Lower glucagon response and attenuated hepatic glucagon signaling in MASLD.

BACKGROUND: While glucagon plays a role in hepatic lipid metabolism, alterations in circulating glucagon profiles and hepatic glucagon signaling in metabolic dysfunction-associated steatotic liver disease (MASLD) in humans remain unclear. We aimed to investigate the relationship between MASLD severity and plasma glucagon dynamics, and evaluate hepatic glucagon signaling using human liver tissue. METHODS: This retrospective cross-sectional study included 137 adults with prediabetes or type 2 diabetes who underwent a 75 g oral glucose tolerance test (OGTT) with fasting and 2-h plasma glucagon measurements. MASLD severity was assessed using noninvasive scores and transient liver elastography. To evaluate hepatic glucagon signaling across MASLD severity, human liver tissue transcriptome and single-cell RNA sequencing were analyzed. RESULTS: Participants with moderate-to-severe hepatic steatosis or high-risk metabolic dysfunction-associated steatohepatitis exhibited a lower integrated glucagon response, assessed by glucagon AUC during the 2-h OGTT, than their respective control groups (46,500 vs. 60,480 pg·min/ml, P = 0.006; and 43,680 vs. 52,620 pg·min/ml, P = 0.014, respectively). In contrast, there was no significant association between plasma glucagon levels and fibrosis severity. Transcriptomic analyses revealed downregulation of the glucagon receptor (GCGR) and downstream signaling pathways in liver tissues from individuals with MASLD, particularly within hepatocytes from those with advanced disease. CONCLUSION: Among individuals with prediabetes or type 2 diabetes, greater hepatic steatosis and inflammation are associated with lower circulating glucagon levels and attenuated hepatic glucagon signaling. These findings may provide a basis for future investigation of glucagon-based therapeutic approaches.