Liver regeneration is associated with lipid reorganization in membranes of the endoplasmic reticulum

Abstract

BACKGROUND: In recent years, an adaptive endoplasmic reticulum (ER) stress response has been actively investigated. The ER membrane, isolated from the intact and regenerating liver, may be an appropriate model for investigating the association between structural and functional characteristics of ER in vivo and their corresponding behavioral characteristics in vitro. The rate of lipid synthesis and that of intracellular lipid exchange between the ER and cytosol were investigated in the intact and regenerating liver (13 h after partial hepatectomy). Particularly, membrane characteristics, surface potential, and glucose 6-phosphatase (G6Pase) activity were investigated, along with the degradation rate of G6Pase in vitro, which was estimated by the loss of G6Pase activity, formation of lipid peroxides, and size of excreted membrane vesicles.

METHODS: The rate of lipid synthesis was determined by measuring the intensity of radioactive precursor (C¹⁴-sodium acetate) in different fractions of lipids (phospholipids, non-esterified fatty acids, and triacylglycerides) after 30 min exposure. The rate of lipid metabolism was assessed by measuring the quantity of lipids with radioactive labels emerging in the cytosol of hepatocytes (CPM). Viscosity and surface potential were determined by fluorescent probes.

RESULTS: It was observed that after 13 h of partial hepatectomy, the rate of lipid synthesis in the ER of hepatocytes in the regenerating liver was 3 times lower than that in ER of hepatocytes in the intact liver, wherein the rate of incorporation of newly synthesized lipids in cytosol was several times higher in the regenerating liver. Increase in the rate of exchange of neutral lipids in cells of the regenerating liver was accompanied by lipid reconstruction in the ER, changing the structural and functional characteristics of the membrane. Such membrane rebuilding also contributed to the rate of degradation of the ER in vitro, which that must be taken into account during development of systems for in vitro assessment of xenobiotic metabolism.

CONCLUSIONS: An increase in the rate of direct (microsomes→cytosol) and reverse transport of lipids (cytosol→microsomes) was observed in the regenerating liver. Microsomes, isolated from the regenerating liver, were degraded in the in vitro system at a higher rate.

Keywords

regeneration / neutral lipids / microsomes in vitro

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Compliance with ethics guidelines

Anatoly Bozhkov, Natalia Menzyanova, Vadim Davydov, Natalia Kurguzova, Vadim Sidorov, and Anastasia Vasilieva declare that they have no conflict of interest.

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2016 Higher Education Press and Springer-Verlag Berlin Heidelberg