TLR4 regulates insulin-resistant proteins to increase apoptosis in the mouse retina

Abstract

Objective and Design Work in multiple organs has suggested that toll-like receptor 4 (TLR4) may play a role in insulin resistance. Additional studies have shown a negative role for TLR4 on retinal health. We have previously reported that β-adrenergic receptors can regulate both TLR4 signal transduction, as well as insulin signaling in the retina and in retinal endothelial cells (REC). Thus, we hypothesized that TLR4 would regulate retinal insulin signaling. Materials and Methods We used endothelial cell specific TLR4 knockout mice, as well as TLR4 overexpressing mice for these studies. Methods Western blotting and ELISA analyses were done for investigations of insulin receptor, insulin receptor substrate 1 (IRS-1) serine 307, and Akt phosphorylation, as well as cleaved caspase 3 levels in the mouse retina. Results We found that loss of TLR4 led to increased insulin receptor and Akt phosphorylation, as well as decreased IRS-1Ser307 levels. In support of these results, TLR4 overexpression decreased insulin signaling and the cleavage of caspase 3. Conclusions Therefore, these results suggest that TLR4 plays a key role in insulin signaling in the retina. Reduction of TLR4 levels may be protective to the retina.

Toll-Like Receptor 4 Reduces Occludin and Zonula Occludens 1 to Increase Retinal Permeability Both in vitro<b> </b>and in vivo

“…1b, d). These data agree with the genotyping and Western blot results for whole retina reported previously [22]. …”

“…At 3 months of age, the TLR4 floxed and TLR4 Cre-Lox mice were used for experiments. Genotyping and Western blot results for TLR4 from these mice have been recently published [22]. …”

Toll-like receptor 4 regulates insulin signal transduction in retinal Müller cells

“…All of the changes induced by high glucose were reduced/reversed when cells were treated with TLR4 siRNA, suggesting that high glucose induced TLR4 to mediate dysfunctional insulin signaling in retinal Müller cells. These findings agree with our previous work in Müller cells, as well as others work in other retinal cell types (9, 16). Future work will include making the Müller cell specific knockout mice diabetic with a high fat diet to better mimic type 2 diabetes in vivo .…”

“…We recently reported that endothelial cell specific knockout of TLR4 led to improved insulin signaling (9), which was not observed in TLR4 overexpressing mice. For this study, we wanted to combine our previous studies on retinal Müller cells and insulin signaling to investigate the actions of TLR4 in retinal Müller cells.…”

“…Additionally, studies recently demonstrated that high glucose causes increased TLR4 signaling in human retinal endothelial cells (REC) through TLR2/4 (8). We have previously demonstrated that loss of TLR4 signaling in endothelial cell specific knockout mice led to increased insulin signaling (9). …”