bims-lypmec 2024-01-07 papers

Proc Natl Acad Sci U S A. 2024 Jan 09. 121(2): e2306454120

HKDC1, a target of TFEB, is essential to maintain both mitochondrial and lysosomal homeostasis, preventing cellular senescence.

Mitochondrial and lysosomal functions are intimately linked and are critical for cellular homeostasis, as evidenced by the fact that cellular senescence, aging, and multiple prominent diseases are associated with concomitant dysfunction of both organelles. However, it is not well understood how the two important organelles are regulated. Transcription factor EB (TFEB) is the master regulator of lysosomal function and is also implicated in regulating mitochondrial function; however, the mechanism underlying the maintenance of both organelles remains to be fully elucidated. Here, by comprehensive transcriptome analysis and subsequent chromatin immunoprecipitation-qPCR, we identified hexokinase domain containing 1 (HKDC1), which is known to function in the glycolysis pathway as a direct TFEB target. Moreover, HKDC1 was upregulated in both mitochondrial and lysosomal stress in a TFEB-dependent manner, and its function was critical for the maintenance of both organelles under stress conditions. Mechanistically, the TFEB-HKDC1 axis was essential for PINK1 (PTEN-induced kinase 1)/Parkin-dependent mitophagy via its initial step, PINK1 stabilization. In addition, the functions of HKDC1 and voltage-dependent anion channels, with which HKDC1 interacts, were essential for the clearance of damaged lysosomes and maintaining mitochondria-lysosome contact. Interestingly, HKDC1 regulated mitophagy and lysosomal repair independently of its prospective function in glycolysis. Furthermore, loss function of HKDC1 accelerated DNA damage-induced cellular senescence with the accumulation of hyperfused mitochondria and damaged lysosomes. Our results show that HKDC1, a factor downstream of TFEB, maintains both mitochondrial and lysosomal homeostasis, which is critical to prevent cellular senescence.

Keywords: HKDC1; TFEB; cellular senescence; mitochondria–lysosome contact; mitophagy

DOI: https://doi.org/10.1073/pnas.2306454120

Mol Cell. 2024 Jan 04. pii: S1097-2765(23)01028-6. [Epub ahead of print]84(1): 17-19

Lysosome identity crisis: Phosphoinositides and mTORC1 negotiate lysosomal behavior.

Mélanie Mansat, Roberto J Botelho.

Ebner et al.1 discovered a nutrient-dependent molecular feedback circuit that employs mTORC1, lipid kinases, and phosphatases to generate phosphatidylinositol-3-phosphate [PI(3)P] or phosphatidylinositol-4-phosphate [PI(4)P] in a mutually exclusive manner on lysosomes, which respectively convert lysosomes into organelles that support anabolism or catabolism.

DOI: https://doi.org/10.1016/j.molcel.2023.12.009

Nat Commun. 2024 Jan 02. 15(1): 93

TMEM55B links autophagy flux, lysosomal repair, and TFE3 activation in response to oxidative stress.

Eutteum Jeong, Rose Willett, Alberto Rissone, Martina La Spina, Rosa Puertollano.

Lysosomes have emerged as critical regulators of cellular homeostasis. Here we show that the lysosomal protein TMEM55B contributes to restore cellular homeostasis in response to oxidative stress by three different mechanisms: (1) TMEM55B mediates NEDD4-dependent PLEKHM1 ubiquitination, causing PLEKHM1 proteasomal degradation and halting autophagosome/lysosome fusion; (2) TMEM55B promotes recruitment of components of the ESCRT machinery to lysosomal membranes to stimulate lysosomal repair; and (3) TMEM55B sequesters the FLCN/FNIP complex to facilitate translocation of the transcription factor TFE3 to the nucleus, allowing expression of transcriptional programs that enable cellular adaptation to stress. Knockout of tmem55 genes in zebrafish embryos increases their susceptibility to oxidative stress, causing early death of tmem55-KO animals in response to arsenite toxicity. Altogether, our work identifies a role for TMEM55B as a molecular sensor that coordinates autophagosome degradation, lysosomal repair, and activation of stress responses.

DOI: https://doi.org/10.1038/s41467-023-44316-6

Nat Commun. 2024 Jan 02. 15(1): 91

Experimental determination and mathematical modeling of standard shapes of forming autophagosomes.

Yuji Sakai, Satoru Takahashi, Ikuko Koyama-Honda, Chieko Saito, Noboru Mizushima.

The formation of autophagosomes involves dynamic morphological changes of a phagophore from a flat membrane cisterna into a cup-shaped intermediate and a spherical autophagosome. However, the physical mechanism behind these morphological changes remains elusive. Here, we determine the average shapes of phagophores by statistically investigating three-dimensional electron micrographs of more than 100 phagophores. The results show that the cup-shaped structures adopt a characteristic morphology; they are longitudinally elongated, and the rim is catenoidal with an outwardly recurved shape. To understand these characteristic shapes, we establish a theoretical model of the shape of entire phagophores. The model quantitatively reproduces the average morphology and reveals that the characteristic shape of phagophores is primarily determined by the relative size of the open rim to the total surface area. These results suggest that the seemingly complex morphological changes during autophagosome formation follow a stable path determined by elastic bending energy minimization.

DOI: https://doi.org/10.1038/s41467-023-44442-1

Mol Metab. 2023 Dec 30. pii: S2212-8778(23)00203-X. [Epub ahead of print]79 101869

Loss of lysosomal acid lipase results in mitochondrial dysfunction and fiber switch in skeletal muscles of mice.

Alena Akhmetshina, Valentina Bianco, Ivan Bradić, Melanie Korbelius, Anita Pirchheim, Katharina B Kuentzel, Thomas O Eichmann, Helga Hinteregger, Dagmar Kolb, Hansjoerg Habisch, Laura Liesinger, Tobias Madl, Wolfgang Sattler, Branislav Radović, Simon Sedej, Ruth Birner-Gruenberger, Nemanja Vujić, Dagmar Kratky.

OBJECTIVE: Lysosomal acid lipase (LAL) is the only enzyme known to hydrolyze cholesteryl esters (CE) and triacylglycerols in lysosomes at an acidic pH. Despite the importance of lysosomal hydrolysis in skeletal muscle (SM), research in this area is limited. We hypothesized that LAL may play an important role in SM development, function, and metabolism as a result of lipid and/or carbohydrate metabolism disruptions.
RESULTS: Mice with systemic LAL deficiency (Lal-/-) had markedly lower SM mass, cross-sectional area, and Feret diameter despite unchanged proteolysis or protein synthesis markers in all SM examined. In addition, Lal-/- SM showed increased total cholesterol and CE concentrations, especially during fasting and maturation. Regardless of increased glucose uptake, expression of the slow oxidative fiber marker MYH7 was markedly increased in Lal-/-SM, indicating a fiber switch from glycolytic, fast-twitch fibers to oxidative, slow-twitch fibers. Proteomic analysis of the oxidative and glycolytic parts of the SM confirmed the transition between fast- and slow-twitch fibers, consistent with the decreased Lal-/- muscle size due to the "fiber paradox". Decreased oxidative capacity and ATP concentration were associated with reduced mitochondrial function of Lal-/- SM, particularly affecting oxidative phosphorylation, despite unchanged structure and number of mitochondria. Impairment in muscle function was reflected by increased exhaustion in the treadmill peak effort test in vivo.
CONCLUSION: We conclude that whole-body loss of LAL is associated with a profound remodeling of the muscular phenotype, manifested by fiber type switch and a decline in muscle mass, most likely due to dysfunctional mitochondria and impaired energy metabolism, at least in mice.

Keywords: Energy metabolism; LAL; LAL deficiency; Lal-deficient mouse; Muscle proteomics

DOI: https://doi.org/10.1016/j.molmet.2023.101869

Cell Metab. 2024 Jan 02. pii: S1550-4131(23)00465-5. [Epub ahead of print]

ABCG2 is an itaconate exporter that limits antibacterial innate immunity by alleviating TFEB-dependent lysosomal biogenesis.

Chao Chen, Zhenxing Zhang, Caiyun Liu, Pengkai Sun, Ping Liu, Xinjian Li.

Itaconate is a metabolite that synthesized from cis-aconitate in mitochondria and transported into the cytosol to exert multiple regulatory effects in macrophages. However, the mechanism by which itaconate exits from macrophages remains unknown. Using a genetic screen, we reveal that itaconate is exported from cytosol to extracellular space by ATP-binding cassette transporter G2 (ABCG2) in an ATPase-dependent manner in human and mouse macrophages. Elevation of transcription factor TFEB-dependent lysosomal biogenesis and antibacterial innate immunity are observed in inflammatory macrophages with deficiency of ABCG2-mediated itaconate export. Furthermore, deficiency of ABCG2-mediated itaconate export in macrophages promotes antibacterial innate immune defense in a mouse model of S. typhimurium infection. Thus, our findings identify ABCG2-mediated itaconate export as a key regulatory mechanism that limits TFEB-dependent lysosomal biogenesis and antibacterial innate immunity in inflammatory macrophages, implying the potential therapeutic utility of blocking itaconate export in treating human bacterial infections.

Keywords: ABCG2; TFEB; exporter; innate immunity; itaconate; lysosomal biogenesis; macrophages

DOI: https://doi.org/10.1016/j.cmet.2023.12.015