Alpha 2-HS glycoprotein increases glucagon synthesis and secretion in cells, mice, and humans

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Alpha-2-HS-glycoprotein (Fet-A), a hepatocyte-derived glycoprotein, is known to influence insulin resistance and inflammation, but its impact on pancreatic alpha cell function and glucagon secretion is not well understood. To unravel the molecular mechanisms underlying Fet-A action on glucagon synthesis, we used pancreatic Alpha TC1 clone 6 cells treated with Fet-A and/or IGF-1 at high glucose concentrations, before switching to low levels of glucose to induce glucagon synthesis. Mechanistic involvement was evaluated using TLR4 gene silencing (siRNA), pharmacological inhibitors, and cell-surface confocal microscopy. To evaluate the role of Fet-A in glucagon regulation in vivo, we treated CD-1 mice with Fet-A or saline for three consecutive days. Finally, we examined the relationship between circulating Fet-A concentrations and fasting glucagon levels in a clinical cohort of 93 non-diabetic adult individuals participating in the CATAMERI study. In pancreatic Alpha TC1 cells, high Fet-A levels stimulated preproglucagon mRNA expression and activated inflammatory signaling via TLR4 under hyperglycemic conditions, an effect abolished by TLR4 knockdown. Fet-A also impaired IGF-1-mediated inhibition of glucagon synthesis during hypoglycemia by disrupting the PI3K/Akt/FoxO1 pathway. Confocal microscopy demonstrated dose-dependent cell-surface co-localization of Fet-A with the IGF-1 receptor, while molecular docking analysis predicted potential structural overlap within its extracellular domain. Overall, these findings are consistent with a model of steric interference with IGF-1R signaling, leading to impaired glucagon suppression. In CD-1 mice, exogenous Fet-A administration increased circulating glucagon and inflammatory cytokines. Furthermore, in a cohort of non-diabetic adults, circulating Fet-A levels positively associated with fasting glucagon concentrations, independent of age, sex, body mass index, insulin, or IGF-1. These results reveal Fetuin-A as a modulator of alpha cell function through inflammatory and IGF-1 signaling interference pathways, suggesting its involvement in glucagon regulation and metabolic disease pathogenesis.

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