Mitochondrial calcium exchange links metabolism with the epigenome to control cellular differentiation.

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 fibrotic signaling alters gating of the mitochondrial calcium uniporter (mtCU) in a MICU1-dependent fashion to reduce mCa2+ uptake and induce coordinated changes in metabolism, i.e., increased glycolysis feeding anabolic pathways and glutaminolysis yielding increased α-ketoglutarate (αKG) bioavailability. mCa2+-dependent metabolic reprogramming leads to the activation of αKG-dependent histone demethylases, enhancing chromatin accessibility in loci specific to the myofibroblast gene program, resulting in differentiation. Our results uncover an important role for the mtCU beyond metabolic regulation and cell death and demonstrate that mCa2+ signaling regulates the epigenome to influence cellular differentiation

SLC25A51 is a mammalian mitochondrial NAD+ transporter

Mitochondria require nicotinamide adenine dinucleotide (NAD+) to carry out the fundamental processes that fuel respiration and mediate cellular energy transduction. Mitochondrial NAD+ transporters have been identified in yeast and plants1,2, but their existence in mammals remains controversial3,4,5. Here we demonstrate that mammalian mitochondria can take up intact NAD+, and identify SLC25A51 (also known as MCART1)—an essential6,7 mitochondrial protein of previously unknown function—as a mammalian mitochondrial NAD+ transporter. Loss of SLC25A51 decreases mitochondrial—but not whole-cell—NAD+ content, impairs mitochondrial respiration, and blocks the uptake of NAD+ into isolated mitochondria. Conversely, overexpression of SLC25A51 or SLC25A52 (a nearly identical paralogue of SLC25A51) increases mitochondrial NAD+ levels and restores NAD+ uptake into yeast mitochondria lacking endogenous NAD+ transporters. Together, these findings identify SLC25A51 as a mammalian transporter capable of importing NAD+ into mitochondria.acceptedVersio

Observation of γγ → ττ in proton-proton collisions and limits on the anomalous electromagnetic moments of the τ lepton

The production of a pair of τ leptons via photon–photon fusion, γγ → ττ, is observed for the f irst time in proton–proton collisions, with a significance of 5.3 standard deviations. This observation is based on a data set recorded with the CMS detector at the LHC at a center-of-mass energy of 13 TeV and corresponding to an integrated luminosity of 138 fb−1. Events with a pair of τ leptons produced via photon–photon fusion are selected by requiring them to be back-to-back in the azimuthal direction and to have a minimum number of charged hadrons associated with their production vertex. The τ leptons are reconstructed in their leptonic and hadronic decay modes. The measured fiducial cross section of γγ → ττ is σfid obs = 12.4+3.8 −3.1 fb. Constraints are set on the contributions to the anomalous magnetic moment (aτ) and electric dipole moments (dτ) of the τ lepton originating from potential effects of new physics on the γττ vertex: aτ = 0.0009+0.0032 −0.0031 and |dτ| < 2.9×10−17ecm (95% confidence level), consistent with the standard model

Abstract 435: The Mitochondrial Calcium Uniporter is Necessary for Cardiac Energetic Signaling During Chronic Stress

The mitochondrial calcium uniporter (MCU) is a multicomponent channel that is the primary mechanism for mitochondrial Ca 2+ uptake ( m Ca 2+ ). We previously reported that the MCU is required for energetic signaling to meet contractile demand during the ‘fight or flight’ response. In addition, we showed that deletion of the pore-forming component ( Mcu gene) protected against mitochondria permeability transition pore (MPTP) opening and ischemia-reperfusion injury. However, results from our study and others questioned the physiological relevance of MCU-mediated Ca 2+ uptake during chronic stress states featuring sustained intracellular Ca 2+ load ( i Ca 2+ ). To address this, we deleted Mcu from cardiomyocytes in adult mice ( Mcu cKO) and implanted osmotic pumps to deliver the β adrenergic agonist isoproterenol (iso, 70 mg/kg/day for 14d). In contrast to controls, Mcu cKO mice lacked contractile responsiveness to chronic βAR stimulation with evidence of LV dysfunction and failure by d14 ( Fig 1 ). Next, we crossed the Mcu cKO with mice overexpressing the β2a subunit (β2a-Tg) of the L-type Ca 2+ channel (LTCC). This model displays enhanced LTCC activity and cardiac contractility, but with added stress such as iso infusion, Ca 2+ overload eventually leads to MPTP-dependent cell death and heart failure. Surprisingly, loss of Mcu in this model was lethal with all mice dying by d13 ( Fig 2 ). Baseline echocardiography revealed that loss of Mcu ablated all β2a-mediated enhancements in LV contractility and accelerated dysfunction post-iso. These findings demonstrate that MCU-mediated m Ca 2+ uptake is critical to meet energetic demand during chronic stress states featuring sustained i Ca 2+ load. </jats:p

Abstract 279: Mitochondrial Bioenergetic Signaling Drives Myofibroblast Transdifferentiation

When the heart is injured, quiescent fibroblasts differentiate into contractile, synthetic myofibroblasts. Initially fibrosis is reparative, but when chronic it becomes maladaptive and contributes to HF. Intracellular Ca 2+ ( i Ca 2+ ) signaling is reported to be necessary for myofibroblast transdifferentiation yet the role of mitochondrial Ca 2+ ( m Ca 2+ ) exchange has not been explored. The Mcu gene encodes the channel-forming subunit of the m Ca 2+ uniporter channel (MCUc) and is required for acute m Ca 2+ uptake. To examine the contribution of m Ca 2+ in cardiac fibrosis, we generated conditional, fibroblast-specific knockout mice by crossbreeding Mcu fl/fl mice with Col1a2-CreERT mice (Col1a2- Mcu -/- ), permitting tamoxifen-inducible gene deletion in adult mice. Col1a2- Mcu -/- mice and controls were subjected to ligation of the left coronary artery and cardiac function was examined by echocardiography. Loss of fibroblast Mcu worsened LV function and increased fibrosis, as evaluated by Mason’s trichrome staining and qPCR analysis of fibrotic gene expression. To examine the cellular mechanisms responsible for the increased fibrosis we isolated mouse embryonic fibroblasts (MEFs) from Mcu fl/fl mice and deleted Mcu with Cre-adenovirus. When challenged with pro-fibrotic ligands (TGF-β and AngII), Mcu -/- MEFs exhibited decreased m Ca 2+ uptake and enhanced i Ca 2+ transient amplitude. Loss of Mcu promoted myofibroblast transdifferentiation: increased α-SMA expression and contractile function (gel retraction) and decreased migration and proliferation. Mcu -/- MEFs were more glycolytic with increased phosphorylation (inactivation) of pyruvate dehydrogenase. Genetic activation of glycolysis with a Pfk2 mutant in WT MEFs promoted myofibroblast differentiation. Conversely, genetic inhibition of glycolytic flux ablated the increased transdifferentiation observed in Mcu -/- MEFs. Further, TGF-β and AngII altered the expression of regulatory MCUc components in WT MEFs. Our results suggest that alterations in m Ca 2+ uptake and bioenergetic pathways are necessary for myofibroblast transdifferentiation. Thus, energetic signaling represents a novel therapeutic target to impede HF progression and other progressive fibrotic diseases. </jats:p

Abstract 851: NCLX Expression Attenuates Pathological Remodeling in Experimental Cardiac Hypertrophy and Non-ischemic Heart Failure

Mitochondrial calcium ( m Ca 2+ ) uptake couples acute changes in cardiomyocyte bioenergetic demand to ATP production, but in excess triggers mitochondrial permeability transition and cardiomyocyte necrosis, as occurs during cardiac injury. Despite established roles for m Ca 2+ flux in response to acute stress, the role of m Ca 2+ signaling in chronic stress is poorly defined. As m Ca 2+ regulates the TCA cycle with the potential to affect mitochondrial signaling and/or metabolite pools required for biosynthesis, we reasoned that altered m Ca 2+ homeostasis may be an essential mechanism underlying hypertrophic growth and remodeling of the myocardium. Here, we used mice with cardiac-specific overexpression (OE) of the mitochondrial Na + /Ca 2+ exchanger (NCLX), the primary mediator of m Ca 2+ efflux in the heart, to test the hypothesis that m Ca 2+ signaling contributes to cardiac remodeling during sustained hemodynamic stress. We subjected NCLX OE (TRE-NCLX x α-MHC-tTA) and control (αMHC-tTA) mice to 12-wk transverse aortic constriction (TAC) or 4-wk infusion with angiotensin II + phenylephrine (AngII/PE) as experimental models of cardiac hypertrophy and non-ischemic heart failure. Cardiac function of NCLX OE and control mice was monitored throughout these studies via echocardiography and remodeling was assessed via tissue gravimetrics, histology, and qPCR gene expression analysis. Cardiac NCLX OE preserved ejection fraction, prevented afterload-induced hypertrophy and fibrosis, and attenuated the induction of both hypertrophic ( Nppa , Nppb , Acta1 ) and fibrotic ( Postn1 , Spp1 ) gene programs in mice subjected to 12-wk TAC. Examination at 2-wk post-TAC revealed attenuated hypertrophy and blunted hypertrophic and fibrotic gene expression in NCLX OE mice. These data indicate that increased capacity for m Ca 2+ efflux mitigates TAC-induced remodeling, prior to the development of contractile dysfunction. NCLX OE similarly attenuated atrial hypertrophy and the induction of hypertrophic and fibrotic gene programs in mice infused with AngII/PE. Together, these findings support a critical role for m Ca 2+ in driving pathological remodeling in non-ischemic heart disease and point to NCLX as a potent therapeutic target for cardiovascular disease. </jats:p