Dataset Information

Retinol binding protein 4 primes the NLRP3 inflammasome by signaling through Toll-like receptors 2 and 4.

ABSTRACT: Adipose tissue (AT) inflammation contributes to systemic insulin resistance. In obesity and type 2 diabetes (T2D), retinol binding protein 4 (RBP4), the major retinol carrier in serum, is elevated in AT and has proinflammatory effects which are mediated partially through Toll-like receptor 4 (TLR4). We now show that RBP4 primes the NLRP3 inflammasome for interleukin-1β (IL1β) release, in a glucose-dependent manner, through the TLR4/MD2 receptor complex and TLR2. This impairs insulin signaling in adipocytes. IL1β is elevated in perigonadal white AT (PGWAT) of chow-fed RBP4-overexpressing mice and in serum and PGWAT of high-fat diet-fed RBP4-overexpressing mice vs. wild-type mice. Holo- or apo-RBP4 injection in wild-type mice causes insulin resistance and elevates PGWAT inflammatory markers, including IL1β. TLR4 inhibition in RBP4-overexpressing mice reduces PGWAT inflammation, including IL1β levels and improves insulin sensitivity. Thus, the proinflammatory effects of RBP4 require NLRP3-inflammasome priming. These studies may provide approaches to reduce AT inflammation and insulin resistance in obesity and diabetes.

SUBMITTER: Moraes-Vieira PM

PROVIDER: S-EPMC7733787 | biostudies-literature | 2020 Dec

REPOSITORIES: biostudies-literature

ACCESS DATA

Publications

Retinol binding protein 4 primes the NLRP3 inflammasome by signaling through Toll-like receptors 2 and 4.

Moraes-Vieira Pedro M PM Yore Mark M MM Sontheimer-Phelps Alexandra A Castoldi Angela A Norseen Julie J Aryal Pratik P Simonyté Sjödin Kotryna K Kahn Barbara B BB

Proceedings of the National Academy of Sciences of the United States of America 20201119 49

Adipose tissue (AT) inflammation contributes to systemic insulin resistance. In obesity and type 2 diabetes (T2D), retinol binding protein 4 (RBP4), the major retinol carrier in serum, is elevated in AT and has proinflammatory effects which are mediated partially through Toll-like receptor 4 (TLR4). We now show that RBP4 primes the NLRP3 inflammasome for interleukin-1β (IL1β) release, in a glucose-dependent manner, through the TLR4/MD2 receptor complex and TLR2. This impairs insulin signaling in ...[more]

PMID: 33214151

Similar Datasets

Project description:PurposeElevation of serum retinol-binding protein 4 (RBP4) induces inflammation in primary human retinal microvascular endothelial cells (HRECs) via a retinol-independent mechanism; thus, it may play a causative role in the development and progression of vascular lesions in diabetic retinopathy (DR). Since HRECs do not express the classical RBP4 receptor, stimulated by retinoic acid gene 6 (STRA6), this study focuses on identifying the endothelial cell receptor and signaling that mediate RBP4-induced inflammation.MethodsHRECs were treated with a toll-like receptor 4 (TLR4) small molecule inhibitor (Cli95, also known as TAK-242), TLR4 neutralizing antibody, or mitogen-activated protein kinase (MAPK) inhibitors before treatment with purified recombinant RBP4. The HREC inflammatory response was quantified by in vitro leukostasis assays, western blotting, and enzyme-linked immunosorbent assay (ELISA). To understand how the serum binding partner for RBP4, transthyretin (TTR), may affect RBP4 activity, we also measured RBP4 and TTR levels in serum and retinal lysates from RBP4-Tg and wild-type mice.ResultsTLR4 inhibition significantly reduced RBP4-induced expression of pro-inflammatory proteins and in vitro leukostasis. RBP4 treatment significantly increased phosphoactivation of p38 and c-Jun N-terminal protein kinase (JNK). The p38 inhibitor (SB203580) attenuated RBP4-stimulated vascular cell adhesion molecule 1 (VCAM-1), intracellular adhesion molecule 1 (ICAM-1), monocyte chemoattractant protein (MCP-1), and interleukin 6 (IL-6) production, while the JNK inhibitor (SP600125) reduced RBP4-stimulated sICAM-1, endothelial cell selectin (E-selectin), and MCP-1 production. The MAPK inhibitors only showed partial (50-70%) suppression of the RBP4-stimulated proinflammatory response. Moreover, TLR4 inhibition did not decrease RBP4-induced MAPK phosphoactivation, suggesting that RBP4-mediated MAPK activation is TLR4 independent and occurs through a secondary unknown receptor. We also found that the RBP4/TTR molar ratio was exceptionally high in the retina of RBP4-Tg mice, indicating an abundance of TTR-free RBP4.ConclusionsRBP4-induced inflammation is largely mediated by TLR4, and in part, through JNK and p38 MAPK signaling. The high TTR/RBP4 molar ratio in serum likely protects the endothelium from the proinflammatory effects of RBP4 in vivo, whereas elevation of serum RBP4 causes a significant increase in TTR-free RBP4 in retinal tissue. This offers insight into how RBP4-Tg mice can develop retinal neurodegeneration without coincident retinal microvascular pathology.

Project description:Neuroinflammation associated with HIV-1 infection is a problem affecting ∼50% of HIV-infected individuals. NLR family pyrin domain containing 3 (NLRP3) inflammasome has been implicated in HIV-induced microglial activation, but the mechanism(s) remain unclear. Because HIV-1 Transactivator of Transcription (Tat) protein continues to be present despite antiretroviral therapy and activates NF-kB, we hypothesized that Tat could prime the NLRP3 inflammasome. We found a dose- and time-dependent induction of NLRP3 expression in microglia exposed to Tat compared with control. Tat exposure also time-dependently increased the mature caspase-1 and IL-1β levels and enhanced the IL-1β secretion. These in vitro findings were validated in archival brain tissues from Simian Immunodeficiency Virus (SIV)-infected and uninfected rhesus macaques. Further validation of NLRP3 priming in vivo involved administration of lipopolysaccharide (LPS) to HIV transgenic (Tg) rats followed by assessment of IL-1β mRNA expression and inflammasome activation (ASC oligomers and mature IL-1β). Intriguingly, LPS potentiated upregulation of IL-1β mRNA and inflammasome activation in HIV-Tg rats compared with the wild-type controls. Interestingly, we found an inverse relationship in the expression of NLRP3 and its negative regulator, miR-223, suggesting a miR-223-mediated mechanism for Tat-induced NLRP3 priming. Furthermore, blockade of NLRP3 resulted in decreased IL-1β secretion. Collectively, these findings suggest a novel role of Tat in priming and activating the NLRP3 inflammasome. Therefore, NLRP3 can be envisioned as a therapeutic target for ameliorating Tat-mediated neuroinflammation.SIGNIFICANCE STATEMENT Despite successful suppression of viremia with increased longevity in the era of combined antiretroviral therapy, chronic inflammation with underlying neurocognitive impairment continues to afflict almost 50% of infected individuals. Viral, bacterial, and cellular products have all been implicated in promoting the chronic inflammation found in these individuals. Understanding the molecular mechanism(s) by which viral proteins such as HIV-1 Transactivator of Transcription (Tat) protein can activate microglia is thus of paramount importance. Herein, we demonstrate a novel role of Tat in priming and activating NLR family pyrin domain containing 3 (NLRP3) inflammasomes in microglial cells and in HIV-Tg rats administered lipopolysaccharide. Targeting NLRP3 inflammasome pathway mediators could thus be developed as therapeutic interventions to alleviate or prevent neuroinflammation and subsequent cognitive impairment in HIV-positive patients.

Dataset Information

Retinol binding protein 4 primes the NLRP3 inflammasome by signaling through Toll-like receptors 2 and 4.

Publications

Retinol binding protein 4 primes the NLRP3 inflammasome by signaling through Toll-like receptors 2 and 4.

Similar Datasets

OmicsDI is part of the ELIXIR infrastructure

Tweets