bims-lypmec Biomed News
on Lysosomal positioning and metabolism in cardiomyocytes
Issue of 2023‒03‒26
three papers selected by
Satoru Kobayashi
New York Institute of Technology

  1. Cell Death Discov. 2023 Mar 21. 9(1): 100
      While the mechanism of lipotoxicity by palmitic acid (PA), an effector of metabolic stress in vitro and in vivo, has been extensively investigated, molecular details of lipotoxicity are still not fully characterized. Since recent studies reported that PA can exert lysosomal stress in addition to well-known ER and mitochondrial stress, we studied the role of lysosomal events in lipotoxicity by PA, focusing on lysosomal Ca2+. We found that PA induced accumulation of mitochondrial ROS and that mitochondrial ROS induced release of lysosomal Ca2+ due to lysosomal Ca2+ exit channel activation. Lysosomal Ca2+ release led to increased cytosolic Ca2+ which induced mitochondrial permeability transition (mPT). Chelation of cytoplasmic Ca2+ or blockade of mPT with olesoxime or decylubiquinone (DUB) suppressed lipotoxicity. Lysosomal Ca2+ release led to reduced lysosomal Ca2+ content which was replenished by ER Ca2+, the largest intracellular Ca2+ reservoir (ER → lysosome Ca2+ refilling), which in turn activated store-operated Ca2+ entry (SOCE). Inhibition of ER → lysosome Ca2+ refilling by blockade of ER Ca2+ exit channel using dantrolene or inhibition of SOCE using BTP2 inhibited lipotoxicity in vitro. Dantrolene or DUB also inhibited lipotoxic death of hepatocytes in vivo induced by administration of ethyl palmitate together with LPS. These results suggest a novel pathway of lipotoxicity characterized by mPT due to lysosomal Ca2+ release which was supplemented by ER → lysosome Ca2+ refilling and subsequent SOCE, and also suggest the potential role of modulation of ER → lysosome Ca2+ refilling by dantrolene or other blockers of ER Ca2+ exit channels in disease conditions characterized by lipotoxicity such as metabolic syndrome, diabetes, cardiomyopathy or nonalcoholic steatohepatitis.
  2. J Mater Chem B. 2023 Mar 22.
      Lipid droplets (LDs) and their autophagy by lysosomes are closely related to a variety of physiological and pathological conditions. Therefore, identifying and tracking LDs and the dynamic process of autophagy can provide useful information for the diagnostics and treatment of related diseases. However, few organic small molecule-based fluorescent probes can specifically recognize LDs and dynamically track their autophagy process. Herein, we synthesized a "discoloration" fluorescent bioprobe DPABP-BI with distinguishable features including red fluorescence emission (630 nm), large Stokes shift (145 nm), two-photon excitation and outstanding photostability and biocompatibility. In particular, LDs could be specifically identified via the red fluorescence emission of DPABP-BI (colocalization constant of 0.98), while autophagolysosomes could be visualized via the green fluorescence emission of its acid-hydrolyzed product (colocalization constant of 0.90) to track the autophagy dynamic process. In addition, DPABP-BI enabled the specific recognition of fatty substances in zebrafish larvae. In this study, a two-photon excited red light small molecule probe was constructed to identify LDs and track their autophagy dynamic process by changing the fluorescence emission wavelength.
  3. Metabolism. 2023 Mar 20. pii: S0026-0495(23)00154-3. [Epub ahead of print] 155551
      OBJECTIVE: Uncorrected obesity is accompanied by unfavorable structural and functional changes in the heart, known as obesity cardiomyopathy. Recent evidence has revealed a crucial role for mitochondria-associated endoplasmic reticulum membranes (MAMs) in obesity-induced cardiac complication. Syntaxin 17 (STX17) serves as a scaffolding molecule localized on MAMs although its role in obesity heart complication remains elusive.METHODS AND MATERIALS: This study examined the role of STX17 in MAMs and mitochondrial Ca2+ homeostasis in HFD-induced obesity cardiomyopathy using tamoxifen-induced cardiac-specific STX17 knockout (STX17cko) and STX17 overexpression mice using intravenously delivered recombinant adeno-associated virus serotype-9 (AAV9-cTNT-STX17).
    RESULTS: STX17 levels were significantly elevated in plasma from obese patients and heart tissues of HFD-fed mice. Our data revealed that cardiac STX17 knockout alleviated cardiac remodeling and dysfunction in obese hearts without eliciting any notable effect itself, while STX17 overexpression aggravated cardiac dysfunction in obese mice. STX17 deletion and STX17 overexpression annihilated and aggravated, respectively, HFD-induced oxidative stress (O2- production) and mitochondrial injury in the heart. Furthermore, STX17 transfection facilitated obesity-induced MAMs formation in cardiomyocytes and evoked excess mitochondrial Ca2+ influx, dependent upon interaction with mitochondrial Ca2+ uniporter dominant negative β (MCUb) through Habc domain. Our data also suggested that STX17 promoted ubiquitination and degradation of MCUb through the E3 ligase parkin in the face of palmitate challenging.
    CONCLUSION: Taken together, our results identified a novel role for STX17 in facilitating obesity-induced MAMs formation, and subsequently mitochondrial Ca2+ overload, mitochondrial O2- accumulation, lipid peroxidation, resulting in cardiac impairment. Our findings denoted therapeutic promises of targeting STX17 in obesity.
    Keywords:  MAMs; MCUb; Mitochondrial Ca(2+) overload; Obesity cardiomyopathy; Syntaxin 17