bims-lypmec 2024-02-04 papers

Nat Commun. 2024 Jan 31. 15(1): 919

DENND6A links Arl8b to a Rab34/RILP/dynein complex, regulating lysosomal positioning and autophagy.

Rahul Kumar, Maleeha Khan, Vincent Francis, Adriana Aguila, Gopinath Kulasekaran, Emily Banks, Peter S McPherson.

Lysosomes help maintain cellular proteostasis, and defects in lysosomal positioning and function can cause disease, including neurodegenerative disorders. The spatiotemporal distribution of lysosomes is regulated by small GTPases including Rabs, which are activated by guanine nucleotide exchange factors (GEFs). DENN domain proteins are the largest family of Rab GEFs. Using a cell-based assay, we screened DENND6A, a member of the DENN domain protein family against all known Rabs and identified it as a potential GEF for 20 Rabs, including Rab34. Here, we demonstrate that DENND6A activates Rab34, which recruits a RILP/dynein complex to lysosomes, promoting lysosome retrograde transport. Further, we identify DENND6A as an effector of Arl8b, a major regulatory GTPase on lysosomes. We demonstrate that Arl8b recruits DENND6A to peripheral lysosomes to activate Rab34 and initiate retrograde transport, regulating nutrient-dependent lysosomal juxtanuclear repositioning. Loss of DENND6A impairs autophagic flux. Our findings support a model whereby Arl8b/DENND6A/Rab34-dependent lysosomal retrograde trafficking controls autophagy.

DOI: https://doi.org/10.1038/s41467-024-44957-1

Exp Mol Med. 2024 Feb 01.

Regulation of autophagy by perilysosomal calcium: a new player in β-cell lipotoxicity.

Ha Thu Nguyen, Andreas Wiederkehr, Claes B Wollheim, Kyu-Sang Park.

Autophagy is an essential quality control mechanism for maintaining organellar functions in eukaryotic cells. Defective autophagy in pancreatic beta cells has been shown to be involved in the progression of diabetes through impaired insulin secretion under glucolipotoxic stress. The underlying mechanism reveals the pathologic role of the hyperactivation of mechanistic target of rapamycin (mTOR), which inhibits lysosomal biogenesis and autophagic processes. Moreover, accumulating evidence suggests that oxidative stress induces Ca2+ depletion in the endoplasmic reticulum (ER) and cytosolic Ca2+ overload, which may contribute to mTOR activation in perilysosomal microdomains, leading to autophagic defects and β-cell failure due to lipotoxicity. This review delineates the antagonistic regulation of autophagic flux by mTOR and AMP-dependent protein kinase (AMPK) at the lysosomal membrane, and both of these molecules could be activated by perilysosomal calcium signaling. However, aberrant and persistent Ca2+ elevation upon lipotoxic stress increases mTOR activity and suppresses autophagy. Therefore, normalization of autophagy is an attractive therapeutic strategy for patients with β-cell failure and diabetes.

DOI: https://doi.org/10.1038/s12276-024-01161-x

Cell Commun Signal. 2024 Jan 31. 22(1): 87

Arginyltransferase 1 modulates p62-driven autophagy via mTORC1/AMPk signaling.

Laura V Bonnet, Anabela Palandri, Jesica B Flores-Martin, Marta E Hallak.

BACKGROUND: Arginyltransferase (Ate1) orchestrates posttranslational protein arginylation, a pivotal regulator of cellular proteolytic processes. In eukaryotic cells, two interconnected systems-the ubiquitin proteasome system (UPS) and macroautophagy-mediate proteolysis and cooperate to maintain quality protein control and cellular homeostasis. Previous studies have shown that N-terminal arginylation facilitates protein degradation through the UPS. Dysregulation of this machinery triggers p62-mediated autophagy to ensure proper substrate processing. Nevertheless, how Ate1 operates through this intricate mechanism remains elusive.
METHODS: We investigated Ate1 subcellular distribution through confocal microscopy and biochemical assays using cells transiently or stably expressing either endogenous Ate1 or a GFP-tagged Ate1 isoform transfected in CHO-K1 or MEFs, respectively. To assess Ate1 and p62-cargo clustering, we analyzed their colocalization and multimerization status by immunofluorescence and nonreducing immunoblotting, respectively. Additionally, we employed Ate1 KO cells to examine the role of Ate1 in autophagy. Ate1 KO MEFs cells stably expressing GFP-tagged Ate1-1 isoform were used as a model for phenotype rescue. Autophagy dynamics were evaluated by analyzing LC3B turnover and p62/SQSTM1 levels under both steady-state and serum-starvation conditions, through immunoblotting and immunofluorescence. We determined mTORC1/AMPk activation by assessing mTOR and AMPk phosphorylation through immunoblotting, while mTORC1 lysosomal localization was monitored by confocal microscopy.
RESULTS: Here, we report a multifaceted role for Ate1 in the autophagic process, wherein it clusters with p62, facilitates autophagic clearance, and modulates its signaling. Mechanistically, we found that cell-specific inactivation of Ate1 elicits overactivation of the mTORC1/AMPk signaling hub that underlies a failure in autophagic flux and subsequent substrate accumulation, which is partially rescued by ectopic expression of Ate1. Statistical significance was assessed using a two-sided unpaired t test with a significance threshold set at P<0.05.
CONCLUSIONS: Our findings uncover a critical housekeeping role of Ate1 in mTORC1/AMPk-regulated autophagy, as a potential therapeutic target related to this pathway, that is dysregulated in many neurodegenerative and cancer diseases.

Keywords: Arginylation; Arginyltransferase 1; Autophagy; Posttranslational modification; mTORC1; p62/SQSTM1

DOI: https://doi.org/10.1186/s12964-024-01499-9

Physiol Rev. 2024 Feb 01.

Ceramides are Fuel Gauges on the Drive to Cardiometabolic Disease.

Joseph L Wilkerson, Sean M Tatum, William L Holland, Scott A Summers.

Ceramides are signals of fatty acid excess that accumulate when a cell's energetic needs have been met and its nutrient storage has reached capacity. As these sphingolipids accrue, they alter the metabolism and survival of cells throughout the body including in the heart, liver, blood vessels, skeletal muscle, brain, and kidney. These ceramide actions elicit the tissue dysfunction that underlies cardiometabolic diseases such as diabetes, coronary artery disease, metabolic-associated steatohepatitis, and heart failure. Here, we review the biosynthesis and degradation pathways which maintain ceramide levels in normal physiology and discuss how the loss of ceramide homeostasis drives cardiometabolic pathologies. We highlight signaling nodes that sense small changes in ceramides, and in turn reprogram cellular metabolism and stimulate apoptosis. Lastly, we evaluate the emerging therapeutic utility of these unique lipids as biomarkers that forecast disease risk and as targets of ceramide-lowering interventions that ameliorate disease.

Keywords: Ceramides; Diabetes; Lipotoxicity; Metabolic Disease; Sphingolipids

DOI: https://doi.org/10.1152/physrev.00008.2023

Biochim Biophys Acta Mol Basis Dis. 2024 Jan 26. pii: S0925-4439(24)00023-1. [Epub ahead of print] 167038

NAD in pathological cardiac remodeling: Metabolic regulation and beyond.

Ignacio Norambuena-Soto, Yingfeng Deng, Charles Brenner, Sergio Lavandero, Zhao V Wang.

Nicotinamide adenine dinucleotide (NAD) coenzymes are carriers of high energy electrons in metabolism and also play critical roles in numerous signaling pathways. NAD metabolism is decreased in various cardiovascular diseases. Importantly, stimulation of NAD biosynthesis protects against heart disease under different pathological conditions. In this review, we describe pathways for both generation and catabolism of NAD coenzymes and the respective changes of these pathways in the heart under cardiac diseases, including pressure overload, myocardial infarction, cardiometabolic disease, cancer treatment cardiotoxicity, and heart failure. We next provide an update on the strategies and treatments to increase NAD levels, such as supplementation of NAD precursors, in the heart that prevent or reverse cardiomyopathy. We also introduce the approaches to manipulate NAD consumption enzymes to ameliorate cardiac disease. Finally, we discuss the mechanisms associated with improvements in cardiac function by NAD coenzymes, differentiating between mitochondria-dependent effects and those independent of mitochondrial metabolism.

Keywords: Cardiac remodeling; Heart failure; NAD; Nicotinamide riboside

DOI: https://doi.org/10.1016/j.bbadis.2024.167038

Endocr Metab Immune Disord Drug Targets. 2024 Jan 31.

Organelle Targeted Drug Delivery: Key Challenges, Recent Advancements and Therapeutic Implications.

Dilpreet Singh.

Organelle-specific targeted drug delivery has emerged as a promising approach in the field of drug delivery and therapeutics. This innovative strategy involves the precise delivery of therapeutic agents to specific organelles within cells, such as the nucleus, mitochondria, endoplasmic reticulum, or lysosomes, with the aim of enhancing drug efficacy while minimizing offtarget effects. Despite its tremendous potential, organelle-specific drug delivery faces several key challenges. One major challenge is the development of delivery systems that can accurately navigate the complex intracellular environment and deliver drugs exclusively to the desired organelles. Achieving this level of precision demands advanced nanotechnology and biomaterials engineering. Furthermore, ensuring the safety and biocompatibility of these delivery systems is paramount. Recent advancements in this field include the development of nanocarriers, such as liposomes, nanoparticles, and dendrimers, designed to target specific organelles through ligandreceptor interactions or pH-responsive mechanisms. Additionally, advancements in molecular biology and genetic engineering have enabled the design of genetically encoded organellespecific drug delivery systems. The therapeutic implications of organelle-specific drug delivery are vast. This approach has the potential to revolutionize the treatment of diseases with organelle- specific pathologies, such as neurodegenerative disorders, cancer, and mitochondrial diseases. By precisely targeting the organelles involved in disease progression, the efficacy of therapies can be significantly improved while minimizing collateral damage to healthy tissues.

Keywords: Organelle; drug delivery; mitochondria; nanocarrier.; targeting; therapeutics

DOI: https://doi.org/10.2174/0118715303282573240112104035