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Hypoxia decreases insulin signaling pathways in adipocytes.

Regazzetti C, Peraldi P, Grémeaux T, Najem-Lendom R, Ben-Sahra I, Cormont M, Bost F, Le Marchand-Brustel Y, Tanti JF, Giorgetti-Peraldi S - Diabetes (2008)

Bottom Line: In 3T3-L1 adipocytes, this inhibition of insulin receptor phosphorylation is followed by a decrease in the phosphorylation state of protein kinase B and AS160, as well as an inhibition of glucose transport in response to insulin.These processes were reversible under normoxic conditions.The mechanism of inhibition seems independent of protein tyrosine phosphatase activities.

View Article: PubMed Central - PubMed

Affiliation: Team Cellular and Molecular Physiopathology of Obesity and Diabetes, Institut National de la Santé et de la Recherche Médicale U 895, Mediterranean Research Centre for Molecular Medicine, Nice, France.

ABSTRACT

Objective: Obesity is characterized by an overgrowth of adipose tissue that leads to the formation of hypoxic areas within this tissue. We investigated whether this phenomenon could be responsible for insulin resistance by studying the effect of hypoxia on the insulin signaling pathway in adipocytes.

Research design and methods: The hypoxic signaling pathway was modulated in adipocytes from human and murine origins through incubation under hypoxic conditions (1% O(2)) or modulation of hypoxia-inducible factor (HIF) expression. Insulin signaling was monitored through the phosphorylation state of several key partners of the pathway and glucose transport.

Results: In both human and murine adipocytes, hypoxia inhibits insulin signaling as revealed by a decrease in the phosphorylation of insulin receptor. In 3T3-L1 adipocytes, this inhibition of insulin receptor phosphorylation is followed by a decrease in the phosphorylation state of protein kinase B and AS160, as well as an inhibition of glucose transport in response to insulin. These processes were reversible under normoxic conditions. The mechanism of inhibition seems independent of protein tyrosine phosphatase activities. Overexpression of HIF-1alpha or -2alpha or activation of HIF transcription factor with CoCl(2) mimicked the effect of hypoxia on insulin signaling, whereas downregulation of HIF-1alpha and -2alpha by small interfering RNA inhibited it.

Conclusions: We have demonstrated that hypoxia creates a state of insulin resistance in adipocytes that is dependent upon HIF transcription factor expression. Hypoxia could be envisioned as a new mechanism that participates in insulin resistance in adipose tissue of obese patients.

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Related in: MedlinePlus

Hypoxia inhibits insulin-induced glucose transport. A: 3T3-L1 adipocytes were incubated for 16 h in normoxia or hypoxia before insulin-stimulated glucose transport was measured as described in research design and methods. Data are the means ± SE of three independent experiments performed in triplicate. B: Cell lysates were analyzed by immunoblots using the indicated antibodies. DOG, deoxyglucose; prot, protein; Reox, reoxygenation. **P < 0.01; ***P < 0.001.
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f3: Hypoxia inhibits insulin-induced glucose transport. A: 3T3-L1 adipocytes were incubated for 16 h in normoxia or hypoxia before insulin-stimulated glucose transport was measured as described in research design and methods. Data are the means ± SE of three independent experiments performed in triplicate. B: Cell lysates were analyzed by immunoblots using the indicated antibodies. DOG, deoxyglucose; prot, protein; Reox, reoxygenation. **P < 0.01; ***P < 0.001.

Mentions: PKB and its substrate AS160 play an important role in insulin-induced GLUT4 translocation and glucose transport. We investigated whether hypoxia inhibited the downstream response of insulin, such as glucose transport in 3T3-L1 adipocytes. 3T3-L1 adipocytes were incubated in normoxia or hypoxia for 16 h or reoxygenated for 1 h. Glucose transport was determined by the increase in [3H]deoxyglucose (Fig. 3A). In normoxic adipocytes, insulin induced a 10-fold increase in glucose transport. Hypoxia upregulated basal glucose transport but inhibited insulin-induced glucose transport. Reoxygenation of adipocytes restored the ability of insulin to stimulate glucose entry to levels comparable to normoxic adipocytes. In reoxygenated adipocytes, basal glucose transport remained elevated. This increase in basal glucose uptake probably resulted from increased GLUT1 expression, which was maintained even after 1 h of reoxygenation, without modifying GLUT4 protein levels (Fig. 3B).


Hypoxia decreases insulin signaling pathways in adipocytes.

Regazzetti C, Peraldi P, Grémeaux T, Najem-Lendom R, Ben-Sahra I, Cormont M, Bost F, Le Marchand-Brustel Y, Tanti JF, Giorgetti-Peraldi S - Diabetes (2008)

Hypoxia inhibits insulin-induced glucose transport. A: 3T3-L1 adipocytes were incubated for 16 h in normoxia or hypoxia before insulin-stimulated glucose transport was measured as described in research design and methods. Data are the means ± SE of three independent experiments performed in triplicate. B: Cell lysates were analyzed by immunoblots using the indicated antibodies. DOG, deoxyglucose; prot, protein; Reox, reoxygenation. **P < 0.01; ***P < 0.001.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2606898&req=5

f3: Hypoxia inhibits insulin-induced glucose transport. A: 3T3-L1 adipocytes were incubated for 16 h in normoxia or hypoxia before insulin-stimulated glucose transport was measured as described in research design and methods. Data are the means ± SE of three independent experiments performed in triplicate. B: Cell lysates were analyzed by immunoblots using the indicated antibodies. DOG, deoxyglucose; prot, protein; Reox, reoxygenation. **P < 0.01; ***P < 0.001.
Mentions: PKB and its substrate AS160 play an important role in insulin-induced GLUT4 translocation and glucose transport. We investigated whether hypoxia inhibited the downstream response of insulin, such as glucose transport in 3T3-L1 adipocytes. 3T3-L1 adipocytes were incubated in normoxia or hypoxia for 16 h or reoxygenated for 1 h. Glucose transport was determined by the increase in [3H]deoxyglucose (Fig. 3A). In normoxic adipocytes, insulin induced a 10-fold increase in glucose transport. Hypoxia upregulated basal glucose transport but inhibited insulin-induced glucose transport. Reoxygenation of adipocytes restored the ability of insulin to stimulate glucose entry to levels comparable to normoxic adipocytes. In reoxygenated adipocytes, basal glucose transport remained elevated. This increase in basal glucose uptake probably resulted from increased GLUT1 expression, which was maintained even after 1 h of reoxygenation, without modifying GLUT4 protein levels (Fig. 3B).

Bottom Line: In 3T3-L1 adipocytes, this inhibition of insulin receptor phosphorylation is followed by a decrease in the phosphorylation state of protein kinase B and AS160, as well as an inhibition of glucose transport in response to insulin.These processes were reversible under normoxic conditions.The mechanism of inhibition seems independent of protein tyrosine phosphatase activities.

View Article: PubMed Central - PubMed

Affiliation: Team Cellular and Molecular Physiopathology of Obesity and Diabetes, Institut National de la Santé et de la Recherche Médicale U 895, Mediterranean Research Centre for Molecular Medicine, Nice, France.

ABSTRACT

Objective: Obesity is characterized by an overgrowth of adipose tissue that leads to the formation of hypoxic areas within this tissue. We investigated whether this phenomenon could be responsible for insulin resistance by studying the effect of hypoxia on the insulin signaling pathway in adipocytes.

Research design and methods: The hypoxic signaling pathway was modulated in adipocytes from human and murine origins through incubation under hypoxic conditions (1% O(2)) or modulation of hypoxia-inducible factor (HIF) expression. Insulin signaling was monitored through the phosphorylation state of several key partners of the pathway and glucose transport.

Results: In both human and murine adipocytes, hypoxia inhibits insulin signaling as revealed by a decrease in the phosphorylation of insulin receptor. In 3T3-L1 adipocytes, this inhibition of insulin receptor phosphorylation is followed by a decrease in the phosphorylation state of protein kinase B and AS160, as well as an inhibition of glucose transport in response to insulin. These processes were reversible under normoxic conditions. The mechanism of inhibition seems independent of protein tyrosine phosphatase activities. Overexpression of HIF-1alpha or -2alpha or activation of HIF transcription factor with CoCl(2) mimicked the effect of hypoxia on insulin signaling, whereas downregulation of HIF-1alpha and -2alpha by small interfering RNA inhibited it.

Conclusions: We have demonstrated that hypoxia creates a state of insulin resistance in adipocytes that is dependent upon HIF transcription factor expression. Hypoxia could be envisioned as a new mechanism that participates in insulin resistance in adipose tissue of obese patients.

Show MeSH
Related in: MedlinePlus