Mice deficient of the survival factor Bcl-2 develop polycystic kidney disease (PKD) that is mediated via the pro-apoptotic BH3-only protein Bim. This indicates that apoptosis contributes to the disease, but the exact step controlled by apoptosis is unknown. Moreover, it has been unclear if other BH3-only proteins such as Puma participate in the process, and if apoptosis is also crucial for the emergence of the slowly progressing, late-onset autosomal dominant polycystic kidney disease (ADPKD) in humans caused by mutations in the Pkd1 gene encoding for polycystin-1 (PC1) in about 85% of all ADPKD patients. The aims of this proposal are to (i) identify if mitochondria-mediated apoptosis plays a role in cystogenesis and the development of PKD not only in mice deficient of Bcl-2, but also in mice conditionally lacking Pkd1 expression, (ii) unravel if and by which molecular mechanisms Bim and/or Puma contribute to apoptosis, cystogenesis and PKD in vivo and in vitro, and (iii) determine if apoptosis is a cause for or a consequence of diminished autophagy or enhanced proliferation associated with PKD. We will monitor several kidney indices to quantify abnormalities and perform immunofluorescence and electron microscopy to detect autophagy and cystogenesis. We will perform apoptosis assays and examine protein kinase signaling to investigate if PKD in our two mouse model systems is caused by the transcriptional induction of Bim (via Foxo3A, CHOP) or Puma (via p53, p73), or by phosphorylation of Bim by JNK1/2 and their upstream ROCK1 and MKK4/7 kinases, or by cAMP-dependent protein kinase A. Moreover, we will isolate and culture primary collecting duct (CD) cells from wild-type, Bcl-2-/- and conditional Pkd1-/- mice to unravel the causal link between anoikis-like apoptosis, proliferation and cystogenesis. Since GSK-3 inhibitors can ameliorate PKD in mice, we also want to know if GSK-3 contributes to PKD via Tip60-mediated Puma induction, degradation of the survival factor Mcl-1, or blockage of Wnt/β-catenin signaling. If apoptosis and/or autophagy are crucial regulators of PKD, our analysis will provide the basis to further explore the efficacy of caspase or GSK-3 inhibitors as therapeutic options in polycystic kidney disease.