Palmitic Acid and TGF-β1 Are Useful for Study of Liver Disease in Human Liver Organoids
Key findings
- In this study, human liver organoids were treated with oleic acid, palmitic acid, or TGF-ß1 to test their ability to model the progression of steatohepatitis and fibrosis caused by metabolic dysfunction–associated steatotic liver disease
- Oleic acid induced patterns of gene expression reflective of benign steatosis
- Palmitic acid induced a robust steatohepatitis gene signature and TGF-ß1 generated a global fibrotic phenotype
- When modeling steatohepatitis in human liver organoids, researchers should favor palmitic acid over oleic acid and use TGF-ß1 to study the combination of inflammation and fibrosis observed in later-stage disease
Metabolic dysfunction–associated steatotic liver disease (MASLD, a newer term for non-alcoholic fatty liver disease) can lead to metabolic dysfunction–associated steatohepatitis (MASH) and the development of fibrosis, and it is the development of fibrosis that is most-associated with increased morbidity and mortality in MASLD. Few options are available to disrupt that process other than weight loss, and no approved treatments target common inflammatory or fibrotic pathways arising from chronic liver injury.
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A critical need in the field is human cell models that can bridge the gap between animal studies and clinical trials for testing new approaches to preventing liver failure. A new method is to use human liver organoids (HLOs)—multi-tissue in vitro organ systems generated from pluripotent stem cells that can recapitulate aspects of liver inflammation and fibrosis.
Researchers at Massachusetts General Hospital recently became the first to systematically evaluate the effects of various lipotoxic agents on MASLD induction in HLOs at single cell resolution. Alan C. Mullen, MD, PhD, of UMass Chan Medical School and formerly a physician–investigator in the Mass General Division of Gastroenterology and the Harvard Stem Cell Institute, Anja Hess, a PhD student, and colleagues report in The EMBO Journal.
Methods
A key prerequisite for MASLD-associated chronic liver injury is continued exposure to excess fatty acids. The researchers examined the effects of two free fatty acids in HLOs:
- Oleic acid (OA), a monounsaturated fatty acid that's the primary component of olive oil and has been reported to protect against MASLD
- Palmitic acid (PA), a saturated fatty acid, which has been reported to promote hepatocyte apoptosis
They also studied transforming growth factor β1 (TGF-β1), which is secreted by liver macrophages and can promote the differentiation of hepatic stellate cells (HSCs) into myofibroblasts, which in turn produce collagen that forms fibrotic scarring.
The team treated HLOs with each of these three agents and examined their ability to model the progression of steatohepatitis and fibrosis caused by MASLD-induced liver disease. They used single-cell RNA sequencing to identify disease signatures at high resolution.
Patterns of Gene Expression
The analysis covered histologic, phenotypic, and gene expression studies, including creating a reference atlas of about 100,000 single-cell transcriptomes of injured and healthy MASLD-HLOs.
A key finding was that the inflammatory and fibrotic responses induced by OA, PA, and TGF-β1 were distinctly different:
- OA induced steatosis, but inflammatory changes were observed only in hepatocyte precursors; moreover, OA significantly ameliorated fibrotic gene signatures across cell types and vastly reduced the HSC population in HLOs
- PA induced inflammatory changes of steatohepatitis from more mature hepatocytes
- The combination of steatohepatitis and fibrosis was most prominent with TGF-β1; it was the only agent tested that generated a global fibrotic phenotype including collagen production, fibrosis, and HSC expansion
Gene Signatures and Disease Progression
The team also investigated how changes in gene expression following treatment of HLOs with OA, PA, or TGF-β1 related to fibrosis progression in patients with MASLD. Those experiments further demonstrated that PA and TGF-β1 induce inflammation and fibrosis more robustly than OA.
The Path Forward
These data suggest researchers should favor PA over OA when modeling steatohepatitis in HLOs and use TGF-β1 to study the combination of inflammation and fibrosis observed in later-stage disease. Such model systems could be used to predict differential outcomes of drug candidates on MASH and fibrosis before clinical trials.
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