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Endoplasmic reticulum stress regulates adipocyte resistin expression.

Lefterova MI, Mullican SE, Tomaru T, Qatanani M, Schupp M, Lazar MA - Diabetes (2009)

Bottom Line: The effects of endoplasmic stress inducers on resistin mRNA and secreted protein levels were examined in differentiated 3T3-L1 adipocytes, focusing on the expression and genomic binding of transcriptional regulators of resistin.ER stress reduced resistin mRNA in 3T3-L1 adipocytes in a time- and dose-dependent manner.The effects of ER stress were transcriptional because of downregulation of CAAT/enhancer binding protein-alpha and peroxisome proliferator-activated receptor-gamma transcriptional activators and upregulation of the transcriptional repressor CAAT/enhancer binding protein homologous protein-10 (CHOP10).

View Article: PubMed Central - PubMed

Affiliation: Division of Endocrinology, Diabetes, and Metabolism, Department of Medicine, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania.

ABSTRACT

Objective: Resistin is a secreted polypeptide that impairs glucose metabolism and, in rodents, is derived exclusively from adipocytes. In murine obesity, resistin circulates at elevated levels but its gene expression in adipose tissue is paradoxically reduced. The mechanism behind the downregulation of resistin mRNA is poorly understood. We investigated whether endoplasmic reticulum (ER) stress, which is characteristic of obese adipose tissue, regulates resistin expression in cultured mouse adipocytes.

Research design and methods: The effects of endoplasmic stress inducers on resistin mRNA and secreted protein levels were examined in differentiated 3T3-L1 adipocytes, focusing on the expression and genomic binding of transcriptional regulators of resistin. The association between downregulated resistin mRNA and induction of ER stress was also investigated in the adipose tissue of mice fed a high-fat diet.

Results: ER stress reduced resistin mRNA in 3T3-L1 adipocytes in a time- and dose-dependent manner. The effects of ER stress were transcriptional because of downregulation of CAAT/enhancer binding protein-alpha and peroxisome proliferator-activated receptor-gamma transcriptional activators and upregulation of the transcriptional repressor CAAT/enhancer binding protein homologous protein-10 (CHOP10). Resistin protein was also substantially downregulated, showing a close correspondence with mRNA levels in 3T3-L1 adipocytes as well as in the fat pads of obese mice.

Conclusions: ER stress is a potent regulator of resistin, suggesting that ER stress may underlie the local downregulation of resistin mRNA and protein in fat in murine obesity. The paradoxical increase in plasma may be because of various systemic abnormalities associated with obesity and insulin resistance.

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Reduced resistin levels in EWAT of obese mice are associated with markers of ER stress. All data are from male C57Bl/6 mice fed NC (n = 5) or HFD (n = 5) for 30 weeks to induce obesity. A: Resistin mRNA levels in EWAT. Data were normalized to the house-keeping gene Arbp/36b4 and presented as mean ± SE. B: Serum resistin levels after 30 weeks of diet. C: Resistin protein levels in EWAT, measured with ELISA in tissue homogenates, and normalized to the total protein concentration of each homogenate. Data are presented as nanogram resistin per milligram total protein, mean ± SE. D: Western blot demonstrating the phosphorylation status of Eukaryotic translation initiation factor 2a (eIF2α) in representative animals selected at random from the NC and HFD groups. Total eIF2α and Ran were used as loading controls. E: mRNA levels of the ER chaperone BiP measured in EWAT. Data were normalized to the house-keeping gene Arbp/36b4 and are presented as mean ± SE. *P < 0.05, **P < 0.01, ***P < 0.001.
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Figure 2: Reduced resistin levels in EWAT of obese mice are associated with markers of ER stress. All data are from male C57Bl/6 mice fed NC (n = 5) or HFD (n = 5) for 30 weeks to induce obesity. A: Resistin mRNA levels in EWAT. Data were normalized to the house-keeping gene Arbp/36b4 and presented as mean ± SE. B: Serum resistin levels after 30 weeks of diet. C: Resistin protein levels in EWAT, measured with ELISA in tissue homogenates, and normalized to the total protein concentration of each homogenate. Data are presented as nanogram resistin per milligram total protein, mean ± SE. D: Western blot demonstrating the phosphorylation status of Eukaryotic translation initiation factor 2a (eIF2α) in representative animals selected at random from the NC and HFD groups. Total eIF2α and Ran were used as loading controls. E: mRNA levels of the ER chaperone BiP measured in EWAT. Data were normalized to the house-keeping gene Arbp/36b4 and are presented as mean ± SE. *P < 0.05, **P < 0.01, ***P < 0.001.

Mentions: It has been reported previously that in obese mice, resistin mRNA levels are decreased while protein levels in the circulation are increased compared with lean mice, raising the possibility that during obesity there is dissociation between resistin mRNA and protein levels. A reasonable prediction, then, would be that protein levels in the fat pad may also be higher in obese versus lean mice, similar to what is seen in the circulation. To address this question, C57Bl/6 mice were fed HFD or NC for 30 weeks, at which point resistin mRNA levels were decreased in epididymal white adipose tissue (EWAT) of the HFD mice (Fig. 2A), despite increased serum resistin levels (Fig. 2B). Surprisingly, EWAT resistin protein levels were not increased, but rather tended to be lower in the HFD mice (Fig. 2C). This indicates that locally in the fat pad, resistin protein levels correspond to the mRNA changes, similar to what was observed in the tunicamycin-treated cells. Furthermore, consistent with previous reports of ER stress in obesity (21,27), markers of ER stress such as phospho-eIF2α (Fig. 2D) and BiP mRNA levels (Fig. 2E) were elevated in the adipose tissue from the HFD-fed obese mice. Taken together, these data suggest that ER stress may be a relevant mechanism in the downregulation of resistin in vivo in the setting of mouse obesity.


Endoplasmic reticulum stress regulates adipocyte resistin expression.

Lefterova MI, Mullican SE, Tomaru T, Qatanani M, Schupp M, Lazar MA - Diabetes (2009)

Reduced resistin levels in EWAT of obese mice are associated with markers of ER stress. All data are from male C57Bl/6 mice fed NC (n = 5) or HFD (n = 5) for 30 weeks to induce obesity. A: Resistin mRNA levels in EWAT. Data were normalized to the house-keeping gene Arbp/36b4 and presented as mean ± SE. B: Serum resistin levels after 30 weeks of diet. C: Resistin protein levels in EWAT, measured with ELISA in tissue homogenates, and normalized to the total protein concentration of each homogenate. Data are presented as nanogram resistin per milligram total protein, mean ± SE. D: Western blot demonstrating the phosphorylation status of Eukaryotic translation initiation factor 2a (eIF2α) in representative animals selected at random from the NC and HFD groups. Total eIF2α and Ran were used as loading controls. E: mRNA levels of the ER chaperone BiP measured in EWAT. Data were normalized to the house-keeping gene Arbp/36b4 and are presented as mean ± SE. *P < 0.05, **P < 0.01, ***P < 0.001.
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Related In: Results  -  Collection

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Figure 2: Reduced resistin levels in EWAT of obese mice are associated with markers of ER stress. All data are from male C57Bl/6 mice fed NC (n = 5) or HFD (n = 5) for 30 weeks to induce obesity. A: Resistin mRNA levels in EWAT. Data were normalized to the house-keeping gene Arbp/36b4 and presented as mean ± SE. B: Serum resistin levels after 30 weeks of diet. C: Resistin protein levels in EWAT, measured with ELISA in tissue homogenates, and normalized to the total protein concentration of each homogenate. Data are presented as nanogram resistin per milligram total protein, mean ± SE. D: Western blot demonstrating the phosphorylation status of Eukaryotic translation initiation factor 2a (eIF2α) in representative animals selected at random from the NC and HFD groups. Total eIF2α and Ran were used as loading controls. E: mRNA levels of the ER chaperone BiP measured in EWAT. Data were normalized to the house-keeping gene Arbp/36b4 and are presented as mean ± SE. *P < 0.05, **P < 0.01, ***P < 0.001.
Mentions: It has been reported previously that in obese mice, resistin mRNA levels are decreased while protein levels in the circulation are increased compared with lean mice, raising the possibility that during obesity there is dissociation between resistin mRNA and protein levels. A reasonable prediction, then, would be that protein levels in the fat pad may also be higher in obese versus lean mice, similar to what is seen in the circulation. To address this question, C57Bl/6 mice were fed HFD or NC for 30 weeks, at which point resistin mRNA levels were decreased in epididymal white adipose tissue (EWAT) of the HFD mice (Fig. 2A), despite increased serum resistin levels (Fig. 2B). Surprisingly, EWAT resistin protein levels were not increased, but rather tended to be lower in the HFD mice (Fig. 2C). This indicates that locally in the fat pad, resistin protein levels correspond to the mRNA changes, similar to what was observed in the tunicamycin-treated cells. Furthermore, consistent with previous reports of ER stress in obesity (21,27), markers of ER stress such as phospho-eIF2α (Fig. 2D) and BiP mRNA levels (Fig. 2E) were elevated in the adipose tissue from the HFD-fed obese mice. Taken together, these data suggest that ER stress may be a relevant mechanism in the downregulation of resistin in vivo in the setting of mouse obesity.

Bottom Line: The effects of endoplasmic stress inducers on resistin mRNA and secreted protein levels were examined in differentiated 3T3-L1 adipocytes, focusing on the expression and genomic binding of transcriptional regulators of resistin.ER stress reduced resistin mRNA in 3T3-L1 adipocytes in a time- and dose-dependent manner.The effects of ER stress were transcriptional because of downregulation of CAAT/enhancer binding protein-alpha and peroxisome proliferator-activated receptor-gamma transcriptional activators and upregulation of the transcriptional repressor CAAT/enhancer binding protein homologous protein-10 (CHOP10).

View Article: PubMed Central - PubMed

Affiliation: Division of Endocrinology, Diabetes, and Metabolism, Department of Medicine, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania.

ABSTRACT

Objective: Resistin is a secreted polypeptide that impairs glucose metabolism and, in rodents, is derived exclusively from adipocytes. In murine obesity, resistin circulates at elevated levels but its gene expression in adipose tissue is paradoxically reduced. The mechanism behind the downregulation of resistin mRNA is poorly understood. We investigated whether endoplasmic reticulum (ER) stress, which is characteristic of obese adipose tissue, regulates resistin expression in cultured mouse adipocytes.

Research design and methods: The effects of endoplasmic stress inducers on resistin mRNA and secreted protein levels were examined in differentiated 3T3-L1 adipocytes, focusing on the expression and genomic binding of transcriptional regulators of resistin. The association between downregulated resistin mRNA and induction of ER stress was also investigated in the adipose tissue of mice fed a high-fat diet.

Results: ER stress reduced resistin mRNA in 3T3-L1 adipocytes in a time- and dose-dependent manner. The effects of ER stress were transcriptional because of downregulation of CAAT/enhancer binding protein-alpha and peroxisome proliferator-activated receptor-gamma transcriptional activators and upregulation of the transcriptional repressor CAAT/enhancer binding protein homologous protein-10 (CHOP10). Resistin protein was also substantially downregulated, showing a close correspondence with mRNA levels in 3T3-L1 adipocytes as well as in the fat pads of obese mice.

Conclusions: ER stress is a potent regulator of resistin, suggesting that ER stress may underlie the local downregulation of resistin mRNA and protein in fat in murine obesity. The paradoxical increase in plasma may be because of various systemic abnormalities associated with obesity and insulin resistance.

Show MeSH
Related in: MedlinePlus