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Gold nanoparticles are promising candidates as vehicles for drug delivery systems and could be developed into effective anticancer treatments. However, concerns about their safety need to be identified, addressed, and satisfactorily answered. Although gold nanoparticles are considered biocompatible and nontoxic, most of the toxicology evidence originates from in vitro studies, which may not reflect the responses in complex living organisms. We used an animal model to study the long-term effects of 20 nm spherical AuNPs coated with bovine serum albumin. Mice received a 1 mg/kg single intravenous dose of nanoparticles, and the biodistribution and accumulation, as well as the organ changes caused by the nanoparticles, were characterized in the liver, spleen, and kidneys during 120 days. The amount of nanoparticles in the organs remained high at 120 days compared with day 1, showing a 39% reduction in the liver, a 53% increase in the spleen, and a 150% increase in the kidneys. The biological effects of chronic nanoparticle exposure were associated with early inflammatory and fibrotic responses in the organs and were more pronounced in the kidneys, despite a negligible amount of nanoparticles found in renal tissues. Our data suggest, that although AuNPs belong to the safest nanomaterial platforms nowadays, due to their slow tissue elimination leading to long-term accumulation in the biological systems, they may induce toxic responses in the vital organs, and so understanding of their long-term biological impact is important to consider their potential therapeutic applications.

Although in flies the atypical cadherin Fat is an upstream regulator of Hippo signalling, the closest mammalian homologue, Fat4, has been shown to regulate tissue polarity rather than growth. Here we show in the mouse heart that Fat4 modulates Hippo signalling to restrict growth. Fat4 mutant myocardium is thicker, with increased cardiomyocyte size and proliferation, and this is mediated by an upregulation of the transcriptional activity of Yap1, an effector of the Hippo pathway. Fat4 is not required for the canonical activation of Hippo kinases but it sequesters a partner of Yap1, Amotl1, out of the nucleus. The nuclear translocation of Amotl1 is accompanied by Yap1 to promote cardiomyocyte proliferation. We, therefore, identify Amotl1, which is not present in flies, as a mammalian intermediate for non-canonical Hippo signalling, downstream of Fat4. This work uncovers a mechanism for the restriction of heart growth at birth, a process which impedes the regenerative potential of the mammalian heart. Growth of the mammalian heart is controlled by Hippo signalling but how this is regulated is unclear. Here, the authors show that Fat4 (an atypical cadherin) acts upstream of Hippo signalling and Fat4 mutant mice have thicker myocardium, which is mediated by the scaffold Amot1 and transcription factor Yap1.

Many recent studies have demonstrated the involvement of endoplasmic reticulum (ER) stress in the development of cardiac diseases and have suggested that modulation of ER stress response could be cardioprotective. Previously, we demonstrated that the deacetylase Sirtuin 1 (SIRT1) attenuates ER stress response and promotes cardiomyocyte survival. Here, we investigated whether and how autophagy plays a role in SIRT1-afforded cardioprotection against ER stress. The results revealed that protective autophagy was initiated before cell death in response to tunicamycin (TN)-induced ER stress in cardiac cells. SIRT1 inhibition decreased ER stress-induced autophagy, whereas its activation enhanced autophagy. In response to TN- or isoproterenol-induced ER stress, mice deficient for SIRT1 exhibited suppressed autophagy along with exacerbated cardiac dysfunction. At the molecular level, we found that in response to ER stress (i) the extinction of eEF2 or its kinase eEF2K not only reduced autophagy but further activated cell death, (ii) inhibition of SIRT1 inhibited the phosphorylation of eEF2, (iii) eIF2α co-immunoprecipitated with eEF2K, and (iv) knockdown of eIF2α reduced the phosphorylation of eEF2. Our results indicate that in response to ER stress, SIRT1 activation promotes cardiomyocyte survival by enhancing autophagy at least through activation of the eEF2K/eEF2 pathway.

Adult striated muscle cells present highly organized structure with densely packed intracellular organelles and a very sparse cytosol accounting for only few percent of cell volume. These cells have a high and fluctuating energy demand that, in continuously working oxidative muscles, is fulfilled mainly by oxidative metabolism. ATP produced by mitochondria should be directed to the main energy consumers, ATPases of the excitation-contraction system; at the same time, ADP near ATPases should rapidly be eliminated. This is achieved by phosphotransfer kinases, the most important being creatine kinase (CK). Specific CK isoenzymes are located in mitochondria and in close proximity to ATPases, forming efficient energy shuttle between these structures. In addition to phosphotransfer kinases, ATP/ADP can be directly channeled between mitochondria co-localized with ATPases in a process called “direct adenine nucleotide channeling, DANC.” This process is highly plastic so that inactivation of the CK system increases the participation of DANC to energy supply owing to the rearrangement of cell structure. The machinery for DANC is built during postnatal development in parallel with the increase in mitochondrial mass, organization, and complexification of the cell structure. Disorganization of cell architecture remodels the mitochondrial network and decreases the efficacy of DANC, showing that this process is intimately linked to cardiomyocyte structure. Accordingly, in heart failure, disorganization of the cell structure along with decrease in mitochondrial mass reduces the efficacy of DANC and together with alteration of the CK shuttle participates in energetic deficiency contributing to contractile failure.

Background The AMP-activated protein kinase (AMPK) is a major regulator of cellular energetics which plays key role in acute metabolic response and in long-term adaptation to stress. Recent works have also suggested non-metabolic effects. Methods To decipher AMPK roles in the heart, we generated a cardio-specific inducible model of gene deletion of the main cardiac catalytic subunit of AMPK ( Ampkα2 ) in mice. This allowed us to avoid the eventual impact of AMPK-KO in peripheral organs. Results Cardio-specific Ampkα2 deficiency led to a progressive left ventricular systolic dysfunction and the development of cardiac fibrosis in males. We observed a reduction in complex I-driven respiration without change in mitochondrial mass or in vitro complex I activity, associated with a rearrangement of the cardiolipins and reduced integration of complex I into the electron transport chain supercomplexes. Strikingly, none of these defects were present in females. Interestingly, suppression of estradiol signaling by ovariectomy partially mimicked the male sensitivity to AMPK loss, notably the cardiac fibrosis and the rearrangement of cardiolipins, but not the cardiac function that remained protected. Conclusion Our results confirm the close link between AMPK and cardiac mitochondrial function, but also highlight links with cardiac fibrosis. Importantly, we show that AMPK is differently involved in these processes in males and females, which may have clinical implications for the use of AMPK activators in the treatment of heart failure. Highlights AMPK is a metabolic sensor of cellular energy which regulates energy homeostasis. We generated a cardiac-specific inducible deletion of Ampkα2 and demonstrated that this deletion induces mild cardiac dysfunction in male only. Cardiac dysfunction observed in males was associated with cardiac fibrosis and cardiac cardiolipin remodeling that are not seen in females. Although no significant cardiac function alteration was noticed in ovariectomized female Ampkα2ciKO mice, these latter exhibited cardiac fibrosis and mild cardiolipins remodeling. Our results show a higher dependence on AMPK signaling fibrosis and cardiolipin biosynthesis/maturation in males, either due to the absence of female hormones protection or/and to the action of male hormones. This may contribute to the known difference in cardiovascular risk and outcome between sexes.

Cardiac excitation-contraction coupling relies on dyads, the intracellular calcium synapses of cardiac myocytes, where the plasma membrane contacts sarcoplasmic reticulum and where electrical excitation triggers calcium release. The morphology of dyads and dynamics of local calcium release vary substantially. To better understand the correspondence between the structure and the functionality of dyads, we estimated incidences of structurally different dyads and of kinetically different calcium release sites and tested their responsiveness to experimental myocardial injury in left ventricular myocytes of rats. According to the structure of dyads estimated in random electron microscopic images of myocardial tissue, the dyads were sorted into ‘compact’ or ‘loose’ types. The calcium release fluxes, triggered at local calcium release sites in patch-clamped ventricular myocytes and recorded by laser scanning confocal fluorescence microscopy, were decomposed into ‘early’ and ‘late’ components. ANOVA tests revealed very high correlation between the relative amplitudes of early and late calcium release flux components and the relative occurrences of compact and loose dyads in the control and in the injured myocardium. This finding ascertained the relationship between the structure of dyads and the functionality of calcium release sites and the responsiveness of calcium release sites to physical load in cardiac myocytes.

AMP-Activated Protein Kinase α2 Deficiency Affects Cardiac Cardiolipin Homeostasis and Mitochondrial Function Yoni Athéa 1 2 3 , Benoît Viollet 4 5 6 7 , Philippe Mateo 1 2 3 , Delphine Rousseau 2 3 8 , Marta Novotova 9 , Anne Garnier 1 2 3 , Sophie Vaulont 4 5 6 7 , James R. Wilding 1 2 3 , Alain Grynberg 2 3 8 , Vladimir Veksler 1 2 3 , Jacqueline Hoerter 1 2 3 and Renée Ventura-Clapier 1 2 3 1 Institut National de la Santé et de la Recherche Médicale U769, Châtenay-Malabry, France 2 Université Paris-Sud 11, Châtenay-Malabry, France 3 Institut Fédératif de Recherche 141, Châtenay-Malabry, France 4 Institut Cochin, Département Endocrinologie Métabolisme et Cancer, Paris, France 5 Institut National de la Santé et de la Recherche Médicale U567, Paris, France 6 Centre National de la Recherche Scientifique, Unité Mixte de Recherche 8104, Paris, France 7 Université Paris 5, Faculté de Médecine René Descartes, Unité mixte 3, Paris, France 8 Institut National de la Recherche Agronomique-Unité Mixte de Recherche 1154, Châtenay-Malabry, France 9 Institute of Molecular Physiology and Genetics, Slovak Academy of Sciences, Bratislava, Slovak Republic Address correspondence and reprint requests to Renée Ventura-Clapier, INSERM U-769, Université Paris-Sud, 5 rue J6B Clément, F-92296 Châtenay-Malabry, France. E-mail: renee.ventura{at}u-psud.fr Abstract AMP-activated protein kinase (AMPK) plays an important role in controlling energy homeostasis and is envisioned as a promising target to treat metabolic disorders. In the heart, AMPK is involved in short-term regulation and in transcriptional control of proteins involved in energy metabolism. Here, we investigated whether deletion of AMPKα2, the main cardiac catalytic isoform, alters mitochondrial function and biogenesis. Body weight, heart weight, and AMPKα1 expression were similar in control littermate and AMPKα2 −/− mice. Despite normal oxygen consumption in perfused hearts, maximal oxidative capacity, measured using saponin permeabilized cardiac fibers, was ∼30% lower in AMPKα2 −/− mice with octanoate, pyruvate, or glutamate plus malate but not with succinate as substrates, showing an impairment at complex I of the respiratory chain. This effect was associated with a 25% decrease in mitochondrial cardiolipin content, the main mitochondrial membrane phospholipid that is crucial for complex I activity, and with a 13% decrease in mitochondrial content of linoleic acid, the main fatty acid of cardiolipins. The decrease in cardiolipin content could be explained by mRNA downregulation of rate-limiting enzymes of both cardiolipin synthesis (CTP:PA cytidylyltransferase) and remodeling (acyl-CoA:lysocardiolipin acyltransferase 1). These data reveal a new role for AMPKα2 subunit in the regulation of cardiac muscle oxidative capacity via cardiolipin homeostasis. ALCAT1, acyl-CoA:lysocardiolipin acyltransferase 1 AMPK, AMP-activated protein kinase CDS2, CTP:PA cytidylyltransferase CK, creatine kinase COX, cytochrome c oxidase CPT-1, carnitine palmitoyl transferase 1 FADH2, reduced flavine adenine dinucleotide G3P, glycerol-3-phosphate MDH, malate dehydrogenase mi-CK, mitochondrial creatine kinase NAO, 10N-nonyl acridine orange OMC, oxoglutarate/malate carrier PGC-1α, peroxisome proliferator–activated receptor-γ coactivator-1α Footnotes The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact. Accepted November 27, 2006. Received February 9, 2006. DIABETES

Electrical pulse stimulation (EPS) represents a useful tool to study exercise‐related adaptations of muscle cells in vitro. Here, we examine the metabolic and secretory response of primary human muscle cells from metabolically healthy individuals to the EPS protocol reflecting the episodic nature of real‐life exercise training. This intermittent EPS protocol alternates high‐frequency stimulation periods with low‐frequency resting periods. Continuous EPS was used as a comparator. Radiometric assessment of glucose and fatty acid metabolism was complemented by examination of mitochondrial OxPHOS proteins, fiber‐type markers, and the release of selected myokines and extracellular vesicles into the media. Both EPS protocols facilitated glycogen synthesis and incomplete fatty acid oxidation (intermediary metabolites accumulation), while complete glucose and fatty acid oxidation (CO2 production) was increased only after the intermittent stimulation. Continuous stimulation elicited robust release of the contraction‐regulated myokines (IL6, IL8) into the media. Both EPS protocols increased expression of oxidative fiber‐type markers (MYH2, MYH7), while inducing protein expression of a putative myokine, growth differentiation factor11 (GDF11) and a release of extracellular vesicles into the media. In conclusion, intermittent electrical pulse stimulation enhanced the rate of complete glucose and fatty acid oxidation in differentiated muscle cells from metabolically healthy individuals, while it was comparable to continuous stimulation in modulating markers of oxidative fibers and a putative myokine GDF11, and less effective in stimulating the release of myokines IL6, IL8, and extracellular vesicles into the media. Intermittent EPS—a protocol mimicking the episodic nature of exercise—can be used for studying metabolism and the secretome of skeletal muscle cells in vitro. Here, we introduced an intermittent electrical stimulation protocol mimicking the episodic nature of real‐life exercise in vitro by alternating low‐ and high‐frequency stimulation. In comparison with widely used continuous stimulation, it enhanced the rate of glucose and fatty acid oxidation, but not the myokine release. Both protocols increased the rate of glycogen synthesis, oxidative fiber‐type markers, and extracellular vesicles' release.

The coronavirus transforms the cytoplasm of susceptible cells to support virus replication. It also activates autophagy-like processes, the role of which is not well understood. Here, we studied SARS-CoV-2-infected Vero E6 cells using transmission electron microscopy and autophagy PCR array. After 6–24 h post-infection (hpi), the cytoplasm of infected cells only contained double-membrane vesicles, phagophores, and phagosomes engulfing virus particles and cytoplasmic debris, including damaged mitochondria. The phagosomes interacted with the viral nucleoprotein complex, virus particles, mitochondria, and lipid droplets. The phagosomes transformed into egress vacuoles, which broke through the plasmalemma and discharged the virus particles. The Vero E6 cells exhibited pronounced virus replication at 6 hpi, which stabilized at 18–24 hpi at a high level. The autophagy PCR array tests revealed a significant upregulation of 10 and downregulation of 8 autophagic gene markers out of 84. Altogether, these results underline the importance of autophagy-like processes for SARS-CoV-2 maturation and egress, and point to deviations from a canonical autophagy response.

The unicellular fission yeast Schizosaccharomyces pombe (S. pombe) has become a prominent model system to elucidate a various range of biological processes which are highly conserved in mammalian cells. Ultrastructure of the cells related to the organelle morphology is useful in the generation of the comprehensive overview of the cell function. Transmission electron microscopy provides a unique tool to study cell architecture under physiological conditions, as well as ultrastructural changes of the cells due to toxic or beneficial effects of diverse additives. In recent years, S. pombe has also proved to be a suitable cell system for transmission electron microscopy investigations. In the current study, general features of S. pombe are described. In addition, conventional specimen preparation technique and the important discoveries of cell architecture emerging from transmission electron microscopy studies of S. pombe are summarized.