During Adipocyte Remodeling, Lipid Droplet Configurations Regulate Insulin Sensitivity through F-Actin and G-Actin Reorganization

The role of adhesion molecules in osteocalcin-induced effects on glucose and lipid metabolism in adipocytes

Recent findings suggest that uncarboxylated osteocalcin (GluOC) promotes glucose and lipid metabolism via its putative receptor GPRC6A; however, its direct effect on adipocytes remains elusive. In this study, we elucidated the effects of GluOC on adipocytes, with an emphasis on the role of cell adhesion molecules. We determined that GluOC promoted the expression of adipocyte adhesion molecule (ACAM) and its transcription factor Krüppel-like factor 4 and enhanced the cortical actin filament assembly, which ameliorated lipid droplet hypertrophy. Additionally, GluOC upregulated the expression of integrin αVβ3 and activation of focal adhesion kinase (FAK) and prevented insulin receptor substrate 1 (IRS1) degradation by inhibiting the ubiquitin-proteasome system via the FAK-PLC-PKC axis, which activated IRS1-Akt-mediated glucose transporter 4 (GLUT4) transport. Furthermore, we showed that GluOC elevated the expression of the insulin-independent glucose transporters GLUT1 and GLUT8, which facilitated insulin stimulation-independent glucose transport. The GluOC-induced activation of integrin αVβ3 signaling promoted microtubule assembly, which improved glucose and lipid metabolism via its involvement in intracellular vesicular transport. GluOC treatment also suppressed collagen type 1 formation, which might prevent adipose tissue fibrosis in obese individuals. Overall, our results imply that GluOC promotes glucose and lipid metabolism via ACAM, integrin αVβ3, and GLUT1 and 8 expression, directly affecting adipocytes.

Designed Ankyrin Repeat Proteins as Actin Labels of Distinct Cytoskeletal Structures in Living Cells

The orchestrated assembly of actin and actin-binding proteins into cytoskeletal structures coordinates cell morphology changes during migration, cytokinesis, and adaptation to external stimuli. The accurate and unbiased visualization of the diverse actin assemblies within cells is an ongoing challenge. We describe here the identification and use of designed ankyrin repeat proteins (DARPins) as synthetic actin binders. Actin-binding DARPins were identified through ribosome display and validated biochemically. When introduced or expressed inside living cells, fluorescently labeled DARPins accumulated at actin filaments, validated through phalloidin colocalization on fixed cells. Nevertheless, different DARPins displayed different actin labeling patterns: some DARPins labeled efficiently dynamic structures, such as filopodia, lamellipodia, and blebs, while others accumulated primarily in stress fibers. This differential intracellular distribution correlated with DARPin-actin binding kinetics, as measured by fluorescence recovery after photobleaching experiments. Moreover, the rapid arrest of actin dynamics induced by pharmacological treatment led to the fast relocalization of DARPins. Our data support the hypothesis that the localization of actin probes depends on the inherent dynamic movement of the actin cytoskeleton. Compared to the widely used LifeAct probe, one DARPin exhibited enhanced signal-to-background ratio while retaining a similar ability to label stress fibers. In summary, we propose DARPins as promising actin-binding proteins for labeling or manipulation in living cells.

Effect of an acute long-duration exercise bout on skeletal muscle lipid droplet morphology, GLUT 4 protein, and perilipin protein expression

PURPOSE

Smaller lipid droplet morphology and GLUT 4 protein expression have been associated with greater muscle oxidative capacity and glucose uptake, respectively. The main purpose of this study was to determine the effect of an acute long-duration exercise bout on skeletal muscle lipid droplet morphology, GLUT4, perilipin 3, and perilipin 5 expressions.

METHODS

Twenty healthy men (age 24.0 ± 1.0 years, BMI 23.6 ± 0.4 kg/m2) were recruited for the study. The participants were subjected to an acute bout of exercise on a cycle ergometer at 50% VO2max until they reached a total energy expenditure of 650 kcal. The study was conducted after an overnight fast. Vastus lateralis muscle biopsies were obtained before and immediately after exercise for immunohistochemical analysis to determine lipid, perilipin 3, perilipin 5, and GLUT4 protein contents while GLUT 4 mRNA was quantified using RT-qPCR.

RESULTS

Lipid droplet size decreased whereas total intramyocellular lipid content tended to reduce (p = 0.07) after an acute bout of endurance exercise. The density of smaller lipid droplets in the peripheral sarcoplasmic region significantly increased (0.584 ± 0.04 to 0.638 ± 0.08 AU; p = 0.01) while larger lipid droplets significantly decreased (p < 0.05). GLUT4 mRNA tended to increase (p = 0.05). There were no significant changes in GLUT 4, perilipin 3, and perilipin 5 protein levels.

CONCLUSION

The study demonstrates that exercise may impact metabolism by enhancing the quantity of smaller lipid droplets over larger lipid droplets.

The Role of Cdc42 in the Insulin and Leptin Pathways Contributing to the Development of Age-Related Obesity

Age-related obesity significantly increases the risk of chronic diseases such as type 2 diabetes, cardiovascular diseases, hypertension, and certain cancers. The insulin-leptin axis is crucial in understanding metabolic disturbances associated with age-related obesity. Rho GTPase Cdc42 is a member of the Rho family of GTPases that participates in many cellular processes including, but not limited to, regulation of actin cytoskeleton, vesicle trafficking, cell polarity, morphology, proliferation, motility, and migration. Cdc42 functions as an integral part of regulating insulin secretion and aging. Some novel roles for Cdc42 have also been recently identified in maintaining glucose metabolism, where Cdc42 is involved in controlling blood glucose levels in metabolically active tissues, including skeletal muscle, adipose tissue, pancreas, etc., which puts this protein in line with other critical regulators of glucose metabolism. Importantly, Cdc42 plays a vital role in cellular processes associated with the insulin and leptin signaling pathways, which are integral elements involved in obesity development if misregulated. Additionally, a change in Cdc42 activity may affect senescence, thus contributing to disorders associated with aging. This review explores the complex relationships among age-associated obesity, the insulin-leptin axis, and the Cdc42 signaling pathway. This article sheds light on the vast molecular web that supports metabolic dysregulation in aging people. In addition, it also discusses the potential therapeutic implications of the Cdc42 pathway to mitigate obesity since some new data suggest that inhibition of Cdc42 using antidiabetic drugs or antioxidants may promote weight loss in overweight or obese patients.

The fat body cortical actin network regulates Drosophila inter-organ nutrient trafficking, signaling, and adipose cell size

Defective nutrient storage and adipocyte enlargement (hypertrophy) are emerging features of metabolic syndrome and type 2 diabetes. Within adipose tissues, how the cytoskeletal network contributes to adipose cell size, nutrient uptake, fat storage, and signaling remain poorly understood. Utilizing the Drosophila larval fat body (FB) as a model adipose tissue, we show that a specific actin isoform-Act5C-forms the cortical actin network necessary to expand adipocyte cell size for biomass storage in development. Additionally, we uncover a non-canonical role for the cortical actin cytoskeleton in inter-organ lipid trafficking. We find Act5C localizes to the FB cell surface and cell-cell boundaries, where it intimately contacts peripheral LDs (pLDs), forming a cortical actin network for cell architectural support. FB-specific loss of Act5C perturbs FB triglyceride (TG) storage and LD morphology, resulting in developmentally delayed larvae that fail to develop into flies. Utilizing temporal RNAi-depletion approaches, we reveal that Act5C is indispensable post-embryogenesis during larval feeding as FB cells expand and store fat. Act5C-deficient FBs fail to grow, leading to lipodystrophic larvae unable to accrue sufficient biomass for complete metamorphosis. In line with this, Act5C-deficient larvae display blunted insulin signaling and reduced feeding. Mechanistically, we also show this diminished signaling correlates with decreased lipophorin (Lpp) lipoprotein-mediated lipid trafficking, and find Act5C is required for Lpp secretion from the FB for lipid transport. Collectively, we propose that the Act5C-dependent cortical actin network of Drosophila adipose tissue is required for adipose tissue size-expansion and organismal energy homeostasis in development, and plays an essential role in inter-organ nutrient transport and signaling.

Physiological and pathological roles of lipogenesis

Lipids are essential metabolites, which function as energy sources, structural components and signalling mediators. Most cells are able to convert carbohydrates into fatty acids, which are often converted into neutral lipids for storage in the form of lipid droplets. Accumulating evidence suggests that lipogenesis plays a crucial role not only in metabolic tissues for systemic energy homoeostasis but also in immune and nervous systems for their proliferation, differentiation and even pathophysiological roles. Thus, excessive or insufficient lipogenesis is closely associated with aberrations in lipid homoeostasis, potentially leading to pathological consequences, such as dyslipidaemia, diabetes, fatty liver, autoimmune diseases, neurodegenerative diseases and cancers. For systemic energy homoeostasis, multiple enzymes involved in lipogenesis are tightly controlled by transcriptional and post-translational modifications. In this Review, we discuss recent findings regarding the regulatory mechanisms, physiological roles and pathological importance of lipogenesis in multiple tissues such as adipose tissue and the liver, as well as the immune and nervous systems. Furthermore, we briefly introduce the therapeutic implications of lipogenesis modulation.

A non-coding variant linked to metabolic obesity with normal weight affects actin remodelling in subcutaneous adipocytes

Recent large-scale genomic association studies found evidence for a genetic link between increased risk of type 2 diabetes and decreased risk for adiposity-related traits, reminiscent of metabolically obese normal weight (MONW) association signatures. However, the target genes and cellular mechanisms driving such MONW associations remain to be identified. Here, we systematically identify the cellular programmes of one of the top-scoring MONW risk loci, the 2q24.3 risk locus, in subcutaneous adipocytes. We identify a causal genetic variant, rs6712203, an intronic single-nucleotide polymorphism in the COBLL1 gene, which changes the conserved transcription factor motif of POU domain, class 2, transcription factor 2, and leads to differential COBLL1 gene expression by altering the enhancer activity at the locus in subcutaneous adipocytes. We then establish the cellular programme under the genetic control of the 2q24.3 MONW risk locus and the effector gene COBLL1, which is characterized by impaired actin cytoskeleton remodelling in differentiating subcutaneous adipocytes and subsequent failure of these cells to accumulate lipids and develop into metabolically active and insulin-sensitive adipocytes. Finally, we show that perturbations of the effector gene Cobll1 in a mouse model result in organismal phenotypes matching the MONW association signature, including decreased subcutaneous body fat mass and body weight along with impaired glucose tolerance. Taken together, our results provide a mechanistic link between the genetic risk for insulin resistance and low adiposity, providing a potential therapeutic hypothesis and a framework for future identification of causal relationships between genome associations and cellular programmes in other disorders.

VLDL-VLDLR axis facilitates brown fat thermogenesis through replenishment of lipid fuels and PPARβ/δ activation

In mammals, brown adipose tissue (BAT) is specialized to conduct non-shivering thermogenesis for survival under cold acclimation. Although emerging evidence suggests that lipid metabolites are essential for heat generation in cold-activated BAT, the underlying mechanisms of lipid uptake in BAT have not been thoroughly understood. Here, we show that very-low-density lipoprotein (VLDL) uptaken by VLDL receptor (VLDLR) plays important roles in thermogenic execution in BAT. Compared with wild-type mice, VLDLR knockout mice exhibit impaired thermogenic features. Mechanistically, VLDLR-mediated VLDL uptake provides energy sources for mitochondrial oxidation via lysosomal processing, subsequently enhancing thermogenic activity in brown adipocytes. Moreover, the VLDL-VLDLR axis potentiates peroxisome proliferator activated receptor (PPAR)β/δ activity with thermogenic gene expression in BAT. Accordingly, VLDL-induced thermogenic capacity is attenuated in brown-adipocyte-specific PPARβ/δ knockout mice. Collectively, these data suggest that the VLDL-VLDLR axis in brown adipocytes is a key factor for thermogenic execution during cold exposure.

The regulation of adipocyte growth in white adipose tissue

Adipocytes can increase in volume up to a thousand-fold, storing excess calories as triacylglycerol in large lipid droplets. The dramatic morphological changes required of adipocytes demands extensive cytoskeletal remodeling, including lipid droplet and plasma membrane expansion. Cell growth-related signalling pathways are activated, stimulating the production of sufficient amino acids, functional lipids and nucleotides to meet the increasing cellular needs of lipid storage, metabolic activity and adipokine secretion. Continued expansion gives rise to enlarged (hypertrophic) adipocytes. This can result in a failure to maintain growth-related homeostasis and an inability to cope with excess nutrition or respond to stimuli efficiently, ultimately leading to metabolic dysfunction. We summarize recent studies which investigate the functional and cellular structure remodeling of hypertrophic adipocytes. How adipocytes adapt to an enlarged cell size and how this relates to cellular dysfunction are discussed. Understanding the healthy and pathological processes involved in adipocyte hypertrophy may shed light on new strategies for promoting healthy adipose tissue expansion.

Low-intensity pulsed ultrasound/nanomechanical force generators enhance osteogenesis of BMSCs through microfilaments and TRPM7

BACKGROUND

Low-intensity pulsed ultrasound (LIPUS) has been reported to accelerate fracture healing, but the mechanism is unclear and its efficacy needs to be further optimized. Ultrasound in combination with functionalized microbubbles has been shown to induce local shear forces and controllable mechanical stress in cells, amplifying the mechanical effects of LIPUS. Nanoscale lipid bubbles (nanobubbles) have high stability and good biosafety. However, the effect of LIPUS combined with functionalized nanobubbles on osteogenesis has rarely been studied.

RESULTS

In this study, we report cyclic arginine-glycine-aspartic acid-modified nanobubbles (cRGD-NBs), with a particle size of ~ 500 nm, able to actively target bone marrow mesenchymal stem cells (BMSCs) via integrin receptors. cRGD-NBs can act as nanomechanical force generators on the cell membrane, and further enhance the BMSCs osteogenesis and bone formation promoted by LIPUS. The polymerization of actin microfilaments and the mechanosensitive transient receptor potential melastatin 7 (TRPM7) ion channel play important roles in BMSCs osteogenesis promoted by LIPUS/cRGD-NBs. Moreover, the mutual regulation of TRPM7 and actin microfilaments promote the effect of LIPUS/cRGD-NBs. The extracellular Ca^2 + influx, controlled partly by TRPM7, could participated in the effect of LIPUS/cRGD-NBs on BMSCs.

CONCLUSIONS

The nanomechanical force generators cRGD-NBs could promote osteogenesis of BMSCs and bone formation induced by LIPUS, through regulation TRPM7, actin cytoskeleton, and intracellular calcium oscillations. This study provides new directions for optimizing the efficacy of LIPUS for fracture healing, and a theoretical basis for the further application and development of LIPUS in clinical practice.

Importance of the Microenvironment and Mechanosensing in Adipose Tissue Biology

The expansion of adipose tissue is an adaptive mechanism that increases nutrient buffering capacity in response to an overall positive energy balance. Over the course of expansion, the adipose microenvironment undergoes continual remodeling to maintain its structural and functional integrity. However, in the long run, adipose tissue remodeling, typically characterized by adipocyte hypertrophy, immune cells infiltration, fibrosis and changes in vascular architecture, generates mechanical stress on adipose cells. This mechanical stimulus is then transduced into a biochemical signal that alters adipose function through mechanotransduction. In this review, we describe the physical changes occurring during adipose tissue remodeling, and how they regulate adipose cell physiology and promote obesity-associated dysfunction in adipose tissue.

Adipose cells and tissues soften with lipid accumulation while in diabetes adipose tissue stiffens

Adipose tissue expansion involves both differentiation of new precursors and size increase of mature adipocytes. While the two processes are well balanced in healthy tissues, obesity and diabetes type II are associated with abnormally enlarged adipocytes and excess lipid accumulation. Previous studies suggested a link between cell stiffness, volume and stem cell differentiation, although in the context of preadipocytes, there have been contradictory results regarding stiffness changes with differentiation. Thus, we set out to quantitatively monitor adipocyte shape and size changes with differentiation and lipid accumulation. We quantified by optical diffraction tomography that differentiating preadipocytes increased their volumes drastically. Atomic force microscopy (AFM)-indentation and -microrheology revealed that during the early phase of differentiation, human preadipocytes became more compliant and more fluid-like, concomitant with ROCK-mediated F-actin remodelling. Adipocytes that had accumulated large lipid droplets were more compliant, and further promoting lipid accumulation led to an even more compliant phenotype. In line with that, high fat diet-induced obesity was associated with more compliant adipose tissue compared to lean animals, both for drosophila fat bodies and murine gonadal adipose tissue. In contrast, adipose tissue of diabetic mice became significantly stiffer as shown not only by AFM but also magnetic resonance elastography. Altogether, we dissect relative contributions of the cytoskeleton and lipid droplets to cell and tissue mechanical changes across different functional states, such as differentiation, nutritional state and disease. Our work therefore sets the basis for future explorations on how tissue mechanical changes influence the behaviour of mechanosensitive tissue-resident cells in metabolic disorders.

Cytoskeleton alterations in non-alcoholic fatty liver disease

BACKGROUND

Due to its extremely high prevalence and severity, non-alcoholic fatty liver disease (NALFD) is a serious health and economic concern worldwide. Developing effective methods of diagnosis and therapy demands a deeper understanding of its molecular basis. One of the strategies in such an endeavor is the analysis of alterations in the morphology of liver cells. Such alterations, widely reported in NAFLD patients and disease models, are related to the cytoskeleton. Therefore, the fate of the cytoskeleton components is useful to uncover the molecular basis of NAFLD, to further design innovative approaches for its diagnosis and therapy.

MAIN FINDINGS

Several cytoskeleton proteins are up-regulated in liver cells of NAFLD patients. Under pathological conditions, keratin 18 is released from hepatocytes and its detection in the blood emerges as a non-invasive diagnosis tool. α-Smooth muscle actin is up-regulated in hepatic stellate cells and its down-regulation has been widely tested as a potential NALFD therapeutic approach. Other cytoskeleton proteins, such as vimentin, are also up-regulated.

CONCLUSIONS

NAFLD progression involves alterations in expression levels of proteins that build the liver cytoskeleton or associate with it. These findings provide a timely opportunity of developing novel approaches for NAFLD diagnosis and therapy.

MYH10 Governs Adipocyte Function and Adipogenesis through Its Interaction with GLUT4

Adipogenesis is dependent on cytoskeletal remodeling that determines and maintains cellular shape and function. Cytoskeletal proteins contribute to the filament-based network responsible for controlling the shape of adipocytes and promoting the intracellular trafficking of cellular components. Currently, the understanding of these mechanisms and their effect on differentiation and adipocyte function remains incomplete. In this study, we identified the non-muscle myosin 10 (MYH10) as a novel regulator of adipogenesis and adipocyte function through its interaction with the insulin-dependent glucose transporter 4 (GLUT4). MYH10 depletion in preadipocytes resulted in impaired adipogenesis, with knockdown cells exhibiting an absence of morphological alteration and molecular signals. MYH10 was shown in a complex with GLUT4 in adipocytes, an interaction regulated by insulin induction. The missing adipogenic capacity of MYH10 knockdown cells was restored when the cells took up GLUT4 vesicles from neighbor wildtype cells in a co-culture system. This signaling cascade is regulated by the protein kinase C ζ (PKCζ), which interacts with MYH10 to modify the localization and interaction of both GLUT4 and MYH10 in adipocytes. Overall, our study establishes MYH10 as an essential regulator of GLUT4 translocation, affecting both adipogenesis and adipocyte function, highlighting its importance in future cytoskeleton-based studies in adipocytes.

Regulatory mechanisms of the early phase of white adipocyte differentiation: an overview

The adipose organ comprises two main fat depots termed white and brown adipose tissues. Adipogenesis is a process leading to newly differentiated adipocytes starting from precursor cells, which requires the contribution of many cellular activities at the genome, transcriptome, proteome, and metabolome levels. The adipogenic program is accomplished through two sequential phases; the first includes events favoring the commitment of adipose tissue stem cells/precursors to preadipocytes, while the second involves mechanisms that allow the achievement of full adipocyte differentiation. While there is a very large literature about the mechanisms involved in terminal adipogenesis, little is known about the first stage of this process. Growing interest in this field is due to the recent identification of adipose tissue precursors, which include a heterogenous cell population within different types of adipose tissue as well as within the same fat depot. In addition, the alteration of the heterogeneity of adipose tissue stem cells and of the mechanisms involved in their commitment have been linked to adipose tissue development defects and hence to the onset/progression of metabolic diseases, such as obesity. For this reason, the characterization of early adipogenic events is crucial to understand the etiology and the evolution of adipogenesis-related pathologies, and to explore the adipose tissue precursors’ potential as future tools for precision medicine.

Adipose-tissue plasticity in health and disease

Adipose tissue, colloquially known as "fat," is an extraordinarily flexible and heterogeneous organ. While historically viewed as a passive site for energy storage, we now appreciate that adipose tissue regulates many aspects of whole-body physiology, including food intake, maintenance of energy levels, insulin sensitivity, body temperature, and immune responses. A crucial property of adipose tissue is its high degree of plasticity. Physiologic stimuli induce dramatic alterations in adipose-tissue metabolism, structure, and phenotype to meet the needs of the organism. Limitations to this plasticity cause diminished or aberrant responses to physiologic cues and drive the progression of cardiometabolic disease along with other pathological consequences of obesity.

The integrin beta1 modulator Tirofiban prevents adipogenesis and obesity by the overexpression of integrin-linked kinase: a pre-clinical approach in vitro and in vivo

Background

Obesity is caused by the enlargement of the white adipose tissue (WAT) depots, characterized by the hypertrophic enlargement of malfunctioning adipocytes within WAT which increases the storage of triglycerides (TG) in the lipid droplets (LD). Adipogenesis pathways as well as the expression and activity of some extracellular matrix receptors integrins are upregulated. Integrinβ1 (INTB1) is the main isoform involved in WAT remodeling during obesity and insulin resistance-related diseases. We recently described Integrin Linked Kinase (ILK), a scaffold protein recruited by INTB1, as an important mediator of WAT remodeling and insulin resistance. As the few approved drugs to fight obesity have brought long-term cardiovascular side effects and given that the consideration of INTB1 and/or ILK modulation as anti-obesogenic strategies remains unexplored, we aimed to evaluate the anti-obesogenic capacity of the clinically approved anticoagulant Tirofiban (TF), stated in preclinical studies as a cardiovascular protector.

Methods

Fully differentiated adipocytes originating from C3H10T1/2 were exposed to TF and were co-treated with specific INTB1 blockers or with siRNA-based knockdown ILK expression. Lipid-specific dyes were used to determine the TG content in LD. The genetic expression pattern of ILK, pro-inflammatory cytokines (MCP1, IL6), adipogenesis (PPARγ, Leptin), thermogenesis (UCP1), proliferation (PCNA), lipid metabolism (FASN, HSL, ATGL), and metabolite transporters (FABP4, FAT, AQP7) were detected using quantitative PCR. Cytoskeletal actin polymerization was detected by confocal microscopy. Immunoblotting was performed to detect INTB1 phosphorylation at Thr788/9 and ILK activity as phosphorylation levels of protein kinase B (AKT) in Ser473 and glycogen synthase kinase 3β (GSK3β) at Ser9. TF was intraperitoneally administered once per day to wildtype and ILK knockdown mice (cKDILK) challenged with a high-fat diet (HFD) or control diet (STD) for 2 weeks. Body and WAT weight gains were compared. The expression of ILK and other markers was determined in the visceral epididymal (epi) and inguinal subcutaneous (sc) WAT.

Results

TF reduced TG content and the expression of adipogenesis markers and transporters in adipocytes, while UCP-1 expression was increased and the expression of lipases, cytokines or PCNA was not affected. Mechanistically, TF rapidly increased and faded the intracellular phosphorylation of INTB1 but not AKT or GSK3β. F-actin levels were rapidly decreased, and INTB1 blockade avoided the TF effect. After 24 h, ILK expression and phosphorylation rates of AKT and GSK3β were upregulated, while ILK silencing increased TG content. INTB1 blockade and ILK silencing avoided TF effects on the TG content and the transcriptional expression of PPARγ and UCP1. In HFD-challenged mice, the systemic administration of TF for several days reduced the weight gain on WAT depots. TF reduced adipogenesis and pro-inflammatory biomarkers and increased lipolysis markers HSL and FAT in epiWAT from HFD, while increased UCP1 in scWAT. In both WATs, TF upregulated ILK expression and activity, while no changes were observed in other tissues. In HFD-fed cKDILK, the blunted ILK in epiWAT worsened weight gain and avoided the anti-obesogenic effect of in vivo TF administration.

Conclusions

ILK downregulation in WAT can be considered a biomarker of obesity establishment. Via an INTB1-ILK axis, TF restores malfunctioning hypertrophied WAT by changing the expression of adipocyte-related genes, increasing ILK expression and activity, and reducing TG storage. TF prevents obesity, a property to be added to its anticoagulant and cardiovascular protective advantages.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13578-022-00746-1.

Phosphorylation of CAP1 regulates lung cancer proliferation, migration, and invasion

Purpose

Cyclase-associated protein 1 (CAP1) is a ubiquitous protein which regulates actin dynamics. Previous studies have shown that S308 and S310 are the two major phosphorylated sites in human CAP1. In the present study, we aimed to investigate the role of CAP1 phosphorylation in lung cancer.

Methods

Massive bioinformatics analysis was applied to determine CAP1’s role in different cancers and especially in lung cancer. Lung cancer patients’ serum and tissue were collected and analyzed in consideration of clinical background. CAP1 shRNA-lentivirus and siRNA were applied to CAP1 gene knockdown, and plasmids were constructed for CAP1 phosphorylation and de-phosphorylation. Microarray analysis was used for CAP1-associated difference analysis. Both in vitro and in vivo experiments were performed to investigate the roles of CAP1 phosphorylation and de-phosphorylation in lung cancer A549 cells.

Results

CAP1 is a kind of cancer-related protein. Its mRNA was overexpressed in most types of cancer tissues when compared with normal tissues. CAP1 high expression correlated with poor prognosis. Our results showed that serum CAP1 protein concentrations were significantly upregulated in non-small cell lung cancer (NSCLC) patients when compared with the healthy control group, higher serum CAP1 protein concentration correlated with shorter overall survival (OS) in NSCLC patients, and higher pCAP1 and CAP1 protein level were observed in lung cancer patients’ tumor tissue compared with adjacent normal tissue. Knockdown CAP1 in A549 cells can inhibit proliferation and migration, and the effect is validated in H1975 cells. It can also lead to an increase ratio of F-actin/G-actin. In addition, phosphorylated S308 and S310 in CAP1 promoted lung cancer cell proliferation, migration, and metastasis both in vitro and in vivo. When de-phosphorylated, these two sites in CAP1 showed the opposite effect. Phosphorylation of CAP1 can promote epithelial–mesenchymal transition (EMT).

Conclusion

These findings indicated that CAP1 phosphorylation can promote lung cancer proliferation, migration, and invasion. Phosphorylation sites of CAP1 might be a novel target for lung cancer treatment.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00432-021-03819-9.

DNMT1 maintains metabolic fitness of adipocytes through acting as an epigenetic safeguard of mitochondrial dynamics

White adipose tissue (WAT) is a key regulator of systemic energy metabolism, and impaired WAT plasticity characterized by enlargement of preexisting adipocytes associates with WAT dysfunction, obesity, and metabolic complications. However, the mechanisms that retain proper adipose tissue plasticity required for metabolic fitness are unclear. Here, we comprehensively showed that adipocyte-specific DNA methylation, manifested in enhancers and CTCF sites, directs distal enhancer-mediated transcriptomic features required to conserve metabolic functions of white adipocytes. Particularly, genetic ablation of adipocyte Dnmt1, the major methylation writer, led to increased adiposity characterized by increased adipocyte hypertrophy along with reduced expansion of adipocyte precursors (APs). These effects of Dnmt1 deficiency provoked systemic hyperlipidemia and impaired energy metabolism both in lean and obese mice. Mechanistically, Dnmt1 deficiency abrogated mitochondrial bioenergetics by inhibiting mitochondrial fission and promoted aberrant lipid metabolism in adipocytes, rendering adipocyte hypertrophy and WAT dysfunction. Dnmt1-dependent DNA methylation prevented aberrant CTCF binding and, in turn, sustained the proper chromosome architecture to permit interactions between enhancer and dynamin-1-like protein gene Dnm1l (Drp1) in adipocytes. Also, adipose DNMT1 expression inversely correlated with adiposity and markers of metabolic health but positively correlated with AP-specific markers in obese human subjects. Thus, these findings support strategies utilizing Dnmt1 action on mitochondrial bioenergetics in adipocytes to combat obesity and related metabolic pathology.

CRTC3 Regulates the Lipid Metabolism and Adipogenic Differentiation of Porcine Intramuscular and Subcutaneous Adipocytes by Activating the Calcium Pathway

Fat deposition, especially the intramuscular (IM) fat deposition, is directly associated with meat quality. The cyclic adenosine monophosphate (cAMP)-responsive element binding-protein (CREB)-regulated transcription coactivator 3 (CRTC3) plays an important role in energy metabolism and various biological processes. The expression of porcine CRTC3 in skeletal muscle is positively associated with intramuscular fat deposition and possesses the capacity to control the intramuscular (IM) adipocyte morphology. However, the metabolic effects and transcriptional mechanism of CRTC3 in porcine intramuscular (IM) adipocytes as well as the regulatory mechanism of CRTC3 on porcine adipocyte differentiation have not been studied. Here, we utilized metabolomics and RNA sequencing (RNA-seq) to determine the metabolic and transcriptome profiles of CRTC3-overexpressing IM adipocytes. Moreover, the effect and regulation mechanism of CRTC3 on porcine IM and subcutaneous (SC) adipocyte differentiation were also studied. Our results showed that CRTC3 overexpression dramatically altered the metabolites in IM adipocytes. Glycerophospholipid (GP) metabolism and related genes were significantly changed in CRTC3-overexpressing IM adipocytes. Moreover, we demonstrated that CRTC3 overexpression promotes adipogenic differentiation by upregulating the Ca²⁺-cAMP signaling pathway in IM and SC adipocytes. We showed alterations in metabolites and in the expression of genes involved in lipid metabolism in CRTC3-overexpressing adipocytes and demonstrated the regulatory mechanism of CRTC3 on the adipogenic differentiation of porcine adipocytes. These results provide new insights into the regulatory roles of CRTC3 in porcine adipocytes, which could be an important target to regulate fat deposition in animals.

Comprehensive understanding of anchorage-independent survival and its implication in cancer metastasis

Detachment is the initial and critical step for cancer metastasis. Only the cells that survive from detachment can develop metastases. Following the disruption of cell-extracellular matrix (ECM) interactions, cells are exposed to a totally different chemical and mechanical environment. During which, cells inevitably suffer from multiple stresses, including loss of growth stimuli from ECM, altered mechanical force, cytoskeletal reorganization, reduced nutrient uptake, and increased reactive oxygen species generation. Here we review the impact of these stresses on the anchorage-independent survival and the underlying molecular signaling pathways. Furthermore, its implications in cancer metastasis and treatment are also discussed.

Adipose Morphology: a Critical Factor in Regulation of Human Metabolic Diseases and Adipose Tissue Dysfunction

Emerging evidence highlights that dysfunction of adipose tissue contributes to impaired insulin sensitivity and systemic metabolic deterioration in obese state. Of note, adipocyte hypertrophy serves as a critical event which associates closely with adipose dysfunction. An increase in cell size exacerbates hypoxia and inflammation as well as excessive collagen deposition, finally leading to metabolic dysregulation. Specific mechanisms of adipocyte hypertrophy include dysregulated differentiation and maturation of preadipocytes, enlargement of lipid droplets, and abnormal adipocyte osmolarity sensors. Also, weight loss therapies exert profound influence on adipocyte size. Here, we summarize the critical role of adipocyte hypertrophy in the development of metabolic disturbances. Future studies are required to establish a standard criterion of size measurement to better clarify the impact of adipocyte hypertrophy on changes in metabolic homeostasis.

Motility and Mechanical Properties of Dendritic Cells Deteriorated by Extracellular Acidosis

Dendritic cells (DCs) are the most powerful antigen-presenting cells known to date and play an important role in initiating and amplifying both innate and adaptive immune responses. Extracellular acidosis is an important hallmark of a variety of inflammatory processes and solid tumors. However, few studies have focused on the effect of extracellular acidosis on DCs and their functions. Cellular mechanical properties reflect the relationship between cell structure and function, including cytoskeleton (especially F-actin organization), membrane negative charges, membrane fluidity, and osmotic fragility. The study investigated the effects of extracellular acidosis on the DCs functions from the perspective of cellular migration and mechanical properties. The results showed that migration ability, F-actin contents, and membrane negative charges of DCs were reduced by extracellular acidosis no matter whether LPS stimulated its maturation or not. And these functions could not return to normal after removing acidic microenvironment, which revealed that the function impairment induced by extracellular acidosis might be irreversible. In addition, the proliferation capacity of stimulated allogeneic T cells was impaired by extracellular acidosis. Our results suggest extracellular acidosis may play an immunosuppressive role in DCs-mediated immune process.

Adipocytes fail to maintain cellular identity during obesity due to reduced PPARγ activity and elevated TGFβ-SMAD signaling

Objective

Obesity due to overnutrition causes adipose tissue dysfunction, which is a critical pathological step on the road to type 2 diabetes (T2D) and other metabolic disorders. In this study, we conducted an unbiased investigation into the fundamental molecular mechanisms by which adipocytes transition to an unhealthy state during obesity.

Methods

We used nuclear tagging and translating ribosome affinity purification (NuTRAP) reporter mice crossed with Adipoq-Cre mice to determine adipocyte-specific 1) transcriptional profiles (RNA-seq), 2) promoter and enhancer activity (H3K27ac ChIP-seq), 3) and PPARγ cistrome (ChIP-seq) profiles in mice fed chow or a high-fat diet (HFD) for 10 weeks. We also assessed the impact of the PPARγ agonist rosiglitazone (Rosi) on gene expression and cellular state of adipocytes from the HFD-fed mice. We integrated these data to determine the transcription factors underlying adipocyte responses to HFD and conducted functional studies using shRNA-mediated loss-of-function approaches in 3T3-L1 adipocytes.

Results

Adipocytes from the HFD-fed mice exhibited reduced expression of adipocyte markers and metabolic genes and enhanced expression of myofibroblast marker genes involved in cytoskeletal organization, accompanied by the formation of actin filament structures within the cell. PPARγ binding was globally reduced in adipocytes after HFD feeding, and Rosi restored the molecular and cellular phenotypes of adipocytes associated with HFD feeding. We identified the TGFβ1 effector protein SMAD to be enriched at HFD-induced promoters and enhancers and associated with myofibroblast signature genes. TGFβ1 treatment of mature 3T3-L1 adipocytes induced gene expression and cellular changes similar to those seen after HFD in vivo, and knockdown of Smad3 blunted the effects of TGFβ1.

Conclusions

Our data demonstrate that adipocytes fail to maintain cellular identity after HFD feeding, acquiring characteristics of a myofibroblast-like cell type through reduced PPARγ activity and elevated TGFβ-SMAD signaling. This cellular identity crisis may be a fundamental mechanism that drives functional decline of adipose tissues during obesity.

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Adipocytes after HFD intake exhibit defects in cellular identity maintenance.

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Adipocytes develop actin filament networks in obesity.

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Altered PPARγ activity mediates defective adipocyte identity phenotypes.

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TGFβ-SMAD pathways promote HFD-induced aberrant phenotype of adipocytes.

Death by lipids: The role of small nucleolar RNAs in metabolic stress

Excess fatty acid accumulation in nonadipose tissues leads to cell dysfunction and cell death that is linked to the pathogenesis of inherited and acquired human diseases. Study of this process, known as lipotoxicity, has provided new insights into the regulation of lipid homeostasis and has revealed new molecular pathways involved in lipid-induced cellular stress. The discovery that disruption of specific small nucleolar RNAs protects against fatty acid-induced cell death and remodels metabolism in vivo opens new opportunities for understanding how nutrient signals influence cellular and systemic metabolic homeostasis through RNA biology.

Uncoupling protein 1 and the capacity for nonshivering thermogenesis are components of the glucose homeostatic system

Uncoupling protein 1 (Ucp1) provides nonshivering thermogenesis (NST) fueled by the dissipation of energy from macronutrients in brown and brite adipocytes. The availability of thermogenic fuels is facilitated by the uptake of extracellular glucose. This conjunction renders thermogenic adipocytes in brown and white adipose tissue (WAT) a potential target against obesity and glucose intolerance. We employed wild-type (WT) and Ucp1-ablated mice to elucidate this relationship. In three experiments of similar setup, Ucp1-ablated mice fed a high-fat diet (HFD) had either reduced or similar body mass gain, food intake, and metabolic efficiency compared with WT mice, challenging the hypothesized role of this protein in the development of diet-induced obesity. Despite the absence of increased body mass, oral glucose tolerance was robustly impaired in Ucp1-ablated mice in response to HFD. Postprandial glucose uptake was attenuated in brown adipose tissue but enhanced in subcutaneous WAT of Ucp1-ablated mice. These differences were explainable by expression of the insulin-responsive member 4 of the facilitated glucose transporter family and fully in line with the capacity for NST in these very tissues. Thus, the postprandial glucose uptake of adipose tissues serves as a surrogate measure for Ucp1-dependent and independent capacity for NST. Collectively, our findings corroborate Ucp1 as a modulator of adipose tissue glucose uptake and systemic glucose homeostasis but challenge its hypothesized causal effect on the development of obesity.

Two Faces of White Adipose Tissue with Heterogeneous Adipogenic Progenitors

Chronic energy surplus increases body fat, leading to obesity. Since obesity is closely associated with most metabolic complications, pathophysiological roles of adipose tissue in obesity have been intensively studied. White adipose tissue is largely divided into subcutaneous adipose tissue (SAT) and visceral adipose tissue (VAT). These two white adipose tissues are similar in their appearance and lipid storage functions. Nonetheless, emerging evidence has suggested that SAT and VAT have different characteristics and functional roles in metabolic regulation. It is likely that there are intrinsic differences between VAT and SAT. In diet-induced obese animal models, it has been reported that adipogenic progenitors in VAT rapidly proliferate and differentiate into adipocytes. In obesity, VAT exhibits elevated inflammatory responses, which are less prevalent in SAT. On the other hand, SAT has metabolically beneficial effects. In this review, we introduce recent studies that focus on cellular and molecular components modulating adipogenesis and immune responses in SAT and VAT. Given that these two fat depots show different functions and characteristics depending on the nutritional status, it is feasible to postulate that SAT and VAT have different developmental origins with distinct adipogenic progenitors, which would be a key determining factor for the response and accommodation to metabolic input for energy homeostasis.

Adipose cell size changes are associated with a drastic actin remodeling

Adipose tissue plays a major role in regulating whole-body insulin sensitivity and energy metabolism. To accommodate surplus energy, the tissue rapidly expands by increasing adipose cell size (hypertrophy) and cell number (hyperplasia). Previous studies have shown that enlarged, hypertrophic adipocytes are less responsive to insulin, and that adipocyte size could serve as a predictor for the development of type 2 diabetes. In the present study, we demonstrate that changes in adipocyte size correlate with a drastic remodeling of the actin cytoskeleton. Expansion of primary adipocytes following 2 weeks of high-fat diet (HFD)-feeding in C57BL6/J mice was associated with a drastic increase in filamentous (F)-actin as assessed by fluorescence microscopy, increased Rho-kinase activity, and changed expression of actin-regulating proteins, favoring actin polymerization. At the same time, increased cell size was associated with impaired insulin response, while the interaction between the cytoskeletal scaffolding protein IQGAP1 and insulin receptor substrate (IRS)-1 remained intact. Reversed feeding from HFD to chow restored cell size, insulin response, expression of actin-regulatory proteins and decreased the amount of F-actin filaments. Together, we report a drastic cytoskeletal remodeling during adipocyte expansion, a process which could contribute to deteriorating adipocyte function.