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Sterol intermediates of cholesterol synthesis are largely dedicated to cholesterol. Here we assess how they influence downstream gene regulatory pathways by developing knockouts (KOs) for consecutive enzymes of cholesterol synthesis. Depletion ofCYP51,DHCR24andSC5Dresulted in accumulation of specific sterols. The overlap of deregulated genes was only 9% in terms of steroid metabolism and proliferation control, with majority of pathways changed in just one KO. TheCYP51KO with highly elevated 24,25-dihydrolanosterol showed significantly higher proportion of cells in the G2+M phase, in line with enriched cancer and cell cycle pathways, and elevatedLEF1by activation of WNT/NFKB/SMAD signalling. In contrast,SC5DandDHCR24KOs (with elevated lathosterol or desmosterol) slowed cell proliferation and promoted apoptosis with downregulated E2F, mitosis, cell cycle transition, and enriched HNF1A tumor suppressor. These findings demonstrate that sterols from cholesterol synthesis control distinct gene regulatory pathways, and only early sterols promote cell proliferation.

Multifactorial metabolic diseases, such as non-alcoholic fatty liver disease, are a major burden of modern societies and frequently present with no clearly defined molecular biomarkers. Herein we used systems medicine approaches to decipher signatures of liver fibrosis in mouse models with malfunction in genes from unrelated biological pathways. Enrichment analyses of KEGG, Reactome and TRANSFAC databases complemented with genome-scale metabolic modelling revealed fibrotic signatures highly similar to liver pathologies in humans. The diverse genetic models of liver fibrosis exposed a common transcriptional programme with activated ERα signalling, and a network of interactions between regulators of lipid metabolism and transcription factors from cancer pathways and immune system. The novel hallmarks of fibrosis are downregulated lipid pathways, including fatty acid, bile acid, and steroid hormone metabolism. Moreover, distinct metabolic subtypes of liver fibrosis were proposed, supported by unique enrichment of transcription factors based on the type of insult, disease stage, or sex.

We uncover novel pathways of sex-dependent hepatocarcinogenesis due to chronic repression of cholesterol synthesis at the lanosterol 14α-demethylase (CYP51) step. The response to metabolic insult determined by global liver transcriptome, qPCR and sterol metabolite analysis, together with blood parameters, revealed molecular signatures that differ between females and males. The data deduced from the mouse model are highly relevant for humans. The dampened hepatic metabolism presents a hallmark of carcinogenesis, particularly in ageing females, with increased plasma cholesterol and HDL, and a substantial negative enrichment of transcription factors from lipid metabolism, such as NR1B1, LXRα, LRH1, and FXR. Importantly, the carcinogenic signalling pathways (ECM-receptor interaction and PI3K/Akt) are positively enriched, albeit with sex-dependent gene targets. The activated TGF-β, mTOR, Wnt, and estrogen signalling worsen the phenotype, with NFATC1/2 being central to the female phenotype. This collectively leads to activated cell death and diminished basal metabolism. In conclusion, our data underline sex as an important biological variable of hepatocarcinogenesis. We uncover novel cholesterol-dependent transcription factors and signalling pathways as cancer markers in the ageing females.SignificanceChronic repression of the late part of cholesterol synthesis provokes hepatocarcinogenesis with sex-dependent modulation of signalling pathways and transcription factors. Aging females show specific metabolic signatures and a more aggrevated phenotype of metabolism-related HCC.