The class III phosphatidylinositol 3-kinase PIK3C3/VPS34 regulates endocytosis and autophagosome-autolysosome formation in podocytes.

Phosphatidylinositol phosphates are key regulators of vesicle identity, formation and trafficking. In mammalian cells, the evolutionarily conserved class III PtdIns 3-kinase PIK3C3/VPS34 is part of a large multiprotein complex that catalyzes the localized phosphorylation of phosphatidylinositol to phosphatidylinositol-3-phosphate (PtdIns3P). We demonstrate that PIK3C3 has a key function in vesicular trafficking, endocytosis and autophagosome-autolysosome formation in the highly specialized glomerular podocytes.

Vps34 deficiency reveals the importance of endocytosis for podocyte homeostasis.

The molecular mechanisms that maintain podocytes and consequently, the integrity of the glomerular filtration barrier are incompletely understood. Here, we show that the class III phosphoinositide 3-kinase vacuolar protein sorting 34 (Vps34) plays a central role in modulating endocytic pathways, maintaining podocyte homeostasis. In mice, podocyte-specific conditional knockout of Vps34 led to early proteinuria, glomerular scarring, and death within 3-9 weeks of age.

Molecular fingerprinting of the podocyte reveals novel gene and protein regulatory networks.

A thorough characterization of the transcriptome and proteome of endogenous podocytes has been hampered by low cell yields during isolation. Here we describe a double fluorescent reporter mouse model combined with an optimized bead perfusion protocol and efficient single cell dissociation to yield more than 500,000 podocytes per mouse allowing for global, unbiased downstream applications. Combining mRNA and miRNA transcriptional profiling with quantitative proteomic analyses revealed programs of highly specific gene regulation tightly controlling cytoskeleton, cell differentiation, endosomal transport, and peroxisome function in podocytes.

Activin-like kinase 3 is important for kidney regeneration and reversal of fibrosis.

Molecules associated with the transforming growth factor β (TGF-β) superfamily, such as bone morphogenic proteins (BMPs) and TGF-β, are key regulators of inflammation, apoptosis and cellular transitions. Here we show that the BMP receptor activin-like kinase 3 (Alk3) is elevated early in diseased kidneys after injury. We also found that its deletion in the tubular epithelium leads to enhanced TGF-β1-Smad family member 3 (Smad3) signaling, epithelial damage and fibrosis, suggesting a protective role for Alk3-mediated signaling in the kidney.

Methylation determines fibroblast activation and fibrogenesis in the kidney.

Fibrogenesis is a pathological wound repair process that fails to cease, even when the initial insult has been removed. Fibroblasts are principal mediators of fibrosis, and fibroblasts from fibrotic tissues fail to return to their quiescent stage, including when cultured in vitro. In a search for underlying molecular mechanisms, we hypothesized that this perpetuation of fibrogenesis is caused by epigenetic modifications.

Modulation of intercellular ROS signaling of human tumor cells.

Tumor cells are resistant against apoptosis-inducing intercellular reactive oxygen species (ROS) signaling but can be resensitized by the inhibition of catalase. Hydrogen peroxide exhibits a dual role in the modulation of intercellular ROS signaling. When suboptimal concentrations of the catalase inhibitior 3-aminotriazole (3-AT) are applied, additional exogenous hydrogen peroxide shifts apoptosis induction to its optimum.

Catalase protects tumor cells from apoptosis induction by intercellular ROS signaling.

Transformed cells are subject to intercellular induction of apoptosis by neighbouring nontransformed cells and to autocrine apoptotic self-destruction. Both processes depend on extracellular superoxide anion generation by the transformed cells and on the release of peroxidase from both nontransformed and transformed cells. This concerted action results in HOCl synthesis, HOCl-superoxide anion interaction and generation of apoptosis-inducing hydroxyl radicals.

Twist: a new link from hypoxia to fibrosis.

Sun et al. demonstrate that hypoxia causes epithelial-to-mesenchymal transition by activating Twist, a transcription factor known to mediate both acquisition of a mesenchymal phenotype and resistance to apoptosis in cancer cells. This study provides clues as to how hypoxia and transforming growth factor-beta can collaborate to drive renal fibrogenesis.

Nitric oxide mediates apoptosis induction selectively in transformed fibroblasts compared to nontransformed fibroblasts.

Nitric oxide (NO) mediates apoptosis induction in fibroblasts with constitutive src or induced ras oncogene expression, whereas nontransformed parental cells and revertants are not affected. This direct link between the transformed phenotype and sensitivity to NO-mediated apoptosis induction seems to be based on the recently described extracellular superoxide anion generation by transformed cells, as NO-mediated apoptosis induction in transformed cells is inhibited by extracellular superoxide dismutase (SOD), by SOD mimetics and by apocynin, an inhibitor of NADPH oxidase. Furthermore, nonresponsive nontransformed cells can be rendered sensitive for NO-mediated apoptosis induction when they are supplemented with xanthine oxidase/xanthine as an extracellular source for superoxide anions.