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Endogenous GLP-1 as a key self-defense molecule against lipotoxicity in pancreatic islets.

Huang C, Yuan L, Cao S - Int. J. Mol. Med. (2015)

Bottom Line: Prolonged exposure to palmitate increased reactive oxygen species (ROS) production, and the antioxidant, N-acetylcysteine (NAC), partially prevented the detrimental effects induced by palmitate on β cells, resulting in decreased GLP-1 levels.Moreover, treatment with the GLP-1R agonist, liraglutide, normalized islet structure and function, resulting in a decrease in cell death and in the amelioration of β cell marker expression.Importantly, liraglutide maintained the oxidative balance and decreased inflammatory factor and p65 expression.

View Article: PubMed Central - PubMed

Affiliation: Department of Endocrinology, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei 430022, P.R. China.

ABSTRACT
The number of pro-α cells is known to increase in response to β cell injury and these cells then generate glucagon-like peptide-1 (GLP-1), thus attenuating the development of diabetes. The aim of the present study was to further examine the role and the mechanisms responsible for intra-islet GLP-1 production as a self-protective response against lipotoxicity. The levels of the key enzyme, prohormone convertase 1/3 (PC1/3), as well as the synthesis and release of GLP-1 in models of lipotoxicity were measured. Furthermore, islet viability, apoptosis, oxidative stress and inflammation, as well as islet structure were assessed after altering GLP-1 receptor signaling. Both prolonged exposure to palmitate and a high-fat diet facilitated PC1/3 expression, as well as the synthesis and release of GLP-1 induced by β cell injury and the generation of pro-α cells. Prolonged exposure to palmitate increased reactive oxygen species (ROS) production, and the antioxidant, N-acetylcysteine (NAC), partially prevented the detrimental effects induced by palmitate on β cells, resulting in decreased GLP-1 levels. Furthermore, the inhibition of GLP-1 receptor (GLP-1R) signaling by treatment with exendin‑(9-39) further decreased cell viability, increased cell apoptosis and caused a stronger inhibition of the β cell-specific transcription factor, pancreatic duodenal homeobox 1 (PDX1). Moreover, treatment with the GLP-1R agonist, liraglutide, normalized islet structure and function, resulting in a decrease in cell death and in the amelioration of β cell marker expression. Importantly, liraglutide maintained the oxidative balance and decreased inflammatory factor and p65 expression. Overall, our data demonstrate that an increase in the number of pro-α cells and the activation of the intra-islet GLP-1 system comprise a self-defense mechanism for enhancing β cell survival to combat lipid overload, which is in part mediated by oxidative stress and inflammation.

No MeSH data available.


Related in: MedlinePlus

Prolonged exposure to palmitate induces reactive oxygen species (ROS) productin and activates the glucagon-like peptide-1 (GLP-1) system. (A) Following incubation with 0.5 mmol/l palmitate for the indicated periods of time, ROS levels were detected by DCFH-DA. Following pre-incubation with 5 mmol/l N-acetylcysteine (NAC) for 48 h, cell (B) viability (by MTT assay) and (C) apoptosis (by examining histone-associated DNA fragments), and (D) prohormone convertase 1/3 (PC1/3) mRNA (by qPCR) and (E) GLP-1 levels (by ELISA) in the cell lysates were determined. n=3 separate isolated islet preparations; *p<0.05; **p<0.01; ***p<0.001.
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f7-ijmm-36-01-0173: Prolonged exposure to palmitate induces reactive oxygen species (ROS) productin and activates the glucagon-like peptide-1 (GLP-1) system. (A) Following incubation with 0.5 mmol/l palmitate for the indicated periods of time, ROS levels were detected by DCFH-DA. Following pre-incubation with 5 mmol/l N-acetylcysteine (NAC) for 48 h, cell (B) viability (by MTT assay) and (C) apoptosis (by examining histone-associated DNA fragments), and (D) prohormone convertase 1/3 (PC1/3) mRNA (by qPCR) and (E) GLP-1 levels (by ELISA) in the cell lysates were determined. n=3 separate isolated islet preparations; *p<0.05; **p<0.01; ***p<0.001.

Mentions: Incubation of the cells with 0.5 mmol/l palmitate for 24, 48 or 72 h markedly increased the intra-islet ROS levels by approximately 3.01-, 5.12- and 6.45-fold, respectively (Fig. 7A). In addition, pre-incubation with 5 mmol/l NAC, neutralized the harmful effects of palmitate, increased islet viability (by 1.43-fold; Fig. 7B) and decreased apoptosis by approximately 64.84% (Fig. 7C) in the presence of 0.5 mmol/l palmitate. Importantly, NAC significantly decreased the PC1/3 mRNA levels (Fig. 7D) and the GLP-1 concentration in the cell lysates (Fig. 7E), which may be due to the attenuation of β cell injury. Nonetheless, the elevated levels of PC1/3 mRNA (Fig. 7D) and GLP-1 protein, which were induced by palmitate, did not return to normal after NAC treatment (Fig. 7E), suggesting that the inhibition did not completely reverse the detrimental effects of palmitate overload in the pancreatic islets.


Endogenous GLP-1 as a key self-defense molecule against lipotoxicity in pancreatic islets.

Huang C, Yuan L, Cao S - Int. J. Mol. Med. (2015)

Prolonged exposure to palmitate induces reactive oxygen species (ROS) productin and activates the glucagon-like peptide-1 (GLP-1) system. (A) Following incubation with 0.5 mmol/l palmitate for the indicated periods of time, ROS levels were detected by DCFH-DA. Following pre-incubation with 5 mmol/l N-acetylcysteine (NAC) for 48 h, cell (B) viability (by MTT assay) and (C) apoptosis (by examining histone-associated DNA fragments), and (D) prohormone convertase 1/3 (PC1/3) mRNA (by qPCR) and (E) GLP-1 levels (by ELISA) in the cell lysates were determined. n=3 separate isolated islet preparations; *p<0.05; **p<0.01; ***p<0.001.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4494597&req=5

f7-ijmm-36-01-0173: Prolonged exposure to palmitate induces reactive oxygen species (ROS) productin and activates the glucagon-like peptide-1 (GLP-1) system. (A) Following incubation with 0.5 mmol/l palmitate for the indicated periods of time, ROS levels were detected by DCFH-DA. Following pre-incubation with 5 mmol/l N-acetylcysteine (NAC) for 48 h, cell (B) viability (by MTT assay) and (C) apoptosis (by examining histone-associated DNA fragments), and (D) prohormone convertase 1/3 (PC1/3) mRNA (by qPCR) and (E) GLP-1 levels (by ELISA) in the cell lysates were determined. n=3 separate isolated islet preparations; *p<0.05; **p<0.01; ***p<0.001.
Mentions: Incubation of the cells with 0.5 mmol/l palmitate for 24, 48 or 72 h markedly increased the intra-islet ROS levels by approximately 3.01-, 5.12- and 6.45-fold, respectively (Fig. 7A). In addition, pre-incubation with 5 mmol/l NAC, neutralized the harmful effects of palmitate, increased islet viability (by 1.43-fold; Fig. 7B) and decreased apoptosis by approximately 64.84% (Fig. 7C) in the presence of 0.5 mmol/l palmitate. Importantly, NAC significantly decreased the PC1/3 mRNA levels (Fig. 7D) and the GLP-1 concentration in the cell lysates (Fig. 7E), which may be due to the attenuation of β cell injury. Nonetheless, the elevated levels of PC1/3 mRNA (Fig. 7D) and GLP-1 protein, which were induced by palmitate, did not return to normal after NAC treatment (Fig. 7E), suggesting that the inhibition did not completely reverse the detrimental effects of palmitate overload in the pancreatic islets.

Bottom Line: Prolonged exposure to palmitate increased reactive oxygen species (ROS) production, and the antioxidant, N-acetylcysteine (NAC), partially prevented the detrimental effects induced by palmitate on β cells, resulting in decreased GLP-1 levels.Moreover, treatment with the GLP-1R agonist, liraglutide, normalized islet structure and function, resulting in a decrease in cell death and in the amelioration of β cell marker expression.Importantly, liraglutide maintained the oxidative balance and decreased inflammatory factor and p65 expression.

View Article: PubMed Central - PubMed

Affiliation: Department of Endocrinology, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei 430022, P.R. China.

ABSTRACT
The number of pro-α cells is known to increase in response to β cell injury and these cells then generate glucagon-like peptide-1 (GLP-1), thus attenuating the development of diabetes. The aim of the present study was to further examine the role and the mechanisms responsible for intra-islet GLP-1 production as a self-protective response against lipotoxicity. The levels of the key enzyme, prohormone convertase 1/3 (PC1/3), as well as the synthesis and release of GLP-1 in models of lipotoxicity were measured. Furthermore, islet viability, apoptosis, oxidative stress and inflammation, as well as islet structure were assessed after altering GLP-1 receptor signaling. Both prolonged exposure to palmitate and a high-fat diet facilitated PC1/3 expression, as well as the synthesis and release of GLP-1 induced by β cell injury and the generation of pro-α cells. Prolonged exposure to palmitate increased reactive oxygen species (ROS) production, and the antioxidant, N-acetylcysteine (NAC), partially prevented the detrimental effects induced by palmitate on β cells, resulting in decreased GLP-1 levels. Furthermore, the inhibition of GLP-1 receptor (GLP-1R) signaling by treatment with exendin‑(9-39) further decreased cell viability, increased cell apoptosis and caused a stronger inhibition of the β cell-specific transcription factor, pancreatic duodenal homeobox 1 (PDX1). Moreover, treatment with the GLP-1R agonist, liraglutide, normalized islet structure and function, resulting in a decrease in cell death and in the amelioration of β cell marker expression. Importantly, liraglutide maintained the oxidative balance and decreased inflammatory factor and p65 expression. Overall, our data demonstrate that an increase in the number of pro-α cells and the activation of the intra-islet GLP-1 system comprise a self-defense mechanism for enhancing β cell survival to combat lipid overload, which is in part mediated by oxidative stress and inflammation.

No MeSH data available.


Related in: MedlinePlus