Work

EP1164 - ECE_1331 - The role of GM3 gangliosides in acromegaly-associated insulin resistance

Year: 2026

Type: conference-abstract

Abstract: Background A significant number of patients with acromegaly develop insulin resistance and diabetes mellitus, the mechanism of which is not fully understood. GM3 gangliosides (GM3), a family of glycosphingolipids which sit within the cell membrane and have important roles within insulin signalling, have previously been mechanistically linked to insulin resistance in patients with diabetes mellitus. Aim We aimed to configure the role of GM3 in acromegaly-associated insulin resistance in 3T3-L1 adipocytes and C2C12 myotubes, mouse adipocyte and muscle cell lines, respectively. Methods 3T3-L1 adipocytes were exposed to growth hormone (GH) (1 μM) and/or insulin like growth factor 1 (IGF-1) (1 μg/ml) for 48 hours. Insulin signalling was assessed by Western(immuno)blot of AKT phosphorylation (pAKT:AKT). Membrane order was assessed through measures of membrane polarisation by confocal microscopy of DI-4-ANEPPDHQ fluorescence. GM3 content in cellular extracts was measured by NMR spectroscopy. The expression of ST3GAL5 (which encodes for GM3 synthase, the enzyme responsible for GM3 synthesis) was assessed by qPCR. C2C12 myotubes were also exposed similarly to GH/IGF-1 and expression of ST3GAL5 was measured. Results Exposure of 3T3-L1 adipocytes to elevated concentrations of GH, IGF-1 and the combination of GH/IGF-1 all led to significantly lowered pAKT:AKT (0.3 ± 0.2-fold, 0.5 ± 0.1-fold and 0.5 ± 0.1-fold, respectively) compared to controls, indicating impaired insulin signalling (P = .01). Similarly, all three hormonal variations were associated with altered plasma membrane fluidity (1.4 ± 0.04-fold, 1.8 ± 0.1 fold and 1.5 ± 0.08-fold, respectively, P ≤ .0001). Whilst only IGF-1 (1.4 ± 0.2-fold) and combined GH/IGF-1 (1.4 ± 0.1-fold) altered internal membrane fluidity (P < .05). In 3T3-L1 adipocytes, both IGF-1 and combined GH/IGF-1 increased cellular levels of GM3 [1.4 ± 0.1-fold (P < .05) and 1.9 ± 0.4-fold (P < .05), respectively] compared to controls. Exposure to elevated GH concentrations also led to increased (1.4 ± 0.1-fold, P ≤ .01) expression of ST3GAL5. Interestingly, combined IGF-1/GH reduced ST3GAL5 expression 0.8 ± 0.1-fold, P < .05, whilst IGF-1 had no effect. In C2C12 myotubes, GH had no effect on ST3GAL5 expression, whilst both IGF-1 and combined GH/IGF-1 reduced expression compared to untreated control cells (0.25-fold ± 0.009 and 0.3-fold ± 0.05, respectively, P ≤ .0005). Conclusions Taken together, these data indicate that exposure to GH and IGF-1, as seen in acromegaly, inhibits insulin signalling in 3T3-L1 adipocytes potentially via alterations in plasma membrane fluidity and increased GM3 content may be implicated in this process. GH and IGF-1 have some divergent effects in different cell types and fluidity plasma and internal membranes, with IGF-1 being the predominant effector hormone.

Source: European Journal of Endocrinology

DOI: 10.1093/ejendo/lvag096.1419