Cryosectioning and immunofluorescence of C. elegans reveals endogenous polyphosphate in intestinal endo-lysosomal organelles.

Polyphosphate (polyP) is a ubiquitous polyanion present throughout the tree of life. While polyP's widely varied functions have been interrogated in single-celled organisms, little is known about the cellular distribution and function of polyP in multicellular organisms. To study polyP in metazoans, we developed the nematode Caenorhabditis elegans as a model system.

Early life changes in histone landscape protect against age-associated amyloid toxicities through HSF-1-dependent regulation of lipid metabolism.

Transient events during development can exert long-lasting effects on organismal lifespan. Here we demonstrate that exposure of Caenorhabditis elegans to reactive oxygen species during development protects against amyloid-induced proteotoxicity later in life. We show that this protection is initiated by the inactivation of the redox-sensitive H3K4me3-depositing COMPASS complex and conferred by a substantial increase in the heat-shock-independent activity of heat shock factor 1 (HSF-1), a longevity factor known to act predominantly during C.

β-cell-selective inhibition of DNA damage response signaling by nitric oxide is associated with an attenuation in glucose uptake.

Nitric oxide (NO) plays a dual role in regulating DNA damage response (DDR) signaling in pancreatic β-cells. As a genotoxic agent, NO activates two types of DDR signaling; however, when produced at micromolar levels by the inducible isoform of NO synthase, NO inhibits DDR signaling and DDR-induced apoptosis in a β-cell-selective manner. DDR signaling inhibition by NO correlates with mitochondrial oxidative metabolism inhibition and decreases in ATP and NAD.

Shaping longevity early in life: developmental ROS and H3K4me3 set the clock.

Studies in have revealed that even a genetically identical population of animals exposed to the same environment displays a remarkable level of variability in individual lifespan. Stochasticity factors, occurring seemingly by chance or at random, are thought to account for a large part of this variability. Recent studies in our lab using now revealed that naturally occurring variations in the levels of reactive oxygen species experienced early in life contribute to the observed lifespan variability, and likely serve as stochasticity factors in aging.

Regulation of ATR-dependent DNA damage response by nitric oxide.

We have shown that nitric oxide limits ataxia-telangiectasia mutated signaling by inhibiting mitochondrial oxidative metabolism in a β-cell selective manner. In this study, we examined the actions of nitric oxide on a second DNA damage response transducer kinase, ataxia-telangiectasia and Rad3-related protein (ATR). In β-cells and non-β-cells, nitric oxide activates ATR signaling by inhibiting ribonucleotide reductase; however, when produced at inducible nitric oxide synthase-derived (low micromolar) levels, nitric oxide impairs ATR signaling in a β-cell selective manner.

Can insulin secreting pancreatic β-cells provide novel insights into the metabolic regulation of the DNA damage response?

Insulin, produced by pancreatic β-cells, is responsible for the control of whole-body glucose metabolism. Insulin is secreted by pancreatic β-cells in a tightly regulated process that is controlled by the serum level of glucose, glucose sensing and glucose oxidative metabolism. The regulation of intermediary metabolism in β-cells is unique as these cells oxidize glucose to CO on substrate supply while mitochondrial oxidative metabolism occurs on demand, for the production of intermediates or energy production, in most cell types.

The location of sensing determines the pancreatic β-cell response to the viral mimetic dsRNA.

Viral infection is an environmental trigger that has been suggested to initiate pancreatic β-cell damage, leading to the development of autoimmune diabetes. Viruses potently activate the immune system and can damage β cells by either directly infecting them or stimulating the production of secondary effector molecules (such as proinflammatory cytokines) during bystander activation. However, how and where β cells recognize viruses is unclear, and the antiviral responses that are initiated following virus recognition are incompletely understood.

Developmental ROS individualizes organismal stress resistance and lifespan.

A central aspect of aging research concerns the question of when individuality in lifespan arises. Here we show that a transient increase in reactive oxygen species (ROS), which occurs naturally during early development in a subpopulation of synchronized Caenorhabditis elegans, sets processes in motion that increase stress resistance, improve redox homeostasis and ultimately prolong lifespan in those animals. We find that these effects are linked to the global ROS-mediated decrease in developmental histone H3K4me3 levels.

The Role of Metabolic Flexibility in the Regulation of the DNA Damage Response by Nitric Oxide.

In this report, we show that nitric oxide suppresses DNA damage response (DDR) signaling in the pancreatic β-cell line INS 832/13 and rat islets by inhibiting intermediary metabolism. Nitric oxide is known to inhibit complex IV of the electron transport chain and aconitase of the Krebs cycle. Non-β cells compensate by increasing glycolytic metabolism to maintain ATP levels; however, β cells lack this metabolic flexibility, resulting in a nitric oxide-dependent decrease in ATP and NAD Like nitric oxide, mitochondrial toxins inhibit DDR signaling in β cells by a mechanism that is associated with a decrease in ATP.

Pancreatic β-cells detoxify HO through the peroxiredoxin/thioredoxin antioxidant system.

Oxidative stress is thought to promote pancreatic β-cell dysfunction and contribute to both type 1 and type 2 diabetes. Reactive oxygen species (ROS), such as superoxide and hydrogen peroxide, are mediators of oxidative stress that arise largely from electron leakage during oxidative phosphorylation. Reports that β-cells express low levels of antioxidant enzymes, including catalase and GSH peroxidases, have supported a model in which β-cells are ill-equipped to detoxify ROS.

Role of Protein Phosphatase 1 and Inhibitor of Protein Phosphatase 1 in Nitric Oxide-Dependent Inhibition of the DNA Damage Response in Pancreatic β-Cells.

Nitric oxide is produced at micromolar levels by pancreatic β-cells during exposure to proinflammatory cytokines. While classically viewed as damaging, nitric oxide also activates pathways that promote β-cell survival. We have shown that nitric oxide, in a cell type-selective manner, inhibits the DNA damage response (DDR) and, in doing so, protects β-cells from DNA damage-induced apoptosis.

Cation-Independent Mannose 6-Phosphate Receptor Deficiency Enhances β-Cell Susceptibility to Palmitate.

Palmitate attenuates insulin secretion and reduces the viability of insulin-producing cells. Previous studies identified the aberrant palmitoylation or mispalmitoylation of proteins as one mechanism by which palmitate causes β-cell damage. In this report, we identify a role for lysosomal protein degradation as a mechanism by which β cells defend themselves against excess palmitate.

Dual Role of Nitric Oxide in Regulating the Response of β Cells to DNA Damage.

Significance: Cytokines released in and around pancreatic islets during islet inflammation are believed to contribute to impaired β cell function and β cell death during the development of diabetes. Nitric oxide, produced by β cells in response to cytokine exposure, controls many of the responses of β cells during islet inflammation. Recent Advances: Although nitric oxide has been shown to inhibit insulin secretion and oxidative metabolism and induce DNA damage in β cells, it also activates protective pathways that promote recovery of insulin secretion and oxidative metabolism and repair of damaged DNA.

Nitric Oxide Suppresses β-Cell Apoptosis by Inhibiting the DNA Damage Response.

Nitric oxide, produced in pancreatic β cells in response to proinflammatory cytokines, plays a dual role in the regulation of β-cell fate. While nitric oxide induces cellular damage and impairs β-cell function, it also promotes β-cell survival through activation of protective pathways that promote β-cell recovery. In this study, we identify a novel mechanism in which nitric oxide prevents β-cell apoptosis by attenuating the DNA damage response (DDR).

Distinct differences in the responses of the human pancreatic β-cell line EndoC-βH1 and human islets to proinflammatory cytokines.

While insulinoma cells have been developed and proven to be extremely useful in studies focused on mechanisms controlling β-cell function and viability, translating findings to human β-cells has proven difficult because of the limited access to human islets and the absence of suitable insulinoma cell lines of human origin. Recently, a human β-cell line, EndoC-βH1, has been derived from human fetal pancreatic buds. The purpose of this study was to determine whether human EndoC-βH1 cells respond to cytokines in a fashion comparable to human islets.

Inhibition of an NAD⁺ salvage pathway provides efficient and selective toxicity to human pluripotent stem cells.

The tumorigenic potential of human pluripotent stem cells (hPSCs) is a major limitation to the widespread use of hPSC derivatives in the clinic. Here, we demonstrate that the small molecule STF-31 is effective at eliminating undifferentiated hPSCs across a broad range of cell culture conditions with important advantages over previously described methods that target metabolic processes. Although STF-31 was originally described as an inhibitor of glucose transporter 1, these data support the reclassification of STF-31 as a specific NAD⁺ salvage pathway inhibitor through the inhibition of nicotinamide phosphoribosyltransferase (NAMPT).

How the location of superoxide generation influences the β-cell response to nitric oxide.

Cytokines impair the function and decrease the viability of insulin-producing β-cells by a pathway that requires the expression of inducible nitric oxide synthase (iNOS) and generation of high levels of nitric oxide. In addition to nitric oxide, excessive formation of reactive oxygen species, such as superoxide and hydrogen peroxide, has been shown to cause β-cell damage. Although the reaction of nitric oxide with superoxide results in the formation of peroxynitrite, we have shown that β-cells do not have the capacity to produce this powerful oxidant in response to cytokines.

Nitric oxide induces ataxia telangiectasia mutated (ATM) protein-dependent γH2AX protein formation in pancreatic β cells.

In this study, the effects of cytokines on the activation of the DNA double strand break repair factors histone H2AX (H2AX) and ataxia telangiectasia mutated (ATM) were examined in pancreatic β cells. We show that cytokines stimulate H2AX phosphorylation (γH2AX formation) in rat islets and insulinoma cells in a nitric oxide- and ATM-dependent manner. In contrast to the well documented role of ATM in DNA repair, ATM does not appear to participate in the repair of nitric oxide-induced DNA damage.

β-Cell responses to nitric oxide.

Autoimmune diabetes is characterized by the selective destruction of insulin-secreting β-cells that occurs during an inflammatory reaction in and around pancreatic islets of Langerhans. Cytokines such as interleukin-1, released by activated immune cells, have been shown to inhibit insulin secretion from pancreatic β-cells and cause islet destruction. In response to cytokines, β-cells express inducible nitric oxide synthase and produce micromolar levels of the free radical nitric oxide.