocytic uptake) encountered in vivo. Generating differentiated, organotypic human microtissues would potentially alleviate these limitations and facilitate drug toxicity studies. Here, we describe the generation and characterization of kidney microtissues from immortalized (HK-2) and primary (HRPTEpiC) human renal proximal tubular epithelial cells under well-defined conditions. Microtissue cultures were done in hanging drop GravityPLUS™ culture plates and were characterized for morphology, proliferation and differentiation markers, and by monitoring the endocytic uptake of albumin. Kidney microtissues were successfully obtained by co-culturing HK-2 or HRPTEpiC cells with fibroblasts. The HK-2 microtissues formed highly proliferative, but dedifferentiated microtissues within 10 days of culture, while co-culture with fibroblasts yielded spherical structures already after 2 days. Low passage HRPTEpiC microtissues (mono- and co-culture) were less proliferative and expressed tissue-specific differentiation markers. Electron microscopy evidenced epithelial differentiation markers including microvilli, tight junctions, endosomes, and lysosomes in the co-cultured HRPTEpiC microtissues. The co-cultured HRPTEpiC microtissues showed specific uptake of albumin that could be inhibited by cadmium and gentamycin. In conclusion, we established a reliable hanging drop protocol to obtain functional kidney microtissues with proximal tubular epithelial cell lines. These microtissues could be used for high-throughput drug and toxicology screenings, with endocytosis as a functional readout.

Engineering melanoma progression in a humanized environment in vivo.

To overcome the lack of effective therapeutics for aggressive melanoma, new research models closely resembling the human disease are required. Here we report the development of a fully orthotopic, humanized in vivo model for melanoma, faithfully recapitulating human disease initiation and progression. To this end, human melanoma cells were seeded into engineered human dermo-epidermal skin substitutes. Transplantation onto the back of immunocompromised rats consistently resulted in the development of melanoma, displaying the hallmarks of their parental tumors. Importantly, all initial steps of disease progression were recapitulated, including the incorporation of the tumor cells into their physiological microenvironment, transition of radial to vertical growth, and establishment of highly vascularized, aggressive tumors with dermal involvement. Because all cellular components can be individually accessed using this approach, it allows manipulation of the tumor cells, as well as of the keratinocyte and stromal cell populations. Therefore, in one defined model system, tumor cell-autonomous and non-autonomous pathways regulating human disease progression can be investigated in a humanized, clinically relevant context.