A subset of Kupffer cells regulates metabolism through the expression of CD36.

Tissue macrophages are immune cells whose phenotypes and functions are dictated by origin and niches. However, tissues are complex environments, and macrophage heterogeneity within the same organ has been overlooked so far. Here, we used high-dimensional approaches to characterize macrophage populations in the murine liver. We identified two distinct populations among embryonically derived Kupffer cells (KCs) sharing a core signature while differentially expressing numerous genes and proteins: a major CD206loESAM- population (KC1) and a minor CD206hiESAM+ population (KC2). KC2 expressed genes involved in metabolic processes, including fatty acid metabolism both in steady-state and in diet-induced obesity and hepatic steatosis. Functional characterization by depletion of KC2 or targeted silencing of the fatty acid transporter Cd36 highlighted a crucial contribution of KC2 in the liver oxidative stress associated with obesity. In summary, our study reveals that KCs are more heterogeneous than anticipated, notably describing a subpopulation wired with metabolic functions.

Kupffer Cell mRNA Sequencing.

The liver is an important organ for the regulation of whole-body metabolism, as well as for immunity. Kupffer cells (KCs) are specialized liver-resident macrophages and the major population of immune cells in the liver. These cells have been shown to play an important role for the regulation of liver homeostasis, and many studies have thus linked these cells to the development of various liver diseases. However, the complexity of macrophage populations and the lack of specific and exclusive markers have so far made it difficult to interpret results from many of these studies. Today, new technologies have emerged including next-generation sequencing allowing for more in depth investigation of multifaceted cell populations such as KCs. Here, we describe a protocol to isolate and prepare cDNA libraries for mRNA sequencing of murine liver macrophages. Using mRNA sequencing to study the gene expression of macrophages in the liver provides a great tool to study the various functions of these cells in the regulation of homeostasis and immunity.

Liver macrophages inhibit the endogenous antioxidant response in obesity-associated insulin resistance.

Obesity and insulin resistance are risk factors for nonalcoholic fatty liver disease (NAFLD), the most common chronic liver disease worldwide. Because no approved medication nor an accurate and noninvasive diagnosis is currently available for NAFLD, there is a clear need to better understand the link between obesity and NAFLD. Lipid accumulation during obesity is known to be associated with oxidative stress and inflammatory activation of liver macrophages (LMs). However, we show that although LMs do not become proinflammatory during obesity, they display signs of oxidative stress. In livers of both humans and mice, antioxidant nuclear factor erythroid 2-related factor 2 (NRF2) was down-regulated with obesity and insulin resistance, yielding an impaired response to lipid accumulation. At the molecular level, a microRNA-targeting NRF2 protein, miR-144, was elevated in the livers of obese insulin-resistant humans and mice, and specific silencing of miR-144 in murine and human LMs was sufficient to restore NRF2 protein expression and the antioxidant response. These results highlight the pathological role of LMs and their therapeutic potential to restore the impaired endogenous antioxidant response in obesity-associated NAFLD.

Liver macrophages regulate systemic metabolism through non-inflammatory factors.

Liver macrophages (LMs) have been proposed to contribute to metabolic disease through secretion of inflammatory cytokines. However, anti-inflammatory drugs lead to only modest improvements in systemic metabolism. Here we show that LMs do not undergo a proinflammatory phenotypic switch in obesity-induced insulin resistance in flies, mice and humans. Instead, we find that LMs produce non-inflammatory factors, such as insulin-like growth factor-binding protein 7 (IGFBP7), that directly regulate liver metabolism. IGFBP7 binds to the insulin receptor and induces lipogenesis and gluconeogenesis via activation of extracellular-signal-regulated kinase (ERK) signalling. We further show that IGFBP7 is subject to RNA editing at a higher frequency in insulin-resistant than in insulin-sensitive obese patients (90% versus 30%, respectively), resulting in an IGFBP7 isoform with potentially higher capacity to bind to the insulin receptor. Our study demonstrates that LMs can contribute to insulin resistance independently of their inflammatory status and indicates that non-inflammatory factors produced by macrophages might represent new drug targets for the treatment of metabolic diseases.

Author Correction: Liver macrophages regulate systemic metabolism through non-inflammatory factors.

In the version of this article initially published, author Volker M. Lauschke had affiliation number 13; the correct affiliation number is 12. The error has been corrected in the HTML and PDF versions of the article.

Draft Genome Sequence of a Novel Rhabdovirus Isolated from Deinocerites Mosquitoes.

We present a draft genome of a novel rhabdovirus, called Grenada mosquito rhabdovirus 1 (GMRV1), with homology to Wuhan mosquito virus 9 (WMV9) (NCBI reference sequence NC_031303), isolated from Deinocerites mosquitoes. The genome has a length of 14,420 nucleotides and encodes five open reading frames.

A simple LC-MS/MS method for determination of kynurenine and tryptophan concentrations in human plasma from HIV-infected patients.

BACKGROUND: Indoleamine 2,3-dioxygenase, catalyzing tryptophan (Trp) metabolism through the kynurenine (Kyn) metabolic pathway, plays important roles in immune suppression and the CNS. In this article, we report a simple, rapid and specific LC-MS/MS method for accurate determination of Kyn and Trp concentrations in human plasma from HIV-infected patients. RESULTS: The human plasma sample (100 µl) was mixed with Kyn-d4 and Trp-d5 internal standards and then precipitated with trifluoroacetic acid. The supernatant was directly analyzed by LC-MS/MS. The assay using surrogate matrix calibrators was validated for precision, accuracy, matrix effect, extraction efficiency and stability. Some assay validation issues for endogenous substance bioanalysis using an LC-MS/MS method are discussed. CONCLUSION: A simple, specific and reproducible LC-MS/MS method has been developed and validated for measuring Kyn and Trp in human plasma samples.