Mitochondrial Calcium Exchange links Metabolism with the Epigenome to Control Cellular Differentiation (RNA-seq)
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ABSTRACT: Fibroblast to myofibroblast differentiation is crucial for the initial healing response but excessive myofibroblast activation leads to pathological fibrosis. Therefore, it is imperative to understand the mechanisms underlying myofibroblast formation. Here we report that mitochondrial calcium (mCa2+) signaling is a regulatory mechanism in myofibroblast differentiation and fibrosis. We demonstrate that inhibition of mCa2+ uptake in fibroblasts enhances myofibroblast formation and this translates to increased fibrosis following injury. Fibrotic signaling alters the gating of the mitochondrial calcium uniporter (mtCU) to reduce mCa2+ uptake and induce specific changes in metabolism. mCa2+-dependent metabolic reprogramming leads to the activation of αKG-dependent demethylases which epigenetically modify promoter regions specific to the myofibroblast gene program resulting in differentiation. Our results uncover an important role for mCa2+ uptake beyond metabolic regulation and cell death and demonstrate that mCa2+ signaling regulates the epigenome to influence cellular differentiation.
Project description:Fibroblast to myofibroblast differentiation is crucial for the initial healing response but excessive myofibroblast activation leads to pathological fibrosis. Therefore, it is imperative to understand the mechanisms underlying myofibroblast formation. Here we report that mitochondrial calcium (mCa2+) signaling is a regulatory mechanism in myofibroblast differentiation and fibrosis. We demonstrate that inhibition of mCa2+ uptake in fibroblasts enhances myofibroblast formation and this translates to increased fibrosis following injury. Fibrotic signaling alters the gating of the mitochondrial calcium uniporter (mtCU) to reduce mCa2+ uptake and induce specific changes in metabolism. mCa2+-dependent metabolic reprogramming leads to the activation of αKG-dependent demethylases which epigenetically modify promoter regions specific to the myofibroblast gene program resulting in differentiation. Our results uncover an important role for mCa2+ uptake beyond metabolic regulation and cell death and demonstrate that mCa2+ signaling regulates the epigenome to influence cellular differentiation.
Project description:T-cell receptor-induced Ca2+ signals are essential for proper T-cell activation and function. In this context, mitochondria play an important role and take up Ca2+ to support elevated bioenergetic demands. The protein machinery that regulates mitochondrial Ca2+ (mCa2+) uptake; the mitochondrial calcium uniporter (MCU) complex, could be thus implicated in T-cell immunity. However, the exact role of MCU in T-cells is not understood. Here, we show that upon activation of naïve T-cells, the MCU complex undergoes a compositional rearrangement that causes elevated mCa2+ uptake and increased bioenergetic output. Transcriptome and proteome analyses reveal molecular determinants involved in mitochondrial functional reprograming and identify signaling pathways controlled by MCU. MCUa knockdown diminishes mCa2+ uptake, mitochondrial respiration and ATP production as well as T-cell invasion and cytokine secretion. In vivo, downregulation of MCUa in rat CD4+ T-cells suppresses autoimmune responses in a multiple sclerosis model of inflammatory experimental autoimmune encephalomyelitis. In summary, Ca2+ uptake through MCU is essential for proper T-cell function and is involved in autoimmunity. T-cell specific MCU inhibition is a potential tool for treating autoimmune disorders.
Project description:Sustained and balanced calcium (Ca2+) increase upon T-cell receptor activation is a fundamental process that regulates essential T-cell functions including proliferation, clonal expansion and cytokine secretion. In this context, mitochondria play an important role and take up Ca2+ to support the elevated bioenergetic demands. Accordingly, alterations in the protein machinery that regulates mitochondrial Ca2+ (mCa2+) flux across the inner mitochondrial membrane; the mitochondrial calcium uniporter (MCU) complex, could be implicated in T-cell immunity. However, the exact role of mCa2+, and thus MCU in T-cells is not fully understood. Here, we show that upon activation of primary human CD4+ T-cells, the MCU complex undergoes a time-dependent compositional rearrangement that causes elevated mCa2+ uptake and increased mitochondrial bioenergetic output. Transcriptome and proteome analyses of naive and effector CD4+ T-cells reveal molecular determinants involved in mitochondrial and T-cell functional reprograming. Moreover, they identify genes, proteins and signaling pathways controlled by mitochondrial Ca2+ homeostasis i.e. the MCU. MCUa knockdown (KD) diminishes mCa2+, mitochondrial respiration and ATP production as well as T-cell invasion and cytokine secretion. In vivo, downregulation of MCUa in rat CD4+ T-cells suppresses autoimmune responses in a multiple sclerosis model of inflammatory experimental autoimmune encephalomyelitis (EAE). In summary, our findings imply that mCa2+ uptake through MCU is essential for proper T-cell function and is involved in autoimmunity. Specific MCU inhibitors targeting T-cells could be beneficial for autoimmune suppression and control of immune system dysregulation.
Project description:MICU1 is a Ca2+-binding protein that regulates the mitochondrial Ca2+ uniporter channel (mtCU ) and mitochondrial Ca2+ (mCa2+) uptake. MICU1 knockout mice display perinatal lethality and disorganized mitochondrial architecture. These phenotypes are distinct from other mtCU loss-of-function models and thus are not explained by changes in mCa2+ content. Utilizing multiple proteomic approaches, we found that MICU1 localized to mitochondrial complexes lacking MCU, suggesting that MICU1 has cellular functions independent of mCa2+ uptake. The overall aim of the current project is to identify the global and mtCU independent MICU1 interactome to characterize the MCU independent functions of the MICU1.
Project description:Rhabdomyosarcoma (RMS), the most common paediatric soft-tissue sarcoma, is characterized by cells of skeletal muscle origin that fail to both irreversibly exit the cell cycle and complete skeletal muscle differentiation. Embryonal rhabdomyosarcoma (ERMS) is the most prevalent subtype of RMS and its molecular signatures has been associated with metabolism defects and increased oxidative stress. However, the details of the contributing factors or molecules have not been studied. Both metabolism and oxidative stress are associated with mitochondrial functions and an important molecule that regulates mitochondrial functions is calcium. Till date, there has been no studies that examine the role of mitochondrial calcium in ERMS. In addition, the molecular component of mitochondrial calcium uniporter complex, which is responsible for the uptake of mitochondrial calcium was only discovered in 2012. Since then, there has been an increasing interest in investigating the role of mitochondrial calcium and mitochondrial calcium uniporter complex in various cancers. Mitochondrial calcium uniporter (MCU), the main channel forming protein is often found to be dysregulated in various cancers. Our preliminary data has shown that mitochondrial calcium is dysregulated in ERMS due to overexpression of MCU. This dysregulation of mitochondrial calcium has led to multiple mitochondrial dysfunctions and oncogenic phenotypes. Hence, we would like to investigate the downstream targets of MCU in order to identify the mechanism through which MCU regulates oncogenic phenotypes in ERMS.
Project description:Metabolic adaptations are essential for survival. The mitochondrial calcium uniporter plays a key role in coordinating metabolic homeostasis by regulating mitochondrial metabolic pathways, and calcium signaling. However, a comprehensive analysis of uniporter-regulated mitochondrial pathways has remained unexplored. Here, we investigate consequences of uniporter loss- and gain-of-function using uniporter knockout cells and fibrolamellar carcinoma (FLC), which we demonstrate to have elevated mitochondrial calcium levels. We find that branched-chain amino acid (BCAA) catabolism, and the urea cycle are uniporter-regulated pathways. Reduced uniporter function boosts expression of BCAA catabolism genes, and the urea cycle enzyme ornithine transcarbamylase. In contrast, high uniporter activity in FLC suppresses their expression. This suppression is mediated by the transcription factor KLF15, a master regulator of liver metabolism. Thus, uniporter plays a central role in FLC-associated metabolic changes, including hyperammonemia. Our study identifies an important role for the uniporter in metabolic adaptation through transcriptional regulation of metabolism and elucidates its importance for BCAA and ammonia metabolism in FLC.
Project description:Differentiation of cardiac fibroblasts (CFs) to myofibroblasts is necessary for matrix remodeling and fibrosis in heart failure. We previously reported mitochondrial calcium signaling drives α-ketoglutarate-dependent histone demethylation, promoting the myofibroblast gene program. Here, we investigated the role of ATP-citrate lyase (ACLY), a key enzyme for acetyl-CoA biosynthesis, in histone acetylation regulating myofibroblast formation and persistence in cardiac fibrosis. Inactivation of ACLY prevented, and importantly reversed, myofibroblasts towards quiescence. Genetic deletion of Acly in activated myofibroblasts prevented fibrosis and preserved cardiac function in murine pressure-overload. TGFβ stimulation enhanced ACLY nuclear localization and increased H3K27ac at fibrotic gene loci. Pharmacological inhibition of ACLY or forced nuclear expression of dominant-negative ACLY mutant prevented myofibroblast formation and H3K27ac. Our data indicate nuclear ACLY activity is necessary for myofibroblast differentiation and persistence by maintaining histone acetylation at TGFβ-induced myofibroblast genes. These findings provide novel clinical rational to prevent and reverse pathological fibrosis. CUT&RUN Sequencing for H3K27ac on the role of ACLY in myofibroblast differentiaton.
Project description:Muscle atrophy contributes to the poor prognosis of many physiopathological conditions, but pharmacological therapies are still limited. Muscle activity leads to major swings in mitochondrial [Ca2+] which control aerobic metabolism, cell death and survival pathways. We have investigated in vivo the effects of mitochondrial Ca2+ homeostasis in skeletal muscle function and trophism, by overexpressing or silencing the Mitochondrial Calcium Uniporter (MCU). The results coherently demonstrate that both in developing and in adult muscles MCU-dependent mitochondrial Ca2+ uptake has a marked trophic effect that does not depend on autophagy or aerobic control, but impinges on two major hypertrophic pathways of skeletal muscle, PGC-1M-NM-14 and Igf1-Akt/PKB. In adult mice, MCU overexpression protects from denervation-induced atrophy. These data reveal a novel Ca2+-dependent organelle-to-nucleus signaling route, which links mitochondrial function to the control of muscle mass and may represent a possible pharmacological target in sarcopenia. Experiments were performed on biological replicates of single skeletal muscle fibres. Seven fibres were chosen for their Mutochondrial Calcium Uniporter (MCU) overexpression and other seven fibres because MCU was silenced. Overexpression and silencing were performed injecting skeletal muscle with AAV containing MCU gene or short interfering oligos specific for MCU. As control was profiled eigth fibres transfected with AAV and eigth wild type fibres. Analyses were performed 7 days and 14 days after the AAV injection (3 fibers after 7 days and 4 fibers after 14 days for MCU overexpression and silencing, four fibres after 7 days and four after 14 days for control).
Project description:The mitochondrial calcium uniporter has been proposed to coordinate the organelle’s energetics with cytosolic calcium signaling. Previous studies have shown that the uniporter current is extremely high in mitochondria from brown adipose tissue (BAT), yet the contribution of the uniporter to BAT physiology in vivo is not known. Here, we report the generation and characterization of a mouse model lacking Mcu, the pore forming subunit of the uniporter, specifically in BAT (BAT-Mcu-KO). BAT-Mcu-KO mice are born in Mendelian ratios on a C57BL6/J genetic background, without any overt phenotypes. Although uniporter based calcium uptake is selectively ablated in BAT mitochondria, these mice are able to defend their body temperature in response to cold challenge and exhibit a normal body weight trajectory on a high fat diet. BAT transcriptional profiles at baseline and following cold-challenge are intact and not impacted by loss of Mcu. Unexpectedly, we found that cold powerfully activates the ATF4-dependent integrated stress response in BAT, and increases both circulating FGF21 and GDF15 levels, raising the hypothesis that the integrated stress response partly underlies the pleiotropic effects of BAT on systemic metabolism. Our study demonstrates that the uniporter is largely dispensable for BAT thermogenesis, and unexpectedly, uncovers a striking activation of the integrated stress response of BAT to cold challenge.
Project description:Metabolic adaptations in response to changes in energy supply and demand are essential for survival. The mitochondrial calcium uniporter plays a key role in coordinating metabolic homeostasis by regulating TCA cycle activation, mitochondrial fatty acid oxidation and cellular calcium signaling. However, a comprehensive analysis of uniporter-regulated mitochondrial metabolic pathways has remained unexplored. Here, we investigate metabolic consequences of uniporter loss- and gain-of-function using uniporter knock out cells and the liver cancer fibrolamellar carcinoma (FLC), which we demonstrate to have elevated mitochondrial calcium levels. Our results reveal that branched chain amino acid (BCAA) catabolism and the urea cycle are uniporter-regulated metabolic pathways. Reduced uniproter function increases expression of BCAA catabolism genes, and the urea cycle enzyme ornithine transcarbamylase (OTC). In contrast, high uniporter activity in FLC suppresses their expression. This suppression happens via the transcription factor KLF15, a master regulator of liver metabolism, suggesting that calcium signaling plays a central role in FLC-associated metabolic changes, including hyperammonemia. Consistent with this, activation of BCAA catabolism in FLC cells impairs their growth. Collectively, our study identifies an important role for mitochondrial calcium signaling in metabolic adaptation through transcriptional regulation of metabolism and elucidates its importance for BCAA and ammonia metabolism in FLC.