TLR2 inhibition ameliorates the amplification effect of LPS on lipid accumulation and lipotoxicity in hepatic cells

Abstract

Background: Gut microbiome dysbiosis is related to the pathogenesis of nonalcoholic fatty liver disease (NAFLD), and the role of toll-like receptor 2 (TLR2) in its molecular mechanism is controversial. Here, we investigated the effects and mechanisms of Escherichia coli-derived lipopolysaccharide (LPS) on lipid accumulation and lipotoxicity in palmitic acid (PA)-treated L02 cell as an NAFLD cell model, and the role of TLR2 in this process.Methods: Oil red O staining assay and free fatty acid (FFA) content test were performed to determine the effects of LPS on lipid accumulation in a PA-induced NAFLD cell model with or without TLR2 inhibition.The levels of IL-6 and TNF-α were measured to investigate inflammation conditions. Hoechst 33342 staining assay and Caspase-3 activity assay were used to test cell apoptosis, and the expression levels of proteins in the IRS1/PI3K/AKT signaling pathway, TLR2/MyD88/IKKα/NF-κB signaling pathway, and mitochondrion-dependent apoptotic signaling pathway were detected using Western blot.Results: Lipid accumulation, pro-inflammatory cytokine release, and cell apoptosis with high levels were observed in the PA-induced NAFLD cell model, and LPS aggravated these processes. Whereas TLR2 inhibition could significantly ameliorate PA-induced and LPS-amplified lipid accumulation, inflammatory, and cell apoptosis, it had no significant effect on L02 cells treated with LPS alone.Conclusions: These results were confirmed by activation or inhibition of the IRS1/PI3K/AKT signaling pathway, TLR2/MyD88/IKKα/NF-κB signaling pathway, and mitochondrion-dependent apoptotic signaling pathway, and were reflected by changes on their proteins expression. TLR2 is involved in PA-induced lipid accumulation and lipotoxicity in L02 cells, which could be aggravated by LPS, although LPS-induced amplification might not be through direct interaction with TLR2.

Network pharmacological analysis on the mechanism of Linggui Zhugan decoction for nonalcoholic fatty liver disease

“…[59] Conversely, inhibition of TLR2 improves lipopolysaccharide-induced lipid accumulation and toxicity in hepatocytes. [60] Docking experiments confirmed that quercetin, kaempferol, and naringenin exhibit strong binding affinity with core targets (AKT1, MYC, HSP90AA1, HIF1A, ESR1, TP53, and STAT3), with binding energies less than −5 kcal•mol -1 . This suggests that the therapeutic potential of LGZGD in treating NAFLD may be attributed to the efficacy of these 3 key active ingredients.…”

“…[ 59 ] Conversely, inhibition of TLR2 improves lipopolysaccharide-induced lipid accumulation and toxicity in hepatocytes. [ 60 ]…”

Hepatocyte CYR61 polarizes profibrotic macrophages to orchestrate NASH fibrosis

“…CYR61 reduction before the introduction of a NASH diet improved glucose tolerance in this study through transcriptional rewiring. Several reports suggest that liver inflammation alters hepatic glucose and lipid homeostasis because of direct effects of inflammatory MΦs, like those activated by CYR61 (52)(53)(54). Alternatively, there may be direct effects on hepatocyte metabolism that CYR61 exerts in the context of injury, as has been shown for other cell types (24,55,56).…”

Type 2 Diabetes Mellitus and Liver Disease: Across the Gut–Liver Axis from Fibrosis to Cancer

“…Even if it is not clear yet where the process begins, visceral adiposity certainly plays a key role in initiating IR and subsequent liver injury, even in the absence of increased BMI or an overt diagnosis of diabetes or metabolic syndrome, also conferring an increased risk of NAFLD, especially in PNPLA3 carriers [20,121]. IR, on its hand, drives early LSECs capillarization, contributing to the development of endothelial dysfunction and portal hypertension, even in the absence of fibrosis, worsening liver damage in the long term [58] and providing fertile ground for the development of HCC [44] (Figure 1). IR, endothelial dysfunction, and increased visceral adiposity fuel low-grade systemic inflammation together with metabolic endotoxemia, which appears as a consequence of gut dysbiosis and intestinal barrier dysfunction, probably driven by certain diet components such as fats or AGEs [82].…”

“…Similar to TLR4, Toll-like receptor 2 (TLR2) also triggers inflammation while promoting pancreatic beta-cells dysfunction and diabetes development [42]. TLR2 is mainly activated by palmitate, one of the most abundant free fatty acids, and, after its inhibition, Zhang et al demonstrated a decreased lipotoxicity in hepatic cells [43][44][45]. Peripheral number of macrophages and functions change, switching from an anti-inflammatory (M2) phenotype to a pro-inflammatory (M1) phenotype that produces, among other mediators, TNF-α and interleukin-6 (IL-6), eventually activating the nuclear factor-kappa B (NF-κB) pathway [41].…”