Insulin Resistance In Adipocytes Research Articles

Piperine Attenuates Insulin Resistance in Adipocytes by Modulating the Expression of Proinflammatory Signaling Molecules in Experimental Diabetic Wistar Rats

The development of insulin resistance and diabetes in obese people is caused by metabolic inflammation. In adipose tissues in the abdomen, macrophages infiltrate and cause insulin resistance. As a result of the macrophages adopting an M1 polarization, pro-inflammatory cytokines are released. Piperine, known for its potent anti-inflammatory properties, is being studied as a potential treatment for inflammatory diseases. Our findings suggest that piperine, an immunomodulator, can effectively treat obesity-related diabetes.

Transgenic Overexpression of HDAC9 Promotes Adipocyte Hypertrophy, Insulin Resistance and Hepatic Steatosis in Aging Mice.

Histone deacetylase (HDAC) 9 is a negative regulator of adipogenic differentiation, which is required for maintenance of healthy adipose tissues. We reported that HDAC9 expression is upregulated in adipose tissues during obesity, in conjunction with impaired adipogenic differentiation, adipocyte hypertrophy, insulin resistance, and hepatic steatosis, all of which were alleviated by global genetic deletion of Hdac9. Here, we developed a novel transgenic (TG) mouse model to test whether overexpression of Hdac9 is sufficient to induce adipocyte hypertrophy, insulin resistance, and hepatic steatosis in the absence of obesity. HDAC9 TG mice gained less body weight than wild-type (WT) mice when fed a standard laboratory diet for up to 40 weeks, which was attributed to reduced fat mass (primarily inguinal adipose tissue). There was no difference in insulin sensitivity or glucose tolerance in 18-week-old WT and HDAC9 TG mice; however, at 40 weeks of age, HDAC9 TG mice exhibited impaired insulin sensitivity and glucose intolerance. Tissue histology demonstrated adipocyte hypertrophy, along with reduced numbers of mature adipocytes and stromovascular cells, in the HDAC9 TG mouse adipose tissue. Moreover, increased lipids were detected in the livers of aging HDAC9 TG mice, as evaluated by oil red O staining. In conclusion, the experimental aging HDAC9 TG mice developed adipocyte hypertrophy, insulin resistance, and hepatic steatosis, independent of obesity. This novel mouse model may be useful in the investigation of the impact of Hdac9 overexpression associated with metabolic and aging-related diseases.

Study of association of leptin with leukocyte telomere length in a Chinese rural population

BackgroundPrevious studies have demonstrated the relationship between adipocyte factors, insulin resistance, and other indicators with telomere length. However, these studies did not consider the influence of changes in different indicators on telomere length over time. Therefore, the aim of this study is to elucidate the impact of changes in adipocyte factors, HOMA-IR, and other indicators on the dynamic variation of telomere length.MethodsThe data were from a cohort study conducted in Ningxia, China. A total of 1624 subjects were analyzed. Adipokines and relative leukocyte telomere length (RLTL) were measured, and changes in Homeostatic Model Assessment for Insulin Resistance (HOMA-IR), Homeostatic Model Assessment for β-Cell Function (HOMA-β), and Quantitative Insulin Sensitivity Check Index (QUICKI) were calculated. Generalized linear models evaluated associations between changes in adipokines and RLTL changes. Furthermore, univariate analyses examined the effects of changes in adipokines and insulin resistance indicators on ΔRLTL.ResultsThe research findings indicate that females generally have shorter telomeres compared to males. In comparison to the low-level group of Δleptin (LEP), the high-level group of ΔLEP shows a negative correlation with ΔRLTL (B=-1.32, 95% CI (-2.38, -0.27)). Even after multivariable adjustments, this relationship persists (B=-1.31, 95% CI (-2.24, -0.23)). Further analysis reveals that after adjusting for ΔHOMA-IR, ΔHOMA-β, and ΔQUICKI, the high-level group of ΔLEP still exhibits a significant negative correlation with ΔRLTL (B=-1.37, 95% CI (-2.43, -0.31)). However, the interaction effects between ΔHOMA-IR, ΔHOMA-β, ΔQUICKI, and ΔLEP do not affect ΔRLTL.ConclusionsElevated levels of leptin were significantly correlated with shortened telomere length. This suggests that increased leptin levels may impact overall individual health by affecting telomere length, underscoring the importance of measures to reduce leptin levels to mitigate the onset and progression of related diseases.

Fungal Depsidones Stimulate AKT-Dependent Glucose Uptake in 3T3-L1 Adipocytes.

Enhanced glucose uptake in insulin-sensitive tissues is one of the therapeutic strategies to ameliorate hyperglycemia and maintain glucose homeostasis in type 2 diabetes. This study disclosed the role of fungal depsidones in glucose uptake and the underlying mechanism in 3T3-L1 adipocytes. Depsidones, including nidulin, nornidulin, and unguinol, isolated from Aspergillus unguis, stimulate glucose uptake in adipocytes. Compared to the others, nidulin exhibited an upward trend in glucose uptake. The effect of nidulin was found to be dose- and time-dependent. Nidulin also enhanced insulin- and metformin-stimulated glucose uptake. Upregulation of GLUT4 expression and AKT and AMPK phosphorylation were observed with nidulin treatment. Blockage of AKT, but not AMPK, phosphorylation was largely accompanied by diminished glucose uptake. In agreement, nidulin triggered the translocation of GLUT4 to the plasma membrane. Importantly, nidulin elevated glucose uptake associated with increased AKT phosphorylation in insulin-resistant adipocytes. Taken together, nidulin could stimulate glucose uptake mainly through AKT-dependent GLUT4 translocation, serving as a seed compound in drug discovery for type 2 diabetes.

EPA and DHA Differentially Improve Insulin Resistance by Reducing Adipose Tissue Inflammation — Targeting GPR120/PPARγ Pathway

Insulin resistance (IR) is a global health challenge, often initiated by dysfunctional adipose tissue. Eicosapentaenoic acid (EPA) and Docosahexaenoic acid (DHA) may have different effects on IR, but the mechanisms are unknown. This study aims to evaluate the protective effect of EPA and DHA against IR in a high-fat diet (HFD) mice model and investigate whether EPA and DHA alter IR modulate the G-protein-poupled receptor 120/peroxisome proliferator-activated receptor γ (GPR120/PPARγ) pathway in macrophages and adipocytes, which may affect IR in adipocytes. The findings of this study show that 4% DHA had a better effect in improving IR and reducing inflammatory cytokines in adipose tissue of mice. Additionally, in the cell experiment, the use of AH7614 (a GPR120 antagonist) inhibited the glucose consumption increase and the increasable expression of PPARγ and insulin signaling molecules mediated by DHA in adipocytes. Furthermore, GW9662 (a PPARγ antagonist) hindered the upregulation of glucose consumption and insulin signaling molecule expression induced by EPA and DHA in adipocytes. DHA exhibited significant effects in reducing the number of migrated cells and inflammation. The compounds AH7614 and GW9662 hindered the suppressive effects of EPA and DHA on macrophage-induced IR in adipocytes. These findings suggest that DHA has a stronger potential in improving IR in adipocytes through the GPR120/PPARγ pathway in macrophages, when compared to EPA.

Anti-Inflammatory and Anti-Adipocyte Dysfunction Effects of Ficus lindsayana Latex and Root Extracts.

Low-grade chronic inflammation and adipocyte dysfunction are prominent risk factors of insulin resistance and type 2 diabetes mellitus (T2DM) in obesity. Thus, prevention of inflammation and adipocyte dysfunction could be one possible approach to mitigate T2DM development. Several Ficus species have been used in traditional medicine for ameliorating inflammation and T2DM. Our previous studies reported biological effects of Ficus lindsayana including antioxidant, anti-cancer, and anti-α-glucosidase activities. Further, this study therefore investigated whether F. lindsayana latex (FLLE) and root (FLRE) extracts inhibit inflammation-stimulated insulin resistance in adipocytes and inflammation in macrophages. FLLE and FLRE (200 µg/mL) had no significant cytotoxicity for macrophages, adipocytes, and blood cells (PBMCs and RBCs). FLRE had a total flavonoid content about three times higher than FLLE, while both had similar levels of total phenolic content. FLRE showed higher abilities than FLLE in suppressing inflammation in both macrophages and adipocytes and reversing the inflammation-induced insulin resistance in adipocytes. In TNF-α-induced adipocytes, FLRE significantly improved insulin-induced glucose uptake and insulin-suppressed lipolysis, while FLLE only significantly improved glucose uptake. Moreover, FLRE and FLLE remarkably reduced chemoattractant (MCP-1) but improved adipogenic (PPARγ and CEBPα) gene expression, leading to the promotion of adipogenesis and the suppression of insulin resistance. In LPS-induced macrophages, FLRE, but not FLLE, significantly inhibited LPS-induced NO production. Moreover, FLRE significantly reduced LPS-stimulated iNOS, COX-2, IL-1β, IL-6, and TNF-α gene expression. These results may provide the potential data for the development of this plant, especially the root part, as an alternative medicine, functional ingredient, or food supplement for the prevention of inflammation and obesity-associated insulin resistance, as well as T2DM.

Examining the molecular mechanisms of topiramate in alleviating insulin resistance: A study on C2C12 myocytes and 3T3L-1 adipocytes.

Migraine, a severely debilitating condition, may be effectively managed with topiramate, known for its migraine prevention and weight loss properties due to changes in body muscle and fat composition and improved insulin sensitivity. However, the mechanism of topiramate in modulating insulin response in adipocytes and myocytes remains elusive. This study aims to elucidate these molecular mechanisms, offering insights into its role in weight management for migraine sufferers and underpinning its clinical application. Insulin resistance improvements were evaluated through glucose uptake measurements in C2C12 muscle cells and 3T3L-1 adipocytes, with Oil red O staining conducted on adipocytes. RNA-seq transcriptome analysis was used to identify the regulatory target genes of topiramate in these cells. The involvement of key genes and pathways was further validated through western blot analysis. Topiramate effectively reduced insulin resistance in C2C12 and 3T3L-1 cells. In C2C12 cells, it significantly lowered SORBS1 gene and protein levels. In 3T3L-1 cells, topiramate upregulated CTGF and downregulated MAPK8 and KPNA1 genes. Changes were notable in nuclear cytoplasmic transport and circadian signaling pathways. Furthermore, it caused downregulation of MKK7, pJNK1/ JNK1, BMAL1, and CLOCK proteins compared to the insulin-resistant model. This study provides preliminary insights into the mechanisms through which topiramate modulates insulin resistance in C2C12 myocytes and 3T3L-1 adipocytes, enhancing our understanding of its therapeutic potential in managing weight and insulin sensitivity in migraine patients.

Improving the Effect of Ferulic Acid on Inflammation and Insulin Resistance by Regulating the JNK/ERK and NF-κB Pathways in TNF-α-Treated 3T3-L1 Adipocytes.

In this study, ferulic acid was investigated for its potential in suppressing TNF-α-treated inflammation and insulin resistance in adipocytes. Ferulic acid suppressed TNF-α, IL-6, IL-1β, and MCP-1. TNF-α increased p-JNK and ERK1/2, but treatment with ferulic acid (1, 10, and 50 μM) decreased p-JNK and ERK1/2. TNF-α induced the activation of IKK, IκBα, and NF-κB p65 compared to the control, but ferulic acid inhibited the activation of IKK, IκBα, and NF-κB p65. Following treatment with TNF-α, pIRS-1ser307 increased and pIRS-1tyr612 decreased compared to the control. Conversely, as a result of treatment with 1, 10, and 50 μM ferulic acid, pIRS-1ser307 was suppressed, and pIRS-1tyr612 was increased. Therefore, ferulic acid reduced inflammatory cytokine secretion by regulating JNK, ERK, and NF-κB and improved insulin resistance by suppressing pIRS-1ser. These findings indicate that ferulic acid can improve inflammation and insulin resistance in adipocytes.

Novel Therapeutic Agents for Management of Diabetes Mellitus: A Hope for Drug Designing against Diabetes Mellitus.

Diabetes mellitus (DM) is characterized by an absolute decline in insulin secretion and peripheral resistance and is the most prevalent metabolic and endocrine disorder. However, the pathogenesis of DM also includes adipocyte insulin resistance, increased glucagon secretion, increased renal glomerular glucose absorption, and neurotransmitter dysfunction. Although there is a wide spectrum of therapeutics available for glycemic control, owing to the identification of various pathogenic determinants of DM, management of DM remains challenging and complex. Current therapeutic interventions against DM focus mostly on glycemic control without considering the other pathological determinants that eventually lead to treatment failure and the progression of DM. Furthermore, long-term use of these conventionally available anti-diabetic drugs leads to various side effects, henceforth development of novel drugs against DM remains an unending search strategy for researchers. Various studies conducted in various parts of the world have proposed that these novel therapeutic interventions target multiple and alternate pathogenic hotspots involved in DM. The current review article discusses novel therapeutic options that hold particular promise to support their safety and discuss the side effects resulting from their use so that these novel candidate drugs can be effectively fabricated into potential drugs for the treatment of DM.

Mitochondrial electron transport chain, ceramide, and coenzyme Q are linked in a pathway that drives insulin resistance in skeletal muscle.

Insulin resistance (IR) is a complex metabolic disorder that underlies several human diseases, including type 2 diabetes and cardiovascular disease. Despite extensive research, the precise mechanisms underlying IR development remain poorly understood. Previously we showed that deficiency of coenzyme Q (CoQ) is necessary and sufficient for IR in adipocytes and skeletal muscle (Fazakerley et al., 2018). Here, we provide new insights into the mechanistic connections between cellular alterations associated with IR, including increased ceramides, CoQ deficiency, mitochondrial dysfunction, and oxidative stress. We demonstrate that elevated levels of ceramide in the mitochondria of skeletal muscle cells result in CoQ depletion and loss of mitochondrial respiratory chain components, leading to mitochondrial dysfunction and IR. Further, decreasing mitochondrial ceramide levels in vitro and in animal models (mice, C57BL/6J) (under chow and high-fat diet) increased CoQ levels and was protective against IR. CoQ supplementation also rescued ceramide-associated IR. Examination of the mitochondrial proteome from human muscle biopsies revealed a strong correlation between the respirasome system and mitochondrial ceramide as key determinants of insulin sensitivity. Our findings highlight the mitochondrial ceramide-CoQ-respiratory chain nexus as a potential foundation of an IR pathway that may also play a critical role in other conditions associated with ceramide accumulation and mitochondrial dysfunction, such as heart failure, cancer, and aging. These insights may have important clinical implications for the development of novel therapeutic strategies for the treatment of IR and related metabolic disorders.

Mitochondrial electron transport chain, ceramide, and coenzyme Q are linked in a pathway that drives insulin resistance in skeletal muscle

Insulin resistance (IR) is a complex metabolic disorder that underlies several human diseases, including type 2 diabetes and cardiovascular disease. Despite extensive research, the precise mechanisms underlying IR development remain poorly understood. Previously we showed that deficiency of coenzyme Q (CoQ) is necessary and sufficient for IR in adipocytes and skeletal muscle (Fazakerley et al., 2018). Here, we provide new insights into the mechanistic connections between cellular alterations associated with IR, including increased ceramides, CoQ deficiency, mitochondrial dysfunction, and oxidative stress. We demonstrate that elevated levels of ceramide in the mitochondria of skeletal muscle cells result in CoQ depletion and loss of mitochondrial respiratory chain components, leading to mitochondrial dysfunction and IR. Further, decreasing mitochondrial ceramide levels in vitro and in animal models (mice, C57BL/6J) (under chow and high-fat diet) increased CoQ levels and was protective against IR. CoQ supplementation also rescued ceramide-associated IR. Examination of the mitochondrial proteome from human muscle biopsies revealed a strong correlation between the respirasome system and mitochondrial ceramide as key determinants of insulin sensitivity. Our findings highlight the mitochondrial ceramide–CoQ–respiratory chain nexus as a potential foundation of an IR pathway that may also play a critical role in other conditions associated with ceramide accumulation and mitochondrial dysfunction, such as heart failure, cancer, and aging. These insights may have important clinical implications for the development of novel therapeutic strategies for the treatment of IR and related metabolic disorders.

The P2Y2 receptor mediates terminal adipocyte differentiation and insulin resistance: Evidence for a dual G-protein coupling mode

Several P2Y nucleotide receptors have been shown to be involved in the early stage of adipocyte differentiation in vitro and insulin resistance in obese mice; however, the exact receptor subtype(s) and its underlying molecular mechanism in relevant human cells are unclear. Here, using human primary visceral preadipocytes as a model, we found that during preadipocyte-to-mature adipocyte differentiation, the P2Y2 nucleotide receptor (P2Y2R) was the most upregulated subtype among the eight known P2Y receptors and the only one further dramatically upregulated after inflammatory TNFα treatment. Functional studies indicated that the P2Y2R induced intracellular Ca2+, ERK1/2, and JNK signaling but not the p38 pathway. In addition, stimulation of the P2Y2R suppressed basal and insulin-induced phosphorylation of AKT, accompanied by decreased GLUT4 membrane translocation and glucose uptake in mature adipocytes, suggesting a role of P2Y2R in insulin resistance. Mechanistically, we found that activation of P2Y2R did not increase lipolysis but suppressed PIP3 generation. Interestingly, activation of P2Y2R triggered Gi-protein coupling, and pertussis toxin pretreatment largely inhibited P2Y2R-mediated ERK1/2 signaling and cAMP suppression. Further, treatment of the cells with AR-C 118925XX, a selective P2Y2R antagonist, significantly inhibited adipogenesis, and P2Y2R knockout decreased mouse body weight gain with smaller eWAT mass infiltrated with fewer macrophages as compared to wild-type mice in response to a Western diet. Thus, we revealed that terminal adipocyte differentiation and inflammation selectively upregulate P2Y2R expression and that P2Y2R mediates insulin resistance by suppressing the AKT signaling pathway, highlighting P2Y2R as a potential new drug target to combat obesity and type-2 diabetes.

Insulin resistance in adipocytes: Novel insights into the pathophysiology of metabolic syndrome

Insulin resistance in all major target tissues is present in metabolic syndrome (MetS). The resistance in adipocytes is not well described and was presently examined. In this observational study on isolated abdominal white subcutaneous adipocytes from 419 adults, concentration-response effects of insulin on lipolysis inhibition (glycerol release) and lipogenesis stimulation (glucose conversion to total lipids) were determined. Insights into early and late insulin signaling events were obtained through the determination of insulin sensitivity (half maximum effective concentration) and responsiveness (maximum effect), respectively. In a subgroup of 132 subjects, we analyzed the subcutaneous adipose mRNA expression of genes in the canonical insulin signaling pathway using microarray. These results were validated using quantitative real-time polymerase chain reaction in 74 individuals. While the insulin responsiveness was similar in subjects with or without Mets, the sensitivity to insulin-mediated inhibition of lipolysis and stimulation of lipogenesis was ∼tenfold lower in subjects with MetS (p<0.0001). When age, sex, adipocyte volume, body mass index and body shape were considered, only the antilipolytic resistance was independently associated with MetS. The mRNA expression of several genes in the canonical insulin signaling pathway were altered in MetS (p<0.0006 or better) where the mRNA levels of insulin receptor substrate 2 associated with the antilipolytic effect (Rho=0.34; p=0.0016). The sensitivities of the antilipolytic and lipogenic effects of insulin are decreased in the MetS but only antilipolysis remains significant after multiple regression analysis. This resistance is localized at initial and receptor-near events in hormone signaling involving insulin receptor substrate 2.

Lactobacillus amylovorus KU4 induces adipose browning in obese mice by regulating PP4C.

We previously reported that Lactobacillus amylovorus KU4 (LKU4) promotes adipocyte browning in mice fed a high-fat diet (HFD mice) in part by remodeling the PPARγ transcription complex. However, the mechanism through which LKU4 enables PPARγ to drive adipocyte browning remains elusive. Here, we report that LKU4 inhibits the expression of PP4C in inguinal white adipose tissue of HFD mice and in insulin-resistant 3T3-L1 adipocytes, which promotes SIRT1-dependent PPARγ deacetylation by activating AMPK, leading to the browning of adipocytes. Consistently, the silencing of PP4C further enhances this pathway. Furthermore, we observed that lactate, a key LKU4 metabolite, reduces insulin-induced PP4C expression and suppresses PP4C inhibition of PPARγ deacetylation and transcriptional activity via AMPK-SIRT1, thereby facilitating the browning of adipocytes. Together, these data demonstrate that LKU4 promotes the AMPK-SIRT1-PPARγ pathway by inhibiting PP4C, thereby facilitating adipocyte browning in HFD mice.

Environmental chemicals change extracellular lipidome of mature human white adipocytes

Certain environmental chemicals affect the body's energy balance and are known as metabolism disrupting chemicals (MDCs). MDCs have been implicated in the development of metabolic diseases, such as obesity and type 2 diabetes. In contrast to their well-known impact on developing adipocytes, MDC effects leading to altered energy balance and development of insulin resistance in mature white adipocytes, constituents of adult adipose tissue, are largely unclear.Here, we investigated the effects of six well-established environmental MDCs (bisphenol A (BPA), perfluorooctanoic acid (PFOA), triclosan (TCS), p,p-dichlorodiphenyl-dichloroethylene (ppDDE), tributyltin chloride (TBT) and triphenyl phosphate (TPP)) on mature human white adipocytes derived from mesenchymal stem cells in vitro. We aimed to identify biomarkers and sensitive endpoints of their metabolism disrupting effects. While most of the tested exposures had no effect on adipocyte glucose consumption, lipid storage and assessed gene expression endpoints, the highest concentration of triclosan affected the total lipid storage and adipocyte size, as well as glucose consumption and mRNA expression of the glucose transporter GLUT1, leptin and adiponectin. Additionally, an increased expression of adiponectin was observed with TPP and the positive control PPARγ agonist rosiglitazone.In contrast, the lipidomic analysis of the cell culture medium after a 3-day exposure was extremely sensitive and revealed concentration-dependent changes in the extracellular lipidome of adipocytes exposed to nearly all studied chemicals. While some of the extracellular lipidome changes were specific for the MDC used, some effects were found common to several tested chemicals and included increases in lysophosphatidylcholines, glycerophospholipids and ceramides and a decrease in fatty acids, with possible implications in inflammation, lipid and glucose uptake.This study points to early signs of metabolic disruption and likely systemic effects of mature adipocyte exposure to environmental chemicals, as well as to the need to include lipidomic endpoints in the assessment of adverse effects of MDCs.

Cimifugin inhibits adipogenesis and TNF-α-induced insulin resistance in 3T3-L1 cells.

To investigate the effects of cimifugin on adipogenesis and tumor necrosis factor (TNF-α)-induced insulin resistance (IR) and inflammation in 3T3-L1 adipocytes. 3T3-L1 adipocytes were treated with 3-isobutyl-1-methyl-xanthine, dexamethasone, and insulin or cimifugin and then Oil Red O staining and intracellular triglyceride content detection were performed to assess adipogenesis. Subsequently, after cimifugin treatment, TNF-α was used to induce IR and inflammation. The results showed that cimifugin reduced intracellular lipids accumulation of 3T3-L1 adipocytes. Cimifugin improved IR of 3T3-L1 adipocytes induced by TNF-α, as reflected in decreased adiponectin, GLUT-4, and IRS-1 mRNA and protein expression. Moreover, cimifugin reduced TNF-α-induced pro-inflammatory factors production and phospho-P65 expression, and MAPK pathway activation in the 3T3-L1 adipocytes. These findings suggested that cimifugin might be useful for the prevention and therapy of obesity-related IR and inflammation.

FRI027 Regulation Of A Novel Sortilin Splice Variant Expression In Human Diabetic Adipocytes By GLP-1 To Maintain Glucose Homeostasis

Abstract Disclosure: N.A. Patel: None. R.S. Patel: None. A. Liu: None. Type 2 diabetes mellitus (T2DM) is a chronic and progressive metabolic disease with no cure. 37.3 million Americans have T2DM as of 2021 and 96 million (1 in 3) are prediabetic. Globally 462 million people are estimated to be living with T2DM. T2DM is a complex, polygenic metabolic disease characterized by hyperglycemia and insulin resistance. Adipocytes play a crucial role in glucose homeostasis. In response to insulin, translocation of major glucose transporter-4 (Glut4) from cytoplasm to the plasma membrane facilitates uptake of glucose into the adipocytes. Sortilin, an important constituent of Glut4 storage vesicles, binds to Glut4 with its luminal domain while its C-terminal tail guides intracellular trafficking. In insulin resistant adipocytes, glucose uptake is impaired. In this study, we used human adipose stem cells (hASC) from diabetic (DM) and nondiabetic (NDM) donors and differentiated them in vitro to mature adipocytes. We report that in addition to constitutively spliced full-length sortilin (Sort_FL), we identified an alternatively spliced sortilin variant in human adipocytes. Results show that alternative exon inclusion resulted in inclusion of STOP codon which produced a truncated C-terminal (Sort_T) protein whose expression was significantly increased in DM adipocytes. We elucidated the role and function of Sort_T and our results show that hyperglycemic conditions promoted an increase in Sort_T levels in NDM adipocytes. Overexpression of Sort_T in NDM adipocytes resulted in reduced insulin-stimulated Glut4 translocation and decreased glucose uptake. However, overexpression of Sort_FL does not rescue glucose uptake in DM adipocytes. Computational modeling and molecular dynamics results suggested that Glut4 bound tightly to both Sort_T and Sort_FL. This was validated using co-immunoprecipitation assays which demonstrated robust binding of Sort_T to Glut4. Immunocytochemistry was performed to determine localization of sortilin variants in DM and NDM adipocytes. Results demonstrated that Glut4 co-localized with both Sort_T and Sort_FL and Pearson’s coefficient demonstrated increased Sort_T co-localization with Glut4 in DM adipocytes. Incretin hormone glucagon-like peptide-1 (GLP1) and its analog liraglutide is used to manage T2DM. We evaluated the effect of GLP1 and liraglutide treatment in DM adipocytes on sortilin variant expression and our results demonstrate decreased Sort_T levels at physiological doses (8nM). Using a sortilin splicing minigene, our results demonstrate that GLP1 regulates splicing of Sort_T pre-mRNA and splice factor SRSF10 is involved in GLP1-mediated sortilin alternative splicing in adipocytes. Our study concludes that Sort_T expression in diabetic adipocytes hinders glucose metabolism and Sort_T is a target of GLP1 for maintaining glucose homeostasis. Presentation: Friday, June 16, 2023

Astragaloside IV Regulates Insulin Resistance and Inflammatory Response of Adipocytes via Modulating MIR-21/PTEN/PI3K/AKT Signaling.

The progression of Type 2 Diabetes Mellitus (T2DM) can lead to various complications. Compounds derived from natural products have been found to be effective in combatting T2DM. This study aimed to investigate the effects of Astragaloside IV (AS-IV) on insulin resistance and the inflammatory response of adipocytes. The study also aimed to determine the downstream signaling pathways involved. The glucose consumption of adipocytes was assessed using a glucose assay kit. qRT-PCR, Western blot, and ELISA assays were used to measure mRNA and protein levels. The interaction between miR-21 and PTEN was assessed using a Dual-luciferase reporter assay. The results showed that AS-IV increased glucose consumption and the expression of GLUT-4 in adipocytes with insulin resistance in a concentration-dependent manner. However, ASIV decreased the protein levels of TNF-α and IL-6 in these cells. Additionally, AS-IV up-regulated miR-21 expression in adipocytes with insulin resistance in a concentration-dependent manner. Furthermore, miR-21 overexpression increased glucose consumption and GLUT-4 expression but decreased TNF-α and IL-6 protein levels in adipocytes. Conversely, miR-21 inhibition attenuated the AS-IV-induced increase in glucose consumption and GLUT-4 expression and the decrease in TNF- α and IL-6 protein levels in adipocytes. MiR-21 also inversely regulated PTEN in adipocytes, and PTEN overexpression had effects similar to miR-21 inhibition in AS-IV-treated adipocytes. Finally, AS-IV up-regulated p-PI3K and p-AKT protein expression in adipocytes, which was attenuated by miR-21 inhibition. The study concluded that AS-IV attenuated insulin resistance and the inflammatory response in adipocytes. The mechanistic studies indicated that AS-IV modulated the miR- 21/PTEN/PI3K/AKT signaling in adipocytes to exert these effects.

TGS1/PIMT regulates pro-inflammatory macrophage mediated paracrine insulin resistance: Crosstalk between macrophages and skeletal muscle cells

Macrophage-driven chronic low-grade inflammatory response is intimately associated with pathogenesis of insulin resistance and type 2 diabetes (T2D). However, the molecular basis for skewing of pro-inflammatory macrophage is still elusive. Here, we describe the mechanism and significance of TGS1/PIMT (PRIP-Interacting protein with Methyl Transferase domain) in regulating macrophage activation and polarization and its impact on the development of insulin resistance in skeletal muscle cells. We show altered expression of TGS1 in M1 polarized cultured macrophages, bone marrow-derived (BMDM) and adipose tissue macrophages. Moreover, in High Fat Diet (HFD)-fed mice enhanced TGS1 expression is predominantly localized to the nucleus of adipose tissue macrophages suggesting its potential functional role. Gain and loss of TGS1 expression in macrophage further established its role in the secretion of pro-inflammatory mediators. Mechanistically, TGS1 controls the transcription of numerous genes linked to inflammation by forming a complex with Histone Acetyl Transferase (HAT)-containing transcriptional co-activators CBP and p300. Functionally, TGS1 mediated macrophage inflammatory response induces the development of insulin resistance in skeletal muscle cells and adipocytes. Our findings thus demonstrate an unexpected contribution of TGS1 in the regulation of macrophage mediated inflammation and insulin resistance highlighting that TGS1 antagonism could be a promising therapeutic target for the management of inflammation and insulin resistance in T2D.

LncRNA MEG3 aggravates adipocyte inflammation and insulin resistance by targeting IGF2BP2 to activate TLR4/NF-κB signaling pathway.

Recently, emerging evidence has shown that LncRNA MEG3 is involved in adipocyte inflammation and insulin resistance progression, however, the specific mechanism of action remains unclear. In this study, we found that LncRNA MEG3 expression was increased in TNF-α stimulated 3T3-L1 mature adipocytes, and inflammatory factors IL-6 and MCP-1 secretion levels were increased, cell apoptosis and caspase3 activity was enhanced, ROS content was increased, and iNOS protein expression was increased. Moreover, TNF-α treatment attenuated glucose uptake, promoted triglyceride accumulation, inhibited GLUT4 protein expression at the plasma membrane, and reduced the phosphorylation levels of AMPK and ACC in the cells. Interestingly, we found that transfection of si-MEG3 reversed TNF-α caused inflammatory injury and insulin resistance of 3T3-L1 mature adipocytes. Next, we found that IGF2BP2 is an RNA binding protein of LncRNA MGE3 and transfection of si-IGF2BP2 reversed TNF-α caused inflammatory injury and insulin resistance in 3T3-L1 mature adipocytes, the same effects as transfection of si-MEG3. Mechanistically, LncRNA MGE3 was able to aggravate adipocyte inflammatory injury and dysregulation of insulin sensitivity by activating TLR4 pathway through upregulating the protein expression of IGF2BP2. In vivo findings showed that HFD mice with knockdown of MEG3 had reduced body weight, lower glucose concentrations and insulin levels in plasma, decreased inflammatory factors secretion, and reduced MEG3 and IGF2BP2 expression in epididymal adipose tissues and reduced fat accumulation in mice compared with HFD mice. Our results indicate that LncRNA MEG3 can aggravate chronic inflammation and insulin resistance in adipocytes by activating TLR4/NF-κB signaling pathway via targeting IGF2BP2.