GPR40/FFA1 and neutral sphingomyelinase are involved in palmitate-boosted inflammatory response of microvascular endothelial cells to LPS

Abstract

Objectives Increased levels of both saturated fatty acids (SFAs) and lipopolysaccharide (LPS) are associated with type 2 diabetes. However, it remains largely unknown how SFAs interact with LPS to regulate inflammatory responses in microvascular endothelial cells (MIC ECs) that are critically involved in atherosclerosis as a diabetic complication. In this study, we compared the effects of LPS, palmitic acid (PA), the most abundant saturated fatty acid, or the combination of LPS and PA on interleukin (IL)-6 expression by MIC ECs and explored the underlying mechanisms. Methods Human cardiac MIC ECs were treated with LPS, PA and LPS plus PA and the regulatory pathways including receptors, signal transduction, transcription and post-transcription, and sphingolipid metabolism for IL-6 expression were investigated. Results G protein-coupled receptor (GPR)40 or free fatty acid receptor 1 (FFA1), but not toll-like receptor 4, was involved in PA-stimulated IL-6 expression. PA not only stimulated IL-6 expression by itself, but also remarkably enhanced LPS-stimulated IL-6 expression via a cooperative stimulation on mitogen-activated protein kinase and nuclear factor kappa B signaling pathways, and both transcriptional and post-transcriptional activation. Furthermore, PA induced a robust neutral sphingomyelinase (nSMase)-mediated sphingomyelin hydrolysis that was involved in PA-augmented IL-6 upregulation. Conclusion PA boosted inflammatory response of microvascular endothelial cells to LPS via GPR40 and nSMase.

Upregulation of free fatty acid receptors in periodontal tissues of patients with metabolic syndrome and periodontitis

“…It has been also shown that GPR40 mediated thiazolidinediones‐activated proinflammatory signaling pathways . Furthermore, we have shown that GPR40 mediates palmitate‐enhanced TLR4 inflammatory signaling in vascular endothelial cells . However, a number of studies have shown that GPR40 also had anti‐inflammatory properties.…”

“…Our previous studies have shown that SFA augments LPS-induced proinflammatory gene expression in macrophages and vascular endothelial cells by amplifying TLR4-mediated inflammatory signaling such as mitogen-activated protein kinase (MAPK) and nuclear factor kappa B (NFκB) cascades. 15,25 These findings strongly suggest that free fatty acid receptors such as GPR40 and CD36 are involved in SFA-enhanced proinflammatory gene expression since SFA engages GPR40 and CD36, which mediate MAPK and NFκB signaling activation. 29,30 The role of GPR40 and CD36 in the upregulation of proinflammatory cytokine expression was further supported by our findings that inhibition of GPR40 or CD36 attenuated proinflammatory cytokine expression in gingival fibroblasts stimulated by palmitate and LPS (Figure 3).…”

“…Our previous studies have shown that SFA augments LPS‐induced proinflammatory gene expression in macrophages and vascular endothelial cells by amplifying TLR4‐mediated inflammatory signaling such as mitogen‐activated protein kinase (MAPK) and nuclear factor kappa B (NFκB) cascades . These findings strongly suggest that free fatty acid receptors such as GPR40 and CD36 are involved in SFA‐enhanced proinflammatory gene expression since SFA engages GPR40 and CD36, which mediate MAPK and NFκB signaling activation .…”

“…The solution was kept at 55°C for 10 minutes, mixed, and brought to room temperature. GW1100, an antagonist of GPR40 and Sulfo‐N‐succinimidyl oleate (SSO), an inhibitor of CD36, were purchased from Sigma‐Aldrich.…”

Preliminary in vitro analysis of mechanism of cardiac microvascular endothelial barrier function

“…Injury to the vascular endothelium can lead to dysfunction involving multiple viscera and organs, which can lead to onset and progression of heart failure (Xie et al, 2015). Endothelial barrier, composed of ECs joined through interaction of proteins, such as VE-cadherin, controls the liquid infiltrating the adjacent stroma and maintains vascular selective permeability (Lu et al, 2015). Distribution of VE-cadherin in cells can be adjusted by endocytosis, which can remove VE-cadherins from cell surface and can destroy the connection between ECs.…”