Type of intrahepatic cholestasis shows abnormal cellular processes

More than 250 proteins in liver organoids of mice with PFIC3 impaired

Patricia Inacio, PhD avatar

by Patricia Inacio, PhD |

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The levels of more than 250 proteins are abnormal in lab-grown liver organoids, or mini-livers, derived from a mouse model of progressive familial intrahepatic cholestasis type 3 (PFIC3), compared with mini-livers from healthy mice.

PFIC3 is marked by alterations in how liver cells interact with their surroundings, along with changes in liver metabolism, and cell growth and maturation, say researchers, and these abnormalities may “provide relevant insights on the early events associated with the progression of the disease,” they wrote in “Molecular Insights of Cholestasis in MDR2 Knockout Murine Liver Organoids,” which was published in the Journal of Proteome Research.

Progressive familial intrahepatic cholestasis (PFIC) is an umbrella term for rare liver diseases in early childhood that are caused by genetic mutations that result in hepatocytes, the liver’s predominant cell type, defectively producing and/or secreting bile, a digestive fluid.

In intrahepatic cholestasis, the flow of bile is slowed or stalled in the tubes that transport bile inside the liver, the intrahepatic bile ducts. The condition can result in permanent liver scarring, or cirrhosis, and hepatocellular carcinoma (HCC), the most common type of liver cancer.

PFIC3 is caused by mutations in the ABCB4 gene, which provides instructions for making the protein MDR3, which is involved in transporting compounds that neutralize bile salts and prevent damage to bile duct cells. About 300 ABCB4 mutations that result in different levels of MDR3 dysfunction have been described.

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Effects of MDR3 deficiency in the liver

“Despite the heavy societal burden represented by PFIC3, therapeutic options for patients with PFIC are currently very limited,” wrote a research team led by scientists at the Centro Nacional de Biotecnología, Madrid, who developed liver organoids from a 3-month-old PFIC3 mouse model to study the early molecular effects of MDR3 deficiency in the liver. The researchers said a better understating of the molecular mechanisms behind PFIC3 is vital for developing new treatment strategies.

The mice are genetically engineered to lack the ABCB4 gene, which in mice codes the MDR2 protein. Organoids are lab-grown stem cell-derived 3D structures that mimic the genetic and behavioral profiles of their tissue of origin.

The researchers performed mass spectroscopy-based proteomics, a technique that can help profile proteins, along with their interactions and modifications, in liver organoids from the mouse model and from healthy mice.

The levels of 279 proteins were significantly different between the two groups, the analysis revealed. Levels of 105 proteins were increased in the PFIC3 mini-livers relative to healthy organoids, while 174 other protein levels were reduced.

An analysis of the proteins with altered production showed that MDR2 deficiency affects how liver cells interact with their environment. The levels of mucins and laminins, two main protein groups involved in this interaction, were reduced with the loss of MDR2, “which might indicate a severe condition at risk of progression to cancer.”

Also, the lack of MDR2 altered the liver metabolism of fatty molecules, with cholesterol production enhanced, but the production of fatty acids, another type of fatty molecule, reduced. The levels of several enzymes involved in producing cholesterol were increased compared with healthy organoids.

But the lack of MDR2 in liver organoids did promote the reprogramming of cellular metabolism toward using blood sugar, or glucose, for energy production.

Also, the levels of epidermal growth factor receptor (EGFR), a pivotal regulator of liver cells’ growth during regeneration and response to damage, were reduced in the PFIC3 organoids. EGFR “deregulation might be one of the factors driving the progression of PFIC3,” the researchers wrote.

Moreover, several liver-specific functions were impaired in PFIC3 liver organoids, suggesting problems in liver cell maturation.

Overall, “our results point to molecular mechanisms associated with PFIC3 that may drive the progression to liver cirrhosis and HCC and suggest proteins and cellular processes that could be targeted for the development of early detection strategies for these severe liver diseases,” the researchers wrote.