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Obesity-related upregulation of monocyte chemotactic factors in adipocytes: involvement of nuclear factor-kappaB and c-Jun NH2-terminal kinase pathways.

Jiao P, Chen Q, Shah S, Du J, Tao B, Tzameli I, Yan W, Xu H - Diabetes (2008)

Bottom Line: The effects of fatty acids on stimulation of chemokine expression in adipocytes and underlying mechanisms were investigated.Free fatty acids (FFAs) are found to be inducers for upregulating these chemokines in 3T3-L1 adipocytes, and this effect can be partially blunted by reducing Toll-like receptor 4 expression.Multiple chemokines derived from adipocytes might contribute to obesity-related WAT macrophage infiltration with FFAs as potential triggers and involvement of both IKKbeta and JNK pathways.

View Article: PubMed Central - PubMed

Affiliation: Hallett Center for Diabetes and Endocrinology, Brown Medical School, Providence, Rhode Island, USA.

ABSTRACT

Objective: We sought to evaluate the entire picture of all monocyte chemotactic factors that potentially contribute to adipose tissue macrophage accumulation in obesity.

Research design and methods: Expression and regulation of members in the entire chemokine superfamily were evaluated in adipose tissue and isolated adipocytes of obese versus lean mice. Kinetics of adipose tissue macrophage infiltration was characterized by fluorescence-activated cell sorting. The effects of fatty acids on stimulation of chemokine expression in adipocytes and underlying mechanisms were investigated.

Results: Six monocyte chemotactic factors were found to be predominantly upregulated in isolated adipocytes versus stromal vascular cells in obese mice for the first time, although most of them were previously reported to be upregulated in whole adipose tissue. In diet-induced obese mice, adipose tissue enlargement, increase of adipocyte number, and elevation of multiple chemokine expression precede the initiation of macrophage infiltration. Free fatty acids (FFAs) are found to be inducers for upregulating these chemokines in 3T3-L1 adipocytes, and this effect can be partially blunted by reducing Toll-like receptor 4 expression. FFAs induce expression of monocyte chemotactic factors in adipocytes via both transcription-dependent and -independent mechanisms. In contrast to the reported role of JNK as the exclusive mediator of FFA-induced monocyte chemoattractant protein-1 (MCP-1) expression in macrophages, we show a novel role of inhibitor of kappaB kinase-beta (IKKbeta) in mediating FFA-induced upregulation of all six chemokines and a role of JNK in FFA-induced upregulation of MCP-1 and MCP-3.

Conclusions: Multiple chemokines derived from adipocytes might contribute to obesity-related WAT macrophage infiltration with FFAs as potential triggers and involvement of both IKKbeta and JNK pathways.

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Related in: MedlinePlus

Time course of FFA-induced upregulation of monocyte chemotactic factors in 3T3-L1 adipocytes. After overnight incubation with serum-free medium, 3T3-L1 adipocytes were treated with ethanol/BSA or FFA/BSA for 1, 3, 5, 7, or 9 h before RNA extraction. Expression of chemokines were evaluated by real-time PCR analysis. Error bars represent ±SE. *P < 0.05, treated vs. vehicle. Results shown here are representative of three independent experiments.
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f3: Time course of FFA-induced upregulation of monocyte chemotactic factors in 3T3-L1 adipocytes. After overnight incubation with serum-free medium, 3T3-L1 adipocytes were treated with ethanol/BSA or FFA/BSA for 1, 3, 5, 7, or 9 h before RNA extraction. Expression of chemokines were evaluated by real-time PCR analysis. Error bars represent ±SE. *P < 0.05, treated vs. vehicle. Results shown here are representative of three independent experiments.

Mentions: Massive expansion of adipose tissue reflects the need for the body to store excessive amount of energy in the form of triglyceride, which is synthesized using FFAs and glycerol as substrates. The effects of FFAs and glycerol on chemokine production in adipocytes have not been documented. To determine whether a surplus of FFAs and/or glycerol could be the stimuli for increased chemokine production, 3T3-L1 adipocytes were stimulated with a mixture of either 0.5 mmol/l FFA/BSA or 0.5 mmol/l glycerol. We chose to use a mixture of 0.5 mmol/l saturated (lauric and myristic acid) and unsaturated (oleic, linoleic, and arachidonic acid) FFAs for stimulation. FFAs dramatically upregulated MCP-1 expression, whereas glycerol had no effect (Fig. 2A). Further experiments indicated that FFAs are also able to upregulate MCP-2, MCP-3, MIP-1α, MRP-1, and MRP-2 in 3T3-L1 adipocytes (Fig. 2A). As a negative control, expression of eotaxin 2, which is not upregulated in obese adipose tissue, was examined in 3T3-L1 adipocytes and was found not to be increased by FFA treatment (Fig. 2A). The upregulation of mRNA level of the above chemokines by FFA treatment is accompanied by increased protein secretion into conditioned medium (Fig. 2B). FFA-stimulated chemokine production in 3T3-L1 adipocytes is dose (data not shown) and time dependent (Fig. 3). Detailed chemokine expression time course revealed that the peak expression of MCP-1, MCP-2, MCP-3, and MIP-1α is ∼3 h after treatment (Fig. 3). Interestingly, FFA-stimulated upregulation of MRP-1 and MRP-2 is due to delayed decrease rather than increase of the actual mRNA levels compared with vehicle-treated cells (Fig. 3). Experiments using individual FFAs indicate that the effect is most likely attributed to unsaturated FFAs (supplementary Fig. 1, available in the online appendix).


Obesity-related upregulation of monocyte chemotactic factors in adipocytes: involvement of nuclear factor-kappaB and c-Jun NH2-terminal kinase pathways.

Jiao P, Chen Q, Shah S, Du J, Tao B, Tzameli I, Yan W, Xu H - Diabetes (2008)

Time course of FFA-induced upregulation of monocyte chemotactic factors in 3T3-L1 adipocytes. After overnight incubation with serum-free medium, 3T3-L1 adipocytes were treated with ethanol/BSA or FFA/BSA for 1, 3, 5, 7, or 9 h before RNA extraction. Expression of chemokines were evaluated by real-time PCR analysis. Error bars represent ±SE. *P < 0.05, treated vs. vehicle. Results shown here are representative of three independent experiments.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2606857&req=5

f3: Time course of FFA-induced upregulation of monocyte chemotactic factors in 3T3-L1 adipocytes. After overnight incubation with serum-free medium, 3T3-L1 adipocytes were treated with ethanol/BSA or FFA/BSA for 1, 3, 5, 7, or 9 h before RNA extraction. Expression of chemokines were evaluated by real-time PCR analysis. Error bars represent ±SE. *P < 0.05, treated vs. vehicle. Results shown here are representative of three independent experiments.
Mentions: Massive expansion of adipose tissue reflects the need for the body to store excessive amount of energy in the form of triglyceride, which is synthesized using FFAs and glycerol as substrates. The effects of FFAs and glycerol on chemokine production in adipocytes have not been documented. To determine whether a surplus of FFAs and/or glycerol could be the stimuli for increased chemokine production, 3T3-L1 adipocytes were stimulated with a mixture of either 0.5 mmol/l FFA/BSA or 0.5 mmol/l glycerol. We chose to use a mixture of 0.5 mmol/l saturated (lauric and myristic acid) and unsaturated (oleic, linoleic, and arachidonic acid) FFAs for stimulation. FFAs dramatically upregulated MCP-1 expression, whereas glycerol had no effect (Fig. 2A). Further experiments indicated that FFAs are also able to upregulate MCP-2, MCP-3, MIP-1α, MRP-1, and MRP-2 in 3T3-L1 adipocytes (Fig. 2A). As a negative control, expression of eotaxin 2, which is not upregulated in obese adipose tissue, was examined in 3T3-L1 adipocytes and was found not to be increased by FFA treatment (Fig. 2A). The upregulation of mRNA level of the above chemokines by FFA treatment is accompanied by increased protein secretion into conditioned medium (Fig. 2B). FFA-stimulated chemokine production in 3T3-L1 adipocytes is dose (data not shown) and time dependent (Fig. 3). Detailed chemokine expression time course revealed that the peak expression of MCP-1, MCP-2, MCP-3, and MIP-1α is ∼3 h after treatment (Fig. 3). Interestingly, FFA-stimulated upregulation of MRP-1 and MRP-2 is due to delayed decrease rather than increase of the actual mRNA levels compared with vehicle-treated cells (Fig. 3). Experiments using individual FFAs indicate that the effect is most likely attributed to unsaturated FFAs (supplementary Fig. 1, available in the online appendix).

Bottom Line: The effects of fatty acids on stimulation of chemokine expression in adipocytes and underlying mechanisms were investigated.Free fatty acids (FFAs) are found to be inducers for upregulating these chemokines in 3T3-L1 adipocytes, and this effect can be partially blunted by reducing Toll-like receptor 4 expression.Multiple chemokines derived from adipocytes might contribute to obesity-related WAT macrophage infiltration with FFAs as potential triggers and involvement of both IKKbeta and JNK pathways.

View Article: PubMed Central - PubMed

Affiliation: Hallett Center for Diabetes and Endocrinology, Brown Medical School, Providence, Rhode Island, USA.

ABSTRACT

Objective: We sought to evaluate the entire picture of all monocyte chemotactic factors that potentially contribute to adipose tissue macrophage accumulation in obesity.

Research design and methods: Expression and regulation of members in the entire chemokine superfamily were evaluated in adipose tissue and isolated adipocytes of obese versus lean mice. Kinetics of adipose tissue macrophage infiltration was characterized by fluorescence-activated cell sorting. The effects of fatty acids on stimulation of chemokine expression in adipocytes and underlying mechanisms were investigated.

Results: Six monocyte chemotactic factors were found to be predominantly upregulated in isolated adipocytes versus stromal vascular cells in obese mice for the first time, although most of them were previously reported to be upregulated in whole adipose tissue. In diet-induced obese mice, adipose tissue enlargement, increase of adipocyte number, and elevation of multiple chemokine expression precede the initiation of macrophage infiltration. Free fatty acids (FFAs) are found to be inducers for upregulating these chemokines in 3T3-L1 adipocytes, and this effect can be partially blunted by reducing Toll-like receptor 4 expression. FFAs induce expression of monocyte chemotactic factors in adipocytes via both transcription-dependent and -independent mechanisms. In contrast to the reported role of JNK as the exclusive mediator of FFA-induced monocyte chemoattractant protein-1 (MCP-1) expression in macrophages, we show a novel role of inhibitor of kappaB kinase-beta (IKKbeta) in mediating FFA-induced upregulation of all six chemokines and a role of JNK in FFA-induced upregulation of MCP-1 and MCP-3.

Conclusions: Multiple chemokines derived from adipocytes might contribute to obesity-related WAT macrophage infiltration with FFAs as potential triggers and involvement of both IKKbeta and JNK pathways.

Show MeSH
Related in: MedlinePlus