Liver international : official journal of the International Association for the Study of the Liver · 2025
Reduced Esterification Rather Than Increased Hydrolysis Is Causative for Loss of Hepatic Retinoids Upon CCl4-Induced Liver Injury.
СтатьяПоддержка исследования: вне правительства СШАНазвание и аннотация: Перевод в очереди
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Wagner Carina, Košić Kristina, Bulfon Dominik, Breithofer Johannes, Jamnik Alina, Zitta Clara, Horvat Paula, Bilweis Kim, Schupp Michael, Zimmermann Robert, Taschler Ulrike, Lass Achim
Аннотация
BACKGROUND AND AIMS: Advanced liver disease leads to liver fibrosis that is characterised by the activation of non-parenchymal stellate cells, accumulation of extracellular matrix proteins, and the loss of hepatic vitamin A stores. To date, the molecular mechanisms and enzymes mediating the loss of hepatic vitamin A stores are incompletely understood.
APPROACH AND RESULTS: Using a fibrosis mouse model induced by the hepatotoxin carbon tetrachloride (CCl4), we investigated which cellular processes in the liver mediate the loss of hepatic retinyl ester stores. We found that repeated CCl4 injections into mice over six weeks led to a biphasic change in plasma retinol levels that were increased after three and decreased after six weeks as compared to control mice. As expected, livers of mice receiving CCl4 injections showed increased expression of pro-fibrogenic genes that were accompanied by decreased hepatic retinoid content, which was mainly due to loss of retinoids in non-parenchymal cells (NPCs). In the liver and NPCs, decreased retinyl ester levels correlated with reduced gene expression of lecithin:retinol acyltransferase and reduced hepatic ex vivo retinol acyltransferase activity. Conversely, gene expression of lipases known to exhibit retinyl ester hydrolase activity (REHA) remained unchanged or was decreased, consistent with decreased neutral REHA in homogenates of respective livers and lysates of isolated NPCs, respectively. Albeit hepatic expression levels of marker proteins for autophagosomal and lysosomal membranes were increased, gene expression of the major acidic retinyl ester hydrolase, lysosomal acid lipase, as well as ex vivo acidic REHA were reduced in NPC lysates.
CONCLUSION: Together, these results indicate that the loss of hepatic retinyl ester stores upon liver injury and stellate cell activation is rather a consequence of reduced retinol esterification than neutral or acidic hydrolysis.
APPROACH AND RESULTS: Using a fibrosis mouse model induced by the hepatotoxin carbon tetrachloride (CCl4), we investigated which cellular processes in the liver mediate the loss of hepatic retinyl ester stores. We found that repeated CCl4 injections into mice over six weeks led to a biphasic change in plasma retinol levels that were increased after three and decreased after six weeks as compared to control mice. As expected, livers of mice receiving CCl4 injections showed increased expression of pro-fibrogenic genes that were accompanied by decreased hepatic retinoid content, which was mainly due to loss of retinoids in non-parenchymal cells (NPCs). In the liver and NPCs, decreased retinyl ester levels correlated with reduced gene expression of lecithin:retinol acyltransferase and reduced hepatic ex vivo retinol acyltransferase activity. Conversely, gene expression of lipases known to exhibit retinyl ester hydrolase activity (REHA) remained unchanged or was decreased, consistent with decreased neutral REHA in homogenates of respective livers and lysates of isolated NPCs, respectively. Albeit hepatic expression levels of marker proteins for autophagosomal and lysosomal membranes were increased, gene expression of the major acidic retinyl ester hydrolase, lysosomal acid lipase, as well as ex vivo acidic REHA were reduced in NPC lysates.
CONCLUSION: Together, these results indicate that the loss of hepatic retinyl ester stores upon liver injury and stellate cell activation is rather a consequence of reduced retinol esterification than neutral or acidic hydrolysis.