Ganglioside Biosynthesis Research Articles

Alterations of membrane lipids and in gene expression of ganglioside metabolism in different brain structures in a mouse model of mucopolysaccharidosis type I (MPS I)

Mucopolysaccharidosis I (MPS I) is a congenital disorder caused by the deficiency of α-l-iduronidase (IDUA), with the accumulation of glycosaminoglycans (GAGs) in the CNS. Although GAG toxicity is not fully understood, previous works suggest a GAG-induced alteration in neuronal membrane composition. This study is aimed to evaluate the levels and distribution of gangliosides and cholesterol in different brain regions (cortex, cerebellum, hippocampus and hypothalamus) in a model using IDUA knockout (KO) mice (C57BL/6). Lipids were extracted with chloroform–methanol and then total gangliosides and cholesterol were determined, followed by ganglioside profile analyses. While no changes in cholesterol content were observed, the results showed a tissue dependent ganglioside alteration in KO mice: a total ganglioside increase in cortex and cerebellum, and a selective presence of GM3, GM2 and GD3 gangliosides in the hippocampus and hypothalamus. To elucidate this, we evaluated gene expression of ganglioside synthesis (GM3, GD3 and GM2/GD2 synthases) and degradation of (Neuraminidase1) enzymes in the cerebellum and hippocampus by RT-sq-PCR. The results obtained with KO mice showed a reduced expression of GD3 and GM2/GD2 synthases and Neuraminidase1 in cerebellum; and a decrease in GM2/GD2 synthase and Neuraminidase1 in the hippocampus. These data suggest that the observed ganglioside changes result from a combined effect of GAGs on ganglioside biosynthesis and degradation.

Alteration of Ganglioside Biosynthesis Responsible for Complex Hereditary Spastic Paraplegia

Hereditary spastic paraplegias (HSPs) form a heterogeneous group of neurological disorders. A whole-genome linkage mapping effort was made with three HSP-affected families from Spain, Portugal, and Tunisia and it allowed us to reduce the SPG26 locus interval from 34 to 9 Mb. Subsequently, a targeted capture was made to sequence the entire exome of affected individuals from these three families, as well as from two additional autosomal-recessive HSP-affected families of German and Brazilian origins. Five homozygous truncating (n = 3) and missense (n = 2) mutations were identified in B4GALNT1. After this finding, we analyzed the entire coding region of this gene in 65 additional cases, and three mutations were identified in two subjects. All mutated cases presented an early-onset spastic paraplegia, with frequent intellectual disability, cerebellar ataxia, and peripheral neuropathy as well as cortical atrophy and white matter hyperintensities on brain imaging. B4GALNT1 encodes β-1,4-N-acetyl-galactosaminyl transferase 1 (B4GALNT1), involved in ganglioside biosynthesis. These findings confirm the increasing interest of lipid metabolism in HSPs. Interestingly, although the catabolism of gangliosides is implicated in a variety of neurological diseases, SPG26 is only the second human disease involving defects of their biosynthesis.

Ethylenedioxy-PIP2 Oxalate Reduces Ganglioside Storage in Juvenile Sandhoff Disease Mice

Sandhoff disease is an incurable neurodegenerative disorder caused by mutations in the lysosomal hydrolase β-hexosaminidase. Deficiency in this enzyme leads to excessive accumulation of ganglioside GM2 and its asialo derivative, GA2, in brain and visceral tissues. Small molecule inhibitors of ceramide-specific glucosyltransferase, the first committed step in ganglioside biosynthesis, reduce storage of GM2 and GA2. Limited brain access or adverse effects have hampered the therapeutic efficacy of the clinically approved substrate reduction molecules, eliglustat tartrate and the imino sugar NB-DNJ (Miglustat). The novel eliglustat tartrate analog, 2-(2,3-dihydro-1H-inden-2-yl)-N-((1R,2R)-1-(2,3-dihydrobenzo[b][1, 4]dioxin-6-yl)-1-hydroxy-3-(pyrrolidin-1-yl)propan-2-yl)acetamide (EtDO-PIP2, CCG-203586 or "3h"), was recently reported to reduce glucosylceramide in murine brain. Here we assessed the therapeutic efficacy of 3h in juvenile Sandhoff (Hexb-/-) mice. Sandhoff mice received intraperitoneal injections of phosphate buffered saline (PBS) or 3h (60 mg/kg/day) from postnatal day 9 (p-9) to postnatal day 15 (p-15). Brain weight and brain water content was similar in 3h and PBS-treated mice. 3h significantly reduced total ganglioside sialic acid, GM2, and GA2 content in cerebrum, cerebellum and liver of Sandhoff mice. Data from the liver showed that 3h reduced the key upstream ganglioside precursor (glucosylceramide), providing evidence for an on target mechanism of action. No significant differences were seen in the distribution of cholesterol or of neutral and acidic phospholipids. These data suggest that 3h can be an effective alternative to existing substrate reduction molecules for ganglioside storage diseases.

Novel orally available brain penetrant small molecule inhibitors of ganglioside biosynthesis for the treatment of Sandhoff and Tay–Sachs diseases

Novel orally available brain penetrant small molecule inhibitors of ganglioside biosynthesis for the treatment of Sandhoff and Tay–Sachs diseases

The Regulation of Ganglioside GM3 Synthesis

Glycosphingolipids (GSLs) exist in the outer leaflet of the plasma membrane, where they form lipid microdomains that function as platforms for the regulation of trans-membrane signal transduction. In mammals, complex GSLs differing in the number and/or type of sugar species are produced in a cell-type specific manner, and the variety of glycan structures in GSLs are believed to determine specific cell functions. The glycan moieties of GSLs are synthesized at the luminal side of the Golgi apparatus by multiple Golgi-resident glycosyltransferases. Since the expression levels of most endogenous glycosyltransferases are relatively low, their detection is generally difficult. Nevertheless, we have succeeded in detecting endogenous mouse GM3 synthase (GM3S), the primary glycosyltransferase responsible for the biosynthesis of ganglio-series gangliosides. Mouse GM3S (mGM3S) has three isoforms (M1-GM3S, M2-GM3S, and M3-GM3S), each with a distinct length in its NH2-terminal cytoplasmic tail. These isoforms are produced by leaky scanning from two mRNA variants, mGM3Sa and mGM3Sb. M1-GM3S is stably localized in the endoplasmic reticulum (ER), as a result of retrograde transport signals (arginine [R]-based motifs); consequently, its in vivo GM3 synthesis activity is very low compared with that of other isoforms. In contrast, both M2-GM3S and M3-GM3S are localized in the Golgi apparatus, yet each exhibits a distinct intracellular fate. M2-GM3S is rapidly degraded in the lysosomes, whereas M3-GM3S is retained in the Golgi apparatus. A system that produces GM3S isoforms having such distinct characteristics is likely to be of critical importance in the regulation of GM3 biosynthesis under various pathological and physiological conditions.

Ganglioside Biosynthesis in Developing Brains and Apoptotic Cancer Cells: X. Regulation of Glyco-genes Involved in GD3 and Sialyl-Lex/a Syntheses

Gangliosides, the acidic glycosphingolipids (GSLs) containing N-acetylgalactosamine and sialic acid are ubiquitous in the central nervous system. At least six DSL-glycosyltransferase activities (GLTs Gangliosides, the acidic glycosphingolipids (GSLs) containing N-acetylgalactosamine and sialic acid (or NAc-Neuraminic acid) are ubiquitous in the central nervous system. At least six GSL-glycosyltransferase activities (GLTs) of Basu-Roseman pathway catalyzing the biosynthesis of these gangliosides have been characterized in developing chicken brains. Most of these glyco-genes are expressed in the early stages (7-17 days) of brain development and lowered in the adult stage, but the cause of reduction of enzymatic activities of these GLTs in the adult stages is not known. In order to study glyco-gene regulation we used four clonal metastatic cancer cells of colon and breast cancer tissue origin (Colo-205, SKBR-3, MDA-468, and MCF-3). The glyco-genes for synthesis of SA-LeX and SA-LeA (which contain N-acetylglucosamine, sialic acid and fucose) in these cells were modulated differently at different phases (between 2 and 48 h) of apoptotic inductions. L-PPMP, D-PDMP (inhibitor of glucosylceramide biosynthesis), Betulinic Acid (a triterpinoid isolated from bark of certain trees and used for cancer treatment in China), Tamoxifen a drug in use in the west for treatment of early stages of the disease in breast cancer patients), and cis-platin (an inhibitor of DNA biosynthesis used for testicular cancer patients) were used for induction of apoptosis in the above-mentioned cell lines. Within 2-6 h, transcriptional modulation of a number of glyco-genes was observed by DNA-micro-array (containing over 300 glyco genes attached to the glass cover slips) studies. Under long incubation time (24-48 h) almost all of the glyco-genes were downregulated. The cause of these glyco-gene regulations during apoptotic induction in metastatic carcinoma cells is unknown and needs future investigations for further explanations. These apoptotic agents could be employed as a new generation of anti-cancer drugs after properly delivered to the patients.

Therapeutic Effects of Stem Cells and Substrate Reduction in Juvenile Sandhoff Mice

Sandhoff Disease (SD) involves the CNS accumulation of ganglioside GM2 and asialo-GM2 (GA2) due to inherited defects in the β-subunit gene of β-hexosaminidase A and B (Hexb gene). Substrate reduction therapy, utilizing imino sugar N-butyldeoxygalactonojirimycin (NB-DGJ), reduces ganglioside biosynthesis and levels of stored GM2 in SD mice. Intracranial transplantation of Neural Stem Cells (NSCs) can provide enzymatic cross correction, to help reduce ganglioside storage and extend life. Here we tested the effect of NSCs and NB-DGJ, alone and together, on brain β-hexosaminidase activity, GM2, and GA2 content in juvenile SD mice. The SD mice received either cerebral NSC transplantation at post-natal day 0 (p-0), intraperitoneal injection of NB-DGJ (500mg/kg/day) from p-9 to p-15, or received dual treatments. The brains were analyzed at p-15. β-galactosidase staining confirmed engraftment of lacZ-expressing NSCs in the cerebral cortex. Compared to untreated and sham-treated SD controls, NSC treatment alone provided a slight increase in Hex activity and significantly decreased GA2 content. However, NSCs had no effect on GM2 content when analyzed at p-15. NB-DGJ alone had no effect on Hex activity, but significantly reduced GM2 and GA2 content. Hex activity was slightly elevated in the NSC+drug-treated mice. GM2 and GA2 content in the dual treated mice were similar to that of the NB-DGJ treated mice. These data indicate that NB-DGJ alone was more effective in targeting storage in juvenile SD mice than were NSCs alone. No additive or synergistic effect between NSC and drug was found in these juvenile SD mice.

Small Molecule Inhibitors of Ganglioside Biosynthesis as Substrate Reduction Therapy for the Gangliosidoses

seizures, generalized tonic-clonic seizures were most common (89.7%), followed by complex partial or absence seizures (64.7%). Other seizure types included atonic (14.7%), myoclonic (29.4%), and focal seizures (10.3%). Most subjects (57%) experienced only one seizure type. An average of 1.71 seizure management medications were used; valproate was the most commonly used anti-epileptic. On the UBDRS seizure sub-scale, mean seizure severity was 7.41 at the most recent evaluation. Mean clinical global impression (CGI) was 2.88 (0–5 scale), representing mild seizure severity. Seizure severity did not correlate with disease duration. Conclusion: Although myoclonic seizures do occur in JNCL, they are not the most common seizure type. Seizures in JNCL are most commonly generalized tonic-clonic in nature and are well managed with two or fewer anti-epileptic drugs. For most children, seizures are infrequent and are not progressive in nature.

Impairment of hippocampal long-term potentiation and failure of learning in mice treated with d-threo-1-phenyl-2-decanoylamino-3-morpholino-1-propanol

Gangliosides (sialic acid-containing glycosphingolipids) play important roles in many physiological functions, including synaptic plasticity in the hippocampus, which has been suggested as the basal cellular process of learning and memory in the brain. In the present study, long-term potentiation (LTP) and long-term depression (LTD) in CA1 hippocampal neurons and learning behavior were examined in mice treated with (D)-threo-1-phenyl-2-decanoylamino-3-morpholino-1-propanol ((D)-PDMP), an inhibitor of ganglioside biosynthesis. Mice treated with (D)-PDMP, but not those treated with (L)-PDMP, showed impairment of LTP induction in hippocampal CA1 neurons without any significant change in LTD formation and also showed a failure of learning in the 4-pellet taking test. These results indicate that de novo synthesis of gangliosides in the brain is involved in synaptic plasticity of LTP in mouse hippocampal CA1 neurons and plays important roles in learning and memory.

My journey into the world of sphingolipids and sphingolipidoses.

Analysis of lipid storage in postmortem brains of patients with amaurotic idiocy led to the recognition of five lysosomal ganglioside storage diseases and identification of their inherited metabolic blocks. Purification of lysosomal acid sphingomyelinase and ceramidase and analysis of their gene structures were the prerequisites for the clarification of Niemann-Pick and Farber disease. For lipid catabolism, intraendosomal vesicles are formed during the endocytotic pathway. They are subjected to lipid sorting processes and were identified as luminal platforms for cellular lipid and membrane degradation. Lipid binding glycoproteins solubilize lipids from these cholesterol poor membranes and present them to water-soluble hydrolases for digestion. Biosynthesis and intracellular trafficking of lysosomal hydrolases (hexosaminidases, acid sphingomyelinase and ceramidase) and lipid binding and transfer proteins (GM2 activator, saposins) were analyzed to identify the molecular and metabolic basis of several sphingolipidoses. Studies on the biosynthesis of glycosphingolipids yielded the scheme of Combinatorial Ganglioside Biosynthesis involving promiscuous glycosyltransferases. Their defects in mutagenized mice impair brain development and function.

Dissociation of the insulin receptor from caveolae during TNFα-induced insulin resistance and its recovery by d-PDMP

Previously, we demonstrated that an inhibitor of ganglioside biosynthesis, d-PDMP, could restore impaired insulin signaling in tumor necrosis factor α (TNFα)-treated adipocytes by blocking the increase of GM3 ganglioside. Here, we analyzed the interaction between insulin receptor (IR) and GM3 in the plasma membranes using immunoelectron microscopy. In normal adipocytes, most GM3 molecules localized at planar and non-caveolar regions. Approximately 19% of IR molecules were detected in caveolar regions. The relative ratio of IRs associated with caveolae in TNFα-treated adipocytes was decreased to one-fifth of that in normal adipocytes, but this decrease was restored by d-PDMP. Thus, we could obtain direct evidence that insulin resistance is a membrane microdomain disorder caused by aberrant expression of ganglioside.

Metabolic pathways and intracellular trafficking of gangliosides

Gangliosides constitute a large and heterogeneous family of acidic glycosphingolipids that contain one or more sialic acid residues and are expressed in nearly all vertebrate cells. Their de novo synthesis starts at the endoplasmic reticulum and is continued by a combination of glycosyltransferase activities at the Golgi complex, followed by vesicular delivery to the plasma membrane. At the cell surface, gangliosides participate in a variety of physiological as well as pathological processes. The cloning of genes for most of the glycosyltransferases responsible for ganglioside biosynthesis has produced a better understanding of the cellular and molecular basis of the ganglioside metabolism. In addition, the ability to delete groups of glycosphingolipid structures in mice has been enormously important in determining their physiological roles. Recently, a number of enzymes for ganglioside anabolism and catabolism have been shown to be associated with the plasma membrane, which might contribute to modulate local glycolipid composition, and consequently, the cell function.

Abstract 2934: Novel approach for treating neural crest derived tumors: Selective inhibition of ganglioside biosynthesis with small molecules

Abstract Neural crest derived tumors express high levels of a unique class of lipid linked glycan known as gangliosides. Gangliosides are involved in growth factor signaling by regulating complexes in lipid rafts. Genetic studies show that through aberrant expression of gangliosides, these tumors acquire aggressive growth properties. Prior to this research, the only ganglioside inhibitors identified were non-specific and broadly blocked virtually all glycolipid classes. These non-specific glycolipid inhibitors demonstrated anti-cancer activity in animal models of neural crest tumors. However, due to substantial off-target dose-limiting toxicity from lack of specificity for the ganglioside sub-class, they effectively cannot be used in humans for cancer treatment. Selective inhibition of gangliosides without affecting other glycan classes could potentially avoid these problems and provide an effective treatment for neural crest and other ganglioside-dependent tumors. To identify the first known selective inhibitors of gangliosides, we developed a novel molecular screening strategy for identifying selective small-molecule ganglioside inhibitors. This platform identified the first drug-like selective inhibitors of gangliosides. ZP10395, a lead compound, selectively and dose-dependently reduces gangliosides in multiple tumor cell lines and is 10-15 fold more potent than the existing non-specific inhibitors. Importantly, it does not inhibit other glycolipid classes associated with dose-limiting toxicity. Administering ZP10395 to a mouse xenograph melanoma model significantly reduced ganglioside production and slowed tumor growth in the presence of a reduced T-cell response. These results demonstrate the potential utility of specific ganglioside inhibitors for treating ganglioside dependent tumors. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2934. doi:10.1158/1538-7445.AM2011-2934

Cellular and molecular biology of glycosphingolipid glycosylation

Brain tissue is characterized by its high glycosphingolipid content, particularly those containing sialic acid (gangliosides). As a result of this observation, brain tissue was a focus for studies leading to the characterization of the enzymes participating in ganglioside biosynthesis, and their participation in driving the compositional changes that occur in glycolipid expression during brain development. Later on, this focus shifted to the study of cellular aspects of the synthesis, which lead to the identification of the site of synthesis in the neuronal soma and their axonal transport toward the periphery. In this review article, we will focus in subcellular aspects of the biosynthesis of glycosphingolipid oligosaccharides, particularly the mechanisms underlying the trafficking of glycosphingolipid glycosyltransferases from the endoplasmic reticulum to the Golgi, those that promote their retention in the Golgi and those that participate in their topological organization as part of the complex membrane bound machinery for the synthesis of glycosphingolipids.

Small molecule inhibitors of ganglioside biosynthesis as substrate reduction therapy for the gangliosidoses

Small molecule inhibitors of ganglioside biosynthesis as substrate reduction therapy for the gangliosidoses

Physiopathological function of hematoside (GM3 ganglioside)

Since I was involved in the molecular cloning of GM3 synthase (SAT-I), which is the primary enzyme for the biosynthesis of gangliosides in 1998, my research group has been concentrating on our efforts to explore the physiological and pathological implications of gangliosides especially for GM3. During the course of study, we demonstrated the molecular pathogenesis of type 2 diabetes and insulin resistance focusing on the interaction between insulin receptor and gangliosides in membrane microdomains and propose a new concept: Life style-related diseases, such as type 2 diabetes, are a membrane microdomain disorder caused by aberrant expression of gangliosides. We also encountered an another interesting aspect indicating the indispensable role of gangliosides in auditory system. After careful behavioral examinations of SAT-I knockout mice, their hearing ability was seriously impaired with selective degeneration of the stereocilia of hair cells in the organ of Corti. This is the first observation demonstrating a direct link between gangliosides and hearing functions.

Lipid and ganglioside alterations in tumor cells treated with antimitoticoleyl glycoside

Oleyl 2-acetamido-2-deoxy-α-D-glucopyranoside (1) was previously shown to exhibit antimitotic activity on glioma (C6) and melanoma (A375) cell lines. Preliminary studies about its mechanism of action using (1)H MAS NMR suggested that 1 may be altering the metabolism of lipids. We have now studied the effect of 1 on the fatty acid, sphingolipid and ganglioside content in a line of carcinomic human alveolar epithelial cells (A549) using UPLC-MS. Oleic acid and NB-DNJ were used as positive controls for inhibition of fatty acid and ganglioside synthesis, respectively. Compound 1 (10 μM) was more efficient than oleic acid in reducing fatty acid levels of A549 cells, producing a decrease in the range of 40-15%, depending on the acyl chain length and the number of insaturations. In addition, glycoside 1 caused a reduction on ganglioside content of A549 tumor cell line and accumulation of lactosylceramide, the common metabolic precursor for ganglioside biosynthesis. Alteration of ganglioside metabolism was also observed with two galactosylated derivatives of 1, which caused a more pronounced increase in lactosylceramide levels. Compound 1 at higher concentrations (above 30 μM) produced drastic alterations in glycosphingolipid metabolism, leading to cell metabolic profiles very different from those obtained at 10 μM. These biochemical changes were ascribed to activation of endoplasmic reticulum stress pathways.

Effect of lipid raft disruption on TRPV1 receptor activation of trigeminal sensory neurons and transfected cell line

The transient receptor potential vanilloid 1 (TRPV1) is a noxious heat-sensitive, chemonociceptive cation channel which is expressed in primary sensory neurons of polymodal nociceptors. The present study is devoted to analyse the role of lipid raft constituents in calcium influx evoked by various TRPV1 agonists on sensory neurons and on rTRPV1-transfected CHO cell line. Depletion of cholesterol by methyl β-cyclodextrin (MCD, 1–10 mM) diminished the percent of the calcium uptake response of cultured trigeminal neurons to capsaicin (100 nM) or resiniferatoxin (RTX, 3 nM). In contrast, in TRPV1-transfected cells the inhibition was observed only when capsaicin or N-oleoyldopamine (OLDA, 10 µM) was applied, but not when RTX, anandamide (AEA, 10 µM) or pH 5.5 was used for gating. The magnitude of Ca 2+-transients evoked by capsaicin (330 nM) was also inhibited in both cell types. Treatment of rTRPV1-expressing cells with sphinomyelinase inhibited the capsaicin-evoked 45Ca-uptake leaving the RTX-induced response unchanged. On the other hand, in trigeminal neurons the effect of both compounds was inhibited by sphingomyelinase treatment. Inhibition of ganglioside biosynthesis by d-threo-1-Phenyl-2-decanoylamino-3-morpholino-1-propanol (D-PDMP, 10–20 µM) or myriocyn (5–50 nM) diminished similarly capsaicin- or RTX-evoked calcium uptake in both cultured trigeminal neurons and rTRPV1-expressing cells. The present study revealed that depletion of different constituents of lipid raft inhibited gating the TRPV1 cation channel by various vanilloid and non-vanilloid agents. Evidence for a supporting role of cholesterol, sphingomyelin and gangliosides were obtained both in native and TRPV1-transfected cells. Differential modulation of responses to capsaicin and RTX was often observed.

Gangliosides are involved in neural differentiation of human dental pulp-derived stem cells

Human dental pulp-derived stem cells (hDPSCs) have been considered alternative sources of adult stem cells because of their potential to differentiate into multiple cell lineages. This study investigated the possible role of gangliosides in the neural differentiation of hDPSCs. When hDPSCs were cultured under neural differentiation conditions, expression of neural cell marker genes such as Nestin, MAP-2, and NeuN was detected. Immunostaining and high-performance thin-layer chromatography analysis showed that an increase in ganglioside biosynthesis was associated with neural differentiation of hDPSCs. Specifically, a significant increase in GD3 and GD1a expression was observed during neural differentiation. To confirm the role of gangliosides in neural differentiation, ganglioside biosynthesis was inhibited in hDPSCs by knockdown of UDP-glucose ceramide glucosyltransferase ( Ugcg), which prevented differentiation into neural cells. These results suggest that gangliosides may play a role in the neural differentiation process of hDPSCs.

The Cytoplasmic Tail of GM3 Synthase Defines Its Subcellular Localization, Stability, and In Vivo Activity

GM3 synthase (SAT-I) is the primary glycosyltransferase responsible for the biosynthesis of ganglio-series gangliosides. In this study, we identify three isoforms of mouse SAT-I proteins, named M1-SAT-I, M2-SAT-I, and M3-SAT-I, which possess distinct lengths in their NH(2)-terminal cytoplasmic tails. These isoforms are produced by leaky scanning from mRNA variants of mSAT-Ia and mSAT-Ib. M2-SAT-I and M3-SAT-I were found to be localized in the Golgi apparatus, as expected, whereas M1-SAT-I was exclusively found in the endoplasmic reticulum (ER). Specific multiple arginines (R) arranged in an R-based motif, RRXXXXR necessary for ER targeting, were found in the cytoplasmic tail of M1-SAT-I, and in vivo GM3 biosynthesis by M1-SAT-I was very low because of restricted transport to the Golgi apparatus. In addition, M1-SAT-I and M3-SAT-I had a long half-life relative to M2-SAT-I. This is the first report demonstrating the presence of an ER-targeting R-based motif in the cytoplasmic tail of a protein in the mammalian glycosyltransferase family of enzymes. The system, which produces SAT-I isoforms having distinct characteristics, is likely to be of critical importance for the regulation of GM3 biosynthesis under various pathological and physiological conditions.