Ganglioside GM3 inhibits the high glucose- and TGF-beta1-induced proliferation of rat glomerular mesangial cells

Enhanced Levels of Glycosphingolipid GM3 Delay the Progression of Diabetic Nephropathy

We recently found that albuminuria levels in patients with minimal change disease (MCD) and focal segmental glomerulosclerosis (FSGS) inversely correlate with glycosphingolipid GM3 expression levels in glomerular podocytes. Moreover, we showed enhanced expression of GM3 via activation of the GM3 synthase gene upon administration of valproic acid (VPA) is effective in suppressing albuminuria and podocyte injury in mice with anti-nephrin antibody-induced podocytopathy. However, the therapeutic effect of GM3 on diabetic nephropathy, which is the most common underlying disease in patients undergoing dialysis and with podocyte injury, remains unclear. Here, we investigated the therapeutic effect of enhanced GM3 expression via VPA on podocyte injury using streptozotocin-induced diabetic nephropathy model mice. Administration of VPA clearly decreased levels of albuminuria and glomerular lesions and inhibited the loss of podocytes and expansion in the mesangial area. Furthermore, we found that albuminuria levels in patients with diabetic nephropathy inversely correlate with the expression of GM3 in podocytes. These results indicate that maintaining GM3 expression in podocytes by administration of VPA may be effective in treating not only podocyte injury, such as MCD and FSGS, but also the late stage of diabetic nephropathy.

Ganglioside GD1a enhances osteogenesis by activating ERK1/2 in mesenchymal stem cells of Lmna mutant mice

Mutations in Lmna usually cause a series of human disorders, such as premature aging syndrome (progeria) involving the skeletal system. Gangliosides are known to be involved in cell surface differentiation and proliferation of stem cells. However, the role of gangliosides in Lmna dysfunctional mesenchymal stem cells (MSCs) is unclear. Therefore, Ganglioside's role in osteogenesis of Lmna dysfunctional MSCs analyzed. As a result of the analysis, it was confirmed that the expression of ganglioside GD1a was significantly reduced in MSCs derived from LmnaDhe/+ mice and in MSCs subjected to Lamin A/C knockdown using siRNA. Osteogenesis-related bone morphogenetic protein-2 and Osteocalcin protein, and gene expression were significantly decreased due to Lmna dysfunction. A result of treating MSCs with Lmna dysfunction with ganglioside GD1a (3 μg/ml), significantly increased bone differentiation in ganglioside GD1a treatment to Lmna-mutated MSCs. In addition, the level of pERK1/2, related to bone differentiation mechanisms was significantly increased. Ganglioside GD1a was treated to Congenital progeria LmnaDhe/+ mice. As a result, femur bone volume in ganglioside GD1a-treated LmnaDhe/+ mice was more significantly increased than in the LmnaDhe/+ mice. Therefore, it was confirmed that the ganglioside GD1a plays an important role in enhancing osteogenic differentiation in MSC was a dysfunction of Lmna.

The role of neuraminidase in TLR4-MAPK signalling and the release of cytokines by lupus serum-stimulated mesangial cells

Previously, we demonstrated neuraminidase (NEU) activity or NEU1 expression, specifically, is increased in the kidneys of lupus mice and urine of human patients with nephritis. Additionally, NEU activity mediates IL-6 secretion from lupus-prone MRL/lpr primary mouse mesangial cells (MCs) in response to an IgG mimic. IL-6 mediates glomerular inflammation and promotes tissue damage in patients and mouse strains with lupus nephritis. This study further elucidates the mechanisms by which NEU activity and NEU1 specifically mediates the release of IL-6 and other cytokines from lupus-prone MCs. We demonstrate significantly increased release of multiple cytokines and NEU activity in MRL/lpr MCs in response to serum from MRL/lpr mice (lupus serum). Inhibiting NEU activity significantly reduced secretion of three of those cytokines: IL-6, GM-CSF and MIP1α. Message levels of Il-6 and Gm-csf were also increased in response to lupus serum and reduced when NEU activity was inhibited. Neutralizing antibodies to cell-surface receptors and MAPK inhibitors in lupus serum- or LPS-stimulated MCs indicate TLR4 and p38 or ERK MAP kinase signalling play key roles in the NEU-mediated secretion of IL-6. Significantly reduced IL-6 release was observed in C57BL/6 (B6) Neu1+/+ primary MCs compared with wild-type (Neu1+/+) B6 MCs in response to lupus serum. Additional results show inhibiting NEU activity significantly increases sialic acid-containing N-glycan levels. Together, our novel observations support a role for NEU activity, and specifically NEU1, in mediating release of IL-6 from lupus-prone MCs in response to lupus serum through a TLR4-p38/ERK MAPK signalling pathway that likely includes desialylation of glycoproteins.

Ganglioside GM3 Up-Regulate Chondrogenic Differentiation by Transform Growth Factor Receptors

Mesenchymal stem cells, also known as multipotent stromal progenitor cells, can differentiate into cells of mesodermal lineage. Gangliosides are sialic acid-conjugated glycosphingolipids that are believed to regulate cell differentiation and several signaling molecules. These molecules are localized in glycosphingolipid-enriched microdomains on the cell surface and are regulated by glycosphingolipid composition. Transforming growth factor-beta (TGF-β) signaling plays a critical role in chondrogenic differentiation. However, the role of gangliosides in chondrogenesis is not understood. In this study, the relationship between the ganglioside GM3 and TGF-β activation, during chondrogenic differentiation, was investigated using an aggregate culture of human synovial membrane-derived mesenchymal stem cells. We showed that the gangliosides GM3 and GD3 were expressed after the chondrogenic differentiation of hSMSC aggregates. To test whether GM3 affected the chondrogenic differentiation of hSMSC aggregates, we used GM3 treatment during chondrogenic differentiation. The results showed that the group treated with 5 μM GM3 had higher expression of chondrogenic specific markers, increased toluidine blue, and safranin O staining, and increased accumulation of glycosaminoglycans compared with the untreated group. Furthermore, GM3 treatment enhanced TGF-β signaling via SMAD 2/3 during the chondrogenic differentiation of hSMSC aggregates. Taken together, our results suggested that GM3 may be useful in developing therapeutic agents for cell-based articular cartilage regeneration in articular cartilage disease.

GM1 Ganglioside Promotes Osteogenic Differentiation of Human Tendon Stem Cells

Gangliosides, the sialic acid-conjugated glycosphingolipids present in the lipid rafts, have been recognized as important regulators of cell proliferation, migration, and apoptosis. Due to their peculiar localization in the cell membrane, they modulate the activity of several key cell receptors, and increasing evidence supports their involvement also in stem cell differentiation. In this context, herein we report the role played by the ganglioside GM1 in the osteogenic differentiation of human tendon stem cells (hTSCs). In particular, we found an increase of GM1 levels during osteogenesis that is instrumental for driving the process. In fact, supplementation of the ganglioside in the medium significantly increased the osteogenic differentiation capability of hTSCs. Mechanistically, we found that GM1 supplementation caused a reduction in the phosphorylation of the platelet-derived growth factor receptor-β (PDGFR-β), which is a known inhibitor of osteogenic commitment. These results were further corroborated by the observation that GM1 supplementation was able to revert the inhibitory effects on osteogenesis when the process was inhibited with exogenous PDGF.

Neuraminidase activity mediates IL-6 production by activated lupus-prone mesangial cells

The development of nephritis is a leading cause of morbidity and mortality in lupus patients. Although the general pathophysiological progression of lupus nephritis is known, the molecular mediators and mechanisms are incompletely understood. Previously, we demonstrated that the glycosphingolipid (GSL) catabolic pathway is elevated in the kidneys of MRL/lpr lupus mice and human lupus patients with nephritis. Specifically, the activity of neuraminidase (NEU) and expression of Neu1, an enzyme in the GSL catabolic pathway is significantly increased. To better understand the role and mechanisms by which this pathway contributes to the progression of LN, we analyzed the expression and effects of NEU activity on the function of MRL/lpr lupus-prone mesangial cells (MCs). We demonstrate that NEU1 and NEU3 promote IL-6 production in MES13 MCs. Neu1 expression, NEU activity, and IL-6 production are significantly increased in stimulated primary MRL/lpr lupus-prone MCs, and blocking NEU activity inhibits IL-6 production. NEU1 and NEU3 expression overlaps IgG deposits in MCs in vitro and in renal sections from nephritic MRL/lpr mice. Together, our results suggest that NEU activity mediates IL-6 production in lupus-prone MCs possibly through an IgG-receptor complex signaling pathway.

Ganglioside GM3 and its biological functions

Metabolism, topology, and possible mechanisms for regulation of the ganglioside GM3 content in the cell are reviewed. Under consideration are biological functions of GM3, such as involvement in cell differentiation, proliferation, oncogenesis, and apoptosis.