Esculin ameliorates obesity-induced insulin resistance by improving adipose tissue remodeling and activating the IRS1/PI3K/AKT/GLUT4 pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Cortex fraxini (also known as qinpi)-the bark of Fraxinus rhynchophylla Hance (Oleaceae)-is widely used as a Chinese traditional medicinal for its anti-inflammatory and anti-hyperuricemic activities.

AIM OF THE STUDY

Obesity-induced insulin resistance (IR) is driving the rising incidence of type 2 diabetes mellitus and is related to pathological adipose tissue remodeling. Esculin, a major active component of Cortex fraxini, has anti-diabetic effects. However, whether esculin improves obesity-induced IR by regulating adipose tissue remodeling is unclear. The aims of the present study were to assess the effects of esculin on obesity-induced IR and to explore the underlying mechanisms.

MATERIALS AND METHODS

Obese IR C57BL/6J mice were treated with esculin (40 or 80 mg/kg/day) for 4 weeks. Oral glucose tolerance tests were used to assess insulin sensitivity. Histological analyses were performed to analyze the number and size distribution of adipocytes. Glucose uptake was assessed using 2-NBDG.

RESULTS

Esculin had no effect on body weight gain but reduced fasting blood glucose, improved oral glucose tolerance, and increased insulin sensitivity. Esculin reduced adipocyte size and the expression levels of collagen 4A1 and tumor necrosis factor α and increased the number of adipocytes and the expression of vascular endothelial growth factor A. Esculin promoted the differentiation of 3T3-L1 cells and upregulated the mRNA expression of CCAAT/enhancer-binding protein α and peroxisome proliferator-activated receptor-γ, activated the insulin receptor substrate 1 (IRS1)/phosphatidylinositol 3-kinase (PI3K)/protein kinase B (AKT) signaling pathway, and enhanced the translocation of glucose transporter type 4 (GLUT4) and glucose uptake in adipocytes treated with palmitic acid.

CONCLUSIONS

These data suggest that esculin increases insulin sensitivity by improving adipose tissue remodeling and activating the IRS1/PI3K/AKT/GLUT4 pathway.

The Emerging Importance of Mitochondria in White Adipocytes: Neither Last nor Least

The growing recognition of mitochondria's crucial role in the regulation of white adipose tissue remodeling and energy balance underscores its significance. The marked metabolic diversity of mitochondria provides the molecular and cellular foundation for enabling adipose tissue plasticity in response to various metabolic cues. Effective control of mitochondrial function at the cellular level, not only in thermogenic brown and beige adipocytes but also in energy-storing white adipocytes, exerts a profound influence on adipose homeostasis. Furthermore, mitochondria play a pivotal role in intercellular communication within adipose tissue via production of metabolites with signaling properties. A more comprehensive understanding of mitochondrial regulation within white adipocytes will empower the development of targeted and efficacious strategies to enhance adipose function, leading to advancements in overall metabolic health.

Characteristic and fate determination of adipose precursors during adipose tissue remodeling

Adipose tissues are essential for actively regulating systemic energy balance, glucose homeostasis, immune responses, reproduction, and longevity. Adipocytes maintain dynamic metabolic needs and possess heterogeneity in energy storage and supply. Overexpansion of adipose tissue, especially the visceral type, is a high risk for diabetes and other metabolic diseases. Changes in adipocytes, hypertrophy or hyperplasia, contribute to the remodeling of obese adipose tissues, accompanied by abundant immune cell accumulation, decreased angiogenesis, and aberrant extracellular matrix deposition. The process and mechanism of adipogenesis are well known, however, adipose precursors and their fate decision are only being defined with recent information available to decipher how adipose tissues generate, maintain, and remodel. Here, we discuss the key findings that identify adipose precursors phenotypically, with special emphasis on the intrinsic and extrinsic signals in instructing and regulating the fate of adipose precursors under pathophysiological conditions. We hope that the information in this review lead to novel therapeutic strategies to combat obesity and related metabolic diseases.

α-Linolenic acid rich-chia seed modulates visceral adipose tissue collagen deposition, lipolytic enzymes expression, insulin signaling and GLUT-4 levels in a diet-induced adiposity rodent model

Given obesity and its associated metabolic disorders have reached epidemic proportions, the study of therapeutic strategies targeting white adipose tissue (WAT) are of main research interest. We previously shown that α-linolenic acid-rich chia seed was able to ameliorate a wide range of metabolic disorders including body fat accretion in sucrose-rich diet (SRD)-fed rats, an experimental model of visceral adiposity and insulin resistance. However, the mechanisms involved are not fully clarified. The aim of this study was to evaluate the effect of chia seed administration upon WAT remodeling and key enzymes that controls lipolysis, insulin signaling (tAKT, pAKT), and GLUT-4 levels in different visceral fat pad depots (epididymal -eWAT- and retroperitoneal -rWAT- adipose tissues) of SRD-fed rats. Results showed that chia seed reduces adipocytes hypertrophy, the increased lipid content and collagen deposition in both WAT. These changes were accompanied by a significant reduction of HSL and ATGL protein levels in eWAT and HSL protein levels in rWAT. Moreover, chia seed restored the altered expression pattern of the pAKT observed in SRD-fed rats, and modulated GLUT-4 levels. Chia seed could be a dietary intervention of great relevance with potential beneficial effects in the management of body fat excess and WAT function.

TREM2 regulates obesity-induced insulin resistance via adipose tissue remodeling in mice of high-fat feeding

Background

Adipose tissue remodeling plays a significant role in obesity-induced insulin resistance. Published studies reported that level of trigger receptor expressed on myeloid cells 2 (TREM2) in adipose tissue is up-regulated in animal models of obesity. This study aims to investigate whether TREM2 regulates obesity-induced insulin resistance via modulating adipose tissue remodeling in mice of high-fat diet (HFD).

Methods

Wild-type (WT) and TREM2^−/− mice were both fed with a controlled-fat diet (CFD) or HFD for 12 weeks and studied for obesity and insulin resistance. Meanwhile, epididymal adipose tissue (EAT) was examined for morphological and pathological changes to determine adipose tissue remodeling. After that, adipocyte-derived MCP-1 was measured in adipocytes, adipose tissue and circulation. Next, inflammatory cytokines were determined in adipose tissue macrophages (ATM). At last, livers were analyzed for hepatic steatosis.

Results

TREM2^−/− mice on HFD had increased obesity and insulin resistance compared with WT counterparts. Adipose tissue from TREM2^−/− mice exhibited reduced mass but greater adipocyte hypertrophy and increased adipocyte death. Besides, adipocyte-derived MCP-1 was down-regulated in TREM2^−/− mice, and circulating MCP-1 level was lower than that of WT mice. Furthermore, TREM2^−/− mice displayed reduced infiltration of F4/80⁺CD11c⁺ macrophages into adipose tissue, which was unable to form crown-like structures (CLS) to clean dead adipocytes and cellular contents. Also, TREM2 deficiency augmented inflammatory response of adipose tissue macrophages in HFD mice. In addition, TREM2^−/− mice demonstrated more severe hepatic steatosis than WT counterparts under HFD feeding.

Conclusions

Trigger receptor expressed on myeloid cells 2 may function as a feedback mechanism to curb obesity-induced insulin resistance via regulating adipose tissue remodeling.

The long noncoding RNA Blnc1 orchestrates homeostatic adipose tissue remodeling to preserve metabolic health

Objective

Long noncoding RNAs (lncRNAs) are emerging as powerful regulators of adipocyte differentiation and gene expression. However, their significance in adipose tissue metabolism and physiology has not been demonstrated in vivo. We previously identified Blnc1 as a conserved lncRNA regulator of brown and beige adipocyte differentiation. In this study, we investigated the physiological role of Blnc1 in thermogenesis, adipose remodeling and systemic metabolism.

Methods

We generated fat-specific Blnc1 transgenic and conditional knockout mouse strains and investigated how adipocyte Blnc1 levels are causally linked to key aspects of metabolic health following diet-induced obesity. We performed studies using cultured adipocytes to establish cell-autonomous role of Blnc1 in regulating adipocyte gene programs.

Results

Blnc1 is highly induced in both brown and white fats from obese mice. Fat-specific inactivation of Blnc1 impairs cold-induced thermogenesis and browning and exacerbates obesity-associated brown fat whitening, adipose tissue inflammation and fibrosis, leading to more severe insulin resistance and hepatic steatosis. On the contrary, transgenic expression of Blnc1 in adipose tissue elicits the opposite and beneficial metabolic effects, supporting a critical role of Blnc1 in driving adipose adaptation and homeostatic remodeling during obesity. Mechanistically, Blnc1 cell-autonomously attenuates proinflammatory cytokine signaling and promotes fuel storage in adipocytes through its protein partner Zbtb7b.

Conclusions

This study illustrates a surprisingly pleiotropic and dominant role of lncRNA in driving adaptive adipose tissue remodeling and preserving metabolic health.

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Adipocyte-specific Blnc1 inactivation accelerates BAT whitening and impairs healthy WAT expansion.

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Blnc1 transgenic mice are protected from diet-induced metabolic disorders.

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Blnc1 attenuates adipose tissue inflammation and preserves metabolic health in obesity.

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Blnc1 suppresses NF-kB signaling and TNFα-induced cytokine/chemokine release by adipocytes.

Physical training improves thermogenesis and insulin pathway, and induces remodeling in white and brown adipose tissues

Physical training (PT) has been considered as a treatment in metabolic syndrome (MS), since it induces thermogenic activity in brown (BAT) and white (WAT) adipose tissues. We evaluated the therapeutic effect of PT on activity of WAT and BAT in rats with MS induced by high-fat diet (30% lard) for 13 weeks and submitted, for the last 6 weeks, to swimming or kept sedentary (SED) rats. MS-SED rats compared to control diet (CT-SED) rats showed low physical fitness and high levels of glucose, insulin, homeostasis evaluation of insulin resistance (HOMA-IR), homeostasis evaluation of the functional capacity of β-cells (HOMA-β), and blood pressure. The gastrocnemius muscle decreased in peroxisome proliferator-activated receptor gamma coactivator 1-alpha and beta (PGC-1α, PGC-1β), and uncoupled protein 2 and 3 (UCP2 and UCP3) expressions. Both WAT and BAT increased in the adipocyte area and decreased in blood vessels and fibroblast numbers. WAT increased in expression of pro-inflammatory adipokines and decreased in anti-inflammatory adipokine and adiponectin. WAT and gastrocnemius showed impairment in the insulin signaling pathway. In response to PT, MS rats showed increased physical fitness and restoration of certain biometric and biochemical parameters and blood pressure. PT also induced thermogenic modulations in skeletal muscle, WAT and BAT, and also improved the insulin signaling pathway. Collectively, PT was effective in treating MS by inducing improvement in physical fitness and interchangeable effects between skeletal muscle, WAT and BAT, suggesting a development of brown-like adipocyte cells.

Adipose tissue lipolysis and remodeling during the transition period of dairy cows

Elevated concentrations of plasma fatty acids in transition dairy cows are significantly associated with increased disease susceptibility and poor lactation performance. The main source of plasma fatty acids throughout the transition period is lipolysis from adipose tissue depots. During this time, plasma fatty acids serve as a source of calories mitigating the negative energy balance prompted by copious milk synthesis and limited dry matter intake. Past research has demonstrated that lipolysis in the adipose organ is a complex process that includes not only the activation of lipolytic pathways in response to neural, hormonal, or paracrine stimuli, but also important changes in the structure and cellular distribution of the tissue in a process known as adipose tissue remodeling. This process involves an inflammatory response with immune cell migration, proliferation of the cellular components of the stromal vascular fraction, and changes in the extracellular matrix. This review summarizes current knowledge on lipolysis in dairy cattle, expands on the new field of adipose tissue remodeling, and discusses how these biological processes affect transition cow health and productivity.

Effects of sleeve gastrectomy and rs9930506 FTO variants on angiopoietin/Tie-2 system in fat expansion and M1 macrophages recruitment in morbidly obese subjects

Angiogenesis in inflammation are hallmarks for adipose tissue expansion in obesity. The role of angiopoietin/Tie-2 system in adipose tissue expansion and immune cell recruitment is unclear. We studied the effect of sleeve gastrectomy and the influence of FTO rs9930506 polymorphism on Tie-2, angiopoietin-1 and angiopoietin-2 expression in morbid obesity. Fifteen morbidly obese subjects (4 men and 11 women) aged 24-55 years were followed-up 3 and 6 months after sleeve gastrectomy. Serum sTie-2, angiopoietin-1, angiopoietin-2, and hypoxia-inducible factor-1α concentrations were determined by ELISA. Tie-2 and its ligands in visceral and subcutaneous adipose tissue were localized by immunohistochemistry. Tie-2 expression was measured by flow cytometry in circulating monocytes and infiltrated macrophages. Comparisons before and after sleeve gastrectomy were carried out using ANOVA for repeated measures. rs9930506FTO genotyping was performed by PCR-RFLP. Circulating sTie-2 and angiopoietin-2 were higher before sleeve gastrectomy. Tie-2 and angiopoietin-2 mRNA levels were higher in subcutaneous adipose tissue than visceral and both decreased after surgery. Monocytes and infiltrated macrophages showed a pro-inflammatory phenotype, with increased Tie-2 expression that decreased 3 and 6 months after sleeve gastrectomy. Baseline sTie-2 correlated inversely with adiponectin levels. At baseline the rs9930506FTO AG ó GG genotypes carriers had more 34 kg than genotype carriers of rs9930506 AA. Weight and body mass index decreased at 6 months. We found that angiopoietin/Tie-2 system is mainly expressed in subcutaneous adipose tissue, contributing to expandability, fat accumulation, and monocytes attachment in obesity. Bariatric surgery favorably modifies the pro-angiogenic profile, allowed a reduced angiogenic expression in the circulation and adipose tissue.

Obesity-associated mechanisms of hepatocarcinogenesis

Obesity has been recognized as a key component of the metabolic syndrome, a cluster of risk factors associated with diabetes and cardiovascular morbidity. In addition, obesity has been linked to higher frequency of cancers in a variety of tissues including the liver. Liver cancer most often occurs as hepatocellular carcinoma (HCC) complicating cirrhosis due to chronic viral infection or toxic injury and remains the third leading cause of cancer death in the world. However, HCC is increasingly diagnosed among individuals with obesity and related disorders. As these metabolic conditions have become globally prevalent, they coexist with well-established risk factors of HCC and create a unique challenge for the liver as a chronically diseased organ. Obesity-associated HCC has recently been attributed to molecular mechanisms such as chronic inflammation due to adipose tissue remodeling and pro-inflammatory adipokine secretion, ectopic lipid accumulation and lipotoxicity, altered gut microbiota, and disrupted senescence in stellate cells, as well as insulin resistance leading to increased levels of insulin and insulin-like growth factors. These mechanisms synergize with those occurring in chronic liver disease resulting from other etiologies and accelerate the development of HCC before or after the onset of cirrhosis. Increasingly common interactions between oncogenic pathways linked to obesity and chronic liver disease may explain why HCC is one of the few malignancies with rising incidence in developed countries. Better understanding of this complex process will improve our strategies of cancer prevention, prediction, and surveillance.