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TBC1D4 (AS160) and TBC1D1 are Rab GTPase-activating proteins that play a key role in the regulation of glucose and possibly the transport of long chain fatty acids (LCFAs) into muscle and fat cells. Knockdown (KD) of TBC1D4 increased CD36/SR-B2 and FABPpm protein expressions in L6 myotubes, whereas in murine cardiomyocytes, TBC1D4 deficiency led to a redistribution of CD36/SR-B2 to the sarcolemma. In our study, we investigated the previously unexplored role of both Rab-GAPs in LCFAs uptake in human adipocytes differentiated from the ADMSCs of subcutaneous and visceral adipose tissue origin. To this end we performed a single- and double-knockdown of the proteins (TBC1D1 and TBC1D4). Herein, we provide evidence that AS160 mediates fatty acid entry into the adipocytes derived from ADMSCs. TBC1D4 KD resulted in quite a few alterations to the cellular phenotype, the most obvious of which was the shift of the CD36/SR-B2 transport protein to the plasma membrane. The above translated into an increased uptake of saturated long-chain fatty acid. Interestingly, we observed a tissue-specific pattern, with more pronounced changes present in the adipocytes derived from subADMSCs. Altogether, our data show that in human adipocytes, TBC1D4, but not TBC1D1, deficiency increases LCFAs transport via CD36/SR-B2 translocation.

A prominent example of seasonal phenotypic flexibility is the winter increase in thermogenic capacity (=summit metabolism, [Formula: see text]) in small birds, which is often accompanied by increases in pectoralis muscle mass and lipid catabolic capacity. Temperature or photoperiod may be drivers of the winter phenotype, but their relative impacts on muscle remodeling or lipid transport pathways are little known. We examined photoperiod and temperature effects on pectoralis muscle expression of myostatin, a muscle growth inhibitor, and its tolloid-like protein activators (TLL-1 and TLL-2), and sarcolemmal and intracellular lipid transporters in dark-eyed juncos Junco hyemalis. We acclimated winter juncos to four temperature (3 °C or 24 °C) and photoperiod [short-day (SD) = 8L:16D; long-day (LD) = 16L:8D] treatments. We found that myostatin, TLL-1, TLL-2, and lipid transporter mRNA expression and myostatin protein expression did not differ among treatments, but treatments interacted to influence lipid transporter protein expression. Fatty acid translocase (FAT/CD36) levels were higher for cold SD than for other treatments. Membrane-bound fatty acid binding protein (FABPpm) levels, however, were higher for the cold LD treatment than for cold SD and warm LD treatments. Cytosolic fatty acid binding protein (FABPc) levels were higher on LD than on SD at 3 °C, but higher on SD than on LD at 24 °C. Cold temperature groups showed upregulation of these lipid transporters, which could contribute to elevated Msum compared to warm groups on the same photoperiod. However, interactions of temperature or photoperiod effects on muscle remodeling and lipid transport pathways suggest that these effects are context-dependent.

[Purpose] Pueraria lobata/rehmannia glutinosa (PR) and exercise have been receiving a lot of attention from postmenopausal women, as a result of the side effects of estrogen replacement therapy. However, the effects of PR and exercise on fatty acid transporters (FATPs), which play essential role in fatty acid transport, have not been studied. In this study, we evaluated the effects of PR and aerobic exercise on FATP1, FABPpm and FAT/CD36 expression in ovariectomized rat skeletal muscles. [Methods] Sixty rats were randomly divided into 6 groups: (1)HSV; high fat diet (HFD)+sedentary+vehicle, (2)HSP; HFD+sedentary+PR, (3)HSH; HFD+sedentary+17β-estradiol, (4)HEV; HFD+exercise+vehicle, (5) HEP; HFD+exercise+PR, (6)HEH; HFD+exercise+17β-estradiol. Exercise consisted of treadmill exercise (1-4th week: 15 m/min for 30 min, 5-8th week: 18 m/min for 40 min, 5 times/week). [Results] Exercise does not alter FATP1 and FAT/CD36 gene levels in soleus and plantaris muscles. In contrast, exercise had main effect on up-regulation of FABPpm mRNA expression in both muscles. However, FABPpm level was not increased by exercise combined with treatments, indicative of no additive effects of PR or hormone on FABPpm gene expression. On the other hand, immunohistochemistry result showed that translocation of FATPs proteins to plasma membrane were higher in PR, exercise groups, and exercise combined with PR groups in both muscles. [Conclusion] These result showed that aerobic exercise and PR may help increase fat-oxidation through the induction of FABPpm, a muscle specific transporter, in OVX rat skeletal muscles. In addition, FABPpm expression is possibly regulated post-transcriptionally in exercise, or pre-translationally in PR.

PGC-1α coactivator plays a decisive role in the maintenance of lipid balance via engagement in numerous metabolic processes (i.e., Krebs cycle, β-oxidation, oxidative phosphorylation and electron transport chain). It constitutes a link between fatty acids import and their complete oxidation or conversion into bioactive fractions through the coordination of both the expression and subcellular relocation of the proteins involved in fatty acid transmembrane movement. Studies on cell lines and/or animal models highlighted the existence of an upregulation of the total and mitochondrial FAT/CD36, FABPpm and FATPs content in skeletal muscle in response to PGC-1α stimulation. On the other hand, the association between PGC-1α level or activity and the fatty acids transport in the heart and adipocytes is still elusive. So far, the effects of PGC-1α on the total and sarcolemmal expression of FAT/CD36, FATP1, and FABPpm in cardiomyocytes have been shown to vary in relation to the type of PPAR that was coactivated. In brown adipose tissue (BAT) PGC-1α knockdown was linked with a decreased level of lipid metabolizing enzymes and fatty acid transporters (FAT/CD36, FABP3), whereas the results obtained for white adipose tissue (WAT) remain contradictory. Furthermore, dysregulation in lipid turnover is often associated with insulin intolerance, which suggests the coactivator's potential role as a therapeutic target.

To support the high energetic demands of reproduction, female mammals display plasticity in many physiological processes, such as the lipid transport system. Lipids support the energy demands of females during reproduction, and energy and structural demands of the developing offspring via the placenta in utero or milk during the suckling period. We hypothesized that key proteins supporting lipid transport in reproductive females will increase during pregnancy and lactation, but drop to non-reproductive levels shortly after reproduction has ended. We compared the relative protein levels of liver-type cytosolic fatty acid transporter (L-FABPc), plasma membrane fatty acid transporter (FABPpm), fatty acid translocase (FAT/CD36) in the liver, a key site of lipid storage and synthesis, and free fatty acid transporter albumin and triglyceride transporter [represented by apolipoprotein B (apoB)] levels in serum in reproductive Sprague-Dawley rats during late pregnancy, peak-lactation, and 1-week post-lactation as well as in non-reproductive rats. We found that all lipid transporter levels were greater in pregnant rats compared to non-reproductive rats. Lactating rats also showed higher levels of FAT/CD36 and FABPpm than non-reproductive rats. Moreover, all fat transporters also dropped back to non-reproductive levels during post-lactation except for FAT/CD36. These results indicate that fat uptake and transport capacities in liver cells are elevated during late gestation and lactation. Liver lipid secretion is up-regulated during gestation but not during lactation. These data supported the plasticity of lipid transport capacities in liver and blood during reproductive stages.

Protein-mediated LCFA transport across plasma membranes is highly regulated by the fatty acid transporters FAT/CD36 and FABPpm. Physiologic stimuli (insulin stimulation, AMP kinase activation) induce the translocation of one or both transporters to the plasma membrane and increase the rate of LCFA transport. In the hypoxic/ischemic heart, intramyocardial lipid accumulation has been attributed to a reduced rate of fatty acid oxidation. However, since acute hypoxia (15 min) activates AMPK, we examined whether an increased accumulation of intramyocardial lipid during hypoxia was also attributable to an increased rate of LCFA uptake as a result AMPK-induced translocation of FAT/CD36 and FABPpm. In cardiac myocytes, hypoxia (15 min) induced the redistribution of FAT/CD36 from an intracellular pool (LDM) (−25%, P < 0.05) to the plasma membranes (PM) (+54%, P < 0.05). Hypoxia also induced an increase in FABPpm at the PM (+56%, P < 0.05) and a concomitant FABPpm reduction in the LDM (−24%, P < 0.05). Similarly, in intact, Langendorff perfused hearts, hypoxia induced the translocation of a both FAT/CD36 and FABPpm to the PM (+66% and +61%, respectively, P < 0.05), with a concomitant decline in FAT/CD36 and FABPpm in the LDM (−24% and −23%, respectively, P < 0.05). Importantly, the increased plasmalemmal content of these transporters was associated with increases in the initial rates of palmitate uptake into cardiac myocytes (+40%, P < 0.05). Acute hypoxia also redirected palmitate into intracellular lipid pools, mainly to PL and TG (+48% and +28%, respectively, P < 0.05), while fatty acid oxidation was reduced (−35%, P < 0.05). Thus, our data indicate that the increased intracellular lipid accumulation in hypoxic hearts is attributable to both: (a) a reduced rate of fatty acid oxidation and (b) an increased rate of fatty acid transport into the heart, the latter being attributable to a hypoxia-induced translocation of fatty acid transporters.

Cellular fatty acid uptake is facilitated by a number of fatty acid transporters, FAT/CD36, FABPpm and FATP1. It had been presumed that FABPpm, was confined to the plasma membrane and was not regulated. Here, we demonstrate for the first time that FABPpm and FATP1 are also present in intracellular depots in cardiac myocytes. While we confirmed previous work that insulin and AICAR each induced the translocation of FAT/CD36 from an intracellular depot to the PM, only AICAR, but not insulin, induced the translocation of FABPpm. Moreover, neither insulin nor AICAR induced the translocation of FATP1. Importantly, the increased plasmalemmal content of these LCFA transporters was associated with a concomitant increase in the initial rate of palmitate uptake into cardiac myocytes. Specifically, the insulin-stimulated increase in the rate of palmitate uptake (+60%) paralleled the insulin-stimulated increase in plasmalemmal FAT/CD36 (+34%). Similarly, the greater AICAR-stimulated increase in the rate of palmitate uptake (+90%) paralleled the AICAR-induced increase in both plasmalemmal proteins (FAT/CD36 (+40%)+FABPpm (+36%)). Inhibition of palmitate uptake with the specific FAT/CD36 inhibitor SSO indicated that FABPpm interacts with FAT/CD36 at the plasma membrane to facilitate the uptake of palmitate. In conclusion, (1) there appears to be tissue-specific sensitivity to insulin-induced FATP1 translocation, as it has been shown elsewhere that insulin induces FATP1 translocation in 3T3-L1 adipocytes, and (2) clearly, the subcellular distribution of FABPpm, as well as FAT/CD36, is acutely regulated in cardiac myocytes, although FABPpm and FAT/CD36 do not necessarily respond identically to the same stimuli.

Giant sarcolemmal vesicles were isolated from rat heart and hindlimb muscles for a) characterization of long-chain fatty acid transport in the absence of metabolism and b) comparison of fatty acid transport protein expression with fatty acid transport. Giant vesicles contained cytosolic fatty acid binding protein. Palmitate uptake was completely divorced from its metabolism. All palmitate taken up was recovered in the intravesicular cytosol as unesterified FA. Palmitate uptake by heart vesicles exhibited a Km of 9.7 nm, similar to that of muscle (Km = 9.7 nm). Vmax (2.7 pmol/mg protein/s) in heart was 8-fold higher than in muscle (0.34 pmol/mg protein/s). Palmitate uptake was inhibited in heart (55–80%) and muscle (31–50%) by trypsin, phloretin, sulfo-N-succinimidyloleate (SSO), or a polyclonal antiserum against the 40 kDa plasma membrane fatty acid binding protein (FABPpm). Palmitate uptake by heart and by red and white muscle vesicles correlated well with the expression of fatty acid translocase (FAT/CD36) and fatty acid binding protein FABPpm, which may act in concert. The expression of fatty acid transport protein (FATP), was 10-fold lower in heart vesicles than in white muscle vesicles. It is concluded that long-chain fatty acid uptake by heart and muscle vesicles is largely protein-mediated, involving FAT/CD36 and FABPpm. The role of FATP in muscle and heart remains uncertain.—Luiken, J. J. F. P., L. P. Turcotte, and A. Bonen. Protein-mediated palmitate uptake and expression of fatty acid transport proteins in heart giant vesicles. J. Lipid Res. 1999. 40: 1007–1016.

Insulin-, and contraction-induced GLUT4 and fatty acid (FA) transporter translocation may share common trafficking mechanisms. Our objective was to examine the effects of partial Munc18c ablation on muscle glucose and FA transport, FA oxidation, GLUT4 and FA transporter (FAT/CD36, FABPpm, FATP1, FATP4) trafficking to the sarcolemma, and FAT/CD36 to mitochondria. In Munc18c−/+ mice, insulin-stimulated glucose transport and GLUT4 sarcolemmal appearance were impaired, but were unaffected by contraction. Insulin- and contraction-stimulated FA transport, sarcolemmal FA transporter appearance, and contraction-mediated mitochondrial FAT/CD36 were increased normally in Munc18c−/+ mice. Hence, Munc18c provides stimulus-specific regulation of GLUT4 trafficking, but not FA transporter trafficking.