To further explore the value of feline liver

To further explore the value of feline liver organoids as a research model for steatosis, we tested the effect of small molecules on lipid metabolism. Lipid accumulation was enhanced in the presence of etomoxir, indicating that β-oxidation is an important metabolic pathway handling excess fatty acids in feline liver cells. Conversely, supplementation of L-carnitine of feline liver organoids attenuated lipid accumulation in high-fat conditions and improved cellular viability. This is in concordance with the finding that exogenous L-carnitine supplementation can ameliorate FFA oxidation in cats with FHL (Center et al., 2012). The possibility to interfere in vitro with organoid lipid accumulation offers opportunities to test new drugs that enhance β-oxidation or promote VLDL secretion, with the aim of eliminating superfluous triglycerides from hepatocytes in vivo.
Experimental Procedures
Author Contributions
Acknowledgments The authors would like to thank the Utrecht University Center for Cell Imaging for technical assistance with imaging, Stefan van der Elst from the Hubrecht Institute for technical assistance with flow cytometry experiments, Dr. Sathidpak Nantasanti for technical advice, Dr. Hilda Toussaint for providing surplus mouse liver samples, and Sarah Opitz for editing the manuscript. This study was sponsored by the Winn Feline Foundation (grant no. W15-037). Parts of this work were funded by the Dutch Research Council NWO ZON/MW (116004121).
Introduction Degenerative retinal diseases and damage, such as retinitis pigmentosa, result in a loss of retinal K03861 cost and deterioration of vision, and can lead to blindness. A current effort to mitigate these effects involves intravitreal injections of stem cells or retinal precursors, hoping for successful integration and connection to existing neuronal circuits (Barber et al., 2013; Hanus et al., 2016; MacLaren et al., 2006; Pearson et al., 2012; Santos-Ferreira et al., 2015). Though improving, these therapies are inefficient and not yet capable of restoring vision (Barber et al., 2013; Bringmann et al., 2006; Pearson, 2014; Pearson et al., 2010). An alternative method would be to prompt the retina to endogenously regenerate and replace lost cells. Mammalian retinas do not possess the ability to regenerate following disease or damage. Instead, damage commonly results in reactive gliosis (Bringmann et al., 2006; Pearson, 2014). Zebrafish, however, mount a robust spontaneous regeneration response upon damage (Goldman, 2014). In this way, Müller glia (MG) serve as adult stem cells in the retina capable of dedifferentiation, asymmetric division, and the production of progenitor cells that are capable of restoring all lost cell types (Bernardos et al., 2007; Fausett and Goldman, 2006; Nagashima et al., 2013; Rajaram et al., 2014a, 2014b; Ramachandran et al., 2012; Thummel et al., 2008; Vihtelic and Hyde, 2000; Wan et al., 2012; Zhao et al., 2014). Because overall retinal architecture and cell types are largely conserved between fish and mammals, understanding how zebrafish regulate retina regeneration may help develop novel treatments or therapeutic targets for retinal damage or diseases, especially treatments that target or induce regeneration from MG. Select regions of the mammalian CNS are capable of adult neurogenesis, particularly the subgranular zone (SGZ) of the mouse hippocampus. Recently, the inhibitory neurotransmitter γ-aminobutyric acid (GABA) was shown to play an important role in regulating quiescence of radial glia-like stem cells (RGLs) in the mouse hippocampus (Song et al., 2012). Synaptic input from glutamatergic granule cells regulates activity of parvalbumin-positive (PV+) GABAergic interneurons in the SGZ. When input from granule cells is low, decreased extracellular GABA levels are detected in a non-synaptic, tonic response by GABAA receptors on RGLs, resulting in proliferation. We sought to test whether this could be an evolutionarily conserved mechanism to regulate MG-derived regeneration in the damaged zebrafish retina. In the retina, photoreceptors (PRs) release glutamate onto GABAergic horizontal cells (HCs). When PRs die they no longer stimulate HCs to release GABA. We hypothesize that MG detect decreases in ambient GABA levels and initiate regeneration in a response similar to activation of RGLs in the mouse hippocampus. We show here that disrupting GABA signaling causes spontaneous proliferation in undamaged zebrafish retinas and that increasing GABA signaling in damaged retinas suppresses regeneration.