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Retinoid X receptor α overexpression alleviates mitochondrial dysfunction-induced insulin resistance through transcriptional regulation of insulin receptor substrate 1.

Lee SE, Koo YD, Lee JS, Kwak SH, Jung HS, Cho YM, Park YJ, Chung SS, Park KS - Mol. Cells (2015)

Bottom Line: RXRα overexpression also increased IRS1 transcription and mitochondrial function.Because RXRα overexpression, knock-down, or activation by LG1506 regulated IRS1 transcription mostly independently of mitochondrial function, it is likely that RXRα directly regulates IRS1 transcription.Consistent with the hypothesis, we showed that RXRα bound to the IRS1 promoter as a heterodimer with peroxisome proliferator-activated receptor δ (PPARδ).

View Article: PubMed Central - PubMed

Affiliation: Department of Internal Medicine, Seoul National University College of Medicine, Seoul 110-744, Korea.

ABSTRACT
Mitochondrial dysfunction is associated with insulin resistance and diabetes. We previously showed that retinoid X receptor α (RXRα) played an important role in transcriptional regulation of oxidative phosphorylation (OXPHOS) genes in cells with mitochondrial dysfunction caused by mitochondrial DNA mutation. In this study, we investigated whether mitochondrial dysfunction induced by incubation with OXPHOS inhibitors affects insulin receptor substrate 1 (IRS1) mRNA and protein levels and whether RXRα activation or overexpression can restore IRS1 expression. Both IRS1 and RXRα protein levels were significantly reduced when C2C12 myotubes were treated with the OXPHOS complex inhibitors, rotenone and antimycin A. The addition of RXRα agonists, 9-cis retinoic acid (9cRA) and LG1506, increased IRS1 transcription and protein levels and restored mitochondrial function, which ultimately improved insulin signaling. RXRα overexpression also increased IRS1 transcription and mitochondrial function. Because RXRα overexpression, knock-down, or activation by LG1506 regulated IRS1 transcription mostly independently of mitochondrial function, it is likely that RXRα directly regulates IRS1 transcription. Consistent with the hypothesis, we showed that RXRα bound to the IRS1 promoter as a heterodimer with peroxisome proliferator-activated receptor δ (PPARδ). These results suggest that RXRα overexpression or activation alleviates insulin resistance by increasing IRS1 expression.

No MeSH data available.


Related in: MedlinePlus

RXRα directly regulates IRS1 transcription. (A, B) C2C12 myotubes were infected with Ad-RXRα in different dosages (10, 30 and 50 MOI) for 48 h. Cell lysates were subjected to real time PCR (A) and western blot analysis (B). The mRNA levels of control cells (Ad-GFP infected) was set to 1 and the other values were expressed as the relatives to that (n = 4). *, P < 0.05 vs. Ad-GFP infected cells. (C, D) C2C12 myotubes were treated with 9cRA (5 μM) or LG1506 (2 μM) for 24 h, and then real time PCR (C) and western blot analysis (D) were performed (n = 5). *, P < 0.05 vs. Veh. (E) C2C12 myotubes were transfected with siNS or siRXR (50 nM). Total RNAs were prepared 3 days after siRNA transfection and then real time PCR was performed (n = 3). *, P < 0.05 vs. siNS.
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f3-molce-38-4-356: RXRα directly regulates IRS1 transcription. (A, B) C2C12 myotubes were infected with Ad-RXRα in different dosages (10, 30 and 50 MOI) for 48 h. Cell lysates were subjected to real time PCR (A) and western blot analysis (B). The mRNA levels of control cells (Ad-GFP infected) was set to 1 and the other values were expressed as the relatives to that (n = 4). *, P < 0.05 vs. Ad-GFP infected cells. (C, D) C2C12 myotubes were treated with 9cRA (5 μM) or LG1506 (2 μM) for 24 h, and then real time PCR (C) and western blot analysis (D) were performed (n = 5). *, P < 0.05 vs. Veh. (E) C2C12 myotubes were transfected with siNS or siRXR (50 nM). Total RNAs were prepared 3 days after siRNA transfection and then real time PCR was performed (n = 3). *, P < 0.05 vs. siNS.

Mentions: Although our data clearly showed that RXRα activation or overexpression ameliorated mitochondrial dysfunction and increased IRS1 transcription, it was not clear whether RXRα directly regulates IRS1 transcription or if the recovery of IRS1 transcription is a secondary effect of improved mitochondrial function. We therefore tested whether RXRα affected IRS1 transcription in the myotubes that were not treated with rote-none. RXRα overexpression increased IRS1 mRNA and protein levels in a dose-dependent manner (Figs. 3A and 3B). Similarly, activation of RXRα by LG1506 treatment also increased IRS1 mRNA and protein levels. However, the RXRα agonist 9cRA did not increase IRS1 mRNA or protein levels (Figs. 3C and 3D). We also examined the effect of RXRα knockdown on IRS1 mRNA levels and found that they were significantly reduced when siRNAs against RXRα were transfected into C2C12 myotubes (Fig. 3E). These results suggest that RXRα is directly involved in IRS1 transcription independently of mitochondrial function, even though 9cRA did not increase IRS1 mRNA levels.


Retinoid X receptor α overexpression alleviates mitochondrial dysfunction-induced insulin resistance through transcriptional regulation of insulin receptor substrate 1.

Lee SE, Koo YD, Lee JS, Kwak SH, Jung HS, Cho YM, Park YJ, Chung SS, Park KS - Mol. Cells (2015)

RXRα directly regulates IRS1 transcription. (A, B) C2C12 myotubes were infected with Ad-RXRα in different dosages (10, 30 and 50 MOI) for 48 h. Cell lysates were subjected to real time PCR (A) and western blot analysis (B). The mRNA levels of control cells (Ad-GFP infected) was set to 1 and the other values were expressed as the relatives to that (n = 4). *, P < 0.05 vs. Ad-GFP infected cells. (C, D) C2C12 myotubes were treated with 9cRA (5 μM) or LG1506 (2 μM) for 24 h, and then real time PCR (C) and western blot analysis (D) were performed (n = 5). *, P < 0.05 vs. Veh. (E) C2C12 myotubes were transfected with siNS or siRXR (50 nM). Total RNAs were prepared 3 days after siRNA transfection and then real time PCR was performed (n = 3). *, P < 0.05 vs. siNS.
© Copyright Policy
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC4400311&req=5

f3-molce-38-4-356: RXRα directly regulates IRS1 transcription. (A, B) C2C12 myotubes were infected with Ad-RXRα in different dosages (10, 30 and 50 MOI) for 48 h. Cell lysates were subjected to real time PCR (A) and western blot analysis (B). The mRNA levels of control cells (Ad-GFP infected) was set to 1 and the other values were expressed as the relatives to that (n = 4). *, P < 0.05 vs. Ad-GFP infected cells. (C, D) C2C12 myotubes were treated with 9cRA (5 μM) or LG1506 (2 μM) for 24 h, and then real time PCR (C) and western blot analysis (D) were performed (n = 5). *, P < 0.05 vs. Veh. (E) C2C12 myotubes were transfected with siNS or siRXR (50 nM). Total RNAs were prepared 3 days after siRNA transfection and then real time PCR was performed (n = 3). *, P < 0.05 vs. siNS.
Mentions: Although our data clearly showed that RXRα activation or overexpression ameliorated mitochondrial dysfunction and increased IRS1 transcription, it was not clear whether RXRα directly regulates IRS1 transcription or if the recovery of IRS1 transcription is a secondary effect of improved mitochondrial function. We therefore tested whether RXRα affected IRS1 transcription in the myotubes that were not treated with rote-none. RXRα overexpression increased IRS1 mRNA and protein levels in a dose-dependent manner (Figs. 3A and 3B). Similarly, activation of RXRα by LG1506 treatment also increased IRS1 mRNA and protein levels. However, the RXRα agonist 9cRA did not increase IRS1 mRNA or protein levels (Figs. 3C and 3D). We also examined the effect of RXRα knockdown on IRS1 mRNA levels and found that they were significantly reduced when siRNAs against RXRα were transfected into C2C12 myotubes (Fig. 3E). These results suggest that RXRα is directly involved in IRS1 transcription independently of mitochondrial function, even though 9cRA did not increase IRS1 mRNA levels.

Bottom Line: RXRα overexpression also increased IRS1 transcription and mitochondrial function.Because RXRα overexpression, knock-down, or activation by LG1506 regulated IRS1 transcription mostly independently of mitochondrial function, it is likely that RXRα directly regulates IRS1 transcription.Consistent with the hypothesis, we showed that RXRα bound to the IRS1 promoter as a heterodimer with peroxisome proliferator-activated receptor δ (PPARδ).

View Article: PubMed Central - PubMed

Affiliation: Department of Internal Medicine, Seoul National University College of Medicine, Seoul 110-744, Korea.

ABSTRACT
Mitochondrial dysfunction is associated with insulin resistance and diabetes. We previously showed that retinoid X receptor α (RXRα) played an important role in transcriptional regulation of oxidative phosphorylation (OXPHOS) genes in cells with mitochondrial dysfunction caused by mitochondrial DNA mutation. In this study, we investigated whether mitochondrial dysfunction induced by incubation with OXPHOS inhibitors affects insulin receptor substrate 1 (IRS1) mRNA and protein levels and whether RXRα activation or overexpression can restore IRS1 expression. Both IRS1 and RXRα protein levels were significantly reduced when C2C12 myotubes were treated with the OXPHOS complex inhibitors, rotenone and antimycin A. The addition of RXRα agonists, 9-cis retinoic acid (9cRA) and LG1506, increased IRS1 transcription and protein levels and restored mitochondrial function, which ultimately improved insulin signaling. RXRα overexpression also increased IRS1 transcription and mitochondrial function. Because RXRα overexpression, knock-down, or activation by LG1506 regulated IRS1 transcription mostly independently of mitochondrial function, it is likely that RXRα directly regulates IRS1 transcription. Consistent with the hypothesis, we showed that RXRα bound to the IRS1 promoter as a heterodimer with peroxisome proliferator-activated receptor δ (PPARδ). These results suggest that RXRα overexpression or activation alleviates insulin resistance by increasing IRS1 expression.

No MeSH data available.


Related in: MedlinePlus