Adipose cell size: importance in health and disease

Sex differences in white adipose tissue expansion: emerging molecular mechanisms

The escalating prevalence of individuals becoming overweight and obese is a rapidly rising global health problem, placing an enormous burden on health and economic systems worldwide. Whilst obesity has well described lifestyle drivers, there is also a significant and poorly understood component that is regulated by genetics. Furthermore, there is clear evidence for sexual dimorphism in obesity, where overall risk, degree, subtype and potential complications arising from obesity all differ between males and females. The molecular mechanisms that dictate these sex differences remain mostly uncharacterised. Many studies have demonstrated that this dimorphism is unable to be solely explained by changes in hormones and their nuclear receptors alone, and instead manifests from coordinated and highly regulated gene networks, both during development and throughout life. As we acquire more knowledge in this area from approaches such as large-scale genomic association studies, the more we appreciate the true complexity and heterogeneity of obesity. Nevertheless, over the past two decades, researchers have made enormous progress in this field, and some consistent and robust mechanisms continue to be established. In this review, we will discuss some of the proposed mechanisms underlying sexual dimorphism in obesity, and discuss some of the key regulators that influence this phenomenon.

Aging Affects KV7 Channels and Perivascular Adipose Tissue-Mediated Vascular Tone

Aging is an independent risk factor for hypertension, cardiovascular morbidity, and mortality. However, detailed mechanisms linking aging to cardiovascular disease are unclear. We studied the aging effects on the role of perivascular adipose tissue and downstream vasoconstriction targets, voltage-dependent K_V7 channels, and their pharmacological modulators (flupirtine, retigabine, QO58, and QO58-lysine) in a murine model. We assessed vascular function of young and old mesenteric arteries in vitro using wire myography and membrane potential measurements with sharp electrodes. We also performed bulk RNA sequencing and quantitative reverse transcription-polymerase chain reaction tests in mesenteric arteries and perivascular adipose tissue to elucidate molecular underpinnings of age-related phenotypes. Results revealed impaired perivascular adipose tissue-mediated control of vascular tone particularly via K_V7.3–5 channels with increased age through metabolic and inflammatory processes and release of perivascular adipose tissue-derived relaxation factors. Moreover, QO58 was identified as novel pharmacological vasodilator to activate XE991-sensitive KCNQ channels in old mesenteric arteries. Our data suggest that targeting inflammation and metabolism in perivascular adipose tissue could represent novel approaches to restore vascular function during aging. Furthermore, K_V7.3–5 channels represent a promising target in cardiovascular aging.

Differential Effects of Insulin-Deficient Diabetes Mellitus on Visceral vs. Subcutaneous Adipose Tissue-Multi-omics Insights From the Munich MIDY Pig Model

Adipose tissue (AT) is no longer considered to be responsible for energy storage only but is now recognized as a major endocrine organ that is distributed across different parts of the body and is actively involved in regulatory processes controlling energy homeostasis. Moreover, AT plays a crucial role in the development of metabolic disease such as diabetes. Recent evidence has shown that adipokines have the ability to regulate blood glucose levels and improve metabolic homeostasis. While AT has been studied extensively in the context of type 2 diabetes, less is known about how different AT types are affected by absolute insulin deficiency in type 1 or permanent neonatal diabetes mellitus. Here, we analyzed visceral and subcutaneous AT in a diabetic, insulin-deficient pig model (MIDY) and wild-type (WT) littermate controls by RNA sequencing and quantitative proteomics. Multi-omics analysis indicates a depot-specific dysregulation of crucial metabolic pathways in MIDY AT samples. We identified key proteins involved in glucose uptake and downstream signaling, lipogenesis, lipolysis and β-oxidation to be differentially regulated between visceral and subcutaneous AT in response to insulin deficiency. Proteins related to glycogenolysis, pyruvate metabolism, TCA cycle and lipogenesis were increased in subcutaneous AT, whereas β-oxidation-related proteins were increased in visceral AT from MIDY pigs, pointing at a regionally different metabolic adaptation to master energy stress arising from diminished glucose utilization in MIDY AT. Chronic, absolute insulin deficiency and hyperglycemia revealed fat depot-specific signatures using multi-omics analysis. The generated datasets are a valuable resource for further comparative and translational studies in clinical diabetes research.

PPARγ-A Factor Linking Metabolically Unhealthy Obesity with Placental Pathologies

Obesity is a known factor in the development of preeclampsia. This paper links adipose tissue pathologies with aberrant placental development and the resulting preeclampsia. PPARγ, a transcription factor from the ligand-activated nuclear hormone receptor family, appears to be one common aspect of both pathologies. It is the master regulator of adipogenesis in humans. At the same time, its aberrantly low activity has been observed in placental pathologies. Overweight and obesity are very serious health problems worldwide. They have negative effects on the overall mortality rate. Very importantly, they are also conducive to diseases linked to impaired placental development, including preeclampsia. More and more people in Europe are suffering from overweight (35.2%) and obesity (16%) (EUROSTAT 2021 data), some of them young women planning pregnancy. As a result, we will be increasingly encountering obese pregnant women with a considerable risk of placental development disorders, including preeclampsia. An appreciation of the mechanisms shared by these two conditions may assist in their prevention and treatment. Clearly, it should not be forgotten that health education concerning the need for a proper diet and physical activity is of utmost importance here.

Association of cell death mechanisms and fibrosis in visceral white adipose tissue with pathological alterations in the liver of morbidly obese patients with NAFLD

The role of visceral white adipose tissue (vWAT) in the progression of non-alcoholic liver disease (NAFLD) with its sub entities non-alcoholic fatty liver and steatohepatitis (NAFL; NASH) is underinvestigated. We thus explored mechanisms of fibrosis and regulated cell death in vWAT and liver tissue. In NAFLD, women displayed significantly more fibrosis in vWAT than men, and collagen 1α mRNA expression was significantly upregulated. The degrees of fibrosis in vWAT and liver tissue correlated significantly. The size of vWAT-resident adipocytes in NAFLD correlated negatively with the local degree of fibrosis. The extent of apoptosis, as measured by circulating M30, positively correlated with the degree of fibrosis in vWAT; necrosis-associated HMGB1 mRNA expression was significantly downregulated in vWAT and liver tissue; (iii) necroptosis-related RIPK-3 mRNA expression was significantly upregulated in vWAT; and autophagy-related LC3 mRNA expression was significantly downregulated in vWAT, while upregulated in the liver. Thus, the different cell death mechanisms in the vWAT in NAFLD are regulated independently while not ruling out their interaction. Fibrosis in vWAT may be associated with reduced adipocyte size and thus partially protective against NAFLD progression.

Abbreviations: ATG5: autophagy related 5; BAS: bariatric surgery; BMI: body mass index; ELISA: enzyme-linked immunosorbent assay; EtOH: ethanol; FFAs: free fatty acids; HCC: hepatocellular carcinoma; HMGB1: high-mobility group box 1 protein; IHC: immunohistochemistry; IL: interleukin; LC3: microtubule-associated proteins 1A/1B light chain 3B; M30: neoepitope K18Asp396-NE displayed on the caspase-cleaved keratin 18 fragment; M65: epitope present on both caspase-cleaved and intact keratin 18; NAFL: non-alcoholic fatty liver; NAFLD: non-alcoholic fatty liver disease; NAS: NAFLD activity score; NASH: non-alcoholic steatohepatitis; NLRP3: nucleotide-binding oligomerization domain, leucine-rich repeat and pyrin domain containing 3; qRT-PCR: quantitative real-time polymerase-chain reaction; r: Pearson’s correlation coefficient (r); r_s: Spearman’s rank correlation coefficient; RIPK3: receptor-interacting serine/threonine-protein kinase 3; T2DM: type 2 diabetes mellitus (T2DM); TUNEL: terminal deoxynucleotidyl transferase-mediated dUTP nick-end labelling; vWAT: visceral WAT; WAT: white adipose tissue

The Metabolic Significance of Intermuscular Adipose Tissue: Is IMAT a Friend or a Foe to Metabolic Health?

Adipose tissues are not homogeneous and show site-specific properties. An elusive and understudied adipose tissue depot, most likely due to its limited accessibility, is the intermuscular adipose tissue (IMAT) depot. Adipose tissue is a pliable organ with the ability to adapt to its physiological context, yet whether that adaptation is harmful or beneficial in the IMAT depot remains to be explored in humans. Potential reasons for IMAT accumulation in humans being deleterious or beneficial include 1) sex and related circulating hormone levels, 2) race and ethnicity, and 3) lifestyle factors (e.g., diet and physical activity level). IMAT quantity per se may not be the driving factor in the etiology of insulin resistance and type 2 diabetes, but rather the quality of the IMAT itself is the true puppeteer. Adipose tissue quality likely influences its secreted factors, which are also likely to influence metabolism of surrounding tissues. The advent of molecular assessments such as transcriptome sequencing (RNAseq), assay for transposase-accessible chromatin using sequencing (ATACseq), and DNA methylation at the single-cell and single-nucleus levels, as well as the potential for ultrasound-guided biopsies specifically for IMAT, will permit more sophisticated investigations of human IMAT and dramatically advance our understanding of this enigmatic adipose tissue.

Translational products of adipose tissue-derived mesenchymal stem cells: Bench to bedside applications

With developments in the field of tissue engineering and regenerative medicine, the use of biological products for the treatment of various disorders has come into the limelight among researchers and clinicians. Among all the available biological tissues, research and exploration of adipose tissue have become more robust. Adipose tissue engineering aims to develop by-products and their substitutes for their regenerative and immunomodulatory potential. The use of biodegradable scaffolds along with adipose tissue products has a major role in cellular growth, proliferation, and differentiation. Adipose tissue, apart from being the powerhouse of energy storage, also functions as the largest endocrine organ, with the release of various adipokines. The progenitor cells among the heterogeneous population in the adipose tissue are of paramount importance as they determine the capacity of regeneration of these tissues. The results of adipose-derived stem-cell assisted fat grafting to provide numerous growth factors and adipokines that improve vasculogenesis, fat graft integration, and survival within the recipient tissue and promote the regeneration of tissue are promising. Adipose tissue gives rise to various by-products upon processing. This article highlights the significance and the usage of various adipose tissue by-products, their individual characteristics, and their clinical applications.

The Importance of Food for Endotoxemia and an Inflammatory Response

Bacterial endotoxin is a potent inflammatory antigen abundant in the human intestine. Endotoxins circulate in the blood at low concentrations in all healthy individuals. Elevated levels of circulatory endotoxins may cause inflammation with the development of chronic disease, either affecting metabolism, neurological disease, or resistance to viral and bacterial infections. The most important endotoxin is LPS, being a superantigen. In this narrative review, the effect of various food components to postprandially elevate circulating LPS and inflammatory markers is described. There is evidence that the intake of food enriched in fat, in particular saturated fat, may elevate LPS and pro-inflammatory markers. This occurs in both normal-weight and obese subjects. In obese subjects, inflammatory markers are already elevated before meal consumption. The importance of food choice for endotoxemia and inflammatory response is discussed.

Liver Fat, Adipose Tissue, and Body Composition Changes After Switching from a Protease Inhibitor or Efavirenz to Raltegravir

Integrase inhibitors appear to increase body weight, but paradoxically some data indicate that raltegravir (RAL) may decrease liver fat. Our objective was to study the effects of switching from a protease inhibitor (PI) or efavirenz (EFV) to RAL on liver fat, body composition, and metabolic parameters among people living with HIV (PLWH) with high risk for nonalcoholic fatty liver disease (NAFLD). We randomized overweight PLWH with signs of metabolic syndrome to switch a PI or EFV to RAL (n = 19) or to continue unchanged antiretroviral therapy (control, n = 24) for 24 weeks. Liver fat was measured by magnetic resonance spectroscopy (MRS), body composition by magnetic resonance imaging, and bioimpedance analysis; subcutaneous fat biopsies were obtained. Median (interquartile range) liver fat content was normal in RAL 2.3% (1.1-6.0) and control 3.1% (1.6-7.3) group at baseline. Liver fat and visceral adipose tissue remained unchanged during the study. Body weight [from 85.9 kg (76.1-97.7) to 89.3 (78.7-98.7), p = 0.019], body fat mass [from 20.3 kg (14.6-29.7) to 22.7 (17.0-29.7), p = 0.015], and subcutaneous adipose tissue (SAT) volume [from 3979 mL (2068-6468) to 4043 (2206-6433), p = 0.048] increased, yet, adipocyte size [from 564 pL (437-733) to 478 (423-587), p = 0.019] decreased in RAL but remained unchanged in control group. Circulating lipids and inflammatory markers improved in RAL compared to control group. The median liver fat measured by MRS was unexpectedly within normal range in this relatively small study population with presumably high risk for NAFLD contradicting high prevalence of NAFLD reported with other methods. Despite weight gain, increase in SAT together with decreased adipocyte size and reduced inflammation may reflect improved adipose tissue function. Clinical Trial Registration number: NCT03374358.

Depot and sex-specific implications for adipose tissue expandability and functional traits in adulthood of late prenatal and early postnatal malnutrition in a precocial sheep model

The aim was to investigate long‐term, tissue and sex‐specific impacts of pre and postnatal malnutrition on expandability and functional traits of different adipose tissues. Twin‐pregnant ewes were fed NORM (~requirements), LOW (50% of NORM) or HIGH (150%/110% of energy/protein) diets the last 6 weeks prepartum (term ~147‐days). Lambs received moderate, low‐fat (CONV) or high‐carbohydrate‐high‐fat (HCHF) diets from 3 days until 6 months of age, and thereafter CONV diet. At 2½ years of age (adulthood), histomorphometric and gene expression patterns were characterized in subcutaneous (SUB), perirenal (PER), mesenteric (MES), and epicardial (EPI) adipose tissues. SUB had sex‐specific (♂<♀) upper‐limits for adipocyte size and cell‐number indices, irrespective of early life nutrition. PER mass and contents of adipocytes were highest in females and HIGH♂, whereas adipocyte cross‐sectional area was lowest in LOW♂. Pre/postnatal nutrition affected gene expression sex‐specifically in SUB + PER, but unrelated to morphological changes. In PER, LOW/LOW♂ were specific targets of gene expression changes. EPI was affected by postnatal nutrition, and HCHF sheep had enlarged adipocytes and upregulated expressions for adipogenic and lipogenic genes. Conclusion: upper‐limits for SUB expandability were markedly lower in males. Major targets for prenatal malnutrition were PER and males. LOW♂ had the lowest PER expandability, whereas HIGH♂ had an adaptive advantage due to increased hypertrophic ability equivalent to females. Fixed expandability in SUB meant PER became a determining factor for MES and ectopic fat deposition, rendering LOW♂ particularly predisposed for obesity‐associated metabolic risks. EPI, in contrast to other tissues, was targeted particularly by early postnatal obesity, resulting in adipocyte hypertrophy in adulthood.

3D Adipose Tissue Culture Links the Organotypic Microenvironment to Improved Adipogenesis

Obesity and type 2 diabetes are strongly associated with adipose tissue dysfunction and impaired adipogenesis. Understanding the molecular underpinnings that control adipogenesis is thus of fundamental importance for the development of novel therapeutics against metabolic disorders. However, translational approaches are hampered as current models do not accurately recapitulate adipogenesis. Here, a scaffold-free versatile 3D adipocyte culture platform with chemically defined conditions is presented in which primary human preadipocytes accurately recapitulate adipogenesis. Following differentiation, multi-omics profiling and functional tests demonstrate that 3D adipocyte cultures feature mature molecular and cellular phenotypes similar to freshly isolated mature adipocytes. Spheroids exhibit physiologically relevant gene expression signatures with 4704 differentially expressed genes compared to conventional 2D cultures (false discovery rate < 0.05), including the concerted expression of factors shaping the adipogenic niche. Furthermore, lipid profiles of >1000 lipid species closely resemble patterns of the corresponding isogenic mature adipocytes in vivo (R2 = 0.97). Integration of multi-omics signatures with analyses of the activity profiles of 503 transcription factors using global promoter motif inference reveals a complex signaling network, involving YAP, Hedgehog, and TGFβ signaling, that links the organotypic microenvironment in 3D culture to the activation and reinforcement of PPARγ and CEBP activity resulting in improved adipogenesis.

Role of natriuretic peptides in the cardiovascular-adipose communication: a tale of two organs

Natriuretic peptides have long been known for their cardiovascular function. However, a growing body of evidence emphasizes the role of natriuretic peptides in the energy metabolism of several substrates in humans and animals, thus interrelating the heart, as an endocrine organ, with various insulin-sensitive tissues and organs such as adipose tissue, muscle skeletal, and liver. Adipose tissue dysfunction is associated with altered regulation of the natriuretic peptide system, also indicated as a natriuretic disability. Evidence points to a contribution of this natriuretic disability to the development of obesity, type 2 diabetes mellitus, and cardiometabolic complications; although the causal relationship is not fully understood at present. However, targeting the natriuretic peptide pathway may improve metabolic health in obesity and type 2 diabetes mellitus. This review will focus on the current literature on the metabolic functions of natriuretic peptides with emphasis on lipid metabolism and insulin sensitivity. Natriuretic peptide system alterations could be proposed as one of the linking mechanisms between adipose tissue dysfunction and cardiovascular disease.

The Effects of High-Protein Diet and Resistance Training on Glucose Control and Inflammatory Profile of Visceral Adipose Tissue in Rats

High-protein diets (HPDs) are widely accepted as a way to stimulate muscle protein synthesis when combined with resistance training (RT). However, the effects of HPDs on adipose tissue plasticity and local inflammation are yet to be determined. This study investigated the impact of HPDs on glucose control, adipocyte size, and epididymal adipose inflammatory biomarkers in resistance-trained rats. Eighteen Wistar rats were randomly assigned to four groups: normal-protein (NPD; 17% protein total dietary intake) and HPD (26.1% protein) without RT and NPD and HPD with RT. Trained groups received RT for 12 weeks with weights secured to their tails. Glucose and insulin tolerance tests, adipocyte size, and an array of cytokines were determined. While HPD without RT induced glucose intolerance, enlarged adipocytes, and increased TNF-α, MCP-1, and IL1-β levels in epididymal adipose tissue (p < 0.05), RT diminished these deleterious effects, with the HPD + RT group displaying improved blood glucose control without inflammatory cytokine increases in epididymal adipose tissue (p < 0.05). Furthermore, RT increased glutathione expression independent of diet (p < 0.05). RT may offer protection against adipocyte hypertrophy, pro-inflammatory states, and glucose intolerance during HPDs. The results highlight the potential protective effects of RT to mitigate the maladaptive effects of HPDs.

PPA1 Regulates Systemic Insulin Sensitivity by Maintaining Adipocyte Mitochondria Function as a Novel PPARγ Target Gene

Downregulation of mitochondrial function in adipose tissue is considered as one important driver for the development of obesity-associated metabolic disorders. Inorganic pyrophosphatase 1 (PPA1) is an enzyme that catalyzes the hydrolysis of inorganic pyrophosphate to inorganic phosphate and is required for anabolism to take place in cells. Although alteration of PPA1 has been related to some diseases, the importance of PPA1 in metabolic syndromes has never been discussed. In this study, we found that global PPA1 knockout mice (PPA1^+/-) showed impaired glucose tolerance and severe insulin resistance under high-fat-diet feeding. In addition, impaired adipose tissue development and ectopic lipid accumulation were observed. Conversely, overexpression of PPA1 in adipose tissue by adeno-associated virus injection can partly reverse the metabolic disorders in PPA1^+/- mice, suggesting that impaired adipose tissue function is responsible for the metabolic disorders observed in PPA1^+/- mice. Mechanistic studies revealed that PPA1 acted as a PPARγ target gene to maintain mitochondrial function in adipocytes. Furthermore, specific knockdown of PPA1 in fat body of Drosophila led to impaired mitochondria morphology, decreased lipid storage, and made Drosophila more sensitive to starvation. In conclusion, for the first time, our findings demonstrate the importance of PPA1 in maintaining adipose tissue function and whole-body metabolic homeostasis.

Transcriptomics analysis of differentially expressed genes in subcutaneous and perirenal adipose tissue of sheep as affected by their pre- and early postnatal malnutrition histories

BACKGROUND

Early life malnutrition is known to target adipose tissue with varying impact depending on timing of the insult. This study aimed to identify differentially expressed genes in subcutaneous (SUB) and perirenal (PER) adipose tissue of 2.5-years old sheep to elucidate the biology underlying differential impacts of late gestation versus early postnatal malnutrition on functional development of adipose tissues. Adipose tissues were obtained from 37 adult sheep born as twins to dams fed either NORM (fulfilling energy and protein requirements), LOW (50% of NORM) or HIGH (110% of protein and 150% of energy requirements) diets in the last 6-weeks of gestation. From day 3 to 6 months of age, lambs were fed high-carbohydrate-high-fat (HCHF) or moderate low-fat (CONV) diets, and thereafter the same moderate low-fat diet.

RESULTS

The gene expression profile of SUB in the adult sheep was not affected by the pre- or early postnatal nutrition history. In PER, 993 and 186 differentially expressed genes (DEGs) were identified in LOW versus HIGH and NORM, respectively, but no DEG was found between HIGH and NORM. DEGs identified in the mismatched pre- and postnatal nutrition groups LOW-HCHF (101) and HIGH-HCHF (192) were largely downregulated compared to NORM-CONV. Out of 831 DEGs, 595 and 236 were up- and downregulated in HCHF versus CONV, respectively. The functional enrichment analyses revealed that transmembrane (ion) transport activities, motor activities related to cytoskeletal and spermatozoa function (microtubules and the cytoskeletal motor protein, dynein), and responsiveness to the (micro) environmental extracellular conditions, including endocrine and nervous stimuli were enriched in the DEGs of LOW versus HIGH and NORM. We confirmed that mismatched pre- and postnatal feeding was associated with long-term programming of adipose tissue remodeling and immunity-related pathways. In agreement with phenotypic measurements, early postnatal HCHF feeding targeted pathways involved in kidney cell differentiation, and mismatched LOW-HCHF sheep had specific impairments in cholesterol metabolism pathways.

CONCLUSIONS

Both pre- and postnatal malnutrition differentially programmed (patho-) physiological pathways with implications for adipose functional development associated with metabolic dysfunctions, and PER was a major target.

Histological and transcriptomic analysis of adipose and muscle of dairy calves supplemented with 5-hydroxytryptophan

In mammals, peripheral serotonin is involved in regulating energy balance. Herein, we characterized the transcriptomic profile and microstructure of adipose and muscle in pre-weaned calves with increased circulating serotonin. Holstein bull calves (21 ± 2 days old) were fed milk replacer supplemented with saline (CON, 8 mL/day n = 4) or 5-hydroxytryptophan (5-HTP, 90 mg/day, n = 4) for 10 consecutive days. Calves were euthanized on d10 to harvest adipose and muscle for RNA-Sequencing and histological analyses. Twenty-two genes were differentially expressed in adipose, and 33 in muscle. Notably, Interferon gamma inducible protein-47 was highly expressed and upregulated in muscle and adipose (avg. log FC = 6.5). Enriched pathways in adipose tissue revealed serotonin’s participation in lipid metabolism and PPAR signaling. In muscle, enriched pathways were related to histone acetyltransferase binding, Jak-STAT signaling, PI3K-Akt signaling and cell proliferation. Supplementation of 5-HTP increased cell proliferation and total cell number in adipose and muscle. Adipocyte surface area was smaller and muscle fiber area was not different in the 5-HTP group. Manipulating the serotonin pathway, through oral supplementation of 5-HTP, influences signaling pathways and cellular processes in adipose and muscle related to endocrine and metabolic functions which might translate into improvements in calf growth and development.

Toward Adipose Tissue Engineering Using Thiol-Norbornene Photo-Crosslinkable Gelatin Hydrogels

Nowadays, breast implants, lipofilling, and microsurgical free tissue transfer are the most often applied procedures to repair soft tissue defects resulting from mastectomies/lumpectomies following breast cancer. Due to the drawbacks and limitations associated with these conventional clinical practices, there is a need for alternative reconstructive strategies. The development of biomimetic materials able to promote cell proliferation and adipogenic differentiation has gained increasing attention in the context of adipose reconstructive purposes. Herein, thiol-norbornene crosslinkable gelatin-based materials were developed and benchmarked to the current commonly applied methacryloyl-modified gelatin (GelMA) with different degrees of substitutions focussing on bottom-up tissue engineering. The developed hydrogels resulted in similar gel fractions, swelling, and in vitro biodegradation properties compared to the benchmark materials. Furthermore, the thiol-ene hydrogels exhibited mechanical properties closer to those of native fatty tissue compared to GelMA. The mechanical cues of the equimolar GelNB DS55% + GelSH DS75% composition resulted not only in similar biocompatibility but also, more importantly, in superior differentiation of the encapsulated cells into the adipogenic lineage, as compared to GelMA. It can be concluded that the photo-crosslinkable thiol-ene systems offer a promising strategy toward adipose tissue engineering through cell encapsulation compared to the benchmark GelMA.

Lipid and glucose metabolism in white adipocytes: pathways, dysfunction and therapeutics

In mammals, the white adipocyte is a cell type that is specialized for storage of energy (in the form of triacylglycerols) and for energy mobilization (as fatty acids). White adipocyte metabolism confers an essential role to adipose tissue in whole-body homeostasis. Dysfunction in white adipocyte metabolism is a cardinal event in the development of insulin resistance and associated disorders. This Review focuses on our current understanding of lipid and glucose metabolic pathways in the white adipocyte. We survey recent advances in humans on the importance of adipocyte hypertrophy and on the in vivo turnover of adipocytes and stored lipids. At the molecular level, the identification of novel regulators and of the interplay between metabolic pathways explains the fine-tuning between the anabolic and catabolic fates of fatty acids and glucose in different physiological states. We also examine the metabolic alterations involved in the genesis of obesity-associated metabolic disorders, lipodystrophic states, cancers and cancer-associated cachexia. New challenges include defining the heterogeneity of white adipocytes in different anatomical locations throughout the lifespan and investigating the importance of rhythmic processes. Targeting white fat metabolism offers opportunities for improved patient stratification and a wide, yet unexploited, range of therapeutic opportunities.

Short-term fasting reshapes fat tissue

Intermittent fasting, which can effectively reduce obesity and improve the related metabolic syndrome has become an exciting research area in recent years. Adipose tissue is pivotal in regulating the metabolism and determining the occurrence of obesity. In the current study, we aimed to investigate the effects of acute fasting (AF) on fat tissue. Mice were subjected to AF for 36 h, receiving normal chow (low-fat diet [LFD]) or a high-fat diet (HFD), with free ad libitum access to drinking water, and those fed on free-diet counterparts without fasting serveding as controls. We found that AF obviously reshaped the morphology of fat tissue (WAT) and promoted the beiging of white adipose tissue in both LFD- and HFD-fed mice. AF principally improved the lipid metabolism, and increased the M2- polarization of macrophages in WAT white fat tissue of HFD-fed mice. Interestingly, we found that AF dramatically upregulated Sirt5 expression levels and fat tissue succinylation, suggesting that AF-induced beneficial effects on fat might occur via the regulation of Sirt5 levels and altered succinylation in fatty tissues. Our study clearly showed the remodeling function of adipose tissue during AF; in terms of mechanism, the regulation of succinylation levels by AF might provide new insights into the mechanism(s) underlying the improvement in fat metabolism by energy restriction.

Exceptional stability of a perilipin on lipid droplets depends on its polar residues, suggesting multimeric assembly

Numerous proteins target lipid droplets (LDs) through amphipathic helices (AHs). It is generally assumed that AHs insert bulky hydrophobic residues in packing defects at the LD surface. However, this model does not explain the targeting of perilipins, the most abundant and specific amphipathic proteins of LDs, which are weakly hydrophobic. A striking example is Plin4, whose gigantic and repetitive AH lacks bulky hydrophobic residues. Using a range of complementary approaches, we show that Plin4 forms a remarkably immobile and stable protein layer at the surface of cellular or in vitro generated oil droplets, and decreases LD size. Plin4 AH stability on LDs is exquisitely sensitive to the nature and distribution of its polar residues. These results suggest that Plin4 forms stable arrangements of adjacent AHs via polar/electrostatic interactions, reminiscent of the organization of apolipoproteins in lipoprotein particles, thus pointing to a general mechanism of AH stabilization via lateral interactions.

Unbiased analysis of obesity related, fat depot specific changes of adipocyte volumes and numbers using light sheet fluorescence microscopy

In translational obesity research, objective assessment of adipocyte sizes and numbers is essential to characterize histomorphological alterations linked to obesity, and to evaluate the efficacies of experimental medicinal or dietetic interventions. Design-based quantitative stereological techniques based on the analysis of 2D-histological sections provide unbiased estimates of relevant 3D-parameters of adipocyte morphology, but often involve complex and time-consuming tissue processing and analysis steps. Here we report the application of direct 3D light sheet fluorescence microscopy (LSFM) for effective and accurate analysis of adipocyte volumes and numbers in optically cleared adipose tissue samples from a porcine model of diet-induced obesity (DIO). Subcutaneous and visceral adipose tissue samples from DIO-minipigs and lean controls were systematically randomly sampled, optically cleared with 3DISCO (3-dimensional imaging of solvent cleared organs), stained with eosin, and subjected to LSFM for detection of adipocyte cell membrane autofluorescence. Individual adipocytes were unbiasedly sampled in digital 3D reconstructions of the adipose tissue samples, and their individual cell volumes were directly measured by automated digital image analysis. Adipocyte numbers and mean volumes obtained by LSFM analysis did not significantly differ from the corresponding values obtained by unbiased quantitative stereological analysis techniques performed on the same samples, thus proving the applicability of LSFM for efficient analysis of relevant morphological adipocyte parameters. The results of the present study demonstrate an adipose tissue depot specific plasticity of adipocyte growth responses to nutrient oversupply. This was characterized by an exclusively hypertrophic growth of visceral adipocytes, whereas adipocytes in subcutaneous fat tissue depots also displayed a marked (hyperplastic) increase in cell number. LSFM allows for accurate and efficient determination of relevant quantitative morphological adipocyte parameters. The applied stereological methods and LSFM protocols are described in detail and can serve as a guideline for unbiased quantitative morphological analyses of adipocytes in other studies and species.

Effect of Forskolin on Body Weight, Glucose Metabolism and Adipocyte Size of Diet-Induced Obesity in Mice

The purpose of this study was to investigate the effects of forskolin on body weight, glucose metabolism and fat cell diameter in high-fat diet-induced obese mice. Four-week-old male mice (C57BL/6) were randomly assigned to 1 of 3 treatment groups: a high-fat diet plus 5% dimethyl sulfoxide (vehicle), high-fat diet plus 2 mg/kg of forskolin (dissolved in 5% dimethyl sulfoxide) and high-fat diet plus 4 mg/kg of forskolin (dissolved in 5% dimethyl sulfoxide). Forskolin or dimethyl sulfoxide was administered intraperitoneally every two days. The results indicated that no significant difference was observed in the body weight, feed intake and serum lipid parameters among groups at 20 weeks of age. The blood glucose levels were significantly reduced in the groups treated with 2 mg/kg of forskolin before glucose tolerance test. Forskolin administration linearly decreased blood glucose levels of high-fat diet-fed mice at 90 min and total area under curve (AUC) after insulin tolerance test. The subcutaneous adipocyte diameter was significantly reduced in the groups treated with 2 mg/kg of forskolin. Forskolin administration linearly reduced the gonadal adipocyte diameter of high-fat diet-fed mice. Forskolin significantly reduced the differentiation of murine mesenchymal stem cells into adipocytes and this was accompanied by a decrease in intracellular triglyceride content and an increase in glycerol concentration in the culture medium. The subcutaneous adipocyte diameter, gonadal adipocyte diameter and total AUC of insulin tolerance test were moderately negatively correlated with the concentration of forskolin in the high-fat diet-induced obese model. These results demonstrate that forskolin can regulate glucose metabolism and reduce fat cell diameter of high-fat diet-fed mice and inhibit the adipocyte differentiation of murine mesenchymal stem cells.

Chemically Defined Xeno- and Serum-Free Cell Culture Medium to Grow Human Adipose Stem Cells

Adipose tissue is an abundant source of stem cells. However, liposuction cannot yield cell quantities sufficient for direct applications in regenerative medicine. Therefore, the development of GMP-compliant ex vivo expansion protocols is required to ensure the production of a "cell drug" that is safe, reproducible, and cost-effective. Thus, we developed our own basal defined xeno- and serum-free cell culture medium (UrSuppe), specifically formulated to grow human adipose stem cells (hASCs). With this medium, we can directly culture the stromal vascular fraction (SVF) cells in defined cell culture conditions to obtain hASCs. Cells proliferate while remaining undifferentiated, as shown by Flow Cytometry (FACS), Quantitative Reverse Transcription PCR (RT-qPCR) assays, and their secretion products. Using the UrSuppe cell culture medium, maximum cell densities between 0.51 and 0.80 × 10⁵ cells/cm² (=2.55-4.00 × 10⁵ cells/mL) were obtained. As the expansion of hASCs represents only the first step in a cell therapeutic protocol or further basic research studies, we formulated two chemically defined media to differentiate the expanded hASCs in white or beige/brown adipocytes. These new media could help translate research projects into the clinical application of hASCs and study ex vivo the biology in healthy and dysfunctional states of adipocytes and their precursors. Following the cell culture system developers' practice and obvious reasons related to the formulas' patentability, the defined media's composition will not be disclosed in this study.

Roflumilast Suppresses Adipogenic Differentiation via AMPK Mediated Pathway

Obesity and related disorders have increasingly become global health problems over the years. In recent years, obesity has been recognized as the most important risk factor for a variety of diseases including cardiovascular diseases, type 2 diabetes, steatohepatitis, and cancer. The medical anti-obesity treatment is to intervene in the metabolic process of adipocytes by suppressing adipogenesis and promoting lipolysis. The Phosphodiesterase-4 (PDE4) pathway is involved in fat mass control and metabolic regulation. The present study aimed to investigate the effects of Roflumilast, a selective PDE4 inhibitor, on the differentiation of 3T3-L1 cells and the high fat diet-induced obesity in mice. We showed that treatment with Roflumilast inhibited lipid accumulation and triglycerides storage in mature 3T3-L1 cells, suggesting that Roflumilast suppressed adipogenesis. Mechanistically, we found that Roflumilast decreased the differentiation-induced expression of the adipogenesis genes including SREBP1C, FABP4, and Glut4, as well as their regulators including PPAR-γ and C/EBPα. Moreover, we proved that the effect of Roflumilast was dependent on the activation of the metabolic regulator AMPKα. The treatment with Roflumilast remarkably decreased the animals' body weight, visceral adipose tissue weight, and adipocyte size in high fat diet-induced obese mice. In conclusion, our study revealed that Roflumilast suppressed adipogenesis and promoted lipolysis in cell culture and mice models via AMPK-mediated inhibition of PPAR-γ and C/EBPα. These findings imply roflumilast could have therapeutic potential in obesity-related diseases.

Improvement of Hypertriglyceridemia by Roasted Nelumbinis folium in High Fat/High Cholesterol Diet Rat Model

Hypertriglyceridemia is a condition characterized by high triglyceride levels and is a major risk factor for the development of cardiovascular diseases. The present study was designed to investigate the inhibitory effect of roasted Nelumbinis folium (RN), which is a medicinal substance produced by heating lotus leaves, on lipid metabolism in high fat/cholesterol (HFC) diet-induced hypertriglyceridemia. Except for those in the control group, Sprague–Dawley rats were fed an HFC diet for four weeks to induce hypertriglyceridemia. During the next nine weeks, the control, regular diet; HFC, HFC diet, FLU, fluvastatin (3 mg/kg/day); RNL, RN (100 mg/kg/day); RNH, RN (200 mg/kg/day) were orally administered together with the diet, and the experiments were conducted for a total of 13 weeks. The weight of the epididymal adipose tissue, liver, and heart of rats in the HFC diet group significantly increased compared to those in the control group but improved in the RN-treated group. It was also confirmed that vascular function, which is damaged by an HFC diet, was improved after RN treatment. The levels of insulin, glucose, triglycerides, total cholesterol, and low-density lipoprotein increased in the HFC diet group compared to those in the control group, while the administration of RN attenuated these parameters. In addition, the administration of RN significantly reduced the gene expression of both LXR and SREBP-1, which indicated the inhibitory effect of the biosynthesis of triglycerides caused by RN. The results indicated that RN administration resulted in an improvement in the overall lipid metabolism and a decrease in the concentration of triglycerides in the HFC diet-induced rat model of hypertriglyceridemia. Therefore, our findings suggest that the RN can be a candidate material to provide a new direction for treating hypertriglyceridemia.

Differential Effect of Four-Week Feeding of Different Dietary Fats on the Accumulation of Fat and the Cholesterol and Triglyceride Contents in the Different Fat Depots

The aim of the present study was to determine the effects of feeding of a high-fat diet containing different types of lipids for four weeks on the cholesterol and triglyceride contents of different fat depots and on body temperature in rats. Four groups of adult rats were fed 10% fat, containing either beef tallow, safflower oil, or fish oil, respectively, as well as a normal rodent diet with 4% fat, for four weeks. The rats on normal rodent diet consumed significantly more food and water than the rats in the other three groups. Rectal temperature increased only after four-week feeding with safflower oil fat. Increased fat deposition and adipocyte size were observed in rats fed safflower oil and beef tallow. In all fat pads of safflower oil-fed rats, cholesterol content was significantly higher than the other three groups. Feeding of beef tallow increased triglyceride depot without increasing cholesterol content. The rats fed fish oil had significantly less triglyceride and cholesterol deposition in adipose tissues than the rats fed safflower oil or beef tallow. These results clearly demonstrated the differences in fat deposition, adipocyte size and number, triglyceride and cholesterol accumulation in fat cells are dependent on the dietary lipid composition.

Influence of Nutritional Intake of Carbohydrates on Mitochondrial Structure, Dynamics, and Functions during Adipogenesis

Obesity is an alarming yet increasing phenomenon worldwide, and more effective obesity management strategies have become essential. In addition to the numerous anti-adipogenic treatments promising a restauration of a healthy white adipose tissue (WAT) function, numerous studies reported on the critical role of nutritional parameters in obesity development. In a metabolic disorder context, a better control of nutrient intake is a key step in slowing down adipogenesis and therefore obesity. Of interest, the effect on WAT remodeling deserves deeper investigations. Among the different actors of WAT plasticity, the mitochondrial network plays a central role due to its dynamics and essential cellular functions. Hence, the present in vitro study, conducted on the 3T3-L1 cell line, aimed at evaluating the incidence of modulating the carbohydrates intake on adipogenesis through an integrated assessment of mitochondrial structure, dynamics, and functions-correlated changes. For this purpose, our experimental strategy was to compare the occurrence of adipogenesis in 3T3-L1 cells cultured either in a high-glucose (HG) medium (25 mM) or in a low-glucose (LG) medium (5 mM) supplemented with equivalent galactose (GAL) levels (20 mM). The present LG-GAL condition was associated, in differentiating adipocytes, to a reduced lipid droplet network, lower expressions of early and late adipogenic genes and proteins, an increased mitochondrial network with higher biogenesis marker expression, an equilibrium in the mitochondrial fusion/fission pattern, and a decreased expression of mitochondrial metabolic overload protein markers. Therefore, those main findings show a clear effect of modulating glucose accessibility on 3T3-L1 adipogenesis through a combined effect of adipogenesis modulation and overall improvement of the mitochondrial health status. This nutritional approach offers promising opportunities in the control and prevention of obesity.

Hyperplasia and accelerated hypertrophy of marrow adipocytes with knee immobilization were sustained despite remobilization

Skeletal disuse can cause an accumulation of bone marrow adipose tissue (MAT) characterized by a combination of marrow adipocyte hyperplasia and/or hypertrophy. The malleability of MAT accumulation and of the hyperplasia and hypertrophy upon remobilization is unknown. In this study, we showed extensive hyperplasia and accelerated hypertrophy of bone marrow adipocytes in the proximal tibia epiphysis of rat knees immobilized for durations between 1 and 32 wk. Similar histomorphometric measures of adipocytes carried out in unoperated controls allowed distinguishing the effects of immobilization from the effects of aging. Although both knee immobilization and aging led to adipocyte hypertrophy, adipocyte hyperplasia was the hallmark signature effect of immobilization on MAT. Both bone marrow adipocyte hyperplasia and hypertrophy were sustained despite knee remobilization for durations up to four times the duration of immobilization. These results suggest that adipocyte hyperplasia is the predominant mechanism explaining MAT accumulation in skeletal disuse. In this model, the changes were unremitting for the investigated time points. Investigating the cellular and molecular mechanisms of marrow adipocyte mechanoregulation will be important to better understand how adipocytes adapt to changes in mechanical environments.NEW & NOTEWORTHY This longitudinal study elucidates the response of marrow adipose tissue adipocytes in weight-bearing joints to changes in different mechanical environments, and we provide insight on the malleability of the changes over time. In a rat animal model, knee immobilization induced hyperplasia and accelerated the age-dependent hypertrophy of adipocytes. Changes in adipocyte number and size were sustained despite unassisted remobilization. Multimodal distributions of cell size were characteristic of bone marrow adipocytes.

Impact of weight loss and partial weight regain on immune cell and inflammatory markers in adipose tissue in male mice

Weight fluctuations are common among individuals with obesity and are associated with increased morbidity. We examined adipose tissue immune and inflammatory markers in mice following weight loss and partial weight regain. Male C57BL/6 mice were randomized into four groups (n = 8-10/group): low-fat diet for 32 wk (LFD), high-fat diet for 32 wk (HFD), LFD for 28 wk and then changed to a HFD for 4 wk (LFD→H), and HFD for 21 wk and then changed to LFD for 7 wk and then changed to HFD for 4 wk (HFD→L→H). LFD→H and HFD→L→H mice did not differ in body weight, fat mass, or fat percentage; however, these parameters were greater than in LFD (P < 0.05) but lower than in HFD (P < 0.05). HFD→L→H mice had smaller adipocytes than HFD and LFD→H (P < 0.05) but not LFD mice. Expressions of CD11c and CD8a genes were elevated in epididymal fat of HFD→L→H compared with LFD→H and LFD (P < 0.05)mice. However, CD11c was lower in HFD→L→H than in HFD mice (P < 0.05), but there was no difference in CD8a between these groups. TNFα and IFNγ expressions were increased in HFD→L→H compared with LFD and LFD→H mice (P < 0.05), although HFD→L→H had lower expression of these cytokines than HFD (P < 0.05). IL-1β was greater in HFD→L→H compared with LFD (P < 0.05) but was not different from LFD→H or HFD mice. Monocyte chemoattractant protein-1 was lower (P < 0.05) in HFD→L→H than in LFD→H. These data reinforce the importance of maintaining a body weight in the range that is recommended for optimal health to reduce immune and inflammatory perturbations associated with obesity.NEW & NOTEWORTHY We examined the immune and inflammatory status of adipose tissue in mice after they underwent weight loss followed by partial weight regain. We show an increase in selected immune cells and inflammatory mediators, in high-fat diet-fed mice that had prior exposure to a high-fat diet. Although weight fluctuations appear to exacerbate immune cell abundance and inflammation in adipose tissue, severity is less than in mice that were exposed to sustained high-fat diet feedings.

Administration of small-molecule guanabenz acetate attenuates fatty liver and hyperglycemia associated with obesity

Nonalcoholic fatty liver disease (NAFLD) is characterized by excessive accumulation of hepatic triglycerides (TG) and hyperglycemia arising due to persistent insulin resistance, and is profoundly linked to obesity. However, there is currently no established treatment for NAFLD in obese human subjects. We previously isolated Helz2, the expression of which was upregulated in human and mouse NAFLD, and its deletion activated the hepatic expression of functional leptin receptor long form (Leprb) and suppressed NAFLD development and body weight (BW) gain in obese mice. A high-throughput assay of small-molecule drugs revealed that guanabenz acetate (Ga), originally used to treat hypertension, possesses a high affinity constant against HELZ2, and its administration activates LEPRB expression in HepG2 cells in vitro. The chronic oral administration of Ga shows the selective leptin sensitization in the liver via upregulation of hepatic Leprb expression, which affects expression of genes involved in lipogenesis and fatty acid β-oxidation and diminishes hepatocyte hypertrophy with droplets enriched in TG in high-fat diet-induced obese mice. This activity significantly improves insulin resistance to decrease hyperglycemia and hepatocyte and adipocyte weights, resulting in BW reduction without reducing food intake. Regarding drug repositioning, Ga has the potential to effectively treat NAFLD and hyperglycemia in obese patients.

Adipose tissue macrophage burden, systemic inflammation, and insulin resistance

Adipose tissue inflammation, as defined by macrophage accumulation, is proposed to cause insulin resistance and systemic inflammation. Because the strength of this relationship for humans is unclear, we tested whether adipose tissue macrophage (ATM) burden is correlated with these health indicators. Using immunohistochemistry, we measured abdominal subcutaneous CD68+ (total ATM), CD14+ (proinflammatory/M1), and CD206+ (anti-inflammatory/M2) ATM in 97 volunteers (BMI 20-38 kg/m², in addition to body composition, adipocyte size, homeostasis model assessment of insulin resistance, ADIPO-IR, adipose tissue insulin resistance measured by palmitate, plasma lipids, TNF, and IL-6 concentrations. There were several significant univariate correlations between metabolic parameters to IL-6 and ATM per 100 adipocytes, but not ATM per gram tissue; adipocyte size was a confounding variable. We used matching strategies and multivariate regression analyses to investigate the relationships between ATM and inflammatory/metabolic parameters independent of adipocyte size. Matching approaches revealed that the groups discordant for CD206 but concordant for adipocyte size had significantly different fasting insulin and IL-6 concentrations. However, groups discordant for adipocyte size but concordent for ATM differeded in that visceral fat, plasma triglyceride, glucose, and TNF concentrations were greater in those with large adipocytes. Multivariate regression analysis indicated that indexes of insulin resistance and fasting triglycerides were predicted by body composition; the predictive value of ATM per 100 adipocytes or per gram tissue was variable between males and females. We conclude that the relationship between ATM burden and metabolic/inflammatory variables is confounded by adipocyte size/body composition and that ATM do not predict insulin resistance, systemic inflammation, or dyslipidemia. ATM may primarily play a role in tissue remodeling rather than in metabolic pathology.

Thigh Adipocyte Size is Inversely Related to Energy Intake and Respiratory Quotient in Healthy Women

OBJECTIVE

The relationship between adipocyte size and ad libitum energy intake has not been previously examined. This study hypothesized an inverse relationship between adipocyte size and daily energy intake (DEI).

METHODS

Seventy healthy adults (39 men and 31 women; BMI 30.0  [SD 6.3]) underwent dual-energy x-ray absorptiometry and subcutaneous fat biopsies from the abdomen and thigh. Osmium-fixed adipocytes were sized with a Coulter counter. Volunteers self-selected food from a vending machine paradigm as the only source of energy intake over 3 days as inpatients. Volunteers also had 24-hour respiratory quotient (RQ) measured in a whole-room indirect calorimeter.

RESULTS

In women, the large cell peak diameter of the thigh depot was greater than that of the abdominal depot (Δ = +15.8 μm; P < 0.0001). In women, thigh peak diameter was inversely associated with DEI (β = -264.7 kcal/d per 10-μm difference; P = 0.03) after adjusting for demographics and body composition. The thigh peak diameter in women was associated with 24-hour RQ (r = -0.47, P = 0.04) after adjusting for demographics, body composition, and 24-hour energy balance. These associations did not extend to men or the abdominal depot.

CONCLUSIONS

In women, thigh adipocyte size was associated with reduced DEI and 24-hour RQ, indicating a special role for thigh fat in women. This depot-specific sexual dimorphism indicates common regulation of energy intake and adipocyte size in the thigh region of women.

In-Vitro-Generated Hypertrophic-Like Adipocytes Displaying PPARG Isoforms Unbalance Recapitulate Adipocyte Dysfunctions In Vivo

Reduced neo-adipogenesis and dysfunctional lipid-overloaded adipocytes are hallmarks of hypertrophic obesity linked to insulin resistance. Identifying molecular features of hypertrophic adipocytes requires appropriate in vitro models. We describe the generation of a model of human hypertrophic-like adipocytes directly comparable to normal adipose cells and the pathologic evolution toward hypertrophic state. We generate in vitro hypertrophic cells from mature adipocytes, differentiated from human mesenchymal stem cells. Combining optical, confocal, and transmission electron microscopy with mRNA/protein quantification, we characterize this cellular model, confirming specific alterations also in subcutaneous adipose tissue. Specifically, we report the generation and morphological/molecular characterization of human normal and hypertrophic-like adipocytes. The latter displays altered morphology and unbalance between canonical and dominant negative (PPARGΔ5) transcripts of PPARG, paralleled by reduced expression of PPARγ targets, including GLUT4. Furthermore, the unbalance of PPARγ isoforms associates with GLUT4 down-regulation in subcutaneous adipose tissue of individuals with overweight/obesity or impaired glucose tolerance/type 2 diabetes, but not with normal weight or glucose tolerance. In conclusion, the hypertrophic-like cells described herein are an innovative tool for studying molecular dysfunctions in hypertrophic obesity and the unbalance between PPARγ isoforms associates with down-regulation of GLUT4 and other PPARγ targets, representing a new hallmark of hypertrophic adipocytes.

Adipocyte Piezo1 mediates obesogenic adipogenesis through the FGF1/FGFR1 signaling pathway in mice

White adipose tissue (WAT) expansion in obesity occurs through enlargement of preexisting adipocytes (hypertrophy) and through formation of new adipocytes (adipogenesis). Adipogenesis results in WAT hyperplasia, smaller adipocytes and a metabolically more favourable form of obesity. How obesogenic WAT hyperplasia is induced remains, however, poorly understood. Here, we show that the mechanosensitive cationic channel Piezo1 mediates diet-induced adipogenesis. Mice lacking Piezo1 in mature adipocytes demonstrated defective differentiation of preadipocyte into mature adipocytes when fed a high fat diet (HFD) resulting in larger adipocytes, increased WAT inflammation and reduced insulin sensitivity. Opening of Piezo1 in mature adipocytes causes the release of the adipogenic fibroblast growth factor 1 (FGF1), which induces adipocyte precursor differentiation through activation of the FGF-receptor-1. These data identify a central feed-back mechanism by which mature adipocytes control adipogenesis during the development of obesity and suggest Piezo1-mediated adipocyte mechano-signalling as a mechanism to modulate obesity and its metabolic consequences.

Adipose tissue expansion occurs via enlargement of adipocytes as well as the generation of new fat cells, the latter being associated with more favorable metabolic outcomes. Here, the authors show that activation of adipocyte Piezo1 results in release of FGF1 and stimulates the differentiation of adipocyte precursor cells.

CTRL - a label-free artificial intelligence method for dynamic measurement of single-cell volume

Measuring the physical size of a cell is valuable in understanding cell growth control. Current single-cell volume measurement methods for mammalian cells are labor intensive, inflexible and can cause cell damage. We introduce CTRL: Cell Topography Reconstruction Learner, a label-free technique incorporating the deep learning algorithm and the fluorescence exclusion method for reconstructing cell topography and estimating mammalian cell volume from differential interference contrast (DIC) microscopy images alone. The method achieves quantitative accuracy, requires minimal sample preparation, and applies to a wide range of biological and experimental conditions. The method can be used to track single-cell volume dynamics over arbitrarily long time periods. For HT1080 fibrosarcoma cells, we observe that the cell size at division is positively correlated with the cell size at birth (sizer), and there is a noticeable reduction in cell size fluctuations at 25% completion of the cell cycle in HT1080 fibrosarcoma cells.

Influence of Aging and Menstrual Status on Subcutaneous Fat Cell Lipolysis

CONTEXT

Aging is accompanied by inhibited fat cell mobilization of fatty acids through lipolysis, which may contribute to decreased energy expenditure in elderly subjects. However, the influence of menstrual status is unknown.

OBJECTIVE

To investigate the role of menstrual status on changes in lipolysis induced by aging.

DESIGN

A longitudinal investigation with a mean 13-year interval.

SETTING

Ambulatory study at a clinical academic unit.

PARTICIPANTS

Eighty-two continuously recruited women between 24 and 62 years of age and with body mass index 21 to 48 kg/m2 at first examination. Twenty-nine women continued to have normal menstruation, 42 developed irregular menstruation/menopause, and 11 had a perimenstrual/menopausal phenotype already at the first examination.

MAIN OUTCOME MEASURE

Lipolysis measured as glycerol release from isolated subcutaneous fat cells incubated in vitro.

RESULTS

On average, body weight/body fat mass levels did not change over time. In all 3 groups, aging was associated with a similar decrease in spontaneous (basal) and catecholamine-stimulated lipolysis. The latter was due to decreased signal transduction through stimulatory beta adrenoceptors and increased alpha-2-adrenoceptor-mediated antilipolytic effects. Gene microarray data from adipose tissue at baseline and follow-up (n = 53) showed that a limited set of lipolysis-linked genes, including phosphodiesterase-3B, were altered over time, but this was independent of menstrual status. Fat cell size also decreased during aging, but this could not explain the decrease in lipolysis.

CONCLUSIONS

In women, the rate of fat cell lipolysis decreases during aging due to multiple alterations in spontaneous (basal) and catecholamine-induced lipolysis. This is independent of changes in menstrual status or fat cell size.

Low prolactin levels are associated with visceral adipocyte hypertrophy and insulin resistance in humans

PURPOSE

Low prolactin (PRL) serum levels are associated with glucose intolerance and type 2 diabetes in adults, and with metabolic syndrome and obesity in children. In obese rodents, PRL treatment promotes insulin sensitivity by maintaining adipose tissue fitness, and lack of PRL signaling exacerbates obesity-derived metabolic alterations. Since adipose tissue dysfunction is a key factor triggering metabolic alterations, we evaluated whether PRL serum levels are associated with adipocyte hypertrophy (a marker of adipose tissue dysfunction), insulin resistance, and metabolic syndrome in lean, overweight, and obese adult men and women.

METHODS

Samples of serum and adipose tissue from 40 subjects were obtained to evaluate insulin resistance index (homeostasis model assessment of insulin resistance (HOMA-IR)), signs of metabolic syndrome (glucose levels, high-density lipoproteins, triglycerides, blood pressure, and waist circumference), as well as adipocyte size and gene expression in fat.

RESULTS

Lower PRL serum levels are associated with adipocyte hypertrophy, in visceral but not in subcutaneous fat, and with a higher HOMA-IR. Furthermore, low systemic PRL levels together with high waist circumference predict an elevated HOMA-IR whereas low serum PRL values in combination with high blood glucose predicts visceral adipocyte hypertrophy. In agreement, visceral fat from insulin resistant subjects shows reduced expression of prolactin receptor. However, there is no association between PRL levels and obesity or signs of metabolic syndrome.

CONCLUSIONS

Our results support that low levels of PRL are markers of visceral fat dysfunction and insulin resistance, and suggest the potential therapeutic value of medications elevating PRL levels to help maintain metabolic homeostasis.

Early weaning leads to specific glucocorticoid signalling in fat depots of adult rats

PURPOSE

Early weaning (EW) is a stressful condition that programmes a child to be overweight in adult life. Fat mass depends on glucocorticoids (GC) to regulate adipogenesis and lipogenesis. We hypothesised that the increased adiposity in models of EW was due to a disturbed HPA axis and/or disrupted GC function.

METHODS

We used two experimental models, pharmacological early weaning (PEW, dams were bromocriptine-treated) and non-pharmacological early weaning (NPEW, dams' teats were wrapped with a bandage), which were initiated during the last 3 days of lactation. Offspring from both genders was analysed on postnatal day 180.

RESULTS

Offspring in both models were overweight with increased visceral fat mass, but plasma corticosterone was increased in both genders in the PEW group but not the NPEW group. NPEW males had increased GRα expression in visceral adipose tissue (VAT), and GRα expression decreased in PEW males in subcutaneous adipose tissue (SAT). Females in both EW groups had increased 11βHSD1 expression in SAT. PEW males had increased C/EBPβ expression in SAT. PEW females had lower PPARy and FAS expression in VAT than the NPEW females. We detected a sex dimorphism in VAT and SAT in the EW groups regarding 11βHSD1, GRα and C/EBPβ expression.

CONCLUSIONS

The accumulated adiposity induced by EW exhibited distinct mechanisms depending on gender, specific fat deposition and GC metabolism and action. The higher proportion of VAT/SAT in both sets of EW males may be related to the action of GC in these tissues, and the higher conversion of GC in SAT in females may explain the differences in the fat distribution.

Dysregulation of Amyloid Precursor Protein Impairs Adipose Tissue Mitochondrial Function and Promotes Obesity

Mitochondrial function in white adipose tissue (WAT) is an important yet understudied aspect in adipocyte biology. Here, we report a role for amyloid precursor protein (APP) in compromising WAT mitochondrial function through a high-fat diet (HFD)-induced, unconventional mis-localization to mitochondria that further promotes obesity. In humans and mice, obese conditions significantly induce APP production in WAT and its enrichment in mitochondria. Mechanistically, a HFD-induced dysregulation of signal recognition particle subunit 54c is responsible for the mis-targeting of APP to adipocyte mitochondria. Mis-localized APP blocks the protein import machinery, leading to mitochondrial dysfunction in WAT. Adipocyte-specific and mitochondria-targeted APP overexpressing mice display increased body mass and reduced insulin sensitivity, along with dysfunctional WAT due to a dramatic hypertrophic program in adipocytes. Elimination of adipocyte APP rescues HFD-impaired mitochondrial function with significant protection from weight gain and systemic metabolic deficiency. Our data highlights an important role of APP in modulating WAT mitochondrial function and obesity-associated metabolic dysfunction.

Adipocyte hyperplasia: the primary mechanism of supraspinatus intramuscular fat accumulation after a complete rotator cuff tendon tear: a study in the rabbit

Intramuscular fat (IMF) accumulates in muscles of the rotator cuff after tendon tear. The number and cross-sectional area of fat clumps and of adipocytes were quantified on osmium tetroxide stained sections of the proximal, middle and distal quarters of SSP muscles 4, 8 and 12 weeks after SSP tendon division in a rabbit model. Linear mixed-effects models were fitted to the data and statistical significance was evaluated by ANOVA. Both the number (P<0.001) and cross-sectional area (P<0.0005) of fat clumps increased after tendon detachment while time had no significant effect (both at P>0.01). IMF accumulation was more important in the distal quarter of detached SSP muscle near tendon sectioning and characterized by increases of the number (P<0.0005) and cross-sectional area of fat clumps (P<0.0005) compared to the proximal quarter. Adipocyte number increased after tendon detachment (P<0.0005) and over time (P<0.01). The cross-sectional area of adipocytes increased in the detached group compared to controls (P<0.01) while time had no significant effect (P>0.01). Interestingly, the number of adipocytes in the distal quarter increased (P<0.0005) but the cross-sectional area was smaller (P<0.0005) compared to adipocytes in the proximal quarter. Adipocyte hyperplasia localized near tendon sectioning was the main contributor to fat accumulation in the detached SSP muscles.

Chrysin mitigated obesity by regulating energy intake and expenditure in rats

Background and aim

Chrysin is a flavonoid found in plant extracts from Passiflora species, honey and propolis. It has demonstrated anti-adipogenic activity in vitro but there are no studies substantiating the anti-obesity activity of chrysin in vivo.

Experimental procedure

The pancreatic lipase (PL) inhibitory potential of chrysin was determined by preliminary in silico screening and further confirmed by in vitro PL inhibitory assay and oral fat tolerance test (OFTT). The effect of chrysin on acute feed intake and sucrose preference test was determined in normal rats. Obesity was induced by feeding of high fructose diet (HFD) to the rats. The rats were divided into six groups: normal control, HFD control, orlistat and three doses of chrysin (25, 50 and 100 mg/kg body weight). Body weight, body mass index (BMI), abdominal circumference/thoracic circumference (AC/TC) ratio, calorie intake, adiposity index, fecal cholesterol, locomotor activity and histopathology of the adipose tissue of the rats were evaluated.

Results

Chrysin showed good affinity to PL with competitive type of inhibition. It significantly reduced serum triglycerides in OFTT. Chrysin also significantly reduced acute feed intake and sucrose preference in rats. Chrysin significantly decreased the body weight, BMI, AC/TC ratio, adiposity index, calorie intake while it significantly increased the fecal cholesterol and locomotor activity of the rats. Chrysin was found to reduce the size of the adipocytes when compared to the HFD control group.

Conclusion

Thus, chrysin exerted anti-obesity effect by inhibiting PL, reducing sucrose preference, reducing calorie intake and increasing the locomotor activity of rats.

Insulin action is severely impaired in adipocytes of apparently healthy overweight and obese subjects

OBJECTIVE

Many overweight/obese subjects appear metabolically healthy with normal in vivo insulin sensitivity. Still, they have increased long-term risk of developing type 2 diabetes. We hypothesized that adipose tissue dysfunction involving decreased insulin action in adipocytes is present in apparently healthy overweight/obese subjects.

DESIGN/METHODS

Subjects with normal metabolic health according to Adult Treatment Panel-III or Framingham risk score criteria were subdivided into 67 lean, 32 overweight and 37 obese according to body mass index. They were compared with 200 obese individuals with metabolic syndrome. Insulin sensitivity and maximum action on inhibition of lipolysis and stimulation of lipogenesis was determined in subcutaneous adipocytes. Gene expression was determined by micro-array and qPCR. DNA methylation was assessed by array, pyrosequencing and reporter assays.

RESULTS

Compared with lean, adipocytes in overweight/obese displayed marked reductions in insulin sensitivity in both antilipolysis and lipogenesis as well as an attenuated maximum lipogenic response. Among these, only antilipolysis sensitivity correlated with whole-body insulin sensitivity. These differences were already evident in the overweight state, were only slightly worse in the unhealthy obese state and were not related to fat cell size. Adipose tissue analyses linked this to reduced expression of the insulin signalling protein AKT2, which associated with increased methylation at regulatory sites in the AKT2 promoter.

CONCLUSIONS

Apparently healthy subjects have severely disturbed adipocyte insulin signalling already in the overweight state which involves epigenetic dysregulation of AKT2. This may constitute an early defect in insulin action that appears even upon modest increases in fat mass.

Neutrophil-to-lymphocyte ratio and its relation with pro-inflammatory mediators, visceral adiposity and carotid intima-media thickness in population with obesity

BACKGROUND

Atherosclerosis represents a cardiovascular risk. Chronic inflammation is a key factor for atherogenic progression. Neutrophil-to-lymphocyte ratio (NLR) has been proposed as a novel biomarker for cardiovascular risks. We aimed to explore whether NLR was related to surrogate pro-atherogenic promoters driving atherogenic progression, as measured by carotid intima-media thickness (CIMT).

STUDY DESIGN

Thirty-one patients with obesity candidates for bariatric surgery were recruited from Centro Médico Nacional "20 de Noviembre", ISSSTE, Mexico City. The results are part of the "CROP" study (NCT03561987). NLR was calculated from routine complete blood count, and its relation with plasma pro-inflammatory mediators (hsCRP, TNF-α and IL-1β), adipokines (adiponectin and leptin), adiposity markers (visceral adipose tissue [VAT] determined from CT scan image and VAT individual adipocyte area at histological sample) and CIMT were determined.

RESULTS

Neutrophil-to-lymphocyte ratio correlated with hsCRP (Spearman's r = 0.70 [95% CI 0.46 to 0.85], P < 0.01), TNF-α (r = 0.69 [0.44 to 0.84], P < 0.0001) and adiponectin (r = -0.69 [-0.84 to -0.45], P < 0.03), as well as with VAT individual adipocyte area (r = 0.64 [0.37 to 0.81], P < 0.0001) and with VAT area (r = 0.43; [0.07 to 0.68], P < 0.01). Leptin and adiponectin showed further independent association with higher NLR (multivariate regression analysis OR 7.9 [95% CI 1.1 to 56.2] P = 0.03 and 0.1 [0.01 to 1.0] P = 0.05, respectively). Moreover, NLR distribution significantly varied between subgroups divided according to progressive CIMT (P = 0.05); whereas adiponectin and VAT adipocyte area associated with CIMT > 0.9 mm (univariate analysis OR 0.1 [0.01 to 1.0] P = 0.05 and 13.1 [1.4 to 126.3] P = 0.03, respectively).

CONCLUSION

Neutrophil-to-lymphocyte ratio was related to pro-inflammatory, adiposity biomarkers and progressive subclinical atherogenesis.