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1. Metabolic alterations caused by the mutation and overexpression of the Tmem135 gene

   https://doi.org/10.1177/1535370220932856  

   Lee, Wei-Hua ; Bhute, Vijesh J ; Higuchi, Hitoshi ; Ikeda, Sakae ; Palecek, Sean P ; Ikeda, Akihiro ( November 2020 , Experimental Biology and Medicine)

   null (Ed.)

   Mitochondria are dynamic organelles that undergo fission and fusion. While they are essential for cellular metabolism, the effect of dysregulated mitochondrial dynamics on cellular metabolism is not fully understood. We previously found that transmembrane protein 135 ( Tmem135) plays a role in the regulation of mitochondrial dynamics in mice. Mice homozygous for a Tmem135 mutation ( Tmem135 FUN025/FUN025 ) display accelerated aging and age-related disease pathologies in the retina including the retinal pigment epithelium (RPE). We also generated a transgenic mouse line globally overexpressing the Tmem135 gene ( Tmem135 TG). In several tissues and cells that we studied such as the retina, heart, and fibroblast cells, we observed that the Tmem135 mutation causes elongated mitochondria, while overexpression of Tmem135 results in fragmented mitochondria. To investigate how abnormal mitochondrial dynamics affect metabolic signatures of tissues and cells, we identified metabolic changes in primary RPE cell cultures as well as heart, cerebellum, and hippocampus isolated from Tmem135 FUN025/FUN025 mice (fusion > fission) and Tmem135 TG mice (fusion < fission) using nuclear magnetic resonance spectroscopy. Metabolomics analysis revealed a tissue-dependent response to Tmem135 alterations, whereby significant metabolic changes were observed in the heart of both Tmem135 mutant and TG mice as compared to wild-type, while negligible effects were observed in the cerebellum and hippocampus. We also observed changes in Tmem135 FUN025/FUN025 and Tmem135 TG RPE cells associated with osmosis and glucose and phospholipid metabolism. We observed depletion of NAD + in both Tmem135 FUN025/FUN025 and Tmem135 TG RPE cells, indicating that imbalance in mitochondrial dynamics to both directions lowers the cellular NAD + level. Metabolic changes identified in this study might be associated with imbalanced mitochondrial dynamics in heart tissue and RPE cells which can likely lead to functional abnormalities. Impact statement Mitochondria are dynamic organelles undergoing fission and fusion. Proper regulation of this process is important for healthy aging process, as aberrant mitochondrial dynamics are associated with several age-related diseases/pathologies. However, it is not well understood how imbalanced mitochondrial dynamics may lead to those diseases and pathologies. Here, we aimed to determine metabolic alterations in tissues and cells from mouse models with over-fused (fusion > fission) and over-fragmented (fusion < fission) mitochondria that display age-related disease pathologies. Our results indicated tissue-dependent sensitivity to these mitochondrial changes, and metabolic pathways likely affected by aberrant mitochondrial dynamics. This study provides new insights into how dysregulated mitochondrial dynamics could lead to functional abnormalities of tissues and cells. 

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2. The role of lysine acetylation in the function of mitochondrial ribosomal protein L12

   https://doi.org/10.1002/prot.26654  

   Paluch, Katelynn V. ; Platz, Karlie R. ; Rudisel, Emma J. ; Erdmann, Ryan R. ; Laurin, Taylor R. ; Dittenhafer‐Reed, Kristin E. ( December 2023 , Proteins: Structure, Function, and Bioinformatics)

   Mitochondria play a central role in energy production and cellular metabolism. Mitochondria contain their own small genome (mitochondrial DNA, mtDNA) that carries the genetic instructions for proteins required for ATP synthesis. The mitochondrial proteome, including the mitochondrial transcriptional machinery, is subject to post‐translational modifications (PTMs), including acetylation and phosphorylation. We set out to determine whether PTMs of proteins associated with mtDNA may provide a potential mechanism for the regulation of mitochondrial gene expression. Here, we focus on mitochondrial ribosomal protein L12 (MRPL12), which is thought to stabilize mitochondrial RNA polymerase (POLRMT) and promote transcription. Numerous acetylation sites of MRPL12 were identified by mass spectrometry. We employed amino acid mimics of the acetylated (lysine to glutamine mutants) and deacetylated (lysine to arginine mutants) versions of MRPL12 to interrogate the role of lysine acetylation in transcription initiation in vitro and mitochondrial gene expression in HeLa cells. MRPL12 acetyl and deacetyl protein mimics were purified and assessed for their ability to impact mtDNA promoter binding of POLRMT. We analyzed mtDNA content and mitochondrial transcript levels in HeLa cells upon overexpression of acetyl and deacetyl mimics of MRPL12. Our results suggest that MRPL12 single‐site acetyl mimics do not change the mtDNA promoter binding ability of POLRMT or mtDNA content in HeLa cells. Individual acetyl mimics may have modest effects on mitochondrial transcript levels. We found that the mitochondrial deacetylase, Sirtuin 3, is capable of deacetylating MRPL12 in vitro, suggesting a potential role for dynamic acetylation controlling MRPL12 function in a role outside of the regulation of gene expression.

    

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3. Multiparametric High‐Content Assays to Measure Cell Health and Oxidative Damage as a Model for Drug‐Induced Liver Injury

   https://doi.org/10.1002/cpch.90  

   Pohan, Grace ; Espinosa, Jether Amos ; Chen, Steven ; Ang, Kenny K. ; Arkin, Michelle R. ; Markossian, Sarine ( December 2020 , Current Protocols in Chemical Biology)

   Drug‐induced liver injury is an important cause of non‐approval in drug development and the withdrawal of already approved drugs from the market. Screening human hepatic cell lines for toxicity has been used extensively to predict drug‐induced liver injury in preclinical drug development. Assessing hepatic‐cell health with more diverse markers will increase the value of in vitro assays and help predict the mechanism of toxicity. We describe three live cell‐based assays using HepG2 cells to measure cell health parameters indicative of hepatotoxicity. The first assay measures cellular ATP levels using luciferase. The second and third assays are multiparametric high‐content screens covering a panel of cell health markers including cell count, mitochondrial membrane potential and structure, nuclear morphology, vacuolar density, and reactive oxygen species and glutathione levels. © 2020 Wiley Periodicals LLC.

   Basic Protocol 1: Measurement of cellular ATP content

   Basic Protocol 2: High‐content analysis assay to assess cell count, mitochondrial membrane potential and structure, and reactive oxygen species

   Basic Protocol 3: High‐content analysis assay to assess nuclear morphology, vacuoles, and glutathione content

   Support Protocol 1: Subculturing and maintaining HepG2 cells

   Support Protocol 2: Plating HepG2 cell line

   Support Protocol 3: Transferring compounds by pin tool

   Support Protocol 4: Generating dose‐response curves

    

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4. Cellular and molecular responses to acute cocaine treatment in neuronal-like N2a cells: potential mechanism for its resistance in cell death

   https://doi.org/10.1038/s41420-018-0078-x  

   Badisa, Ramesh B. ; Wi, Sungsool ; Jones, Zachary ; Mazzio, Elizabeth ; Zhou, Yi ; Rosenberg, Jens T. ; Latinwo, Lekan M. ; Grant, Samuel C. ; Goodman, Carl B. ( July 2018 , Cell Death Discovery)

   Cocaine is a highly abused drug that causes psychiatric and neurological problems. Its entry into neurons could alter cell-biochemistry and contribute in the manifestation of early pathological symptoms. We have previously shown the acute cocaine effects in rat C6 astroglia-like cells and found that these cells were highly sensitive to cocaine in terms of manifesting certain pathologies known to underlie psychological disorders. The present study was aimed to discern acute cocaine effects on the early onset of various changes in Neuro-2a (N2a) cells. Whole-cell patch-clamp recording of differentiated cells displayed the functional voltage-gated Na⁺and K⁺channels, which demonstrated the neuronal characteristics of the cells. Treatment of these cells with acute cocaine (1 h) at in vivo (nM to μM) and in vitro (mM) concentrations revealed that the cells remained almost 100% viable. Cocaine administration at 6.25 μM or 4 mM doses significantly reduced the inward currents but had no significant effect on outward currents, indicating the Na⁺channel-blocking activity of cocaine. While no morphological change was observed at in vivo doses, treatment at in vitro doses altered the morphology, damaged the neurites, and induced cytoplasmic vacuoles; furthermore, general mitochondrial activity and membrane potential were significantly decreased. Mitochondrial dysfunction enabled the cells switch to anaerobic glycolysis, evidenced by dose-dependent increases in lactate and H₂S, resulting unaltered ATP level in the cells. Further investigation on the mechanism of action unfolded that the cell’s resistance to cocaine was through the activation of nuclear factor E2-related factor-2 (Nrf-2) gene and subsequent increase of antioxidants (glutathione [GSH], catalase and GSH peroxidase [GPx]). The data clearly indicate that the cells employed a detoxifying strategy against cocaine. On a broader perspective, we envision that extrapolating the knowledge of neuronal resistance to central nervous system (CNS) diseases could delay their onset or progression.

    

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5. AMPK activator-treated human cardiac spheres enhance maturation and enable pathological modeling

   https://doi.org/10.1186/s13287-023-03554-7  

   Li, Dong ; Armand, Lawrence C. ; Sun, Fangxu ; Hwang, Hyun ; Wolfson, David ; Rampoldi, Antonio ; Liu, Rui ; Forghani, Parvin ; Hu, Xin ; Yu, Wen-Mei ; et al ( December 2023 , Stem Cell Research & Therapy)

   Cardiac pathological outcome of metabolic remodeling is difficult to model using cardiomyocytes derived from human-induced pluripotent stem cells (hiPSC-CMs) due to low metabolic maturation.

   hiPSC-CM spheres were treated with AMP-activated protein kinase (AMPK) activators and examined for hiPSC-CM maturation features, molecular changes and the response to pathological stimuli.

   Treatment of hiPSC-CMs with AMPK activators increased ATP content, mitochondrial membrane potential and content, mitochondrial DNA, mitochondrial function and fatty acid uptake, indicating increased metabolic maturation. Conversely, the knockdown of AMPK inhibited mitochondrial maturation of hiPSC-CMs. In addition, AMPK activator-treated hiPSC-CMs had improved structural development and functional features—including enhanced Ca²⁺transient kinetics and increased contraction. Transcriptomic, proteomic and metabolomic profiling identified differential levels of expression of genes, proteins and metabolites associated with a molecular signature of mature cardiomyocytes in AMPK activator-treated hiPSC-CMs. In response to pathological stimuli, AMPK activator-treated hiPSC-CMs had increased glycolysis, and other pathological outcomes compared to untreated cells.

   AMPK activator-treated cardiac spheres could serve as a valuable model to gain novel insights into cardiac diseases.

    

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