| Popis: |
Acute kidney injury (AKI) is a very frequent and challenging clinical problem associated with high morbidity and mortality, and can be triggered e.g. by hypoxic or toxic damage of the kidney. Other than dialysis, there is currently no therapeutic intervention to improve the survival of AKI patients. Therefore, there is an urgent medical need to identify novel therapeutic approaches for the treatment of AKI. In contrast to other epithelial organs such as the intestine or skin, the kidney lacks a functionally relevant stem cell compartment. Therefore, kidney repair after damage depends on surviving renal tubular epithelial cells (rTECs), which dedifferentiate, proliferate, replace lost cells, and finally re-differentiate to become mitotically quiescent again. This property of epithelial cells to tune their differentiation state is known as “cellular plasticity”. A targeted modulation of cellular plasticity could open new therapeutic avenues for AKI. However, the molecular mechanisms underlying cellular plasticity in the kidney have remained elusive. The glucocorticoid receptor (GR) is an almost ubiquitously expressed receptor for cortisol and other glucocorticoids (GCs). Upon ligand binding, the GR translocates to the nucleus, where it acts as a transcription factor to regulate the expression of genes controlling immune responses and metabolism. Due to their immunosuppressive functions, GCs are frequently administered as a treatment of AKI. However, the direct effects of GCs on rTECs are largely unclear. In particular, it is unknown whether activation of the GR by GCs plays a role in cellular plasticity of the kidney tubular epithelium. The elucidation of the molecular mechansisms controlling plasticity of rTECs has been hampered by the lack of biologically revelant in vitro systems amenable to experimental manipulation. Therefore, in this thesis, three-dimensional kidney organoids, so-called tubuloids, were generated from primary kidney tissue of mice and humans, and tested for their potential to serve as a model system for AKI-induced cellular plasticity. Indeed, following hypoxic or toxic damage, renal tubuloids underwent a dedifferentiation-redifferentiation sequence with characteristic morphological and molecular changes. This novel organoid model system was then employed to assess the significance of the GR for cellular plasticity. Pharmacological experiments showed that an activation of the GR by dexamethasone significantly delayed the dedifferentiation-redifferentiation sequence and aggravated cellular injury, while genetic inactivation of the GR rendered kidney organoids more resistant to stress. Mechanistically, this thesis provides evidence that GR signaling inhibits epithelial plasticity by suppressing the Wnt/β-catenin and mTOR pathways as well as cellular energy production. In summary, the results of this thesis establish kidney organoids as a model system to study cellular plasticity of the renal tubular epithelium. Moreover, the data of this thesis identify the glucocorticoid receptor as a central negative regulator of injury-induced plasticity of rTECs. |
