Soluble LR11/SorLA represses thermogenesis in adipose tissue and correlates with BMI in humans

An update on the secretory functions of brown, white, and beige adipose tissue: Towards therapeutic applications

Adipose tissue, including white adipose tissue (WAT), brown adipose tissue (BAT), and beige adipose tissue, is vital in modulating whole-body energy metabolism. While WAT primarily stores energy, BAT dissipates energy as heat for thermoregulation. Beige adipose tissue is a hybrid form of adipose tissue that shares characteristics with WAT and BAT. Dysregulation of adipose tissue metabolism is linked to various disorders, including obesity, type 2 diabetes, cardiovascular diseases, cancer, and infertility. Both brown and beige adipocytes secrete multiple molecules, such as batokines, packaged in extracellular vesicles or as soluble signaling molecules that play autocrine, paracrine, and endocrine roles. A greater understanding of the adipocyte secretome is essential for identifying novel molecular targets in treating metabolic disorders. Additionally, microRNAs show crucial roles in regulating adipose tissue differentiation and function, highlighting their potential as biomarkers for metabolic disorders. The browning of WAT has emerged as a promising therapeutic approach in treating obesity and associated metabolic disorders. Many browning agents have been identified, and nanotechnology-based drug delivery systems have been developed to enhance their efficacy. This review scrutinizes the characteristics of and differences between white, brown, and beige adipose tissues, the molecular mechanisms involved in the development of the adipocytes, the significant roles of batokines, and regulatory microRNAs active in different adipose tissues. Finally, the potential of WAT browning in treating obesity and atherosclerosis, the relationship of BAT with cancer and fertility disorders, and the crosstalk between adipose tissue with circadian system and circadian disorders are also investigated.

Internally tagged Vps10p-domain receptors reveal uptake of the neurotrophin BDNF

The Vps10p-domain (Vps10p-D) receptor family consists of Sortilin, SorLA, SorCS1, SorCS2, and SorCS3. They mediate internalization and intracellular sorting of specific cargo in various cell types, but underlying molecular determinants are incompletely understood. Deciphering the dynamic intracellular itineraries of Vps10p-D receptors is crucial for understanding their role in physiological and cytopathological processes. However, studying their spatial and temporal dynamics by live imaging has been challenging so far, as terminal tagging with fluorophores presumably impedes several of their protein interactions and thus functions. Here, we addressed the lack of appropriate tools and developed functional versions of all family members internally tagged in their ectodomains. We predict folding of the newly designed receptors by bioinformatics and show their exit from the endoplasmic reticulum. We examined their subcellular localization in immortalized cells and primary cultured neurons by immunocytochemistry and live imaging. This was, as far as known, identical to that of wt counterparts. We observed homodimerization of fluorophore-tagged SorCS2 by coimmunoprecipitation and fluorescence lifetime imaging, suggesting functional leucine-rich domains. Through ligand uptake experiments, live imaging and fluorescence lifetime imaging, we show for the first time that all Vps10p-D receptors interact with the neurotrophin brain-derived neurotrophic factor and mediate its uptake, indicating functionality of the Vps10p-Ds. In summary, we developed versions of all Vps10p-D receptors, with internal fluorophore tags that preserve several functions of the cytoplasmic and extracellular domains. These newly developed fluorophore-tagged receptors are likely to serve as powerful functional tools for accurate live studies of the individual cellular functions of Vps10p-D receptors.

Hypothalamic GABRA5-positive neurons control obesity via astrocytic GABA

The lateral hypothalamic area (LHA) regulates food intake and energy balance. Although LHA neurons innervate adipose tissues, the identity of neurons that regulate fat is undefined. Here we show that GABRA5-positive neurons in LHA (GABRA5LHA) polysynaptically project to brown and white adipose tissues in the periphery. GABRA5LHA are a distinct subpopulation of GABAergic neurons and show decreased pacemaker firing in diet-induced obesity mouse models in males. Chemogenetic inhibition of GABRA5LHA suppresses fat thermogenesis and increases weight gain, whereas gene silencing of GABRA5 in LHA decreases weight gain. In the diet-induced obesity mouse model, GABRA5LHA are tonically inhibited by nearby reactive astrocytes releasing GABA, which is synthesized by monoamine oxidase B (Maob). Gene silencing of astrocytic Maob in LHA facilitates fat thermogenesis and reduces weight gain significantly without affecting food intake, which is recapitulated by administration of a Maob inhibitor, KDS2010. We propose that firing of GABRA5LHA suppresses fat accumulation and selective inhibition of astrocytic GABA is a molecular target for treating obesity.

Differentiation of Human Pluripotent Stem Cells (hPSCs) into Brown-Like Adipocytes

Increasing brown adipose tissue (BAT) mass and activation is a therapeutic strategy to prevent and treat obesity and associated complications. Obese and diabetic patients possess less BAT; thus, finding an efficient way to expand their mass is necessary. There is limited knowledge about how human BAT develops, differentiates, and is optimally activated. Accessing human BAT is challenging, given its scarcity and anatomical dispersion. These constraints make detailed BAT-related developmental and functional mechanistic studies in human subjects virtually impossible. We have developed a new chemically defined protocol for differentiating human pluripotent stem cells (hPSCs) into bona fide brown adipocytes (BAs) that overcomes current limitations. This protocol recapitulates step by step the physiological developmental path of human BAT.

Finding memo: versatile interactions of the VPS10p-Domain receptors in Alzheimer’s disease

The family of VPS10p-Domain (D) receptors comprises five members named SorLA, Sortilin, SorCS1, SorCS2 and SorCS3. While their physiological roles remain incompletely resolved, they have been recognized for their signaling engagements and trafficking abilities, navigating a number of molecules between endosome, Golgi compartments, and the cell surface. Strikingly, recent studies connected all the VPS10p-D receptors to Alzheimer’s disease (AD) development. In addition, they have been also associated with diseases comorbid with AD such as diabetes mellitus and major depressive disorder. This systematic review elaborates on genetic, functional, and mechanistic insights into how dysfunction in VPS10p-D receptors may contribute to AD etiology, AD onset diversity, and AD comorbidities. Starting with their functions in controlling cellular trafficking of amyloid precursor protein and the metabolism of the amyloid beta peptide, we present and exemplify how these receptors, despite being structurally similar, regulate various and distinct cellular events involved in AD. This includes a plethora of signaling crosstalks that impact on neuronal survival, neuronal wiring, neuronal polarity, and synaptic plasticity. Signaling activities of the VPS10p-D receptors are especially linked, but not limited to, the regulation of neuronal fitness and apoptosis via their physical interaction with pro- and mature neurotrophins and their receptors. By compiling the functional versatility of VPS10p-D receptors and their interactions with AD-related pathways, we aim to further propel the AD research towards VPS10p-D receptor family, knowledge that may lead to new diagnostic markers and therapeutic strategies for AD patients.

The evolving view of thermogenic fat and its implications in cancer and metabolic diseases

The incidence of metabolism-related diseases like obesity and type 2 diabetes mellitus has reached pandemic levels worldwide and increased gradually. Most of them are listed on the table of high-risk factors for malignancy, and metabolic disorders systematically or locally contribute to cancer progression and poor prognosis of patients. Importantly, adipose tissue is fundamental to the occurrence and development of these metabolic disorders. White adipose tissue stores excessive energy, while thermogenic fat including brown and beige adipose tissue dissipates energy to generate heat. In addition to thermogenesis, beige and brown adipocytes also function as dynamic secretory cells and a metabolic sink of nutrients, like glucose, fatty acids, and amino acids. Accordingly, strategies that activate and expand thermogenic adipose tissue offer therapeutic promise to combat overweight, diabetes, and other metabolic disorders through increasing energy expenditure and enhancing glucose tolerance. With a better understanding of its origins and biological functions and the advances in imaging techniques detecting thermogenesis, the roles of thermogenic adipose tissue in tumors have been revealed gradually. On the one hand, enhanced browning of subcutaneous fatty tissue results in weight loss and cancer-associated cachexia. On the other hand, locally activated thermogenic adipocytes in the tumor microenvironment accelerate cancer progression by offering fuel sources and is likely to develop resistance to chemotherapy. Here, we enumerate current knowledge about the significant advances made in the origin and physiological functions of thermogenic fat. In addition, we discuss the multiple roles of thermogenic adipocytes in different tumors. Ultimately, we summarize imaging technologies for identifying thermogenic adipose tissue and pharmacologic agents via modulating thermogenesis in preclinical experiments and clinical trials.

The armadillo-repeat containing X-linked protein 3, ARMCX3, is a negative regulator of the browning of adipose tissue associated with obesity

OBJECTIVES

To determine the role of armadillo repeat-containing X-linked protein 3 (ARMCX3) in the thermogenic plasticity of adipose tissue.

METHODS

Adipose tissues were characterized in Armcx3-KO male mice. Armcx3 gene expression was analyzed in adipose tissue from mice exposed to thermogenic inducers (cold, β3-adenergic stimulus) and in differentiating brown and beige cells in culture. Analyses encompassed circulating metabolite and hormonal profiling, tissue characterization, histology, gene expression patterns, and immunoblot assays. Armcx3 gene expression was assessed in subcutaneous adipose tissue from lean individuals and individuals with obesity and was correlated with expression of marker genes of adipose browning. The effects of adenoviral-mediated overexpression of ARMCX3 on differentiating brown adipocyte gene expression and respiratory activity were determined.

RESULTS

Male mice lacking ARMCX3 showed significant induction of white adipose tissue browning. In humans, ARMCX3 expression in subcutaneous adipose tissue was inversely correlated with the expression of marker genes of thermogenic activity, including CIDEA, mitochondrial transcripts, and creatine kinase-B. Armcx3 expression in adipose tissues was repressed by thermogenic activation (cold or β3-adrenergic stimulation) and was upregulated by obesity in mice and humans. Experimentally-induced increases in Armcx3 caused down-regulation of thermogenesis-related genes and reduced mitochondrial oxidative activity of adipocytes in culture, whereas siRNA-mediated Armcx3 knocking-down enhanced expression of thermogenesis-related genes.

CONCLUSION

ARMCX3 is a novel player in the control of thermogenic adipose tissue plasticity that acts to repress acquisition of the browning phenotype and shows a direct association with indicators of obesity in mice and humans.

Circulating sLR11 levels predict severity of pulmonary hypertension due to left heart disease

BACKGROUND

Heart failure is a severe condition often involving pulmonary hypertension (PH). Soluble low-density lipoprotein receptor with 11 ligand-binding repeats (sLR11) has been associated with pulmonary artery hypertension. We examined whether sLR11 correlates with PH in left heart disease and can be used as a predictive marker.

METHOD

We retrospectively analyzed patients with severe mitral regurgitation who underwent right heart catheterization before surgery for valve replacement or valvuloplasty from November 2005 to October 2012 at Juntendo University. We measured sLR11 levels before right heart catheterization and analyzed correlations with pulmonary hemodynamics. We compared prognoses between a group with normal sLR11 (≤9.4 ng/ml) and a group with high sLR11 (>9.4 ng/ml). Follow-up was continued for 5 years, with end points of hospitalization due to HF and death due to cardiovascular disease.

RESULTS

Among 34 patients who met the inclusion criteria, sLR11 correlated with mean pulmonary artery pressure (r = 0.54, p<0.001), transpulmonary pressure gradient (r = 0.42, p = 0.012), pulmonary vascular resistance (r = 0.36, p<0.05), and log brain natriuretic peptide (BNP). However, logBNP did not correlate with pulmonary vascular resistance (p = 0.6). Levels of sLR11 were significantly higher in the 10 patients with PH (14.4±4.3 ng/ml) than in patients without PH (9.9±3.9 ng/ml; p = 0.002). At 5 years, the event rate was higher in the high-sLR11 group than in the normal-sLR11 group. The high-sLR11 group showed 5 hospitalizations due to HF (25.0%) and 2 deaths (10.0%), whereas the normal-sLR11 group showed no hospitalizations or deaths. Analyses using receiver operating characteristic curves showed a higher area under the concentration-time curve (AUC) for sLR11 level (AUC = 0.85; 95% confidence interval (CI) = 0.72-0.98) than for BNP (AUC = 0.80, 95%CI = 0.62-0.99) in the diagnosis of PH in left heart disease.

CONCLUSIONS

Concentration of sLR11 is associated with severity of PH and offers a strong predictor of severe mitral regurgitation in patients after surgery.

SORLA is required for insulin-induced expansion of the adipocyte precursor pool in visceral fat

Visceral adipose tissue shows remarkable plasticity, constantly replacing mature adipocytes from an inherent pool of adipocyte precursors. The number of precursors is set in the juvenile organism and remains constant in adult life. Which signals drive precursor pool expansion in juveniles and why they operate in visceral but not in subcutaneous white adipose tissue (WAT) are unclear. Using mouse models, we identified the insulin-sensitizing receptor SORLA as a molecular factor explaining the distinct proliferative capacity of visceral WAT. High levels of SORLA activity in precursors of juvenile visceral WAT prime these cells for nutritional stimuli provided through insulin, promoting mitotic expansion of the visceral precursor cell pool in overfed juvenile mice. SORLA activity is low in subcutaneous precursors, blunting their response to insulin and preventing diet-induced proliferation of this cell type. Our findings provide a molecular explanation for the unique proliferative properties of juvenile visceral WAT, and for the genetic association of SORLA with visceral obesity in humans.

Thermogenic Fat: Development, Physiological Function, and Therapeutic Potential

The concerning worldwide increase of obesity and chronic metabolic diseases, such as T2D, dyslipidemia, and cardiovascular disease, motivates further investigations into preventive and alternative therapeutic approaches. Over the past decade, there has been growing evidence that the formation and activation of thermogenic adipocytes (brown and beige) may serve as therapy to treat obesity and its associated diseases owing to its capacity to increase energy expenditure and to modulate circulating lipids and glucose levels. Thus, understanding the molecular mechanism of brown and beige adipocytes formation and activation will facilitate the development of strategies to combat metabolic disorders. Here, we provide a comprehensive overview of pathways and players involved in the development of brown and beige fat, as well as the role of thermogenic adipocytes in energy homeostasis and metabolism. Furthermore, we discuss the alterations in brown and beige adipose tissue function during obesity and explore the therapeutic potential of thermogenic activation to treat metabolic syndrome.

Unraveling the Developmental Roadmap toward Human Brown Adipose Tissue

Increasing brown adipose tissue (BAT) mass and activation is a therapeutic strategy to treat obesity and complications. Obese and diabetic patients possess low amounts of BAT, so an efficient way to expand their mass is necessary. There is limited knowledge about how human BAT develops, differentiates, and is optimally activated. Accessing human BAT is challenging, given its low volume and anatomical dispersion. These constraints make detailed BAT-related developmental and functional mechanistic studies in humans virtually impossible. We have developed and characterized functionally and molecularly a new chemically defined protocol for the differentiation of human pluripotent stem cells (hPSCs) into brown adipocytes (BAs) that overcomes current limitations. This protocol recapitulates step by step the physiological developmental path of human BAT. The BAs obtained express BA and thermogenic markers, are insulin sensitive, and responsive to β-adrenergic stimuli. This new protocol is scalable, enabling the study of human BAs at early stages of development.

Truncation of Pik3r1 causes severe insulin resistance uncoupled from obesity and dyslipidaemia by increased energy expenditure

OBJECTIVE

Insulin signalling via phosphoinositide 3-kinase (PI3K) requires PIK3R1-encoded regulatory subunits. C-terminal PIK3R1 mutations cause SHORT syndrome, as well as lipodystrophy and insulin resistance (IR), surprisingly without fatty liver or metabolic dyslipidaemia. We sought to investigate this discordance.

METHODS

The human pathogenic Pik3r1 Y657∗ mutation was knocked into mice by homologous recombination. Growth, body composition, bioenergetic and metabolic profiles were investigated on chow and high-fat diet (HFD). We examined adipose and liver histology, and assessed liver responses to fasting and refeeding transcriptomically.

RESULTS

Like humans with SHORT syndrome, Pik3r1WT/Y657∗ mice were small with severe IR, and adipose expansion on HFD was markedly reduced. Also as in humans, plasma lipid concentrations were low, and insulin-stimulated hepatic lipogenesis was not increased despite hyperinsulinemia. At odds with lipodystrophy, however, no adipocyte hypertrophy nor adipose inflammation was found. Liver lipogenic gene expression was not significantly altered, and unbiased transcriptomics showed only minor changes, including evidence of reduced endoplasmic reticulum stress in the fed state and diminished Rictor-dependent transcription on fasting. Increased energy expenditure, which was not explained by hyperglycaemia nor intestinal malabsorption, provided an alternative explanation for the uncoupling of IR from dyslipidaemia.

CONCLUSIONS

Pik3r1 dysfunction in mice phenocopies the IR and reduced adiposity without lipotoxicity of human SHORT syndrome. Decreased adiposity may not reflect bona fide lipodystrophy, but rather, increased energy expenditure, and we suggest that further study of brown adipose tissue in both humans and mice is warranted.

Soluble SORLA Enhances Neurite Outgrowth and Regeneration through Activation of the EGF Receptor/ERK Signaling Axis

SORLA is a transmembrane trafficking protein associated with Alzheimer's disease risk. Although SORLA is abundantly expressed in neurons, physiological roles for SORLA remain unclear. Here, we show that cultured transgenic neurons overexpressing SORLA feature longer neurites, and accelerated neurite regeneration with wounding. Enhanced release of a soluble form of SORLA (sSORLA) is observed in transgenic mouse neurons overexpressing human SORLA, while purified sSORLA promotes neurite extension and regeneration. Phosphoproteomic analyses demonstrate enrichment of phosphoproteins related to the epidermal growth factor (EGFR)/ERK pathway in SORLA transgenic mouse hippocampus from both genders. sSORLA coprecipitates with EGFR in vitro, and sSORLA treatment increases EGFR Y1173 phosphorylation, which is involved in ERK activation in cultured neurons. Furthermore, sSORLA triggers ERK activation, whereas pharmacological EGFR or ERK inhibition reverses sSORLA-dependent enhancement of neurite outgrowth. In search for downstream ERK effectors activated by sSORLA, we identified upregulation of Fos expression in hippocampus from male mice overexpressing SORLA by RNAseq analysis. We also found that Fos is upregulated and translocates to the nucleus in an ERK-dependent manner in neurons treated with sSORLA. Together, these results demonstrate that sSORLA is an EGFR-interacting protein that activates EGFR/ERK/Fos signaling to enhance neurite outgrowth and regeneration.SIGNIFICANCE STATEMENT SORLA is a transmembrane trafficking protein previously known to reduce the levels of amyloid-β, which is critical in the pathogenesis of Alzheimer's disease. In addition, SORLA mutations are a risk factor for Alzheimer's disease. Interestingly, the SORLA ectodomain is cleaved into a soluble form, sSORLA, which has been shown to regulate cytoskeletal signaling pathways and cell motility in cells outside the nervous system. We show here that sSORLA binds and activates the EGF receptor to induce downstream signaling through the ERK serine/threonine kinase and the Fos transcription factor, thereby enhancing neurite outgrowth. These findings reveal a novel role for sSORLA in promoting neurite regeneration through the EGF receptor/ERK/Fos pathway, thereby demonstrating a potential neuroprotective mechanism involving SORLA.

The kallikrein-kinin pathway as a mechanism for auto-control of brown adipose tissue activity

Brown adipose tissue (BAT) is known to secrete regulatory factors in response to thermogenic stimuli. Components of the BAT secretome may exert local effects that contribute to BAT recruitment and activation. Here, we found that a thermogenic stimulus leads to enhanced secretion of kininogen (Kng) by BAT, owing to induction of kininogen 2 (Kng2) gene expression. Noradrenergic, cAMP-mediated signals induce KNG2 expression and release in brown adipocytes. Conversely, the expression of kinin receptors, that are activated by the Kng products bradykinin and [Des-Arg9]-bradykinin, are repressed by thermogenic activation of BAT in vivo and of brown adipocytes in vitro. Loss-of-function models for Kng (the circulating-Kng-deficient BN/Ka rat) and bradykinin (pharmacological inhibition of kinin receptors, kinin receptor-null mice) signaling were coincident in showing abnormal overactivation of BAT. Studies in vitro indicated that Kng and bradykinin exert repressive effects on brown adipocyte thermogenic activity by interfering the PKA/p38 MAPK pathway of control of Ucp1 gene transcription, whereas impaired kinin receptor expression enhances it. Our findings identify the kallikrein–kinin system as a relevant component of BAT thermogenic regulation that provides auto-regulatory inhibitory signaling to BAT.

Brown adipose tissue, known produce heat by metabolizing fat, is also secretes molecules capable of communicating with other organs. Here the authors show that brown adipose tissue secretes kininogen, a component of heat system regulation, that provides auto-regulatory inhibitory signaling in brown adipose tissue.

Auricular Acupuncture Associated with Reduced Waist Circumference in Overweight Women-A Randomized Controlled Trial

Obesity and subsequent ill health have reached epidemic proportions in developed countries, and many developing countries are on the same trajectory. Weight loss and sustaining a healthy weight have posed a significant challenge for individuals, patients, health-care providers, and public health experts. The literature suggests that dietary advice and lifestyle changes alone have limited sustainable impact for those who are seeking to achieve a healthy weight. Supplementary techniques to control weight, such as acupuncture and auricular acupuncture (AA), have shown mixed results and failed to clearly demonstrate a conclusive impact. This study aimed to provide clarity about the impact of AA on weight loss via a randomized controlled trial. Data were collected from patients to identify measurable girth reduction, weight loss, dietary choices, and mood changes over seven weekly sessions of AA (n = 30) versus sham needle as control (n = 28). Results demonstrated a large and highly significant AA treatment effect for reduced waist circumference over the course of the seven-week intervention. While the treatment effect for weight loss and BMI was not significant, this negative result may have been mediated by the relatively short duration of the study. Results also demonstrated a significant mood improvement across participants in both the AA intervention and control group as the intervention progressed. Further studies are required to determine if the reduction in waist circumference is driven specifically by the AA alone or in conjunction with improved mood. The results also have potentially significant implications for healthcare delivery in the fight against overweight and obesity.

Circulating soluble LR11, a differentiation regulator for vascular cells, is increased during pregnancy and exaggerated in patients with pre-eclampsia

BACKGROUND

Pre-eclampsia is a pregnancy-specific disease characterized by onset of hypertension and proteinuria, sometimes progressing into damaging other organs. Here, we investigated the pathological significance of the soluble fragment of LR11 (sLR11), a cell differentiation regulator, in comparison to circulating IL-6 and TNF-α, in pre-eclampsia.

METHODS

The study was conducted in a cross-sectional research design with fourteen pre-eclampsia patients and fifty healthy pregnant subjects. Pre-eclampsia was defined as hypertensive disorders in pregnancy at over 20 weeks of gestation with proteinuria.

RESULTS

Plasma levels of sLR11 as well as IL-6 in pre-eclampsia were increased compared with those in the healthy pregnant subjects at the first, the second, and the third trimester. Receiver operating characteristic analysis for the detection of pre-eclampsia among third-trimester subjects showed that the areas under the curves of sLR11 and IL-6 were equivalent. sLR11 and IL-6 correlated positively with TNF-α in healthy pregnant subjects. In the pre-eclampsia patients, there was neither a correlation between sLR11 and IL-6 nor between sLR11 and TNF-α.

CONCLUSIONS

sLR11 increases during pregnancy, with levels further exaggerated in pre-eclampsia, and may be related to the pathology of pre-eclampsia.

Adipose Tissue-Derived Signatures for Obesity and Type 2 Diabetes: Adipokines, Batokines and MicroRNAs

: Obesity is one of the main risk factors for type 2 diabetes mellitus (T2DM). It is closely related to metabolic disturbances in the adipose tissue that primarily functions as a fat reservoir. For this reason, adipose tissue is considered as the primary site for initiation and aggravation of obesity and T2DM. As a key endocrine organ, the adipose tissue communicates with other organs, such as the brain, liver, muscle, and pancreas, for the maintenance of energy homeostasis. Two different types of adipose tissues-the white adipose tissue (WAT) and brown adipose tissue (BAT)-secrete bioactive peptides and proteins, known as "adipokines" and "batokines," respectively. Some of them have beneficial anti-inflammatory effects, while others have harmful inflammatory effects. Recently, "exosomal microRNAs (miRNAs)" were identified as novel adipokines, as adipose tissue-derived exosomal miRNAs can affect other organs. In the present review, we discuss the role of adipose-derived secretory factors-adipokines, batokines, and exosomal miRNA-in obesity and T2DM. It will provide new insights into the pathophysiological mechanisms involved in disturbances of adipose-derived factors and will support the development of adipose-derived factors as potential therapeutic targets for obesity and T2DM.

SORLA regulates endosomal trafficking and oncogenic fitness of HER2

The human epidermal growth factor receptor 2 (HER2) is an oncogene targeted by several kinase inhibitors and therapeutic antibodies. While the endosomal trafficking of many other receptor tyrosine kinases is known to regulate their oncogenic signalling, the prevailing view on HER2 is that this receptor is predominantly retained on the cell surface. Here, we find that sortilin-related receptor 1 (SORLA; SORL1) co-precipitates with HER2 in cancer cells and regulates HER2 subcellular distribution by promoting recycling of the endosomal receptor back to the plasma membrane. SORLA protein levels in cancer cell lines and bladder cancers correlates with HER2 levels. Depletion of SORLA triggers HER2 targeting to late endosomal/lysosomal compartments and impairs HER2-driven signalling and in vivo tumour growth. SORLA silencing also disrupts normal lysosome function and sensitizes anti-HER2 therapy sensitive and resistant cancer cells to lysosome-targeting cationic amphiphilic drugs. These findings reveal potentially important SORLA-dependent endosomal trafficking-linked vulnerabilities in HER2-driven cancers.

The EGF receptor HER2 is an oncogene protein thought to reside at the plasma membrane, but its endosomal trafficking is currently unclear. Here, the authors report that HER2 is endocytosed and that sortillin-related receptor 1 (SORLA) promotes endosomal HER2 recycling and HER2 oncogenic signalling.

Interleukin-6 released from differentiating human beige adipocytes improves browning

Brown and beige adipocytes contribute significantly to the regulation of whole body energy expenditure and systemic metabolic homeostasis not exclusively by thermogenesis through mitochondrial uncoupling. Several studies have provided evidence in rodents that brown and beige adipocytes produce a set of adipokines ("batokines") which regulate local tissue homeostasis and have beneficial effects on physiological functions of the entire body. We observed elevated secretion of Interleukin (IL)-6, IL-8 and monocyte chemoattractant protein (MCP)-1, but not tumor necrosis factor alpha (TNFα) or IL-1β pro-inflammatory cytokines, by ex vivo differentiating human beige adipocytes (induced by either PPARγ agonist or irisin) compared to white. Higher levels of IL-6, IL-8 and MCP-1 were released from human deep neck adipose tissue biopsies (enriched in browning cells) than from subcutaneous ones. IL-6 was produced in a sustained manner and mostly by the adipocytes and not by the undifferentiated progenitors. Continuous blocking of IL-6 receptor by specific antibody during beige differentiation resulted in downregulation of brown marker genes and increased morphological changes that are characteristic of white adipocytes. The data suggest that beige adipocytes adjust their production of IL-6 to reach an optimal level for differentiation in the medium enhancing browning in an autocrine manner.

Regulatory Roles of Sortilin and SorLA in Immune-Related Processes

Sortilin, also known as Neurotensin Receptor-3, and the sorting-related receptor with type-A repeats (SorLA) are both members of the Vps10p domain receptor family. Initially identified in CNS cells, they are expressed in various other cell types where they exert multiple functions. Although mostly studied for its involvement in Alzheimer’s disease, SorLA has recently been shown to be implicated in immune response by regulating IL-6-mediated signaling, as well as driving monocyte migration. Sortilin has been shown to act as a receptor, as a co-receptor and as an intra- and extracellular trafficking regulator. In the last two decades, deregulation of sortilin has been demonstrated to be involved in many human pathophysiologies, including neurodegenerative disorders (Alzheimer and Parkinson diseases), type 2 diabetes and obesity, cancer, and cardiovascular pathologies such as atherosclerosis. Several studies highlighted different functions of sortilin in the immune system, notably in microglia, pro-inflammatory cytokine regulation, phagosome fusion and pathogen clearance. In this review, we will analyze the multiple roles of sortilin and SorLA in the human immune system and how their deregulation may be involved in disease development.

Brown Adipokines

Brown adipokines are regulatory factors secreted by brown and beige adipocytes that exhibit endocrine, paracrine, and autocrine actions. Peptidic and non-peptidic molecules, including miRNAs and lipids, are constituents of brown adipokines. Brown adipose tissue remodeling to meet thermogenic needs is dependent on the secretory properties of brown/beige adipocytes. The association between brown fat activity and a healthy metabolic profile, in relation to energy balance and glucose and lipid homeostasis, is influenced by the endocrine actions of brown adipokines. A comprehensive knowledge of the brown adipocyte secretome is still lacking. Advancements in the identification and characterization of brown adipokines will facilitate therapeutic interventions for metabolic diseases, as these molecules are obvious candidates to therapeutic agents. Moreover, identification of brown adipokines as circulating biomarkers of brown adipose tissue activity may be particularly useful for noninvasive assessment of brown adipose tissue alterations in human pathologies.

Effective weight control via an implanted self-powered vagus nerve stimulation device

In vivo vagus nerve stimulation holds great promise in regulating food intake for obesity treatment. Here we present an implanted vagus nerve stimulation system that is battery-free and spontaneously responsive to stomach movement. The vagus nerve stimulation system comprises a flexible and biocompatible nanogenerator that is attached on the surface of stomach. It generates biphasic electric pulses in responsive to the peristalsis of stomach. The electric signals generated by this device can stimulate the vagal afferent fibers to reduce food intake and achieve weight control. This strategy is successfully demonstrated on rat models. Within 100 days, the average body weight is controlled at 350 g, 38% less than the control groups. This work correlates nerve stimulation with targeted organ functionality through a smart, self-responsive system, and demonstrated highly effective weight control. This work also provides a concept in therapeutic technology using artificial nerve signal generated from coordinated body activities.

Developing new technologies for the neuromodulation of the vagus nerve can enable therapeutic strategies for body weight control in obese patients. Here, the authors present a battery-free self-powered implantable vagus nerve stimulation system that electrically responds to stomach movement.

Biochemical and cognitive effects of docosahexaenoic acid differ in a developmental and SorLA dependent manner

Beneficial effects of omega-3 fatty acid intake on cognition are under debate as some studies show beneficial effects while others show no effects of omega-3 supplementation. These inconsistencies may be a result of inter-individual response variations, potentially caused by gene and diet interactions. SorLA is a multifunctional receptor involved in ligand trafficking including lipoprotein lipase and amyloid precursor protein. Decreased SorLA levels have been correlated to Alzheimer's disease, and omega-3 fatty acid supplementation is known to increase SorLA expression in neuronal cell lines and mouse models. We therefore addressed potential correlations between Sorl1 and dietary omega-3 in SorLA deficient mice (Sorl1^-/-) and controls exposed to diets supplemented with or deprived of omega-3 during their entire development and lifespan (lifelong) or solely from the time of weaning (post weaning). Observed diet-induced effects were only evident when exposed to lifelong omega-3 supplementation or deprivation as opposed to post weaning exposure only. Lifelong exposure to omega-3 supplementation resulted in impaired spatial learning in Sorl1^-/- mice. The vitamin C antioxidant capacity in the brains of Sorl1^-/- mice was reduced, but reduced glutathione and vitamin E levels were increased, leaving the overall antioxidant capacity of the brain inconclusive. No gross morphological differences of hippocampal neurons were found to account for the altered behavior. We found a significant adverse effect in cognitive performance by combining SorLA deficiency with lifelong exposure to omega-3. Our results stress the need for investigations of the underlying molecular mechanisms to clarify the precise circumstances under which omega-3 supplementation may be beneficial.

Multifaceted Roles of Beige Fat in Energy Homeostasis Beyond UCP1

Beige adipocytes are an inducible form of thermogenic adipose cells that emerge within the white adipose tissue in response to a variety of environmental stimuli, such as chronic cold acclimation. Similar to brown adipocytes that reside in brown adipose tissue depots, beige adipocytes are also thermogenic; however, beige adipocytes possess unique, distinguishing characteristics in their developmental regulation and biological function. This review highlights recent advances in our understanding of beige adipocytes, focusing on the diverse roles of beige fat in the regulation of energy homeostasis that are independent of the canonical thermogenic pathway via uncoupling protein 1.

Transcriptional control of intestinal cholesterol absorption, adipose energy expenditure and lipid handling by Sortilin

The sorting receptor Sortilin functions in the regulation of glucose and lipid metabolism. Dysfunctional lipid uptake, storage, and metabolism contribute to several major human diseases including atherosclerosis and obesity. Sortilin associates with cardiovascular disease; however, the role of Sortilin in adipose tissue and lipid metabolism remains unclear. Here we show that in the low-density lipoprotein receptor-deficient (Ldlr^−/−) atherosclerosis model, Sortilin deficiency (Sort1^−/−) in female mice suppresses Niemann-Pick type C1-Like 1 (Npc1l1) mRNA levels, reduces body and white adipose tissue weight, and improves brown adipose tissue function partially via transcriptional downregulation of Krüppel-like factor 4 and Liver X receptor. Female Ldlr^−/−Sort1^−/− mice on a high-fat/cholesterol diet had elevated plasma Fibroblast growth factor 21 and Adiponectin, an adipokine that when reduced is associated with obesity and cardiovascular disease-related factors. Additionally, Sort1 deficiency suppressed cholesterol absorption in both female mice ex vivo intestinal tissue and human colon Caco-2 cells in a similar manner to treatment with the NPC1L1 inhibitor ezetimibe. Together our findings support a novel role of Sortilin in energy regulation and lipid homeostasis in female mice, which may be a potential therapeutic target for obesity and cardiovascular disease.

Brown and beige fat: From molecules to physiology and pathophysiology

The adipose organ portrays adipocytes of diverse tones: white, brown and beige, each type with distinct functions. Adipocytes orchestrate their adaptation and expansion to provide storage to excess nutrients, the quick mobilisation of fuel to supply peripheral functional demands, insulation, and, in their thermogenic form, heat generation to maintain core body temperature. Thermogenic adipocytes could be targets for anti-obesity and anti-diabetic therapeutic approaches aiming to restore adipose tissue functionality and increase energy dissipation. However, for thermogenic adipose tissue to become therapeutically relevant, a better understanding of its development and origins, its progenitors and their characteristics and the composition of its niche, is essential. Also crucial is the identification of stimuli and molecules promoting its specific differentiation and activation. Here we highlight the structural/cellular differences between human and rodent brown adipose tissue and discuss how obesity and metabolic complication affects brown and beige cells as well as how they could be targeted to improve their activation and improve global metabolic homeostasis. Finally, we describe the limitations of current research models and the advantages of new emerging approaches.

Loss of P2X7 receptor function dampens whole body energy expenditure and fatty acid oxidation

The established role of ATP-responsive P2X7 receptor in inflammatory, neurodegenerative, and immune diseases is now expanding to include several aspects of metabolic dysregulation. Indeed, P2X7 receptors are involved in β cell function, insulin secretion, and liability to diabetes, and loss of P2X7 function may increase the risk of hepatic steatosis and disrupt adipogenesis. Recently, body weight gain, abnormal lipid accumulation, adipocyte hyperplasia, increased fat mass, and ectopic fat distribution have been found in P2X7 KO mice. Here, we hypothesized that such clinical picture of dysregulated lipid metabolism might be the result of altered in vivo energy metabolism. By indirect calorimetry, we assessed 24 h of energy expenditure (EE) and respiratory exchange ratio (RER) as quotient of carbohydrate to fat oxidation in P2X7 KO mice. Moreover, we assessed the same parameters in aged-matched WT counterparts that underwent a 7-day treatment with the P2X7 antagonist A804598. We found that loss of P2X7 function elicits a severe decrease of EE that was less pronounced in A804598-treated mice. In parallel, P2X7KO mice show a drastic increase of RER, thus indicating the occurrence of a greater ratio of carbohydrate to fat oxidation. Decreased EE and fat oxidation is predictive of body weight gain, which was here confirmed. Taken together, our data provide evidence that P2X7 loss of function produces defective energy homeostasis that, together with disrupted adipogenesis, might help to explain accumulation of adipose tissue and contribute to disclose the potential role of P2X7 in metabolic diseases.

Exploring the sortilin related receptor, SorLA, in depression

BACKGROUND

Studies of individual biomarkers for depression have shown insufficient sensitivity and specificity for clinical use, and most likely combinations of biomarkers may provide a better signature. The sorting-related receptor with A-type repeats (SorLA) is a well-studied pathogenic factor for Alzheimer's. SorLA belongs to the Vps10p domain receptor family, which also encompasses sortilin and SorCS1-3. All family members have been implicated in neurological and mental disorders. Notably, the SORCS3 gene is genome-wide significantly associated with depression and serum protein levels of sortilin are reduced in depressed individuals. SorLA regulates the activity of neurotrophic factors and cytokines and we hence speculated that SorLA might be implicated in depression.

METHODS

Serum SorLA levels were measured in two well-defined clinical samples using ELISA. Generalized linear models were used in the statistical analyses.

RESULTS

We identified a multivariate model to discriminate depressed individuals from healthy controls. Interestingly, the model consisted of serum SorLA levels and additional four predictors: previous depressive episode, stressful life events, serum levels of sortilin and VEGF. However, as an isolated factor, we observed no significant difference in SorLA levels between 140 depressed individuals and 140 healthy controls. Nevertheless, we observed a significant increase in SorLA levels following 12 weeks of treatment with nortriptyline, but not escitalopram.

LIMITATIONS

The number of biomarkers included in the multivariate model for depression and lack of replication limit our study.

CONCLUSIONS

Our results suggest SorLA as one of five factors that in combination may support the depression diagnosis, but not as an individual biomarker for depression or treatment response.

Susceptibilities of epicardial and subcutaneous fat tissue for browning-gene expression and diet-induced volume reduction are different

The upregulation of brown or brown-like beige adipocytes is a potential strategy for the prevention or treatment of diabetes and coronary artery diseases in obese patients. Epicardial adipose tissue (EAT) differs significantly from subcutaneous fat tissue (SAT) in metabolic properties. To investigate properties of EAT further, thermogenesis gene expression was investigated in human autopsy and murine samples, and adipocytes differentiated from EAT mesenchymal cells. Subsequently, analyzed EAT volume alterations were observed to be associated with weight reduction in obese patients by imaging. Gene expression analyses of autopsy samples revealed that UCP‑1 mRNA levels in EAT were significantly increased compared with SAT, and β3‑adrenergic receptor (AR) levels tended to be increased; this finding was verified in comparing EAT with SAT in mice. Browning stimulation of human EAT‑derived MCs increased uncoupling protein‑1 and β3‑AR levels by 3.2 fold‑ and 12.6‑fold compared with SAT‑derived MCs, respectively. Subsequent imaging for EAT volume measurement using multi‑detector computed tomography in 10 obese patients revealed that mean EAT volumes did not significantly decrease following weight loss therapy. The EAT volume alterations were not correlated with weight changes, whereas positive correlations were observed in SAT and visceral adipose tissue. Therefore, the studies in man and mouse on EAT properties demonstrated that susceptibilities of EAT and SAT for browning‑gene expression and diet‑induced volume reduction were grossly different. The data suggest a potential association of EAT with local thermogenetic and metabolic homeostasis in cardiac and/or cardiovascular cells, in conjunction with systemic energy metabolism.

Brown and beige adipose tissues: phenotype and metabolic potential in mice and men

With the recent rediscovery of brown fat in adult humans, our outlook on adipose tissue biology has undergone a paradigm shift. While we attempt to identify, recruit, and activate classic brown fat stores in humans, identification of beige fat has also raised the possibility of browning our white fat stores. Whether such transformation of human white fat depots can be achieved to enhance the whole body oxidative potential remains to be seen. Evidence to date, however, largely points toward a major oxidative role only for classic brown fat depots, at least in rodents. White fat stores seem to provide the main fuel for sustaining thermogenesis via lipolysis. Interestingly, molecular markers consistent with both classic brown and beige fat identity can be observed in human supraclavicular depot, thereby complicating the discussion on beige fat in humans. Here, we review the recent advances made in our understanding of brown and beige fat in humans and mice. We further provide an overview of their plausible physiological relevance to whole body energy metabolism.

Microfluidic systems for studying dynamic function of adipocytes and adipose tissue

Recent breakthroughs in organ-on-a-chip and related technologies have highlighted the extraordinary potential for microfluidics to not only make lasting impacts in the understanding of biological systems but also to create new and important in vitro culture platforms. Adipose tissue (fat), in particular, is one that should be amenable to microfluidic mimics of its microenvironment. While the tissue was traditionally considered important only for energy storage, it is now understood to be an integral part of the endocrine system that secretes hormones and responds to various stimuli. As such, adipocyte function is central to the understanding of pathological conditions such as obesity, diabetes, and metabolic syndrome. Despite the importance of the tissue, only recently have significant strides been made in studying dynamic function of adipocytes or adipose tissues on microfluidic devices. In this critical review, we highlight new developments in the special class of microfluidic systems aimed at culture and interrogation of adipose tissue, a sub-field of microfluidics that we contend is only in its infancy. We close by reflecting on these studies as we forecast a promising future, where microfluidic technologies should be capable of mimicking the adipose tissue microenvironment and provide novel insights into its physiological roles in the normal and diseased states. Graphical abstract This critical review focuses on recent developments and challenges in applying microfluidic systems to the culture and analysis of adipocytes and adipose tissue.

The Lives and Times of Brown Adipokines

Brown adipose tissue (BAT) is responsible for adaptive non-shivering thermogenesis. Moreover, brown fat secretes regulatory factors, so-called brown adipokines, that have autocrine, paracrine, and endocrine actions. Brown adipokines are either polypeptides or nonpeptidic molecules including lipid molecules and microRNAs. The secretory properties of brown fat are essential for tissue remodeling adaptations to thermogenic necessities. The endocrine properties of brown adipokines are thought to contribute to the association between BAT activity and a healthy metabolic profile in relation to glucose and lipid homeostasis. The identification and characterization of brown adipokines may allow the discovery of circulating biomarkers of BAT activity in humans, and will lead to the development of candidate tools for therapeutic interventions in metabolic diseases.

Endocrine and autocrine/paracrine modulators of brown adipose tissue mass and activity as novel therapeutic strategies against obesity and type 2 diabetes

The dramatically increasing world-wide prevalence of obesity is recognized as a risk factor for the development of various diseases. The growing research on the role of adipose tissue in controlling energy homeostasis and insulin sensitivity has revealed that the promotion of brown adipose tissue (BAT) activity and the browning of white adipose tissue (WAT) leads to multiple health benefits and prevents obesity and type 2 diabetes (T2D). Inducible thermogenic adipocytes do exist in adult humans and are linked with increased energy combustion and lower body fat mass. Thus brown adipocytes are currently placed at the center of attention for novel therapeutic strategies against metabolic diseases such as obesity and diabetes. Besides the classical, norepinephrine-mediated sympathetic recruitment and activation of thermogenic adipocytes, a number of novel circulating factors have been recently identified to have a positive or negative impact on thermogenic adipocyte formation and activity. In this review their mechanism of action and the plausible therapeutic applications will be summarized and discussed.

ANGPTL8 Blockade With a Monoclonal Antibody Promotes Triglyceride Clearance, Energy Expenditure, and Weight Loss in Mice

Angiopoietin-like protein (ANGPTL)8 is a negative regulator of lipoprotein lipase-mediated plasma triglyceride (TG) clearance. In this study, we describe a fully human monoclonal antibody (REGN3776) that binds monkey and human ANGPTL8 with high affinity. Inhibition of ANGPTL8 with REGN3776 in humanized ANGPTL8 mice decreased plasma TGs and increased lipoprotein lipase activity. Additionally, REGN3776 reduced body weight and fat content. The reduction in body weight was secondary to increased energy expenditure. Finally, single administration of REGN3776 normalized plasma TGs in dyslipidemic cynomolgus monkeys. In conclusion, we show that blockade of ANGPTL8 with monoclonal antibody strongly reduced plasma TGs in mice and monkeys. These data suggest that inhibition of ANGPTL8 may provide a new therapeutic avenue for the treatment of dyslipidemia with beneficial effects on body weight.

The dual role of BMP4 in adipogenesis and metabolism

BMP4 has a well-established role in triggering commitment of mesenchymal stem cells into the osteogenic and adipogenic linage. We recently described an additional dual function in adipogenesis: after promoting the formation of both white and brown pre-adipocytes, Bmp4 drives terminal differentiation into mature white rather than brown fat cells. Besides this, Bmp4 seems to have a dual role in metabolism either promoting or repressing oxidative metabolism in a cell context dependent manner.

miRNAs in human subcutaneous adipose tissue: Effects of weight loss induced by hypocaloric diet and exercise

OBJECTIVE

Obesity is central in the development of insulin resistance. However, the underlying mechanisms still need elucidation. Dysregulated microRNAs (miRNAs; post-transcriptional regulators) in adipose tissue may present an important link.

METHODS

The miRNA expression in subcutaneous adipose tissue from 19 individuals with severe obesity (10 women and 9 men) before and after a 15-week weight loss intervention was studied using genome-wide microarray analysis. The microarray results were validated with RT-qPCR, and pathway enrichment analysis of in silico predicted targets was performed to elucidate the biological consequences of the miRNA dysregulation. Lastly, the messenger RNA (mRNA) and/or protein expression of multiple predicted targets as well as several proteins involved in lipolysis were investigated.

RESULTS

The intervention led to upregulation of miR-29a-3p and miR-29a-5p and downregulation of miR-20b-5p. The mRNA and protein expression of predicted targets was not significantly affected by the intervention. However, negative correlations between miR-20b-5p and the protein levels of its predicted target, acyl-CoA synthetase long-chain family member 1, were observed. Several other miRNA-target relationships correlated negatively, indicating possible miRNA regulation, including miR-29a-3p and lipoprotein lipase mRNA levels. Proteins involved in lipolysis were not affected by the intervention.

CONCLUSIONS

Weight loss influenced several miRNAs, some of which were negatively correlated with predicted targets. These dysregulated miRNAs may affect adipocytokine signaling and forkhead box protein O signaling.

Brown adipose tissue as a secretory organ

Brown adipose tissue (BAT) is the main site of adaptive thermogenesis and experimental studies have associated BAT activity with protection against obesity and metabolic diseases, such as type 2 diabetes mellitus and dyslipidaemia. Active BAT is present in adult humans and its activity is impaired in patients with obesity. The ability of BAT to protect against chronic metabolic disease has traditionally been attributed to its capacity to utilize glucose and lipids for thermogenesis. However, BAT might also have a secretory role, which could contribute to the systemic consequences of BAT activity. Several BAT-derived molecules that act in a paracrine or autocrine manner have been identified. Most of these factors promote hypertrophy and hyperplasia of BAT, vascularization, innervation and blood flow, processes that are all associated with BAT recruitment when thermogenic activity is enhanced. Additionally, BAT can release regulatory molecules that act on other tissues and organs. This secretory capacity of BAT is thought to be involved in the beneficial effects of BAT transplantation in rodents. Fibroblast growth factor 21, IL-6 and neuregulin 4 are among the first BAT-derived endocrine factors to be identified. In this Review, we discuss the current understanding of the regulatory molecules (the so-called brown adipokines or batokines) that are released by BAT that influence systemic metabolism and convey the beneficial metabolic effects of BAT activation. The identification of such adipokines might also direct drug discovery approaches for managing obesity and its associated chronic metabolic diseases.

Sorting receptor SORLA: cellular mechanisms and implications for disease

Sorting-related receptor with A-type repeats (SORLA) is an intracellular sorting receptor that directs cargo proteins, such as kinases, phosphatases, and signaling receptors, to their correct location within the cell. The activity of SORLA assures proper function of cells and tissues, and receptor dysfunction is the underlying cause of common human malignancies, including Alzheimer’s disease, atherosclerosis, and obesity. Here, we discuss the molecular mechanisms that govern sorting of SORLA and its cargo in multiple cell types, and why genetic defects in this receptor results in devastating diseases.

Risk factor SORL1: from genetic association to functional validation in Alzheimer's disease

Alzheimer's disease (AD) represents one of the most dramatic threats to healthy aging and devising effective treatments for this devastating condition remains a major challenge in biomedical research. Much has been learned about the molecular concepts that govern proteolytic processing of the amyloid precursor protein to amyloid-β peptides (Aβ), and how accelerated accumulation of neurotoxic Aβ peptides underlies neuronal cell death in rare familial but also common sporadic forms of this disease. Out of a plethora of proposed modulators of amyloidogenic processing, one protein emerged as a key factor in AD pathology, a neuronal sorting receptor termed SORLA. Independent approaches using human genetics, clinical pathology, or exploratory studies in animal models all converge on this receptor that is now considered a central player in AD-related processes by many. This review will provide a comprehensive overview of the evidence implicating SORLA-mediated protein sorting in neurodegenerative processes, and how receptor gene variants in the human population impair functional receptor expression in sporadic but possibly also in autosomal-dominant forms of AD.

Adiposity-Dependent Regulatory Effects on Multi-tissue Transcriptomes

Obesity is a global epidemic that is causally associated with a range of diseases, including type 2 diabetes and cardiovascular disease, at the population-level. However, there is marked heterogeneity in obesity-related outcomes among individuals. This might reflect genotype-dependent responses to adiposity. Given that adiposity, measured by BMI, is associated with widespread changes in gene expression and regulatory variants mediate the majority of known complex trait loci, we sought to identify gene-by-BMI (G × BMI) interactions on the regulation of gene expression in a multi-tissue RNA-sequencing (RNA-seq) dataset from the TwinsUK cohort (n = 856). At a false discovery rate of 5%, we identified 16 cis G × BMI interactions (top cis interaction: CHURC1, rs7143432, p = 2.0 × 10(-12)) and one variant regulating 53 genes in trans (top trans interaction: ZNF423, rs3851570, p = 8.2 × 10(-13)), all in adipose tissue. The interactions were adipose-specific and enriched for variants overlapping adipocyte enhancers, and regulated genes were enriched for metabolic and inflammatory processes. We replicated a subset of the interactions in an independent adipose RNA-seq dataset (deCODE genetics, n = 754). We also confirmed the interactions with an alternate measure of obesity, dual-energy X-ray absorptiometry (DXA)-derived visceral-fat-volume measurements, in a subset of TwinsUK individuals (n = 682). The identified G × BMI regulatory effects demonstrate the dynamic nature of gene regulation and reveal a functional mechanism underlying the heterogeneous response to obesity. Additionally, we have provided a web browser allowing interactive exploration of the dataset, including of association between expression, BMI, and G × BMI regulatory effects in four tissues.

Implications of thermogenic adipose tissues for metabolic health

Excess and ectopic fat accumulation in obesity is a major risk factor for developing hyperlipidemia, type 2 diabetes and cardiovascular disease. The activation of brown and/or beige adipocytes is a promising target for the treatment of metabolic disorders as the combustion of excess energy by these thermogenic adipocytes may help losing weight and improving plasma parameters including triglyceride, cholesterol and glucose levels. The regulation of heat production by thermogenic adipose tissues is based on a complex crosstalk between the autonomous nervous system, intracellular and secreted factors. This multifaceted alignment regulates thermogenic demands to environmental circumstances in dependence on available energy resources. This review summarizes the current knowledge how thermogenic tissues can be targeted to combat the burden of diseases with a special focus on lipid metabolism and diseases related to lipoprotein metabolism.

SORLA facilitates insulin receptor signaling in adipocytes and exacerbates obesity

In humans, genetic variation of sortilin-related receptor, L(DLR class) A repeats containing (SORL1), which encodes the intracellular sorting receptor SORLA, is a major genetic risk factor for familial and sporadic forms of Alzheimer's disease. Recent GWAS analysis has also associated SORL1 with obesity in humans and in mouse models, suggesting that this receptor may play a role in regulating metabolism. Here, using mouse models with genetic loss or tissue-specific overexpression of SORLA as well as data from obese human subjects, we observed a gene-dosage effect that links SORLA expression to obesity and glucose tolerance. Overexpression of human SORLA in murine adipose tissue blocked hydrolysis of triacylglycerides and caused excessive adiposity. In contrast, Sorl1 gene inactivation in mice accelerated breakdown of triacylglycerides in adipocytes and protected animals from diet-induced obesity. We then identified the underlying molecular mechanism whereby SORLA promotes insulin-induced suppression of lipolysis in adipocytes. Specifically, we determined that SORLA acts as a sorting factor for the insulin receptor (IR) that redirects internalized receptor molecules from endosomes to the plasma membrane, thereby enhancing IR surface expression and strengthening insulin signal reception in target cells. Our findings provide a molecular mechanism for the association of SORL1 with human obesity and confirm a genetic link between neurodegeneration and metabolism that converges on the receptor SORLA.

Circulating soluble form of LR11, a regulator of smooth muscle cell migration, is a novel marker for intima-media thickness of carotid arteries in type 2 diabetes

BACKGROUND

Smooth muscle cell (SMC) migration from the media to the intima, a process affecting plaque stability in advanced-stage atherosclerosis, is under the control of LR11. To delineate the clinical significance of the circulating soluble form of LR11 (sLR11) in patients with type 2 diabetes (T2D), we analyzed the correlation of sLR11 levels with intima-media thickness (IMT) of carotid arteries.

METHODS

Plasma sLR11 levels were measured in 165 patients with T2D (mean age 56.2±10.4 y, 58.2% males, and BMI 24.6±3.6) by ELISA. Averaged IMT levels of common carotid arteries were determined by ultrasonography.

RESULTS

Circulating sLR11 levels were 9.8±3.5ng/ml, and correlated positively with the classical atherosclerosis risk factors age, sex, systolic blood pressure, low-density lipoprotein-cholesterol (LDL-C), fasting plasma-glucose (FPG), and glycosylated hemoglobin. Multivariate linear regression analysis indicated that only FPG was associated with sLR11; sLR11 correlated positively with IMT, together with age and FPG, but less with LDL-C. Among the serum risk factors for IMT, multivariate linear regression analysis uncovered that sLR11 was independently associated with IMT. Subsequent logistic analysis revealed that FPG correlated best with IMT values at a cut-off of 0.80mm and sLR11 at a cut-off of 0.90mm, respectively, while LDL-C showed lower discriminatory power at any IMT cut-off values.

CONCLUSION

Increased sLR11 concentrations are highly associated with increased IMT as well as with FPG in middle-aged, non-obese patients with T2D. Circulating sLR11 may be a novel marker representing the pathophysiology of intimal SMCs in patients with T2D.

Cell-Autonomous Brown-Like Adipogenesis of Preadipocytes From Retinoblastoma Haploinsufficient Mice

Mechanisms behind the emergence of brown adipocyte-like (brite or beige) adipocytes within white adipose tissue (WAT) are of interest. Retinoblastoma protein gene (Rb) haploinsufficiency associates in mice with improved metabolic regulation linked to a greater capacity for fatty acid oxidation and thermogenesis in WAT. We aimed to explain a feasible mechanism of WAT-to-BAT remodeling in this model. Differentiated primary adipocytes and Sca1-positive preadipocytes derived from adipose depots of Rb(+/-) mice and wild-type siblings were compared. Primary white Rb(+/-) adipocytes displayed under basal conditions increased glucose uptake and an enhanced expression of brown adipocyte-related genes (Pparg, Ppargc1a, Ppargc1b, Prdm16, Cpt1b) but not of purported beige/brite transcriptional markers (Cd137, Tmem26, Tbx1, Slc27a1, Hoxc9, Shox2). Lack of induction of beige markers phenocopied results in WAT of adult Rb(+/-) mice. Flow cytometry analysis evidenced an increased number of preadipocytes in WAT depots of Rb(+/-) mice. Sca1(+) preadipocytes from WAT of Rb(+/-) mice displayed increased gene expression of several transcription factors common to the brown and beige adipogenic programs (Prdm16, Pparg, Ppargc1a) and of receptors of bone morphogenetic proteins (BMPs); however, among the recently proposed beige markers, only Tbx1 was upregulated. Adult Rb(+/-) mice had increased circulating levels of BMP7. These results indicate that preadipose cells resident in WAT depots of Rb(+/-) mice retain an increased capacity for brown-like adipogenesis that appears to be different from beige adipogenesis, and suggest that the contribution of these precursors to the Rb(+/-) adipose phenotype is driven, at least in part, by interaction with BMP7 pathways. J. Cell. Physiol. 231: 1941-1952, 2016. © 2016 Wiley Periodicals, Inc.