bims-lymeca 2023-05-07 papers

Issue of 2023‒05‒07
seven papers selected by
Harilaos Filippakis
University of New England

Sci Adv. 2023 May 03. 9(18): eadf0138

Inter-organelle cross-talk supports acetyl-coenzyme A homeostasis and lipogenesis under metabolic stress.

Ramya S Kuna, Avi Kumar, Karl A Wessendorf-Rodriguez, Hector Galvez, Courtney R Green, Grace H McGregor, Thekla Cordes, Reuben J Shaw, Robert U Svensson, Christian M Metallo.

Proliferating cells rely on acetyl-CoA to support membrane biogenesis and acetylation. Several organelle-specific pathways are available for provision of acetyl-CoA as nutrient availability fluctuates, so understanding how cells maintain acetyl-CoA homeostasis under such stresses is critically important. To this end, we applied 13C isotope tracing cell lines deficient in these mitochondrial [ATP-citrate lyase (ACLY)]-, cytosolic [acetyl-CoA synthetase (ACSS2)]-, and peroxisomal [peroxisomal biogenesis factor 5 (PEX5)]-dependent pathways. ACLY knockout in multiple cell lines reduced fatty acid synthesis and increased reliance on extracellular lipids or acetate. Knockout of both ACLY and ACSS2 (DKO) severely stunted but did not entirely block proliferation, suggesting that alternate pathways can support acetyl-CoA homeostasis. Metabolic tracing and PEX5 knockout studies link peroxisomal oxidation of exogenous lipids as a major source of acetyl-CoA for lipogenesis and histone acetylation in cells lacking ACLY, highlighting a role for inter-organelle cross-talk in supporting cell survival in response to nutrient fluctuations.

DOI: https://doi.org/10.1126/sciadv.adf0138

FEBS J. 2023 May 02.

Amino acid metabolism, redox balance and epigenetic regulation in cancer.

Xiang Li, Hong-Sheng Zhang.

Amino acids act as the versatile nutrients driving cell growth and survival, especially in cancer cells. Amino acid metabolism comprises numerous metabolic networks and is closely linked with intracellular redox balance and epigenetic regulation. Reprogrammed amino acid metabolism has been recognized as a ubiquitous feature in tumor cells. This review outlines the metabolism of several primary amino acids in cancer cells and highlights the pivotal role of amino acid metabolism in sustaining redox homeostasis and regulating epigenetic modification in response to oxidative and genetic stress in cancer cells.

Keywords: amino acids; cancer; epigenetic regulation; metabolism; redox balance

DOI: https://doi.org/10.1111/febs.16803

Traffic. 2023 May 02.

Oxidized cholesteryl ester induces exocytosis of dysfunctional lysosomes in lipidotic macrophages.

Neuza Domingues, André R A Marques, Rita Diogo Almeida Calado, Inês S Ferreira, Cristiano Ramos, José Ramalho, Maria I L Soares, Telmo Pereira, Luís Oliveira, José R Vicente, Louise H Wong, Inês C M Simões, Teresa M V D Pinho E Melo, Andrew Peden, Cláudia Guimas Almeida, Clare E Futter, Rosa Puertollano, Winchil L C Vaz, Otília V Vieira.

A key event in atherogenesis is the formation of lipid-loaded macrophages, lipidotic cells, which exhibit irreversible accumulation of undigested modified low-density lipoproteins (LDL) in lysosomes. This event culminates in the loss of cell homeostasis, inflammation, and cell death. Nevertheless, the exact chemical etiology of atherogenesis and the molecular and cellular mechanisms responsible for the impairment of lysosome function in plaque macrophages are still unknown. Here, we demonstrate that macrophages exposed to cholesteryl hemiazelate (ChA), one of the most prevalent products of LDL-derived cholesteryl ester oxidation, exhibit enlarged peripheral dysfunctional lysosomes full of undigested ChA and neutral lipids. Both lysosome area and accumulation of neutral lipids are partially irreversible. Interestingly, the dysfunctional peripheral lysosomes are more prone to fuse with the plasma membrane, secreting their undigested luminal content into the extracellular milieu with potential consequences for the pathology. We further demonstrate that this phenotype is mechanistically linked to the nuclear translocation of the MiT/TFE family of transcription factors. The induction of lysosome biogenesis by ChA appears to partially protect macrophages from lipid-induced cytotoxicity. In sum, our data show that ChA is involved in the etiology of lysosome dysfunction and promotes the exocytosis of these organelles. This latter event is a new mechanism that may be important in the pathogenesis of atherosclerosis.

Keywords: cholesteryl hemiesters; lysosome dysfunction; lysosome exocytosis; oxidized low-density lipoproteins

DOI: https://doi.org/10.1111/tra.12888

Cell Commun Signal. 2023 May 04. 21(1): 91

mTOR-dependent TFEB activation and TFEB overexpression enhance autophagy-lysosome pathway and ameliorate Alzheimer's disease-like pathology in diabetic encephalopathy.

Lizhen Cheng, Yixin Chen, Donghao Guo, Yuan Zhong, Wei Li, Yijia Lin, Ya Miao.

BACKGROUND: Diabetic encephalopathy (DE) is a complication of type 2 diabetes mellitus (T2DM) that features Alzheimer's disease (AD)-like pathology, which can be degraded by the autophagy-lysosome pathway (ALP). Since transcription factor EB (TFEB) is a master regulator of ALP, TFEB-mediated ALP activation might have a therapeutic effect on DE, but this has yet to be investigated.METHODS: We established T2DM mouse models and cultured HT22 cells under high-glucose (HG) conditions to confirm the role of ALP in DE. To further investigate this, both mice and HT22 cells were treated with 3-methyladenine (3-MA). We also analyzed the content of TFEB in the nucleus and cytoplasm to evaluate its role in ALP. To confirm the effect of TFEB activation at the post-translational level in DE, we used rapamycin to inhibit the mechanistic target of rapamycin (mTOR). We transduced both mice and cells with TFEB vector to evaluate the therapeutic effect of TFEB overexpression on DE. Conversely, we conducted TFEB knockdown to verify its role in DE in another direction.
RESULTS: We found that T2DM mice experienced compromised cognitive function, while HG-cultured HT22 cells exhibited increased cell apoptosis. Additionally, both T2DM mice and HG-cultured HT22 cells showed impaired ALP and heavier AD-like pathology. This pathology worsened after treatment with 3-MA. We also observed decreased TFEB nuclear translocation in both T2DM mice and HG-cultured HT22 cells. However, inhibiting mTOR with rapamycin or overexpressing TFEB increased TFEB nuclear translocation, enhancing the clearance of ALP-targeted AD-like pathology. This contributed to protection against neuronal apoptosis and alleviation of cognitive impairment. Conversely, TFEB knockdown lessened ALP-targeted AD-like pathology clearance and had a negative impact on DE.
CONCLUSION: Our findings suggest that impaired ALP is responsible for the aggravation of AD-like pathology in T2DM. We propose that mTOR-dependent TFEB activation and TFEB overexpression are promising therapeutic strategies for DE, as they enhance the clearance of ALP-targeted AD-like pathology and alleviate neuronal apoptosis. Our study provides insight into the underlying mechanisms of DE and offers potential avenues for the development of new treatments for this debilitating complication of T2DM. Video abstract.

Keywords: Autophagy-lysosome pathway; Aβ; Diabetic encephalopathy; Neuronal apoptosis; TFEB; p-Tau

DOI: https://doi.org/10.1186/s12964-023-01097-1

Front Pharmacol. 2023 ;14 1148611

Berberine stimulates lysosomal AMPK independent of PEN2 and maintains cellular AMPK activity through inhibiting the dephosphorylation regulator UHRF1.

Gang Ren, Yu-Wei Ding, Lu-Lu Wang, Jian-Dong Jiang.

Aim: AMPK is the key regulatory kinase mediating the effect of berberine (BBR) and metformin on metabolic improvement. The present study investigated the mechanism of BBR on AMPK activation at low doses, which was different from that of metformin. Methods: Lysosomes were isolated, and AMPK activity assay was performed. PEN2, AXIN1 and UHRF1 were investigated through gain/loss of function approaches, including overexpression, RNA interfering and CRISPR/Cas9-mediated gene knockout. Immunoprecipitation was utilized for detecting the interaction of UHRF1 and AMPKα1 after BBR treatment. Results: BBR activated lysosomal AMPK, but weaker than metformin. AXIN1 mediated BBR's effect on lysosomal AMPK activation, while PEN2 did not. BBR, but not metformin, decreased UHRF1 expression by promoting its degradation. BBR reduced the interaction between UHRF1 and AMPKα1. And overexpression of UHRF1 abolished the effect of BBR on AMPK activation. Conclusion: BBR activated lysosomal AMPK as dependent on AXIN1, but not PEN2. BBR maintained cellular AMPK activity by reducing UHRF1 expression and its interaction with AMPKα1. The mode of action of BBR was different from that of metformin on AMPK activation.

Keywords: AMPK; AXIN1; UHRF1; berberine; metformin

DOI: https://doi.org/10.3389/fphar.2023.1148611

Cell Metab. 2023 May 02. pii: S1550-4131(23)00136-5. [Epub ahead of print]35(5): 725-727

Remote control of autophagy and metabolism in the liver.

Nektarios Tavernarakis.

Systemic control of homeostatic processes is of fundamental importance for survival and adaptation in metazoans. In this issue of Cell Metabolism, Chen and colleagues identify and methodically dissect a signaling cascade that is mobilized by the agouti-related peptide (AgRP)-expressing neurons in the hypothalamus, to ultimately modulate autophagy and metabolism in the liver upon starvation.

DOI: https://doi.org/10.1016/j.cmet.2023.04.009

Cell Rep. 2023 May 02. pii: S2211-1247(23)00458-8. [Epub ahead of print]42(5): 112447

Dissecting the effects of GTPase and kinase domain mutations on LRRK2 endosomal localization and activity.

Capria Rinaldi, Christopher S Waters, Zizheng Li, Karl Kumbier, Lee Rao, R Jeremy Nichols, Matthew P Jacobson, Lani F Wu, Steven J Altschuler.

Parkinson's disease-causing leucine-rich repeat kinase 2 (LRRK2) mutations lead to varying degrees of Rab GTPase hyperphosphorylation. Puzzlingly, LRRK2 GTPase-inactivating mutations-which do not affect intrinsic kinase activity-lead to higher levels of cellular Rab phosphorylation than kinase-activating mutations. Here, we investigate whether mutation-dependent differences in LRRK2 cellular localization could explain this discrepancy. We discover that blocking endosomal maturation leads to the rapid formation of mutant LRRK2+ endosomes on which LRRK2 phosphorylates substrate Rabs. LRRK2+ endosomes are maintained through positive feedback, which mutually reinforces membrane localization of LRRK2 and phosphorylated Rab substrates. Furthermore, across a panel of mutants, cells expressing GTPase-inactivating mutants form strikingly more LRRK2+ endosomes than cells expressing kinase-activating mutants, resulting in higher total cellular levels of phosphorylated Rabs. Our study suggests that the increased probability that LRRK2 GTPase-inactivating mutants are retained on intracellular membranes compared to kinase-activating mutants leads to higher substrate phosphorylation.

Keywords: CP: Cell biology; LRRK2; Parkinson's disease; Rab phosphorylation; VPS34 inhibition; endosomal localization; positive feedback

DOI: https://doi.org/10.1016/j.celrep.2023.112447