A brain-sparing diphtheria toxin for chemical genetic ablation of peripheral cell lineages.

Conditional expression of diphtheria toxin receptor (DTR) is widely used for tissue-specific ablation of cells. However, diphtheria toxin (DT) crosses the blood-brain barrier, which limits its utility for ablating peripheral cells using Cre drivers that are also expressed in the central nervous system (CNS). Here we report the development of a brain-sparing DT, termed BRAINSPAReDT, for tissue-specific genetic ablation of cells outside the CNS. We prevent blood-brain barrier passage of DT through PEGylation, which polarizes the molecule and increases its size. We validate BRAINSPAReDT with regional genetic sympathectomy: BRAINSPAReDT ablates peripheral but not central catecholaminergic neurons, thus avoiding the Parkinson-like phenotype associated with full dopaminergic depletion. Regional sympathectomy compromises adipose tissue thermogenesis, and renders mice susceptible to obesity. We provide a proof of principle that BRAINSPAReDT can be used for Cre/DTR tissue-specific ablation outside the brain using CNS drivers, while consolidating the link between adiposity and the sympathetic nervous system

Neuro-immune interactions in obesity

For the past few decades, obesity has emerged as one of the major complex diseases affecting human populations. Despite recent breakthroughs in ameliorating some of the complications associated with this disease, there are still no effective therapies against obesity To understand obesity one must know how the adipose tissue (AT) is regulated in normal and affected conditions. Our knowledge on AT biology has grown significantly in the last few years. This knowledge has resulted in a clearer picture of how obesity shapes the AT. In this regard, we have decided to focus our work on one important aspect of AT biology: its neuro-immune regulation. More specifically, we set out to understand if signals originating from the sympathetic nervous system (SNS) can modulate the adipose mass, and if such signaling may be regulated at the immunological level. Here we show that sympathetic nerve bundles target the subcutaneous white AT (WAT). Furthermore, we demonstrate that the sympathetic axons in the WAT mediate the lipolytic response to leptin. Importantly, local ablation of the SNS in WAT resulted in decreased leptin activity and blunted lipolysis. Conversely, by using optogenetics to selectively activate these sympathetic bundles, we observed a local release of the neurotransmitter norepinephrine (NE) and subsequent fat loss. Our data provide evidence supporting that sympathetic axons in the AT are both necessary and sufficient for leptin-driven lipolysis in WAT. Obesity has long been associated with low-grade inflammation in peripheral tissues and in the central nervous system (CNS). We have observed that obesity-associated low-grade inflammation also occurs in the SNS. By using multiphoton microscopy tools, we demonstrate that sympathetic axons in WAT are populated by a discrete population of macrophages with cellular characteristics different from those of the macrophages in the surrounding AT. Such Sympathetic-neuron Associated Macrophages (SAM) exhibit profuse dendritiform processes, which dynamically extend and retract over time. On the other hand, AT macrophages (ATMs) were smaller, round and had a substantially different cellular displacement. Our study demonstrates that obesity-induced inflammation of the AT preferentially affects the sympathetic nerve fibers targeting the WAT and is closely associated with the accumulation of SAMs. Furthermore, we also observed that obesity drove the up-regulation of pro-inflammatory profiles in both SAMs and ATMs. We provide some insight into the possible mechanism that may link macrophages in the AT to the neurotransmitter NE. Our results suggest that SAMs possess the machinery to incorporate NE (via the Norepinephrine Transporter SLC6A2) and to catabolize it (via the enzyme Monoamine Oxidase-A). Of note, this machinery was not present in any other macrophage population we studied. In this regard, the deletion of SLC6A2 in the hematopoietic compartment (by bone marrow transfer from SLC6A2- KO mice into genetically obese ob/ob mice), improved thermogenic capacities and fat oxidation in this mouse model of obesity. Overall, our results demonstrate the functional significance of the neuro-immune interface for the regulation of the adipose tissue during obesity

Macrophages in obesity

Obesity is a worldwide public health concern yet no safe therapies are currently available. The activity of sympathetic neurons is necessary and sufficient for fat mass reduction, via norepinephrine (NE) signaling. Macrophage accumulation in the adipose tissue is thought to play the central role in the onset of obesity, yet their relation to NE has been controversial. We have identified a population of sympathetic neuron-associated macrophages (SAMs) that control obesity via the uptake and clearing of NE. Here we focus on the neuro-immune regulation of obesity by discussing the genetic, cellular and functional signatures of SAMs vis-a-vis adipose tissue macrophages (ATMs)

Macrophages in obesity

Obesity is a worldwide public health concern yet no safe therapies are currently available. The activity of sympathetic neurons is necessary and sufficient for fat mass reduction, via norepinephrine (NE) signaling. Macrophage accumulation in the adipose tissue is thought to play the central role in the onset of obesity, yet their relation to NE has been controversial. We have identified a population of sympathetic neuron-associated macrophages (SAMs) that control obesity via the uptake and clearing of NE. Here we focus on the neuro-immune regulation of obesity by discussing the genetic, cellular and functional signatures of SAMs vis-a-vis adipose tissue macrophages (ATMs)

Diabetes and Cannabinoid CB1 receptor deficiency promotes similar early onset aging-like changes in the skin

Background: The cannabinoid receptor type-1 (CB1R) is a major regulator of metabolism, growth and inflammation. Yet, its potential role in the skin is not well understood. Our aim was to evaluate the role of CB1R in aging-like diabetic skin changes by using a CB1R knockout mouse model. Methods: We evaluated several signals of skin aging in wild-type control (WT), WT streptozotocin-induced type 1 diabetic mice (WT DM), CB1R knockout (CB1RKO) and CB1RKO DM mice. We quantified markers of inflammation, angiogenesis, antioxidant enzymes and collagen content. Moreover, we evaluate reactive oxygen species (ROS) levels and macrophage phenotype, M1 and M2. Results: CB1R expression is decreased in the skin of WT DM mice and collagen levels are decreased in the skin of WT DM, CB1RKO and CB1RKO DM mice. Additionally, the absence of CB1R correlated with higher expression of pro-inflammatory markers, also evident in WT DM or CB1RKO DM mice. Moreover, the M1/M2 macrophage ratio and ROS levels were significantly elevated but in the diabetic WT and the CB1RKO mice, consistent with a significant decrease in the antioxidant capacity of the skin. Conclusions: Our results indicate that CB1R deficiency in the skin may lead to accelerated skin aging due to the increased production of ROS, a decrease in the antioxidant defenses and a higher pro-inflammatory environment. A significant decrease in the CB1R expression may be a significant contributing factor to the early aging-like changes in diabetes.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Sympathetic neuro-adipose connections mediate leptin-driven lipolysis

Leptin is a hormone produced by the adipose tissue that acts in the brain, stimulating white fat breakdown. We find that the lipolytic effect of leptin is mediated through the action of sympathetic nerve fibers that innervate the adipose tissue. Using intravital two-photon microscopy, we observe that sympathetic nerve fibers establish neuro-adipose junctions, directly “enveloping” adipocytes. Local optogenetic stimulation of sympathetic inputs induces a local lipolytic response and depletion of white adipose mass. Conversely, genetic ablation of sympathetic inputs onto fat pads blocks leptin-stimulated phosphorylation of hormone-sensitive lipase and consequent lipolysis, as do knockouts of dopamine β-hydroxylase, an enzyme required for catecholamine synthesis. Thus, neuro-adipose junctions are necessary and sufficient for the induction of lipolysis in white adipose tissue and are an efferent effector of leptin action. Direct activation of sympathetic inputs to adipose tissues may represent an alternative approach to induce fat loss, circumventing central leptin resistance. </p

Corrigendum: A brain-sparing diphtheria toxin for chemical genetic ablation of peripheral cell lineages.

The financial support for this Article was not fully acknowledged. The Acknowledgements should have included the following: [***Human Frontiers Science Program (HFSP) funds the labs of A.I.D. and P.C. ***]