The degradation of polyethylene terephthalate (PET) fibers in alkaline environments limits their use in strain-hardening cementitious composites (SHCC). Prolonged PET exposure to alkaline ...environments has a detrimental effect on its mechanical performance, mainly due to the physicochemical transformation caused by alkaline hydrolysis. This study presents a tailored cementitious matrix design containing high amounts of limestone and calcined clay, replacing 75 wt% of Portland cement, to attain and maintain the strain-hardening response of composites incorporating PET fibers as dispersed reinforcement. Analytical and mechanical tests were carried out at different curing ages, ranging from 7 to 60 days, to study the effects of aging on virgin PET fibers, both within the matrix and outside it (in the pore solution). The results showed a pronounced degradation of the PET fibers in the test pore solution at pH 12.5, manifested by a progressive reduction in the load-bearing capacity of the individual fibers with prolonged immersion. Conversely, when the PET fibers were aged in-matrix under laboratory conditions and tested under tension, the performance of the corresponding composites showed resilience to aging, exhibiting reasonable tensile strength and remarkable strain capacities that exceeded 4 %.
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•PET fibers are among the most synthesized and recyclable fibers globally.•PET’s application in alkaline cementitious systems is restricted by their chemical stability.•The low-carbon LC3-25 matrix stabilizes PET’s performance and allows for strain-hardening.•PET fibers in SH-LC3-25 exhibited an unprecedented strain capacity of more than 4 %.•Mechanical performance metrics of PET-reinforced SH-LC3-25 stabilized after 14 days.
Limestone calcined clay cement (LC3) incorporates calcined clay and limestone as supplementary cementitious materials that can replace up to 50 % of conventional cement, significantly reducing the ...carbon emissions associated with cement production. However, challenges remain, including the inefficiencies of traditional curing methods and suboptimal early strength properties. Consequently, this study presents the low-carbon microwave curing approach for LC3 mortar. A comparative analysis of 15 different microwave curing systems was carried out. The results show that the optimum microwave curing efficiency is 300 W of heating power, 5 minutes of heating, 25 minutes of rest, and eight cycles. Three curing methods, including microwave curing, standard curing, and steam curing, were also compared. Microwave curing significantly increased the early strength of LC3 mortar, with 1-day compressive strength 1.78 times greater than standard curing and 1.26 times greater than steam curing. Microscopic studies show that the “thermal effect” of microwaving increases the internal Hc content of LC3, promotes the secondary hydration reaction of Ca(OH)2 within the LC3 material, and reduces the porosity of LC3, achieving reductions of 37.8 % and 8.9 % compared to standard and steam curing, respectively. This helps to improve the efficiency of the curing process. The results of this research will advance the use of low-carbon LC3 in building structures.
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•The temperature rise rules of the LC3 system under different microwave powers were studied.•An effective curing system through intermittent microwave was developed for LC3 system•The carbon emissions of LC3 under standard curing, steam curing and microwave were comparatively analyzed.
To obtain mechanistic insights into the cross talk between lipolysis and autophagy, two key metabolic responses to starvation, we screened the autophagy‐inducing potential of a panel of fatty acids ...in human cancer cells. Both saturated and unsaturated fatty acids such as palmitate and oleate, respectively, triggered autophagy, but the underlying molecular mechanisms differed. Oleate, but not palmitate, stimulated an autophagic response that required an intact Golgi apparatus. Conversely, autophagy triggered by palmitate, but not oleate, required AMPK, PKR and JNK1 and involved the activation of the BECN1/PIK3C3 lipid kinase complex. Accordingly, the downregulation of BECN1 and PIK3C3 abolished palmitate‐induced, but not oleate‐induced, autophagy in human cancer cells. Moreover, Becn1+/− mice as well as yeast cells and nematodes lacking the ortholog of human BECN1 mounted an autophagic response to oleate, but not palmitate. Thus, unsaturated fatty acids induce a non‐canonical, phylogenetically conserved, autophagic response that in mammalian cells relies on the Golgi apparatus.
Synopsis
A systematic screen in cancer cells reveals that unsaturated and saturated fatty acids induce autophagy via distinct pathways, with unsaturated fatty acids acting in a Golgi‐dependent but Beclin‐1‐independent manner.
Saturated and unsaturated fatty acids promote autophagy, in vitro and in vivo, via different molecular mechanisms.
The saturated fatty acid palmitate stimulates canonical, BECN1‐ and PIK3C3‐dependent autophagic responses that involve JNK1, PKR and AMPK.
The unsaturated fatty acid oleate promotes a non‐canonical BECN1‐independent autophagic response that requires an intact Golgi apparatus.
Oleate‐induced non‐canonical autophagy is conserved in human cells, mice, yeast and nematodes.
A systematic screen in cancer cells reveals that unsaturated and saturated fatty acids induce autophagy via distinct pathways, with unsaturated fatty acids acting in a Golgi‐dependent but Beclin‐1‐independent manner.
In 2008, we published the first set of guidelines for standardizing research in autophagy. Since then, this topic has received increasing attention, and many scientists have entered the field. Our ...knowledge base and relevant new technologies have also been expanding. Thus, it is important to formulate on a regular basis updated guidelines for monitoring autophagy in different organisms. Despite numerous reviews, there continues to be confusion regarding acceptable methods to evaluate autophagy, especially in multicellular eukaryotes. Here, we present a set of guidelines for investigators to select and interpret methods to examine autophagy and related processes, and for reviewers to provide realistic and reasonable critiques of reports that are focused on these processes. These guidelines are not meant to be a dogmatic set of rules, because the appropriateness of any assay largely depends on the question being asked and the system being used. Moreover, no individual assay is perfect for every situation, calling for the use of multiple techniques to properly monitor autophagy in each experimental setting. Finally, several core components of the autophagy machinery have been implicated in distinct autophagic processes (canonical and noncanonical autophagy), implying that genetic approaches to block autophagy should rely on targeting two or more autophagy-related genes that ideally participate in distinct steps of the pathway. Along similar lines, because multiple proteins involved in autophagy also regulate other cellular pathways including apoptosis, not all of them can be used as a specific marker for bona fide autophagic responses. Here, we critically discuss current methods of assessing autophagy and the information they can, or cannot, provide. Our ultimate goal is to encourage intellectual and technical innovation in the field.
Selective autophagy relies on soluble or membrane-bound cargo receptors that recognize cargo and bring about autophagosome formation at the cargo. The cargo-bound receptors interact with lipidated ...ATG8 family proteins anchored in the membrane at the concave side of the forming autophagosome. The interaction is mediated by 15- to 20-amino-acid-long sequence motifs called LC3-interacting region (LIR) motifs that bind to the LIR docking site (LDS) of ATG8 proteins. In this review, we focus on LIR–ATG8 interactions and the soluble mammalian selective autophagy receptors. We discuss the roles of ATG8 family proteins as membrane scaffolds in autophagy and the LIR–LDS interaction and how specificity for binding to GABARAP or LC3 subfamily proteins is achieved. We also discuss atypical LIR–LDS interactions and a novel LIR-independent interaction. Recently, it has become clear that several of the soluble cargo receptors are able to recruit components of the core autophagy apparatus to aid in assembling autophagosome formation at the site of cargo sequestration. A model on phagophore recruitment and expansion on a selective autophagy receptor-coated cargo incorporating the latest findings is presented.
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Summary
Autophagy describes catabolic pathways that deliver cytoplasmic constituents for lysosomal degradation. Since major histocompatibility complex (MHC) molecules sample protein degradation ...products and present them to T cells for adaptive immunity, it is maybe not too surprising that autophagy contributes to this protein antigen processing for MHC presentation. However, the recently recognized breath of pathways, by which autophagy contributes to MHC antigen processing, is exciting. Macroautophagy does not only seem to deliver intracellular but facilitates also extracellular antigen processing by lysosomal hydrolysis for MHC class II presentation. Moreover, even MHC class I molecules that usually display proteasomal products are regulated by macroautophagy, probably using a pool of these molecules outside the endoplasmic reticulum, where MHC class I molecules are loaded with peptide during canonical MHC class I antigen processing. This review aims to summarize these recent developments and point out gaps of knowledge, which should be filled by further investigation, in order to harness the different antigen‐processing pathways via autophagy for vaccine improvement.
Autophagy, self-eating, is a pivotal catabolic mechanism that ensures homeostasis and survival of the cell in the face of stressors as different as starvation, infection, or protein misfolding. The ...importance of the research in this field was recognized by the general public after the Nobel Prize for Physiology or Medicine was awarded in 2016 to Yoshinori Ohsumi for discoveries of the mechanisms of autophagy using yeast as a model organism. One of the seminal findings of Ohsumi was on the role ubiquitin-like proteins (UBLs)—Atg5, Atg12, and Atg8—play in the formation of the double-membrane vesicle autophagosome, which is the functional unit of autophagy. Subsequent work by several groups demonstrated that, like the founding member of the UBL family ubiquitin, these small but versatile protein and lipid modifiers interact with a plethora of proteins, which either directly regulate autophagosome formation, for example, components of the Atg1/ULK1 complex, or are involved in cargo recognition, for example, Atg19 and p62/SQSTM1. By tethering the cargo to the UBLs present on the forming autophagosome, the latter proteins were proposed to effectively act as selective autophagy receptors. The discovery of the selective autophagy receptors brought a breakthrough in the autophagy field, supplying the mechanistic underpinning for the formation of an autophagosome selectively around the cytosolic cargo, that is, a protein aggregate, a mitochondrion, or a cytosolic bacterium. In this historical overview, I highlight key steps that the research into selective autophagy has been taking over the past 20 years. I comment on their significance and discuss current challenges in developing more detailed knowledge of the mechanisms of selective autophagy. I will conclude by introducing the new directions that this dynamic research field is taking into its third decade.
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•Historical overview of selective autophagy research over past 20 years•Discussion and modeling of selective autophagy pathway•Critical discussion on open questions•Indication of new directions in the field
The clearance of surplus, broken, or dangerous components is key for maintaining cellular homeostasis. The failure to remove protein aggregates, damaged organelles, or intracellular pathogens leads ...to diseases, including neurodegeneration, cancer, and infectious diseases. Autophagy is the evolutionarily conserved pathway that sequesters cytoplasmic components in specialized vesicles, autophagosomes, which transport the cargo to the degradative compartments (vacuoles or lysosomes). Research during the past few decades has elucidated how autophagosomes engulf their substrates selectively. This type of autophagy involves a growing number of selective autophagy receptors (SARs) (e.g., Atg19 in yeasts, p62/SQSTM1 in mammals), which bind to the cargo and simultaneously engage components of the core autophagic machinery via direct interaction with the ubiquitin-like proteins (UBLs) of the Atg8/LC3/GABARAP family and adaptors, Atg11 (in yeasts) or FIP200 (in mammals). In this Review, we critically discuss the biology of the SARs with special emphasis on their interactions with UBLs.
Efficient degradation of protein aggregates, damaged mitochondria, or intracellular pathogens is key for cellular homeostasis. Their specific elimination is mediated by selective autophagy receptors (SARs) that bind to their cargo, triggering the formation of an autophagosome. In their Review, Kirkin and Rogov discuss SAR biology with a special focus on the interactions of SARs with ubiquitin-like proteins.
Autophagy is a highly conserved bulk protein degradation pathway responsible for the turnover of long-lived proteins, disposal of damaged organelles, and clearance of aggregate-prone proteins. Thus, ...inactivation of autophagy results in cytoplasmic protein inclusions, which are composed of misfolded proteins and excess accumulation of deformed organelles, leading to liver injury, diabetes, myopathy, and neurodegeneration. Although autophagy has been considered non-selective, growing lines of evidence indicate the selectivity of autophagy in sorting vacuolar enzymes and in the removal of aggregate-prone proteins, unwanted organelles and microbes. Such selectivity by autophagy enables diverse cellular regulations, similar to the ubiquitin–proteasome pathway. In this review, we introduce the selective turnover of the ubiquitin- and LC3-binding protein ‘p62’ through autophagy and discuss its physiological significance.
ABSTRACT
Necroptosis is an inflammatory form of programmed cell death mediated by the pseudokinase mixed-lineage kinase domain-like protein (MLKL). Upon phosphorylation by receptor-interacting ...protein kinase-3 (RIPK3), MLKL oligomerizes, and translocates to and disrupts the plasma membrane, thereby causing necroptotic cell lysis. Herein, we show that activation of necroptosis in mouse dermal fibroblasts (MDFs) and HT-29 human colorectal cancer cells results in accumulation of the autophagic marker, lipidated LC3B (also known as MAP1LC3B), in an MLKL-dependent manner. Unexpectedly, the necroptosis-induced increase in lipidated LC3B was due to inhibition of autophagic flux, not the activation of autophagy. Inhibition of autophagy by MLKL correlated with a decrease in autophagosome and/or autolysosome function, and required the association of activated MLKL with intracellular membranes. Collectively, our findings uncover an additional role for the MLKL pseudokinase, namely to inhibit autophagy during necroptosis.
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