Hypothalamic AMPK-ER Stress-JNK1 Axis Mediates the Central Actions of Thyroid Hormones on Energy Balance

Exploring the therapeutic effects of sulforaphane: an in-depth review on endoplasmic reticulum stress modulation across different disease contexts

The endoplasmic reticulum (ER) is an intracellular organelle that contributes to the folding of proteins and calcium homeostasis. Numerous elements can disrupt its function, leading to the accumulation of proteins that are unfolded or misfolded in the lumen of the ER, a condition that is known as ER stress. This phenomenon can trigger cell death through the activation of apoptosis and inflammation. Glucoraphanin (GRA) is the predominant glucosinolate found in cruciferous vegetables. Various mechanical and biochemical processes activate the enzyme myrosinase, leading to the hydrolysis of glucoraphanin into the bioactive compound sulforaphane. Sulforaphane is an organosulfur compound that belongs to the isothiocyanate group. It possesses a wide range of activities and has shown remarkable potential as an anti-inflammatory, antioxidant, antitumor, and anti-angiogenic substance. Additionally, sulforaphane is resistant to oxidation, has been demonstrated to have low toxicity, and is considered well-tolerable in individuals. These properties make it a valuable natural dietary supplement for research purposes. Sulforaphane has been demonstrated as a potential candidate drug molecule for managing a range of diseases, primarily because of its potent antioxidant, anti-inflammatory, and anti-apoptotic properties, which can be mediated by modulation of ER stress pathways. This review seeks to cover a wealth of data supporting the broad range of protective functions of sulforaphane, improving various diseases, such as cardiovascular, central nervous system, liver, eye, and reproductive diseases, as well as diabetes, cancer, gastroenteritis, and osteoarthritis, through the amelioration of ER stress in both in vivo and in vitro studies.

Ceramides in the central control of metabolism

Central ceramides regulate energy metabolism by impacting hypothalamic neurons. This allows ceramides to integrate endocrine signals - such as leptin, ghrelin, thyroid hormones, or estradiol - and to modulate the central control of puberty. In this forum article we discuss recent evidence suggesting that specific ceramide species and neuronal populations are involved in these effects.

Obesity disrupts the pituitary-hepatic UPR communication leading to NAFLD progression

Obesity alters levels of pituitary hormones that govern hepatic immune-metabolic homeostasis, dysregulation of which leads to nonalcoholic fatty liver disease (NAFLD). However, the impact of obesity on intra-pituitary homeostasis is largely unknown. Here, we uncovered a blunted unfolded protein response (UPR) but elevated inflammatory signatures in pituitary glands of obese mice and humans. Furthermore, we found that obesity inflames the pituitary gland, leading to impaired pituitary inositol-requiring enzyme 1α (IRE1α)-X-box-binding protein 1 (XBP1) UPR branch, which is essential for protecting against pituitary endocrine defects and NAFLD progression. Intriguingly, pituitary IRE1-deletion resulted in hypothyroidism and suppressed the thyroid hormone receptor B (THRB)-mediated activation of Xbp1 in the liver. Conversely, activation of the hepatic THRB-XBP1 axis improved NAFLD in mice with pituitary UPR defect. Our study provides the first evidence and mechanism of obesity-induced intra-pituitary cellular defects and the pathophysiological role of pituitary-liver UPR communication in NAFLD progression.

Ceramides are fuel gauges on the drive to cardiometabolic disease

Ceramides are signals of fatty acid excess that accumulate when a cell's energetic needs have been met and its nutrient storage has reached capacity. As these sphingolipids accrue, they alter the metabolism and survival of cells throughout the body including in the heart, liver, blood vessels, skeletal muscle, brain, and kidney. These ceramide actions elicit the tissue dysfunction that underlies cardiometabolic diseases such as diabetes, coronary artery disease, metabolic-associated steatohepatitis, and heart failure. Here, we review the biosynthesis and degradation pathways that maintain ceramide levels in normal physiology and discuss how the loss of ceramide homeostasis drives cardiometabolic pathologies. We highlight signaling nodes that sense small changes in ceramides and in turn reprogram cellular metabolism and stimulate apoptosis. Finally, we evaluate the emerging therapeutic utility of these unique lipids as biomarkers that forecast disease risk and as targets of ceramide-lowering interventions that ameliorate disease.

Estrogens prevent the hypothalamus-periphery crosstalk induced by olanzapine intraperitoneal treatment in female mice: Effects on brown/beige adipose tissues and liver

Olanzapine (OLA) is a highly obesogenic second-generation antipsychotic (SGA). Recently we demonstrated that, contrarily to OLA oral treatment, intraperitoneal (i.p.) administration resulted in weight loss and absence of hepatic steatosis in wild-type (WT) and protein tyrosine phosphatase 1B (PTP1B)-deficient (KO) male mice. This protection relied on two central-peripheral axes connecting hypothalamic AMPK with brown/inguinal white adipose tissue (BAT/iWAT) uncoupling protein-1 (UCP-1) and hypothalamic JNK with hepatic fatty acid synthase (FAS). Herein, we addressed OLA i.p. treatment effects in WT and PTP1B-KO female mice. Contrarily to our previous results in WT females receiving OLA orally, the i.p. treatment did not induce weight gain or hyperphagia. Molecularly, in females OLA failed to diminish hypothalamic phospho-AMPK or elevate BAT UCP-1 and energy expenditure (EE) despite the preservation of iWAT browning. Conversely, OLA i.p. treatment in ovariectomized mice reduced hypothalamic phospho-AMPK, increased BAT/iWAT UCP-1 and EE, and induced weight loss as occurred in males. Pretreatment of hypothalamic neurons with 17β-estradiol (E2) abolished OLA effects on AMPK. Moreover, neither hypothalamic JNK activation nor hepatic FAS upregulation were found in WT and PTP1B-KO females receiving OLA via i.p. Importantly, this axis was reestablished upon ovariectomy. In this line, E2 prevented OLA-induced phospho-JNK in hypothalamic neurons. These results support the role of estrogens in sex-related dimorphism in OLA treatment. This study evidenced the benefit of OLA i.p. administration in preventing its obesogenic effects in female mice that could offer clinical value.

Metabolic Messengers: Thyroid Hormones

Thyroid hormones (THs) are key hormones that regulate development and metabolism in mammals. In man, the major target tissues for TH action are the brain, liver, muscle, heart, and adipose tissue. Defects in TH synthesis, transport, metabolism, and nuclear action have been associated with genetic and endocrine diseases in man. Over the past few years, there has been renewed interest in TH action and the therapeutic potential of THs and thyromimetics to treat several metabolic disorders such as hypercholesterolemia, dyslipidaemia, non-alcoholic fatty liver disease (NAFLD), and TH transporter defects. Recent advances in the development of tissue and TH receptor isoform-targeted thyromimetics have kindled new hope for translating our fundamental understanding of TH action into an effective therapy. This review provides a concise overview of the historical development of our understanding of TH action, its physiological and pathophysiological effects on metabolism, and future therapeutic applications to treat metabolic dysfunction.

Hypothalamic AMP-Activated Protein Kinase as a Whole-Body Energy Sensor and Regulator

5´-Adenosine monophosphate (AMP)-activated protein kinase (AMPK), a cellular energy sensor, is an essential enzyme that helps cells maintain stable energy levels during metabolic stress. The hypothalamus is pivotal in regulating energy balance within the body. Certain neurons in the hypothalamus are sensitive to fluctuations in food availability and energy stores, triggering adaptive responses to preserve systemic energy equilibrium. AMPK, expressed in these hypothalamic neurons, is instrumental in these regulatory processes. Hypothalamic AMPK activity is modulated by key metabolic hormones. Anorexigenic hormones, including leptin, insulin, and glucagon-like peptide 1, suppress hypothalamic AMPK activity, whereas the hunger hormone ghrelin activates it. These hormonal influences on hypothalamic AMPK activity are central to their roles in controlling food consumption and energy expenditure. Additionally, hypothalamic AMPK activity responds to variations in glucose concentrations. It becomes active during hypoglycemia but is deactivated when glucose is introduced directly into the hypothalamus. These shifts in AMPK activity within hypothalamic neurons are critical for maintaining glucose balance. Considering the vital function of hypothalamic AMPK in the regulation of overall energy and glucose balance, developing chemical agents that target the hypothalamus to modulate AMPK activity presents a promising therapeutic approach for metabolic conditions such as obesity and type 2 diabetes mellitus.

Palmitoylation of PKCδ by ZDHHC5 in hypothalamic microglia presents as a therapeutic target for fatty liver disease

The hypothalamus plays a fundamental role in controlling lipid metabolism through neuroendocrine signals. However, there are currently no available drug targets in the hypothalamus that can effectively improve human lipid metabolism. In this study, we found that the antimalarial drug artemether (ART) significantly improved lipid metabolism by specifically inhibiting microglial activation in the hypothalamus of high-fat diet-induced mice. Mechanically, ART protects the thyrotropin-releasing hormone (TRH) neurons surrounding microglial cells from inflammatory damage and promotes the release of TRH into the peripheral circulation. As a result, TRH stimulates the synthesis of thyroid hormone (TH), leading to a significant improvement in hepatic lipid disorders. Subsequently, we employed a biotin-labeled ART chemical probe to identify the direct cellular target in microglial cells as protein kinase Cδ (PKCδ). Importantly, ART directly targeted PKCδ to inhibit its palmitoylation modification by blocking the binding of zinc finger DHHC-type palmitoyltransferase 5 (ZDHHC5), which resulted in the inhibition of downstream neuroinflammation signaling. In vivo, hypothalamic microglia-specific PKCδ knockdown markedly impaired ART-dependent neuroendocrine regulation and lipid metabolism improvement in mice. Furthermore, single-cell transcriptomics analysis in human brain tissues revealed that the level of PKCδ in microglia positively correlated with individuals who had hyperlipemia, thereby highlighting a clinical translational value. Collectively, these data suggest that the palmitoylation of microglial PKCδ in the hypothalamus plays a role in modulating peripheral lipid metabolism through hypothalamus-liver communication, and provides a promising therapeutic target for fatty liver diseases.

Hypothalamic free fatty acid receptor-1 regulates whole-body energy balance

OBJECTIVE

Free fatty acid receptor-1 (FFAR1) is a medium- and long-chain fatty acid sensing G protein-coupled receptor that is highly expressed in the hypothalamus. Here, we investigated the central role of FFAR1 on energy balance.

METHODS

Central FFAR1 agonism and virogenic knockdown were performed in mice. Energy balance studies, infrared thermographic analysis of brown adipose tissue (BAT) and molecular analysis of the hypothalamus, BAT, white adipose tissue (WAT) and liver were carried out.

RESULTS

Pharmacological stimulation of FFAR1, using central administration of its agonist TUG-905 in diet-induced obese mice, decreases body weight and is associated with increased energy expenditure, BAT thermogenesis and browning of subcutaneous WAT (sWAT), as well as reduced AMP-activated protein kinase (AMPK) levels, reduced inflammation, and decreased endoplasmic reticulum (ER) stress in the hypothalamus. As FFAR1 is expressed in distinct hypothalamic neuronal subpopulations, we used an AAV vector expressing a shRNA to specifically knockdown Ffar1 in proopiomelanocortin (POMC) neurons of the arcuate nucleus of the hypothalamus (ARC) of obese mice. Our data showed that knockdown of Ffar1 in POMC neurons promoted hyperphagia and body weight gain. In parallel, these mice developed hepatic insulin resistance and steatosis.

CONCLUSIONS

FFAR1 emerges as a new hypothalamic nutrient sensor regulating whole body energy balance. Moreover, pharmacological activation of FFAR1 could provide a therapeutic advance in the management of obesity and its associated metabolic disorders.

CerS6-dependent ceramide synthesis in hypothalamic neurons promotes ER/mitochondrial stress and impairs glucose homeostasis in obese mice

Dysregulation of hypothalamic ceramides has been associated with disrupted neuronal pathways in control of energy and glucose homeostasis. However, the specific ceramide species promoting neuronal lipotoxicity in obesity have remained obscure. Here, we find increased expression of the C16:0 ceramide-producing ceramide synthase (CerS)6 in cultured hypothalamic neurons exposed to palmitate in vitro and in the hypothalamus of obese mice. Conditional deletion of CerS6 in hypothalamic neurons attenuates high-fat diet (HFD)-dependent weight gain and improves glucose metabolism. Specifically, CerS6 deficiency in neurons expressing pro-opiomelanocortin (POMC) or steroidogenic factor 1 (SF-1) alters feeding behavior and alleviates the adverse metabolic effects of HFD feeding on insulin sensitivity and glucose tolerance. POMC-expressing cell-selective deletion of CerS6 prevents the diet-induced alterations of mitochondrial morphology and improves cellular leptin sensitivity. Our experiments reveal functions of CerS6-derived ceramides in hypothalamic lipotoxicity, altered mitochondrial dynamics, and ER/mitochondrial stress in the deregulation of food intake and glucose metabolism in obesity.

Transgenic mice producing the trans 10, cis 12-conjugated linoleic acid present reduced adiposity and increased thermogenesis and fibroblast growth factor 21 (FGF21)

Trans 10, cis 12-conjugated linoleic acid (t10c12-CLA) from ruminant-derived foodstuffs can induce body fat loss after oral administration. In the current study, a transgenic mouse that produced t10c12-CLA had been generated by inserting the Propionibacterium acnes isomerase (Pai) expression cassette into the Rosa26 locus, and its male offspring were used to elucidate the enduring influence of t10c12-CLA on overall health. Compared to their wild-type (wt) C57BL/6J littermates, both biallelic Pai/Pai and monoallelic Pai/wt mice exhibited reduced plasma triglycerides levels, and Pai/wt mice exclusively showed increased serum fibroblast growth factor 21. Further analysis of Pai/Pai mice found a decrease in white fat and an increase in brown fat, with more heat release and less physical activity. Analysis of Pai/Pai brown adipose tissues revealed that hyperthermia was associated with the over-expression of carnitine palmitoyltransferase 1B, uncoupling proteins 1 and 2. These findings suggest that the systemic and long-term impact of t10c12-CLA on obesity might be mediated through the pathway of fibroblast growth factor 21 when low doses are administered or through enhanced thermogenesis of brown adipose tissues when high doses are employed.

Hypothalamic astrocytic-BMAL1 regulates energy homeostasis in a sex-dependent manner

Here, we demonstrate that hypothalamic astrocytic BMAL1 computes cyclic metabolic information to optimize energetic resources in a sexually dimorphic manner. Knockdown of BMAL1 in female astrocytes leads to negative energy balance and alters basal metabolic cycles without affecting circadian locomotor activity. Thus, astrocytic BMAL1 contributes to the control of energy balance through the modulation of the metabolic rate, hepatic and white adipose tissue lipogenesis, and the activity of brown adipose tissue. Importantly, most of these alterations are specific to hypothalamic astrocytic BMAL1. Moreover, female mice with BMAL1 knockdown in astrocytes exhibited a "male-like" metabolic obese phenotype when fed a high-fat diet. Overall, our results suggest a sexually dimorphic effect of astrocytic BMAL1 on the regulation of energy homeostasis, which may be of interest in the physiopathology of obesity and related comorbidities.

Obesity wars: hypothalamic sEVs a new hope

There are currently several pharmacological therapies available for the treatment of obesity, targeting both the central nervous system (CNS) and peripheral tissues. In recent years, small extracellular vesicles (sEVs) have been shown to be involved in many pathophysiological conditions. Because of their special nanosized structure and contents, sEVs can activate receptors and trigger intracellular pathways in recipient cells. Notably, in addition to transferring molecules between cells, sEVs can also alter their phenotypic characteristics. The purpose of this review is to discuss how sEVs can be used as a CNS-targeted strategy for treating obesity. Furthermore, we will evaluate current findings, such as the sEV-mediated targeting of hypothalamic AMP-activated protein kinase (AMPK), and discuss how they can be translated into clinical application.

Hypothalamic JNK1-hepatic fatty acid synthase axis mediates a metabolic rewiring that prevents hepatic steatosis in male mice treated with olanzapine via intraperitoneal: Additional effects of PTP1B inhibition

Olanzapine (OLA), a widely used second-generation antipsychotic (SGA), causes weight gain and metabolic alterations when administered orally to patients. Recently, we demonstrated that, contrarily to the oral treatment which induces weight gain, OLA administered via intraperitoneal (i.p.) in male mice resulted in body weight loss. This protection was due to an increase in energy expenditure (EE) through a mechanism involving the modulation of hypothalamic AMPK activation by higher OLA levels reaching this brain region compared to those of the oral treatment. Since clinical studies have shown hepatic steatosis upon chronic treatment with OLA, herein we further investigated the role of the hypothalamus-liver interactome upon OLA administration in wild-type (WT) and protein tyrosine phosphatase 1B knockout (PTP1B-KO) mice, a preclinical model protected against metabolic syndrome. WT and PTP1B-KO male mice were fed an OLA-supplemented diet or treated via i.p. Mechanistically, we found that OLA i.p. treatment induces mild oxidative stress and inflammation in the hypothalamus in a JNK1-independent and dependent manner, respectively, without features of cell dead. Hypothalamic JNK activation up-regulated lipogenic gene expression in the liver though the vagus nerve. This effect concurred with an unexpected metabolic rewiring in the liver in which ATP depletion resulted in increased AMPK/ACC phosphorylation. This starvation-like signature prevented steatosis. By contrast, intrahepatic lipid accumulation was observed in WT mice treated orally with OLA; this effect being absent in PTP1B-KO mice. We also demonstrated an additional benefit of PTP1B inhibition against hypothalamic JNK activation, oxidative stress and inflammation induced by chronic OLA i.p. treatment, thereby preventing hepatic lipogenesis. The protection conferred by PTP1B deficiency against hepatic steatosis in the oral OLA treatment or against oxidative stress and neuroinflammation in the i.p. treatment strongly suggests that targeting PTP1B might be also a therapeutic strategy to prevent metabolic comorbidities in patients under OLA treatment in a personalized manner.

Brown Adipose Tissue-A Translational Perspective

Brown adipose tissue (BAT) displays the unique capacity to generate heat through uncoupled oxidative phosphorylation that makes it a very attractive therapeutic target for cardiometabolic diseases. Here, we review BAT cellular metabolism, its regulation by the central nervous and endocrine systems and circulating metabolites, the plausible roles of this tissue in human thermoregulation, energy balance, and cardiometabolic disorders, and the current knowledge on its pharmacological stimulation in humans. The current definition and measurement of BAT in human studies relies almost exclusively on BAT glucose uptake from positron emission tomography with 18F-fluorodeoxiglucose, which can be dissociated from BAT thermogenic activity, as for example in insulin-resistant states. The most important energy substrate for BAT thermogenesis is its intracellular fatty acid content mobilized from sympathetic stimulation of intracellular triglyceride lipolysis. This lipolytic BAT response is intertwined with that of white adipose (WAT) and other metabolic tissues, and cannot be independently stimulated with the drugs tested thus far. BAT is an interesting and biologically plausible target that has yet to be fully and selectively activated to increase the body's thermogenic response and shift energy balance. The field of human BAT research is in need of methods able to directly, specifically, and reliably measure BAT thermogenic capacity while also tracking the related thermogenic responses in WAT and other tissues. Until this is achieved, uncertainty will remain about the role played by this fascinating tissue in human cardiometabolic diseases.

An insight into brown/beige adipose tissue whitening, a metabolic complication of obesity with the multifactorial origin

Brown adipose tissue (BAT), a thermoregulatory organ known to promote energy expenditure, has been extensively studied as a potential avenue to combat obesity. Although BAT is the opposite of white adipose tissue (WAT) which is responsible for energy storage, BAT shares thermogenic capacity with beige adipose tissue that emerges from WAT depots. This is unsurprising as both BAT and beige adipose tissue display a huge difference from WAT in terms of their secretory profile and physiological role. In obesity, the content of BAT and beige adipose tissue declines as these tissues acquire the WAT characteristics via the process called "whitening". This process has been rarely explored for its implication in obesity, whether it contributes to or exacerbates obesity. Emerging research has demonstrated that BAT/beige adipose tissue whitening is a sophisticated metabolic complication of obesity that is linked to multiple factors. The current review provides clarification on the influence of various factors such as diet, age, genetics, thermoneutrality, and chemical exposure on BAT/beige adipose tissue whitening. Moreover, the defects and mechanisms that underpin the whitening are described. Notably, the BAT/beige adipose tissue whitening can be marked by the accumulation of large unilocular lipid droplets, mitochondrial degeneration, and collapsed thermogenic capacity, by the virtue of mitochondrial dysfunction, devascularization, autophagy, and inflammation.

Brain nuclear receptors and cardiovascular function

Brain-heart interaction has raised up increasing attentions. Nuclear receptors (NRs) are abundantly expressed in the brain, and emerging evidence indicates that a number of these brain NRs regulate multiple aspects of cardiovascular diseases (CVDs), including hypertension, heart failure, atherosclerosis, etc. In this review, we will elaborate recent findings that have established the physiological relevance of brain NRs in the context of cardiovascular function. In addition, we will discuss the currently available evidence regarding the distinct neuronal populations that respond to brain NRs in the cardiovascular control. These findings suggest connections between cardiac control and brain dynamics through NR signaling, which may lead to novel tools for the treatment of pathological changes in the CVDs.

Modulation of hypothalamic AMPK phosphorylation by olanzapine controls energy balance and body weight

BACKGROUND

Second-generation antipsychotics (SGAs) are a mainstay therapy for schizophrenia. SGA-treated patients present higher risk for weight gain, dyslipidemia and hyperglycemia. Herein, we evaluated the effects of olanzapine (OLA), widely prescribed SGA, in mice focusing on changes in body weight and energy balance. We further explored OLA effects in protein tyrosine phosphatase-1B deficient (PTP1B-KO) mice, a preclinical model of leptin hypersensitivity protected against obesity.

METHODS

Wild-type (WT) and PTP1B-KO mice were fed an OLA-supplemented diet (5 mg/kg/day, 7 months) or treated with OLA via intraperitoneal (i.p.) injection or by oral gavage (10 mg/kg/day, 8 weeks). Readouts of the crosstalk between hypothalamus and brown or subcutaneous white adipose tissue (BAT and iWAT, respectively) were assessed. The effects of intrahypothalamic administration of OLA with adenoviruses expressing constitutive active AMPKα1 in mice were also analyzed.

RESULTS

Both WT and PTP1B-KO mice receiving OLA-supplemented diet presented hyperphagia, but weight gain was enhanced only in WT mice. Unexpectedly, all mice receiving OLA via i.p. lost weight without changes in food intake, but with increased energy expenditure (EE). In these mice, reduced hypothalamic AMPK phosphorylation concurred with elevations in UCP-1 and temperature in BAT. These effects were also found by intrahypothalamic OLA injection and were abolished by constitutive activation of AMPK in the hypothalamus. Additionally, OLA i.p. treatment was associated with enhanced Tyrosine Hydroxylase (TH)-positive innervation and less sympathetic neuron-associated macrophages in iWAT. Both central and i.p. OLA injections increased UCP-1 and TH in iWAT, an effect also prevented by hypothalamic AMPK activation. By contrast, in mice fed an OLA-supplemented diet, BAT thermogenesis was only enhanced in those lacking PTP1B. Our results shed light for the first time that a threshold of OLA levels reaching the hypothalamus is required to activate the hypothalamus BAT/iWAT axis and, therefore, avoid weight gain.

CONCLUSION

Our results have unraveled an unexpected metabolic rewiring controlled by hypothalamic AMPK that avoids weight gain in male mice treated i.p. with OLA by activating BAT thermogenesis and iWAT browning and a potential benefit of PTP1B inhibition against OLA-induced weight gain upon oral treatment.

Reduction of Obesity and Insulin Resistance through Dual Targeting of VAT and BAT by a Novel Combination of Metabolic Cofactors

Obesity is an epidemic disease worldwide, characterized by excessive fat accumulation associated with several metabolic perturbations, such as metabolic syndrome, insulin resistance, hypertension, and dyslipidemia. To improve this situation, a specific combination of metabolic cofactors (MC) (betaine, N-acetylcysteine, L-carnitine, and nicotinamide riboside) was assessed as a promising treatment in a high-fat diet (HFD) mouse model. Obese animals were distributed into two groups, orally treated with the vehicle (obese + vehicle) or with the combination of metabolic cofactors (obese + MC) for 4 weeks. Body and adipose depots weights; insulin and glucose tolerance tests; indirect calorimetry; and thermography assays were performed at the end of the intervention. Histological analysis of epidydimal white adipose tissue (EWAT) and brown adipose tissue (BAT) was carried out, and the expression of key genes involved in both fat depots was characterized by qPCR. We demonstrated that MC supplementation conferred a moderate reduction of obesity and adiposity, an improvement in serum glucose and lipid metabolic parameters, an important improvement in lipid oxidation, and a decrease in adipocyte hypertrophy. Moreover, MC-treated animals presented increased adipose gene expression in EWAT related to lipolysis and fatty acid oxidation. Furthermore, MC supplementation reduced glucose intolerance and insulin resistance, with an increased expression of the glucose transporter Glut4; and decreased fat accumulation in BAT, raising non-shivering thermogenesis. This treatment based on a specific combination of metabolic cofactors mitigates important pathophysiological characteristics of obesity, representing a promising clinical approach to this metabolic disease.

Temperature modulates systemic and central actions of thyroid hormones on BAT thermogenesis

Thyroid hormones (THs) play a major role regulating energy balance and brown adipose tissue (BAT) thermogenesis, as well as body temperature, as shown in hyperthyroid patients. However, the current landscape of preclinical thyroid hormone models is complex. For example, while rats become catabolic after TH administration, mice gain weight; so, these differences in species need to be analyzed in detail and specially whether temperature could be a factor. Here, we aimed to investigate the effect of environmental temperature on those actions. Rats were subcutaneously treated with L-thyroxine (T4) or stereotaxically within the ventromedial nucleus of the hypothalamus (VMH) with triiodothyronine (T3) and housed at 23°C, 4°C or 30°C; energy balance, BAT thermogenesis and AMP-activated protein kinase (AMPK) in the VMH were analyzed. Our data showed that the effect of both systemic T4 of central T3 on energy balance and BAT thermogenesis was dependent upon environmental temperature. This evidence is of interest in the design of experimental settings highlighting the species-specific metabolic actions of THs, and in understanding its physiological role in the adaptation to temperature.

Microarray analysis of mRNA expression profiles in liver of ob/ob mice with real-time atmospheric PM2.5 exposure

Epidemiological studies have demonstrated the association between exposure to fine particulate matter (PM_2.5) and the onset of non-alcoholic fatty liver disease (NAFLD). However, the potential biological mechanism is largely unknown. Our study was aimed to explore the impact of PM_2.5 on the transcriptome level in the liver of ob/ob mice by atmosphere PM_2.5 whole-body dynamic exposure system, and meanwhile preliminarily investigated the effects of metformin intervention in this process. More than three thousand differentially expressed genes (DEGs) was screened out by microarray analysis (p < 0.05, |FC|> 1.5). KEGG pathway enrichment analysis showed that these DEGs were mainly enriched in cancers, infectious diseases, and signal transduction, and the most significant pathways were thyroid hormone signaling pathway, chronic myeloid leukemia and metabolic pathways. Then, 12 hub genes were gained through weighted gene correlation network analysis (WGCNA) and verified by qRT-PCR. The expression of 5 genes in darkslateblue module (cd53, fcer1g, cd68, ctss, laptm5) increased after PM_2.5 exposure and decreased after metformin intervention. They were related to insulin resistance, glucose and lipid metabolism and other liver metabolism, and also neurodegenerative diseases. This study provided valuable clues and possible protective measures to the liver damage in ob/ob mice caused by PM_2.5 exposure, and further research is needed to explore the related mechanism in detail.

Validation of Mct8/Oatp1c1 dKO mice as a model organism for the Allan-Herndon-Dudley Syndrome

OBJECTIVE

The Allan-Herndon-Dudley syndrome (AHDS) is a severe disease caused by dysfunctional central thyroid hormone transport due to functional loss of the monocarboxylate transporter 8 (MCT8). In this study, we assessed whether mice with concomitant deletion of the thyroid hormone transporters Mct8 and the organic anion transporting polypeptide (Oatp1c1) represent a valid preclinical model organism for the AHDS.

METHODS

We generated and metabolically characterized a new CRISPR/Cas9 generated Mct8/Oatp1c1 double-knockout (dKO) mouse line for the clinical features observed in patients with AHDS.

RESULTS

We show that Mct8/Oatp1c1 dKO mice mimic key hallmarks of the AHDS, including decreased life expectancy, central hypothyroidism, peripheral hyperthyroidism, impaired neuronal myelination, impaired motor abilities and enhanced peripheral thyroid hormone action in the liver, adipose tissue, skeletal muscle and bone.

CONCLUSIONS

We conclude that Mct8/Oatp1c1 dKO mice are a valuable model organism for the preclinical evaluation of drugs designed to treat the AHDS.

Hindbrain insulin controls feeding behavior

OBJECTIVE

Pancreatic insulin was discovered a century ago, and this discovery led to the first lifesaving treatment for diabetes. While still controversial, nearly one hundred published reports suggest that insulin is also produced in the brain, with most focusing on hypothalamic or cortical insulin-producing cells. However, specific function for insulin produced within the brain remains poorly understood. Here we identify insulin expression in the hindbrain's dorsal vagal complex (DVC), and determine the role of this source of insulin in feeding and metabolism, as well as its response to diet-induced obesity in mice.

METHODS

To determine the contribution of Ins2-producing neurons to feeding behavior in mice, we used the cross of transgenic RipHER-cre mouse and channelrhodopsin-2 expressing animals, which allowed us to optogenetically stimulate neurons expressing Ins2 in vivo. To confirm the presence of insulin expression in Rip-labeled DVC cells, in situ hybridization was used. To ascertain the specific role of insulin in effects discovered via optogenetic stimulation a selective, CNS applied, insulin receptor antagonist was used. To understand the physiological contribution of insulin made in the hindbrain a virogenetic knockdown strategy was used.

RESULTS

Insulin gene expression and presence of insulin-promoter driven fluorescence in rat insulin promoter (Rip)-transgenic mice were detected in the hypothalamus, but also in the DVC. Insulin mRNA was present in nearly all fluorescently labeled cells in DVC. Diet-induced obesity in mice altered brain insulin gene expression, in a neuroanatomically divergent manner; while in the hypothalamus the expected obesity-induced reduction was found, in the DVC diet-induced obesity resulted in increased expression of the insulin gene. This led us to hypothesize a potentially divergent energy balance role of insulin in these two brain areas. To determine the acute impact of activating insulin-producing neurons in the DVC, optic stimulation of light-sensitive channelrhodopsin 2 in Rip-transgenic mice was utilized. Optogenetic photoactivation induced hyperphagia after acute activation of the DVC insulin neurons. This hyperphagia was blocked by central application of the insulin receptor antagonist S961, suggesting the feeding response was driven by insulin. To determine whether DVC insulin has a necessary contribution to feeding and metabolism, virogenetic insulin gene knockdown (KD) strategy, which allows for site-specific reduction of insulin gene expression in adult mice, was used. While chow-fed mice failed to reveal any changes of feeding or thermogenesis in response to the KD, mice challenged with a high-fat diet consumed less food. No changes in body weight were identified, possibly resulting from compensatory reduction in thermogenesis.

CONCLUSIONS

Together, our data suggest an important role for hindbrain insulin and insulin-producing cells in energy homeostasis.

The role of hypothalamic endoplasmic reticulum stress in schizophrenia and antipsychotic-induced weight gain: A narrative review

Schizophrenia (SCZ) is a serious mental illness that affects 1% of people worldwide. SCZ is associated with a higher risk of developing metabolic disorders such as obesity. Antipsychotics are the main treatment for SCZ, but their side effects include significant weight gain/obesity. Despite extensive research, the underlying mechanisms by which SCZ and antipsychotic treatment induce weight gain/obesity remain unclear. Hypothalamic endoplasmic reticulum (ER) stress is one of the most important pathways that modulates inflammation, neuronal function, and energy balance. This review aimed to investigate the role of hypothalamic ER stress in SCZ and antipsychotic-induced weight gain/obesity. Preliminary evidence indicates that SCZ is associated with reduced dopamine D2 receptor (DRD2) signaling, which significantly regulates the ER stress pathway, suggesting the importance of ER stress in SCZ and its related metabolic disorders. Antipsychotics such as olanzapine activate ER stress in hypothalamic neurons. These effects may induce decreased proopiomelanocortin (POMC) processing, increased neuropeptide Y (NPY) and agouti-related protein (AgRP) expression, autophagy, and leptin and insulin resistance, resulting in hyperphagia, decreased energy expenditure, and central inflammation, thereby causing weight gain. By activating ER stress, antipsychotics such as olanzapine activate hypothalamic astrocytes and Toll-like receptor 4 signaling, thereby causing inflammation and weight gain/obesity. Moreover, evidence suggests that antipsychotic-induced ER stress may be related to their antagonistic effects on neurotransmitter receptors such as DRD2 and the histamine H1 receptor. Taken together, ER stress inhibitors could be a potential effective intervention against SCZ and antipsychotic-induced weight gain and inflammation.

Regulation of metabolic and transcriptional responses by the thyroid hormone in cellular models of murine macrophages

Oncogene-immortalized bone marrow-derived macrophages are considered to be a good model for the study of immune cell functions, but the factors required for their survival and proliferation are still unknown. Although the effect of the thyroid hormones on global metabolic and transcriptional responses in macrophages has not yet been examined, there is increasing evidence that they could modulate macrophage functions. We show here that the thyroid hormone T3 is an absolute requirement for the growth of immortal macrophages. The hormone regulates the activity of the main signaling pathways required for proliferation and anabolic processes, including the phosphorylation of ERK and p38 MAPKs, AKT, ribosomal S6 protein, AMPK and Sirtuin-1. T3 also alters the levels of metabolites controlling transcriptional and post-transcriptional actions in macrophages, and causes widespread transcriptomic changes, up-regulating genes needed for protein synthesis and cell proliferation, while down-regulating genes involved in immune responses and endocytosis, among others. This is not observed in primary bone marrow-derived macrophages, where only p38 and AMPK activation is regulated by T3 and in which the metabolic and transcriptomic effects of the hormone are much weaker. However, the response to IFN-γ is reduced by T3 similarly in immortalized macrophages and in the primary cells, confirming previous results showing that the thyroid hormones can antagonize JAK/STAT-mediated signaling. These results provide new perspectives on the relevant pathways involved in proliferation and survival of macrophage cell culture models and on the crosstalk between the thyroid hormones and the immune system.

Contribution of specific ceramides to obesity-associated metabolic diseases

Ceramides are a heterogeneous group of bioactive membrane sphingolipids that play specialized regulatory roles in cellular metabolism depending on their characteristic fatty acyl chain lengths and subcellular distribution. As obesity progresses, certain ceramide molecular species accumulate in metabolic tissues and cause cell-type-specific lipotoxic reactions that disrupt metabolic homeostasis and lead to the development of cardiometabolic diseases. Several mechanisms for ceramide action have been inferred from studies in vitro, but only recently have we begun to better understand the acyl chain length specificity of ceramide-mediated signaling in the context of physiology and disease in vivo. New discoveries show that specific ceramides affect various metabolic pathways and that global or tissue-specific reduction in selected ceramide pools in obese rodents is sufficient to improve metabolic health. Here, we review the tissue-specific regulation and functions of ceramides in obesity, thus highlighting the emerging concept of selectively inhibiting production or action of ceramides with specific acyl chain lengths as novel therapeutic strategies to ameliorate obesity-associated diseases.

Triiodothyronine (T3) promotes brown fat hyperplasia via thyroid hormone receptor α mediated adipocyte progenitor cell proliferation

The thyroid hormone (TH)-controlled recruitment process of brown adipose tissue (BAT) is not fully understood. Here, we show that long-term treatment of T3, the active form of TH, increases the recruitment of thermogenic capacity in interscapular BAT of male mice through hyperplasia by promoting the TH receptor α-mediated adipocyte progenitor cell proliferation. Our single-cell analysis reveals the heterogeneous nature and hierarchical trajectory within adipocyte progenitor cells of interscapular BAT. Further analyses suggest that T3 facilitates cell state transition from a more stem-like state towards a more committed adipogenic state and promotes cell cycle progression towards a mitotic state in adipocyte progenitor cells, through mechanisms involving the action of Myc on glycolysis. Our findings elucidate the mechanisms underlying the TH action in adipocyte progenitors residing in BAT and provide a framework for better understanding of the TH effects on hyperplastic growth and adaptive thermogenesis in BAT depot at a single-cell level.

Thyroid hormone (TH) action regulates brown adipose tissue thermogenic capacity through incompletely understood mechanisms. Here the authors report that T3, the active form of TH, increases thermogenic capacity via thyroid hormone receptor α-mediated hyperplasia of brown adipose tissue adipocyte progenitor cells.

The central nervous system control of energy homeostasis: high fat diet induced hypothalamic microinflammation and obesity

Obesity is believed to arise through the imbalance of energy homeostasis controlled by the central nervous system, where the hypothalamus plays the fundamental role in energy metabolism. In this review, we will provide an overview regarding the functions of POMC neurons and AgRP neurons in acute nucleus of the hypothalamus which mediated the energy metabolism, highlighting their interactions with peripheral organs derived hormones in control of energy homeostasis. Furthermore, the role of high fat diet induced hypothalamic microinflammation in the pathogenesis of obesity will be discussed. We hope this review could help researchers to understand the mechanism of hypothalamus in control of energy metabolism, and design related drugs to block the pathways involving in the impaired metabolism in obese patients.

Hypothyroidism confers tolerance to cerebral malaria

The modulation of the host's metabolism to protect tissue from damage induces tolerance to infections increasing survival. Here, we examined the role of the thyroid hormones, key metabolic regulators, in the outcome of malaria. Hypothyroidism confers protection to experimental cerebral malaria by a disease tolerance mechanism. Hypothyroid mice display increased survival after infection with Plasmodium berghei ANKA, diminishing intracranial pressure and brain damage, without altering pathogen burden, blood-brain barrier disruption, or immune cell infiltration. This protection is reversed by treatment with a Sirtuin 1 inhibitor, while treatment of euthyroid mice with a Sirtuin 1 activator induces tolerance and reduces intracranial pressure and lethality. This indicates that thyroid hormones and Sirtuin 1 are previously unknown targets for cerebral malaria treatment, a major killer of children in endemic malaria areas.

Hypothalamic control of energy expenditure and thermogenesis

Energy expenditure and energy intake need to be balanced to maintain proper energy homeostasis. Energy homeostasis is tightly regulated by the central nervous system, and the hypothalamus is the primary center for the regulation of energy balance. The hypothalamus exerts its effect through both humoral and neuronal mechanisms, and each hypothalamic area has a distinct role in the regulation of energy expenditure. Recent studies have advanced the understanding of the molecular regulation of energy expenditure and thermogenesis in the hypothalamus with targeted manipulation techniques of the mouse genome and neuronal function. In this review, we elucidate recent progress in understanding the mechanism of how the hypothalamus affects basal metabolism, modulates physical activity, and adapts to environmental temperature and food intake changes.

The hypothalamus is a key regulator of metabolism, controlling resting metabolism, activity levels, and responses to external temperature and food intake. The balance between energy intake and expenditure must be tightly controlled, with imbalances resulting in metabolic disorders such as obesity or diabetes. Obin Kwon at Seoul National University College of Medicine and Ki Woo Kim at Yonsei University College of Dentistry, Seoul, both in South Korea, and coworkers reviewed how metabolism is regulated by the hypothalamus, a small hormone-producing brain region. They report that hormonal and neuronal signals from the hypothalamus influence the ratio of lean to fatty tissue, gender-based differences in metabolism, activity levels, and weight gain in response to food intake. They note that further studies to untangle cause-and-effect relationships and other genetic factors will improve our understanding of metabolic regulation.

Olfactomedin 2 deficiency protects against diet-induced obesity

BACKGROUND AND AIMS

Olfactomedin 2 (OLFM2; also known as noelin 2) is a pleiotropic protein that plays a major role in olfaction and Olfm2 null mice exhibit reduced olfactory sensitivity, as well as abnormal motor coordination and anxiety-related behavior. Here, we investigated the possible metabolic role of OLFM2.

METHODS

Olfm2 null mice were metabolically phenotyped. Virogenetic modulation of central OLFM2 was also performed.

RESULTS

Our data showed that, the global lack of OLFM2 in mice promoted anorexia and increased energy expenditure due to elevated brown adipose tissue (BAT) thermogenesis and browning of white adipose tissue (WAT). This phenotype led to resistance to high fat diet (HFD)-induced obesity. Notably, virogenetic overexpression of Olfm2 in the lateral hypothalamic area (LHA) induced weight gain associated with decreased BAT thermogenesis.

CONCLUSION

Overall, this evidence first identifies central OLFM2 as a new molecular actor in the regulation of whole-body energy homeostasis.

Methionine adenosyltransferase 1a antisense oligonucleotides activate the liver-brown adipose tissue axis preventing obesity and associated hepatosteatosis

Altered methionine metabolism is associated with weight gain in obesity. The methionine adenosyltransferase (MAT), catalyzing the first reaction of the methionine cycle, plays an important role regulating lipid metabolism. However, its role in obesity, when a plethora of metabolic diseases occurs, is still unknown. By using antisense oligonucleotides (ASO) and genetic depletion of Mat1a, here, we demonstrate that Mat1a deficiency in diet-induce obese or genetically obese mice prevented and reversed obesity and obesity-associated insulin resistance and hepatosteatosis by increasing energy expenditure in a hepatocyte FGF21 dependent fashion. The increased NRF2-mediated FGF21 secretion induced by targeting Mat1a, mobilized plasma lipids towards the BAT to be catabolized, induced thermogenesis and reduced body weight, inhibiting hepatic de novo lipogenesis. The beneficial effects of Mat1a ASO were abolished following FGF21 depletion in hepatocytes. Thus, targeting Mat1a activates the liver-BAT axis by increasing NRF2-mediated FGF21 secretion, which prevents obesity, insulin resistance and hepatosteatosis.

Obesity induces resistance to central action of BMP8B through a mechanism involving the BBSome

Objective

Bone morphogenetic protein 8B (BMP8B) plays a major role in the regulation of energy homeostasis by modulating brown adipose tissue (BAT) thermogenesis and white adipose tissue (WAT) browning. Here, we investigated whether BMP8B's role in metabolism is affected by obesity and the possible molecular mechanisms underlying that action.

Methods

Central treatments with BMP8B were performed in rats fed a standard (SD) and high-fat diet (HFD), as well as in genetically modified mice. Energy balance studies, infrared thermographic analysis of BAT and molecular analysis of the hypothalamus, BAT and WAT were carried out.

Results

We show for the first time that HFD-induced obesity elicits resistance to the central actions of BMP8B on energy balance. This obesity-induced BMP8B resistance is explained by i) lack of effects on AMP-activated protein kinase (AMPK) signaling, ii) decreased BMP receptors signaling and iii) reduced expression of Bardet-Biedl Syndrome 1 (BBS1) protein, a key component of the protein complex BBSome in the ventromedial nucleus of the hypothalamus (VMH). The possible mechanistic involvement of BBS1 in this process is demonstrated by lack of a central response to BMP8B in mice carrying a single missense disease-causing mutation in the Bbs1 gene.

Conclusions

Overall, our data uncover a new mechanism of central resistance to hormonal action that may be of relevance in the pathophysiology of obesity.

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Central BMP8B induces BAT activation and browning through hypothalamic AMPK.

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Obesity elicits resistance to the central effects of BMP8B on energy balance.

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Obesity impairs the effect of BMP8B on AMPK, BMP Type I receptors signaling and BBS1 in the hypothalamus.

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Lack of BBS1 function recapitulates the thermogenic-induced resistance to central BMP8B.

The evolving view of thermogenic adipocytes - ontogeny, niche and function

The worldwide incidence of obesity and its sequelae, such as type 2 diabetes mellitus, have reached pandemic levels. Central to the development of these metabolic disorders is adipose tissue. White adipose tissue stores excess energy, whereas brown adipose tissue (BAT) and beige (also known as brite) adipose tissue dissipate energy to generate heat in a process known as thermogenesis. Strategies that activate and expand BAT and beige adipose tissue increase energy expenditure in animal models and offer therapeutic promise to treat obesity. A better understanding of the molecular mechanisms underlying the development of BAT and beige adipose tissue and the activation of thermogenic function is the key to creating practical therapeutic interventions for obesity and metabolic disorders. In this Review, we discuss the regulation of the tissue microenvironment (the adipose niche) and inter-organ communication between BAT and other tissues. We also cover the activation of BAT and beige adipose tissue in response to physiological cues (such as cold exposure, exercise and diet). We highlight advances in harnessing the therapeutic potential of BAT and beige adipose tissue by genetic, pharmacological and cell-based approaches in obesity and metabolic disorders.

Orally Induced Hyperthyroidism Regulates Hypothalamic AMP-Activated Protein Kinase

Besides their direct effects on peripheral metabolic tissues, thyroid hormones (TH) act on the hypothalamus to modulate energy homeostasis. However, since most of the hypothalamic actions of TH have been addressed in studies with direct central administration, the estimation of the relative contribution of the central vs. peripheral effects in physiologic conditions of peripheral release (or administration) of TH remains unclear. In this study we used two different models of peripherally induced hyperthyroidism (i.e., T4 and T3 oral administration) to assess and compare the serum and hypothalamic TH status and relate them to the metabolic effects of the treatment. Peripheral TH treatment affected feeding behavior, overall growth, core body temperature, body composition, brown adipose tissue (BAT) morphology and uncoupling protein 1 (UCP1) levels and metabolic activity, white adipose tissue (WAT) browning and liver metabolism. This resulted in an increased overall uncoupling capacity and a shift of the lipid metabolism from WAT accumulation to BAT fueling. Both peripheral treatment protocols induced significant changes in TH concentrations within the hypothalamus, with T3 eliciting a downregulation of hypothalamic AMP-activated protein kinase (AMPK), supporting the existence of a central action of peripheral TH. Altogether, these data suggest that peripherally administered TH modulate energy balance by various mechanisms; they also provide a unifying vision of the centrally mediated and the direct local metabolic effect of TH in the context of hyperthyroidism.

Phytochemical Composition, Anti-Inflammatory and ER Stress-Reducing Potential of Sambucus ebulus L. Fruit Extract

Sambucus ebulus L. (SE) fruits are used for their immunostimulation, hematopoietic and antiviral potential. Recently, we focused on analyzing the mechanism underlying SE fruit aqueous extract's (FAE) immunomodulation and anti-inflammatory activities, with attention to its endoplasmic reticulum (ER) stress-reducing potential. J774A.1 macrophages were treated with SE FAE alone or in conditions of lipopolysaccharides (LPS) stimulation. Using GC-MS and LC-MS/MS, its phytochemical composition was analyzed. To measure transcription and protein levels, we used qPCR and Western blot, respectively. The prevailing phytochemicals in SE FAE were hydroxycinnamic acids, proanthocyanidins and anthocyanins. The content of some amino acids, organic acids, alcohols, fatty acids and esters were newly reported. Extracts exerted an immunostimulation potential by stimulating IL-6, TNFα, Ccl2, COX2 and iNOS transcription, without inducing ER stress. SE FAE suppressed the LPS-induced transcription of inflammation related genes (IL-1β, IL-6, TNFα, Ccl2, Icam-1, Fabp4, COX2, iNOS, Noxo1, IL-1ra, Sirt-1) and reduced the protein levels of iNOS, peIF2α, ATF6α and CHOP. The effects were comparable to that of salicylic acid. SE suppresses LPS-stimulated inflammatory markers on the transcription and translation levels. Targeting ER stress is possibly another mechanism underlying its anti-inflammatory potential. These findings reveal the potential of SE fruits as a beneficial therapeutic of inflammation and ER stress-related pathological conditions.

3,5-Diiodothyronine protects against cardiac ischaemia-reperfusion injury in male rats

NEW FINDINGS

What is the central question of this study? 3,5-Diiodothyronine (3,5-T2) administration increases resting metabolic rate, prevents or treats liver steatosis in rodent models, and ameliorates insulin resistance: what are its effects on cardiac electrical and contractile properties and autonomic regulation? What is the main finding and its importance? Chronic 3,5-T2 administration has no adverse effects on cardiac function. Remarkably, 3,5-T2 improves the autonomous control of the rat heart and protects against ischaemia-reperfusion injury.

ABSTRACT

The use of 3,5,3'-triiodothyronine (T3) and thyroxine (T4) to treat metabolic diseases has been hindered by potential adverse effects on liver, lipid metabolism and cardiac electrical properties. It is recognized that 3,5-diiodothyronine (3,5-T2) administration increases resting metabolic rate, prevents or treats liver steatosis in rodent models and ameliorates insulin resistance, suggesting 3,5-T2 as a potential therapeutic tool. However, a comprehensive assessment of cardiac electrical and contractile properties has not been made so far. Three-month-old Wistar rats were daily administered vehicle, 3,5-T2 or 3,5-T2+T4 and no signs of atrial or ventricular arrhythmia were detected in non-anaesthetized rats during 90 days. Cardiac function was preserved as heart rate, left ventricle diameter and shortening fraction in 3,5-T2-treated rats compared to vehicle and 3,5-T2+T4 groups. Power spectral analysis indicated an amelioration of the heart rate variability only in 3,5-T2-treated rats. An increased baroreflex sensitivity at rest was observed in both 3,5-T2-treated groups. Finally, 3,5-T2 Langendorff-perfused hearts presented a significant recovery of left ventricular function and remarkably smaller infarction area after ischaemia-reperfusion injury. In conclusion, chronic 3,5-T2 administration ameliorates tonic cardiac autonomic control and confers cardioprotection against ischaemia-reperfusion injury in healthy male rats.

Ventromedial Nucleus of the Hypothalamus Neurons Under the Magnifying Glass

The ventromedial nucleus of the hypothalamus (VMH) is a complex brain structure that is integral to many neuroendocrine functions, including glucose regulation, thermogenesis, and appetitive, social, and sexual behaviors. As such, it is of little surprise that the nucleus is under intensive investigation to decipher the mechanisms which underlie these diverse roles. Developments in genetic and investigative tools, for example the targeting of steroidogenic factor-1-expressing neurons, have allowed us to take a closer look at the VMH, its connections, and how it affects competing behaviors. In the current review, we aim to integrate recent findings into the literature and contemplate the conclusions that can be drawn.

Ovarian insufficiency impairs glucose-stimulated insulin secretion through activation of hypothalamic de novo ceramide synthesis

Oestrogens regulate body weight through their action on hypothalamus to modulate food intake and energy expenditure. Hypothalamic de novo ceramide synthesis plays a central role on obesity induced by oestrogen deficiency. Depletion in oestrogens is also known to be associated with glucose intolerance, which favours type 2 diabetes (T2D). However, the implication of hypothalamic ceramide in the regulation of glucose homeostasis by oestrogen is unknown. Here, we studied glucose homeostasis and insulin secretion in ovariectomized (OVX) female rats. OVX induces body weight gain associated with a hypothalamic inflammation and impaired glucose homeostasis. Genetic blockade of ceramide synthesis in the ventromedial nucleus of the hypothalamus (VMH) reverses hypothalamic inflammation and partly restored glucose tolerance induced by OVX. Furthermore, glucose-stimulated insulin secretion (GSIS) is increased in OVX rats due to a raise of insulin secretion second phase, a characteristic of early stage of T2D. In contrast, GSIS from isolated islets of OVX rats is totally blunted. Inhibition of ceramide synthesis in the VMH restores GSIS from isolated OVX islets and represses the second phase of insulin secretion. Stimulation of oestrogen receptor α (ERα) by oestradiol (E2) down-regulates ceramide synthesis in hypothalamic neuronal GT1-7 cells but no in microglial SIM-A9 cells. In contrast, genetic inactivation of ERα in VMH upregulates ceramide synthesis. These results indicate that hypothalamic neuronal de novo ceramide synthesis triggers the OVX-dependent impairment of glucose homeostasis which is partly mediated by a dysregulation of GSIS.

Small extracellular vesicle-mediated targeting of hypothalamic AMPKα1 corrects obesity through BAT activation

Current pharmacological therapies for treating obesity are of limited efficacy. Genetic ablation or loss of function of AMP-activated protein kinase alpha 1 (AMPKα1) in steroidogenic factor 1 (SF1) neurons of the ventromedial nucleus of the hypothalamus (VMH) induces feeding-independent resistance to obesity due to sympathetic activation of brown adipose tissue (BAT) thermogenesis. Here, we show that body weight of obese mice can be reduced by intravenous injection of small extracellular vesicles (sEVs) delivering a plasmid encoding an AMPKα1 dominant negative mutant (AMPKα1-DN) targeted to VMH-SF1 neurons. The beneficial effect of SF1-AMPKα1-DN-loaded sEVs is feeding-independent and involves sympathetic nerve activation and increased UCP1-dependent thermogenesis in BAT. Our results underscore the potential of sEVs to specifically target AMPK in hypothalamic neurons and introduce a broader strategy to manipulate body weight and reduce obesity.

Thyroid wars: the rise of central actions

In the field of thyroid hormone (TH) action on energy balance, huge advances have been achieved in the past decade, from human, animal, and in vitro studies. A key achievement was the demonstration of the TH 'central' metabolic action, which was recently discovered in rodent models and challenged the previous 'peripheral' paradigm. In this opinion, we dissect and try to unify the two paradigms, from analyzing the respective bench models to extrapolating the possible translational bedside implications.

Key role for hypothalamic interleukin-6 in food-motivated behavior and body weight regulation

The pro-inflammatory role of interleukin-6 (IL-6) is well-characterized. Blockade of IL-6, by Tocilizumab, is used in patients with rheumatoid arthritis and those diagnosed with cytokine storm. However, brain-produced IL-6 has recently emerged as a critical mediator of gut/adipose communication with the brain. Central nervous system (CNS) IL-6 is engaged by peripheral and central signals regulating energy homeostasis. IL-6 is critical for mediating hypophagia and weight loss effects of a GLP-1 analog, exendin-4, a clinically utilized drug. However, neuroanatomical substrates and behavioral mechanisms of brain IL-6 energy balance control remain poorly understood. We propose that the lateral hypothalamus (LH) is an IL-6-harboring brain region, key to food intake and food reward control. Microinjections of IL-6 into the LH reduced chow and palatable food intake in male rats. In contrast, female rats responded with reduced motivated behavior for sucrose, measured by the progressive ratio operant conditioning test, a behavioral mechanism previously not linked to IL-6. To test whether IL-6, produced in the LH, is necessary for ingestive and motivated behaviors, and body weight homeostasis, virogenetic knockdown by infusion of AAV-siRNA-IL6 into the LH was utilized. Attenuation of LH IL-6 resulted in a potent increase in sucrose-motivated behavior, without any effect on ingestive behavior or body weight in female rats. In contrast, the treatment did not affect any parameters measured (chow intake, sucrose-motivated behavior, locomotion, and body weight) in chow-fed males. However, when challenged with a high-fat/high-sugar diet, the male LH IL-6 knockdown rats displayed rapid weight gain and hyperphagia. Together, our data suggest that LH-produced IL-6 is necessary and sufficient for ingestive behavior and weight homeostasis in male rats. In females, IL-6 in the LH plays a critical role in food-motivated, but not ingestive behavior control or weight regulation. Thus, collectively these data support the idea that brain-produced IL-6 engages the hypothalamus to control feeding behavior.

Activation of hypothalamic AMPK ameliorates metabolic complications of experimental arthritis

OBJECTIVE

To investigate whether thermogenesis and the hypothalamus may be involved in the physiopathology of experimental arthritis (EA).

METHODS

EA was induced in Lewis male rats by intradermal injection of Freund's complete adjuvant (FCA). Food intake, body weight, plasma cytokines, thermographic analysis, gene and protein expression of thermogenic markers in brown (BAT) and white (WAT) adipose tissue and hypothalamic AMP-activated protein kinase (AMPK) were analyzed. Virogenetic activation of hypothalamic AMPK was performed.

RESULTS

We first demonstrate that EA is associated with increased BAT thermogenesis and browning of subcutaneous WAT (sWAT) leading to elevated energy expenditure. Moreover, rats suffering EA show inhibition of hypothalamic AMPK, a canonical energy sensor modulating energy homeostasis at central level. Notably, specific genetic activation of AMPK in the ventromedial nucleus of the hypothalamus (VMH; a key site modulating energy metabolism) reverses the effect of EA on energy balance, brown fat and browning, as well as promoting an amelioration of the inflammatory status.

CONCLUSION

Overall, these data indicate that EA promotes a central catabolic state that can be targeted and reversed by the activation of hypothalamic AMPK. This might open new therapeutic alternatives to treat rheumatoid arthritis (RA)-associated metabolic comorbidities, improving RA-patients overall prognosis.

AMPK in the brain: its roles in glucose and neural metabolism

The adenosine monophosphate-activated protein kinase (AMPK) is an integrative metabolic sensor that maintains energy balance at the cellular level and plays an important role in orchestrating intertissue metabolic signaling. AMPK regulates cell survival, metabolism, and cellular homeostasis basally as well as in response to various metabolic stresses. Studies so far show that the AMPK pathway is associated with neurodegeneration and CNS pathology, but the mechanisms involved remain unclear. AMPK dysregulation has been reported in neurodegenerative diseases such as amyotrophic lateral sclerosis, multiple sclerosis, Alzheimer's disease, Parkinson's disease, Huntington's disease, and other neuropathies. AMPK activation appears to be both neuroprotective and pro-apoptotic, possibly dependent upon neural cell types, the nature of insults, and the intensity and duration of AMPK activation. While embryonic brain development in AMPK null mice appears to proceed normally without any overt structural abnormalities, our recent study confirmed the full impact of AMPK loss in the postnatal and aging brain. Our studies revealed that Ampk deletion in neurons increased basal neuronal excitability and reduced latency to seizure upon stimulation. Three major pathways, glycolysis, pentose phosphate shunt, and glycogen turnover, contribute to utilization of glucose in the brain. AMPK's regulation of aerobic glycolysis in astrocytic metabolism warrants further deliberation, particularly glycogen turnover and shuttling of glucose- and glycogen-derived lactate from astrocytes to neurons during activation. In this minireview, we focus on recent advances in AMPK and energy-sensing in the brain.

3D Adipose Tissue Culture Links the Organotypic Microenvironment to Improved Adipogenesis

Obesity and type 2 diabetes are strongly associated with adipose tissue dysfunction and impaired adipogenesis. Understanding the molecular underpinnings that control adipogenesis is thus of fundamental importance for the development of novel therapeutics against metabolic disorders. However, translational approaches are hampered as current models do not accurately recapitulate adipogenesis. Here, a scaffold-free versatile 3D adipocyte culture platform with chemically defined conditions is presented in which primary human preadipocytes accurately recapitulate adipogenesis. Following differentiation, multi-omics profiling and functional tests demonstrate that 3D adipocyte cultures feature mature molecular and cellular phenotypes similar to freshly isolated mature adipocytes. Spheroids exhibit physiologically relevant gene expression signatures with 4704 differentially expressed genes compared to conventional 2D cultures (false discovery rate < 0.05), including the concerted expression of factors shaping the adipogenic niche. Furthermore, lipid profiles of >1000 lipid species closely resemble patterns of the corresponding isogenic mature adipocytes in vivo (R2 = 0.97). Integration of multi-omics signatures with analyses of the activity profiles of 503 transcription factors using global promoter motif inference reveals a complex signaling network, involving YAP, Hedgehog, and TGFβ signaling, that links the organotypic microenvironment in 3D culture to the activation and reinforcement of PPARγ and CEBP activity resulting in improved adipogenesis.

Role of hypothalamic de novo ceramides synthesis in obesity and associated metabolic disorders

Background

Sphingolipid-mediated signalling pathways are described as important players in the normal functioning of neurons and nonneuronal cells in the central nervous system (CNS).

Scope of review

This review aims to show role of de novo ceramide synthesis in the CNS in controling key physiological processes, including food intake, energy expenditure, and thermogenesis. The corollary is a condition that leads to a dysfunction in ceramide metabolism in these central regions that can have major consequences on the physiological regulation of energy balance.

Major conclusions

Excessive hypothalamic de novo ceramide synthesis has been shown to result in the establishment of central insulin resistance, endoplasmic reticulum stress, and inflammation. Additionally, excessive hypothalamic de novo ceramide synthesis has also been associated with changes in the activity of the autonomic nervous system. Such dysregulation of hypothalamic de novo ceramide synthesis forms the key starting point for the initiation of pathophysiological conditions such as obesity – which may or may not be associated with type 2 diabetes.

Activation of AMP kinase ameliorates kidney vascular dysfunction, oxidative stress and inflammation in rodent models of obesity

BACKGROUND AND PURPOSE

Obesity is a risk factor for the development of chronic kidney disease independent of diabetes, hypertension and other co-morbidities. Obesity-associated nephropathy is linked to dysregulation of the cell energy sensor AMP-activated protein kinase (AMPK). We aimed here to assess whether impairment of AMPK activity may cause renal arterial dysfunction in obesity and to evaluate the therapeutic potential of activating renal AMPK.

EXPERIMENTAL APPROACH

Effects of the AMPK activator A769662 were assessed on intrarenal arteries isolated from ob/ob mice and obese Zucker rats and then mounted in microvascular myographs. Superoxide and hydrogen peroxide production were measured by chemiluminescence and fluorescence, respectively, and protein expression was analysed by western blotting.

KEY RESULTS

Endothelium-dependent vasodilation and PI3K/Akt/eNOS pathway were impaired in preglomerular arteries from genetically obese rats and mice, along with impaired arterial AMPK activity and blunted relaxations induced by the AMPK activator A769662. Acute ex vivo exposure to A769662 restored endothelial function and enhanced activity of PI3K/Akt/eNOS pathway in obese rats, whereas in vivo treatment with A769662 improved metabolic state and ameliorated endothelial dysfunction, reduced inflammatory markers and vascular oxidative stress in renal arteries and restored redox balance in renal cortex of obese mice.

CONCLUSION AND IMPLICATIONS

These results demonstrate that AMPK dysregulation underlies obesity-associated kidney vascular dysfunction and activation of AMPK improves metabolic state, protects renal endothelial function and exerts potent vascular antioxidant and anti-inflammatory effects. The beneficial effects of vascular AMPK activation might represent a promising therapeutic approach to the treatment of obesity-related kidney injury.