Enhancement of LPS-Induced Microglial Inflammation Response via TLR4 Under High Glucose Conditions

Background/Aims: Diabetic subjects are more susceptible to infections, which is partially due to insulin deficiency and hyperglycemia. We hypothesized that insulin influences cytokine release by macrophages from diabetic C57BL/6 mice stimulated with lipopolysaccharides (LPS). Methods: Bone marrow-derived macrophages (BMDM) and tissue-specific macrophages from diabetic (alloxan 60 mg/kg, i.v.) male C57BL/6 mice were stimulated by LPS (100 ng/mL) and/or treated by insulin (1 mU/mL). Results: Using BMDM from diabetic mice, we showed that LPS induced an increase in TNF-α and IL-6 release and p38, SAPK/JNK, ERK 1/2, and Akt (308-Thr and 473-Ser) phosphorylation but not in PKCα/β II and delta. Insulin increased TNF-α and IL-6 secretion in LPS-stimulated macrophages as well as p-p38, p-SAPK/JNK, p-ERK 1/2, p-PI3K (p55) and p-Akt (473-Ser) expression. Furthermore, PI3-kinase inhibition by wortmannin decreased TNF-α release, and inhibition by LY294002 decreased both TNF-α and IL-6 levels after LPS-insulin treatment. PD98059, which inhibits the ERK upstream activators MAPK kinase (MKK) 1 and MKK2, reduced the effect promoted by insulin in BMDM stimulated by LPS In tissue-specific macrophages, insulin reduced LPS-induced TNF-α, IL-6 and IL-1β secretion in alveolar and peritoneal macrophages. Conclusion: These data suggest that insulin through the modulation of PI3-kinase and ERK 1/2 pathways drive different responses in macrophages, thereby enhancing our understanding of the plasticity of these cells.

Section: Discussionmentioning

confidence: 99%

Insulin Influences LPS-Induced TNF-α and IL-6 Release Through Distinct Pathways in Mouse Macrophages from Different Compartments

Tessaro¹,

Ayala²,

Nolasco³

et al. 2017

“…LPS, as newly recognized inflammatory substance, has a strong proliferative effect on VSMCs. Substantial evidence indicates that TLR4 initiates signalling downstream of LPS stimulation [18] and may participate in the progression of various vascular proliferative diseases, including atherosclerosis and neointima formation [19-21]. Moreover, blocking the progress of atherosclerosis by inhibiting TLR4-mediated signalling has been verified in different animal models [22-25].…”

Section: Discussionmentioning

confidence: 99%

LPS Promotes Vascular Smooth Muscle Cells Proliferation Through the TLR4/Rac1/Akt Signalling Pathway

Yin

Jiang²,

et al. 2017

Background/Aims: Lipopolysaccharide (LPS) is a potent activator of vascular smooth muscle cells (VSMCs) proliferation, but the underlying mechanism remains unknown. In this study, we knocked down Toll-like receptor 4 (TLR4) and Ras-related C3 botulinum toxin substrate 1 (Rac1) expression using small interfering RNA (siRNA) in order to investigate the effects and possible mechanisms of LPS-induced VSMCs proliferation. Methods: VSMCs proliferation was monitored by 5-ethynyl-2’-deoxyuridine staining, and Rac1 activity was measured via Glutathione S-transferase pull-down assay. mRNAs encoding proliferating cell nuclear antigen (PCNA), smooth muscle 22α (SM22α), myosin heavy chain (MYH) and transient receptor potential channel 1 (TRPC1) were detected by qRT-PCR. The expression of total Akt, p-Akt (308), p-Akt (473), SM22α, MYH and TRPC1 protein was analysed by Western blot. Results: Treatment with TLR4 siRNA (siTLR4) or Rac1 siRNA (siRac1) significantly decreased LPS-induced VSMCs proliferation. Moreover, LPS-induced activation of Rac1 through TLR4 was observed. Western blot analysis revealed that transfection with siTLR4 or siRac1 inhibited LPS-induced Akt phosphorylation. We discovered that LPS stimulated VSMCs proliferation via phenotypic modulation and that this effect was partially inhibited by pre-treatment with siTLR4 or siRac1. Further, TLR4 and Rac1 are involved in LPS-induced activation of TRPC1. Conclusion: This study suggests that LPS exerts an effect on VSMCs proliferation and that the TLR4/Rac1/Akt signalling pathway mediates this effect.

“…It is known that the TLR4-Myd88-IL-6 pathway plays very different roles in LPS-induced systemic inflammatory response syndrome (SIRS) and radiation exposure [26-31]. In addition, LPS from Gram-negative bacteria is one of the most potent innate immune-activating stimuli.…”

Section: Discussionmentioning

confidence: 99%

Polymyxin B Attenuates LPS-Induced Death but Aggravates Radiation-Induced Death via TLR4-Myd88-IL-6 Pathway

Cheng¹,

Du²,

Han³

et al. 2017

Background/Aims: Polymyxin B (PMB) is a cyclic cationic polypeptide antibiotic widely used to counteract the effects of endotoxin contamination, both in vitro and in vivo. Lipopolysaccharide (LPS) is an endotoxin that acts as a radiation protection factor. In this study, we focus on the role of PMB in LPS-induced and radiation-induced mortality in mice. Methods: Mice received total-body radiation or were pretreated by LPS or PMB, and the survival of mice was recorded. Elisa were used to detect the cytokines levels. Results: PMB decreased LPS-induced, but increased radiation-induced mortality in mice. Moreover, PMB could block the LPS-induced radioprotective effect. The ELISA and gene knock-out experiments indicated that PMB reduces TNF-α level to block LPS-induced mortality in mice, and inhibits IL-6, G-CSF and IL-10 to increase radiation-induced mortality via the TLR4-Myd88-IL-6 pathway. Conclusions: Our study revealed a role of PMB in LPS-induced endotoxemia and radiation exposure. We infer that the TLR4-Myd88-IL-6 pathway may play a crucial role in the process.