The Hsd17b13P260S patient variant knock-in male mouse model provides translational insights into HSD17B13 biology.

Metabolic dysfunction-associated steatotic liver disease (MASLD) is a prevalent liver disease that can progress to metabolic dysfunction-associated steatohepatitis (MASH), a condition marked by inflammation and fibrosis that increases the risk of cirrhosis, liver failure, and hepatocellular carcinoma. Loss-of-function (LoF) variants of hydroxysteroid 17-β dehydrogenase 13 (HSD17B13), a lipid droplet-associated enzyme, protect against progression from MASLD to MASH and more severe types of liver disease. We generated a knock-in mouse model harbouring the human orthologue of the HSD17B13 P260S patient variant and investigated the molecular mechanisms underlying its protective phenotype upon dietary challenge, by applying comprehensive spatial transcriptomics, histological analysis, matrix-assisted laser desorption/ionisation (MALDI) imaging, and in vitro cellular characterisation. Male Hsd17b13P260S mice showed reduced liver fibrosis (p < 0.0001) upon dietary challenge, reflecting the protective effect seen in patients and supporting the model's translatability. Despite similar transcript levels, HSD17B13 P260S protein in the liver was significantly lower compared to wild-type (WT). Interestingly, HSD17B13 WT protein lost its periportal zonation when switching mice from a chow to a high trans-fat diet (HTF), whereas the HSD17B13 P260S protein retained periportal expression. Male Hsd17b13P260S mice showed increased steatosis (p < 0.05), while spatial transcriptomics revealed the suppression of pro-fibrotic and immune response-related genes. MALDI imaging identified significant differences in phospholipids across genotypes and diets. Both HSD17B13 WT and P260S variant protein localised to lipid droplets, but the latter showed reduced enzymatic activity. Lastly, we observed reduced expression of CCND1 (p < 0.05) and an increase in multinucleated hepatocytes (p < 0.0001) in livers from male Hsd17b13P260S compared to WT upon HTF feeding. Our study suggests that the Hsd17b13P260S mouse model is translatable towards human physiology and useful for understanding the protective mechanisms of the human HSD17B13 P260S LoF variant. Lower HSD17B13 P260S protein abundance, reduced enzymatic activity and retained periportal localisation may contribute to protection from liver disease progression by maintaining zonated transcriptomic and lipidomic profiles. These findings provide key insights into HSD17B13 biology and its role in MASLD to MASH progression. Novartis Biomedical Research Postdoctoral program, Sigrid Jusélius Foundation, Forendo Pharma.