Global transcriptome analysis identifies weight regain-induced activation of adaptive immune responses in white adipose tissue of mice

E4bp4-Cyp3a11 axis in high-fat diet-induced obese mice with weight fluctuation

OBJECTIVE

Weight regain after weight loss is a challenge in obesity management. The metabolic changes and underlying mechanisms in obese people with weight fluctuation remain to be elucidated. In the present study, we aimed to profile the features and clinical significance of liver transcriptome in obese mice with weight regain after weight loss.

METHODS

The male C57BL/6J mice were fed with standard chow diet or high-fat diet (HFD). After 9 weeks, the HFD-induced obese mice were randomly divided into weight gain (WG), weight loss (WL) and weight regain (WR) group. After 10 weeks of dietary intervention, body weight, fasting blood glucose (FBG), intraperitoneal glucose tolerance, triglycerides (TG), total cholesterol (T-CHO) and low-density lipoprotein cholesterol (LDL-C) were measured. Morphological structure and lipid droplet accumulation in the liver were observed by H&E staining and oil red O staining, respectively. The liver transcriptome was detected by RNA sequencing. Protein expressions of liver cytochrome P450 3a11 (Cyp3a11) and E4 promoter-binding protein 4 (E4bp4) were determined by Western blot.

RESULTS

After 10 weeks of dietary intervention, the body weight, FBG, glucose area under the curve, T-CHO and LDL-C in WL group were significantly lower than those in WG group (P < 0.05). At 4 weeks of HFD re-feeding, the mice in WR group presented body weight and T-CHO significantly lower than those in WG group, whereas higher than those in WL group (P < 0.05). Hepatic vacuolar degeneration and lipid droplet accumulation in the liver were significantly alleviated in WL group and WR group, compared to those in WG group. The liver transcriptome associated with lipid metabolism was significantly altered during weight fluctuation in obese mice. Compared with those in WG group, Cyp3a11 in the liver was significantly upregulated, and E4bp4 was significantly downregulated in WL and WR groups.

CONCLUSION

Obese mice experience weight regain after weight loss by HFD re-feeding, but their glucose and lipid metabolism disorders are milder than those induced by the persistence of obesity. Downregulated E4bp4 and upregulated Cyp3a11 are detected in obese mice after weight loss, suggesting that the E4bp4-Cyp3a11 axis may involved in metabolic mechanisms underlying weight regulation.

Metaflammation in obesity and its therapeutic targeting

Obesity-associated inflammation is a systemic process that affects all metabolic organs. Prominent among these is adipose tissue, where cells of the innate and adaptive immune system are markedly changed in obesity, implicating these cells in a range of processes linking immune memory to metabolic regulation. Furthermore, weight loss and weight cycling have unexpected effects on adipose tissue immune populations. Here, we review the current literature on the roles of various immune cells in lean and obese adipose tissue. Within this context, we discuss pharmacological and nonpharmacological approaches to obesity treatment and their impact on systemic inflammation.

Weight cycling based on altered immune microenvironment as a result of metaflammation

As a result of the obesity epidemic, more people are concerned about losing weight; however, weight regain is common, leading to repeated weight loss and weight cycling. The health benefits of early weight loss are nullified by weight regain after weight cycling, which has much more severe metabolic consequences. Weight cycling alters body composition, resulting in faster fat recovery and slower muscle reconstruction. This evident fat accumulation, muscle loss, and ectopic fat deposition destroy the intestinal barrier, increase the permeability of the small intestinal epithelium, and cause the lipotoxicity of lipid metabolites and toxins to leak into extraintestinal tissues and circulation. It causes oxidative stress and hypoxia in local tissues and immune cell infiltration in various tissues, all contributing to the adaptation to this metabolic change. Immune cells transmit inflammatory responses in adipose and skeletal muscle tissue by secreting cytokines and adipokines, which mediate immune cell pathways and cause metaflammation and inefficient metabolic degradation. In this review, we focus on the regulatory function of the immunological microenvironment in the final metabolic outcome, with a particular emphasis on the cellular and molecular processes of local and systemic metaflammation induced by weight cycling-induced changes in body composition. Metaflammation in adipose and muscle tissues that is difficult to relieve may cause weight cycling. As this chronic low-grade inflammation spreads throughout the body, metabolic complications associated with weight cycling are triggered. Inhibiting the onset and progression of metabolic inflammation and enhancing the immune microenvironment of adipose and muscle tissues may be the first step in addressing weight cycling.

Adipocytes control food intake and weight regain via Vacuolar-type H+ ATPase

Energy metabolism becomes dysregulated in individuals with obesity and many of these changes persist after weight loss and likely play a role in weight regain. In these studies, we use a mouse model of diet-induced obesity and weight loss to study the transcriptional memory of obesity. We found that the 'metabolic memory' of obesity is predominantly localized in adipocytes. Utilizing a C. elegans-based food intake assay, we identify 'metabolic memory' genes that play a role in food intake regulation. We show that expression of ATP6v0a1, a subunit of V-ATPase, is significantly induced in both obese mouse and human adipocytes that persists after weight loss. C. elegans mutants deficient in Atp6v0A1/unc32 eat less than WT controls. Adipocyte-specific Atp6v0a1 knockout mice have reduced food intake and gain less weight in response to HFD. Pharmacological disruption of V-ATPase assembly leads to decreased food intake and less weight re-gain. In summary, using a series of genetic tools from invertebrates to vertebrates, we identify ATP6v0a1 as a regulator of peripheral metabolic memory, providing a potential target for regulation of food intake, weight loss maintenance and the treatment of obesity.

The impact of weight cycling on health outcomes in animal models: A systematic review and meta-analysis

The pattern of weight loss and regain, termed "weight cycling," is common in overweight individuals. It is unclear whether the well-established benefits of weight loss persist following weight regain or whether weight cycling is harmful. Human studies of weight cycling have conflicting results reflecting limitations of the observational designs of these studies. By controlling the macronutrient content of diets in animal studies, weight cycling can be studied in a highly controlled manner, thereby overcoming the limitations of human studies. We conducted a systematic review and meta-analysis of animal studies which assessed the health consequences of weight cycling. Studies were classified into those which compared weight cycling to lifelong obesity and those which compared weight cycling to later onset obesity. There were no differences in health outcomes between weight cycled animals and those with lifelong obesity, highlighting that weight regain reverses health benefits achieved by weight loss. In comparison with animals with later onset obesity, weight cycled animals had higher fasting glucose levels and more impaired glucose tolerance following weight regain. Our review of animal studies suggests that health benefits of diet-induced weight loss do not persist after weight regain and weight cycling results in adverse metabolic outcomes.

Body mass cycling and predictors of body mass regain and its impact on cardiometabolic health

Caloric restriction (CR) is the first line intervention to reduce adiposity and total body mass (BM) to improve insulin resistance and ameliorate metabolic derangements. However, the lost adipose mass is difficult to maintain reduced in the long term due to several factors including compensatory changes in orexigenic hormones, adipokine release, pro-inflammatory state, adipose tissue morphology, and resting metabolic rate as a consequence of the caloric deficit. Hence, most patients undergoing a BM reduction intervention ultimately regain the lost mass and too often additional adipose mass overtime, which is hypothesized to have increased deleterious effects chronically. In this mini-review we describe the effects of BM cycling (loss and regain) on insulin resistance and cardiometabolic health and factors that may predict BM regain in clinical studies. We also describe the factors that contribute to the chronic deleterious effects of BM cycling in rodent models of diet-induced obesity (DIO) and other metabolic defects. We conclude that most of the improvements in insulin resistance are observed after a profound loss in BM regardless of the diet and that BM cycling abrogates these beneficial effects. We also suggest that more BM cycling studies are needed in rodent models resembling the development of type 2 diabetes mellitus (T2DM) in humans.

Metabolomic Profiling Demonstrates Postprandial Changes in Fatty Acids and Glycerophospholipids Are Associated with Fasting Inflammation in Guatemalan Adults

BACKGROUND

Metabolic flexibility is the responsiveness to heterogeneous physiological conditions, such as food ingestion. A key unresolved question is how inflammation affects metabolic flexibility.

OBJECTIVES

Our study objective was to compare metabolic flexibility, specifically the metabolomic response to a standardized meal, by fasting inflammation status.

METHODS

Participants in Guatemala (n = 302, median age 44 y, 43.7% men) received a standardized, mixed-macronutrient liquid meal. Plasma samples (fasting, 2 h postmeal) were assayed by dual-column LC [reverse phase (C18) and hydrophilic interaction LC (HILIC)] with ultra-high-resolution MS, for concentrations of 6 inflammation biomarkers: high-sensitivity C-reactive protein (hsCRP), leptin, resistin, IL-10, adiponectin, and soluble TNF receptor II (TNFsR). We summed the individual inflammation biomarker z-scores, after reverse-coding of anti-inflammation biomarkers. We identified features with peak areas that differed between fasting and postmeal (false discovery rate-adjusted q <0.05) and compared median log2 postprandial/fasting peak area ratios by inflammation indicators.

RESULTS

We found 1397 C18 and 974 HILIC features with significant postprandial/fasting feature ratios (q <0.05). Overall inflammation z-score was directly associated with the postprandial/fasting feature ratios of arachidic acid, and inversely associated with the feature ratio of lysophosphatidic acid (LPA), adjusting for age and sex (all P < 0.05). The postprandial/fasting ratio of arachidic acid was negatively correlated with resistin, IL-10, adiponectin, and TNFsR concentrations (all P < 0.05). Feature ratios of several fatty acids-myristic acid [m/z 227.2018, retention time (RT) 229], heptadecanoic acid (m/z 269.2491, RT 276), linoleic acid (m/z 280.2358, RT 236)-were negatively correlated with fasting plasma concentrations of leptin (nanograms per milliliter) and adiponectin (micrograms per milliliter), respectively (all P < 0.05). The postprandial/fasting ratio of LPA was positively correlated with IL-10 and adiponectin (both P < 0.05); and the ratio of phosphatidylinositol was positively correlated with hsCRP (P < 0.05).

CONCLUSIONS

Postprandial responses of fatty acids and glycerophospholipids are associated with fasting inflammation status in adults in Guatemala.

Physiological Responses of Post-Dietary Effects: Lessons from Pre-Clinical and Clinical Studies

Dieting regimens such as calorie restriction (CR) are among the most commonly practiced interventions for weight management and metabolic abnormalities. Due to its independence from pharmacological agents and considerable flexibility in regimens, many individuals turn to dieting as a form of mitigation and maintenance of metabolic health. While metabolic benefits of CR have been widely studied, weight loss maintenance and metabolic benefits are reported to be lost overtime when the diet regimen has been terminated—referred to as post-dietary effects. Specifically, due to the challenges of long-term adherence and compliance to dieting, post-dietary repercussions such as body weight regain and loss of metabolic benefits pose as major factors in the efficacy of CR. Intermittent fasting (IF) regimens, which are defined by periodic energy restriction, have been deemed as more flexible, compliant, and easily adapted diet interventions that result in many metabolic benefits which resemble conventional CR diets. Many individuals find that IF regimens are easier to adhere to, resulting in fewer post-dietary effects; therefore, IF may be a more effective intervention. Unfortunately, there is a severe gap in current research regarding IF post-dietary effects. We recognize the importance of understanding the sustainability of dieting; as such, we will review the known physiological responses of CR post-dietary effects and its potential mechanisms through synthesizing lessons from both pre-clinical and clinical studies. This review aims to provide insight from a translational medicine perspective to allow for the development of more practical and effective diet interventions. We suggest more flexible and easily practiced dieting regimens such as IF due to its more adaptable and practical nature.

Adipose tissue macrophages: Unique polarization and bioenergetics in obesity

Macrophages comprise a majority of the resident immune cells in adipose tissue (AT) and regulate both tissue homeostasis in the lean state and metabolic dysregulation in obesity. Since the AT environment rapidly changes based upon systemic energy status, AT macrophages (ATMs) must adapt phenotypically and metabolically. There is a distinct dichotomy in the polarization and bioenergetics of in vitro models, with M2 macrophages utilizing oxidative phosphorylation (OX PHOS) and M1 macrophages utilizing glycolysis. Early studies suggested differential polarization of ATMs, with M2-like macrophages predominant in lean AT and M1-like macrophages in obese AT. However, recent studies show that the phenotypic plasticity of ATMs is far more complicated, which is also reflected in their bioenergetics. Multiple ATM populations exist along the M2 to M1 continuum and appear to utilize both glycolysis and OX PHOS in obesity. The significance of the dual fuel bioenergetics is unclear and may be related to an intermediate polarization, their buffering capacity, or the result of a mixed population of distinct polarized ATMs. Recent evidence also suggests that ATMs of lean mice serve as a substrate buffer or reservoir to modulate lipid, catecholamine, and iron availability. Furthermore, recent models of weight loss and weight cycling reveal additional roles for ATMs in systemic metabolism. Evaluating ATM phenotype and intracellular metabolism together may more accurately illuminate the consequences of ATM accumulation in obese AT, lending further insight into obesity-related comorbidities in humans.

Stratifying cellular metabolism during weight loss: an interplay of metabolism, metabolic flexibility and inflammation

Obesity is a global epidemic, contributing significantly to chronic non-communicable diseases, such as type 2 diabetes mellitus, cardiovascular diseases and metabolic syndrome. Metabolic flexibility, the ability of organisms to switch between metabolic substrates, is found to be impaired in obesity, possibly contributing to the development of chronic illnesses. Several studies have shown the improvement of metabolic flexibility after weight loss. In this study, we have mapped the cellular metabolism of the adipose tissue from a weight loss study to stratify the cellular metabolic processes and metabolic flexibility during weight loss. We have found that for a majority of the individuals, cellular metabolism was downregulated during weight loss, with gene expression of all major cellular metabolic processes (such as glycolysis, fatty acid β-oxidation etc.) being lowered during weight loss and weight maintenance. Parallel to this, the gene expression of immune system related processes involving interferons and interleukins increased. Previously, studies have indicated both negative and positive effects of post-weight loss inflammation in the adipose tissue with regards to weight loss or obesity and its co-morbidities; however, mechanistic links need to be constructed in order to determine the effects further. Our study contributes towards this goal by mapping the changes in gene expression across the weight loss study and indicates possible cross-talk between cellular metabolism and inflammation.

Immunomodulatory Effects of the Meretrix Meretrix Oligopeptide (QLNWD) on Immune-Deficient Mice

The aim of this study was to explore the immunomodulatory effects of the Meretrix meretrix oligopeptide (MMO, QLNWD) in cyclophosphamide (CTX)-induced immune-deficient mice. Compared to untreated, CTX-induced immune-deficient mice, the spleen and thymus indexes of mice given moderate (100 mg/kg) and high (200 mg/kg) doses of MMO were significantly higher (p < 0.05), and body weight loss was alleviated. Hematoxylin-eosin (H&E) staining revealed that MMO reduced spleen injury, thymus injury, and liver injury induced by CTX in mice. Furthermore, MMO boosted the production of immunoglobulin G (IgG) and hemolysin in the serum and promoted the proliferation and differentiation of spleen T-lymphocytes. Taken together, our findings suggest that MMO plays a vital role in protection against immunosuppression in CTX-induced immune-deficient mice and could be a potential immunomodulatory candidate for use in functional foods or immunologic adjuvants.

Determining sample size adequacy for animal model studies in nutrition research: limits and ethical challenges of ordinary power calculation procedures

Animal models are widely used in the field of nutrition research. Scientifically and ethically sound experiments need an adequate number of experimental units. The use of 5-10 units is common, but such sample sizes can be justified for large effect sizes only. We reviewed animal model studies recently published in selected journals in the field of nutrition sciences. We performed a simulation study aimed at determining the adequate sample size for normality assessment. We then performed power calculations for a number of statistical tests commonly found in rodent model studies in nutrition research. Among the selected papers, sample sizes ranged from 6-18 units per group. None of them justified the sample size. However, such sample sizes do not allow for normality testing, thus, graphical approaches should be used. Parametric approaches result in higher statistical power when compared to their non-parametric counterparts. Repeated measures analysis should always be preferred, when possible.

Lipolysis defect in white adipose tissue and rapid weight regain

Weight regain after weight loss is a well-described phenomenon in both humans and animal models of obesity. Reduced energy expenditure and increased caloric intake are considered the main drivers of weight regain. We hypothesized that adipose tissue with obesity memory (OM) has a tissue-autonomous lipolytic defect, allowing for increased efficiency of lipid storage. We utilized a mouse model of diet-induced obesity, which was subjected to 60% caloric restriction to achieve lean body weight, followed by a short period of high-fat diet (HFD) rechallenge. Age-matched lean mice fed HFD for the first time were used as the control group. Upon rechallenge with HFD, mice with OM had higher respiratory exchange ratios than lean mice with no OM despite comparable body weight, suggesting higher utilization of glucose over fatty acid oxidation. White adipose tissue explants with OM had comparable lipolytic response after caloric restriction; however, reduced functional lipolytic response to norepinephrine was noted as early as 5 days after rechallenge with HFD and was accompanied by reduction in hormone-sensitive lipase serine phosphorylation. The relative lipolytic defect was associated with increased expression of inflammatory genes and a decrease in adrenergic receptor genes, most notably Adrb3. Taken together, white adipose tissue of lean mice with OM shows increased sensitization to HFD compared with white adipose tissue with no OM, rendering it resistant to catecholamine-induced lipolysis. This relative lipolytic defect is tissue-autonomous and could play a role in the rapid weight regain observed after weight loss.

Links between Immunologic Memory and Metabolic Cycling

Treatments for metabolic diseases, such as diet and therapeutics, often provide short-term therapy for metabolic stressors, but relapse is common. Repeated bouts of exposure to, and relief from, metabolic stimuli results in a phenomenon we call "metabolic cycling." Recent human and rodent data suggest metabolic cycling promotes an exaggerated response and ultimately worsened metabolic health. This is particularly evident with cycling of body weight and hypertension. The innate and adaptive immune systems have a profound impact on development of metabolic disease, and current data suggest that immunologic memory may partially explain this association, especially in the context of metabolic cycling. In this Brief Review, we highlight recent work in this field and discuss potential immunologic mechanisms for worsened disease prognosis in individuals who experience metabolic cycling.