Egr1 loss-of-function promotes beige adipocyte differentiation and activation specifically in inguinal subcutaneous white adipose tissue.

In mice, exercise, cold exposure and fasting lead to the differentiation of inducible-brown adipocytes, called beige adipocytes, within white adipose tissue and have beneficial effects on fat burning and metabolism, through heat production. This browning process is associated with an increased expression of the key thermogenic mitochondrial uncoupling protein 1, Ucp1. Egr1 transcription factor has been described as a regulator of white and beige differentiation programs, and Egr1 depletion is associated with a spontaneous increase of subcutaneous white adipose tissue browning, in absence of external stimulation. Here, we demonstrate that Egr1 mutant mice exhibit a restrained Ucp1 expression specifically increased in subcutaneous fat, resulting in a metabolic shift to a more brown-like, oxidative metabolism, which was not observed in other fat depots. In addition, Egr1 is necessary and sufficient to promote white and alter beige adipocyte differentiation of mouse stem cells. These results suggest that modulation of Egr1 expression could represent a promising therapeutic strategy to increase energy expenditure and to restrain obesity-associated metabolic disorders.

Mitochondrial Lon protease - depleted HeLa cells exhibit proteome modifications related to protein quality control, stress response and energy metabolism.

The ATP-dependent Lon protease is located in the mitochondrial matrix and oxidized proteins are among its primary targets for their degradation. Impairment of mitochondrial morphology and function together with apoptosis were observed in lung fibroblasts depleted for Lon expression while accumulation of carbonylated mitochondrial proteins has been reported for yeast and HeLa Lon deficient cells. In addition, age-related mitochondrial dysfunction has been associated with an impairment of Lon expression. Using a HeLa cell line stably transfected with an inducible shRNA directed against Lon, we have previously observed that Lon depletion results in a mild phenotype characterized by an increase of both production of reactive oxygen species and level of oxidized proteins (Bayot et al., 2014, Biochimie, 100: 38-47). In this study using the same cell line, we now show that Lon knockdown leads to modifications of the expression of a number of specific proteins involved in protein quality control, stress response and energy metabolism, as evidenced using a 2D gel-based proteomic approach, and to alteration of the mitochondrial network morphology. We also show that these effects are associated with decreased proliferation and can be modulated by culture conditions in galactose versus glucose containing medium.

Modulation of the specific glutathionylation of mitochondrial proteins in the yeast Saccharomyces cerevisiae under basal and stress conditions.

The potential biological consequences of oxidative stress and changes in glutathione levels include the oxidation of susceptible protein thiols and reversible covalent binding of glutathione to the -SH groups of proteins by S-glutathionylation. Mitochondria are central to the response to oxidative stress and redox signaling. It is therefore crucial to explore the adaptive response to changes in thiol-dependent redox status in these organelles. We optimized the purification protocol of glutathionylated proteins in the yeast Saccharomyces cerevisiae and present a detailed proteomic analysis of the targets of protein glutathionylation in cells undergoing constitutive metabolism and after exposure to various stress conditions. This work establishes the physiological importance of the glutathionylation process in S. cerevisiae under basal conditions and provides evidence for an atypical and unexpected cellular distribution of the process between the cytosol and mitochondria. In addition, our data indicate that each oxidative condition (diamide, GSSG, H2O2, or the presence of iron) elicits an adaptive metabolic response affecting specific mitochondrial metabolic pathways, mainly involved in the energetic maintenance of the cells. The correlation of protein modifications with intracellular glutathione levels suggests that protein deglutathionylation may play a role in protecting mitochondria from oxidative stress. This work provides further insights into the diversity of proteins undergoing glutathionylation and the role of this post-translational modification as a regulatory process in the adaptive response of the cell.