Hepatic phenotype of liver fatty acid binding protein gene-ablated mice

Abstract

Although the function of liver fatty acid binding protein in hepatic fatty acid metabolism has been extensively studied, its potential role in hepatic cholesterol homeostasis is less clear. Although hepatic cholesterol accumulation was initially reported in L-FABP-null female mice, that study was performed with early N2 backcross generation mice. To resolve whether the hepatic cholesterol phenotype in these L-FABP(-/-) mice was attributable to genetic inhomogeneity, these L-FABP(-/-) mice were further backcrossed to C57Bl/6 mice up to the N10 (99.9% homogeneity) generation. Hepatic total cholesterol accumulation was observed in female, but not male, L-FABP(-/-) mice at all (N2, N4, N6, N10) backcross generations examined. The greater total cholesterol was due to increased hepatic levels of both unesterified (free) cholesterol and esterified cholesterol. Altered hepatic cholesterol accumulation correlated directly with L-FABP's ability to bind cholesterol with high affinity as shown by direct L-FABP binding of fluorescent cholesterol analogs (NBD-cholesterol, dansyl-cholesterol), a photoactivatable cholesterol analog [free cholesterol benzophenone (FCBP)], and free cholesterol (circular dichroism, isothermal titration microcalorimetry). One mole of fluorescent sterol was bound per mole of L-FABP. This was confirmed by photo-cross-linking studies with the photoactivatable cholesterol analog FCBP and by isothermal titration calorimetry with free cholesterol, which showed that L-FABP bound only one sterol molecule per L-FABP molecule. In contrast, the hepatic phenotype of male, but not female, L-FABP(-/-) mice was characterized by decreased hepatic triacylglycerol levels at all backcross generations examined. Taken together, these data support the hypothesis that L-FABP plays a role in physiological regulation of not only hepatic fatty acid metabolism, but also that of hepatic cholesterol.

Recent insights into the biological functions of liver fatty acid binding protein 1

“…Both lines of mice exhibit some similar phenotypes with the human FABP1 T94A variants, such as defective hepatic fatty acid uptake, oxidation, VLDL secretion, and triglyceride metabolism ( 100,(104)(105)(106)(107)(108)(109)(110). However, results of studies on the roles of FABP1 in obesity and by guest, on May 10, 2018 www.jlr.org Downloaded from models.…”

Loss of liver FA binding protein significantly alters hepatocyte plasma membrane microdomains

“…Hepatocyte cytosol is especially rich in the cholesterol binding/transport proteins SCP-2 and L-FABP ( 20,44,53,54 ). Studies with overexpression and gene-ablated mice have shown that both L-FABP ( 24,33,34,(55)(56)(57) and SCP-2 ( 58-60 ) play important roles in hepatic cholesterol accumulation and biliary cholesterol effl ux. Consequently, we hypothesized both SCP-2 and L-FABP to be candidate proteins regulating cholesterol distribution and properties within cholesterol-rich versus cholesterol-poor microdomains in microdomains.…”

“…L-FABP gene ablation increased hepatic cholesterol accumulation in mice ( 24,33 ). L-FABP upregulation in SCP-2-/SCP-x-null mice decreased hepatic cholesterol concomitant with biliary hypersecretion of cholesterol ( 34 ).…”

“…[20][21][22][23], increasing evidence also suggests a role for L-FABP in intracellular cholesterol traffi cking. L-FABP bound two different fl uor escent sterol probes, NBD -cholesterol and dansyl-cholestanol, with similar affi nity as sterol carrier protein-2 (SCP-2) ( 24,25 ) and L-FABP cross-linked with a photoactivatable cholesterol derivative ( 3 H-FCBP) ( 24 ). Both purifi ed-protein and cultured-cell studies suggested roles for L-FABP in cholesterol transfer from the plasma membrane to intracellular sites.…”

Intracellular cholesterol transport proteins enhance hydrolysis of HDL-CEs and facilitate elimination of cholesterol into bile

“…To date several sterol carrier/transport proteins have been identified, including the two high affinity cholesterol binding proteins present in hepatocyte cytosol, namely, sterol carrier protein 2 (SCP2) (7) and fatty acid binding protein-1 (FABP1) (8)(9)(10)(11). SCP2 is thought to be involved in the delivery of FC to the endoplasmic reticulum for ACATdependent esterification (12) and in facilitating the transport of HDL-derived FC to the canalicular membrane for secretion into bile (10).…”