Linoleic acid stimulates gluconeogenesis via Ca²⁺/PLC, cPLA₂, and PPAR pathways through GPR40 in primary cultured chicken hepatocytes

Abstract

Fatty acids serve vital functions as sources of energy, building materials for cellular structures, and modulators of physiological responses. Therefore, this study examined the effect of linoleic acid on glucose production and its related signal pathways in primary cultured chicken hepatocytes. Linoleic acid (double-unsaturated, long chain) increased glucose production in a dose (> or =10(-4) M)- and time (> or =8 h)-dependent manner. Both oleic acid (monounsaturated, long chain) and palmitic acid (saturated, long chain) also increased glucose production, whereas caproic acid (saturated, short chain) failed to increase glucose production. Linoleic acid increased G protein-coupled receptor 40 (GPR40; also known as free fatty acid receptor-1) protein expression and glucose production that was blocked by GPR40-specific small interfering RNA. Linoleic acid increased intracellular calcium concentration, which was blocked by EGTA (extracellular calcium chelator)/BAPTA-AM (intracellular calcium chelator), U-73122 (phospholipase C inhibitor), nifedipine, or methoxyverapamil (L-type calcium channel blockers). Linoleic acid increased cytosolic phospholipase A(2) (cPLA(2)) phosphorylation and the release of [(3)H]-labeled arachidonic acid. Moreover, linoleic acid increased the level of cyclooxygenase-2 (COX-2) protein expression, which stimulated the synthesis of prostaglandin E(2) (PGE(2)). The increase in PGE(2) production subsequently stimulated peroxisome proliferator-activated receptor (PPAR) expression, and MK-886 (PPAR-alpha antagonist) and GW-9662 (PPAR-delta antagonist) inhibited glucose-6-phosphatase and phosphoenolpyruvate carboxykinase. In addition, linoleic acid-induced glucose production was blocked by inhibition of extracellular and intracellular calcium, cPLA(2), COX-2, or PPAR pathways. In conclusion, linoleic acid promoted glucose production via Ca(2+)/PLC, cPLA(2)/COX-2, and PPAR pathways through GPR40 in primary cultured chicken hepatocytes.

Inflammation and insulin resistance induced by trans-10, cis-12 conjugated linoleic acid depend on intracellular calcium levels in primary cultures of human adipocytes

“…In agreement with other studies, the phosphatidylcholine-specifi c (PC)-PLC inhibitor D609 ( Fig. 5A ) ] i levels via conversion of diacylglycerol (DAG) by DAG kinase to phosphatidic acid, which mobilizes calcium from inositiol-3-phosphate-independent calcium pools ( 26,(31)(32)(33). Therefore, it appears that 10,12 CLA initially stimulates an effl ux of calcium from intracellular stores like the ER, followed by calcium has been reported to increase [Ca 2+ ] i levels and activate CaMKII in murine adipocytes, leading to decreased adipocyte differentiation ( 23 ).…”

Diacylglycerol kinase inhibitor R59022 attenuates conjugated linoleic acid-mediated inflammation in human adipocytes

“…An alternative mechanism has been proposed by Camina and colleagues, whereby PC-specifi c PLC, activated by a pertussis toxin-sensitive Gprotein, generates choline and DAG, which is converted into PA by DGKs. Subsequently, PA triggers calcium mobilization from IP3-independent calcium pools ( 18,(26)(27)(28).…”

Oleic acid activates peroxisome proliferator-activated receptor δ to compensate insulin resistance in steatotic cells

“…Moreover, elevated expression of PPARδ by OA negatively regulates PTEN and increased insulin sensitivity to facilitate glycogen synthesis. the precise signalling pathways are unclear [26]. GPR40 is a Gprotein-coupled receptor and highly expressed in brain and pancreatic islet [42] and a large range of both medium-to longchain SFA and UFA are agonists for GPR40 [43].…”

“…Although the functions of PPARδ in muscle and adipose tissue are well investigated, the role of PPARδ in liver is still obscure. In addition, a previous study indicated that linoleic acid, an UFA, up-regulates the expression of PPARδ in liver to stimulate gluconeogenesis [26]. OA decreases the expression of PPARα [27] and increases the expression of PPARγ [28] to facilitate hepatic steatosis.…”