Female Mice are Resistant to Fabp1 Gene Ablation‐Induced Alterations in Brain Endocannabinoid Levels

Abstract

Although liver fatty acid binding protein (FABP1, L-FABP) is not detectable in brain, Fabp1 gene ablation (LKO) markedly increases endocannabinoids (EC) in brains of male mice. Since the brain EC system of females differs significantly from that of males, it was important to determine if LKO differently impacted the brain EC system. LKO did not alter brain levels of arachidonic acid (ARA)-containing ECs, i.e arachidonoylethanolamide (AEA) and 2-arachidonoylglycerol (2-AG), but decreased non-ARA-containing N-acylethanolamides (OEA, PEA) and 2-oleoylglycerol (2-OG) that potentiate the actions of AEA and 2-AG. These changes in brain potentiating EC levels were not associated with: i) a net decrease in levels of brain membrane proteins associated with fatty acid uptake and EC synthesis; ii) a net increase in brain protein levels of cytosolic EC chaperones and enzymes in EC degradation; or iii) increased brain protein levels of EC receptors (CB1, TRVP1). Instead, the reduced or opposite responsiveness of female brain EC levels to loss of FABP1 (LKO) correlated with intrinsically lower FABP1 level in livers of WT females than males. These data show that female mouse brain endocannabinoid levels were unchanged (AEA, 2-AG) or decreased (OEA, PEA, 2-OG) by complete loss of FABP1 (LKO).

Ablating both Fabp1 and Scp2/Scpx (TKO) induces hepatic phospholipid and cholesterol accumulation in high fat-fed mice

“…Second, protein sterol carrier protein-2 (SCP2, encoded by the Scp2/Scpx gene) also binds/chaperones such lipidic ligands. SCP2 binds, transports, and targets bound lipidic ligands such as long chain fatty acids and their CoA thioesters [19,27,28], endocannabinoids [61,70], bile acids [32], cholesterol [101,111], and phospholipids [20,31,105] to intracellular organelles for storage, oxidation, excretion, or receptor regulation. Although ablating the Scp2/Scpx gene decreases hepatic lipid accumulation in control rodent chow-fed male mice [56], the impact of sex differences especially in the context of HFD are unclear.…”

Sterol Carrier Protein‐2/Sterol Carrier Protein‐x/Fatty Acid Binding Protein‐1 Ablation Impacts Response of Brain Endocannabinoid to High‐Fat Diet

“…Both male and female mice were pair‐fed instead of ad libitum fed HFD to avoid: (1) strong preference of mice for and consumption of more HFD than normal chow (Douglass et al, ); (2) concomitant ad libitum fed HFD‐induced upregulation of hepatic FABP1 (Baumgardner et al, ; Gaemers et al, ); and (3) potential brain EC gender differences in response to HFD and TKO (Fengler et al, ; Martin et al, , b, ). Pair‐feeding HFD to 8–week‐old mice was performed for 12 weeks (Martin et al, ; Milligan et al, ).…”

“…Brain lipids were extracted by a modification of an established procedure (Wang et al, ). In this modification (Martin et al, , b, ), 2000 pg each of deuterated internal standards (AEA‐d 4 , OEA‐d 2 , PEA‐d 4 , DHEA‐d 4 , EPEA‐d 4 , and 2‐AG‐d 8 ) was added to 1.0 mL of ice‐cold homogenization buffer (10 mM potassium phosphate, pH 8.0/1 mM dithiothreitol), and the internal standard/buffer was added to a 100–200 mg (wet weight) portion of frozen mouse brain. Deuterated internal standards were added prior to the extraction process in order to allow correction for any metabolite losses during the extraction process.…”

“…Protein was quantified using a modified Bradford protein assay with bovine serum albumin as protein standard (Murphy and Horrocks, ). Individual NAE or 2‐MG in aliquots of the above brain lipid extracts were resolved, identified, and quantified by LC/MS using the above deuterated internal standards and external standard curves (50, 100, 250, 500, 1000, 2500, 5000, 10,000, 25,000, 50,000 pg of each metabolite) as described earlier by our lab (Martin et al, , b, ).…”

“…Nevertheless, ablation of the Fabp1 gene (LKO) in male mice dramatically increased brain AEA and 2‐AG (Martin et al, , ). Interestingly, in females, the brain AEA and 2‐AG levels are less impacted by LKO—likely due to their much lower basal level of FABP1 and potentially also due to the selective LKO‐induced reduction in brain SCP‐2 level in females (Martin et al, , b). Thus, deletion of a peripheral cytosolic lipidic/lipophilic ligand binding/“Chaperone” protein, highly expressed in cytosol of nonbrain tissues of the gastrointestinal tract (but not brain), markedly impacts brain EC level (Martin et al, , ).…”