Tetrahydropteridines possess antioxidant roles to guard against glucose-induced oxidative stress in Dictyostelium discoideum

Microfluidic single-cell measurements of oxidative stress as a function of cell cycle position

Single-cell measurements routinely demonstrate high levels of variation between cells, but fewer studies provide insight into the analytical and biological sources of this variation. This is particularly true of chemical cytometry, in which individual cells are lysed and their contents separated, compared to more established single-cell measurements of the genome and transcriptome. To characterize population-level variation and its sources, we analyzed oxidative stress levels in 1278 individual Dictyostelium discoideum cells as a function of exogenous stress level and cell cycle position. Cells were exposed to varying levels of oxidative stress via singlet oxygen generation using the photosensitizer Rose Bengal. Single-cell data reproduced the dose-response observed in ensemble measurements by CE-LIF, superimposed with high levels of heterogeneity. Through experiments and data analysis, we explored possible biological sources of this heterogeneity. No trend was observed between population variation and oxidative stress level, but cell cycle position was a major contributor to heterogeneity in oxidative stress. Cells synchronized to the same stage of cell division were less heterogeneous than unsynchronized cells (RSD of 37-51% vs 93%), and mitotic cells had higher levels of reactive oxygen species than interphase cells. While past research has proposed changes in cell size during the cell cycle as a source of biological noise, the measurements presented here use an internal standard to normalize for effects of cell volume, suggesting a more complex contribution of cell cycle to heterogeneity of oxidative stress.

Lysosomes appear as the auto-fluorescent vacuoles in Dictyostelium discoideum cells

Dictyostelium discoideum cells contain auto-fluorescent vacuoles. To determine the identity of these vacuoles, the fluorescent dye 4-nitro-7-(1-piperazinyl)-2,1,3-benzoxadiazole (NBD-PZ) was used to stain the lysosomes in D. discoideum cells. Neither the auto-fluorescent vacuoles nor lysosomes were observed in D. discoideum cells immediately after they arose from spores or in stationary phase cells. However, both the auto-fluorescent vacuoles and lysosomes were visible in cells that had entered growth phase. Auto-fluorescent vacuoles and lysosomes were also observed in stationary phase cells incubated with chloroquine. When the cells were allowed to phagocytose BioParticles Fluorescent Bacteria (orange fluorescence) for 1 h, orange phagosomes and blue auto-fluorescent vacuoles were observed as independent moieties. However, after an additional 2 h of incubation, we observed vacuoles with mixed fluorescence (orange and blue) in the cells, suggestive of secondary lysosomes. These results suggest that the auto-fluorescent vacuoles in D. discoideum cells are lysosomes.

Mutation of the lbp-5 gene alters metabolic output in Caenorhabditis elegans

Intracellular lipid-binding proteins (LBPs) impact fatty acid homeostasis in various ways, including fatty acid transport into mitochondria. However, the physiological consequences caused by mutations in genes encoding LBPs remain largely uncharacterized. Here, we explore the metabolic consequences of lbp-5 gene deficiency in terms of energy homeostasis in Caenorhabditis elegans. In addition to increased fat storage, which has previously been reported, deletion of lbp-5 attenuated mitochondrial membrane potential and increased reactive oxygen species levels. Biochemical measurement coupled to proteomic analysis of the lbp-5(tm1618) mutant revealed highly increased rates of glycolysis in this mutant. These differential expression profile data support a novel metabolic adaptation of C. elegans, in which glycolysis is activated to compensate for the energy shortage due to the insufficient mitochondrial β-oxidation of fatty acids in lbp-5 mutant worms. This report marks the first demonstration of a unique metabolic adaptation that is a consequence of LBP-5 deficiency in C. elegans. [BMB Reports 2014; 47(1): 15-20]