Fate of adipocyte progenitors during adipogenesis in mice fed a high-fat diet

ISM1 regulates white adipose tissue remodelling by dampening adipocyte differentiation and enhancing inflammation

AIMS

Isthmin-1 (ISM1), a secretory protein predominantly derived from brown adipose tissue, enhances glucose tolerance and attenuates hepatic steatosis. However, its potential involvement in white adipose tissue remodelling remains elusive, which profoundly impacts adipocyte insulin sensitivity and consequently alters systemic metabolic homeostasis.

MATERIALS AND METHODS

ISM1 expression profiles in human and mouse were systematically characterized using Tabula Sapiens. With the intervention of ISM1 expression, mouse preadipocyte cell lines were employed to observe adipocyte differentiation. Furthermore, inflammatory responses of preadipocytes and macrophages induced by palmitic acid (PA) were also studied in vitro. In vivo, overexpression of ISM1 in white adipose tissue followed by 4 weeks of high-fat diet (HFD) was compared.

RESULTS

ISM1 exhibited exclusive expression in adipose stem cells and progenitor cells in white adipose tissue. Stable overexpression of ISM1 in 3T3-F442A could significantly impair the ability to differentiate into adipocytes and promote myofibroblast-like differentiation. Notably, under PA stimuli, ISM1 amplified pro-inflammatory responses elicited by mouse adipocyte progenitors and macrophages with an increase in a couple of inflammatory factors. In mice, ISM1 overexpression could inhibit the differentiation of adipocyte progenitors in inguinal white adipose tissue and enhance macrophage accumulation in epididymal white adipose tissue with a short-term HFD.

CONCLUSIONS

ISM1 may primarily be derived from stem/progenitor cells in white adipose tissues. ISM1 plays an important role in HFD-induced white adipose tissue remodelling, suggesting its complex potential in improving insulin resistance and treating metabolic disorders.

Baden M, Eguchi H, Shimomura I. Hyperplasia of Fat-Containing Cells With Mature Adipocyte Marker Is Associated With Pancreatic Fat Enlargement

OBJECTIVES

To elucidate the specific characteristics of fat-containing cells in the pancreas and the mechanism of intrapancreatic fat deposition in humans.

MATERIALS AND METHODS

Fifteen Japanese patients who had undergone pancreatic resection were enrolled, and the normal region from each samples was examined. Immunostaining for adiponectin and perilipin 1 was performed, and the relationships between the pancreatic fat-cell area or clinical parameters and the density or the diameter of the fat cells were analyzed.

RESULTS

The expression of adiponectin in the cytoplasm and perilipin 1 along the plasma membrane was observed in fat-containing cells in the pancreas. The fat-containing cell area had a significant positive correlation with cell density. In addition, fat-containing cell density was significantly positively correlated with homeostasis model assessment insulin resistance. The diameter of fat-containing cells had significant positive correlations with BMI, fasting immunoreactive insulin, and homeostasis model assessment insulin resistance. Of all fat-containing cells, 10.4% were intralobular cells, and the diameter of intralobular cells showed a tendency for positive correlation with age.

CONCLUSIONS

The characteristics of fat-containing cells in the pancreas indicate that some of them may be mature adipocytes, and fat volume may be increased by hyperplasia of fat-containing cells associated with insulin resistance.

Role of transforming growth factor-β1 in regulating adipocyte progenitors

Adipose tissue (AT) metabolism involves coordinating various cells and cellular processes to regulate energy storage, release, and overall metabolic homeostasis. Therein, macrophage and its cytokine are important in controlling tissue homeostasis. Among cytokines, the role of transforming growth factor-β1 (Tgf-β1), a cytokine abundantly expressed in CD206+ M2-like macrophage and correlated with the expansion of AT and fibrosis, in AT metabolism, remains unknown. We used CD206CreERT2; Tgf-β1f/f mouse model in which the Tgf-β1 gene was conditionally deleted in CD206+ M2-like macrophages followed by tamoxifen administration, to investigate the role of the Tgf-β1 gene in glucose and insulin metabolism. Our data demonstrated that lack of CD206+ M2-like macrophages derived Tgf-β1 gene improved glucose metabolism and insulin sensitivity by enhancing adipogenesis via hyperplasia. The Tgf-β1 gene, specifically from CD206+ M2-like macrophages, deletion stimulated APs' proliferation and differentiation, leading to the generation of smaller mature adipocytes, therefore enhancing insulin sensitivity and improving glucose metabolism under normal chow conditions. Our study brings a new perspective that Tgf-β1 gene deletion specific from CD206+ M2-like macrophage promotes adipocyte hyperplasia, improving glucose homeostasis and insulin sensitivity in the lean state.

Olivetol's Effects on Metabolic State and Gut Microbiota Functionality in Mouse Models of Alimentary Obesity, Diabetes Mellitus Type 1 and 2, and Hypercholesterolemia

BACKGROUND

Disorders of glucose and lipid metabolism, such as obesity, diabetes mellitus, or hypercholesterolemia, can cause serious complications, reduce quality of life, and lead to increased premature mortality. Olivetol, a natural compound, could be proposed as a promising therapeutic agent for preventing, treating, or alleviating metabolic complications of such pathological conditions.

METHODS

In this study, the researchers conducted a broad parallel investigation of olivetol's effects on metabolic state and gut microbiota functionality in mouse models of alimentary obesity, diabetes mellitus type 1 and 2, and hypercholesterolemia.

RESULTS

According to the results of the study, olivetol caused a lowering of body weight in C57Bl6 mice fed a high-fat diet and in ldlr(-/-) mice, decreased serum glucose levels in db/db mice, improved lipid metabolism in ldlr(-/-) mice, and prevented inflammatory infiltration of the pancreas and loss of insulin secretion in NOD mice. In addition, olivetol affected the composition and functional activity of gut microbiota communities, inducing an expansion of probiotic species such as Akkermansia muciniphila and Bacteroides acidifaciens and depleting the representation of pathobionts such as Prevotella, although olivetol supplementation did not influence the diversity or richness of the communities.

CONCLUSIONS

These results suggest that olivetol is a promising therapeutic agent for preventing, treating, or alleviating the metabolic complications of obesity, diabetes mellitus type 1 and 2, and hypercholesterolemia; however, more investigations are required in order to attain a full understanding of its physiological effects.

Effects of duration of high-fat diet on adipocyte hyperplasia in rat epididymis

BACKGROUND

High-fat diet (HFD) contributes to obesity and enhances the expression of mature adipocyte markers. However, the effect of HFD on adipocyte hyperplasia remains controversial. This may be due to variations in the duration of HFD. This study aimed to investigate the effects of different durations of HFD on adipocyte hyperplasia and the expression of mature adipocyte-related markers in obese rats.

METHODS

We divided 32 Sprague-Dawley rats into four groups: B (standard diet control), H1 (HFD for four weeks), H2 (HFD for eight weeks), and H3 (HFD for 12 weeks). We evaluated the morphological changes in epididymal fat cells, measured serum inflammatory markers using enzyme-linked immunosorbent assay (ELISA) kits, and quantified adipocyte hyperplasia and maturation markers using western blotting.

RESULTS

We observed progressive increases in body weight, epididymal fat weight, serum leptin, TNF-α, IL-6, irisin, PPARγ, adiponectin, and FNDC5 protein expression over 8 weeks of HFD. 12 weeks of HFD intervention resulted in significant decreases in irisin, PPARγ, adiponectin, and FNDC5. Concurrently, the expression of perilipin A and ATGL declined with prolonged HFD.

CONCLUSIONS

Our results suggest that the duration of HFD significantly affects adipocyte ability to undergo hyperplasia in the epididymis of obese rats. Specifically, 4 weeks of HFD did not change the capacity for adipocyte hyperplasia, while 8 weeks of the diet enhanced this capacity. Interestingly, a longer diet duration (12 weeks) led to a decrease in adipocyte hyperplasia.

Adipose stem cells are sexually dimorphic cells with dual roles as preadipocytes and resident fibroblasts

Cell identities are defined by intrinsic transcriptional networks and spatio-temporal environmental factors. Here, we explored multiple factors that contribute to the identity of adipose stem cells, including anatomic location, microvascular neighborhood, and sex. Our data suggest that adipose stem cells serve a dual role as adipocyte precursors and fibroblast-like cells that shape the adipose tissue's extracellular matrix in an organotypic manner. We further find that adipose stem cells display sexual dimorphism regarding genes involved in estrogen signaling, homeobox transcription factor expression and the renin-angiotensin-aldosterone system. These differences could be attributed to sex hormone effects, developmental origin, or both. Finally, our data demonstrate that adipose stem cells are distinct from mural cells, and that the state of commitment to adipogenic differentiation is linked to their anatomic position in the microvascular niche. Our work supports the importance of sex and microvascular function in adipose tissue physiology.

MicroRNA Profile of Mouse Adipocyte-Derived Extracellular Vesicles

The post-transcriptional control of gene expression is a complex and evolving field in adipocyte biology, with the premise that the delivery of microRNA (miRNA) species to the obese adipose tissue may facilitate weight loss. Cells shed extracellular vesicles (EVs) that may deliver miRNAs as intercellular messengers. However, we know little about the miRNA profile of EVs secreted by adipocytes during postnatal development. Here, we defined the miRNA cargo of EVs secreted by mouse adipocytes in two distinct phases of development: on postnatal day 6, when adipocytes are lipolytic and thermogenic, and on postnatal day 56, when adipocytes have active lipogenesis. EVs were collected from cell culture supernatants, and their miRNA profile was defined by small RNA sequencing. The most abundant miRNA of mouse adipocyte-derived EVs was mmu-miR-148a-3p. Adipocyte EVs on postnatal day 6 were hallmarked with mmu-miR-98-5p, and some miRNAs were specific to this developmental stage, such as mmu-miR-466i-5p and 12 novel miRNAs. Adipocytes on postnatal day 56 secreted mmu-miR-365-3p, and 16 miRNAs were specific to this developmental stage. The miRNA cargo of adipocyte EVs targeted gene networks of cell proliferation, insulin signaling, interferon response, thermogenesis, and lipogenesis. We provided here a database of miRNAs secreted by developing mouse adipocytes, which may be a tool for further studies on the regulation of gene networks that control mouse adipocyte development.

Morin Prevents Non-Alcoholic Hepatic Steatosis in Obese Rats by Targeting the Peroxisome Proliferator-Activated Receptor Alpha (PPARα)

BACKGROUND

Obesity has become a widespread issue globally. Morin, a flavonoid with traditional use in managing hyperglycemia and hyperlipidemia, has demonstrated antioxidant and anti-inflammatory properties in experimental studies. This research aims to explore the anti-obesity potential of morin in rats subjected to a high-fat diet (HFD) and investigate whether its effects are mediated through PPARα regulation.

METHODS

Young adult male Wistar albino rats were divided into four groups (n = 8/group): normal, morin (50 mg/kg/BWT, oral), HFD, and HFD + morin (50 mg/kg/BWT, oral). Treatments were administered daily for 17 consecutive weeks.

RESULTS

Morin mitigated the elevation in glucose levels and decreased fasting glucose and insulin levels, along with the HOMA-IR index, in HFD-fed rats. Furthermore, morin reduced calorie intake, final body weights, and the masses of subcutaneous, epididymal, peritoneal, and mesenteric fat in these rats. It also attenuated the rise in systolic blood pressure in HFD-fed rats and decreased serum levels of triglycerides, cholesterol, free fatty acids, LDL-c, and leptin, while increasing levels of HDL-c and adiponectin in both normal and HFD-fed rats. Moreover, morin restored normal liver structure and reduced fat vacuole accumulation in HFD-fed rats. Notably, it upregulated mRNA levels of PPARα in the livers and white adipose tissue of both normal and HFD-fed rats.

CONCLUSIONS

These findings suggest the potential use of morin to enhance fatty acid oxidation in white adipose tissue and mitigate obesity, warranting further clinical investigation into its therapeutic applications.

Mechanisms and metabolic consequences of adipocyte progenitor replicative senescence

In recent decades, obesity has become a worldwide epidemic. As a result, the importance of adipose tissue (AT) as a metabolically active storage depot for lipids and a key mediator of body-wide metabolism and energy balance has been increasingly recognized. Emerging from the studies of AT in metabolic disease is a recognition of the importance of the adipocyte progenitor cell (APC) population of AT being the gatekeeper of adipocyte function. APCs have the capability to self-renew and undergo adipogenesis to propagate new adipocytes capable of lipid storage, which is important for maintaining a healthy fat pad, devoid of dysfunctional lipid droplet hypertrophy, inflammation, and fibrosis, which is linked to metabolic diseases, including type 2 diabetes. Like other dividing cells, APCs are at risk for undergoing cell senescence, a state of irreversible cell proliferation arrest that occurs under a variety of stress conditions, including DNA damage and telomere attrition. APC proliferation is controlled by a variety of factors, including paracrine and endocrine factors, quality and timing of energy intake, and the circadian clock system. Therefore, alteration in any of the underlying signaling pathways resulting in excessive proliferation of APCs can lead to premature APC senescence. Better understanding of APCs senescence mechanisms will lead to new interventions extending metabolic health.

The hedonic overdrive model best explains high-fat diet-induced obesity in C57BL/6 mice

OBJECTIVE

High-fat diets cause obesity in male mice; however, the underlying mechanisms remain controversial. Here, three contrasting ideas were assessed: hedonic overdrive, reverse causality, and passive overconsumption models.

METHODS

A total of 12 groups of 20 individually housed 12-week-old C57BL/6 male mice were exposed to 12 high-fat diets with varying fat content from 40% to 80% (by calories), protein content from 5% to 30%, and carbohydrate content from 8.4% to 40%. Body weight and food intake were monitored for 30 days after 7 days at baseline on a standard low-fat diet.

RESULTS

After exposure to the diets, energy intake increased first, and body weight followed later. Intake then declined. The peak energy intake was dependent on both dietary protein and carbohydrate, but not the dietary fat and energy density, whereas the rate of decrease in intake was only related to dietary protein. On high-fat diets, the weight of food intake declined, but despite this average reduction of 14.4 g in food intake, they consumed, on average, 357 kJ more energy than at baseline.

CONCLUSIONS

The hedonic overdrive model fit the data best. The other two models were not supported.

TET3 plays a critical role in white adipose development and diet-induced remodeling

Maintaining healthy adipose tissue is crucial for metabolic health, requiring a deeper understanding of adipocyte development and response to high-calorie diets. This study highlights the importance of TET3 during white adipose tissue (WAT) development and expansion. Selective depletion of Tet3 in adipose precursor cells (APCs) reduces adipogenesis, protects against diet-induced adipose expansion, and enhances whole-body metabolism. Transcriptomic analysis of wild-type and Tet3 knockout (KO) APCs unveiled TET3 target genes, including Pparg and several genes linked to the extracellular matrix, pivotal for adipogenesis and remodeling. DNA methylation profiling and functional studies underscore the importance of DNA demethylation in gene regulation. Remarkably, targeted DNA demethylation at the Pparg promoter restored its transcription. In conclusion, TET3 significantly governs adipogenesis and diet-induced adipose expansion by regulating key target genes in APCs.

Kuanoniamine C Suppresses Adipogenesis and White Adipose Tissue Expansion by Modulating Mitochondrial Function

Obesity is characterized by the excessive accumulation of fat to adipose tissue, which is related to abnormal increasing white adipose tissue (WAT) in the body, and it upregulates the risk of multiple diseases. Here, kuanoniamine C, which is a pyridoacridine alkaloid, suppressed the differentiation of pre-adipose cells into white adipocytes via the modulation of mitochondrial function, and inhibited WAT expansion in the early phase of high-fat-diet-induced obesity model. Pharmacological analysis revealed that inhibition of mitochondrial respiratory complex II, which new target of kuanoniamine C, activated reactive oxygen species (ROS)-extracellular signal-regulated kinase (ERK)-β-catenin signaling, and this signaling was antagonized by insulin-, IBMX-, and dexamethasone-induced adipogenesis. Therefore, the kuanoniamine C might prevent abnormal WAT expansion even when eating a diet that is not calorie restricted.

Sirtuins: Key players in obesity-associated adipose tissue remodeling

Obesity, a complex disease involving an excessive amount of body fat and a major threat to public health all over the world, is the determining factor of the onset and development of metabolic disorders, including type 2 diabetes, cardiovascular diseases, and non-alcoholic fatty liver disease. Long-term overnutrition results in excessive expansion and dysfunction of adipose tissue, inflammatory responses and over-accumulation of extracellular matrix in adipose tissue, and ectopic lipid deposit in other organs, termed adipose tissue remodeling. The mammalian Sirtuins (SIRT1-7) are a family of conserved NAD⁺-dependent protein deacetylases. Mounting evidence has disclosed that Sirtuins and their prominent substrates participate in a variety of physiological and pathological processes, including cell cycle regulation, mitochondrial biogenesis and function, glucose and lipid metabolism, insulin action, inflammatory responses, and energy homeostasis. In this review, we provided up-to-date and comprehensive knowledge about the roles of Sirtuins in adipose tissue remodeling, focusing on the fate of adipocytes, lipid mobilization, adipose tissue inflammation and fibrosis, and browning of adipose tissue, and we summarized the clinical trials of Sirtuin activators and inhibitors in treating metabolic diseases, which might shed light on new therapeutic strategies for obesity and its associated metabolic diseases.

Bifidobacterium animalis subsp. lactis MN-Gup protects mice against gut microbiota-related obesity and endotoxemia induced by a high fat diet

Obesity has become a public health concern due to its global prevalence and high risk of complications such as endotoxemia. Given the important role of gut microbiota in obesity, probiotics targeting gut microbiota have been developed and applied to alleviate obesity. However, most studies focused on the effects of probiotics on pre-existing obesity, and the preventive effects of probiotics against obesity were rarely studied. This study aimed to investigate the preventive effects of Bifidobacterium animalis subsp. lactis MN-Gup (MN-Gup) and fermented milk containing MN-Gup against high fat diet (HFD)-induced obesity and endotoxemia in C57BL/6J mice. The results showed that MN-Gup, especially the high dose of MN-Gup (1 × 1010CFU/kg b.w.), could significantly protect mice against HFD-induced body weight gain, increased fat percentage, dyslipidemia, and increased lipopolysaccharides (LPS). Fermented milk containing MN-Gup had better preventive effects on fat percentage and dyslipidemia than fermented milk without MN-Gup, but its overall performance was less effective than MN-Gup. Furthermore, MN-Gup and fermented milk containing MN-Gup could alter HFD-affected gut microbiota and regulate obesity- or endotoxemia-correlated bacteria, which may contribute to the prevention of obesity and endotoxemia. This study revealed that MN-Gup could reduce obesity and endotoxemia under HFD, thereby providing a potential application of MN-Gup in preventing obesity.

Serum and Adipose Dipeptidyl Peptidase 4 in Cardiovascular Surgery Patients: Influence of Dipeptidyl Peptidase 4 Inhibitors

Dipeptidyl peptidase 4 (DPP-4) is a novel adipokine and may be involved in the association between adipose tissue and metabolic syndrome. We investigated DPP-4 and adiponectin levels in the serum, subcutaneous adipose tissue (SAT), and epicardial adipose tissue (EAT), and their relationship with preoperative factors, as well as comparing the DPP-4 levels in SAT and EAT with and without DPP-4 inhibitors. This study included 40 patients (25 men, age 67.5 ± 13.8 years). The serum adipokine, DPP-4, and adiponectin levels in SAT and EAT were measured using ELISA and Western blotting. The DPP-4 and adiponectin levels were significantly higher in the SAT than in the EAT. The serum DPP-4 and DPP-4 activity levels had no correlation with the DPP-4 levels in the SAT and EAT, but the DPP-4 levels in the SAT and EAT had a positive correlation. The DPP-4 levels in the SAT were positively correlated with atherosclerosis, diabetes mellitus, DPP-4-inhibitor use, and fasting blood glucose. The DPP-4 levels in the EAT showed a negative correlation with eGFR and a positive correlation with atrial fibrillation. The DPP-4 activity in the serum had a lower tendency in the group taking DPP-4 inhibitors than in the group not taking them. DPP-4 inhibitors may suppress angiogenesis and adipose-tissue hypertrophy.

A polysaccharide from Inonotus obliquus ameliorates intestinal barrier dysfunction in mice with type 2 diabetes mellitus

Type 2 diabetes mellitus is a global disease that endangers human health, and the need for the development of nontoxic treatment candidates is urgent. In the present work, one homogeneous polysaccharide from Inonotus obliquus (IN) was isolated, and the protective effect and mechanism of IN on type 2 diabetes mellitus were investigated from the aspects of the intestinal barrier. IN mainly consisted of 9 monosaccharides with a Mw of 373 kDa. IN attenuated body weight loss, alleviated pathological damage, and suppressed the production of proinflammatory cytokines. Additionally, IN repaired the intestinal barrier by upregulating the expression of Ki-67, ZO-1 and MUC2. Furthermore, the abundance of Firmicutes was significantly increased with IN treatment, while the levels of Bacteroidetes were significantly inhibited. In conclusion, IN protected against type 2 diabetes mellitus by ameliorating intestinal barrier dysfunction and might serve as a novel drug candidate for type 2 diabetes mellitus.

Astaxanthin, a Marine Carotenoid, Maintains the Tolerance and Integrity of Adipose Tissue and Contributes to Its Healthy Functions

Recently, obesity-induced insulin resistance, type 2 diabetes, and cardiovascular disease have become major social problems. We have previously shown that Astaxanthin (AX), which is a natural antioxidant, significantly ameliorates obesity-induced glucose intolerance and insulin resistance. It is well known that AX is a strong lipophilic antioxidant and has been shown to be beneficial for acute inflammation. However, the actual effects of AX on chronic inflammation in adipose tissue (AT) remain unclear. To observe the effects of AX on AT functions in obese mice, we fed six-week-old male C57BL/6J on high-fat-diet (HFD) supplemented with or without 0.02% of AX for 24 weeks. We determined the effect of AX at 10 and 24 weeks of HFD with or without AX on various parameters including insulin sensitivity, glucose tolerance, inflammation, and mitochondrial function in AT. We found that AX significantly reduced oxidative stress and macrophage infiltration into AT, as well as maintaining healthy AT function. Furthermore, AX prevented pathological AT remodeling probably caused by hypoxia in AT. Collectively, AX treatment exerted anti-inflammatory effects via its antioxidant activity in AT, maintained the vascular structure of AT and preserved the stem cells and progenitor's niche, and enhanced anti-inflammatory hypoxia induction factor-2α-dominant hypoxic response. Through these mechanisms of action, it prevented the pathological remodeling of AT and maintained its integrity.