bims-lypmec 2023-03-19 papers

Issue of 2023‒03‒19
five papers selected by
Satoru Kobayashi
New York Institute of Technology

Nat Commun. 2023 Mar 13. 14(1): 1362

De novo lipogenesis fuels adipocyte autophagosome and lysosome membrane dynamics.

Leslie A Rowland, Adilson Guilherme, Felipe Henriques, Chloe DiMarzio, Sean Munroe, Nicole Wetoska, Mark Kelly, Keith Reddig, Gregory Hendricks, Meixia Pan, Xianlin Han, Olga R Ilkayeva, Christopher B Newgard, Michael P Czech.

Adipocytes robustly synthesize fatty acids (FA) from carbohydrate through the de novo lipogenesis (DNL) pathway, yet surprisingly DNL contributes little to their abundant triglyceride stored in lipid droplets. This conundrum raises the hypothesis that adipocyte DNL instead enables membrane expansions to occur in processes like autophagy, which requires an abundant supply of phospholipids. We report here that adipocyte Fasn deficiency in vitro and in vivo markedly impairs autophagy, evident by autophagosome accumulation and severely compromised degradation of the autophagic substrate p62. Our data indicate the impairment occurs at the level of autophagosome-lysosome fusion, and indeed, loss of Fasn decreases certain membrane phosphoinositides necessary for autophagosome and lysosome maturation and fusion. Autophagy dependence on FA produced by Fasn is not fully alleviated by exogenous FA in cultured adipocytes, and interestingly, imaging studies reveal that Fasn colocalizes with nascent autophagosomes. Together, our studies identify DNL as a critical source of FAs to fuel autophagosome and lysosome maturation and fusion in adipocytes.

DOI: https://doi.org/10.1038/s41467-023-37016-8

Expert Rev Proteomics. 2023 Mar 16. 1-9

Updates on the study of lysosomal protein dynamics: possibilities for the clinic.

Dhriti Arora, Yannic Hackenberg, Jiaran Li, Dominic Winter.

INTRODUCTION: The lysosome is the main degradative organelle of almost all mammalian cells, fulfilling important functions in macromolecule recycling, metabolism, and signaling. Lysosomal dysfunction is connected to a continuously growing number of pathologic conditions, and lysosomal proteins present potential biomarkers for a variety of diseases. Therefore, there is an increasing interest in their analysis in patient samples.AREAS COVERED: We provide an overview of OMICs studies which identified lysosomal proteins as potential biomarkers for pathological conditions, covering proteomics, genomics, and transcriptomics approaches, identified through PubMed searches. With respect to discovery proteomics analyses, mainly lysosomal luminal and associated proteins were detected, while membrane proteins were found less frequently. Comprehensive coverage of the lysosomal proteome was only achieved by ultra-deep-coverage studies, but targeted approaches allowed for the reproducible quantification of lysosomal proteins in diverse sample types.
EXPERT OPINION: The low abundance of lysosomal proteins complicates their reproducible analysis in patient samples. Whole proteome shotgun analyses fail in many instances to cover the lysosomal proteome, which is due to under-sampling and/or a lack of sensitivity. With the current state of the art, targeted proteomics assays provide the best performance for the characterization of lysosomal proteins in patient samples.

Keywords: Lysosomes; OMICs; biomarkers; cancer; mass spectrometry; neurodegenerative diseases; proteomics; targeted quantification

DOI: https://doi.org/10.1080/14789450.2023.2190515

J Cell Biochem. 2023 Mar 16.

Role of VPS39, a key tethering protein for endolysosomal trafficking and mitochondria-lysosome crosstalk, in health and disease.

Hanbing Li, Wenwen Gong, Weiyun Sun, Yuanfa Yao, Yubing Han.

The coordinated interaction between mitochondria and lysosomes, mainly manifested by mitophagy, mitochondria-derived vesicles, and direct physical contact, is essential for maintaining cellular life activities. The VPS39 subunit of the homotypic fusion and protein sorting complex could play a key role in the regulation of organelle dynamics, such as endolysosomal trafficking and mitochondria-vacuole/lysosome crosstalk, thus contributing to a variety of physiological functions. The abnormalities of VPS39 and related subunits have been reported to be involved in the pathological process of some diseases. Here, we analyze the potential mechanisms and the existing problems of VPS39 in regulating organelle dynamics, which, in turn, regulate physiological functions and disease pathogenesis, so as to provide new clues for facilitating the discovery of therapeutic targets for mitochondrial and lysosomal diseases.

Keywords: HOPS complex; VPS39; diseases; endolysosomal trafficking; mitochondria-lysosome crosstalk

DOI: https://doi.org/10.1002/jcb.30396

Mol Metab. 2023 Mar 11. pii: S2212-8778(23)00039-X. [Epub ahead of print] 101705

The lysosomal LAMTOR / Ragulator complex is essential for nutrient homeostasis in brown adipose tissue.

Gudrun Liebscher, Nemanja Vujic, Renate Schreiber, Markus Heine, Caroline Krebiehl, Madalina Duta-Mare, Giorgia Lamberti, Cedric H de Smet, Michael W Hess, Thomas O Eichmann, Sarah Hölzl, Ludger Scheja, Joerg Heeren, Dagmar Kratky, Lukas A Huber.

OBJECTIVE: In brown adipose tissue (iBAT), the balance between lipid/glucose uptake and lipolysis is tightly regulated by insulin signaling. Downstream of the insulin receptor, PDK1 and mTORC2 phosphorylate AKT, which activates glucose uptake and lysosomal mTORC1 signaling. The latter requires the late endosomal/lysosomal adaptor and MAPK and mTOR activator (LAMTOR/Ragulator) complex, which serves to translate the nutrient status of the cell to the respective kinase. However, the role of LAMTOR in metabolically active iBAT has been elusive.METHODS: Using an AdipoqCRE-transgenic mouse line, we deleted LAMTOR2 (and thereby the entire LAMTOR complex) in adipose tissue (LT2 AKO). To examine the metabolic consequences, we performed metabolic and biochemical studies in iBAT isolated from mice housed at different temperatures (30 °C, room temperature and 5 °C), after insulin treatment, or in fasted and refed condition. For mechanistic studies, mouse embryonic fibroblasts (MEFs) lacking LAMTOR 2 were analyzed.
RESULTS: Deletion of the LAMTOR complex in mouse adipocytes resulted in insulin-independent AKT hyperphosphorylation in iBAT, causing increased glucose and fatty acid uptake, which led to massively enlarged lipid droplets. As LAMTOR2 was essential for the upregulation of de novo lipogenesis, LAMTOR2 deficiency triggered exogenous glucose storage as glycogen in iBAT. These effects are cell autonomous, since AKT hyperphosphorylation was abrogated by PI3K inhibition or by deletion of the mTORC2 component Rictor in LAMTOR2-deficient MEFs.
CONCLUSIONS: We identified a homeostatic circuit for the maintenance of iBAT metabolism that links the LAMTOR-mTORC1 pathway to PI3K-mTORC2-AKT signaling downstream of the insulin receptor.

Keywords: AKT; Brown adipose tissue; LAMTOR; Lysosome; Ragulator; mTORC1/2

DOI: https://doi.org/10.1016/j.molmet.2023.101705

Ann Med. 2023 Dec;55(1): 1102-1110

Diabetes type 2: relationships between lysosomal exocytosis of circulating normal-sized platelets and in vitro ɑ-thrombin-evoked platelet responses.

Maria Edvardsson, Magnus Oweling, Petter Järemo.

BACKGROUND/OBJECTIVE: Type 2 diabetes is a major risk factor for atherosclerotic disease. It is well agreed that the reactivity of diabetic platelets is increased but how platelet reactivity regulates is unknown. In our laboratory, density separated platelets have been investigated extensively and high- and low-density platelets circulate in an activated state. The density distribution of circulating platelets is altered in diabetes type 2 as well. We hypothesize that such platelets modify whole blood (WB) in vitro α-thrombin-evoked (10 μM/mL) activity in type 2 diabetes. Thus, the study aims to identify features of circulating normal-sized density subpopulations affecting whole blood (WB) platelet reactivity in type 2 diabetes.PATIENTS AND METHODS: Patients with type 2 diabetes (n = 16) were enrolled. Their normal-sized platelets were divided into density subfractions (n = 16) using continuous polyvinylpyrrolidone-coated silica (Percoll™) gradients (density span, 1.090-1.040 kg/L) containing prostaglandin E1. The proportions (%) of such density-separated platelets expressing lysosomal-associated membrane protein 1 (LAMP-1) were analyzed using a flow cytometer. Further, determinations of WB ɑ-thrombin-evoked (10 U/mL) surface LAMP-1 (an assessment of lysosomal release), the fibrinogen (αIIbβ3) receptor activity, annexin V (binds to exposed membrane phosphatidylserine), and mitochondrial transmembrane potentials (an estimate of organelle integrity) were performed. Surface LAMP-1 expressions of individual normal-sized platelet density subpopulations were stratified into equal-sized groups (n = 2) depending on reactivity, as judged from the ɑ-thrombin-induced WB activity markers.
RESULTS: With some exceptions, the proportion of normal-sized circulating platelets showing spontaneous LAMP-1 was strongly associated with WB ɑ-thrombin-evoked (10 U/mL) surface LAMP-1 and αIIbβ3 receptor activity. LAMP-1-expressing normal-sized platelets also displayed inverse associations with WB ɑ-thrombin-induced surface annexin V and mitochondrial damage, which are features of procoagulant platelets.
CONCLUSIONS: From the current descriptive work only involving type 2 diabetes, it is impossible to judge whether the findings are features of the disease or if they occur in healthy individuals as well. However, the study describes LAMP-1 expressing subpopulations of circulating normal-sized platelets that associate with WB α-thrombin (10 U/mL) responses in vitro. Increased proportions of such platelets induced lysosomal release and αIIbβ3 receptor activity, whereas lower proportions promoted WB agonist-induced procoagulant platelet creation. It is to hypothesize that the new described regulatory mechanism could in the future offer a possibility to influence platelet behavior in type 2 diabetes.Key messagesLysosomal exocytosis of circulating platelets influences reactivity, as determined by agonist-induced platelet reactions in vitroThus, the low release of lysosomes by normal-sized platelets in vivo increases agonist-evoked procoagulant platelet production.Higher lysosomal exocytosis of circulating normal-sized platelets promotes platelet aggregation and secretion.

Keywords: Annexin V; lysosomal-associated membrane protein 1; platelet reactivity; platelets; αIIbβ3 activity

DOI: https://doi.org/10.1080/07853890.2023.2171108