Microenvironmental Control of Adipocyte Fate and Function

Cancer-associated adipocytes: key players in breast cancer progression

Adipocytes are one of the primary stromal cells in many tissues, and they are considered to play an active role in the tumor microenvironment. Cancer-associated adipocytes (CAAs) are not only found adjacent to cancer cells, but also communicate with cancer cells through releasing various factors that can mediate local and systemic effects. The adipocyte-cancer cell crosstalk leads to phenotypical and functional changes of both cell types, which can further enhance tumor progression. Indeed, obesity, which is associated with an increase in adipose mass and an alteration of adipose tissue, is becoming pandemic in some countries and it is now considered to be an independent risk factor for cancer progression. In this review, we focus on the potential mechanisms involved with special attention to the adipocyte-cancer cell circle in breast cancer. We envisage that besides having a direct impact on tumor cells, CAAs systemically preconditions the tumor microenvironment by favoring anti-tumor immunity. A better understanding of cancer-associated adipocytes and the key molecular events in the adipocyte-cancer cell crosstalk will provide insights into tumor biology and permit the optimization of therapeutic strategies.

Comparing the use of differentiated adipose-derived stem cells and mature adipocytes to model adipose tissue in vitro

In vitro models of human adipose tissue may serve as beneficial alternatives to animal models to study basic biological processes, identify new drug targets, and as soft tissue implants. With this approach, we aimed to evaluate adipose-derived stem cells (ASC) and mature adipocytes (MA) comparatively for the application in the in vitro setup of adipose tissue constructs to imitate native adipose tissue physiology. We used human primary MAs and human ASCs, differentiated for 14 days, and encapsulated them in collagen type I hydrogels to build up a three-dimensional (3D) adipose tissue model. The maintenance of the models was analyzed after seven days based on a viability staining. Further, the expression of the adipocyte specific protein perilipin A and the release of leptin and glycerol were evaluated. Gene transcription profiles of models based on dASCs and MAs were analyzed with regard to native adipose tissue. Compared to MAs, dASCs showed an immature differentiation state. Further, gene transcription of MAs suggests a behavior closer to native tissue in terms of angiogenesis, which supports MAs as preferred cell type. In contrast to native adipose tissue, genes of de novo lipogenesis and tissue remodeling were upregulated in the in vitro attempts.

Predicted secreted protein analysis reveals synaptogenic function of Clstn3 during WAT browning and BAT activation in mice

Promoting white adipose tissue (WAT) browning and enhancing brown adipose tissue (BAT) activity are attractive therapeutic strategies for obesity and its metabolic complications. Targeting sympathetic innervation in WAT and BAT represents a promising therapeutic concept. However, there are few reports on extracellular microenvironment remodeling, especially changes in nerve terminal connections. Identifying the key molecules mediating the neuro-adipose synaptic junctions is a key point. In this study, we used bioinformatics methods to identify the differentially expressed predicted secreted genes (DEPSGs) during WAT browning and BAT activation. These DEPSGs largely reflect changes of cytokines, extracellular matrix remodeling, vascularization, and adipocyte-neuronal cross-talk. We then performed functional enrichment and cellular distribution specificity analyses. The upregulated and downregulated DEPDGs during WAT browning displayed a distinctive biological pattern and cellular distribution. We listed a cluster of adipocyte-enriched DEPSGs, which might participate in the cross-talk between mature adipocytes and other cells; then identified a synaptogenic adhesion molecule, Clstn3, as the top gene expressed enriched in both mature white and brown adipocytes. Using Q-PCR and immunohistochemistry, we found significantly increased Clstn3 expression level during WAT browning and BAT activation in mice subjected to cold exposure (4 °C). We further demonstrated that treatment with isoproterenol significantly increased Clstn3 and UCP1 expression in differentiated white and beige adipocytes in vitro. In conclusion, our study demonstrates that the secretion pattern was somewhat different between WAT browning and BAT activation. We reveal that Clstn3 may be a key gene mediating the neuro-adipose junction formation or remodeling in WAT browning and BAT activation process.

Adipocyte size in morbidly obese women and its relation to type 2 diabetes

Aim of the study: The aim was to perform a morphometric analysis of subcutaneous and visceral adipose tissue of morbidly obese women and to determine the relationship between adipocyte size and the development of type 2 diabetes (T2D).

Materials and methods: White adipose tissue of morbidly obese women was obtained from subcutaneous and omental adipose tissue during bariatric surgery. The same tissues were obtained at judicial autopsy in non-obese (lean) non-diabetic patients. The harvested tissue was embedded in paraffin and 5 μm thick hematoxylin-eosin stained sections were analyzed by the Olympus cellSens system. Statistical evaluation was performed by GraphPad Prism 6.1 software.

Results: We found a relationship between adipocyte size and the presence of T2D. The most pronounced changes were seen in visceral adipocytes (cell diameter increased from 61.9 μm in controls to 79.5 μm in patients with T2D). Also, the size of the subcutaneous adipocytes increased against the control. A statistically significant difference between diabetic and non-diabetic patients was not proven in subcutaneous adipocytes. We also observed differences in the distribution of adipocyte mean diameters. Whilst in the control group there was a normal (Gaussian) distribution, in the morbidly obese we found an asymmetric distribution with a positive skewness to the right.

Conclusion: We have demonstrated that in morbidly obese women a significant increase in visceral adipocyte size is associated with the development of both insulin resistance and T2D.

Microglia-Derived Adiposomes are Potential Targets for the Treatment of Ischemic Stroke

It is known that cerebral ischemia can cause brain inflammation and adiposome can serve as a depot of inflammatory mediators. In the study, the pro-inflammatory and pro-death role of adiposome in ischemic microglia and ischemic brain was newly investigated. The contribution of PPARγ to adiposome formation was also evaluated for the first time in ischemic microglia. Focal cerebral ischemia/reperfusion (I/R) animal model and the in vitro glucose-oxygen-serum deprivation (GOSD) cell model were both applied in the study. GOSD- or I/R-induced adiposome formation, inflammatory activity, cell death of microglia, and brain infarction were, respectively, determined, in the absence or presence of NS-398 (adiposome inhibitor) or GW9662 (PPARγ antagonist). GOSD-increased adiposome formation played a critical role in stimulating the inflammatory activity (production of TNF-α and IL-1β) and cell death of microglia. Similar results were also found in ischemic brain tissues. GOSD-induced PPARγ partially contributed to the increase of adiposomes and adiposome-mediated inflammatory responses of microglia. Blockade of adiposome formation with NS-398 or GW9662 significantly reduced not only the inflammatory activity and death rate of GOSD-treated microglia but also the brain infarct volume and motor function deficit of ischemic rats. The pathological role of microglia-derived adiposome in cerebral ischemia has been confirmed and attributed to its pro-inflammatory and/or pro-death effect upon ischemic brain cells and tissues. Adiposome and its upstream regulator PPARγ were therefore as potential targets for the treatment of ischemic stroke. Therapeutic values of NS-398 and GW9662 have been suggested.

Adipose Tissue CTGF Expression is Associated with Adiposity and Insulin Resistance in Humans

OBJECTIVE

Connective tissue growth factor (CTGF) is an important regulator of fibrogenesis in many organs. This study evaluated the interrelationship among adipose tissue CTGF expression, fat mass, and insulin resistance in humans.

METHODS

This study examined (1) CTGF gene expression in human subcutaneous preadipocytes before and after inducing adipogenesis; (2) relationships among abdominal subcutaneous adipose tissue CTGF gene expression, body fat mass, and indices of insulin sensitivity, including the hepatic insulin sensitivity index and the hyperinsulinemic-euglycemic clamp procedure in conjunction with stable isotope glucose tracer infusion, in 72 people who had marked differences in adiposity and insulin sensitivity; (3) localization of CTGF protein in subcutaneous adipose tissue; and (4) effect of progressive (5%, 11%, and 16%) weight loss on adipose tissue CTGF gene expression.

RESULTS

CTGF was highly expressed in preadipocytes, not adipocytes. Adipose tissue CTGF expression was strongly correlated with body fat mass and both skeletal muscle and liver insulin sensitivity, and CTGF-positive cells were predominantly found in areas of fibrosis. Progressive weight loss caused a stepwise decrease in adipose tissue CTGF expression.

CONCLUSIONS

It was concluded that increased CTGF expression is associated with adipose tissue expansion, adipose tissue fibrosis, and multi-organ insulin resistance in people with obesity.

RDH1 suppresses adiposity by promoting brown adipose adaptation to fasting and re-feeding

RDH1 is one of the several enzymes that catalyze the first of the two reactions to convert retinol into all-trans-retinoic acid (atRA). Here, we show that Rdh1-null mice fed a low-fat diet gain more weight as adiposity (17% males, 13% females) than wild-type mice by 20 weeks old, despite neither consuming more calories nor decreasing activity. Glucose intolerance and insulin resistance develop following increased adiposity. Despite the increase in white fat pads, epididymal white adipose does not express Rdh1, nor does muscle. Brown adipose tissue (BAT) and liver express Rdh1 at relatively high levels compared to other tissues. Rdh1 ablation lowered body temperatures during ambient conditions. Given the decreased body temperature, we focused on BAT. A lack of differences in BAT adipogenic gene expression between Rdh1-null mice and wild-type mice, including Pparg, Prdm16, Zfp516 and Zfp521, indicated that the phenotype was not driven by brown adipose hyperplasia. Rather, Rdh1 ablation eliminated the increase in BAT atRA that occurs after re-feeding. This disruption of atRA homeostasis increased fatty acid uptake, but attenuated lipolysis in primary brown adipocytes, resulting in increased lipid content and larger lipid droplets. Rdh1 ablation also decreased mitochondrial proteins, including CYCS and UCP1, the mitochondria oxygen consumption rate, and disrupted the mitochondria membrane potential, further reflecting impaired BAT function, resulting in both BAT and white adipose hypertrophy. RNAseq revealed dysregulation of 424 BAT genes in null mice, which segregated predominantly into differences after fasting vs after re-feeding. Exceptions were Rbp4 and Gbp2b, which increased during both dietary conditions. Rbp4 encodes the serum retinol-binding protein-an insulin desensitizer. Gbp2b encodes a GTPase. Because Gbp2b increased several hundred-fold, we overexpressed it in brown adipocytes. This caused a shift to larger lipid droplets, suggesting that GBP2b affects signaling downstream of the β-adrenergic receptor during basal thermogenesis. Thus, Rdh1-generated atRA in BAT regulates multiple genes that promote BAT adaptation to whole-body energy status, such as fasting and re-feeding. These gene expression changes promote optimum mitochondria function and thermogenesis, limiting adiposity. Attenuation of adiposity and insulin resistance suggests that RDH1 mitigates metabolic syndrome.

Temporal Observation of Adipocyte Microfiber Using Anchoring Device

In this paper, we propose an anchoring device with pillars to immobilize an adipocyte microfiber that has a fiber-shaped adipocyte tissue covered by an alginate gel shell. Because the device enabled the immobilization of the microfiber in a culture dish even after its transportation and the exchange of the culture medium, we can easily track the specific positions of the microfiber for a long period. Owing to the characteristics of the anchoring device, we successfully performed temporal observations of the microfiber on the device for a month to investigate the function and morphology of three-dimensional cultured adipocytes. Furthermore, to demonstrate the applicability of the anchoring device to drug testing, we evaluated the lipolysis of the microfiber's adipocytes by applying reagents with an anti-obesity effect. Therefore, we believe that the anchoring device with the microfiber will be a useful tool for temporal biochemical analyses.

Exosomes from the tumour-adipocyte interplay stimulate beige/brown differentiation and reprogram metabolism in stromal adipocytes to promote tumour progression

BACKGROUND

Emerging evidence supports the pivotal roles of adipocytes in breast cancer progression. Tumour induced beige/brown adipose tissue differentiation contributes to the hypermetabolic state of the breast cancer. However, the mediators and mechanisms remain unclear.

METHODS

Survival probabilities were estimated using the Kaplan-Meier method based on immunohistochemistry results. Biochemical studies were performed to characterize the novel interrelation between breast cancer cells and adipocytes.

RESULTS

We show that tumour-surrounding adipocytes exhibit an altered phenotype in terms of upregulated beige/brown characteristics and increased catabolism associated with an activated state characterized by the release of metabolites, including free fatty acids, pyruvate, lactate and ketone bodies. Likewise, tumour cells cocultivated with mature adipocytes exhibit metabolic adaptation and an aggressive phenotype in vitro and in vivo. Mechanistically, we show that tumour cells induce beige/brown differentiation and remodel metabolism in resident adipocytes by exosomes from the co-culture system that carry high levels of miRNA-144 and miRNA-126. miRNA-144 promotes beige/brown adipocyte characteristics by downregulating the MAP3K8/ERK1/2/PPARγ axis, and exosomal miRNA-126 remodels metabolism by disrupting IRS/Glut-4 signalling, activating the AMPK/autophagy pathway and stabilizing HIF1α expression in imminent adipocytes. In vivo inhibition of miRNA-144 or miRNA-126 decreases adipocyte-induced tumour growth.

CONCLUSIONS

These results demonstrate that by inducing beige/brown differentiation and enhancing catabolism in recipient adipocytes, exosomal miRNA-144 and miRNA-126 from the tumour-adipocyte interaction reprogram systemic energy metabolism to facilitate tumour progression.

Caveolin-1 as a pathophysiological factor and target in psoriasis

Low expression of caveolin-1 (Cav-1) is typical in psoriatic lesions and overexpression of Cav-1 leads to a reduction of inflammation and suppression of epidermal hyperproliferation, thus ameliorating these two well-known hallmarks of psoriasis. At the same time, the interfacial layers of the white adipose tissue (WAT) adjacent to psoriatic lesions demonstrate much higher stiffness, which also points to a modification of Cav-1 expression in this tissue. These processes are connected with each other and regulated via exosomal exchange. Here we discuss the role of Cav-1 expression in inflammatory and hyperproliferative processes and analyze the ways to provide spatially different modulation of Cav-1 expression in the skin and WAT. Such modulation can be induced by different pharmacological and physical factors. These include application of mechanical stress and supra-physiological temperatures. Cav-1 should therefore be considered as an important target in treatment of psoriasis.

3D collagen microfibers stimulate the functionality of preadipocytes and maintain the phenotype of mature adipocytes for long term cultures

Although adipose tissue is one of the most abundant tissues of the human body, its reconstruction remains a competitive challenge. The conventional in vitro two or three-dimensional (2D or 3D) models of mature adipocytes unfortunately lead to their quick dedifferentiation after one week, and complete differentiation of adipose derived stem cells (ADSC) usually requires more than one month. In this context, we developed biomimetic 3D adipose tissues with high density collagen by mixing type I collagen microfibers with primary mouse mature adipocytes or human ADSC in transwells. These 3D-tissues ensured a better long-term maintained phenotype of unilocular mature adipocytes, compared to 2D, with a viability of 96 ± 2% at day 14 and a good perilipin immunostaining, - the protein necessary for stabilizing the fat vesicles. For comparison, in 2D culture, mature adipocytes released their fat until splitting their single adipose vesicle into several ones with significantly 4 times smaller size. Concerning ADSC, the adipogenic genes expression in 3D-tissues was found at least doubled throughout the differentiation (over 8 times higher for GLUT4 at day 21), along with it, almost 4 times larger fat vesicles were observed (10 ± 4 µm at day 14). Perilipin immunostaining and leptin secretion, the satiety protein, attested the significantly doubled better functionality of ADSC in 3D adipose tissues. These obtained long-term maintained phenotype and fast adipogenesis make this model relevant for either cosmetic/pharmaceutical assays or plastic surgery purposes. STATEMENT OF SIGNIFICANCE: Adipose tissue has important roles in our organism, providing energy from its lipids storage and secreting many vital proteins. However, its reconstruction in a functional in vitro adipose tissue is still a challenge. Mature adipocytes directly extracted from surgery liposuctions quickly lose their lipids after a week in vitro and the use of differentiated adipose stem cells is too time-consuming. We developed a new artificial fat tissue using collagen microfibers. These tissues allowed the maintenance of viable big unilocular mature adipocytes up to two weeks and the faster adipogenic differentiation of adipose stem cells. Moreover, the adipose functionality confirmed by perilipin and leptin assessments makes this model suitable for further applications in cosmetic/pharmaceutical drug assays or for tissue reconstruction.

Fat fibrosis: friend or foe?

At the simplest level, obesity is the manifestation of an imbalance between caloric intake and expenditure; however, the pathophysiological mechanisms that govern the development of obesity and associated complications are enormously complex. Fibrosis within the adipose tissue compartment is one such factor that may influence the development of obesity and/or obesity-related comorbidities. Furthermore, the functional consequences of adipose tissue fibrosis are a matter of considerable debate, with evidence that fibrosis serves both adaptive and maladaptive roles. Tissue fibrosis itself is incompletely understood, and multiple cellular and molecular pathways are involved in the development, maintenance, and resolution of the fibrotic state. Within the context of obesity, fibrosis influences molecular and cellular events that relate to adipocytes, inflammatory cells, inflammatory mediators, and supporting adipose stromal tissue. In this Review, we explore what is known about the interplay between the development of adipose tissue fibrosis and obesity, with a view toward future investigative and therapeutic avenues.

Calorie restriction prevents diet-induced insulin resistance independently of PGC-1-driven mitochondrial biogenesis in white adipose tissue

Calorie restriction (CR) exerts remarkable, beneficial effects on glucose homeostasis by mechanisms that are not fully understood. Given the relevance of white adipose tissue (WAT) in glucose homeostasis, we aimed at identifying the main cellular processes regulated in WAT in response to CR in a pathologic context of obesity. For this, a gene-expression profiling study was first conducted in mice fed ad libitum or subjected to 40% CR. We found that the gene network related to mitochondria was the most highly upregulated in WAT by CR. To study the role that increased mitochondrial biogenesis plays on glucose homeostasis following CR, we generated a mouse model devoid of the coactivators peroxisome proliferator-activated receptor γ coactivator 1 (PGC-1)α and PGC-1β specifically in adipocytes. Our results show that mice lacking PGC-1s in adipocytes are unable to increase mitochondrial biogenesis in WAT upon CR. Despite a blunted induction of mitochondrial biogenesis in response to calorie deprivation, mice lacking adipose PGC-1s still respond to CR by improving their glucose homeostasis. Our study demonstrates that PGC-1 coactivators are major regulators of CR-induced mitochondrial biogenesis in WAT and that increased mitochondrial biogenesis and oxidative function in adipose tissue are not required for the improvement of glucose homeostasis mediated by CR.-Pardo, R., Vilà, M., Cervela, L., de Marco, M., Gama-Pérez, P., González-Franquesa, A., Statuto, L., Vilallonga, R., Simó, R., Garcia-Roves, P. M., Villena, J. A. Calorie restriction prevents diet-induced insulin resistance independently of PGC-1-driven mitochondrial biogenesis in white adipose tissue.

Adipoinductive effect of extracellular matrix involves cytoskeleton changes and SIRT1 activity in adipose tissue stem/stromal cells

Adipose tissue (AT) homeostasis and expansion are dependent on complex crosstalk between resident adipose stromal/stem cells (ASCs) and AT extracellular matrix (ECM). Although adipose tissue ECM (atECM) is one of the key players in the stem cell niche, data on bidirectional interaction of ASCs and atECM are still scarce. Here, we investigated how atECM guides ASCs' differentiation. atECM altered shape and cytoskeleton organization of ASCs without changing their proliferation, β-galactosidase activity and adhesion. Cytoskeleton modifications occurred due to fostered parallel organization of F-actin and elevated expression of Vimentin in ASCs. After seven-day cultivation, atECM impaired osteogenesis of ASCs, simultaneously decreasing expression of Runx2. In addition, atECM accelerated early adipogenesis concomitantly with altered Vimentin organization in ASCs, slightly increasing PPARγ, while elevated Adiponectin and Vimentin mRNA expression. Early adipogenesis triggered by atECM was followed by upregulated mitochondrial activity and Sirtuin 1 (SIRT1) expression in ASCs. Proadipogenic events induced by atECM were mediated by SIRT1, indicating the supportive role of atECM in adipogenesis-related metabolic state of ASCs. These results provide a closer look at the effects of atECM on ASC physiology and may support the advancement of engineering design in soft tissue reconstruction and fundamental research of AT.

Generation of Gellan Gum-Based Adipose-Like Microtissues

Adipose tissue is involved in many physiological processes. Therefore, the need for adipose tissue-like analogues either for soft tissue reconstruction or as in vitro testing platforms is undeniable. In this work, we explored the natural features of gellan gum (GG) to recreate injectable stable adipose-like microtissues. GG hydrogel particles with different percentages of polymer (0.5%, 0.75%, 1.25%) were developed and the effect of obtained mechanical properties over the ability of hASCs to differentiate towards the adipogenic lineage was evaluated based on the expression of the early (PPARγ) and late (FABP4) adipogenic markers, and on lipids formation and accumulation. Constructs were cultured in adipogenic induction medium up to 21 days or for six days in induction plus nine days in maintenance media. Overall, no significant differences were observed in terms of hASCs adipogenic differentiation within the range of Young’s moduli between 2.7 and 12.9 kPa. The long-term (up to six weeks) stability of the developed constructs supported its application in soft tissue reconstruction. Moreover, their ability to function as adipose-like microtissue models for drug screening was demonstrated by confirming its sensitivity to TNFα and ROCK inhibitor, respectively involved in the repression and induction of the adipogenic differentiation.

Brown and beige fat: From molecules to physiology and pathophysiology

The adipose organ portrays adipocytes of diverse tones: white, brown and beige, each type with distinct functions. Adipocytes orchestrate their adaptation and expansion to provide storage to excess nutrients, the quick mobilisation of fuel to supply peripheral functional demands, insulation, and, in their thermogenic form, heat generation to maintain core body temperature. Thermogenic adipocytes could be targets for anti-obesity and anti-diabetic therapeutic approaches aiming to restore adipose tissue functionality and increase energy dissipation. However, for thermogenic adipose tissue to become therapeutically relevant, a better understanding of its development and origins, its progenitors and their characteristics and the composition of its niche, is essential. Also crucial is the identification of stimuli and molecules promoting its specific differentiation and activation. Here we highlight the structural/cellular differences between human and rodent brown adipose tissue and discuss how obesity and metabolic complication affects brown and beige cells as well as how they could be targeted to improve their activation and improve global metabolic homeostasis. Finally, we describe the limitations of current research models and the advantages of new emerging approaches.

Monocarboxylate transporters in breast cancer and adipose tissue are novel biomarkers and potential therapeutic targets

Monocarboxylate transporters (MCTs) are transmembrane proteins that control the lactate metabolism and associated with poor prognosis in solid tumours including breast cancer (BC). This study aimed to evaluate the clinical and prognostic value of MCTs used by immunohistochemistry and quantum dots-based fluorescent imaging technique in BC and surrounding stroma with emphasis on the interaction between tumour and stroma. Moreover, the data from The Cancer Genome Atlas (TCGA) was analyzed to evaluate the association between MCTs mRNA expression and prognosis of breast cancer patients. Our study found that MCT1 overexpression was observed in hormone receptor-negative and high-proliferation subtypes. High expression of MCT1 and MCT4 in tumour tissues was associated with poor patient outcome; further the correlation between MCT1 expression and poor prognosis in breast cancer was further strengthened when combined with MCT4 overexpression in the adjacent adipose tissue. These results demonstrate that MCTs tend to play a role in the aggressive BC subtypes through the dynamic interaction between breast cancer cells and adipocytes, and developing therapeutics to block this interaction will be a promising strategy in cancer therapy.

Deciphering adipose tissue heterogeneity

Obesity is an excess accumulation of adipose tissue mass, and, together with its sequelae, in particular type II diabetes and metabolic syndrome, obesity presents a major health crisis. Although obesity is simply caused by increased adipose mass, the heterogeneity of adipose tissue in humans means that the response to increased energy balance is highly complex. Individual subjects with similar phenotypes may respond very differently to the same treatments; therefore, obesity may benefit from a personalized precision medicine approach. The variability in the development of obesity is indeed driven by differences in sex, genetics, and environment, but also by the various types of adipose tissue as well as the different cell types that compose it. By describing the distinct cell populations that reside in different fat depots, we can interpret the complex effect of these various players in the maintenance of whole-body energy homeostasis. To further understand adipose tissue, adipogenic differentiation and the transcriptional program of lipid accumulation must be investigated. As the cell- and depot-specific functions are described, they can be placed in the context of energy excess to understand how the heterogeneity of adipose tissue shapes individual metabolic status and condition.

Symposium review: Modulating adipose tissue lipolysis and remodeling to improve immune function during the transition period and early lactation of dairy cows

Despite major advances in our understanding of transition and early lactation cow physiology and the use of advanced dietary, medical, and management tools, at least half of early lactation cows are reported to develop disease and over half of cow deaths occur during the first week of lactation. Excessive lipolysis, usually measured as plasma concentrations of free fatty acids (FFA), is a major risk factor for the development of displaced abomasum, ketosis, fatty liver, and metritis, and may also lead to poor lactation performance. Lipolysis triggers adipose tissue (AT) remodeling that is characterized by enhanced humoral and cell-mediated inflammatory responses and changes in its distribution of cellular populations and extracellular matrix composition. Uncontrolled AT inflammation could perpetuate lipolysis, as we have observed in cows with displaced abomasum, especially in those animals with genetic predisposition for excessive lipolysis responses. Efficient transition cow management ensures a moderate rate of lipolysis that is rapidly reduced as lactation progresses. Limiting FFA release from AT benefits immune function as several FFA are known to promote dysregulation of inflammation. Adequate formulation of pre- and postpartum diet reduces the intensity of AT lipolysis. Additionally, supplementation with niacin, monensin, and rumen-protected methyl donors (choline and methionine) during the transition period is reported to minimize FFA release into systemic circulation. Targeted supplementation of energy sources during early lactation improves energy balance and increases insulin concentration, which limits AT lipolytic responses. This review elaborates on the mechanisms by which uncontrolled lipolysis triggers inflammatory disorders. Details on current nutritional and pharmacological interventions that aid the modulation of FFA release from AT and their effect on immune function are provided. Understanding the inherent characteristics of AT biology in transition and early lactation cows will reduce disease incidence and improve lactation performance.

The FGF21-CCL11 Axis Mediates Beiging of White Adipose Tissues by Coupling Sympathetic Nervous System to Type 2 Immunity

Type 2 cytokines are important signals triggering biogenesis of thermogenic beige adipocytes in white adipose tissue (WAT) during cold acclimation. However, how cold activates type 2 immunity in WAT remains obscure. Here we show that cold-induced type 2 immune responses and beiging in subcutaneous WAT (scWAT) are abrogated in mice with adipose-selective ablation of FGF21 or its co-receptor β-Klotho, whereas such impairments are reversed by replenishment with chemokine CCL11. Mechanistically, FGF21 acts on adipocytes in an autocrine manner to promote the expression and secretion of CCL11 via activation of ERK1/2, which drives recruitment of eosinophils into scWAT, leading to increases in accumulation of M2 macrophages, and proliferation and commitment of adipocyte precursors into beige adipocytes. These FGF21-elicited type 2 immune responses and beiging are blocked by CCL11 neutralization. Thus, the adipose-derived FGF21-CCL11 axis triggers cold-induced beiging and thermogenesis by coupling sympathetic nervous system to activation of type 2 immunity in scWAT.

Physiological regulation and metabolic role of browning in white adipose tissue

Great progress has been made in our understanding of the browning process in white adipose tissue (WAT) in rodents. The recognition that i) adult humans have physiologically inducible brown adipose tissue (BAT) that may facilitate resistance to obesity and ii) that adult human BAT molecularly and functionally resembles beige adipose tissue in rodents, reignited optimism that obesity and obesity-related diabetes type 2 can be battled by controlling the browning of WAT. In this review the main cellular mechanisms and molecular mediators of browning of WAT in different physiological states are summarized. The relevance of browning of WAT in metabolic health is considered primarily through a modulation of biological role of fat tissue in overall metabolic homeostasis.

Inter-adipocyte Adhesion and Signaling by Collagen IV Intercellular Concentrations in Drosophila

Sheet-forming Collagen IV is the main component of basement membranes, which are planar polymers of extracellular matrix underlying epithelia and surrounding organs in all animals. Adipocytes in both insects and mammals are mesodermal in origin and often classified as mesenchymal. However, they form true tissues where cells remain compactly associated. Neither the mechanisms providing this tissue-level organization nor its functional significance are known. Here we show that discrete Collagen IV intercellular concentrations (CIVICs), distinct from basement membranes and thicker in section, mediate inter-adipocyte adhesion in Drosophila. Loss of these Collagen-IV-containing structures in the larval fat body caused intercellular gaps and disrupted continuity of the adipose tissue layer. We also found that Integrin and Syndecan matrix receptors attach adipocytes to CIVICs and direct their formation. Finally, we show that Integrin-mediated adhesion to CIVICs promotes normal adipocyte growth and prevents autophagy through Src-Pi3K-Akt signaling. Our results evidence a surprising non-basement membrane role of Collagen IV in non-epithelial tissue morphogenesis while demonstrating adhesion and signaling functions for these structures.

Adipose derived delivery vehicle for encapsulated adipogenic factors

Hydrogels derived from adipose tissue extracellular matrix (AdECM) have shown potential in the ability to generate new adipose tissue in vivo. To further enhance adipogenesis, a composite adipose derived delivery system (CADDS) containing single- and double-walled dexamethasone encapsulated microspheres (SW and DW Dex MS) has been developed. Previously, our laboratory has published the use of Dex MS as an additive to enhance adipogenesis and angiogenesis in adipose tissue grafts. In the current work, AdECM and CADDS are extensively characterized, in addition to conducting in vitro cell culture analysis. Study results indicate the AdECM used for the CADDS has minimal cellular and lipid content allowing for gelation of its collagen structure under physiological conditions. Adipose-derived stem cell (ASC) culture studies confirmed biocompatibility with the CADDS, and adipogenesis was increased in experimental groups containing the hydrogel scaffold. In vitro studies of AdECM hydrogel containing microspheres demonstrated a controlled release of dexamethasone from SW and DW formulations. The delivery of Dex MS via an injectable hydrogel scaffold combines two biologically responsive components to develop a minimally, invasive, off-the-shelf biomaterial for adipose tissue engineering.

STATEMENT OF SIGNIFICANCE

Scientists and doctors have yet to develop an off-the-shelf product for patients with soft tissue defects. Recently, the use of adipose derived extracellular matrix (adECM) to generate new adipose tissue in vivo has shown great promise but individually, adECM still has limitations in terms of volume and consistency. The current work introduces a novel composite off-the-shelf construct comprised of an adECM-based hydrogel and dexamethasone encapsulated microspheres (Dex MS). The hydrogel construct serves not only as an injectable protein-rich scaffold but also a delivery system for the Dex MS for non-invasive application to the defect site. The methods and results presented are a progressive step forward in the field of adipose tissue engineering.

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.

Profibrotic Infrapatellar Fat Pad Remodeling Without M1 Macrophage Polarization Precedes Knee Osteoarthritis in Mice With Diet-Induced Obesity

OBJECTIVE

To test the hypothesis that high-fat (HF) diet-induced obesity increases proinflammatory cytokine expression, macrophage infiltration, and M1 polarization in the infrapatellar fat pad (IFP) prior to knee cartilage degeneration.

METHODS

We characterized the effect of HF feeding on knee OA pathology, body adiposity, and glucose intolerance in male C57BL/6J mice and identified a diet duration that induces metabolic dysfunction prior to cartilage degeneration. Magnetic resonance imaging and histomorphology were used to quantify changes in the epididymal, subcutaneous, and infrapatellar fat pads and in adipocyte sizes. Finally, we used targeted gene expression and protein arrays, immunohistochemistry, and flow cytometry to quantify differences in fat pad markers of inflammation and immune cell populations.

RESULTS

Twenty weeks of feeding with an HF diet induced marked obesity, glucose intolerance, and early osteoarthritis (OA), including osteophytes and cartilage tidemark duplication. This duration of HF feeding increased the IFP volume. However, it did not increase IFP inflammation, macrophage infiltration, or M1 macrophage polarization as observed in epididymal fat. Furthermore, leptin protein levels were reduced. This protection from obesity-induced inflammation corresponded to increased IFP fibrosis and the absence of adipocyte hypertrophy.

CONCLUSION

The IFP does not recapitulate classic abdominal adipose tissue inflammation during the early stages of knee OA in an HF diet-induced model of obesity. Consequently, these findings do not support the hypothesis that IFP inflammation is an initiating factor of obesity-induced knee OA. Furthermore, the profibrotic and antihypertrophic responses of IFP adipocytes to HF feeding suggest that intraarticular adipocytes are subject to distinct spatiotemporal structural and metabolic regulation among fat pads.

Cellular Mechanisms Driving Sex Differences in Adipose Tissue Biology and Body Shape in Humans and Mouse Models

Sex differences in adipose tissue distribution and the metabolic, endocrine, and immune functions of different anatomical fat depots have been described, but they are incompletely documented in the literature. It is becoming increasingly clear that adipose depots serve distinct functions in males and females and have specific physiological roles. However, the mechanisms that regulate the size and function of specific adipose tissues in men and women remain poorly understood. New insights from mouse models have advanced our understanding of depot differences in adipose growth and remodeling via the proliferation and differentiation of adipose progenitors that can expand adipocyte number in the tissue or simply replace dysfunctional older and larger adipocytes. A limited ability of a depot to expand or remodel can lead to excessive adipocyte hypertrophy, which is often correlated with metabolic dysfunction. However, the relationship of adipocyte size and function varies by depot and sex. For example, femoral adipose tissues of premenopausal women appear to have a greater capacity for adipose expansion via hyperplasia and hypertrophy; although larger, these gluteal-femoral adipocytes remain insulin sensitive. The microenvironment of specific depots, including the composition of the extracellular matrix and cellular composition, as well as cell-autonomous genetic differences, influences sex- and depot-dependent metabolic and growth properties. Although there are some species differences, studies of the molecular and physiological determinants of sex differences in adipocyte growth and function in humans and rodents are both needed for understanding sex differences in health and disease.

Addressing the Role of Obesity in Endometrial Cancer Risk, Prevention, and Treatment

In sharp contrast to many other cancer types, the incidence and mortality of endometrial cancer continue to grow. This unfortunate trend is, in no small part, a result of the worldwide obesity epidemic. More than half of endometrial cancers are currently attributable to obesity, which is recognized as an independent risk factor for this disease. In this review, we identify the molecular mechanisms by which obesity and adipose tissue contribute to the pathogenesis of endometrial cancer. We further discuss the impact of obesity on the clinical management of the disease and examine the development of rational behavioral and pharmaceutical interventions aimed at reducing endometrial cancer risk, improving cancer outcomes, and preserving fertility in an increasingly younger population of patients with endometrial cancer.