Emerging roles for human glycolipid transfer protein superfamily members in the regulation of autophagy, inflammation, and cell death

Unveiling the role of AGT in lipid metabolism and regulated cell death in colon cancer

BACKGROUND

Lipid metabolism and regulated cell death (RCD) play a role in the remodeling of tumor immune microenvironment and regulation of cancer progression. Since the underlying immune mechanisms of colon cancer remain elusive, this study aims to identify potential therapeutic target genes.

METHODS

Differential genes related to lipid metabolism and RCD in COAD patients were identified using R language and online tools. Based on the expression of genes, two groups were classified using consensus clustering. CIBERSORT and ssGSEA were used to detect immune infiltration in both groups. Prognostic signature genes for colon cancer were screened using machine learning algorithms. KEGG, GO and GSEA for gene pathway enrichment. In addition, interacting genes in the immune module were obtained using a weighted gene co-expression network (WGCNA). Finally, expression and mutation of key in colon cancer genes were detected using TIMER, HPR, cBioPortal website and qPCR.

RESULTS

The consensus clustering analysis revealed that 231 relevant differential genes were highly associated with immune infiltration. A series of machine learning and website analyses identified AGT as a hub gene linked to lipid metabolism and regulated cell death, which is overexpressed in colon cancer.

CONCLUSION

AGT, as a signature gene of lipid metabolism and regulated cell death, plays a critical role in the development of COAD and is associated with tumor immune infiltration.

Sphingolipid metabolism and regulated cell death in malignant melanoma

Malignant melanoma (MM) is a highly invasive and therapeutically resistant skin malignancy, posing a significant clinical challenge in its treatment. Programmed cell death plays a crucial role in the occurrence and progression of MM. Sphingolipids (SP), as a class of bioactive lipids, may be associated with many kinds of diseases. SPs regulate various forms of programmed cell death in tumors, including apoptosis, necroptosis, ferroptosis, and more. This review will delve into the mechanisms by which different types of SPs modulate various forms of programmed cell death in MM, such as their regulation of cell membrane permeability and signaling pathways, and how they influence the survival and death fate of MM cells. An in-depth exploration of the role of SPs in programmed cell death in MM aids in unraveling the molecular mechanisms of melanoma development and holds significant importance in developing novel therapeutic strategies.

Sphingolipids: Less Enigmatic but Still Many Questions about the Role(s) of Ceramide in the Synthesis/Function of the Ganglioside Class of Glycosphingolipids

While much has been learned about sphingolipids, originally named for their sphinx-like enigmatic properties, there are still many unanswered questions about the possible effect(s) of the composition of ceramide on the synthesis and/or behavior of a glycosphingolipid (GSL). Over time, studies of their ceramide component, the sphingoid base containing the lipid moiety of GSLs, were frequently distinct from those performed to ascertain the roles of the carbohydrate moieties. Due to the number of classes of GSLs that can be derived from ceramide, this review focuses on the possible role(s) of ceramide in the synthesis/function of just one GSL class, derived from glucosylceramide (Glc-Cer), namely sialylated ganglio derivatives, initially characterized and named gangliosides (GGs) due to their presence in ganglion cells. While much is known about their synthesis and function, much is still being learned. For example, it is only within the last 15-20 years or so that the mechanism by which the fatty acyl component of ceramide affected its transport to different sites in the Golgi, where it is used for the synthesis of Glu- or galactosyl-Cer (Gal-Cer) and more complex GSLs, was defined. Still to be fully addressed are questions such as (1) whether ceramide composition affects the transport of partially glycosylated GSLs to sites where their carbohydrate chain can be elongated or affects the activity of glycosyl transferases catalyzing that elongation; (2) what controls the differences seen in the ceramide composition of GGs that have identical carbohydrate compositions but vary in that of their ceramide and vice versa; (3) how alterations in ceramide composition affect the function of membrane GGs; and (4) how this knowledge might be applied to the development of therapies for treating diseases that correlate with abnormal expression of GGs. The availability of an updatable data bank of complete structures for individual classes of GSLs found in normal tissues as well as those associated with disease would facilitate research in this area.

Ceramide-1-phosphate is a regulator of Golgi structure and is co-opted by the obligate intracellular bacterial pathogen Anaplasma phagocytophilum

Many intracellular pathogens structurally disrupt the Golgi apparatus as an evolutionarily conserved promicrobial strategy. Yet, the host factors and signaling processes involved are often poorly understood, particularly for Anaplasma phagocytophilum, the agent of human granulocytic anaplasmosis. We found that A. phagocytophilum elevated cellular levels of the bioactive sphingolipid, ceramide-1-phosphate (C1P), to promote Golgi fragmentation that enables bacterial proliferation, conversion from its non-infectious to infectious form, and productive infection. A. phagocytophilum poorly infected mice deficient in ceramide kinase, the Golgi-localized enzyme responsible for C1P biosynthesis. C1P regulated Golgi morphology via activation of a PKCα/Cdc42/JNK signaling axis that culminates in phosphorylation of Golgi structural proteins, GRASP55 and GRASP65. siRNA-mediated depletion of Cdc42 blocked A. phagocytophilum from altering Golgi morphology, which impaired anterograde trafficking of trans-Golgi vesicles into and maturation of the pathogen-occupied vacuole. Cells overexpressing phosphorylation-resistant versions of GRASP55 and GRASP65 presented with suppressed C1P- and A. phagocytophilum-induced Golgi fragmentation and poorly supported infection by the bacterium. By studying A. phagocytophilum, we identify C1P as a regulator of Golgi structure and a host factor that is relevant to disease progression associated with Golgi fragmentation.IMPORTANCECeramide-1-phosphate (C1P), a bioactive sphingolipid that regulates diverse processes vital to mammalian physiology, is linked to disease states such as cancer, inflammation, and wound healing. By studying the obligate intracellular bacterium Anaplasma phagocytophilum, we discovered that C1P is a major regulator of Golgi morphology. A. phagocytophilum elevated C1P levels to induce signaling events that promote Golgi fragmentation and increase vesicular traffic into the pathogen-occupied vacuole that the bacterium parasitizes. As several intracellular microbial pathogens destabilize the Golgi to drive their infection cycles and changes in Golgi morphology is also linked to cancer and neurodegenerative disorder progression, this study identifies C1P as a potential broad-spectrum therapeutic target for infectious and non-infectious diseases.

The therapeutic potential of sphingolipids for cardiovascular diseases

Cardiovascular diseases (CVDs) are the leading cause of morbidity and mortality worldwide and Inflammation plays a critical role in the development of CVD. Despite considerable progress in understanding the underlying mechanisms and various treatment options available, significant gaps in therapy necessitate the identification of novel therapeutic targets. Sphingolipids are a family of lipids that have gained attention in recent years as important players in CVDs and the inflammatory processes that underlie their development. As preclinical studies have shown that targeting sphingolipids can modulate inflammation and ameliorate CVDs, targeting sphingolipids has emerged as a promising therapeutic strategy. This review discusses the current understanding of sphingolipids' involvement in inflammation and cardiovascular diseases, the existing therapeutic approaches and gaps in therapy, and explores the potential of sphingolipids-based drugs as a future avenue for CVD treatment.

Ceramide-1-phosphate transfer protein enhances lipid transport by disrupting hydrophobic lipid-membrane contacts

Cellular distributions of the sphingolipid ceramide-1-phosphate (C1P) impact essential biological processes. C1P levels are spatiotemporally regulated by ceramide-1-phosphate transfer protein (CPTP), which efficiently shuttles C1P between organelle membranes. Yet, how CPTP rapidly extracts and inserts C1P into a membrane remains unknown. Here, we devise a multiscale simulation approach to elucidate biophysical details of CPTP-mediated C1P transport. We find that CPTP binds a membrane poised to extract and insert C1P and that membrane binding promotes conformational changes in CPTP that facilitate C1P uptake and release. By significantly disrupting a lipid's local hydrophobic environment in the membrane, CPTP lowers the activation free energy barrier for passive C1P desorption and enhances C1P extraction from the membrane. Upon uptake of C1P, further conformational changes may aid membrane unbinding in a manner reminiscent of the electrostatic switching mechanism used by other lipid transfer proteins. Insertion of C1P into an acceptor membrane, eased by a decrease in membrane order by CPTP, restarts the transfer cycle. Most notably, we provide molecular evidence for CPTP's ability to catalyze C1P extraction by breaking hydrophobic C1P-membrane contacts with compensatory hydrophobic lipid-protein contacts. Our work, thus, provides biophysical insights into how CPTP efficiently traffics C1P between membranes to maintain sphingolipid homeostasis and, additionally, presents a simulation method aptly suited for uncovering the catalytic mechanisms of other lipid transfer proteins.

Glycolipid transfer protein knockout disrupts vesicle trafficking to the plasma membrane

The glycolipid transfer protein (GLTP) has been linked to many cellular processes aside from its best-known in vitro function as a lipid transport protein. It has been proposed to act as a sensor and regulator of glycosphingolipid homeostasis in cells. Furthermore, through its previously determined interaction with the endoplasmic reticulum (ER) membrane protein VAP-A (vesicle-associated membrane protein-associated protein A), GLTP may also be involved in facilitating vesicular transport in cells. In this study, we characterized the phenotype of CRISPR/Cas9-mediated GLTP knockout HeLa cells. We showed that motility, three-dimensional growth, and cellular metabolism were all altered by GLTP knockout. Expression of a GLTP mutant incapable of binding VAP disrupted cell spheroid formation, indicating that the GLTP-VAP interaction is linked to cellular adhesion, cohesion, and three-dimensional growth. Most notably, we found evidence that GLTP, through its interaction with VAP-A, affects vesicular trafficking, marking the first cellular process discovered to be directly impacted by a change in GLTP expression.

The repertoire of protein-sulfatide interactions reveal distinct modes of sulfatide recognition

Sulfatide is an abundant glycosphingolipid in the mammalian nervous system, kidney, trachea, gastrointestinal tract, spleen, and pancreas and is found in low levels in other tissues. Sulfatide is characterized by the presence of a sulfate group in the hydrophilic galactose moiety, with isoforms differing in their sphingosine base and the length, unsaturation, and hydroxylation of their acyl chain. Sulfatide has been associated with a variety of cellular processes including immune responses, cell survival, myelin organization, platelet aggregation, and host-pathogen interactions. Structural studies of protein-sulfatide interactions markedly advanced our understanding of their molecular contacts, key-interacting residues, orientation of the sulfatide in its binding site, and in some cases, sulfatide-mediated protein oligomerization. To date, all protein-sulfatide interactions are reported to display dissociation constants in the low micromolar range. At least three distinct modes of protein-sulfatide binding were identified: 1) protein binding to short consensus stretches of amino acids that adopt α-helical-loop-α-helical conformations; 2) sulfatide-bound proteins that present the sulfatide head group to another protein; and 3) proteins that cage sulfatides. The scope of this review is to present an up-to-date overview of these molecular mechanisms of sulfatide recognition to better understand the role of this glycosphingolipid in physiological and pathological states.

Protein tyrosine kinase inhibitor resistance in malignant tumors: molecular mechanisms and future perspective

Protein tyrosine kinases (PTKs) are a class of proteins with tyrosine kinase activity that phosphorylate tyrosine residues of critical molecules in signaling pathways. Their basal function is essential for maintaining normal cell growth and differentiation. However, aberrant activation of PTKs caused by various factors can deviate cell function from the expected trajectory to an abnormal growth state, leading to carcinogenesis. Inhibiting the aberrant PTK function could inhibit tumor growth. Therefore, tyrosine kinase inhibitors (TKIs), target-specific inhibitors of PTKs, have been used in treating malignant tumors and play a significant role in targeted therapy of cancer. Currently, drug resistance is the main reason for limiting TKIs efficacy of cancer. The increasing studies indicated that tumor microenvironment, cell death resistance, tumor metabolism, epigenetic modification and abnormal metabolism of TKIs were deeply involved in tumor development and TKI resistance, besides the abnormal activation of PTK-related signaling pathways involved in gene mutations. Accordingly, it is of great significance to study the underlying mechanisms of TKIs resistance and find solutions to reverse TKIs resistance for improving TKIs efficacy of cancer. Herein, we reviewed the drug resistance mechanisms of TKIs and the potential approaches to overcome TKI resistance, aiming to provide a theoretical basis for improving the efficacy of TKIs.

Kaempferol Mediated AMPK/mTOR Signal Pathway Has a Protective Effect on Cerebral Ischemic-Reperfusion Injury in Rats by Inducing Autophagy

Ischemia/reperfusion (I/R) caused by ischemic stroke treatments leads to brain injury and its pathological mechanism is related to autophagy. The underlying mechanism of kaempferol on cerebral I/R injury needs to be explored. To establish I/R injury, we used a middle cerebral artery occlusion-reperfusion (MCAO) model in rats. MCAO rats were treated with the same amount of saline (I/R group); Treatment group rats were treated orally with kaempferol (50, 100, 200 mg/kg) for 7 days before surgery. After reperfusion for 24 h, the scores of neurological deficits and infarct volume in each group were evaluated. LC3, Beclin-1 p62, AMPK and mTOR protein expression levels were examined by TTC staining, immunofluorescence staining, qRT-PCR and western blotting assay. H&E and TTC staining showed that compared with model group, the infarction size of rats in kaempferol group was markedly reduced. Meanwhile, the results showed that kaempferol had a dose-dependent nerve function repairability. Nissl and TUNEL staining showed that kaempferol could reduce neuronal apoptosis and ameliorate neuronal impairment after I/R. Western blotting and qRT-PCR results showed that kaempferol could protect the brain from ischemia reperfusion by activating autophagy. In addition, add AMPK inhibitor, western blotting and immumohistochemical staining showed that kaempferol mediated AMPK/mTOR signal pathway in MCAO rats. Kaempferol could mediate the AMPK signal pathway to regulate autophagy and inhibit apoptosis to protect brain against I/R injury.

Ceramide kinase regulates acute wound healing by suppressing 5-oxo-ETE biosynthesis and signaling via its receptor OXER1

The sphingolipid, ceramide-1-phosphate (C1P), has been shown to promote the inflammatory phase and inhibit the proliferation and remodeling stages of wound repair via direct interaction with group IVA cytosolic phospholipase A2, a regulator of eicosanoid biosynthesis that fine-tunes the behaviors of various cell types during wound healing. However, the anabolic enzyme responsible for the production of C1P that suppresses wound healing as well as bioactive eicosanoids and target receptors that drive enhanced wound remodeling have not been characterized. Herein, we determined that decreasing C1P activity via inhibitors or genetic ablation of the anabolic enzyme ceramide kinase (CERK) significantly enhanced wound healing phenotypes. Importantly, postwounding inhibition of CERK enhanced the closure rate of acute wounds, improved the quality of healing, and increased fibroblast migration via a "class switch" in the eicosanoid profile. This switch reduced pro-inflammatory prostaglandins (e.g., prostaglandin E2) and increased levels of 5-hydroxyeicosatetraenoic acid and the downstream metabolite 5-oxo-eicosatetraenoic acid (5-oxo-ETE). Moreover, dermal fibroblasts from mice with genetically ablated CERK showed enhanced wound healing markers, while blockage of the murine 5-oxo-ETE receptor (oxoeicosanoid receptor 1) inhibited the enhanced migration phenotype of these cell models. Together, these studies reinforce the vital roles eicosanoids play in the wound healing process and demonstrate a novel role for CERK-derived C1P as a negative regulator of 5-oxo-ETE biosynthesis and the activation of oxoeicosanoid receptor 1 in wound healing. These findings provide foundational preclinical results for the use of CERK inhibitors to shift the balance from inflammation to resolution and increase the wound healing rate.

miR-196a Upregulation Contributes to Gefitinib Resistance through Inhibiting GLTP Expression

Tyrosine kinase inhibitor (TKI) therapy has greatly improved lung cancer survival in patients with epidermal growth factor receptor (EGFR) mutations. However, the development of TKI-acquired resistance is the major problem to be overcome. In this study, we found that miR-196a expression was greatly induced in gefitinib-resistant lung cancer cells. To understand the role and mechanism of miR-196a in TKI resistance, we found that miR-196a-forced expression alone increased cell resistance to gefitinib treatment in vitro and in vivo by inducing cell proliferation and inhibiting cell apoptosis. We identified the transcription factor nuclear factor erythroid 2-related factor 2 (NRF2) bound to the promoter region of miR-196a and induced miR-196a expression at the transcriptional level. NRF2-forced expression also significantly increased expression levels of miR-196a, and was an upstream inducer of miR-196a to mediate gefitinib resistance. We also found that glycolipid transfer protein (GLTP) was a functional direct target of miR-196a, and downregulation of GLTP by miR-196a was responsible for gefitinib resistance. GLTP overexpression alone was sufficient to increase the sensitivity of lung cancer cells to gefitinib treatment. Our studies identified a new role and mechanism of NRF2/miR-196a/GLTP pathway in TKI resistance and lung tumor development, which may be used as a new biomarker (s) for TKI resistance or as a new therapeutic target in the future.

Ceramide-1-phosphate transfer protein promotes sphingolipid reorientation needed for binding during membrane interaction

Lipid transfer proteins acquire and release their lipid cargoes by interacting transiently with source and destination biomembranes. In the GlycoLipid Transfer Protein (GLTP) superfamily, the two-layer all-α-helical GLTP-fold defines proteins that specifically target sphingolipids (SLs) containing either sugar or phosphate headgroups via their conserved but evolutionarily-modified SL recognitions centers. Despite comprehensive structural insights provided by X-ray crystallography, the conformational dynamics associated with membrane interaction and SL uptake/release by GLTP superfamily members have remained unknown. Herein, we report insights gained from molecular dynamics (MD) simulations into the conformational dynamics that enable ceramide-1-phosphate transfer proteins (CPTPs) to acquire and deliver ceramide-1-phosphate (C1P) during interaction with 1-palmitoyl-2-oleoyl phosphatidylcholine bilayers. The focus on CPTP reflects this protein's involvement in regulating pro-inflammatory eicosanoid production and autophagy-dependent inflammasome assembly that drives interleukin (IL-1β and IL-18) production and release by surveillance cells. We found that membrane penetration by CPTP involved α-6 helix and the α-2 helix N-terminal region, was confined to one bilayer leaflet, and was relatively shallow. Large-scale dynamic conformational changes were minimal for CPTP during membrane interaction or C1P uptake except for the α-3/α-4 helices connecting loop, which is located near the membrane interface and interacts with certain phosphoinositide headgroups. Apart from functioning as a shallow membrane-docking element, α-6 helix was found to adeptly reorient membrane lipids to help guide C1P hydrocarbon chain insertion into the interior hydrophobic pocket of the SL binding site.These findings support a proposed 'hydrocarbon chain-first' mechanism for C1P uptake, in contrast to the 'lipid polar headgroup-first' uptake used by most lipid-transfer proteins.

Beclin1 controls caspase-4 inflammsome activation and pyroptosis in mouse myocardial reperfusion-induced microvascular injury

BACKGROUND

Myocardial reperfusion injury is often accompanied by cell death and inflammatory reactions. Recently, pyroptosis is gradually recognized as pivotal role in cardiovascular disease. However, little is known about the regulatory role of beclin1 in the control of caspase-4 activation and pyroptosis. The present study confirmed whether beclin1 regulates caspase-4 mediated pyroptosis and thereby protects Human Cardiac microvascular endothelial cells (HCMECs) against injury.

METHODS

TTC and Evan's blue dye, western blot, immunofluorescence and immunohistochemistry staining were performed in wild mice and transgenic mice with overexpression of beclin 1(BECN1-Tg). CMECs were transfected with a beclin1 lentivirus. The cell cytotoxicity was analyzed by LDH-Cytotoxicity Assay Kit. The protein levels of autophagy protein (Beclin1, p62 and LC3II/LC3I) and caspase-4/GSDMD pathway were determined by western blot. Autophagic vacuoles in cells were monitored with RFP-GFP-LC3 using fluorescence microscope.

RESULTS

I/R caused caspase-4 activity and gasdermin D expression increase in vivo and in vitro. Overexpression of beclin1 in heart tissue and CMECs suppressed the caspase-4 activity and decreased the levels of gasdermin D; meanwhile beclin1 overexpression also reduced IL-1β levels, promoted autophagy (p62 expression was inhibited while LC3II expression was increased) in the heart and CMECs. Interestingly, beclin1 overexpression increased animal survival and attenuated myocardial infarct size (45 ± 6.13 vs 22 ± 4.37), no-reflow area (39 ± 5.22 vs 16 ± 2.54) post-myocardial ischemia reperfusion.

CONCLUSIONS

Induction of beclin-1 signaling can be a potential therapeutic target in myocardial reperfusion-induced microvascular injury. Video Abstract.

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.

Who moves the sphinx? An overview of intracellular sphingolipid transport

Lipid bilayers function as boundaries that enclose their content from the surrounding media, and the composition of different membrane types is accurately and dynamically tailored so that they can perform their function. To achieve this balance, lipid biosynthetic machinery and lipid trafficking events are intertwined into an elegant network. In this review, we focus on the intracellular movement of sphingolipids mediated by sphingolipid transfer proteins. Additionally, we will focus on the best characterized and understood mammalian sphingolipid transfer proteins and provide an overview of how they are hypothesized to function. Some are already well understood, while others remain enigmatic. A few are actual lipid transfer proteins, moving lipids from membrane to membrane, while others may have more of a sensor role, possibly reacting to changes in the concentrations of their ligands. Considering the substrates available for cytosolic sphingolipid transfer proteins, one open question that is discussed is whether galactosylceramide is a target. Another question is the exact mechanics by which sphingolipid transfer proteins are targeted to different organelles, such as how four phosphate adapter protein-2, FAPP2 is targeted to the endoplasmic reticulum. The aim of this review is to discuss what is known within the field today and to provide a basic understanding of how these proteins may work.

Ceramide-1-phosphate transfer protein (CPTP) regulation by phosphoinositides

Ceramide-1-phosphate transfer proteins (CPTPs) are members of the glycolipid transfer protein (GLTP) superfamily that shuttle ceramide-1-phosphate (C1P) between membranes. CPTPs regulate cellular sphingolipid homeostasis in ways that impact programmed cell death and inflammation. CPTP downregulation specifically alters C1P levels in the plasma and trans-Golgi membranes, stimulating proinflammatory eicosanoid production and autophagy-dependent inflammasome-mediated cytokine release. However, the mechanisms used by CPTP to target the trans-Golgi and plasma membrane are not well understood. Here, we monitored C1P intervesicular transfer using fluorescence energy transfer (FRET) and showed that certain phosphoinositides (phosphatidylinositol 4,5 bisphosphate (PI-(4,5)P2) and phosphatidylinositol 4-phosphate (PI-4P)) increased CPTP transfer activity, whereas others (phosphatidylinositol 3-phosphate (PI-3P) and PI) did not. PIPs that stimulated CPTP did not stimulate GLTP, another superfamily member. Short-chain PI-(4,5)P2, which is soluble and does not remain membrane-embedded, failed to activate CPTP. CPTP stimulation by physiologically relevant PI-(4,5)P2 levels surpassed that of phosphatidylserine (PS), the only known non-PIP stimulator of CPTP, despite PI-(4,5)P2 increasing membrane equilibrium binding affinity less effectively than PS. Functional mapping of mutations that led to altered FRET lipid transfer and assessment of CPTP membrane interaction by surface plasmon resonance indicated that di-arginine motifs located in the α-6 helix and the α3-α4 helix regulatory loop of the membrane-interaction region serve as PI-(4,5)P2 headgroup-specific interaction sites. Haddock modeling revealed specific interactions involving the PI-(4,5)P2 headgroup that left the acyl chains oriented favorably for membrane embedding. We propose that PI-(4,5)P2 interaction sites enhance CPTP activity by serving as preferred membrane targeting/docking sites that favorably orient the protein for function.

Metabolism of Glycosphingolipids and Their Role in the Pathophysiology of Lysosomal Storage Disorders

Glycosphingolipids (GSLs) are a specialized class of membrane lipids composed of a ceramide backbone and a carbohydrate-rich head group. GSLs populate lipid rafts of the cell membrane of eukaryotic cells, and serve important cellular functions including control of cell-cell signaling, signal transduction and cell recognition. Of the hundreds of unique GSL structures, anionic gangliosides are the most heavily implicated in the pathogenesis of lysosomal storage diseases (LSDs) such as Tay-Sachs and Sandhoff disease. Each LSD is characterized by the accumulation of GSLs in the lysosomes of neurons, which negatively interact with other intracellular molecules to culminate in cell death. In this review, we summarize the biosynthesis and degradation pathways of GSLs, discuss how aberrant GSL metabolism contributes to key features of LSD pathophysiology, draw parallels between LSDs and neurodegenerative proteinopathies such as Alzheimer's and Parkinson's disease and lastly, discuss possible therapies for patients.