Department of Physiology

Glucose-fructose ingestion increases glucose and lactate oxidation during exercise. We hypothesized that training with glucose-fructose would induce key adaptations in lactate metabolism. Two groups of eight sedentary males were endurance-trained for three weeks while ingesting either glucose-fructose (GF) or water (C). Effects of glucose-fructose on lactate appearance, oxidation, and clearance were measured at rest and during exercise, pre-training, and post-training. Pre-training, resting lactate appearance was 3.6 ± 0.5 vs. 3.6 ± 0.4 mg·kg −1 ·min −1 in GF and C, and was increased to 11.2 ± 1.4 vs. 8.8 ± 0.7 mg·kg −1 ·min −1 by exercise (Exercise: p < 0.01). Lactate oxidation represented 20.6% ± 1.0% and 17.5% ± 1.7% of lactate appearance at rest, and 86.3% ± 3.8% and 86.8% ± 6.6% during exercise (Exercise: p < 0.01) in GF and C, respectively. Training with GF increased resting lactate appearance and oxidation (Training × Intervention: both p < 0.05), but not during exercise (Training × Intervention: both p > 0.05). Training with GF and C had similar effects to increase lactate clearance during exercise (+15.5 ± 9.2 and +10.1 ± 5.9 mL·kg −1 ·min −1 ; Training: p < 0.01; Training × Intervention: p = 0.97). The findings of this study show that in sedentary participants, glucose-fructose ingestion leads to high systemic lactate appearance, most of which is disposed non-oxidatively at rest and is oxidized during exercise. Training with or without glucose-fructose increases lactate clearance, without altering lactate appearance and oxidation during exercise.

This paper aims to compare the metabolic effects of glucose-fructose co-ingestion (GLUFRU) with glucose alone (GLU) in exercising individuals with type 1 diabetes mellitus. Fifteen male individuals with type 1 diabetes (HbA1c 7.0% ± 0.6% (53 ± 7 mmol/mol)) underwent a 90 min iso-energetic continuous cycling session at 50% VO 2max while ingesting combined glucose-fructose (GLUFRU) or glucose alone (GLU) to maintain stable glycaemia without insulin adjustment. GLUFRU and GLU were labelled with 13 C-fructose and 13 C-glucose, respectively. Metabolic assessments included measurements of hormones and metabolites, substrate oxidation, and stable isotopes. Exogenous carbohydrate requirements to maintain stable glycaemia were comparable between GLUFRU and GLU (p = 0.46). Fat oxidation was significantly higher (5.2 ± 0.2 vs. 2.6 ± 1.2 mg·kg −1 ·min −1 , p < 0.001) and carbohydrate oxidation lower (18.1 ± 0.8 vs. 24.5 ± 0.8 mg·kg −1 ·min −1 p < 0.001) in GLUFRU compared to GLU, with decreased muscle glycogen oxidation in GLUFRU (10.2 ± 0.9 vs. 17.5 ± 1.0 mg·kg −1 ·min −1 , p < 0.001). Lactate levels were higher (2.2 ± 0.2 vs. 1.8 ± 0.1 mmol/L, p = 0.012) in GLUFRU, with comparable counter-regulatory hormones between GLUFRU and GLU (p > 0.05 for all). Glucose and insulin levels, and total glucose appearance and disappearance were comparable between interventions. Glucose-fructose co-ingestion may have a beneficial impact on fuel metabolism in exercising individuals with type 1 diabetes without insulin adjustment, by increasing fat oxidation whilst sparing glycogen.

Macroautophagy has important physiological roles and its cytoprotective or detrimental function is compromised in various diseases such as many cancers and metabolic diseases. However, the importance of autophagy for cell responses has also been demonstrated in many other physiological and pathological situations. In this review, we discuss some of the recently discovered mechanisms involved in specific and unspecific autophagy related to mitochondrial dysfunction and organelle degradation, lipid metabolism and lipophagy as well as recent findings and evidence that link autophagy to unconventional protein secretion.

We show that mitochondrial DNA (mtDNA)-depleted 143B cells are hypersensitive to staurosporine-induced cell death as evidenced by a more pronounced DNA fragmentation, a stronger activation of caspase-3, an enhanced poly-(ADP-ribose) polymerase-1 (PARP-1) cleavage, and a more dramatic cytosolic release of cytochrome c. We also show that B-cell CLL/ lymphoma-2 (Bcl-2), B-cell lymphoma extra large (Bcl-XL), and myeloid cell leukemia-1 (Mcl-1) are constitutively less abundant in mtDNA-depleted cells, that the inhibition of Bcl-2 and Bcl-XL can sensitize the parental cell line to staurosporine-induced apoptosis, and that overexpression of Bcl-2 or Bcl-XL can prevent the activation of caspase-3 in 0 143B cells treated with staurosporine. Moreover, the inactivation of cathepsin B with CA074-Me significantly reduced cytochrome c release, caspase-3 activation, PARP-1 cleavage, and DNA fragmentation in mtDNA-depleted cells, whereas the pancaspase inhibitor failed to completely prevent PARP-1 cleavage and DNA fragmentation in these cells, suggesting that caspaseindependent mechanisms are responsible for cell death even if caspases are activated. Finally, we show that cathepsin B is released in the cytosol of 0 cells in response to staurosporine, suggesting that the absence of mitochondrial activity leads to a facilitated permeabilization of lysosomal membranes in response to staurosporine. mitochondrial DNA depletion; lysosome

Mutations in the mitochondrial DNA can lead to the development of mitochondrial diseases such as Myoclonic Epilepsy with Ragged Red Fibers (MERRF) or Mitochondrial Encephalomyopathy, Lactic Acidosis and Stroke-like episodes (MELAS). We first show that human 143B-derived cybrid cells harboring either the A8344G (MERRF) or the A3243G (MELAS) mutation, are more prone to undergo apoptosis then their wild-type counterpart, when challenged with various apoptotic inducers such as staurosporine, etoposide and TRAIL. In addition, investigating the mechanisms underlying A8344G cybrid cells hypersensitivity to staurosporine-induced cell death, we found that staurosporine treatment activates caspases independently of cytochrome c release in both wild-type and mutated cells. Caspases are activated, at least partly, through the activation of calcium-dependent calpain proteases, a pathway that is more strongly activated in mutated cybrid cells than in wild-type cells exposed to staurosporine. These results suggest that calcium homeostasis perturbation induced by mitochondrial dysfunction could predispose cells to apoptosis, a process that could take part into the progressive cell degeneration observed in MERRF syndrome, and more generally in mitochondrial diseases.

Mitochondria-to-nucleus communication, known as retrograde signaling, is important to adjust the nuclear gene expression in response to organelle dysfunction. Among the transcription factors described to respond to mitochondrial stress, CHOP-10 is activated by respiratory chain inhibition, mitochondrial accumulation of unfolded proteins and mtDNA mutations. In this study, we show that altered/impaired expression of mtDNA induces CHOP-10 expression in a signaling pathway that depends on the eIF2α/ATF4 axis of the integrated stress response rather than on the mitochondrial unfolded protein response.

The excitatory neurotransmitter glutamate has been reported to have a major impact on brain energy metabolism. Using primary cultures of rat hippocampal neurons, we observed that glutamate reduces glucose utilization in this cell type, suggesting alteration in mitochondrial oxidative metabolism. The aquaglyceroporin AQP9 and the monocarboxylate transporter MCT2, two transporters for oxidative energy substrates, appear to be present in mitochondria of these neurons. Moreover, they not only co-localize but they interact with each other as they were found to co-immunoprecipitate from hippocampal neuron homogenates. Exposure of cultured hippocampal neurons to glutamate 100 μM for 1 h led to enhanced expression of both AQP9 and MCT2 at the protein level without any significant change at the mRNA level. In parallel, a similar increase in the protein expression of LDHA was evidenced without an effect on the mRNA level. These data suggest that glutamate exerts an influence on neuronal energy metabolism likely through a regulation of the expression of some key mitochondrial proteins.

The excitatory neurotransmitter glutamate has been reported to have a major impact on brain energy metabolism. Using primary cultures of rat hippocampal neurons, we observed that glutamate reduces glucose utilization in this cell type, suggesting alteration in mitochondrial oxidative metabolism. The aquaglyceroporin AQP9 and the monocarboxylate transporter MCT2, two transporters for oxidative energy substrates, appear to be present in mitochondria of these neurons. Moreover, they not only co-localize but they interact with each other as they were found to co-immunoprecipitate from hippocampal neuron homogenates. Exposure of cultured hippocampal neurons to glutamate 100 μM for 1 h led to enhanced expression of both AQP9 and MCT2 at the protein level without any significant change at the mRNA level. In parallel, a similar increase in the protein expression of LDHA was evidenced without an effect on the mRNA level. These data suggest that glutamate exerts an influence on neuronal energy metabolism likely through a regulation of the expression of some key mitochondrial proteins.

The central hypothesis of the study which has been carried out as part of the NRP38 program, is that perturbations of brain energy metabolism are critically involved in the neurodegeneration occurring in Alzheimer's disease (AD) and that they may correlate with early cognitive dysfunctioning. In the present multidisciplinary study we set out to monitor brain energy metabolism using FDG-PET and HMPAO-SPECT imaging in a cohort of individuals over 65 years of age, drawn from the general population. HMPAO-SPECT imaging, which is a simpler and more widely accessible imaging procedure than FDG-PET, was performed under basal conditions and during the performance of a cognitive task (verbal fluency test). Three groups were studied. Two groups (groups I and II) included individuals age 65 or more, with no cognitive impairment and carrying an APOE4 positive or APOE4 negative phenotype, respectively; a third group (group III) included patients with clinical signs of AD. Each subject entering the study underwent an FDG-PET, an HMPAO-SPECT and an extensive battery of neuropsychological tests which assess various aspects of cognitive functioning, with a strong emphasis on working memory, divided attention and executive functions. A total of 101 participants were submitted to brain imaging and neuropsychological testing. Amomg these, 60 participants received the same set of imaging and neuropsychological tasks 24-36 months after the first set (phase II). In this article, we present a preliminary analysis performed on ten subjects from groups I and II and nine subjects from group III: activation (verbal fluency task) induced a specific pattern of increase in HMPAO retention (including BA 9 / 10, BA 18 bilaterally and right BA 17). In contrast to controls, in nine AD subjects no significant differences in HMPAO retention were observed when comparing activation and basal conditions. The cellular and molecular mechanisms that underlie the retention of HMPAO, the tracer used for single photon emission computed tomography (SPECT) imaging, has been studied in vitro in purified preparations of neurons and astrocytes with the aim of investigating the contribution of different cell types to hexamethyl-propyleneamineoxime labeled with technetium-99m 99m 99m