Authors: Rieck, Adrian
Title: The small GTPase RAB18: Insights into cellular steatosis, lipophagy and the non-alcoholic fatty liver disease
Language (ISO): en
Abstract: Non-alcoholic fatty liver disease is a rapidly growing concern for public health. Its most prevalent marker is steatosis, which is the accumulation of large lipid storage organelles called lipid droplets (LD) in the hepatocytes. RAB18, a member of the Rab family, localizes to the LD membrane. Rab family proteins are regulators of cellular membrane trafficking, therefore RAB18 is expected to play a role regulating LD biology. The presented work aims to elucidate this role as well as the mechanisms behind the localization of RAB18 to the LD membrane. The localization of RAB18 was investigated by overexpressing mutant RAB18 variants in HepG2 cells. RAB18 localization was observed to depend on the reversible cyclical palmitoylation of its C-terminus. Using FRAP experiments, it could be shown that targeting the palmitoylation machinery with small molecule inhibitors modulated RAB18 localization. This coincided with changes in LD size in cells treated with de-palmitoylation inhibitors. An overall increase in LD size was observed in HepG2 cells with RAB18 downregulation. The wild type LD size in these cells was restored by the inhibition of autophagy. This size reduction was due to newly created LDs. Inhibition of autophagy prior to LD accumulation was subsequently tested in vitro on primary human hepatocytes in sandwich culture. Inhibition of autophagy by chloroquine resulted in a dose dependent rise in LD number and a decrease in average LD size in these cells. These effects could be translated to the in vivo situation in mice. Daily chloroquine injection of mice on a steatogenic diet resulted in a significant decrease of LD size in vivo. Conversely, no changes were detected in the blood-values of treated mice compared with the control. This thesis demonstrates, that RAB18 localizes to the LD via a C-terminal acylation cycle. RAB18 reduces the size of LDs by modulating autophagy of newly formed LDs. This mechanism is important for LD number and size regulation in hepatocytes.
Subject Headings: RAB18
NAFLD
Lipid droplets
Subject Headings (RSWK): Fettleber
Biomarker
URI: http://hdl.handle.net/2003/40554
http://dx.doi.org/10.17877/DE290R-22423
Issue Date: 2021
Appears in Collections:Lehrstuhl für Zellbiologie

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