Bioengineering of the thyroid lobe: use of its stromal/vascular matrix as a scaffold for ex situ reconstruction.

Regenerative medicine of endocrine glands is one of the newest fields in biomedical research, and promises to become a primary strategy to treat a number of endocrine disorders. Using computational bioengineering we have recently suggested that the threedimensional (3D) geometry of the thyroid, stromal / vascular matrix may act as an epigenetic guidance for growth and differentiation of developing thyrocytes (1-3). To test this hypothesis, we have bioengineered ex situ (i.e. on the laboratory bench) a bioartificial rat thyroid lobe using its decellularized stromal/vascular matrix as a natural 3D scaffold, to be eventually recellularized with thyroid stem/precursor cells. Sprague-Dawley male rats (125- 225 g) were used as thyroid donors, and lobe matrixes were prepared using a N2 freezing / Trypsin-EDTA / Triton-deoxycholate processing. Test matrixes were made electrondense, and analyzed by microTC (Skyscan 1172) to define their architecture. Primary thyroid cells were isolated after 72 h in primary monolayer culture, whereas presence of ABCG2-positive stem/precursor elements was determined using Western blotting. Following rypsinization, 250 - 450 x 103 cells were harvested and dropped onto the empty follicular cavities of the inner matrix of single lobe halves for homing . Cultures were kept in static conditions up to 14 days. The recellularized matrixes were either fixed in aldheydes and analyzed with light, transmission, and scanning electron microscopy, or denaturated and processed for ABCG2 immunoblotting (polyclonal rabbit anti-human 1:2000, Cell Signalling). Culture supernatants were collected every 48 h for assessment of FT3 and FT4 by immuno-chemiluminescence (Beckman-Coulter). Complete decellularization and maintenance of the 3D native architecture of the lobe matrix were achieved. Thyroid-derived cells including thyrocytes, epithelialmesenchymal elements, and stem/precursors were found to migrate inside matrix septa, selfassemble like follicule, and recellularize the decellularized native follicular spaces. Thyroid hormone secretion occurred for at least 7 days. These results show that the 3D matrix of the rat thyroid may guide both differentiated and stem-like elements to self-assemble into functional follicular units, up to the lobar recellularization. This raises the possibility that a bioartificial, immuno-tolerant thyroid gland be bioengineered ex situ using autologous stem cells, and eventually transplanted.