BackgroundNeuronal degeneration in multiple sclerosis has been linked to oxidative stress. Dimethyl fumarate is a promising novel oral therapeutic option shown to reduce disease activity and progression in patients with relapsing-remitting multiple sclerosis. These effects are presumed to originate from a combination of immunomodulatory and neuroprotective mechanisms. We aimed to clarify whether neuroprotective concentrations of dimethyl fumarate have immunomodulatory effects.FindingsWe determined time- and concentration-dependent effects of dimethyl fumarate and its metabolite monomethyl fumarate on viability in a model of endogenous neuronal oxidative stress and clarified the mechanism of action by quantitating cellular glutathione content and recycling, nuclear translocation of transcription factors, and the expression of antioxidant genes. We compared this with changes in the cytokine profiles released by stimulated splenocytes measured by ELISPOT technology and analyzed the interactions between neuronal and immune cells and neuronal function and viability in cell death assays and multi-electrode arrays. Our observations show that dimethyl fumarate causes short-lived oxidative stress, which leads to increased levels and nuclear localization of the transcription factor nuclear factor erythroid 2-related factor 2 and a subsequent increase in glutathione synthesis and recycling in neuronal cells. Concentrations that were cytoprotective in neuronal cells had no negative effects on viability of splenocytes but suppressed the production of proinflammatory cytokines in cultures from C57BL/6 and SJL mice and had no effects on neuronal activity in multi-electrode arrays.ConclusionsThese results suggest that immunomodulatory concentrations of dimethyl fumarate can reduce oxidative stress without altering neuronal network activity.

Bax inhibitor-1 (BI-1) is an evolutionarily conserved pH-dependent Ca²⁺ leak channel in the endoplasmic reticulum and the founding member of a family of six highly hydrophobic mammalian proteins named transmembrane BAX inhibitor motif containing (TMBIM) 1-6 with BI-1 being TMBIM6. Here we compared the structure, subcellular localization, tissue expression and the effect on the cellular Ca²⁺ homeostasis of all family members side by side. We found that all TMBIM proteins possess the di-aspartyl pH sensor responsible for pH sensing identified in TMBIM6 and its bacterial homologue BsYetJ. TMBIM1-3 and TMBIM4-6 represent two phylogenetically distinct groups that are localized in the Golgi apparatus (TMBIM1-3), endoplasmic reticulum (TMBIM4-6) or mitochondria (TMBIM5) but share a common structure of at least seven transmembrane domains with the last domain being semi-hydrophobic. TMBIM1 is mainly expressed in muscle, TMBIM2 and 3 in the nervous system, TMBIM4 and 5 are ubiquitously expressed and TMBIM6 in skeletal muscle, kidney, liver and spleen. All TMBIM proteins reduce the Ca²⁺ content of the endoplasmic reticulum, and all but TMBIM5 also reduce the cytosolic resting Ca²⁺ concentration. These results suggest that the TMBIM family has comparable functions in the maintenance of intracellular Ca²⁺ homeostasis in a wide variety of tissues. This article is part of a Special Issue entitled: 13th European Symposium on Calcium.

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The endoplasmic reticulum (ER) serves as the major intracellular Ca 2+ store and has a role in the synthesis and folding of proteins. BAX (BCL2-associated X protein) inhibitor-1 (BI-1) is a Ca 2+ leak channel also implicated in the response against protein misfolding, thereby connecting the Ca 2+ store and protein-folding functions of the ER. We found that BI-1-deficient mice suffer from leukopenia and erythrocytosis, have an increased number of splenic marginal zone B cells and higher abundance and nuclear translocation of NF-κB (nuclear factor-κ light-chain enhancer of activated B cells) proteins, correlating with increased cytosolic and ER Ca 2+ levels. When put into culture, purified knockout T cells and even more so B cells die spontaneously. This is preceded by increased activity of the mitochondrial initiator caspase-9 and correlated with a significant surge in mitochondrial Ca 2+ levels, suggesting an exhausted mitochondrial Ca 2+ buffer capacity as the underlying cause for cell death in vitro. In vivo, T-cell-dependent experimental autoimmune encephalomyelitis and B-cell-dependent antibody production are attenuated, corroborating the ex vivo results. These results suggest that BI-1 has a major role in the functioning of the adaptive immune system by regulating intracellular Ca 2+ homeostasis in lymphocytes. Cell Death and Differentiation (2016) 23, 358-368; doi:10.1038/cdd.2015; published online 16 October 2015The endoplasmic reticulum (ER) serves as the major intracellular calcium (Ca 2+ ) store, the release of which controls a vast array of cellular functions from short-term responses such as contraction and secretion to long-term regulation of cell growth and proliferation. 1 Dysregulated release of ER Ca 2+ , in contrast, initiates programmed cell death by several mechanisms including mitochondrial Ca 2+ overload, depolarization, ATP loss and cytochrome c release. 2 Besides this, the ER also has a key role in the synthesis, folding and sorting of proteins destined for the secretory pathway. The deleterious consequences of an increase in unfolded proteins is called ER stress and can be antagonized by the unfolded protein response (UPR), a mechanism that coordinates a simultaneous increase in the ER folding capacity and a decrease in folding load. In the case of insufficient adaptation to ER stress, cells undergo apoptosis. 3 BAX (BCL2-associated X protein) inhibitor-1 (BI-1) is an evolutionarily conserved protein that bridges both the Ca 2+ homeostasis and UPR functions of the ER. 4 BI-1 was first identified in a screen for human proteins capable of inhibiting BAX-mediated cell death in yeast. 5 In mammalian cells, BI-1's antiapoptotic function is most pronounced in paradigms of ER stress 6 and involves changes in the amount of Ca 2+ that can be released from intracellular stores. 6,7 BI-1 is a highly hydrophobic protein that forms a Ca 2+ pore responsible for its Ca 2+ leak properties 8 and is the founding member of a family of six proteins with similar properties. 9 The increase in the ER Ca 2+ lea...

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Background: Apoptosis and autophagy are coordinately regulated, but the underlying mechanisms are incompletely understood. Results: Bcl-2 specifically interacts with GABARAP via a conserved EWD motif, resulting in impaired GABARAP lipidation. Conclusion: Sequestration of GABARAP is likely to contribute to the down-regulation of autophagy by Bcl-2. Significance: Interfering with pro-survival functions of Bcl-2 (including its impact on autophagy) represents a promising strategy for cancer therapy.

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Transmembrane BAX inhibitor motif containing 6 (TMBIM6), also known as Bax inhibitor-1, is an evolutionarily conserved protein involved in endoplasmic reticulum (ER) function. TMBIM6 is an ER Ca 2+ leak channel and its deficiency enhances susceptibility to ER stress due to inhibition of the ER stress sensor IRE1α. It was previously shown that TMBIM6 overexpression improves glucose metabolism and that TMBIM6 knockout mice develop obesity. We here examined the metabolic alterations underlying the obese phenotype and subjected TMBIM6 knockout mice to indirect calorimetry and euglycemic-hyperinsulinemic tests with stable isotope dilution to gauge tissue-specific insulin sensitivity. This demonstrated no changes in heat production, food intake, activity or hepatic and peripheral insulin sensitivity. TMBIM6 knockout mice, however, featured a higher glucose-stimulated insulin secretion in vivo as assessed by the hyperglycemic clamp test and hepatic steatosis. This coincided with profound changes in glucose-mediated Ca 2+ regulation in isolated pancreatic β cells and increased levels of IRE1α levels but no differences in downstream effects of IRE1α like increased Xbp1 mRNA splicing or Ire1-dependent decay of insulin mRNA in the pancreas. We therefore conclude that lack of TMBIM6 does not affect insulin sensitivity but leads to hyperinsulinemia, which serves to explain the weight gain. TMBIM6-mediated metabolic alterations are mainly caused by its role as a Ca 2+ release channel in the ER. Key messages & TMBIM6 −/− leads to obesity and hepatic steatosis. & Food intake and energy expenditure are not changed in TMBIM6 −/− mice. & No changes in insulin resistance in TMBIM6 −/− mice. & Increased insulin secretion caused by altered calcium dynamics in β cells. Koenraad Philippaert and Michael Roden shared first authorship.