Phosphoinositides: multipurpose cellular lipids with emerging roles in cell death

Enrichment and MALDI-TOF MS Analysis of Phosphoinositides in Brain Tissue

Triazolium cyclodextrin click cluster (+CCC) is an ideal scaffold to specifically bind phosphoinositides (PIPs) via multivalent electrostatic interaction. A new enrichment material, triazolium cyclodextrin click cluster-magnetic agarose bead conjugate (+CCC-MAB), was synthesized and applied to the PIP enrichment of brain tissue. The enriched sample was analyzed using MALDI-TOF MS in negative ion mode without any derivatization. The PIP extract of brain tissue is known to contain abundant lipid interferences. By employing magnetic pull-down separation using +CCC-MAB, we effectively removed the weak-binding interferences in the PIP extract, thereby improving the signal-to-noise ratio (S/N) of the PIPs. Our +CCC-MAB-based PIP enrichment enabled us to analyze 16 PIP species in brain tissue. Six species with high S/N were assigned by MS/MS, while the remaining 10 species with low S/N were characterized by an empirical selection guide based on the biological relevance of PIPs. We conclude that +CCC-MAB-based PIP enrichment is a promising MALDI sample preparation method for specific PIP analysis in brain tissue.

PRL1 and PRL3 promote macropinocytosis via its lipid phosphatase activity

PRL1 and PRL3, members of the protein tyrosine phosphatase family, have been associated with cancer metastasis and poor prognosis. Despite extensive research on their protein phosphatase activity, their potential role as lipid phosphatases remains elusive. Methods: We conducted comprehensive investigations to elucidate the lipid phosphatase activity of PRL1 and PRL3 using a combination of cellular assays, biochemical analyses, and protein interactome profiling. Functional studies were performed to delineate the impact of PRL1/3 on macropinocytosis and its implications in cancer biology. Results: Our study has identified PRL1 and PRL3 as lipid phosphatases that interact with phosphoinositide (PIP) lipids, converting PI(3,4)P2 and PI(3,5)P2 into PI(3)P on the cellular membranes. These enzymatic activities of PRLs promote the formation of membrane ruffles, membrane blebbing and subsequent macropinocytosis, facilitating nutrient extraction, cell migration, and invasion, thereby contributing to tumor development. These enzymatic activities of PRLs promote the formation of membrane ruffles, membrane blebbing and subsequent macropinocytosis. Additionally, we found a correlation between PRL1/3 expression and glioma development, suggesting their involvement in glioma progression. Conclusions: Combining with the knowledge that PRLs have been identified to be involved in mTOR, EGFR and autophagy, here we concluded the physiological role of PRL1/3 in orchestrating the nutrient sensing, absorbing and recycling via regulating macropinocytosis through its lipid phosphatase activity. This mechanism could be exploited by tumor cells facing a nutrient-depleted microenvironment, highlighting the potential therapeutic significance of targeting PRL1/3-mediated macropinocytosis in cancer treatment.

PLCE1 enhances mitochondrial dysfunction to promote GSDME-mediated pyroptosis in doxorubicin-induced cardiotoxicity

BACKGROUND

The therapeutic value and long-term application of doxorubicin (DOX) were hampered by its severe irreversible cardiotoxicity. Phospholipase C epsilon 1 (PLCE 1) was reported as a new member of the phospholipase C (PLC) family which controls the level of phosphoinositides in cells. Pyroptosis is a newly discovered inflammatory type of regulated cell death. Recent studies have consolidated that chemotherapeutic drugs lead to pyroptosis. Additionally, the phosphoinositide signaling system has remarkable effects on the execution of cell death. We aim to investigate the role of PLCE1 and the mechanism of pyroptosis from the context of DOX-induced cardiotoxicity.

METHODS

In the current study, in vitro and in vivo experiments were performed to dissect the underlying mechanism of cardiomyocyte pyroptosis during DOX-induced cardiac injury. The molecular mechanism of PLCE1 was identified by the human cardiomyocyte AC16 cell line and C57BL/6 mouse model.

RESULTS

The results here indicated that PLCE1 high expressed and pyroptotic cell death presented in cardiomyocytes after DOX application, which was negatively correlated to heart function. DOX-induced cell model disclosed pyroptosis mediated by Gasdermin E (GSDME) protein and involved in mitochondrial damage. Conversely, the deletion of PLCE1 ameliorated mitochondrial dysfunction by suppressing ROS accumulation and reversing mitochondrial membrane potential, and then increased cell viability effectively. More importantly, the in vivo experiment demonstrated that inhibition of PLCE1 reduced pyroptotic cell death and improved heart effect.

CONCLUSIONS

We discovered firstly that PLCE1 inhibition protected cardiomyocytes from DOX-induced pyroptotic injury and promoted cardiac function. This information offers a theoretical basis for promising therapy.

Molecular Mechanism of Autophagosome-Lysosome Fusion in Mammalian Cells

In eukaryotes, targeting intracellular components for lysosomal degradation by autophagy represents a catabolic process that evolutionarily regulates cellular homeostasis. The successful completion of autophagy initiates the engulfment of cytoplasmic materials within double-membrane autophagosomes and subsequent delivery to autolysosomes for degradation by acidic proteases. The formation of autolysosomes relies on the precise fusion of autophagosomes with lysosomes. In recent decades, numerous studies have provided insights into the molecular regulation of autophagosome-lysosome fusion. In this review, an overview of the molecules that function in the fusion of autophagosomes with lysosomes is provided. Moreover, the molecular mechanism underlying how these functional molecules regulate autophagosome-lysosome fusion is summarized.

Prevotella copri variants among a single host diverge in sphingolipid production

Sphingolipids serve as vital structural and signaling components of the cell membranes in both eukaryotes and prokaryotes. Within the gut microbiome, Bacteroides species have been identified as major producers of sphingolipids, and Bacteroides-produced sphingolipids have been shown to be modulators of host immune and metabolic functions. While Bacteroides species are a prominent feature of the gut microbiomes of populations living in industrialized countries, Prevotella copri, a member of the same phyla, albeit a different family, is the dominant feature across the remainder of the global population, although their sphingolipid-producing capabilities have not been as thoroughly investigated. To fill this gap, we examined the genomes of over 60 diverse isolates of P. copri and identified several key enzymes involved in sphingolipid synthesis in P. copri. Combining bioorthogonal labeling and liquid chromatography-mass spectrometry (LC-MS) based lipidomics, we functionally characterized the first step in P. copri de novo sphingolipid synthesis in addition to profiling the sphingolipidomes of P. copri strains, identifying key enzymes that may play roles in producing a diverse set of P. copri sphingolipids. Given the limited genetic engineering tools amenable for use in P. copri, our approach takes advantage of comparative genomics and phenotypic profiling to explore sphingolipid production in these understudied, yet highly prevalent, organisms.IMPORTANCESphingolipids are important signaling molecules for maintaining metabolic and immune homeostasis in the host. These lipids are also produced by gut commensals, most notably by Bacteroides species. Despite the global prevalence of Prevotella copri in gut microbiomes of individuals, little is known about the types of sphingolipids they produce and whether they are similar in composition and structure to those produced by Bacteroides. Given the varied associations of P. copri with diverse sphingolipid-related health outcomes, such as rheumatoid arthritis and glucose intolerance, it is important to first characterize the specific sphingolipids produced by individual strains of P. copri and to identify the genes involved in their pathways of production. This characterization of P. copri-derived sphingolipids provides further insight into how bacterial sphingolipid production can serve as a mechanism for microbial modulation of host phenotypes.

Multimodal Imaging of Pancreatic Cancer Microenvironment in Response to an Antiglycolytic Drug

Lipid metabolism and glycolysis play crucial roles in the progression and metastasis of cancer, and the use of 3-bromopyruvate (3-BP) as an antiglycolytic agent has shown promise in killing pancreatic cancer cells. However, developing an effective strategy to avoid chemoresistance requires the ability to probe the interaction of cancer drugs with complex tumor-associated microenvironments (TAMs). Unfortunately, no robust and multiplexed molecular imaging technology is currently available to analyze TAMs. In this study, the simultaneous profiling of three protein biomarkers using SERS nanotags and antibody-functionalized nanoparticles in a syngeneic mouse model of pancreatic cancer (PC) is demonstrated. This allows for comprehensive information about biomarkers and TAM alterations before and after treatment. These multimodal imaging techniques include surface-enhanced Raman spectroscopy (SERS), immunohistochemistry (IHC), polarized light microscopy, second harmonic generation (SHG) microscopy, fluorescence lifetime imaging microscopy (FLIM), and untargeted liquid chromatography and mass spectrometry (LC-MS) analysis. The study reveals the efficacy of 3-BP in treating pancreatic cancer and identifies drug treatment-induced lipid species remodeling and associated pathways through bioinformatics analysis.

A phosphoinositide switch mediates exocyst recruitment to multivesicular endosomes for exosome secretion

Exosomes are secreted to the extracellular milieu when multivesicular endosomes (MVEs) dock and fuse with the plasma membrane. However, MVEs are also known to fuse with lysosomes for degradation. How MVEs are directed to the plasma membrane for exosome secretion rather than to lysosomes is unclear. Here we report that a conversion of phosphatidylinositol-3-phosphate (PI(3)P) to phosphatidylinositol-4-phosphate (PI(4)P) catalyzed sequentially by Myotubularin 1 (MTM1) and phosphatidylinositol 4-kinase type IIα (PI4KIIα) on the surface of MVEs mediates the recruitment of the exocyst complex. The exocyst then targets the MVEs to the plasma membrane for exosome secretion. We further demonstrate that disrupting PI(4)P generation or exocyst function blocked exosomal secretion of Programmed death-ligand 1 (PD-L1), a key immune checkpoint protein in tumor cells, and led to its accumulation in lysosomes. Together, our study suggests that the PI(3)P to PI(4)P conversion on MVEs and the recruitment of the exocyst direct the exocytic trafficking of MVEs for exosome secretion.

Engineering phosphatidylinositol-4,5-bisphosphate model membranes enriched in endocytic cargo: A neutron reflectometry, AFM and QCM-D structural study

The combination of in vitro models of biological membranes based on solid-supported lipid bilayers (SLBs) and of surface sensitive techniques, such as neutron reflectometry (NR), atomic force microscopy (AFM) and quartz crystal microbalance with dissipation monitoring (QCM-D), is well suited to provide quantitative information about molecular level interactions and lipid spatial distributions. In this work, cellular plasma membranes have been mimicked by designing complex SLB, containing phosphatidylinositol 4,5-bisphosphate (PtdIns4,5P2) lipids as well as incorporating synthetic lipo-peptides that simulate the cytoplasmic tails of transmembrane proteins. The QCM-D results revealed that the adsorption and fusion kinetics of PtdIns4,5P2 are highly dependent of Mg2+. Additionally, it was shown that increasing concentrations of PtdIns4,5P2 leads to the formation of SLBs with higher homogeneity. The presence of PtdIns4,5P2 clusters was visualized by AFM. NR provided important insights about the structural organization of the various components within the SLB, highlighting that the leaflet symmetry of these SLBs is broken by the presence of CD4-derived cargo peptides. Finally, we foresee our study to be a starting point for more sophisticated in vitro models of biological membranes with the incorporation of inositol phospholipids and synthetic endocytic motifs.

INPP4A-related genetic and phenotypic spectrum and functional relevance of subcellular targeting of INPP4A isoforms

Type I inositol polyphosphate-4-phosphatase (INPP4A) belongs to the group of phosphoinositide phosphatases controlling proliferation, apoptosis, and endosome function by hydrolyzing phosphatidylinositol 3,4-bisphosphate. INPP4A produces multiple transcripts encoding shorter and longer INPP4A isoforms with hydrophilic or hydrophobic C-terminus. Biallelic INPP4A truncating variants cause a spectrum of neurodevelopmental disorders ranging from moderate intellectual disability to postnatal microcephaly with developmental and epileptic encephalopathy and (ponto)cerebellar hypoplasia. We report a girl with the novel homozygous INPP4A variant NM_001134224.2:c.2840del/p.(Gly947Glufs*12) (isoform d). She presented with postnatal microcephaly, global developmental delay, visual impairment, myoclonic seizures, and pontocerebellar hypoplasia and died at the age of 27 months. The level of mutant INPP4A mRNAs in proband-derived leukocytes was comparable to controls suggesting production of C-terminally altered INPP4A isoforms. We transiently expressed eGFP-tagged INPP4A isoform a (NM_004027.3) wildtype and p.(Gly908Glufs*12) mutant [p.(Gly947Glufs*12) according to NM_001134224.2] as well as INPP4A isoform b (NM_001566.2) wildtype and p.(Asp915Alafs*2) mutant, previously reported in family members with moderate intellectual disability, in HeLa cells and determined their subcellular distributions. While INPP4A isoform a was preferentially found in perinuclear clusters co-localizing with the GTPase Rab5, isoform b showed a net-like distribution, possibly localizing near and/or on microtubules. Quantification of intracellular localization patterns of the two INPP4A mutants revealed significant differences compared with the respective wildtype and similarity with each other. Our data suggests an important non-redundant function of INPP4A isoforms with hydrophobic or hydrophilic C-terminus in the brain.

ATP5O Hypo-crotonylation Caused by HDAC2 Hyper-Phosphorylation Is a Primary Detrimental Factor for Downregulated Phospholipid Metabolism under Chronic Stress

Objective. Chronic stress (CS)-induced abnormal metabolism and other subsequent aspects of abnormality are threatening human health. Little is known regarding whether and how protein post-translational-modifications (PTMs) correlate with abnormal metabolism under CS. The aim of this study was to address this issue and also identify novel key protein PTM. Methods. First, we screened which pan-PTM had significant change between control and CS female mice and whether clinical CS females had similar pan-PTM change. Second, we performed quantitative PTM-omics and metabolomics to verify the correlation between abnormal protein PTMs and atypical metabolism. Third, we performed quantitative phospho-omics to identify the key PTM-regulating enzyme and investigate the interaction between PTM protein and PTM-regulating enzyme. Fourth, we attempted to rectify the abnormal metabolism by correcting the activity of the PTM-regulating enzyme. Finally, we examined whether the selected key protein was also correlated with stress scores and atypical metabolism in clinical women. Results. We initially found that multiple tissues of CS female mice have downregulated pan-crotonylation, and verified that the plasma of clinical CS females also had downregulated pan-crotonylation. Then we determined that ATP5O-K51 crotonylation decreased the most and also caused gross ATP5O decrement, whereas the plasma of CS mice had downregulated phospholipids. Next, downregulating ATP5O crotonylation partially recapitulated the downregulated phospholipid metabolism in CS mice. Next, we verified that HDAC2-S424 phosphorylation determined its decrotonylation activity on ATP5O-K51. Furthermore, correcting HDAC2 hyper-phosphorylation recovered the gross ATP5O level and partially rescued the downregulated phospholipid metabolism in CS mice. Finally, the ATP5O level was also significantly lower and correlated with high stress scores and downregulated phospholipid metabolism in clinical female plasma. Conclusion. This study discovered a novel PTM mechanism involving two distinct types of PTM in CS and provided a novel reference for the clinical precautions and treatments of CS.

Characterization of inositol lipid metabolism in gut-associated Bacteroidetes

Inositol lipids are ubiquitous in eukaryotes and have finely tuned roles in cellular signalling and membrane homoeostasis. In Bacteria, however, inositol lipid production is relatively rare. Recently, the prominent human gut bacterium Bacteroides thetaiotaomicron (BT) was reported to produce inositol lipids and sphingolipids, but the pathways remain ambiguous and their prevalence unclear. Here, using genomic and biochemical approaches, we investigated the gene cluster for inositol lipid synthesis in BT using a previously undescribed strain with inducible control of sphingolipid synthesis. We characterized the biosynthetic pathway from myo-inositol-phosphate (MIP) synthesis to phosphoinositol dihydroceramide, determined the crystal structure of the recombinant BT MIP synthase enzyme and identified the phosphatase responsible for the conversion of bacterially-derived phosphatidylinositol phosphate (PIP-DAG) to phosphatidylinositol (PI-DAG). In vitro, loss of inositol lipid production altered BT capsule expression and antimicrobial peptide resistance. In vivo, loss of inositol lipids decreased bacterial fitness in a gnotobiotic mouse model. We identified a second putative, previously undescribed pathway for bacterial PI-DAG synthesis without a PIP-DAG intermediate, common in Prevotella. Our results indicate that inositol sphingolipid production is widespread in host-associated Bacteroidetes and has implications for symbiosis.

The pathways responsible for inositol lipid production in human gut Bacteroides are characterized and these lipids are important for capsule expression and antimicrobial peptide resistance in vitro and colonization in vivo.

p53-driven lipidome influences non-cell-autonomous lysophospholipids in pancreatic cancer

Adaptation of the lipid metabolism participates  in cancer pathogenesis, facilitating energy storage and influencing cell fate and control of molecular signalling. The tumour suppressor protein p53 is a molecular hub of cell metabolism, supporting antioxidant capabilities and counteracting oncogene-induced metabolic switch. Despite extensive work has described the p53-dependent metabolic pathways, a global profiling of p53 lipidome is still missing. By high-throughput untargeted lipidomic analysis of pancreatic ductal adenocarcinoma (PDAC) cells, we profile the p53-dependent lipidome, revealing intracellular and secreted lysophospholipids as one of the most affected class. Lysophospholipids are hydrolysed forms of phospholipids that results from phospholipase activity, which can function as signalling molecules, exerting non-cell-autonomous effects and instructing cancer microenvironment and immunity. Here, we reveal that p53 depletion reduces abundance of intracellular lysophosphatidyl-choline, -ethanolamine and -serine and their secretion in the extracellular environment. By integrating this with genomic and transcriptomic studies from in vitro models and human PDAC patients, we identified potential clinically relevant candidate p53-dependent phospholipases. In particular PLD3, PLCB4 and PLCD4 expression is regulated by p53 and chromatin immunoprecipitation followed by deep sequencing (ChIP-seq) indicates a direct transcriptional control on their chromatin accessible genomic loci. Consistently, PLD3, PLCB4 and PLCD4 expression correlates with p53 mutational status in PDAC patients, and these genes display prognostic significance. Overall, our data provide insights into lipidome rewiring driven by p53 loss and identify alterations of lysophospholipids as a potential molecular mechanism for p53-mediated non-cell-autonomous molecular signalling that instructs cancer microenvironment and immunity during PDAC pathogenesis.

Human β-Defensin 2 (HBD-2) Displays Oncolytic Activity but Does Not Affect Tumour Cell Migration

Defensins form an integral part of the cationic host defence peptide (HDP) family, a key component of innate immunity. Apart from their antimicrobial and immunomodulatory activities, many HDPs exert multifaceted effects on tumour cells, notably direct oncolysis and/or inhibition of tumour cell migration. Therefore, HDPs have been explored as promising anticancer therapeutics. Human β-defensin 2 (HBD-2) represents a prominent member of human HDPs, being well-characterised for its potent pathogen-killing, wound-healing, cytokine-inducing and leukocyte-chemoattracting functions. However, its anticancer effects remain largely unknown. Recently, we demonstrated that HBD-2 binds strongly to phosphatidylinositol-4,5-bisphosphate (PI(4,5)P₂), a key mediator of defensin-induced cell death and an instructional messenger during cell migration. Hence, in this study, we sought to investigate the lytic and anti-migratory effects of HBD-2 on tumour cells. Using various cell biological assays and confocal microscopy, we showed that HBD-2 killed tumour cells via acute lytic cell death rather than apoptosis. In addition, our data suggested that, despite the reported PI(4,5)P₂ interaction, HBD-2 does not affect cytoskeletal-dependent tumour cell migration. Together, our findings provide further insights into defensin biology and informs future defensin-based drug development.

Striking a balance: PIP2 and PIP3 signaling in neuronal health and disease

Phosphoinositides are membrane phospholipids involved in a variety of cellular processes like growth, development, metabolism, and transport. This review focuses on the maintenance of cellular homeostasis of phosphatidylinositol 4,5-bisphosphate (PIP₂), and phosphatidylinositol 3,4,5-trisphosphate (PIP₃). The critical balance of these PIPs is crucial for regulation of neuronal form and function. The activity of PIP₂ and PIP₃ can be regulated through kinases, phosphatases, phospholipases and cholesterol microdomains. PIP₂ and PIP₃ carry out their functions either indirectly through their effectors activating integral signaling pathways, or through direct regulation of membrane channels, transporters, and cytoskeletal proteins. Any perturbations to the balance between PIP₂ and PIP₃ signaling result in neurodevelopmental and neurodegenerative disorders. This review will discuss the upstream modulators and downstream effectors of the PIP₂ and PIP₃ signaling, in the context of neuronal health and disease.

A Compendium of Information on the Lysosome

For a long time, lysosomes were considered as mere waste bags for cellular constituents. Thankfully, studies carried out in the past 15 years were brimming with elegant and crucial breakthroughs in lysosome research, uncovering their complex roles as nutrient sensors and characterizing them as crucial multifaceted signaling organelles. This review presents the scientific knowledge on lysosome physiology and functions, starting with their discovery and reviewing up to date ground-breaking discoveries highlighting their heterogeneous functions as well as pending questions that remain to be answered. We also review the roles of lysosomes in anti-cancer drug resistance and how they undergo a series of molecular and functional changes during malignant transformation which lead to tumor aggression, angiogenesis, and metastases. Finally, we discuss the strategy of targeting lysosomes in cancer which could lead to the development of new and effective targeted therapies.

Synthetic Siglec-9 Agonists Inhibit Neutrophil Activation Associated with COVID-19

Severe cases of coronavirus disease 2019 (COVID-19), caused by infection with SARS-CoV-2, are characterized by a hyperinflammatory immune response that leads to numerous complications. Production of proinflammatory neutrophil extracellular traps (NETs) has been suggested to be a key factor in inducing a hyperinflammatory signaling cascade, allegedly causing both pulmonary tissue damage and peripheral inflammation. Accordingly, therapeutic blockage of neutrophil activation and NETosis, the cell death pathway accompanying NET formation, could limit respiratory damage and death from severe COVID-19. Here, we demonstrate that synthetic glycopolymers that activate signaling of the neutrophil checkpoint receptor Siglec-9 suppress NETosis induced by agonists of viral toll-like receptors (TLRs) and plasma from patients with severe COVID-19. Thus, Siglec-9 agonism is a promising therapeutic strategy to curb neutrophilic hyperinflammation in COVID-19.

A narrative review of urinary phospholipids: from biochemical aspect towards clinical application

As a newly emerged discipline, lipidomic studies have focused on the comprehensive characterization and quantification of lipids in a given biological system, which has remarkably advanced in recent years owing to the rapid development of analytical techniques, especially mass spectrometry. Among diverse lipid classes, phospholipids, which have fundamental roles in the formation of cellular membranes, signaling processes, and bioenergetics have gained momentum in several fields of research. The altered composition, concentration, spatial distribution, and metabolism of phospholipids in cells, tissues, and body fluids have been elucidated in various human diseases such as cancer, inflammation, as well as cardiovascular and metabolic disorders. Among the different kinds of phospholipid sources in the human body, urine has not been extensively investigated in recent years owing to the extremely low concentrations of phospholipids and high levels of salts and other contaminants, which can interfere with precise detection. However, with profound advances and rapid expansion in analytical methods, urinary phospholipids have attracted increasing attention in current biomedical research as urine is an easily available source for the discovery of noninvasive biomarkers. In this review, we provide an overview of urinary phospholipids, including their biochemical aspects and clinical applications, aimed at promoting this field of research.

Phosphoinositides: Roles in the Development of Microglial-Mediated Neuroinflammation and Neurodegeneration

Microglia are increasingly recognized as vital players in the pathology of a variety of neurodegenerative conditions including Alzheimer’s (AD) and Parkinson’s (PD) disease. While microglia have a protective role in the brain, their dysfunction can lead to neuroinflammation and contributes to disease progression. Also, a growing body of literature highlights the seven phosphoinositides, or PIPs, as key players in the regulation of microglial-mediated neuroinflammation. These small signaling lipids are phosphorylated derivates of phosphatidylinositol, are enriched in the brain, and have well-established roles in both homeostasis and disease.Disrupted PIP levels and signaling has been detected in a variety of dementias. Moreover, many known AD disease modifiers identified via genetic studies are expressed in microglia and are involved in phospholipid metabolism. One of these, the enzyme PLCγ2 that hydrolyzes the PIP species PI(4,5)P₂, displays altered expression in AD and PD and is currently being investigated as a potential therapeutic target.Perhaps unsurprisingly, neurodegenerative conditions exhibiting PIP dyshomeostasis also tend to show alterations in aspects of microglial function regulated by these lipids. In particular, phosphoinositides regulate the activities of proteins and enzymes required for endocytosis, toll-like receptor signaling, purinergic signaling, chemotaxis, and migration, all of which are affected in a variety of neurodegenerative conditions. These functions are crucial to allow microglia to adequately survey the brain and respond appropriately to invading pathogens and other abnormalities, including misfolded proteins. AD and PD therapies are being developed to target many of the above pathways, and although not yet investigated, simultaneous PIP manipulation might enhance the beneficial effects observed. Currently, only limited therapeutics are available for dementia, and although these show some benefits for symptom severity and progression, they are far from curative. Given the importance of microglia and PIPs in dementia development, this review summarizes current research and asks whether we can exploit this information to design more targeted, or perhaps combined, dementia therapeutics. More work is needed to fully characterize the pathways discussed in this review, but given the strength of the current literature, insights in this area could be invaluable for the future of neurodegenerative disease research.

The immunophilin Zonda controls regulated exocytosis in endocrine and exocrine tissues

Exocytosis is a fundamental process in physiology, that ensures communication between cells, organs and even organisms. Hormones, neuropeptides and antibodies, among other cargoes are packed in exocytic vesicles that need to reach and fuse with the plasma membrane to release their content to the extracellular milieu. Hundreds of proteins participate in this process and several others in its regulation. We report here a novel component of the exocytic machinery, the Drosophila transmembrane immunophilin Zonda (Zda), previously found to participate in autophagy. Zda is highly expressed in secretory tissues, and regulates exocytosis in at least three of them: the ring gland, insulin-producing cells and the salivary gland. Using the salivary gland as a model system, we found that Zda is required at final steps of the exocytic process for fusion of secretory granules to the plasma membrane. In a genetic screen we identified the small GTPase RalA as a crucial regulator of secretory granule exocytosis that is required, similarly to Zda, for fusion between the secretory granule and the plasma membrane.

Identification of Key Phospholipids That Bind and Activate Atypical PKCs

PKCζ and PKCι/λ form the atypical protein kinase C subgroup, characterised by a lack of regulation by calcium and the neutral lipid diacylglycerol. To better understand the regulation of these kinases, we systematically explored their interactions with various purified phospholipids using the lipid overlay assays, followed by kinase activity assays to evaluate the lipid effects on their enzymatic activity. We observed that both PKCζ and PKCι interact with phosphatidic acid and phosphatidylserine. Conversely, PKCι is unique in binding also to phosphatidylinositol-monophosphates (e.g., phosphatidylinositol 3-phosphate, 4-phosphate, and 5-phosphate). Moreover, we observed that phosphatidylinositol 4-phosphate specifically activates PKCι, while both isoforms are responsive to phosphatidic acid and phosphatidylserine. Overall, our results suggest that atypical Protein kinase C (PKC) localisation and activity are regulated by membrane lipids distinct from those involved in conventional PKCs and unveil a specific regulation of PKCι by phosphatidylinositol-monophosphates.

Synthetic Siglec-9 Agonists Inhibit Neutrophil Activation Associated with COVID-19

Severe cases of coronavirus disease 2019 (COVID-19), caused by infection with SARS-Cov-2, are characterized by a hyperinflammatory immune response that leads to numerous complications. Production of proinflammatory neutrophil extracellular traps (NETs) has been suggested to be a key factor in inducing a hyperinflammatory signaling cascade, allegedly causing both pulmonary tissue damage and peripheral inflammation. Accordingly, therapeutic blockage of neutrophil activation and NETosis, the cell death pathway accompanying NET formation, could limit respiratory damage and death from severe COVID-19. Here, we demonstrate that synthetic glycopolymers that activate the neutrophil checkpoint receptor Siglec-9 suppress NETosis induced by agonists of viral toll-like receptors (TLRs) and plasma from patients with severe COVID-19. Thus, Siglec-9 agonism is a promising therapeutic strategy to curb neutrophilic hyperinflammation in COVID-19.
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Phosphoinositide Signaling and Mechanotransduction in Cardiovascular Biology and Disease

Phosphoinositides, which are membrane-bound phospholipids, are critical signaling molecules located at the interface between the extracellular matrix, cell membrane, and cytoskeleton. Phosphoinositides are essential regulators of many biological and cellular processes, including but not limited to cell migration, proliferation, survival, and differentiation, as well as cytoskeletal rearrangements and actin dynamics. Over the years, a multitude of studies have uniquely implicated phosphoinositide signaling as being crucial in cardiovascular biology and a dominant force in the development of cardiovascular disease and its progression. Independently, the cellular transduction of mechanical forces or mechanotransduction in cardiovascular cells is widely accepted to be critical to their homeostasis and can drive aberrant cellular phenotypes and resultant cardiovascular disease. Given the versatility and diversity of phosphoinositide signaling in the cardiovascular system and the dominant regulation of cardiovascular cell functions by mechanotransduction, the molecular mechanistic overlap and extent to which these two major signaling modalities converge in cardiovascular cells remain unclear. In this review, we discuss and synthesize recent findings that rightfully connect phosphoinositide signaling to cellular mechanotransduction in the context of cardiovascular biology and disease, and we specifically focus on phosphatidylinositol-4,5-phosphate, phosphatidylinositol-4-phosphate 5-kinase, phosphatidylinositol-3,4,5-phosphate, and phosphatidylinositol 3-kinase. Throughout the review, we discuss how specific phosphoinositide subspecies have been shown to mediate biomechanically sensitive cytoskeletal remodeling in cardiovascular cells. Additionally, we discuss the direct interaction of phosphoinositides with mechanically sensitive membrane-bound ion channels in response to mechanical stimuli. Furthermore, we explore the role of phosphoinositide subspecies in association with critical downstream effectors of mechanical signaling in cardiovascular biology and disease.

Cytoskeletal Remodeling in Cancer

Simple Summary

Cell migration is an essential process from embryogenesis to cell death. This is tightly regulated by numerous proteins that help in proper functioning of the cell. In diseases like cancer, this process is deregulated and helps in the dissemination of tumor cells from the primary site to secondary sites initiating the process of metastasis. For metastasis to be efficient, cytoskeletal components like actin, myosin, and intermediate filaments and their associated proteins should co-ordinate in an orderly fashion leading to the formation of many cellular protrusions-like lamellipodia and filopodia and invadopodia. Knowledge of this process is the key to control metastasis of cancer cells that leads to death in 90% of the patients. The focus of this review is giving an overall understanding of these process, concentrating on the changes in protein association and regulation and how the tumor cells use it to their advantage. Since the expression of cytoskeletal proteins can be directly related to the degree of malignancy, knowledge about these proteins will provide powerful tools to improve both cancer prognosis and treatment.

Abstract

Successful metastasis depends on cell invasion, migration, host immune escape, extravasation, and angiogenesis. The process of cell invasion and migration relies on the dynamic changes taking place in the cytoskeletal components; actin, tubulin and intermediate filaments. This is possible due to the plasticity of the cytoskeleton and coordinated action of all the three, is crucial for the process of metastasis from the primary site. Changes in cellular architecture by internal clues will affect the cell functions leading to the formation of different protrusions like lamellipodia, filopodia, and invadopodia that help in cell migration eventually leading to metastasis, which is life threatening than the formation of neoplasms. Understanding the signaling mechanisms involved, will give a better insight of the changes during metastasis, which will eventually help targeting proteins for treatment resulting in reduced mortality and longer survival.

Subcellular Localization Relevance and Cancer-Associated Mechanisms of Diacylglycerol Kinases

An increasing number of reports suggests a significant involvement of the phosphoinositide (PI) cycle in cancer development and progression. Diacylglycerol kinases (DGKs) are very active in the PI cycle. They are a family of ten members that convert diacylglycerol (DAG) into phosphatidic acid (PA), two-second messengers with versatile cellular functions. Notably, some DGK isoforms, such as DGKα, have been reported to possess promising therapeutic potential in cancer therapy. However, further studies are needed in order to better comprehend their involvement in cancer. In this review, we highlight that DGKs are an essential component of the PI cycle that localize within several subcellular compartments, including the nucleus and plasma membrane, together with their PI substrates and that they are involved in mediating major cancer cell mechanisms such as growth and metastasis. DGKs control cancer cell survival, proliferation, and angiogenesis by regulating Akt/mTOR and MAPK/ERK pathways. In addition, some DGKs control cancer cell migration by regulating the activities of the Rho GTPases Rac1 and RhoA.

A PI4KIIIα protein complex is required for cell viability during Drosophila wing development

Phosphatidylinositol 4 phosphate (PI4P) and phosphatidylinositol 4,5 bisphosphate [PI(4,5)P₂] are enriched on the inner leaflet of the plasma membrane and proposed to be key determinants of its function. PI4P is also the biochemical precursor for the synthesis of PI(4,5)P₂ but can itself also bind to and regulate protein function. However, the independent function of PI4P at the plasma membrane in supporting cell function in metazoans during development in vivo remains unclear. We find that conserved components of a multi-protein complex composed of phosphatidylinositol 4-kinase IIIα (PI4KIIIα), TTC7 and Efr3 is required for normal vein patterning and wing development. Depletion of each of these three components of the PI4KIIIα complex in developing wing cells results in altered wing morphology. These effects are associated with an increase in apoptosis and can be rescued by expression of an inhibitor of Drosophila caspase. We find that in contrast to previous reports, PI4KIIIα depletion does not alter key outputs of hedgehog signalling in developing wing discs. Depletion of PI4KIIIα results in reduced PI4P levels at the plasma membrane of developing wing disc cells while levels of PI(4,5)P₂, the downstream metabolite of PI4P, are not altered. Thus, PI4P itself generated by the activity of the PI4KIIIα complex plays an essential role in supporting cell viability in the developing Drosophila wing disc.

Cardioprotective Role of Melatonin in Acute Myocardial Infarction

Melatonin is a pleiotropic, indole secreted, and synthesized by the human pineal gland. Melatonin has biological effects including anti-apoptosis, protecting mitochondria, anti-oxidation, anti-inflammation, and stimulating target cells to secrete cytokines. Its protective effect on cardiomyocytes in acute myocardial infarction (AMI) has caused widespread interest in the actions of this molecule. The effects of melatonin against oxidative stress, promoting autophagic repair of cells, regulating immune and inflammatory responses, enhancing mitochondrial function, and relieving endoplasmic reticulum stress, play crucial roles in protecting cardiomyocytes from infarction. Mitochondrial apoptosis and dysfunction are common occurrence in cardiomyocyte injury after myocardial infarction. This review focuses on the targets of melatonin in protecting cardiomyocytes in AMI, the main molecular signaling pathways that melatonin influences in its endogenous protective role in myocardial infarction, and the developmental prospect of melatonin in myocardial infarction treatment.

Phosphoinositides in Retinal Function and Disease

Phosphatidylinositol and its phosphorylated derivatives, the phosphoinositides, play many important roles in all eukaryotic cells. These include modulation of physical properties of membranes, activation or inhibition of membrane-associated proteins, recruitment of peripheral membrane proteins that act as effectors, and control of membrane trafficking. They also serve as precursors for important second messengers, inositol (1,4,5) trisphosphate and diacylglycerol. Animal models and human diseases involving defects in phosphoinositide regulatory pathways have revealed their importance for function in the mammalian retina and retinal pigmented epithelium. New technologies for localizing, measuring and genetically manipulating them are revealing new information about their importance for the function and health of the vertebrate retina.

A lipid perspective on regulated cell death

Lipids are fundamental to life as structural components of cellular membranes and for signaling. They are also key regulators of different cellular processes such as cell division, proliferation, and death. Regulated cell death (RCD) requires the engagement of lipids and lipid metabolism for the initiation and execution of its killing machinery. The permeabilization of lipid membranes is a hallmark of RCD that involves, for each kind of cell death, a unique lipid profile. While the permeabilization of the mitochondrial outer membrane allows the release of apoptotic factors to the cytosol during apoptosis, permeabilization of the plasma membrane facilitates the release of intracellular content in other nonapoptotic types of RCD like necroptosis and ferroptosis. Lipids and lipid membranes are important accessory molecules required for the activation of protein executors of cell death such as BAX in apoptosis and MLKL in necroptosis. Peroxidation of membrane phospholipids and the subsequent membrane destabilization is a prerequisite to ferroptosis. Here, we discuss how lipids are essential players in apoptosis, the most common form of RCD, and also their role in necroptosis and ferroptosis. Altogether, we aim to highlight the contribution of lipids and membrane dynamics in cell death regulation.

Nuclear Phosphoinositides-Versatile Regulators of Genome Functions

The many functions of phosphoinositides in cytosolic signaling were extensively studied; however, their activities in the cell nucleus are much less clear. In this review, we summarize data about their nuclear localization and metabolism, and review the available literature on their involvements in chromatin remodeling, gene transcription, and RNA processing. We discuss the molecular mechanisms via which nuclear phosphoinositides, in particular phosphatidylinositol (4,5)-bisphosphate (PI(4,5)P2), modulate nuclear processes. We focus on PI(4,5)P2’s role in the modulation of RNA polymerase I activity, and functions of the nuclear lipid islets—recently described nucleoplasmic PI(4,5)P2-rich compartment involved in RNA polymerase II transcription. In conclusion, the high impact of the phosphoinositide–protein complexes on nuclear organization and genome functions is only now emerging and deserves further thorough studies.

Nuclear Phosphoinositides: Their Regulation and Roles in Nuclear Functions

Polyphosphoinositides (PPIns) are a family of seven lipid messengers that regulate a vast array of signalling pathways to control cell proliferation, migration, survival and differentiation. PPIns are differentially present in various sub-cellular compartments and, through the recruitment and regulation of specific proteins, are key regulators of compartment identity and function. Phosphoinositides and the enzymes that synthesise and degrade them are also present in the nuclear membrane and in nuclear membraneless compartments such as nuclear speckles. Here we discuss how PPIns in the nucleus are modulated in response to external cues and how they function to control downstream signalling. Finally we suggest a role for nuclear PPIns in liquid phase separations that are involved in the formation of membraneless compartments within the nucleus.