GM1 Oligosaccharide Modulates Microglial Activation and α-Synuclein Clearance in a Human In Vitro Model

Abstract

Neuroinflammation driven by microglial activation and α-synuclein (αSyn) aggregation is one of the central features driving Parkinson's disease (PD) pathogenesis. GM1 ganglioside's oligosaccharide moiety (OligoGM1) has shown neuroprotective potential in PD neuronal models, but its direct effects on inflammation remain poorly defined. This study investigated the ability of OligoGM1 to modulate microglial activation and αSyn handling in a human in vitro model. Human embryonic microglial (HMC3) cells were exposed to αSyn pre-formed fibrils (PFFs) in the presence or absence of OligoGM1. Microglial activation markers, intracellular αSyn accumulation, and cytokine release were assessed by immunofluorescence and ELISA. OligoGM1 had no effect on microglial morphology or cytokine release under basal conditions. Upon αSyn challenge, cells exhibited increased amounts of ionized calcium-binding adaptor molecule 1 (Iba1), triggered receptor expressed on myeloid cells 2 (TREM2), elevated αSyn accumulation, and secreted pro-inflammatory cytokines. OligoGM1 pre-treatment significantly reduced the number and area of Iba1(+) cells, the intracellular αSyn burden in TREM2(+) microglia, and the release of interleukin 6 (IL-6). OligoGM1 selectively attenuated αSyn-induced microglial activation and enhanced αSyn clearance without compromising basal immune function. These findings confirm and support the potential of OligoGM1 as a multitarget therapeutic candidate for PD that is capable of modulating glial reactivity and neuroinflammatory responses.

Keywords: GM1 oligosaccharide; Parkinson’s disease; microglia; neurodegeneration; α-synuclein.

Figure 1

Effects of GM1 oligosaccharide (OligoGM1) application on Human embryonic microglial (HCM3) cells. After 2 days of culture (80% of confluence), HCM3 cells were incubated or not incubated (control, CTRL) with OligoGM1 (100 µM). After 48 h, immunofluorescence staining [(against nuclei, ionized calcium-binding adaptor molecule 1 (Iba1) and triggered receptor expressed on myeloid cells 2 (TREM2)] and ELISA for quantification of released cytokines to medium were performed, as described in the Section 4: (a) Representative immunofluorescence images (20× magnification, scale bar 100 µm) and number of DAPI-positive cells; (b) Representative immunofluorescence images (20× magnification, scale bar 100 µm) of Iba1 expression, quantification of Iba1 accumulation (Iba1 area normalized by the number of cells), and area of Iba1-positive cells (area of microglia cells normalized by the µm² of Iba1); (c) Representative immunofluorescence images (20× magnification, scale bar 100 µm) of TREM2 expression, quantification of TREM2-positive cells (TREM2 area normalized by the number of cells), and area of TREM2-positive cells (area of microglia cells normalized by the µm² of TREM2); (d) Quantification of released cytokines tumor necrosis factor alpha (TNF-α) and interleukin 6 (IL-6). All values are represented as percentage versus CTRL and expressed as mean ± standard error of the mean (SEM, n = 6; ns = not significant, Mann–Whitney test).

Figure 2

OligoGM1 modulation of αSyn-induced activation of HMC3 cells. After 2 days of culture (80% of confluence), HCM3 cells were incubated or not incubated (CTRL) with OligoGM1 (100 µM). After 4 h, αSyn (1 µM) was added to the culture medium for 48 h. At the end of treatment, immunofluorescence staining (against nuclei, Iba1, TREM2, and αSyn) and IL-6/TNF-α quantification from medium were performed as described in the Section 4. (a) Representative immunofluorescence images (20× magnification, scale bar 100 µm) and number of DAPI-positive cells; (b) Representative immunofluorescence images (20× magnification, scale bar 50 µm) of Iba1 expression, quantification of Iba1 accumulation (Iba1 area normalized by the number of cells), and area of Iba1-positive cells (area of microglia cells normalized by the µm² of Iba1); (c) Representative immunofluorescence images (20× magnification, scale bar 25 µm) of TREM2 and αSyn expressions, quantification of TREM2-positive cells (TREM2 area normalized by the number of cells), area of TREM2-positive cells (area of microglia cells normalized by the µm² of TREM2), and quantification of αSyn area accumulated within TREM(+) cells (area of αSyn normalized by the µm² of TREM2); (d) Quantification of released cytokines TNF-α and IL-6. All values are represented as percentage versus CTRL and expressed as mean ± SEM (n = 6; * p < 0.05, ** p < 0.01, *** p < 0.001, **** p < 0.0001, ns = not significant by one-way ANOVA followed by Fisher’s LSD). * p < 0.05 was considered significant.