Inhibition of acid sphingomyelinase disrupts LYNUS signaling and triggers autophagy

Ceramide regulation of autophagy: A biophysical approach

Specific membrane lipids play unique roles in (macro)autophagy. Those include phosphatidylethanolamine, to which LC3/GABARAP autophagy proteins become covalently bound in the process, or cardiolipin, an important effector in mitochondrial autophagy (or mitophagy). Ceramide (Cer), or N-acyl sphingosine, is one of the simplest sphingolipids, known as a stress signal in the apoptotic pathway. Moreover, Cer is increasingly being recognized as an autophagy activator, although its mechanism of action is unclear. In the present review, the proposed Cer roles in autophagy are summarized, together with some biophysical properties of Cer in membranes. Possible pathways for Cer activation of autophagy are discussed, including specific protein binding of the lipid, and Cer-dependent perturbation of bilayer properties. Cer generation of lateral inhomogeneities (domain formation) is given special attention. Recent biophysical results, including fluorescence and atomic force microscopy data, show Cer-promoted enhanced binding of LC3/GABARAP to lipid bilayers. These observations could be interpreted in terms of the putative formation of Cer-rich nanodomains.

Alpha-1 antitrypsin inhibits fractalkine-mediated monocyte-lung endothelial cell interactions

Chronic obstructive pulmonary disease (COPD) is characterized by nonresolving inflammation fueled by breach in the endothelial barrier and leukocyte recruitment into the airspaces. Among the ligand-receptor axes that control leukocyte recruitment, the full-length fractalkine ligand (CX3CL1)-receptor (CX3CR1) ensures homeostatic endothelial-leukocyte interactions. Cigarette smoke (CS) exposure and respiratory pathogens increase expression of endothelial sheddases, such as a-disintegrin-and-metalloproteinase-domain 17 (ADAM17, TACE), inhibited by the anti-protease α-1 antitrypsin (AAT). In the systemic endothelium, TACE cleaves CX3CL1 to release soluble CX3CL1 (sCX3CL1). During CS exposure, it is not known whether AAT inhibits sCX3CL1 shedding and CX3CR1+ leukocyte transendothelial migration across lung microvasculature. We investigated the mechanism of sCX3CL1 shedding, its role in endothelial-monocyte interactions, and AAT effect on these interactions during acute inflammation. We used two, CS and lipopolysaccharide (LPS) models of acute inflammation in transgenic Cx3cr1gfp/gfp mice and primary human endothelial cells and monocytes to study sCX3CL1-mediated CX3CR1+ monocyte adhesion and migration. We measured sCX3CL1 levels in plasma and bronchoalveolar lavage (BALF) of individuals with COPD. Both sCX3CL1 shedding and CX3CR1+ monocytes transendothelial migration were triggered by LPS and CS exposure in mice, and were significantly attenuated by AAT. The inhibition of monocyte-endothelial adhesion and migration by AAT was TACE-dependent. Compared with healthy controls, sCX3CL1 levels were increased in plasma and BALF of individuals with COPD, and were associated with clinical parameters of emphysema. Our results indicate that inhibition of sCX3CL1 as well as AAT augmentation may be effective approaches to decrease excessive monocyte lung recruitment during acute and chronic inflammatory states.NEW & NOTEWORTHY Our novel findings that AAT and other inhibitors of TACE, the sheddase that controls full-length fractalkine (CX3CL1) endothelial expression, may provide fine-tuning of the CX3CL1-CX3CR1 axis specifically involved in endothelial-monocyte cross talk and leukocyte recruitment to the alveolar space, suggests that AAT and inhibitors of sCX3CL1 signaling may be harnessed to reduce lung inflammation.

Antidepressants as Autophagy Modulators for Cancer Therapy

Cancer is a major global public health problem with high morbidity. Depression is known to be a high-frequency complication of cancer diseases that decreases patients' life quality and increases the mortality rate. Therefore, antidepressants are often used as a complementary treatment during cancer therapy. During recent decades, various studies have shown that the combination of antidepressants and anticancer drugs increases treatment efficiency. In recent years, further emerging evidence has suggested that the modulation of autophagy serves as one of the primary anticancer mechanisms for antidepressants to suppress tumor growth. In this review, we introduce the anticancer potential of antidepressants, including tricyclic antidepressants (TCAs), tetracyclic antidepressants (TeCAs), selective serotonin reuptake inhibitors (SSRIs), and serotonin-norepinephrine reuptake inhibitors (SNRIs). In particular, we focus on their autophagy-modulating mechanisms for regulating autophagosome formation and lysosomal degradation. We also discuss the prospect of repurposing antidepressants as anticancer agents. It is promising to repurpose antidepressants for cancer therapy in the future.

Does Chronic Obstructive Pulmonary Disease Originate from Different Cell Types?

The onset of chronic obstructive pulmonary disease (COPD) is heterogeneous, and current approaches to define distinct disease phenotypes are lacking. In addition to clinical methodologies, subtyping COPD has also been challenged by the reliance on human lung samples from late-stage diseases. Different COPD phenotypes may be initiated from the susceptibility of different cell types to cigarette smoke, environmental pollution, and infections at early stages that ultimately converge at later stages in airway remodeling and destruction of the alveoli when the disease is diagnosed. This perspective provides discussion points on how studies to date define different cell types of the lung that can initiate COPD pathogenesis, focusing on the susceptibility of macrophages, T and B cells, mast cells, dendritic cells, endothelial cells, and airway epithelial cells. Additional cell types, including fibroblasts, smooth muscle cells, neuronal cells, and other rare cell types not covered here, may also play a role in orchestrating COPD. Here, we discuss current knowledge gaps, such as which cell types drive distinct disease phenotypes and/or stages of the disease and which cells are primarily affected by the genetic variants identified by whole genome-wide association studies. Applying new technologies that interrogate the functional role of a specific cell type or a combination of cell types as well as single-cell transcriptomics and proteomic approaches are creating new opportunities to understand and clarify the pathophysiology and thereby the clinical heterogeneity of COPD.

The relevance of acid sphingomyelinase as a potential target for therapeutic intervention in hepatic disorders: current scenario and anticipated trends

Acid sphingomyelinase (ASMase) serves as one of the most remarkable enzymes in sphingolipid biology. ASMase facilitates the hydrolysis of sphingomyelin, yielding ceramide and phosphorylcholine via the phospholipase C signal transduction pathway. Owing to its prominent intervention in apoptosis, ASMase, and its product ceramide is now at the bleeding edge of lipid research due to the coalesced efforts of several research institutions over the past 40 years. ASMase-catalyzed ceramide synthesis profoundly alters the physiological properties of membrane structure in response to a broad range of stimulations, orchestrating signaling cascades for endoplasmic reticulum stress, autophagy, and lysosomal membrane permeabilization, which influences the development of hepatic disorders, such as steatohepatitis, hepatic fibrosis, drug-induced liver injury, and hepatocellular carcinoma. As a result, the potential to modulate the ASMase action with appropriate pharmaceutical antagonists has sparked a lot of curiosity. This article emphasizes the fundamental mechanisms of the systems that govern ASMase aberrations in various hepatic pathologies. Furthermore, we present an insight into the potential therapeutic agents used to mitigate ASMase irregularities and the paramountcy of such inhibitors in drug repurposing.

Cellular Recycling Gone Wrong: The Role of Dysregulated Autophagy and Hyperactive mTORC1 in the Pathogenesis of Sarcoidosis

BACKGROUND AND AIMS

Autophagy is a highly regulated, complex intracellular recycling process that is vital to maintaining cellular homeostasis in response to diverse conditions and stressors. Despite the presence of robust regulatory pathways, the intricate and multi-step nature of autophagy creates opportunity for dysregulation. Errors in autophagy have been implicated in the development of a broad range of clinical pathologies including granulomatous disease. Specifically, activation of the mTORC1 pathway has been identified as a key negative regulator of autophagic flux, prompting the study of dysregulated mTORC1 signaling in the pathogenesis of sarcoidosis. Our review: We conducted a thorough search of the extant literature to identify the regulatory pathways of autophagy, and more specifically the implication of upregulated mTORC1 pathways in the pathogenesis of sarcoidosis. We review data showing spontaneous granuloma formation in animal models with upregulate mTORC1 signaling, human genetic studies showing mutation in autophagy genes in sarcoidosis patients, and clinical data showing that targeting autophagy regulatory molecules like mTORC1 may provide new therapeutic approaches for sarcoidosis.

CONCLUSIONS

Given the incomplete understanding of sarcoidosis pathogenesis and the toxicities of current treatments, a more complete understanding of sarcoidosis pathogenesis is crucial for the development of more effective and safer therapies. In this review, we propose a strong molecular pathway driving sarcoidosis pathogenesis at which autophagy is at the center. A more complete understanding of autophagy and its regulatory molecules, like mTORC1, may provide a window into new therapeutic approaches for sarcoidosis.

FDA-Approved Amoxapine Effectively Promotes Macrophage Control of Mycobacteria by Inducing Autophagy

Antibiotic resistance poses a significant hurdle in combating global public health crises, prompting the development of novel therapeutics. Strategies to enhance the intracellular killing of mycobacteria by targeting host defense mechanisms offer numerous beneficial effects, which include reducing cytotoxicity caused by current lengthy anti-tubercular treatment regimens and slowing or circumventing the development of multidrug-resistant strains. The intracellular pathogen Mycobacterium tuberculosis infects macrophages and exploits host machinery to survive and multiply. Using a cell-based screen of FDA-approved drugs, we identified an antidepressant, Amoxapine, capable of inhibiting macrophage cytotoxicity during mycobacterial infection. Notably, this reduced cytotoxicity was related to the enhanced intracellular killing of Mycobacterium bovis BCG and M. tuberculosis within human and murine macrophages. Interestingly, we discovered that postinfection treatment with Amoxapine inhibited mTOR (mammalian target of rapamycin) activation, resulting in the induction of autophagy without affecting autophagic flux in macrophages. Also, inhibition of autophagy by chemical inhibitor 3-MA or knockdown of an essential component of the autophagic pathway, ATG16L1, significantly diminished Amoxapine's intracellular killing effects against mycobacteria in the host cells. Finally, we demonstrated that Amoxapine treatment enhanced host defense against M. tuberculosis in mice. In conclusion, our study identified Amoxapine as a novel host-directed drug that enhances the intracellular killing of mycobacteria by induction of autophagy, with concomitant protection of macrophages against death. IMPORTANCE The emergence and spread of multidrug-resistant (MDR) and extensive drug-resistant (XDR) TB urges the development of new therapeutics. One promising approach to combat drug resistance is targeting host factors necessary for the bacteria to survive or replicate while simultaneously minimizing the dosage of traditional agents. Moreover, repurposing FDA-approved drugs presents an attractive avenue for reducing the cost and time associated with new drug development. Using a cell-based screen of FDA-approved host-directed therapies (HDTs), we showed that Amoxapine inhibits macrophage cytotoxicity during mycobacterial infection and enhances the intracellular killing of mycobacteria within macrophages by activating the autophagy pathway, both in vitro and in vivo. These findings confirm targeted autophagy as an effective strategy for developing new HDT against mycobacteria.

Early secretory pathway-resident Zn transporter proteins contribute to cellular sphingolipid metabolism through activation of sphingomyelin phosphodiesterase 1

Sphingomyelin phosphodiesterase 1 (SMPD1) converts sphingomyelin into ceramide and phosphocholine; hence, loss of SMPD1 function causes abnormal accumulation of sphingomyelin in lysosomes, which results in the lipid-storage disorder Niemann-Pick disease (types A and B). SMPD1 activity is dependent on zinc, which is coordinated at the active site of the enzyme, and although SMPD1 has been suggested to acquire zinc at the sites where the enzyme is localized, precisely how SMPD1 acquires zinc remains to be clarified. Here, we addressed this using a gene-disruption/re-expression strategy. Our results revealed that Zn transporter 5 (ZNT5)-ZNT6 heterodimers and ZNT7 homodimers, which localize in the compartments of the early secretory pathway, play essential roles in SMPD1 activation. Both ZNT complexes contribute to cellular sphingolipid metabolism by activating SMPD1 because cells lacking the functions of the two complexes exhibited a reduced ceramide to sphingomyelin content ratio in terms of their dominant molecular species and an increase in the sphingomyelin content in terms of three minor species. Moreover, mutant cells contained multilamellar body-like structures, indicative of membrane stacking and accumulation, in the cytoplasm. These findings provide novel insights into the molecular mechanism underlying the activation of SMPD1, a key enzyme in sphingolipid metabolism.

Dichotomy in hypoxia-induced mitochondrial fission in placental mesenchymal cells during development and preeclampsia: consequences for trophoblast mitochondrial homeostasis

Dynamic changes in physiologic oxygen are required for proper placenta development; yet, when low-oxygen levels persist, placental development is halted, culminating in preeclampsia (PE), a serious complication of pregnancy. Considering mitochondria’s function is intimately linked to oxygen changes, we investigated the impact of oxygen on mitochondrial dynamics in placental mesenchymal stromal cells (pMSCs) that are vital for proper placental development. Transmission electron microscopy, proximity ligation assays for mitochondrial VDAC1 and endoplasmic reticulum IP3R, and immunoanalyses of p-DRP1 and OPA1, demonstrate that low-oxygen conditions in early 1st trimester and PE promote mitochondrial fission in pMSCs. Increased mitochondrial fission of mesenchymal cells was confirmed in whole PE placental tissue sections. Inhibition of DRP1 oligomerization with MDiVi-1 shows that low oxygen-induced mitochondrial fission is a direct consequence of DRP1 activation, likely via HIF1. Mitophagy, a downstream event prompted by mitochondrial fission, is a prominent outcome in PE, but not 1st trimester pMSCs. We also investigated whether mesenchymal–epithelial interactions affect mitochondrial dynamics of trophoblasts in PE placentae. Exposure of trophoblastic JEG3 cells to exosomes of preeclamptic pMSCs caused heightened mitochondrial fission in the cells via a sphingomyelin-dependent mechanism that was restored by MDiVi-1. Our data uncovered dichotomous regulation of mitochondrial fission and health in human placental mesenchymal cells under physiologic and pathologic hypoxic conditions and its impact on neighboring trophoblast cells.

Ceramide-1-phosphate and its transfer proteins in eukaryotes

Ceramide-1-phosphate (C1P) is a bioactive phosphorylated sphingolipid (SL), produced through the direct phosphorylation of ceramide by ceramide kinase. It plays important roles in regulating cell survival, migration, apoptosis and autophagy and is involved in inflammasome assembly/activation, which can stimulate group IVA cytosolic phospholipase A₂α and subsequently increase the levels of arachidonic acid and pro-inflammatory cytokines. Human C1P transfer protein (CPTP) can selectively transport C1P from the Golgi apparatus to specific cellular sites through a non-vesicular mechanism. Human CPTP also affects specific SL levels, thus regulating cell SL homeostasis. In addition, human CPTP plays a crucial role in the regulation of autophagy, inflammation and cell death; thus, human CPTP is closely associated with autophagy and inflammation-related diseases such as cardiovascular and neurodegenerative diseases, and cancers. Therefore, illustrating the functions and mechanisms of human CPTP is important for providing the research foundations for targeted therapy. The key human CPTP residues for C1P recognition and binding are highly conserved in eukaryotic orthologs, while the human CPTP homolog in Arabidopsis (accelerated cell death 11) also exhibits selective inter-membrane transfer of phyto-C1P. These results demonstrate that C1P transporters play fundamental roles in SL metabolism in cells. The present review summarized novel findings of C1P and its TPs in eukaryotes.

Acid Sphingomyelinase, a Lysosomal and Secretory Phospholipase C, Is Key for Cellular Phospholipid Catabolism

Here, we present the main features of human acid sphingomyelinase (ASM), its biosynthesis, processing and intracellular trafficking, its structure, its broad substrate specificity, and the proposed mode of action at the surface of the phospholipid substrate carrying intraendolysosomal luminal vesicles. In addition, we discuss the complex regulation of its phospholipid cleaving activity by membrane lipids and lipid-binding proteins. The majority of the literature implies that ASM hydrolyses solely sphingomyelin to generate ceramide and ignores its ability to degrade further substrates. Indeed, more than twenty different phospholipids are cleaved by ASM in vitro, including some minor but functionally important phospholipids such as the growth factor ceramide-1-phosphate and the unique lysosomal lysolipid bis(monoacylglycero)phosphate. The inherited ASM deficiency, Niemann-Pick disease type A and B, impairs mainly, but not only, cellular sphingomyelin catabolism, causing a progressive sphingomyelin accumulation, which furthermore triggers a secondary accumulation of lipids (cholesterol, glucosylceramide, GM2) by inhibiting their turnover in late endosomes and lysosomes. However, ASM appears to be involved in a variety of major cellular functions with a regulatory significance for an increasing number of metabolic disorders. The biochemical characteristics of ASM, their potential effect on cellular lipid turnover, as well as a potential impact on physiological processes will be discussed.

Altered Macrophage Function Associated with Crystalline Lung Inflammation in Acid Sphingomyelinase Deficiency

Deficiency of ASM (acid sphingomyelinase) causes the lysosomal storage Niemann-Pick disease (NPD). Patients with NPD type B may develop progressive interstitial lung disease with frequent respiratory infections. Although several investigations using the ASM-deficient (ASMKO) mouse NPD model revealed inflammation and foamy macrophages, there is little insight into the pathogenesis of NPD-associated lung disease. Using ASMKO mice, we report that ASM deficiency is associated with a complex inflammatory phenotype characterized by marked accumulation of monocyte-derived CD11b⁺ macrophages and expansion of airspace/alveolar CD11c⁺ CD11b^- macrophages, both with increased size, granularity, and foaminess. Both the alternative and classical pathways were activated, with decreased in situ phagocytosis of opsonized (Fc-coated) targets, preserved clearance of apoptotic cells (efferocytosis), secretion of Th2 cytokines, increased CD11c⁺/CD11b⁺ cells, and more than a twofold increase in lung and plasma proinflammatory cytokines. Macrophages, neutrophils, eosinophils, and noninflammatory lung cells of ASMKO lungs also exhibited marked accumulation of chitinase-like protein Ym1/2, which formed large eosinophilic polygonal Charcot-Leyden-like crystals. In addition to providing insight into novel features of lung inflammation that may be associated with NPD, our report provides a novel connection between ASM and the development of crystal-associated lung inflammation with alterations in macrophage biology.

A photocaged inhibitor of acid sphingomyelinase

Acid sphingomyelinase (ASM) is a potential drug target and involved in rapid lipid signalling events. However, there are no tools available to adequately study such processes. Based on a non cell-permeable PtdIns(3,5)P2 inhibitor of ASM, we developed a compound with o-nitrobenzyl photocages and butyryl esters to transiently mask hydroxyl groups. This resulted in a potent light-inducible photocaged ASM inhibitor (PCAI). The first example of a time-resolved inhibition of ASM was shown in intact living cells.

Autophagy-targeted therapy to modulate age-related diseases: Success, pitfalls, and new directions

Autophagy is a critical metabolic process that supports homeostasis at a basal level and is dynamically regulated in response to various physiological and pathological processes. Autophagy has some etiologic implications that support certain pathological processes due to alterations in the lysosomal-degradative pathway. Some of the conditions related to autophagy play key roles in highly relevant human diseases, e.g., cardiovascular diseases (15.5%), malignant and other neoplasms (9.4%), and neurodegenerative conditions (3.7%). Despite advances in the discovery of new strategies to treat these age-related diseases, autophagy has emerged as a therapeutic option after preclinical and clinical studies. Here, we discuss the pitfalls and success in regulating autophagy initiation and its lysosome-dependent pathway to restore its homeostatic role and mediate therapeutic effects for cancer, neurodegenerative, and cardiac diseases. The main challenge for the development of autophagy regulators for clinical application is the lack of specificity of the repurposed drugs, due to the low pharmacological uniqueness of their target, including those that target the PI3K/AKT/mTOR and AMPK pathway. Then, future efforts must be conducted to deal with this scenery, including the disclosure of key components in the autophagy machinery that may intervene in its therapeutic regulation. Among all efforts, those focusing on the development of novel allosteric inhibitors against autophagy inducers, as well as those targeting autolysosomal function, and their integration into therapeutic regimens should remain a priority for the field.

Sphingosine 1 Phosphate (S1P) Receptor 1 Is Decreased in Human Lung Microvascular Endothelial Cells of Smokers and Mediates S1P Effect on Autophagy

Destruction of alveoli by apoptosis induced by cigarette smoke (CS) is a major driver of emphysema pathogenesis. However, when compared to cells isolated from non-smokers, primary human lung microvascular endothelial cells (HLMVECs) isolated from chronic smokers are more resilient when exposed to apoptosis-inducing ceramide. Whether this adaptation restores homeostasis is unknown. To better understand the phenotype of HLMVEC in smokers, we interrogated a major pro-survival pathway supported by sphingosine-1-phosphate (S1P) signaling via S1P receptor 1 (S1P1). Primary HLMVECs from lungs of non-smoker or smoker donors were isolated and studied in culture for up to five passages. S1P1 mRNA and protein abundance were significantly decreased in HLMVECs from smokers compared to non-smokers. S1P1 was also decreased in situ in lungs of mice chronically exposed to CS. Levels of S1P1 expression tended to correlate with those of autophagy markers, and increasing S1P (via S1P lyase knockdown with siRNA) stimulated baseline macroautophagy with lysosomal degradation. In turn, loss of S1P1 (siRNA) inhibited these effects of S1P on HLMVECs autophagy. These findings suggest that the anti-apoptotic phenotype of HLMVECs from smokers may be maladaptive, since it is associated with decreased S1P1 expression that may impair their autophagic response to S1P.

Ceramide-Induced Lysosomal Biogenesis and Exocytosis in Early-Onset Preeclampsia Promotes Exosomal Release of SMPD1 Causing Endothelial Dysfunction

Aberrant ceramide build-up in preeclampsia, a serious disorder of pregnancy, causes exuberant autophagy-mediated trophoblast cell death. The significance of ceramide accumulation for lysosomal biogenesis in preeclampsia is unknown. Here we report that lysosome formation is markedly increased in trophoblast cells of early-onset preeclamptic placentae, in particular in syncytiotrophoblasts. This is accompanied by augmented levels of transcription factor EB (TFEB). In vitro and in vivo experiments demonstrate that ceramide increases TFEB expression and nuclear translocation and induces lysosomal formation and exocytosis. Further, we show that TFEB directly regulates the expression of lysosomal sphingomyelin phosphodiesterase (L-SMPD1) that degrades sphingomyelin to ceramide. In early-onset preeclampsia, ceramide-induced lysosomal exocytosis carries L-SMPD1 to the apical membrane of the syncytial epithelium, resulting in ceramide accumulation in lipid rafts and release of active L-SMPD1 via ceramide-enriched exosomes into the maternal circulation. The SMPD1-containing exosomes promote endothelial activation and impair endothelial tubule formation in vitro. Both exosome-induced processes are attenuated by SMPD1 inhibitors. These findings suggest that ceramide-induced lysosomal biogenesis and exocytosis in preeclamptic placentae contributes to maternal endothelial dysfunction, characteristic of this pathology.

Revisiting Drug Development Against the Neglected Tropical Disease, Amebiasis

Amebiasis is a neglected tropical disease which is caused by the protozoan parasite Entamoeba histolytica. This disease is one of the leading causes of diarrhea globally, affecting largely impoverished residents in developing countries. Amebiasis also remains one of the top causes of gastrointestinal diseases in returning international travellers. Despite having many side effects, metronidazole remains the drug of choice as an amebicidal tissue-active agent. However, emergence of metronidazole resistance in pathogens having similar anaerobic metabolism and also in laboratory strains of E. histolytica has necessitated the identification and development of new drug targets and therapeutic strategies against the parasite. Recent research in the field of amebiasis has led to a better understanding of the parasite’s metabolic and cellular pathways and hence has been useful in identifying new drug targets. On the other hand, new molecules effective against amebiasis have been mined by modifying available compounds, thereby increasing their potency and efficacy and also by repurposing existing approved drugs. This review aims at compiling and examining up to date information on promising drug targets and drug molecules for the treatment of amebiasis.

Ceramide and sphingosine-1 phosphate in COPD lungs

Studies of chronic obstructive pulmonary disease (COPD) using animal models and patient plasma indicate dysregulation of sphingolipid metabolism, but data in COPD lungs are sparse. Mass spectrometric and immunostaining measurements of lungs from 69 COPD, 16 smokers without COPD and 13 subjects with interstitial lung disease identified decoupling of lung ceramide and sphingosine-1 phosphate (S1P) levels and decreased sphingosine kinase-1 (SphK1) activity in COPD. The correlation of ceramide abundance in distal COPD lungs with apoptosis and the inverse correlation between SphK1 activity and presence of emphysema suggest that disruption of ceramide-to-S1P metabolism is an important determinant of emphysema phenotype in COPD.

Lysosomotropic Features and Autophagy Modulators among Medical Drugs: Evaluation of Their Role in Pathologies

The concept of lysosomotropic agents significantly changed numerous aspects of cellular biochemistry, biochemical pharmacology, and clinical medicine. In the present review, we focused on numerous low-molecular and high-molecular lipophilic basic compounds and on the role of lipophagy and autophagy in experimental and clinical medicine. Attention was primarily focused on the most promising agents acting as autophagy inducers, which offer a new window for treatment and/or prophylaxis of various diseases, including type 2 diabetes mellitus, Parkinson's disease, and atherosclerosis. The present review summarizes current knowledge on the lysosomotropic features of medical drugs, as well as autophagy inducers, and their role in pathological processes.

Boosting the autophagy-lysosomal pathway by phytochemicals: A potential therapeutic strategy against Alzheimer's disease

The lysosome is a membrane-enclosed organelle in eukaryotic cells, which has basic pattern recognition for nutrient-dependent signal transduction. In Alzheimer's disease, the already declining autophagy-lysosomal function is exacerbated by an increased need for clearance of damaged proteins and organelles in aged cells. Recent evidence suggests that numerous diseases are linked to impaired autophagy upstream of lysosomes. In this way, a comprehensive survey on the pathophysiology of the disease seems necessary. Hence, in the first section of this review, we will discuss the ultimate findings in lysosomal signaling functions and how they affect cellular metabolism and trafficking under neurodegenerative conditions, specifically Alzheimer's disease. In the second section, we focus on how natural products and their derivatives are involved in the regulation of inflammation and lysosomal dysfunction pathways, including how these should be considered a crucial target for Alzheimer's disease therapeutics.

IGSF3 mutation identified in patient with severe COPD alters cell function and motility

Cigarette smoking (CS) and genetic susceptibility determine the risk for development, progression, and severity of chronic obstructive pulmonary diseases (COPD). We posited that an incidental balanced reciprocal chromosomal translocation was linked to a patient's risk of severe COPD. We determined that 46,XX,t(1;4)(p13.1;q34.3) caused a breakpoint in the immunoglobulin superfamily member 3 (IGSF3) gene, with markedly decreased expression. Examination of COPDGene cohort identified 14 IGSF3 SNPs, of which rs1414272 and rs12066192 were directly and rs6703791 inversely associated with COPD severity, including COPD exacerbations. We confirmed that IGSF3 is a tetraspanin-interacting protein that colocalized with CD9 and integrin B1 in tetraspanin-enriched domains. IGSF3-deficient patient-derived lymphoblastoids exhibited multiple alterations in gene expression, especially in the unfolded protein response and ceramide pathways. IGSF3-deficient lymphoblastoids had high ceramide and sphingosine-1 phosphate but low glycosphingolipids and ganglioside levels, and they were less apoptotic and more adherent, with marked changes in multiple TNFRSF molecules. Similarly, IGSF3 knockdown increased ceramide in lung structural cells, rendering them more adherent, with impaired wound repair and weakened barrier function. These findings suggest that, by maintaining sphingolipid and membrane receptor homeostasis, IGSF3 is required for cell mobility-mediated lung injury repair. IGSF3 deficiency may increase susceptibility to CS-induced lung injury in COPD.

Finding pathogenic commonalities between Niemann-Pick type C and other lysosomal storage disorders: Opportunities for shared therapeutic interventions

Lysosomal storage disorders (LSDs) are diseases characterized by the accumulation of macromolecules in the late endocytic system and are caused by inherited defects in genes that encode mainly lysosomal enzymes or transmembrane lysosomal proteins. Niemann-Pick type C disease (NPCD), a LSD characterized by liver damage and progressive neurodegeneration that leads to early death, is caused by mutations in the genes encoding the NPC1 or NPC2 proteins. Both proteins are involved in the transport of cholesterol from the late endosomal compartment to the rest of the cell. Loss of function of these proteins causes primary cholesterol accumulation, and secondary accumulation of other lipids, such as sphingolipids, in lysosomes. Despite years of studying the genetic and molecular bases of NPCD and related-lysosomal disorders, the pathogenic mechanisms involved in these diseases are not fully understood. In this review we will summarize the pathogenic mechanisms described for NPCD and we will discuss their relevance for other LSDs with neurological components such as Niemann- Pick type A and Gaucher diseases. We will particularly focus on the activation of signaling pathways that may be common to these three pathologies with emphasis on how the intra-lysosomal accumulation of lipids leads to pathology, specifically to neurological impairments. We will show that although the primary lipid storage defect is different in these three LSDs, there is a similar secondary accumulation of metabolites and activation of signaling pathways that can lead to common pathogenic mechanisms. This analysis might help to delineate common pathological mechanisms and therapeutic targets for lysosomal storage diseases.

The role of lipids in autophagy and its implication in neurodegeneration

Neurodegenerative diseases are, at present, major socio-economic burdens without effective treatments and their increasing prevalence means that these diseases will be a challenge for future generations. Neurodegenerative diseases may differ in etiology and pathology but are often caused by the accumulation of dysfunctional and aggregation-prone proteins. Autophagy, a conserved cellular mechanism, deals with cellular stress and waste product build-up and has been shown to reduce the accumulation of dysfunctional proteins in animal models of neurodegenerative diseases. Historically, progress in understanding the precise function of lipids has traditionally been far behind other biological molecules (like proteins) but emerging works demonstrate the importance of lipids in the autophagy pathway and how the disturbance of lipid metabolism is connected to neurodegeneration. Here we review how altered autophagy and the disturbance of lipid metabolism, particularly of phosphoinositols and sphingolipids, feature in neurodegenerative diseases and address work from the field that suggests that these potentially offer an opportunity of therapeutic intervention.

Lysophospholipids and Their G-Coupled Protein Signaling in Alzheimer's Disease: From Physiological Performance to Pathological Impairment

Lysophospholipids (LPLs) are bioactive signaling lipids that are generated from phospholipase-mediated hydrolyzation of membrane phospholipids (PLs) and sphingolipids (SLs). Lysophosphatidic acid (LPA) and sphingosine-1-phosphate (S1P) are two of the best-characterized LPLs which mediate a variety of cellular physiological responses via specific G-protein coupled receptor (GPCR) mediated signaling pathways. Considerable evidence now demonstrates the crucial role of LPA and S1P in neurodegenerative diseases, especially in Alzheimer’s disease (AD). Dysfunction of LPA and S1P metabolism can lead to aberrant accumulation of amyloid-β (Aβ) peptides, the formation of neurofibrillary tangles (NFTs), neuroinflammation and ultimately neuronal death. Summarizing LPA and S1P signaling profile may aid in profound health and pathological processes. In the current review, we will introduce the metabolism as well as the physiological roles of LPA and S1P in maintaining the normal functions of the nervous system. Given these pivotal functions, we will further discuss the role of dysregulation of LPA and S1P in promoting AD pathogenesis.

Bioactive Sphingolipids in the Pathogenesis of Chronic Obstructive Pulmonary Disease

A better understanding of the pathogenesis of distinct chronic obstructive pulmonary disease (COPD) phenotypes will improve diagnostic and therapeutic options for this common disease. We present evidence that sphingolipids such as ceramides are involved in the emphysema pathogenesis. Whereas distinct ceramide species cause cell death by apoptosis and necroptosis, cell adaptation leads to accumulation of other sphingolipid metabolites that extend cell survival by triggering autophagy. Cigarette smoke-released sphingolipids have been involved in both the initiation and persistence of lung injury via intracellular signaling and paracrine effects mediated via exosomes and plasma membrane-bound microparticles. Strategies to control sphingolipid metabolite production may promote cellular repair and maintenance to treat COPD.

Acid sphingomyelinase deficiency protects mitochondria and improves function recovery after brain injury

Traumatic brain injury (TBI) is one of the leading causes of disability worldwide and a prominent risk factor for neurodegenerative diseases. The expansion of nervous tissue damage after the initial trauma involves a multifactorial cascade of events, including excitotoxicity, oxidative stress, inflammation, and deregulation of sphingolipid metabolism that further mitochondrial dysfunction and secondary brain damage. Here, we show that a posttranscriptional activation of an acid sphingomyelinase (ASM), a key enzyme of the sphingolipid recycling pathway, resulted in a selective increase of sphingosine in mitochondria during the first week post-TBI that was accompanied by reduced activity of mitochondrial cytochrome oxidase and activation of the Nod-like receptor protein 3 inflammasome. TBI-induced mitochondrial abnormalities were rescued in the brains of ASM KO mice, which demonstrated improved behavioral deficit recovery compared with WT mice. Furthermore, an elevated autophagy in an ASM-deficient brain at the baseline and during the development of secondary brain injury seems to foster the preservation of mitochondria and brain function after TBI. Of note, ASM deficiency attenuated the early stages of reactive astrogliosis progression in an injured brain. These findings highlight the crucial role of ASM in governing mitochondrial dysfunction and brain-function impairment, emphasizing the importance of sphingolipids in the neuroinflammatory response to TBI.

Sphingolipids as Regulators of Autophagy and Endocytic Trafficking

Macroautophagy (herein referred to as autophagy) is a highly conserved stress response that engulfs damaged proteins, lipids, and/or organelles within double-membrane vesicles called autophagosomes for lysosomal degradation. Dysregulated autophagy is a hallmark of cancer; and thus, there is great interest in modulating autophagy for cancer therapy. Sphingolipids regulate each step of autophagosome biogenesis with roles for sphingolipid metabolites and enzymes spanning from the initial step of de novo ceramide synthesis to the sphingosine-1-phosphate lyase 1-mediated exit from the sphingolipid pathway. Notably, sphingolipid metabolism occurs at several of the organelles that contribute to autophagosome biogenesis to suggest that local changes in sphingolipids may regulate autophagy. As sphingolipid metabolism is frequently dysregulated in cancer, a molecular understanding of sphingolipids in stress-induced autophagy may provide insight into the mechanisms driving tumor development and progression. On the contrary, modulation of sphingolipid metabolites and/or enzymes can induce autophagy-dependent cell death for cancer therapy. This chapter will overview the major steps in mammalian autophagy, discuss the regulation of each step by sphingolipid metabolites, and describe the functions of sphingolipid-mediated autophagy in cancer. While our understanding of the signaling and biophysical properties of sphingolipids in autophagy remains in its infancy, the unique cross talk between the two pathways is an exciting area for further development, particularly in the context of cancer therapy.