Endocrine Abstracts

Bile acid (BA) homeostasis is disrupted in MASLD with characteristic changes in BA pool composition. BAs are signalling molecules that modulate hepatic lipid metabolism, inflammation, and cellular proliferation via the activation of nuclear receptors, notably FXR. Altered FXR activation has profound effects on the transcription of genes involved in hepatoprotection. We have previously shown that the hepatic enzyme 5β-reductase (AKR1D1), which catalyses a key step in the synthesis of primary BAs, is progressively downregulated with advancing MASLD and is a marker for advanced fibrosis and cirrhosis. We hypothesise that AKR1D1 downregulation plays a role in altering the BA pool with a consequent disruption of BA signalling, contributing to MASLD pathogenesis. In hepatoma cells, AKR1D1 knockdown increases hepatocyte triglyceride accumulation, induces apoptosis, and alters mRNA and protein expression in inflammation and p53 signalling pathways. To determine whether our in vitro observations are mirrored in vivo, we aged wild-type (WT) and AKR1D1 knock-out (KO) mice to 52-weeks on a normal chow diet. Intrahepatic triglyceride accumulation and gene expression were assessed by biochemical assays and qPCR, respectively. Endorsing our in vitro findings, liver triglyceride content was increased in AKR1D1 KO mice compared to WT. mRNA expression of NFkappaB1 was elevated (0.93±0.17 [WT] vs. 1.19±0.3 [KO], P = 0.013), suggesting an increase in inflammatory signalling. Increased expression of cell cycle regulatory and apoptosis genes was also observed (Tp53: 1.01±0.12 [WT, n = 15] vs. 1.24±0.18 [KO], P = 0.0023); Casp3: 1.12±0.3 [WT] vs. 1.3±0.25 [KO], P = 0.046; Casp9; 1.04±0.13 [WT], vs. 1.24±0.19 [KO], P = 0.0053). mRNA expression of the FXR-induced target gene small heterodimer partner (Shp) was upregulated (1.27.85±0.5 [WT,] vs. 1.7±0.5 [KO], P = 0.05). In conclusion, disruption of BA synthesis following AKR1D1 deletion is associated with increased intrahepatic triglyceride accumulation and expression of inflammatory and apoptotic genes in vivo, suggesting a role in MASLD pathophysiology.