Although stem cells are a promising avenue for harnessing the potential of adipose tissue, conventional two-dimensional (2D) culture methods have limitations. This study explored the use of three-dimensional (3D) cultures to preserve the regenerative potential of adipose-derived stem cells (ADSCs) and investigated their cellular properties. Flow cytometric analysis revealed significant variations in surface marker expressions between the two culture conditions. While 2D cultures showed robust surface marker expressions, 3D cultures exhibited reduced levels of CD44, CD90.2, and CD105. Adipogenic differentiation in 3D organotypic ADSCs faced challenges, with decreased organoid size and limited activation of adipogenesis-related genes. Key adipocyte markers, such as lipoprotein lipase (LPL) and adipoQ, were undetectable in 3D-cultured ADSCs, unlike positive controls in 2D-cultured mesenchymal stem cells (MSCs). Surprisingly, 3D-cultured ADSCs underwent mesenchymal–epithelial transition (MET), evidenced by increased E-cadherin and EpCAM expression and decreased mesenchymal markers. This study highlights successful ADSC organoid formation, notable MSC phenotype changes in 3D culture, adipogenic differentiation challenges, and a distinctive shift toward an epithelial-like state. These findings offer insights into the potential applications of 3D-cultured ADSCs in regenerative medicine, emphasizing the need for further exploration of underlying molecular mechanisms.

In our previous study, adipose-derived stem cells (ASCs) cultured in a three-dimensional (3D) organotypic system exhibited mesenchymal-to-epithelial transition (MET) features, including cobblestone morphology and increased expression of E-cadherin and CK18. In this study, we investigated whether ionizing radiation could reverse this phenotype via epithelial–mesenchymal transition (EMT) and examined the involvement of Notch signaling. Mouse ASCs were cultured in Matrigel-based 3D organotypic conditions and exposed to 8 Gy of γ-radiation, and EMT- and Notch-related gene and protein expression were assessed 96 h post-irradiation using ATP viability assays, RT-qPCR, and Western blotting. Exposure to 8 Gy significantly reduced cell viability in 2D ASCs to 49.50 ± 6.50% compared with 61.02 ± 5.77% in 3D organoids (p < 0.0001). Irradiated 3D organoids showed EMT-like changes, including an increase of ~2.5-fold in fibronectin and an increase of ~2.0-fold in Twist1 expression, while epithelial CK18 was modestly elevated. Notch signaling was concurrently activated, with Notch1 and Jagged1 increasing by more than twofold and Fra-1 being significantly upregulated. Pretreatment with 20 μM of the γ-secretase inhibitor (GSI) kept cell viability above 90% and suppressed radiation-induced fibronectin, Twist1, Notch1, and Jagged1 expression. These findings indicate that ionizing radiation promotes EMT in 3D-cultured ASCs and reverses prior epithelialization, with Notch signaling playing a key regulatory role. The 3D ASC organoid model may thus provide a physiologically relevant platform for investigating radiation-induced plasticity and potential antifibrotic interventions.