Generation of tubular superstructures by piling of renal stem/progenitor cells.

The aim of this study was to assess cell biological processes involved in kidney regeneration. Particular interest was focused on the development of renal stem/progenitor cells into structured tubules. To investigate this process, the availability of a powerful cell culturing system is important. One prerequisite is that embryonic tissue can be maintained for several weeks to observe the progression of tubule development under physiological and under pathological conditions. Additionally, a significant amount of tissue must be harvested to analyze the cellular processes involved in the formation of tubules. In the present experiments, it was demonstrated for the first time that the spatial development of tubules could be modulated by piling stem/progenitor cells derived from neonatal rabbit kidney. Isolated embryonic tissue was mounted inside a specific holder and covered by layers of polyester fleece to create an artificial interstitium. The tissue was cultured in a perfusion container for 13 days in a chemically defined Iscove's modified Dulbecco's medium containing aldosterone (1 x 10(7) M) as a tubulogenic factor. The spatial development of tubules was registered on whole-mount specimens and on cryosections labeled with lectins or tissue-specific antibodies. The experiments revealed that culturing renal stem/progenitor cells in one layer resulted in the development of numerous differentiated tubules lining one row. Increasing the layers of renal stem/progenitor cells by piling resulted in the formation of multiple tubules orientated in parallel rows. Consequently, this technique made it possible to pile renal stem/progenitor cells like bricks and experimentally extend the spatial environment for tubular growth. This novel technique is an important step toward the generation of renal superstructures urgently needed for biomedical research and kidney regeneration.