Limits...
Mitochondrial Respiration in Insulin-Producing β-Cells: General Characteristics and Adaptive Effects of Hypoxia.

Hals IK, Bruerberg SG, Ma Z, Scholz H, Björklund A, Grill V - PLoS ONE (2015)

Bottom Line: Mitochondrial effects were accompanied by unchanged levels of ATP, increased basal and preserved glucose-induced insulin secretion.Such effects are accompanied by up-regulation of mitochondrial complexes also in pancreatic islets, highlighting adaptive capacities of possible importance in an islet transplantation setting.Results also indicate idiosyncrasies of β-cells that do not respire in response to a standard inclusion of malate in SUIT protocols.

View Article: PubMed Central - PubMed

Affiliation: Department of Cancer Research and Molecular Medicine, Faculty of Medicine, Norwegian University of Science and Technology (NTNU), Trondheim, Norway.

ABSTRACT

Objective: To provide novel insights on mitochondrial respiration in β-cells and the adaptive effects of hypoxia.

Methods and design: Insulin-producing INS-1 832/13 cells were exposed to 18 hours of hypoxia followed by 20-22 hours re-oxygenation. Mitochondrial respiration was measured by high-resolution respirometry in both intact and permeabilized cells, in the latter after establishing three functional substrate-uncoupler-inhibitor titration (SUIT) protocols. Concomitant measurements included proteins of mitochondrial complexes (Western blotting), ATP and insulin secretion.

Results: Intact cells exhibited a high degree of intrinsic uncoupling, comprising about 50% of oxygen consumption in the basal respiratory state. Hypoxia followed by re-oxygenation increased maximal overall respiration. Exploratory experiments in peremabilized cells could not show induction of respiration by malate or pyruvate as reducing substrates, thus glutamate and succinate were used as mitochondrial substrates in SUIT protocols. Permeabilized cells displayed a high capacity for oxidative phosphorylation for both complex I- and II-linked substrates in relation to maximum capacity of electron transfer. Previous hypoxia decreased phosphorylation control of complex I-linked respiration, but not in complex II-linked respiration. Coupling control ratios showed increased coupling efficiency for both complex I- and II-linked substrates in hypoxia-exposed cells. Respiratory rates overall were increased. Also previous hypoxia increased proteins of mitochondrial complexes I and II (Western blotting) in INS-1 cells as well as in rat and human islets. Mitochondrial effects were accompanied by unchanged levels of ATP, increased basal and preserved glucose-induced insulin secretion.

Conclusions: Exposure of INS-1 832/13 cells to hypoxia, followed by a re-oxygenation period increases substrate-stimulated respiratory capacity and coupling efficiency. Such effects are accompanied by up-regulation of mitochondrial complexes also in pancreatic islets, highlighting adaptive capacities of possible importance in an islet transplantation setting. Results also indicate idiosyncrasies of β-cells that do not respire in response to a standard inclusion of malate in SUIT protocols.

No MeSH data available.


Related in: MedlinePlus

Oxygen flux in different respiratory states in intact INS-1 832/13 cells.Sequential respiratory states in the ProtocolInt protocol, comparing hypoxia with normoxia ROUTINE: basal respiration measured at physiological substrate conditions, before any reagent additions, LEAK: uncoupled respiration after addition of oligomycin, ETS: flux capacity of the electron transfer system, induced by FCCP, ROX: residual oxygen consumption, a measure of oxidative side reactions obtained by adding rotenone and antimycin A to inhibit complex I and II, respectively. Fluxes are expressed as means ± SEM of five experiments (comprising totally 12 single measurements),*P < 0.03.
© Copyright Policy
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4581632&req=5

pone.0138558.g004: Oxygen flux in different respiratory states in intact INS-1 832/13 cells.Sequential respiratory states in the ProtocolInt protocol, comparing hypoxia with normoxia ROUTINE: basal respiration measured at physiological substrate conditions, before any reagent additions, LEAK: uncoupled respiration after addition of oligomycin, ETS: flux capacity of the electron transfer system, induced by FCCP, ROX: residual oxygen consumption, a measure of oxidative side reactions obtained by adding rotenone and antimycin A to inhibit complex I and II, respectively. Fluxes are expressed as means ± SEM of five experiments (comprising totally 12 single measurements),*P < 0.03.

Mentions: The fully uncoupled respiration, i.e. ETS state respiration, in intact cells was significantly higher in hypoxia-exposed cells; 108.3 ± 4.4 pmol O2/s/106 cells for hypoxia and 94.2 ± 4.6 for normoxia (P < 0.03, n = 5) (Fig 4). ROUTINE and LEAK state respiration was not significantly affected by the hypoxia treatment.


Mitochondrial Respiration in Insulin-Producing β-Cells: General Characteristics and Adaptive Effects of Hypoxia.

Hals IK, Bruerberg SG, Ma Z, Scholz H, Björklund A, Grill V - PLoS ONE (2015)

Oxygen flux in different respiratory states in intact INS-1 832/13 cells.Sequential respiratory states in the ProtocolInt protocol, comparing hypoxia with normoxia ROUTINE: basal respiration measured at physiological substrate conditions, before any reagent additions, LEAK: uncoupled respiration after addition of oligomycin, ETS: flux capacity of the electron transfer system, induced by FCCP, ROX: residual oxygen consumption, a measure of oxidative side reactions obtained by adding rotenone and antimycin A to inhibit complex I and II, respectively. Fluxes are expressed as means ± SEM of five experiments (comprising totally 12 single measurements),*P < 0.03.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4581632&req=5

pone.0138558.g004: Oxygen flux in different respiratory states in intact INS-1 832/13 cells.Sequential respiratory states in the ProtocolInt protocol, comparing hypoxia with normoxia ROUTINE: basal respiration measured at physiological substrate conditions, before any reagent additions, LEAK: uncoupled respiration after addition of oligomycin, ETS: flux capacity of the electron transfer system, induced by FCCP, ROX: residual oxygen consumption, a measure of oxidative side reactions obtained by adding rotenone and antimycin A to inhibit complex I and II, respectively. Fluxes are expressed as means ± SEM of five experiments (comprising totally 12 single measurements),*P < 0.03.
Mentions: The fully uncoupled respiration, i.e. ETS state respiration, in intact cells was significantly higher in hypoxia-exposed cells; 108.3 ± 4.4 pmol O2/s/106 cells for hypoxia and 94.2 ± 4.6 for normoxia (P < 0.03, n = 5) (Fig 4). ROUTINE and LEAK state respiration was not significantly affected by the hypoxia treatment.

Bottom Line: Mitochondrial effects were accompanied by unchanged levels of ATP, increased basal and preserved glucose-induced insulin secretion.Such effects are accompanied by up-regulation of mitochondrial complexes also in pancreatic islets, highlighting adaptive capacities of possible importance in an islet transplantation setting.Results also indicate idiosyncrasies of β-cells that do not respire in response to a standard inclusion of malate in SUIT protocols.

View Article: PubMed Central - PubMed

Affiliation: Department of Cancer Research and Molecular Medicine, Faculty of Medicine, Norwegian University of Science and Technology (NTNU), Trondheim, Norway.

ABSTRACT

Objective: To provide novel insights on mitochondrial respiration in β-cells and the adaptive effects of hypoxia.

Methods and design: Insulin-producing INS-1 832/13 cells were exposed to 18 hours of hypoxia followed by 20-22 hours re-oxygenation. Mitochondrial respiration was measured by high-resolution respirometry in both intact and permeabilized cells, in the latter after establishing three functional substrate-uncoupler-inhibitor titration (SUIT) protocols. Concomitant measurements included proteins of mitochondrial complexes (Western blotting), ATP and insulin secretion.

Results: Intact cells exhibited a high degree of intrinsic uncoupling, comprising about 50% of oxygen consumption in the basal respiratory state. Hypoxia followed by re-oxygenation increased maximal overall respiration. Exploratory experiments in peremabilized cells could not show induction of respiration by malate or pyruvate as reducing substrates, thus glutamate and succinate were used as mitochondrial substrates in SUIT protocols. Permeabilized cells displayed a high capacity for oxidative phosphorylation for both complex I- and II-linked substrates in relation to maximum capacity of electron transfer. Previous hypoxia decreased phosphorylation control of complex I-linked respiration, but not in complex II-linked respiration. Coupling control ratios showed increased coupling efficiency for both complex I- and II-linked substrates in hypoxia-exposed cells. Respiratory rates overall were increased. Also previous hypoxia increased proteins of mitochondrial complexes I and II (Western blotting) in INS-1 cells as well as in rat and human islets. Mitochondrial effects were accompanied by unchanged levels of ATP, increased basal and preserved glucose-induced insulin secretion.

Conclusions: Exposure of INS-1 832/13 cells to hypoxia, followed by a re-oxygenation period increases substrate-stimulated respiratory capacity and coupling efficiency. Such effects are accompanied by up-regulation of mitochondrial complexes also in pancreatic islets, highlighting adaptive capacities of possible importance in an islet transplantation setting. Results also indicate idiosyncrasies of β-cells that do not respire in response to a standard inclusion of malate in SUIT protocols.

No MeSH data available.


Related in: MedlinePlus