Thermoneutral Housing Accelerates Metabolic Inflammation to Potentiate Atherosclerosis but Not Insulin Resistance

Excessive palmitic acid disturbs macrophage α-ketoglutarate/succinate metabolism and causes adipose tissue insulin resistance associated with gestational diabetes mellitus

Abnormal polarization of adipose tissue macrophages (ATMs) results in low-grade systemic inflammation and insulin resistance (IR), potentially contributing to the development of diabetes. However, the underlying mechanisms that regulate the polarization of ATMs associated with gestational diabetes mellitus (GDM) remain unclear. Thus, we aimed to determine the effects of abnormal fatty acids on macrophage polarization and development of insulin resistance in GDM. Levels of fatty acids and inflammation were assessed in the serum samples and adipose tissues of patients with GDM. An in vitro cell model treated with palmitic acid was established, and the mechanisms of palmitic acid in regulating macrophage polarization was clarified. The effects of excessive palmitic acid on the regulation of histone methylations and IR were also explored in the high-fat diet induced GDM mice model. We found that pregnancies with GDM were associated with increased levels of serum fatty acids, and inflammation and IR in adipose tissues. Increased palmitic acid could induce mitochondrial dysfunction and excessive ROS levels in macrophages, leading to abnormal cytoplasmic and nuclear metabolism of succinate and α-ketoglutarate (αKG). Specifically, a decreased nuclear αKG/succinate ratio could attenuate the enrichment of H3K27me3 at the promoters of pro-inflammatory cytokines, such as IL-1β, IL-6, and TNF-α, leading to cytokine secretion. Importantly, GDM mice treated with GSK-J4, an inhibitor of histone lysine demethylase, were protected from abnormal pro-inflammatory macrophage polarization and excessive production of pro-inflammatory cytokines. Our findings highlight the importance of the metabolism of αKG and succinate as transcriptional modulators in regulating the polarization of ATMs and the insulin sensitivity of adipose tissue, ensuring a normal pregnancy. This novel insight sheds new light on gestational fatty acid metabolism and epigenetic alterations associated with GDM.

Mild Cold Stress at Ambient Temperature Elevates Muscle Calcium Cycling and Exercise Adaptations in Obese Female Mice

CONTEXT

Housing temperature is a critical regulator of mouse metabolism and thermoneutral housing can improve model translation to humans. However, the impact of housing temperature on the ability of wheel running exercise training to rescue the detrimental effect of diet-induced obese mice is currently not fully understood.

OBJECTIVE

To investigate how housing temperature affects muscle metabolism in obese mice with regard to calcium handling and exercise training (ET) adaptations in skeletal muscle, and benefits of ET on adiposity and glucometabolic parameters.

METHODS

Lean or obese female mice were housed at standard ambient temperature (22 °C) or thermoneutrality (30 °C) with/without access to running wheels. The metabolic phenotype was investigated using glucose tolerance tests, indirect calorimetry, and body composition. Molecular muscle adaptations were measured using immunoblotting, qPCR, and spectrophotometric/fluorescent assays.

RESULTS

Obese female mice housed at 22 °C showed lower adiposity, lower circulating insulin levels, improved glucose tolerance, and elevated basal metabolic rate compared to 30 °C housing. Mice exposed to voluntary wheel running exhibited a larger fat loss and higher metabolic rate at 22 °C housing compared to thermoneutrality. In obese female mice, glucose tolerance improved after ET independent of housing temperature. Independent of diet and training, 22 °C housing increased skeletal muscle sarco(endo)plasmic reticulum Ca2+ ATPase (SERCA) activity. Additionally, housing at 22 °C elevated the induction of training-responsive muscle proteins in obese mice.

CONCLUSION

Our findings highlight that housing temperature significantly influences adiposity, insulin sensitivity, muscle physiology, and exercise adaptations in diet-induced obese female mice.

Thermoneutrality Inhibits Thermogenic Markers and Exacerbates Nonalcoholic Fatty Liver Disease in Mice

Nonalcoholic fatty liver disease (NAFLD) affects over a third of the US population and 25% globally, with current treatments proving ineffective. This study investigates whether manipulating brown adipose tissue (BAT) and beige fat activity by housing C57BL/6J mice at thermoneutral (27 °C) or standard temperatures (22 °C) impacts NAFLD development. Male mice were fed either a chow diet (CHD) or a "fast food" diet (FFD) for 10 weeks. Mice at 27 °C had reduced food intake but increased body weight and plasma leptin levels. FFD-fed mice at 27 °C had greater liver weight (2.6 vs. 1.8 g), triglyceride content (7.6 vs. 3.9 mg/g), and hepatic steatosis compared to those at 22 °C. Gene expression of fatty acid synthase, sterol regulatory element-binding protein 1, and fatty acid translocase CD36 was elevated in FFD-fed mice at 27 °C, but not in CHD-fed mice. Thermoneutral housing also reduced expression of thermogenic markers in BAT and inguinal white adipose tissue (WAT) and caused BAT whitening. In conclusion, thermoneutrality inhibits thermogenic markers and exacerbates NAFLD. Activating BAT or promoting WAT browning via cold exposure or other stimuli may offer a strategy for managing NAFLD.

Housing mice near vs. below thermoneutrality affects drug-induced weight loss but does not improve prediction of efficacy in humans

Evaluation of weight loss drugs is usually performed in diet-induced obese mice housed at ∼22°C. This is a cold stress that increases energy expenditure by ∼35% compared to thermoneutrality (∼30°C), which may overestimate drug-induced weight loss. We investigated five anti-obesity mechanisms that have been in clinical development, comparing weight loss in mice housed at 22°C vs. 30°C. Glucagon-like peptide-1 (GLP-1), human fibroblast growth factor 21 (hFGF21), and melanocortin-4 receptor (MC4R) agonist induced similar weight losses. Peptide YY elicited greater vehicle-subtracted weight loss at 30°C (7.2% vs. 1.4%), whereas growth differentiation factor 15 (GDF15) was more effective at 22°C (13% vs. 6%). Independent of ambient temperature, GLP-1 and hFGF21 prevented the reduction in metabolic rate caused by weight loss. There was no simple rule for a better prediction of human drug efficacy based on ambient temperature, but since humans live at thermoneutrality, drug testing using mice should include experiments near thermoneutrality.

Navigating Lipodystrophy: Insights from Laminopathies and Beyond

Recent research into laminopathic lipodystrophies-rare genetic disorders caused by mutations in the LMNA gene-has greatly expanded our knowledge of their complex pathology and metabolic implications. These disorders, including Hutchinson-Gilford progeria syndrome (HGPS), Mandibuloacral Dysplasia (MAD), and Familial Partial Lipodystrophy (FPLD), serve as crucial models for studying accelerated aging and metabolic dysfunction, enhancing our understanding of the cellular and molecular mechanisms involved. Research on laminopathies has highlighted how LMNA mutations disrupt adipose tissue function and metabolic regulation, leading to altered fat distribution and metabolic pathway dysfunctions. Such insights improve our understanding of the pathophysiological interactions between genetic anomalies and metabolic processes. This review merges current knowledge on the phenotypic classifications of these diseases and their associated metabolic complications, such as insulin resistance, hypertriglyceridemia, hepatic steatosis, and metabolic syndrome, all of which elevate the risk of cardiovascular disease, stroke, and diabetes. Additionally, a range of published therapeutic strategies, including gene editing, antisense oligonucleotides, and novel pharmacological interventions aimed at addressing defective adipocyte differentiation and lipid metabolism, will be explored. These therapies target the core dysfunctional lamin A protein, aiming to mitigate symptoms and provide a foundation for addressing similar metabolic and genetic disorders.

Smooth muscle cell-derived Cxcl12 directs macrophage accrual and sympathetic innervation to control thermogenic adipose tissue

Sympathetic innervation of brown adipose tissue (BAT) controls mammalian adaptative thermogenesis. However, the cellular and molecular underpinnings contributing to BAT innervation remain poorly defined. Here, we show that smooth muscle cells (SMCs) support BAT growth, lipid utilization, and thermogenic plasticity. Moreover, we find that BAT SMCs express and control the bioavailability of Cxcl12. SMC deletion of Cxcl12 fosters brown adipocyte lipid accumulation, reduces energy expenditure, and increases susceptibility to diet-induced metabolic dysfunction. Mechanistically, we find that Cxcl12 stimulates CD301+ macrophage recruitment and supports sympathetic neuronal maintenance. Administering recombinant Cxcl12 to obese mice or leptin-deficient (Ob/Ob) mice is sufficient to boost macrophage presence and drive sympathetic innervation to restore BAT morphology and thermogenic responses. Altogether, our data reveal an SMC chemokine-dependent pathway linking immunological infiltration and sympathetic innervation as a rheostat for BAT maintenance and thermogenesis.

Targeting adipocyte ESRRA promotes osteogenesis and vascular formation in adipocyte-rich bone marrow

Excessive bone marrow adipocytes (BMAds) accumulation often occurs under diverse pathophysiological conditions associated with bone deterioration. Estrogen-related receptor α (ESRRA) is a key regulator responding to metabolic stress. Here, we show that adipocyte-specific ESRRA deficiency preserves osteogenesis and vascular formation in adipocyte-rich bone marrow upon estrogen deficiency or obesity. Mechanistically, adipocyte ESRRA interferes with E2/ESR1 signaling resulting in transcriptional repression of secreted phosphoprotein 1 (Spp1); yet positively modulates leptin expression by binding to its promoter. ESRRA abrogation results in enhanced SPP1 and decreased leptin secretion from both visceral adipocytes and BMAds, concertedly dictating bone marrow stromal stem cell fate commitment and restoring type H vessel formation, constituting a feed-forward loop for bone formation. Pharmacological inhibition of ESRRA protects obese mice against bone loss and high marrow adiposity. Thus, our findings highlight a therapeutic approach via targeting adipocyte ESRRA to preserve bone formation especially in detrimental adipocyte-rich bone milieu.

Obesity amplifies influenza virus-driven disease severity in male and female mice

Influenza virus-induced respiratory pneumonia remains a major public health concern. Obesity, metabolic diseases, and female sex are viewed as independent risk factors for worsened influenza virus-induced lung disease severity. However, lack of experimental models of severe obesity in female mice limits discovery-based studies. Here, via utility of thermoneutral housing (30 °C) and high-fat diet (HFD) feeding, we induced severe obesity and metabolic disease in female C57BL/6 mice and compared their responses to severely obese male C57BL/6 counterparts during influenza virus infection. We show that lean male and female mice have similar lung edema, inflammation, and immune cell infiltration during influenza virus infection. At standard housing conditions, HFD-fed male, but not female, mice exhibit severe obesity, metabolic disease, and exacerbated influenza disease severity. However, combining thermoneutral housing and HFD feeding in female mice induces severe obesity and metabolic disease, which is sufficient to amplify influenza virus-driven disease severity to a level comparable to severely obese male counterparts. Lastly, increased total body weights of male and female mice at time of infection correlated with worsened influenza virus-driven disease severity metrics. Together, our findings confirm the impact of obesity and metabolic disease as key risk factors to influenza disease severity and present a novel mouse experimental model suitable for future mechanistic interrogation of sex, obesity, and metabolic disease traits in influenza virus-driven disease severity.

Thermoneutral Housing Enables Studies of Vertical Transmission of Obesogenic Diet-Driven Metabolic Diseases

Vertical transmission of obesity is a critical contributor to the unabated obesity pandemic and the associated surge in metabolic diseases. Existing experimental models insufficiently recapitulate "human-like" obesity phenotypes, limiting the discovery of how severe obesity in pregnancy instructs vertical transmission of obesity. Here, via utility of thermoneutral housing and obesogenic diet feeding coupled to syngeneic mating of WT obese female and lean male mice on a C57BL/6 background, we present a tractable, more "human-like" approach to specifically investigate how maternal obesity contributes to offspring health. Using this model, we found that maternal obesity decreased neonatal survival, increased offspring adiposity, and accelerated offspring predisposition to obesity and metabolic disease. We also show that severe maternal obesity was sufficient to skew offspring microbiome and create a proinflammatory gestational environment that correlated with inflammatory changes in the offspring in utero and adulthood. Analysis of a human birth cohort study of mothers with and without obesity and their infants was consistent with mouse study findings of maternal inflammation and offspring weight gain propensity. Together, our results show that dietary induction of obesity in female mice coupled to thermoneutral housing can be used for future mechanistic interrogations of obesity and metabolic disease in pregnancy and vertical transmission of pathogenic traits.

Hypoxia-induced signaling in the cardiovascular system: pathogenesis and therapeutic targets

Hypoxia, characterized by reduced oxygen concentration, is a significant stressor that affects the survival of aerobic species and plays a prominent role in cardiovascular diseases. From the research history and milestone events related to hypoxia in cardiovascular development and diseases, The "hypoxia-inducible factors (HIFs) switch" can be observed from both temporal and spatial perspectives, encompassing the occurrence and progression of hypoxia (gradual decline in oxygen concentration), the acute and chronic manifestations of hypoxia, and the geographical characteristics of hypoxia (natural selection at high altitudes). Furthermore, hypoxia signaling pathways are associated with natural rhythms, such as diurnal and hibernation processes. In addition to innate factors and natural selection, it has been found that epigenetics, as a postnatal factor, profoundly influences the hypoxic response and progression within the cardiovascular system. Within this intricate process, interactions between different tissues and organs within the cardiovascular system and other systems in the context of hypoxia signaling pathways have been established. Thus, it is the time to summarize and to construct a multi-level regulatory framework of hypoxia signaling and mechanisms in cardiovascular diseases for developing more therapeutic targets and make reasonable advancements in clinical research, including FDA-approved drugs and ongoing clinical trials, to guide future clinical practice in the field of hypoxia signaling in cardiovascular diseases.

Thermoneutrality or standard temperature: is there an ideal housing temperature to study the antisteatotic effects of green tea in obese mice?

Metabolic-associated fatty liver disease (MAFLD) is a condition characterized by excessive accumulation of triglycerides in hepatocytes, currently considered the number one cause of chronic liver disease. MAFLD is strongly associated with obesity, type 2 diabetes, hyperlipidaemia, and hypertension. Emphasis has been placed on the use of green tea (GT), produced from the Camellia sinensis plant, rich in antioxidants as polyphenols and catechins, on obesity and MAFLD treatment/prevention. Studies carried out in rodent models housed at a standard temperature (ST, 22°C) are being questioned as ST is a determining factor on generating changes in the physiology of immune response, and energy metabolism. On the other hand, it seems that thermoneutrality (TN, 28°C) represents a closer parallel to human physiology. In this perspective, we investigated the effects of GT (500 mg/kg of body weight, over 12 weeks, 5 days/week) by comparing mice housed at ST or TN in a model of MAFLD of diet-induced obese males C57Bl/6 mice. We show that the liver phenotype at TN exhibits a more severe MAFLD while GT ameliorates this condition. In parallel, GT restores the expression of genes involved in the lipogenic pathway, regardless of temperature, with slight modifications in lipolysis/fatty acid oxidation. We observed an increase promoted by GT in PPARα and PPARγ proteins independently of housing temperature and a dual pattern of bile acid synthesis. Thus, animals' conditioning temperature is a key factor that can interfere in the results involving obesity and MAFLD, although GT has beneficial effects against MAFLD independently of the housing temperature of mice.

Cold exposure protects against medial arterial calcification development via autophagy

Medial arterial calcification (MAC), a systemic vascular disease different from atherosclerosis, is associated with an increased incidence of cardiovascular events. Several studies have demonstrated that ambient temperature is one of the most important factors affecting cardiovascular events. However, there has been limited research on the effect of different ambient temperatures on MAC. In the present study, we showed that cold temperature exposure (CT) in mice slowed down the formation of vitamin D (VD)-induced vascular calcification compared with room temperature exposure (RT). To investigate the mechanism involved, we isolated plasma-derived exosomes from mice subjected to CT or RT for 30 days (CT-Exo or RT-Exo, respectively). Compared with RT-Exo, CT-Exo remarkably alleviated the calcification/senescence formation of vascular smooth muscle cells (VSMCs) and promoted autophagy by activating the phosphorylation of AMP-activated protein kinase (p-AMPK) and inhibiting phosphorylation of mammalian target of rapamycin (p-mTOR). At the same time, CT-Exo promoted autophagy in β-glycerophosphate (β-GP)-induced VSMCs. The number of autophagosomes and the expression of autophagy-related proteins ATG5 and LC3B increased, while the expression of p62 decreased. Based on a microRNA chip microarray assay and real-time polymerase chain reaction, miR-320a-3p was highly enriched in CT-Exo as well as thoracic aortic vessels in CT mice. miR-320a-3p downregulation in CT-Exo using AntagomiR-320a-3p inhibited autophagy and blunted its anti-calcification protective effect on VSMCs. Moreover, we identified that programmed cell death 4 (PDCD4) is a target of miR-320a-3p, and silencing PDCD4 increased autophagy and decreased calcification in VSMCs. Treatment with CT-Exo alleviated the formation of MAC in VD-treated mice, while these effects were partially reversed by GW4869. Furthermore, the anti-arterial calcification protective effects of CT-Exo were largely abolished by AntagomiR-320a-3p in VD-induced mice. In summary, we have highlighted that prolonged cold may be a good way to reduce the incidence of MAC. Specifically, miR-320a-3p from CT-Exo could protect against the initiation and progression of MAC via the AMPK/mTOR autophagy pathway.

"Humanizing" mouse environments: Humidity, diurnal cycles and thermoneutrality

Thermoneutral housing has been shown to promote more accurate and robust development of several pathologies in mice. Raising animal housing temperatures a few degrees may create a relatively straightforward opportunity to improve translatability of mouse models. In this commentary, we discuss the changes of physiology induced in mice housed at thermoneutrality, and review techniques for measuring systemic thermogenesis, specifically those affecting storage and mobilization of lipids in adipose depots. Environmental cues are a component of the information integrated by the brain to calculate food consumption and calorie deposition. We show that relative humidity is one of those cues, inducing a rapid sensory response that is converted to a more chronic susceptibility to obesity. Given high inter-institutional variability in the regulation of relative humidity, study reproducibility may be improved by consideration of this factor. We evaluate a "humanized" environmental cycling protocol, where mice sleep in warm temperature housing, and are cool during the wake cycle. We show that this protocol suppresses adaptation to cool exposure, with consequence for adipose-associated lipid storage. To evaluate systemic cues in mice housed at thermoneutral temperatures, we characterized the circulating lipidome, and show that sera are highly depleted in some HDL-associated phospholipids, specifically phospholipids containing the essential fatty acid, 18:2 linoleic acid, and its derivative, arachidonic acid (20:4) and related ether-phospholipids. Given the role of these fatty acids in inflammatory responses, we propose they may underlie the differences in disease progression observed at thermoneutrality.

Effects of the pesticide deltamethrin on high fat diet-induced obesity and insulin resistance in male mice

Worldwide, rates of metabolic diseases are rapidly increasing and environmental exposure to pesticides, pollutants and/or other chemicals may play a role. Reductions in Brown Adipose Tissue (BAT) thermogenesis, mediated in part by uncoupling protein 1 (Ucp1), are associated with metabolic diseases. In the current study, we investigated whether the pesticide deltamethrin (0.01-1 mg/kg bw/day) incorporated into a high-fat diet and fed to mice housed at either room temperature (21 °C) or thermoneutrality (29 °C) would suppress BAT activity and accelerate the development of metabolic disease. Importantly, thermoneutrality allows for more accurate modeling of human metabolic disease. We found that, 0.01mg/kg bw/day of deltamethrin induced weight loss, improved insulin sensitivity and increased energy expenditure, effects that were associated with increases in physical activity. In contrast, exposure to 0.1 and 1 mg/kg bw/day deltamethrin had no effect on any of the parameters examined. Deltamethrin treatment in mice did not alter molecular markers of BAT thermogenesis, despite observing suppression of UCP1 expression in cultured brown adipocytes. These data indicate that while deltamethrin inhibits UCP1 expression in vitro, 16wks exposure does not alter BAT thermogenesis markers nor exacerbates the development of obesity and insulin resistance in mice.

Thermoneutrality effects on developmental programming of obesity

Developmental programming studies using mouse models have housed the animals at human thermoneutral temperatures (22°C) which imposes constant cold stress. As this impacts energy homeostasis, we investigated the effects of two housing temperatures (22°C and 30°C) on obesity development in male and female offspring of Control and FR dams. Pregnant mice were housed at 22°C (cold-exposed, CE) or 30°C (thermoneutrality, TN) room temperature. At gestational age e10, mice were fed either an ad libitum diet (Control) or were 30% food-restricted (FR) to produce low birth weight newborns. Following delivery, all dams were fed an ad libitum diet and maternal mice continued to nurse their own pups. At 3 weeks of age, offspring were weaned to an ad libitum diet and housed at similar temperatures as their mothers. Body weights and food intake were monitored. At 6 months of age, body composition and glucose tolerance test were determined, after which, brain and adipose tissue were collected for analysis. FR/CE and FR/TN offspring exhibited hyperphagia and were significantly heavier with increased adiposity as compared to their respective Controls. There was sex-specific effects of temperature in both groups. Male offspring at TN were heavier with increased body fat, though the food intake was decreased as compared to CE males. This was reflected by hypertrophic adipocytes and increased arcuate nucleus satiety/appetite ratio. In contrast, female offspring were not impacted by housing temperature. Thus, unlike female offspring, there was a significant interaction of diet and temperature evident in the male offspring with accentuated adverse effects evident in FR/TN males.

The Influence of Ambient Temperature on Adipose Tissue Homeostasis, Metabolic Diseases and Cancers

Adipose tissue is a recognized energy storage organ during excessive energy intake and an endocrine and thermoregulator, which interacts with other tissues to regulate systemic metabolism. Adipose tissue dysfunction is observed in most obese mouse models and humans. However, most studies using mouse models were conducted at room temperature (RT), where mice were chronically exposed to mild cold. In this condition, energy use is prioritized for thermogenesis to maintain body temperature in mice. It also leads to the activation of the sympathetic nervous system, followed by the activation of β-adrenergic signaling. As humans live primarily in their thermoneutral (TN) zone, RT housing for mice limits the interpretation of disease studies from mouse models to humans. Therefore, housing mice in their TN zone (~28–30 °C) can be considered to mimic humans physiologically. However, factors such as temperature ranges and TN pre-acclimatization periods should be examined to obtain reliable results. In this review, we discuss how adipose tissue responds to housing temperature and the outcomes of the TN zone in metabolic disease studies. This review highlights the critical role of TN housing in mouse models for studying adipose tissue function and human metabolic diseases.

Thermoneutral housing shapes hepatic inflammation and damage in mouse models of non-alcoholic fatty liver disease

Introduction

Inflammation is a common unifying factor in experimental models of non-alcoholic fatty liver disease (NAFLD) progression. Recent evidence suggests that housing temperature-driven alterations in hepatic inflammation correlate with exacerbated hepatic steatosis, development of hepatic fibrosis, and hepatocellular damage in a model of high fat diet-driven NAFLD. However, the congruency of these findings across other, frequently employed, experimental mouse models of NAFLD has not been studied.

Methods

Here, we examine the impact of housing temperature on steatosis, hepatocellular damage, hepatic inflammation, and fibrosis in NASH diet, methionine and choline deficient diet, and western diet + carbon tetrachloride experimental models of NAFLD in C57BL/6 mice.

Results

We show that differences relevant to NAFLD pathology uncovered by thermoneutral housing include: (i) augmented NASH diet-driven hepatic immune cell accrual, exacerbated serum alanine transaminase levels and increased liver tissue damage as determined by NAFLD activity score; (ii) augmented methionine choline deficient diet-driven hepatic immune cell accrual and increased liver tissue damage as indicated by amplified hepatocellular ballooning, lobular inflammation, fibrosis and overall NAFLD activity score; and (iii) dampened western diet + carbon tetrachloride driven hepatic immune cell accrual and serum alanine aminotransferase levels but similar NAFLD activity score.

Discussion

Collectively, our findings demonstrate that thermoneutral housing has broad but divergent effects on hepatic immune cell inflammation and hepatocellular damage across existing experimental NAFLD models in mice. These insights may serve as a foundation for future mechanistic interrogations focused on immune cell function in shaping NAFLD progression.

The genetic background shapes the susceptibility to mitochondrial dysfunction and NASH progression

Non-alcoholic steatohepatitis (NASH) is a global health concern without treatment. The challenge in finding effective therapies is due to the lack of good mouse models and the complexity of the disease, characterized by gene-environment interactions. We tested the susceptibility of seven mouse strains to develop NASH. The severity of the clinical phenotypes observed varied widely across strains. PWK/PhJ mice were the most prone to develop hepatic inflammation and the only strain to progress to NASH with extensive fibrosis, while CAST/EiJ mice were completely resistant. Levels of mitochondrial transcripts and proteins as well as mitochondrial function were robustly reduced specifically in the liver of PWK/PhJ mice, suggesting a central role of mitochondrial dysfunction in NASH progression. Importantly, the NASH gene expression profile of PWK/PhJ mice had the highest overlap with the human NASH signature. Our study exposes the limitations of using a single mouse genetic background in metabolic studies and describes a novel NASH mouse model with features of the human NASH.

Utility of Human Relevant Preclinical Animal Models in Navigating NAFLD to MAFLD Paradigm

Fatty liver disease is an emerging contributor to disease burden worldwide. The past decades of work established the heterogeneous nature of non-alcoholic fatty liver disease (NAFLD) etiology and systemic contributions to the pathogenesis of the disease. This called for the proposal of a redefinition in 2020 to that of metabolic dysfunction-associated fatty liver disease (MAFLD) to better reflect the current understanding of the disease. To date, several clinical cohort studies comparing NAFLD and MAFLD hint at the relevancy of the new nomenclature in enriching for patients with more severe hepatic injury and extrahepatic comorbidities. However, the underlying systemic pathogenesis is still not fully understood. Preclinical animal models have been imperative in elucidating key biological mechanisms in various contexts, including intrahepatic disease progression, interorgan crosstalk and systemic dysregulation. Furthermore, they are integral in developing novel therapeutics against MAFLD. However, substantial contextual variabilities exist across different models due to the lack of standardization in several aspects. As such, it is crucial to understand the strengths and weaknesses of existing models to better align them to the human condition. In this review, we consolidate the implications arising from the change in nomenclature and summarize MAFLD pathogenesis. Subsequently, we provide an updated evaluation of existing MAFLD preclinical models in alignment with the new definitions and perspectives to improve their translational relevance.

Ketogenic diet induced weight loss occurs independent of housing temperature and is followed by hyperphagia and weight regain after cessation in mice

KEY POINTS

Ketogenic diets reduce food intake, increase energy expenditure and cause weight loss in rodents Prior preclinical studies have been completed at room temperature, a condition which induces thermal stress and limits clinical translatability We demonstrate that ketogenic diet-induced reductions in food intake, increases in energy expenditure, weight loss and improvements in glucose homeostasis are similar in mice housed at room temperature or thermal neutrality Ketogenic diet induced reductions in food intake appear to explain a large degree of weight loss. Similarly, switching mice from a ketogenic to an obesogenic diet leads to hyperphagia mediated weight gain ABSTRACT: Ketogenic diets (KDs) are a popular tool used for weight management. Studies in mice have demonstrated that KDs reduce food intake, increase energy expenditure and cause weight loss. These studies were completed at room temperature (RT), a condition below the animal's thermal neutral (TN) zone which induces thermal stress. As energy intake and expenditure are sensitive to environmental temperature it's not clear if a KD would exert the same beneficial effects under TN conditions. Adherence to restrictive diets is poor and consequently it is important to examine the effects, and underlying mechanisms, of cycling from a ketogenic to an obesogenic diet. The purpose of the current study was to determine if housing temperature impacted the effects of a KD in obese mice and to determine if the mechanisms driving KD-induced weight loss reverse when mice are switched to an obesogenic high fat diet. We demonstrate that KD-induced reductions in food intake, increases in energy expenditure, weight loss and improvements in glucose homeostasis are not dependent upon housing temperature. KD-induced weight loss, seems to be largely explained by reductions in caloric intake while cycling mice back to an obesogenic diet following a period of KD feeding leads to hyperphagia-induced weight gain. Collectively, our results suggest that prior findings with mice fed a KD at RT are likely not an artifact of how mice were housed and that initial changes in weight when transitioning from an obesogenic to a ketogenic diet or back, are largely dependent on food intake. Abstract figure legend The impact of housing temperature on ketogenic diet mediated changes in energy expenditure, food intake and weight gain. This article is protected by copyright. All rights reserved.

Saturated fatty acid biomarkers and risk of cardiometabolic diseases: A meta-analysis of prospective studies

Background and aims

Evidence regarding associations of circulating saturated fatty acids (SFAs) with chronic diseases is mixed. The objective of this study was to determine the associations between total or individual SFA biomarkers and the risk of cardiometabolic diseases.

Methods

Four electronic databases were searched from inception to March 2022. Three investigators independently assessed for inclusion and extracted data. Random-effects or fixed-effects models was used to estimate the pooled relative risks (RRs) and corresponding 95% confidence intervals (CIs) for the association of total or individual SFA biomarkers, including even-chain SFAs (e.g., 14:0, myristic acid; 16:0, palmitic acid; 18:0, stearic acid), odd-chain SFAs (e.g., 15:0, pentadecanoic acid; 17:0, margaric acid) and very-long-chain SFAs (VLCSFAs; e.g., 20:0, arachidic acid; 22:0, behenic acid; 24:0, lignoceric acid), with risk of incident type 2 diabetes (T2D), cardiovascular disease [CVD; coronary heart disease (CHD) inclusive of stroke], CHD and stroke.

Results

A total of 49 prospective studies reported in 45 articles were included. Higher concentration of circulating total SFAs was associated with an increasing risk of cardiometabolic diseases, the risk increased significantly by 50% for CVD (95%CI:1.31–1.71), 63% for CHD (95%CI:1.38–1.94), 38% for stroke (95%CI:1.05–1.82), respectively. Similarly, levels of even-chain SFAs were positively associated with higher risk of chronic diseases, with RRs ranging from 1.15 to 1.43. In contrast, the risk of cardiometabolic diseases was reduced with increasing odd-chain SFA levels, with RRs ranging from 0.62 to 0.91. A higher level of VLCSFAs corresponded to 19% reduction in CVD. Further dose-response analysis indicated that each 50% increment in percentage of total SFAs in circulating was associated with an 8% higher risk of T2D (RR: 1.08, 95%CI: 1.02–1.14) and trends toward higher risk of CVD (RR: 1.15, 95%CI: 0.98–1.34). Inverse linear relationships were observed between 17:0 biomarker and T2D or CVD risk.

Conclusion

Our findings support the current recommendations of reducing intake of saturated fat as part of healthy dietary patterns. Further studies are needed to confirm our findings on these SFAs in relation to cardiometabolic outcomes and to elucidate underlying mechanisms.

Systematic review registration

[https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42022329182], identifier [CRD42022329182].

How murine models of human disease and immunity are influenced by housing temperature and mild thermal stress

At the direction of The Guide and Use of Laboratory Animals, rodents in laboratory facilities are housed at ambient temperatures between 20°C and 26°C, which fall below their thermoneutral zone (TNZ). TNZ is identified as a range of ambient temperatures that allow an organism to regulate body temperature without employing additional thermoregulatory processes (e.g. metabolic heat production driven by norepinephrine), thus leading to mild, chronic cold stress. For mice, this chronic cold stress leads to increased serum levels of the catecholamine norepinephrine, which has direct effects on various immune cells and several aspects of immunity and inflammation. Here, we review several studies that have revealed that ambient temperature significantly impacts outcomes in various murine models of human diseases, particularly those in which the immune system plays a major role in its pathogenesis. The impact of ambient temperature on experimental outcomes raises questions regarding the clinical relevance of some murine models of human disease, since studies examining rodents housed within thermoneutral ambient temperatures revealed that rodent disease pathology more closely resembled that of humans. Unlike laboratory rodents, humans can modify their surroundings accordingly - by adjusting their clothing, the thermostat, or their physical activity - to live within the appropriate TNZ, offering a possible explanation for why many studies using murine models of human disease conducted at thermoneutrality better represent patient outcomes. Thus, it is strongly recommended that ambient housing temperature in such studies be consistently and accurately reported and recognized as an important experimental variable.

Animal Models of Atherosclerosis-Supportive Notes and Tricks of the Trade

Atherosclerotic cardiovascular disease is a major cause of death among humans. Animal models have shown that cholesterol and inflammation are causatively involved in the disease process. Apolipoprotein B-containing lipoproteins elicit immune reactions and instigate inflammation in the vessel wall. Still, a treatment that is specific to vascular inflammation is lacking, which motivates continued in vivo investigations of the immune-vascular interactions that drive the disease. In this review, we distill old notions with emerging concepts into a contemporary understanding of vascular disease models. Pros and cons of different models are listed and the complex integrative interplay between cholesterol homeostasis, immune activation, and adaptations of the vascular system is discussed. Key limitations with atherosclerosis models are highlighted, and we suggest improvements that could accelerate progress in the field. However, excessively rigid experimental guidelines or limiting usage to certain animal models can be counterproductive. Continued work in improved models, as well as the development of new models, should be of great value in research and could aid the development of cardiovascular disease diagnostics and therapeutics of the future.

Animal Study Translation: The Other Reproducibility Challenge

Animal research is currently an irreplaceable contributor to our efforts to protect and improve public health. Its relevance, importance, and contributions are represented in historical precedent, regulatory expectations, evidence of our rapidly developing understanding of human health and disease, as well as success in the development of novel therapeutics that are improving quality of life and extending human and animal life expectancy. The rapid and evolving success in responding to the current COVID pandemic significantly supported by animal studies is a clear example of the importance of animal research. But there is growing interest in reducing our dependence on animals and challenges to the effective translation of current animal studies to human applications. There are several potential contributors to gaps in the translatability of animal research to humans, including our approaches to choosing or rationalizing the relevance of a particular animal model, our understanding of their biological variability and how that applies to outcomes, the data we collect from animal studies, and even how we manage the animals. These important contributors to the success of animal research are explored in this issue of the ILAR Journal.

Atherosclerosis Vascular Endothelial Secretion Dysfunction and Smooth Muscle Cell Proliferation

Atherosclerosis is a chronic inflammatory disease of the arterial wall and the main cause of cardiovascular disease and cerebrovascular disease. In recent years, the mortality rate of atherosclerotic diseases has become higher and higher. This article aims to study the dysregulation of atherosclerotic vascular endothelial secretion and smooth muscle cell proliferation, and put forward and practice the pathological research of atherosclerotic disease. This article describes in detail atherosclerosis, endothelial dysfunction, and smooth muscle cell proliferation, and studies the causes of atherosclerosis. Research results indicate that atherosclerotic vascular endothelial dysfunction also has a great influence on the proliferation of smooth muscle cells. Many genes and environmental factors can regulate the functions of endothelial cells, vascular smooth muscle cells, and mononuclear macrophages and affect the formation of atherosclerosis. At the same time, diabetes, hypertension, hyperlipidemia, obesity, etc. are the main causes of atherosclerosis. The number of patients with cardiovascular and cerebrovascular diseases dying from atherosclerosis in the country is increasing, and the proportion is close to 30%.

Contrasting recruitment of skin-associated adipose depots during cold challenge of mouse and human

KEY POINTS

Several distinct strategies produce and conserve heat to maintain the body temperature of mammals, each associated with unique physiologies, with consequences for wellness and disease susceptibility Highly regulated properties of skin offset the total requirement for heat production  We hypothesize that the adipose component of skin is primarily responsible for modulating heat flux; here we evaluate the relative regulation of adipose depots in mouse and human, to test their recruitment to heat production and conservation We found that insulating mouse dermal white adipose tissue accumulates in response to environmentally and genetically induced cool stress; this layer is one of two adipose depots closely apposed to mouse skin, where the subcutaneous mammary gland fat pads are actively recruited to heat production In contrast, the body-wide adipose depot associated with human skin produces heat directly, potentially creating an alternative to the centrally regulated brown adipose tissue ABSTRACT: Mammalian skin impacts metabolic efficiency system-wide, controlling the rate of heat loss and consequent heat production. Here we compare the unique fat depots associated with mouse and human skin, to determine whether they have corresponding functions and regulation. For humans, we assay a skin-associated fat (SAF) body-wide depot to distinguish it from the subcutaneous fat pads characteristic of the abdomen and upper limbs. We show that the thickness of SAF is not related to general adiposity; it is much thicker (1.6-fold) in women than men, and highly subject-specific. We used molecular and cellular assays of β-adrenergic-induced lipolysis and found that dermal white adipose tissue (dWAT) in mice is resistant to lipolysis; in contrast, the body-wide human SAF depot becomes lipolytic, generating heat in response to β-adrenergic stimulation. In mice challenged to make more heat to maintain body temperature (either environmentally or genetically), there is a compensatory increase in thickness of dWAT: a corresponding β-adrenergic stimulation of human skin adipose (in vivo or in explant) depletes adipocyte lipid content. We summarize the regulation of skin-associated adipocytes by age, sex and adiposity, for both species. We conclude that the body-wide dWAT depot of mice shows unique regulation that enables it to be deployed for heat preservation; combined with the actively lipolytic subcutaneous mammary fat pads they enable thermal defence. The adipose tissue that covers human subjects produces heat directly, providing an alternative to the brown adipose tissues.

Therapeutic effect and safety of curcumin in women with PCOS: A systematic review and meta-analysis

BACKGROUND

Polycystic ovary syndrome (PCOS) is a multi-factorial heterogeneous syndrome that has both adverse reproductive and metabolic implications for affected women and its management is a challenging clinical problem. Curcumin, as a phenolic compound with potent anti-inflammatory and antioxidant properties exerting positive effects on the lipid profile and insulin resistance, appears to be a valuable treatment regimen for patients with PCOS.

OBJECTIVE

This study aimed to evaluate the efficacy and safety of curcumin in the treatment of PCOS.

METHODS

Chinese databases (Chinese National Knowledge Infrastructure, China Biology Medicine Databases, VIP database, Wanfang Database, and Chinese Clinical Trial Registry) and English databases (PubMed, Web of Science, Embase, Cochrane Library, Scopus and Clinical trials) were thoroughly investigated through screening randomized controlled trials on curcumin in PCOS published from the date of inception to May 2022. Standardized data search and abstraction were conducted following the preferred reporting items for systematic reviews and meta-analysis (PRISMA) statement. Quantitative and qualitative analyses were performed. Heterogeneity was assessed using I² statistics.

RESULTS

A total of 447 patients from seven randomized controlled trials were included in the meta-analysis. Results showed that the ingestion of curcumin decreased body mass index (WMD -0.267, 95% CI -0.450 to -0.084, P = 0.004, I² = 0.0%), fasting plasma glucose (WMD -3.618, 95% CI -5.165 to -2.071, P < 0.001, I² = 20.4%), insulin (WMD -1.834, 95% CI -2.701 to -0.968, P < 0.001, I² = 8.4%), homeostatic model assessment for insulin resistance (WMD -0.565, 95% CI -0.779 to -0.351, P < 0.001, I² = 0.0%), total cholesterol (WMD -15.591, 95% CI -27.908 to -3.273, P = 0.013, I² = 68.9%), C-reactive protein (WMD -0.785, 95% CI -1.553 to -0.017, P = 0.045, I² = 23.9%), and increased the quantitative insulin sensitivity check index (WMD 0.011, 95% CI 0.005 to 0.017, P = 0.001, I² = 39.6%). As for safety, the treatment group did not cause significant adverse reactions than that in the control group.

CONCLUSION

In light of presented findings, curcumin has beneficial effects on serum markers of inflammation, weight loss and glucose and lipid metabolism in patients with PCOS. The incidence of adverse reactions does not increase with the application of curcumin. However, a larger, more definitive study is needed to further investigate these results.

SYSTEMATIC REVIEW REGISTRATION

https://www.crd.york.ac.uk/prospero/, identifier CRD42022332394.

An assessment of thermoneutral housing conditions on murine cardiometabolic function

Mouse models are used to model human diseases and perform pharmacological efficacy testing to advance therapies to humans; most of these studies are conducted in room temperature conditions. At room temperature (22°C), mice are cold stressed and must utilize brown adipose tissue (BAT) to maintain body temperature. This cold stress increases catecholamine tone to maintain adipocyte lipid release via lipolysis, which will fuel adaptive thermogenesis. Maintaining rodents at thermoneutral temperatures (28°C) ameliorates the need for adaptive thermogenesis, thus reducing catecholamine tone and BAT activity. Cardiovascular tone is also determined by catecholamine levels in rodents, as beta adrenergic stimuli are primary drivers of not only lipolytic, but also ionotropic and chronotropic responses. As mice have increased catecholamine tone at room temperature, we investigated how thermoneutral housing conditions would impact cardiometabolic function. Here, we show a rapid and reversible effect of thermoneutrality on both heart rate and blood pressure in chow fed animals, which was blunted in animals fed high fat diet. Animals subjected to transverse aortic constriction displayed compensated hypertrophy at room temperature, while animals displayed less hypertrophy and trends towards worse systolic function at thermoneutrality. Despite these dramatic changes in blood pressure and heart rate at thermoneutral housing conditions, enalapril effectively improved cardiac hypertrophy and gene expression alterations. There were surprisingly few differences in cardiac parameters in high fat fed animals at thermoneutrality. Overall, these data suggest that thermoneutral housing may alter some aspects of cardiac remodeling in preclinical mouse models of heart failure.

Polyphenols: Potential anti-inflammatory agents for treatment of metabolic disorders

Ample evidence highlights the potential benefits of polyphenols in health status especially in obesity-related metabolic disorders such as insulin resistance, type 2 diabetes, and cardiovascular diseases. Mechanistically, due to the key role of "Metainflammation" in the pathomechanism of metabolic disorders, recently much focus has been placed on the properties of polyphenols in obesity-related morbidities. This narrative review summarizes the current knowledge on the role of polyphenols, including genistein, chlorogenic acid, ellagic acid, caffeic acid, and silymarin in inflammatory responses pertinent to metabolic disorders and discusses the implications of this evidence for future directions. This review provides evidence that the aforementioned polyphenols benefit health status in metabolic disorders via direct and indirect regulation of a variety of target proteins involved in inflammatory signaling pathways. However, due to limitations of the in vitro and in vivo studies and also the lack of long-term human clinical trials studies, further high-quality investigations are required to firmly establish the clinical efficacy of the polyphenols for the prevention and management of metabolic disorders.

GDF15: emerging biology and therapeutic applications for obesity and cardiometabolic disease

Growth differentiation factor 15 (GDF15) is a member of the TGFβ superfamily whose expression is increased in response to cellular stress and disease as well as by metformin. Elevations in GDF15 reduce food intake and body mass in animal models through binding to glial cell-derived neurotrophic factor family receptor alpha-like (GFRAL) and the recruitment of the receptor tyrosine kinase RET in the hindbrain. This effect is largely independent of other appetite-regulating hormones (for example, leptin, ghrelin or glucagon-like peptide 1). Consistent with an important role for the GDF15-GFRAL signalling axis, some human genetic studies support an interrelationship with human obesity. Furthermore, findings in both mice and humans have shown that metformin and exercise increase circulating levels of GDF15. GDF15 might also exert anti-inflammatory effects through mechanisms that are not fully understood. These unique and distinct mechanisms for suppressing food intake and inflammation makes GDF15 an appealing candidate to treat many metabolic diseases, including obesity, type 2 diabetes mellitus, non-alcoholic fatty liver disease, cardiovascular disease and cancer cachexia. Here, we review the mechanisms regulating GDF15 production and secretion, GDF15 signalling in different cell types, and how GDF15-targeted pharmaceutical approaches might be effective in the treatment of metabolic diseases.

A20 deficiency in myeloid cells protects mice from diet-induced obesity and insulin resistance due to increased fatty acid metabolism

Obesity-induced inflammation is a major driving force in the development of insulin resistance, type 2 diabetes (T2D), and related metabolic disorders. During obesity, macrophages accumulate in the visceral adipose tissue, creating a low-grade inflammatory environment. Nuclear factor κB (NF-κB) signaling is a central coordinator of inflammatory responses and is tightly regulated by the anti-inflammatory protein A20. Here, we find that myeloid-specific A20-deficient mice are protected from diet-induced obesity and insulin resistance despite an inflammatory environment in their metabolic tissues. Macrophages lacking A20 show impaired mitochondrial respiratory function and metabolize more palmitate both in vitro and in vivo. We hypothesize that A20-deficient macrophages rely more on palmitate oxidation and metabolize the fat present in the diet, resulting in a lean phenotype and protection from metabolic disease. These findings reveal a role for A20 in regulating macrophage immunometabolism.

The pesticide chlorpyrifos promotes obesity by inhibiting diet-induced thermogenesis in brown adipose tissue

Obesity results from a caloric imbalance between energy intake, absorption and expenditure. In both rodents and humans, diet-induced thermogenesis contributes to energy expenditure and involves the activation of brown adipose tissue (BAT). We hypothesize that environmental toxicants commonly used as food additives or pesticides might reduce BAT thermogenesis through suppression of uncoupling protein 1 (UCP1) and this may contribute to the development of obesity. Using a step-wise screening approach, we discover that the organophosphate insecticide chlorpyrifos suppresses UCP1 and mitochondrial respiration in BAT at concentrations as low as 1 pM. In mice housed at thermoneutrality and fed a high-fat diet, chlorpyrifos impairs BAT mitochondrial function and diet-induced thermogenesis, promoting greater obesity, non-alcoholic fatty liver disease (NAFLD) and insulin resistance. This is associated with reductions in cAMP; activation of p38MAPK and AMPK; protein kinases critical for maintaining UCP1 and mitophagy, respectively in BAT. These data indicate that the commonly used pesticide chlorpyrifos, suppresses diet-induced thermogenesis and the activation of BAT, suggesting its use may contribute to the obesity epidemic.

The confounding effects of sub-thermoneutral housing temperatures on aerobic exercise-induced adaptations in mouse subcutaneous white adipose tissue

Mice are the most commonly used model organism for human biology, and failure to acknowledge fundamental differences in thermal biology between these species has confounded the study of adipose tissue metabolism in mice and its translational relevance to humans. Here, using exercise biochemistry as an example, we highlight the subtle yet detrimental effects sub-thermoneutral housing temperatures can have on the study of adipose tissue metabolism in mice. We encourage academics and publishers to consider ambient housing temperature as a key determinant in the methodological conception and reporting of all research on rodent white adipose tissue metabolism.

Macrophage beta2-adrenergic receptor is dispensable for the adipose tissue inflammation and function

OBJECTIVE

Neuroimmune interactions between the sympathetic nervous system (SNS) and macrophages are required for the homeostasis of multiple tissues, including the adipose tissue. It has been proposed that the SNS maintains adipose tissue macrophages (ATMs) in an anti-inflammatory state via direct norepinephrine (NE) signaling to macrophages. This study aimed to investigate the physiological importance of this paradigm by utilizing a mouse model in which the adrenergic signaling from the SNS to macrophages, but not to other adipose tissue cells, was disrupted.

METHODS

We generated a macrophage-specific B2AR knockout mouse (Adrb2ΔLyz2) by crossing Adrb2fl/fl and Lyz2Cre/+ mice. We have previously shown that macrophages isolated from Adrb2ΔLyz2 animals do not respond to NE stimulation in vitro. Herein we performed a metabolic phenotyping of Adrb2ΔLyz2 mice on either chow or high-fat diet (HFD). We also assessed the adipose tissue function of Adrb2ΔLyz2 animals during fasting and cold exposure. Finally, we transplanted Adrb2ΔLyz2 bone marrow to low-density lipoprotein receptor (LDLR) knockout mice and investigated the development of atherosclerosis during Western diet feeding.

RESULTS

We demonstrated that SNS-associated ATMs have a transcriptional profile indicative of activated beta-2 adrenergic receptor (B2AR), the main adrenergic receptor isoform in myeloid cells. However, Adrb2ΔLyz2 mice have unaltered energy balance on a chow or HFD. Furthermore, Adrb2ΔLyz2 mice show similar levels of adipose tissue inflammation and function during feeding, fasting, or cold exposure, and develop insulin resistance during HFD at the same rate as controls. Finally, macrophage-specific B2AR deletion does not affect the development of atherosclerosis on an LDL receptor-null genetic background.

CONCLUSIONS

Overall, our data suggest that the SNS does not directly modulate the phenotype of adipose tissue macrophages in either lean mice or mouse models of cardiometabolic disease. Instead, sympathetic nerve activity exerts an indirect effect on adipose tissue macrophages through the modulation of adipocyte function.

Interleukin-10 Attenuates Liver Fibrosis Exacerbated by Thermoneutrality

Background: Crosstalk between brown adipose tissue (BAT) and the liver is receiving increasing attention. This study investigated the effect of BAT dysfunction by thermoneutral (TN) housing on liver fibrosis in mice and examined the effect of secreted factors from brown adipocytes on the activation of hepatic stellate cells (HSCs).

Methods: The carbon tetrachloride (CCl₄)-induced liver fibrosis mouse model was used to evaluate fibrotic changes in the livers of mice housed under standard and TN conditions. The effect of BAT on the activation of HSCs was examined using cultured cells treated with conditioned media from brown adipocytes.

Results: Under TN conditions, mice with CCl₄-induced liver fibrosis exhibited increased liver injury, collagen deposition, and alpha smooth muscle actin (α-SMA) expression in the liver compared with mice maintained at room temperature. The numbers of liver-infiltrating immune cells and T cells producing IL-17A and IFN-γ were also significantly increased in the livers of mice housed under TN conditions. Treatment of HSCs with conditioned media from brown adipocytes markedly attenuated HSC activation, as shown by down-regulated α-SMA expression at day 4, day 7 and day 10 of culture. At thermoneutrality, with CCl₄ administration, IL-10-deficient mice exhibited more severe liver fibrosis than wild-type mice. Interestingly, conditioned media from IL-10-deficient brown adipocytes could up-regulate the expression of α-SMA and induce HSCs activation.

Conclusions: BAT inactivation by thermoneutrality contributes to the activation of pro-inflammatory and pro-fibrotic pathways in mice with CCl₄-induced liver fibrosis. Normal brown adipocytes secreted factors that impair the activation of HSCs, while this protective effect was lost in IL-10-deficient brown adipocytes. Thus, the BAT–liver axis may serve as a potential therapeutic target for liver fibrosis, and IL-10 may be a key factor regulating the activation of HSCs by BAT.

TFEB deficiency attenuates mitochondrial degradation upon brown adipose tissue whitening at thermoneutrality

OBJECTIVE

Brown adipose tissue (BAT) thermogenesis offers the potential to improve metabolic health in mice and humans. However, humans predominantly live under thermoneutral conditions, leading to BAT whitening, a reduction in BAT mitochondrial content and metabolic activity. Recent studies have established mitophagy as a major driver of mitochondrial degradation in the whitening of thermogenic brite/beige adipocytes, yet the pathways mediating mitochondrial breakdown in whitening of classical BAT remain largely elusive. The transcription factor EB (TFEB), a master regulator of lysosomal biogenesis and autophagy belonging to the MiT family of transcription factors, is the only member of this family that is upregulated during whitening, pointing toward a role of TFEB in whitening-associated mitochondrial breakdown.

METHODS

We generated brown adipocyte-specific TFEB knockout mice, and induced BAT whitening by thermoneutral housing. We characterized gene and protein expression patterns, BAT metabolic activity, systemic metabolism, and mitochondrial localization using in vivo and in vitro approaches.

RESULTS

Under low thermogenic activation conditions, deletion of TFEB preserves mitochondrial mass independently of mitochondriogenesis in BAT and primary brown adipocytes. However, this does not translate into elevated thermogenic capacity or protection from diet-induced obesity. Autophagosomal/lysosomal marker levels are altered in TFEB-deficient BAT and primary adipocytes, and lysosomal markers co-localize and co-purify with mitochondria in TFEB-deficient BAT, indicating trapping of mitochondria in late stages of mitophagy.

CONCLUSION

We identify TFEB as a driver of BAT whitening, mediating mitochondrial degradation via the autophagosomal and lysosomal machinery. This study provides proof of concept that interfering with the mitochondrial degradation machinery can increase mitochondrial mass in classical BAT under human-relevant conditions. However, it must be considered that interfering with autophagy may result in accumulation of non-functional mitochondria. Future studies targeting earlier steps of mitophagy or target recognition are therefore warranted.

BMP4-mediated browning of perivascular adipose tissue governs an anti-inflammatory program and prevents atherosclerosis

Loss of perivascular adipose tissue (PVAT) impairs endothelial function and enhances atherosclerosis. However, the roles of PVAT thermoregulation in vascular inflammation and the development of atherosclerosis remains unclear. Bone morphogenetic protein 4 (BMP4) transforms white adipocyte to beige adipocyte, while promotes a brown-to-white shift in inter-scapular brown adipose tissue (BAT). Here, we found that knockdown of BMP4 in PVAT reduced expression of brown adipocyte-characteristic genes and increased endothelial inflammation in vitro co-culture system. Ablating BMP4 expression either in adipose tissues or specifically in BAT in ApoE^−/− mice demonstrated a marked exacerbation of atherosclerotic plaque formation in vivo. We further demonstrated that proinflammatory factors (especially IL-1β) increased in the supernatant of BMP4 knockdown adipocytes. Overexpression of BMP4 in adipose tissues promotes browning of PVAT and protects against atherosclerosis in ApoE^−/− mice. These findings uncover an organ crosstalk between PVAT and blood endothelial cells that is engaged in atherosclerosis.

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BMP4 expression positively correlates with browning but negatively with coronary artery disease.

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BMP4 KO leads to impaired PVAT metabolism and atherosclerosis.

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Impaired PVAT metabolism mainly induces atherosclerosis by activating inflammation rather than increasing blood lipids.

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Impaired PVAT metabolism drive local inflammation by inducing the secretion of adipocyte-derived proinflammatory factors.

Defining the lineage of thermogenic perivascular adipose tissue

Brown adipose tissue can expend large amounts of energy, and therefore increasing its size or activity is a promising therapeutic approach to combat metabolic disease. In humans, major deposits of brown fat cells are found intimately associated with large blood vessels, corresponding to perivascular adipose tissue (PVAT). However, the cellular origins of PVAT are poorly understood. Here, we determine the identity of perivascular adipocyte progenitors in mice and humans. In mice, thoracic PVAT develops from a fibroblastic lineage, consisting of progenitor cells (Pdgfra+, Ly6a+ and Pparg-) and preadipocytes (Pdgfra+, Ly6a+ and Pparg+), which share transcriptional similarity with analogous cell types in white adipose tissue. Interestingly, the aortic adventitia of adult animals contains a population of adipogenic smooth muscle cells (Myh11+, Pdgfra- and Pparg+) that contribute to perivascular adipocyte formation. Similarly, human PVAT contains presumptive fibroblastic and smooth muscle-like adipocyte progenitor cells, as revealed by single-nucleus RNA sequencing. Together, these studies define distinct populations of progenitor cells for thermogenic PVAT, providing a foundation for developing strategies to augment brown fat activity.

Thermoneutrality Alters Gastrointestinal Antigen Passage Patterning and Predisposes to Oral Antigen Sensitization in Mice

Food allergy is an emerging epidemic, and the underlying mechanisms are not well defined partly due to the lack of robust adjuvant free experimental models of dietary antigen sensitization. As housing mice at thermoneutrality (Tn) - the temperature of metabolic homeostasis (26-30°C) - has been shown to improve modeling various human diseases involved in inflammation, we tested the impact of Tn housing on an experimental model of food sensitization. Here we demonstrate that WT BALB/c mice housed under standard temperature (18-20°C, Ts) conditions translocated the luminal antigens in the small intestine (SI) across the epithelium via goblet cell antigen passages (GAPs). In contrast, food allergy sensitive Il4raF709 mice housed under standard temperature conditions translocated the luminal antigens in the SI across the epithelium via secretory antigen passages (SAPs). Activation of SI antigen passages and oral challenge of Il4raF709 mice with egg allergens at standard temperature predisposed Il4raF709 mice to develop an anaphylactic reaction. Housing Il4raF709 mice at Tn altered systemic type 2 cytokine, IL-4, and the landscape of SI antigen passage patterning (villus and crypt involvement). Activation of SI antigen passages and oral challenge of Il4raF709 mice with egg antigen under Tn conditions led to the robust induction of egg-specific IgE and development of food-induced mast cell activation and hypovolemic shock. Similarly, Tn housing of WT BALB/c mice altered the cellular patterning of SI antigen passage (GAPs to SAPs). Activation of SI antigen passages and the oral challenge of WT BALB/c mice with egg antigen led to systemic reactivity to egg and mast cell activation. Together these data demonstrate that Tn housing alters antigen passage cellular patterning and landscape, and concurrent oral exposure of egg antigens and SAP activation is sufficient to induce oral antigen sensitization.

High Ambient Temperature Aggravates Experimental Autoimmune Uveitis Symptoms

Whether ambient temperature influences immune responses leading to uveitis is unknown. We thus tested whether ambient temperature affects the symptoms of experimental autoimmune uveitis (EAU) in mice and investigated possible mechanisms. C57BL/6 mice were kept at a normal (22°C) or high temperature (30°C) housing conditions for 2 weeks and were then immunized with human interphotoreceptor retinoid-binding protein (IRBP651–670) peptide to induce EAU. Histological changes were monitored to evaluate the severity of uveitis. Frequency of Th1 cells and Th17 cells was measured by flow cytometry (FCM). The expression of IFN-γ and IL-17A mRNA was measured by real-time qPCR. The generation of neutrophil extracellular traps (NETs) was quantified by enzyme-linked immunosorbent assay (ELISA). Differential metabolites in the plasma of the mice kept in the aforementioned two ambient temperatures were measured via ultra-high-performance liquid chromatography triple quadrupole mass spectrometry quadrupole time of flight mass spectrometry (UHPLC-QQQ/MS). The differential metabolites identified were used to evaluate their effects on differentiation of Th1 and Th17 cells and generation of NETs in vitro. The results showed that EAU mice kept at high temperature experienced a more severe histopathological manifestation of uveitis than mice kept at a normal temperature. A significantly increased frequency of Th1 and Th17 cells in association with an upregulated expression of IFN-γ and IL-17A mRNA was observed in the splenic lymphocytes and retinas of EAU mice in high temperature. The expression of NETs as evidenced by myeloperoxidase (MPO) and neutrophil elastase (NE), was significantly elevated in serum and supernatants of neutrophils from EAU mice kept at high temperature compared to the normal temperature group. The metabolites in the plasma from EAU mice, fumaric acid and succinic acid, were markedly increased in the high temperature group and could induce the generation of NETs via the NADPH oxidase-dependent pathway, but did not influence the frequency of Th1 and Th17 cells. Our findings suggest that an increased ambient temperature is a risk factor for the development of uveitis. This is associated with the induction of Th1 and Th17 cells as well as the generation of NETs which could be mediated by the NADPH oxidase-dependent pathway.

Lysates of Methylococcus capsulatus Bath induce a lean-like microbiota, intestinal FoxP3+RORγt+IL-17+ Tregs and improve metabolism

Interactions between host and gut microbial communities are modulated by diets and play pivotal roles in immunological homeostasis and health. We show that exchanging the protein source in a high fat, high sugar, westernized diet from casein to whole-cell lysates of the non-commensal bacterium Methylococcus capsulatus Bath is sufficient to reverse western diet-induced changes in the gut microbiota to a state resembling that of lean, low fat diet-fed mice, both under mild thermal stress (T22 °C) and at thermoneutrality (T30 °C). Concomitant with microbiota changes, mice fed the Methylococcus-based western diet exhibit improved glucose regulation, reduced body and liver fat, and diminished hepatic immune infiltration. Intake of the Methylococcu-based diet markedly boosts Parabacteroides abundances in a manner depending on adaptive immunity, and upregulates triple positive (Foxp3+RORγt+IL-17+) regulatory T cells in the small and large intestine. Collectively, these data point to the potential for leveraging the use of McB lysates to improve immunometabolic homeostasis.

Characterization of the circulating and tissue-specific alterations to the lipidome in response to moderate and major cold stress in mice

This study analyzed the effects of 24 h of cold stress (22°C or 5°C vs. mice maintained at 30 °C) on the plasma, brown adipose tissue (BAT), subcutaneous (SubQ) and epididymal (Epi) white adipose tissue (WAT), liver, and skeletal muscle lipidome of mice. Using mass spectrometry-lipidomics, 624 lipid species were detected, of which 239 were significantly altered in plasma, 134 in BAT, and 51 in the liver. In plasma, acylcarnitines and free fatty acids were markedly increased at 5°C. Plasma triacylglycerols (TGs) were reduced at 22°C and 5°C. We also identified ether lipids as a novel, cold-induced lipid class. In BAT, TGs were the principal lipid class affected by cold stress, being significantly reduced at both 22°C and 5°C. Interestingly, although BAT TG species were uniformly affected at 5°C, at 22°C we observed species-dependent effects, with TGs containing longer and more unsaturated fatty acids particularly sensitive to the effects of cold. In the liver, TGs were the most markedly affected lipid class, increasing in abundance at 5 °C. TGs containing longer and more unsaturated fatty acids accumulated to a greater degree. Our work demonstrates the following: 1) acute exposure to moderate (22°C) cold stress alters the plasma and BAT lipidome; although this effect is markedly less pronounced than at 5°C. 2) Cold stress at 5°C dramatically alters the plasma lipidome, with ether lipids identified as a novel lipid class altered by cold exposure. 3) Cold-induced alterations in liver and BAT TG levels are not uniform, with changes being influenced by acyl chain composition.

Barriers in translating preclinical rodent exercise metabolism findings to human health

Physical inactivity and low aerobic capacity are primary drivers of chronic disease pathophysiology and are independently associated with all-cause mortality. Conversely, increased physical activity and exercise are central to metabolic disease prevention and longevity. Although these relationships are well characterized in the literature, what remains incompletely understood are the mechanisms by which physical activity/exercise prevents disease. Given methodological constraints of clinical research, investigators must often rely on preclinical rodent models to investigate these potential underlying mechanisms. However, there are several key barriers to applying exercise metabolism findings from rodent models to human health. These barriers include housing temperature, nutrient metabolism, exercise modality, exercise testing, and sex differences. Increased awareness and understanding of these barriers will enhance the ability to impact human health through more appropriate experimental design and interpretation of data within the context of these factors.

Diet-induced rodent models of obesity-related metabolic disorders-A guide to a translational perspective

Diet is a critical element determining human health and diseases, and unbalanced food habits are major risk factors for the development of obesity and related metabolic disorders. Despite technological and pharmacological advances, as well as intensification of awareness campaigns, the prevalence of metabolic disorders worldwide is still increasing. Thus, novel therapeutic approaches with increased efficacy are urgently required, which often depends on cellular and molecular investigations using robust animal models. In the absence of perfect rodent models, those induced by excessive consumption of fat and sugars better replicate the key aspects that are the root causes of human metabolic diseases. However, the results obtained using these models cannot be directly compared, particularly because of the use of different dietary protocols, and animal species and strains, among other confounding factors. This review article revisits diet-induced models of obesity and related metabolic disorders, namely, metabolic syndrome, prediabetes, diabetes and nonalcoholic fatty liver disease. A critical analysis focused on the main pathophysiological features of rodent models, as opposed to the criteria defined for humans, is provided as a practical guide with a translational perspective for the establishment of animal models of obesity-related metabolic diseases.

Thermoneutrality and Immunity: How Does Cold Stress Affect Disease?

One of the major challenges the scientific community faces today is the lack of translational data generated from mouse trials for human health application. Housing temperature-dependent chronic cold stress in laboratory rodents is one of the key factors contributing to lack of translatability because it reveals major metabolic differences between humans and rodents. While humans tend to operate at temperatures within their thermoneutral zone, most laboratory rodents are housed at temperatures below this zone and have an increased energy demand to generate heat. This has an impact on the immune system of mice and thus affects results obtained using murine models of human diseases. A limited number of studies and reviews have shown that results obtained on mice housed at thermoneutrality were different from those obtained from mice housed in traditional housing conditions. Most of those studies, focused on obesity and cancer, found that housing mice at thermoneutrality changed the outcomes of the diseases negatively and positively, respectively. In this review, we describe how thermoneutrality impacts the immune system of rodents generally and in the context of different disease models. We show that thermoneutrality exacerbates cardiovascular and auto-immune diseases; alleviates asthma and Alzheimer’s disease; and, changes gut microbiome populations. We also show that thermoneutrality can have exacerbating or alleviating effects on the outcome of infectious diseases. Thus, we join the call of others in this field to urge researchers to refine murine models of disease and increase their translational capacity by considering housing at thermoneutrality for trials involving rodents.

Perivascular mesenchymal cells control adipose-tissue macrophage accrual in obesity

Chronic low-grade white adipose tissue (WAT) inflammation is a hallmark of metabolic syndrome in obesity. Here, we demonstrate that a subpopulation of mouse WAT perivascular (PDGFRβ⁺) cells, termed fibro-inflammatory progenitors (FIPs), activate proinflammatory signalling cascades shortly after the onset of high-fat diet feeding and regulate proinflammatory macrophage accumulation in WAT in a TLR4-dependent manner. FIPs activation in obesity is mediated by the downregulation of zinc-finger protein 423 (ZFP423), identified here as a transcriptional corepressor of NF-κB. ZFP423 suppresses the DNA-binding capacity of the p65 subunit of NF-κB by inducing a p300-to-NuRD coregulator switch. Doxycycline-inducible expression of Zfp423 in PDGFRβ⁺ cells suppresses inflammatory signalling in FIPs and attenuates metabolic inflammation of visceral WAT in obesity. Inducible inactivation of Zfp423 in PDGFRβ⁺ cells increases FIP activity, exacerbates adipose macrophage accrual and promotes WAT dysfunction. These studies implicate perivascular mesenchymal cells as important regulators of chronic adipose-tissue inflammation in obesity and identify ZFP423 as a transcriptional break on NF-κB signalling.

Biochemical adaptations in white adipose tissue following aerobic exercise: from mitochondrial biogenesis to browning

Our understanding of white adipose tissue (WAT) biochemistry has evolved over the last few decades and it is now clear that WAT is not simply a site of energy storage, but rather a pliable endocrine organ demonstrating dynamic responsiveness to the effects of aerobic exercise. Similar to its established effects in skeletal muscle, aerobic exercise induces many biochemical adaptations in WAT including mitochondrial biogenesis and browning. While past research has focused on the regulation of these biochemical processes, there has been renewed interest as of late given the potential of harnessing WAT mitochondrial biogenesis and browning to treat obesity and type II diabetes. Unfortunately, despite increasing evidence that innumerable factors, both exercise induced and pharmacological, can elicit these biochemical adaptations in WAT, the underlying mechanisms remain poorly defined. Here, we begin with a historical account of our understanding of WAT exercise biochemistry before presenting detailed evidence in favour of an up-to-date model by which aerobic exercise induces mitochondrial biogenesis and browning in WAT. Specifically, we discuss how aerobic exercise induces increases in WAT lipolysis and re-esterification and how this could be a trigger that activates the cellular energy sensor 5' AMP-activated protein kinase to mediate the induction of mitochondrial biogenesis and browning via the transcriptional co-activator peroxisome proliferator-activated receptor gamma co-activator-1 alpha. While this review primarily focuses on mechanistic results from rodent studies special attention is given to the translation of these results, or lack thereof, to human physiology.

Metabolic adaptation to calorie restriction

Calorie restriction (CR) enhances health span (the length of time that an organism remains healthy) and increases longevity across species. In mice, these beneficial effects are partly mediated by the lowering of core body temperature that occurs during CR. Conversely, the favorable effects of CR on health span are mitigated by elevating ambient temperature to thermoneutrality (30°C), a condition in which hypothermia is blunted. In this study, we compared the global metabolic response to CR of mice housed at 22°C (the standard housing temperature) or at 30°C and found that thermoneutrality reverted 39 and 78% of total systemic or hypothalamic metabolic variations caused by CR, respectively. Systemic changes included pathways that control fuel use and energy expenditure during CR. Cognitive computing-assisted analysis of these metabolomics results helped to prioritize potential active metabolites that modulated the hypothermic response to CR. Last, we demonstrated with pharmacological approaches that nitric oxide (NO) produced through the citrulline-NO pathway promotes CR-triggered hypothermia and that leucine enkephalin directly controls core body temperature when exogenously injected into the hypothalamus. Because thermoneutrality counteracts CR-enhanced health span, the multiple metabolites and pathways altered by thermoneutrality may represent targets for mimicking CR-associated effects.

Genomic, microbial and environmental standardization in animal experimentation limiting immunological discovery

Background

The use of inbred mice housed under standardized environmental conditions has been critical in identifying immuno-pathological mechanisms in different infectious and inflammatory diseases as well as revealing new therapeutic targets for clinical trials. Unfortunately, only a small percentage of preclinical intervention studies using well-defined mouse models of disease have progressed to clinically-effective treatments in patients. The reasons for this lack of bench-to-bedside transition are not completely understood; however, emerging data suggest that genetic diversity and housing environment may greatly influence muring immunity and inflammation.

Results

Accumulating evidence suggests that certain immune responses and/or disease phenotypes observed in inbred mice may be quite different than those observed in their outbred counterparts. These differences have been thought to contribute to differing immune responses to foreign and/or auto-antigens in mice vs. humans. There is also a growing literature demonstrating that mice housed under specific pathogen free conditions possess an immature immune system that remarkably affects their ability to respond to pathogens and/or inflammation when compared with mice exposed to a more diverse spectrum of microorganisms. Furthermore, recent studies demonstrate that mice develop chronic cold stress when housed at standard animal care facility temperatures (i.e. 22–24 °C). These temperatures have been shown alter immune responses to foreign and auto-antigens when compared with mice housed at their thermo-neutral body temperature of 30–32 °C.

Conclusions

Exposure of genetically diverse mice to a spectrum of environmentally-relevant microorganisms at housing temperatures that approximate their thermo-neutral zone may improve the chances of identifying new and more potent therapeutics to treat infectious and inflammatory diseases.