• Journal of Life Science
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• v.26 no.7
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• pp.758-763
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• 2016

Fatty acid transporters are key mediators of skeletal muscle lipid metabolism. Several protein groups have been implicated in cellular long-chain fatty acid uptake or oxidation, including fatty acid transporter proteins (FATPs), the plasma membrane fatty acid-binding protein (FABPpm), and the fatty acid translocase (FAT/CD36). FAT/CD36 is highly expressed in skeletal muscle and known to be regulated by various factors such as exercise and hormones. Insulin-like growth factor-I (IGF-I) is a well-known regulator of skeletal muscle cells. However, it has not been studied whether there is any interaction between IGF-I and FAT/CD36 in skeletal muscle cells. In this study, the effects of IGF-I treatment on FAT/CD36 induction were examined. Differentiated C2C12 cells were treated with 20 ng/ml of IGF-I at different time points. Treatment of C2C12 cells with IGF-I resulted in increased FAT/CD36 mRNA and protein expression. After 24 and 48 hr of IGF-I treatment, FAT/CD36 mRNA increased 89% and 24% respectively. The increase of both proteins returned to the control level after 72 hr of IGF-I treatment, suggesting that the FAT/CD36 gene is regulated pretranslationally by IGF-I in skeletal muscle cells. These results suggest that IGF-I can regulate the expression of FAT/CD36 in skeletal muscle cells. In conclusion, IGF-I induces a rapid transcriptional modification of the FAT/CD36 gene in C2C12 skeletal muscle cells and has modulating effects on fatty acid uptake proteins as well as oxidative proteins.

• Journal of Life Science
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• v.32 no.10
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• pp.762-770
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• 2022

Hyperglycemia in type 2 diabetes can be alleviated by promoting cellular glucose uptake. Betulinic acid (3β,-3-hydroxy-lup-20(29)-en-28-oic acid) is a pentacyclic lupane-type triterpenoid compound. Although there have been studies on the antidiabetic activity of betulinic acid, studies on cellular glucose uptake are lacking. We investigated the effects of betulinic acid on glucose uptake and its mechanism of action in 3T3-L1 adipocytes. Betulinic acid significantly stimulated glucose uptake in 3T3-L1 adipocytes by increasing the phosphorylation of the insulin receptor substrate 1-tyrosine (IRS-1tyr) in the insulin signaling pathway, which in turn stimulated the activation of phosphoinositide 3-kinase (PI3K) and the phosphorylation of protein kinase B (Akt). The activation of PI3K and Akt by betulinic acid translocated glucose transporter 4 to the plasma membrane (PM-GLUT4), thereby increasing the expression of PM-GLUT4 and thus stimulating cellular glucose uptake. Betulinic acid also significantly increased the phosphorylation/activation of AMP-activated protein kinase (AMPK) and acetyl-CoA carboxylase. The activation of PI3K and AMPK by betulinic acid was confirmed using the PI3K inhibitor wortmannin and the AMPK inhibitor compound C. The increase in glucose uptake induced by betulinic acid was significantly decreased by wortmannin and compound C in the 3T3-L1 adipocytes. These results suggest that betulinic acid stimulates glucose uptake by activating PI3K and AMPK in 3T3-L1 adipocytes.

• Journal of Life Science
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• v.33 no.11
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• pp.859-867
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• 2023

Lupeol is a type of pentacyclic triterpene that has been reported to have therapeutic effects for treating many diseases; however, its effect on insulin resistance is unclear clear. This study examined the inhibitory effect of lupeol on the serine phosphorylation of insulin receptor substrate-1 in insulin resistance-induced 3T3-L1 adipocytes. 3T3-L1 cells were cultured and treated with tumor necrosis factor-α (TNF-α) for 24 hours to induce insulin resistance. Cells treated with different concentrations of lupeol (15 μM or 30 μM) or 100 nM of rosiglitazone were incubated. Then, lysed cells underwent western blotting. Lupeol exhibited a positive effect on the negative regulator of insulin signaling and inflammation-activated protein kinase caused by TNF-α in adipocytes. Lupeol inhibited the activation of protein tyrosine phosphatase-1B (PTP-1B)-a negative regulator of insulin signaling-and c-Jun N-terminal kinase (JNK); it was also an inhibitor of nuclear factor kappa-B kinase (IKK) and inflammation-activated protein kinases. In addition, Lupeol downregulated serine phosphorylation and upregulated tyrosine phosphorylation in insulin receptor substrate-1. Then, the downregulated phosphatidylinositol 3-kinase (PI3K)/protein kinase B (AKT) pathway was activated, the translocation of glucose transporter type 4 was stimulated to the cell membrane, and intracellular glucose uptake increased in the insulin resistance-induced 3T3-L1 adipocytes. Lupeol may improve TNF-α-induced insulin resistance by downregulating the serine phosphorylation of insulin receptor substrate 1 by inhibiting negative regulators of insulin signaling and inflammation-activated protein kinases in 3T3-L1 adipocytes.

• Korean Journal of Soil Science and Fertilizer
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• v.36 no.3
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• pp.134-144
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• 2003

A rhizobacterium Pseudomonas cholororaphis O6 produced several secondary metabolites, such as phenazines, protease, and HCN that may be involved in inhibition of the growth of phytopathogenic fungi. In field study, P. chlororaphis O6 treatment on wheat seed suppressed root rot disease caused by Fusarium culmorum. The major organic acids of cucumber root exudates were fumaric acid, malic acid, benzoic acid, and succinic acid. Glucose and fructose were major monosaccharides in cucumber root exudates. The total amount of organic acids was ten times higher than that of the sugars. P. chlororaphis O6 grew well on cucumber root exudates. The dctA gene of P. chlororaphis O6 consisted of a 1,335 bp open reading frame with a deduced amino acid sequence of 444 residues, corresponding to a molecular size of about 47 kD and pI 8.2. The deduced dctA sequence has ten putative transmembrane domains, as expected of a membrane-embedded protein. Our results indicated that organic acids in cucumber root exudates may play an important role in providing nutrient source for root colonization of biological control bacteria, and the dctA gene of P. chlororaphis O6 may be an important bacterial trait that is involved in utilization of root exudates.

• Journal of Life Science
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• v.29 no.5
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• pp.570-579
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• 2019

Diabetes is one of the serious chronic metabolic diseases caused by Westernized eating habits, and the goal of diabetes treatment is to keep blood glucose at a normal level and prevent diabetic complications. This study was designed to investigate the anti-diabetic effects of a mealworm (Tenebrio molitor larva) extract (MWE) on hyperglycemia in an animal model with type 2 diabetes. Diabetic C57BL/Ksj-db/db mice were divided into three groups: diabetic control, rosiglitazone, and MWE. The mice supplemented with MWE showed significantly lower blood levels of glucose and glycosylated hemoglobin when compared with the diabetic control mice. The homeostatic index of insulin resistance was significantly lower in mice supplemented with MWE than in diabetic control mice. MWE supplementation significantly stimulated the phosphorylation of insulin receptor substrate-1 and Akt, and activation of phosphatidylinositol 3-kinase in insulin signaling pathway of skeletal muscles. Eventually, MWE increased the expression of the plasma membrane glucose transporter 4 (GLUT4) via PI3K/Akt activation. These findings demonstrate that the increase in plasma membrane GLUT4 expression by MWE promoted the uptake of blood glucose into cells and relieved hyperglycemia in skeletal muscles of diabetic C57BL/Ksj-db/db mice. Therefore, mealworms are expected to prove useful for the prevention and treatment of diabetes, and further studies are needed to improve type 2 diabetes in the future.

• Korean Journal of Veterinary Research
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• v.36 no.4
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• pp.783-794
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• 1996

It has been suggested that ion transport systems are intimately involved in mediating the effects of growth regulatory factors on the growth of a number of different types of animal cells in vivo. The functional importance of the apical membrane $Na^+/H^+$ antiporter in the renal proximal tubule is evidenced by estimates that this transporter mediates the reabsorption of approximately one third of the filtered load of sodium and the bulk of the secretion of hydrogen ions. This study was designed to investigate the pathway utilized by IGF-I in regulating sodium transport in primary cultured renal proximal tubule cells. Results were as follows : 1. $Na^+$ was observed to accumulate in the primary cells as a function of time. Raising the concentration of extracellular NaCl induced an decrease in $Na^+$ uptake compared with control cells in a dose dependent manner. The rate of $Na^+$ uptake into the primary cells was about two times higher in the absence of NaCl($40.11{\pm}1.76pmole\;Na^+/mg\;protein/min$) than in the presence of 140mM NaCl($17.82{\pm}0.94pmole\;Na^+/mg\;protein/min$) at the 30 minute uptake. 2. $Na^+$ uptake was inhibited by IAA($1{\times}10^{-4}M$) or valinomycin($5{\times}10^{-6}M$) treatment($50.51{\pm}4.04$ and $57.65{\pm}2.27$ of that of control, respectively). $Na^+$ uptake by the primary proximal tubule cells was significantly increased by ouabain($5{\times}10^{-5}M$) treatment($140.23{\pm}3.37%$ of that of control). When actinomycin D($1{\times}10^{-7}M$) or cycloheximide($4{\times}10^{-5}M$) was applied, $Na^+$ uptake was decreased to $90.21{\pm}2.39%$ or $89.64{\pm}3.69%$ of control in IGF-I($1{\times}10^{-5}M$) treated cells, respectively. 3. Extracellular cAMP decreased $Na^+$ uptake in a dose-dependent manner($10^{-8}-10^{-4}M$). IBMX($5{\times}10^{-5}M$) also inhibited $Na^+$ uptake. Treatment of cells with pertussis toxin(50pg/ml) or cholera toxin($1{\mu}g/ml$) inhibited $Na^+$ uptake. Extracellular PMA decreased $Na^+$ uptake in a dose-dependent manner(1-100ng/ml). 100 ng/ml PMA concentration significantly inhibited $Na^+$ uptake in IGF-I treated cells. However, staurosporine($1{\times}10^{-7}M$) had no effect on $Na^+$ uptake. When PMA and staurosporine were added together, the inhibition of $Na^+$ uptake was not observed. In conclusion, sodium uptake in primary cultured rabbit renal proximal tubule cells was dependent on membrane potentials and intracellular energy levels. IGF-I stimulates sodium uptake through mechanisms that involve some degree of de novo protein and/or RNA synthesis, and cAMP and/or PKC pathway mediating the action mechanisms of IGF-I.

• Journal of Yeungnam Medical Science
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• v.14 no.1
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• pp.53-66
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• 1997

Insulin resistance is a prominent feature of diabetic state and has heterogeneous nature. However, the pathogenetic sequence of events leading to the emergence of the defect in insulin action remains controversial. It is well-known that prolonged hyperglycemia and hyperinsulinemia are one of the causes of development of insulin resistance, but both hyperglycemia and hyperinsulinemia stimulate glucose uptake in peripheral tissue. Therefore, it is hypothesized that insulin resistance may be generated by a kind of protective mechanism preventing cellular hypertrophy. In this study, to evaluate whether the acutely increased glucose uptake inhibits further glucose transport stimulated by insulin, insulin sensitivity was measured after preloaded glucose infusion for 2 hours at various conditions in rats. And also, to evaluate the mechanism of decreased insulin sensitivity, insulin receptor binding affinity and glucose transporter 4 (GLUT4) protein of plasma membrane of gastrocnemius muscle were assayed after hyperinsulinemic euglycemic clamp studies. Experimental animals were divided into five groups according to conditions of preloaded glucose infusion: group I, basal insulin ($14{\pm}1.9{\mu}U/ml$) and basal glucose ($75{\pm}0.7mg/dl$), by normal saline infusion; group II, normal insulin ($33{\pm}3.8{\mu}U/ml$) and hyperglycemia ($207{\pm}6.3mg/dl$), by somatostatin and glucose infusion; group III, hyperinsulinemia ($134{\pm}34.8{\mu}U/ml$) and hyperglycemia ($204{\pm}4.6mg/dl$), by glucose infusion; group IV, supramaximal insulin ($5006{\pm}396.1{\mu}U/ml$) and euglycemia ($l00{\pm}2.2mg/dl$), by insulin and glucose infusion; group V, supramaximal insulin ($4813{\pm}687.9{\mu}U/ml$) and hyperglycemia ($233{\pm}3.1mg/dl$), by insulin and glucose infusion. Insulin sensitivity was assessed with hyperinsulinemic euglycemic clamp technique. The amounts of preloaded glucose infusion(gm/kg) were $1.88{\pm}0.151$ in group II, $2.69{\pm}0.239$ in group III, $3.54{\pm}0.198$ in group IV, and $4.32{\pm}0.621$ in group V. Disappearance rates of glucose (Rd, mg/kg/min) at steady state of hyperinsulinemic euglycemic clamp studies were $16.9{\pm}3.88$ in group I, $13.5{\pm}1.05$ in group II, $11.2{\pm}1.17$ in group III, $13.2{\pm}2.05$ in group IV, and $10.4{\pm}1.01$ in group V. A negative correlation was observed between amount of preloaded glucose and Rd (r=-0.701, p<0.001) when all studies were combined. Insulin receptor binding affinity and content of GLUT4 were not significantly different in all experimental groups. These results suggest that increased glucose uptake may inhibit further glucose transport and lead to decreased insulin sensitivity.