Limits...
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 the activation of the glucagon-like peptide-1 (GLP-1) system in isolated mouse islets. After the islet cells were incubated with 0.5 mmol/l palmitate for the indicated periods of time, the GLP-1 levels in the (A) cell medium and (B) lysates were determined by insulin enzyme-linked immunosorbent assay (ELISA), and (C) prohormone convertase 1/3 (PC1/3) mRNA expression in cell lysates was determined by qPCR and (D) the PC1/3 protein level was determined by immunoblot anlaysis. n=3 separate islet preparations; **p<0.01; ***p<0.001.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4494597&req=5

f2-ijmm-36-01-0173: Prolonged exposure to palmitate induces the activation of the glucagon-like peptide-1 (GLP-1) system in isolated mouse islets. After the islet cells were incubated with 0.5 mmol/l palmitate for the indicated periods of time, the GLP-1 levels in the (A) cell medium and (B) lysates were determined by insulin enzyme-linked immunosorbent assay (ELISA), and (C) prohormone convertase 1/3 (PC1/3) mRNA expression in cell lysates was determined by qPCR and (D) the PC1/3 protein level was determined by immunoblot anlaysis. n=3 separate islet preparations; **p<0.01; ***p<0.001.

Mentions: Importantly, incubation of the cells with 0.5 mmol/l palmitate for 24, 48 or 72 h markedly induced the release of GLP-1 into the culture medium by 3.15-, 6.55- and 5.62-fold, respectively (Fig. 2A). Moreover, in line with the observations of the culture medium, the GLP-1 concentration in the cell lysates was elevated and showed an even greater increase (Fig. 2B). Nonetheless, the GLP-1 levels at 72 h in both the cell medium and the cell lysates were almost equivalent to those at 48 h and even showed a decreasing trend (Fig. 2A and B), which may be due to the severe serious injury induced by 72 h of exposure to palmitate (Fig. 1A and B; increased apoptosis and decreased cell viability). Following prolonged exposure to palmitate, the mRNA (Fig. 2C) and protein levels (Fig. 2D) of PC1/3, the key enzyme of GLP-1 generation, also increased (48 h of exposure resulted in higher mRNA and protein levels than 72 h of exposure).


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 the activation of the glucagon-like peptide-1 (GLP-1) system in isolated mouse islets. After the islet cells were incubated with 0.5 mmol/l palmitate for the indicated periods of time, the GLP-1 levels in the (A) cell medium and (B) lysates were determined by insulin enzyme-linked immunosorbent assay (ELISA), and (C) prohormone convertase 1/3 (PC1/3) mRNA expression in cell lysates was determined by qPCR and (D) the PC1/3 protein level was determined by immunoblot anlaysis. n=3 separate islet preparations; **p<0.01; ***p<0.001.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f2-ijmm-36-01-0173: Prolonged exposure to palmitate induces the activation of the glucagon-like peptide-1 (GLP-1) system in isolated mouse islets. After the islet cells were incubated with 0.5 mmol/l palmitate for the indicated periods of time, the GLP-1 levels in the (A) cell medium and (B) lysates were determined by insulin enzyme-linked immunosorbent assay (ELISA), and (C) prohormone convertase 1/3 (PC1/3) mRNA expression in cell lysates was determined by qPCR and (D) the PC1/3 protein level was determined by immunoblot anlaysis. n=3 separate islet preparations; **p<0.01; ***p<0.001.
Mentions: Importantly, incubation of the cells with 0.5 mmol/l palmitate for 24, 48 or 72 h markedly induced the release of GLP-1 into the culture medium by 3.15-, 6.55- and 5.62-fold, respectively (Fig. 2A). Moreover, in line with the observations of the culture medium, the GLP-1 concentration in the cell lysates was elevated and showed an even greater increase (Fig. 2B). Nonetheless, the GLP-1 levels at 72 h in both the cell medium and the cell lysates were almost equivalent to those at 48 h and even showed a decreasing trend (Fig. 2A and B), which may be due to the severe serious injury induced by 72 h of exposure to palmitate (Fig. 1A and B; increased apoptosis and decreased cell viability). Following prolonged exposure to palmitate, the mRNA (Fig. 2C) and protein levels (Fig. 2D) of PC1/3, the key enzyme of GLP-1 generation, also increased (48 h of exposure resulted in higher mRNA and protein levels than 72 h of exposure).

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