White Adipose Tissue Fibrosis Research Articles

Subacute cadmium exposure changes different metabolic functions, leading to type 1 and 2 diabetes mellitus features in female rats.

Cadmium (Cd) is a heavy metal that acts as endocrine disrupting chemical (EDC). Few studies have investigated the effects of Cd exposure on metabolic dysfunctions, such as type 1 and 2 diabetes mellitus (T1DM and T2DM). Thus, we assessed whether subacute Cd exposure at occupational levels causes abnormalities in white adipose tissue (WAT), liver, pancreas, and skeletal muscle. We administered cadmium chloride (CdCl2) (100 ppm in drinking water for 30 days) to female rats and evaluated Cd levels in serum and metabolic organs, morphophysiology, inflammation, oxidative stress, fibrosis, and gene expression. High Cd levels were found in serum, WAT, liver, pancreas, and skeletal muscle. Cd-exposed rats showed low adiposity, dyslipidemia, insulin resistance, systemic inflammation, and oxidative stress compared to controls. Cd exposure reduced adipocyte size, hyperleptinemia, increased cholesterol levels, inflammation, apoptosis and fibrosis in WAT. Cd-exposed rats had increased liver cholesterol levels, insulin receptor beta (IRβ) and peroxisome proliferator-activated receptor-gamma coactivator-1alpha (PGC1α) expression, karyomegaly, inflammation, and fibrosis. Cd exposure reduced insulin levels and pancreatic islet size and increased inflammation and fibrosis. Cd exposure reduced skeletal muscle fiber diameter and increased IR expression and inflammation. Finally, strong positive correlations were observed between serum, tissue Cd levels, abnormal morphology, tissue inflammation and fibrosis. Thus, these data suggest that subacute Cd exposure impairs WAT, liver, pancreas and skeletal muscle function, leading to T1DM and T2DM features and other complications in female rats.

FRI023 Increased Fibrosis In White Adipose Tissue Of Male And Female bGH Transgenic Mice Appears Independent Of TGF-β Action

Abstract Disclosure: G. Lach: None. S. Bell: None. J.A. Young: None. E.O. List: None. R. Basu: None. D. Geitgey: None. K.Y. Lee: None. D. Swegan: None. L.J. Caggiano: None. S. Okada: None. J.J. Kopchick: None. D.E. Berryman: None. Fibrosis is a pathological state caused by excess deposition of extracellular matrix proteins, which can disrupt tissue structure and function. Previous work has shown that male bovine growth hormone (bGH) transgenic mice have high levels of circulating growth hormone (GH) and insulin-like growth factor 1 (IGF-1), marked decrease in lifespan, and increased fibrosis in several tissues including white adipose tissue (WAT), which is more pronounced in the subcutaneous (Sc) depot. The current study expanded on these findings, evaluating: 1) WAT fibrosis in female bGH mice, 2) levels of circulating factors implicated in fibrosis, and 3) the role of TGF-β, a central mediator of fibrogenesis, in the development of bGH WAT fibrosis. Our findings confirmed that female bGH mice exhibit increased WAT fibrosis, most prominent in the Sc depot, like male bGH mice, but also significantly increased in the perigonadal depot, unlike male bGH mice. bGH mice of both sexes have elevated circulating levels of several markers of collagen turnover (plasma P1NP, P3NP and ICTP) and FGF21 relative to controls but no genotype-dependent alteration in fibroblast activation protein (FAP). TGF-β and TGF-β signaling in serum or WAT was either unchanged or reduced in male and female bGH mice at both young and mature ages. The treatment of bGH mice with a TGF-β antagonist, pirfenidone, did not attenuate bGH WAT fibrosis. Contrary to the effects of the chronic exposure to excess GH, acute GH treatments in vivo or in vitro did elicit a modest increase in TGF-β signaling. Finally, single nucleus RNA sequencing confirmed no perturbation in TGF-β or its receptor gene expression in any WAT cell population within subcutaneous bGH WAT; however, a striking increase in B lymphocyte infiltration in Sc bGH WAT was observed. Overall, these data suggest that bGH WAT fibrosis is independent of the action of TGF-β and reveals an intriguing shift in immune cells, particularly B cells, in bGH WAT that should be further explored considering the increasing importance of B cell-mediated WAT fibrosis and aging. Acknowledgements:This work was sponsored, in part, by ASPIRE grant funding from Pfizer. This work was also supported by the State of Ohio’s Eminent Scholar Program to J. J. K. that includes a gift from Milton and Lawrence Goll and by the startup funds from the Heritage College of Osteopathic Medicine at Ohio University, Athens, OH. Presentation: Friday, June 16, 2023

The Role of IL-13 and IL-4 in Adipose Tissue Fibrosis

White adipose tissue (WAT) fibrosis, characterized by an excess of extracellular (ECM) matrix components, is strongly associated with WAT inflammation and dysfunction due to obesity. Interleukin (IL)-13 and IL-4 were recently identified as critical mediators in the pathogenesis of fibrotic diseases. However, their role in WAT fibrosis is still ill-defined. We therefore established an ex vivo WAT organotypic culture system and demonstrated an upregulation of fibrosis-related genes and an increase of α-smooth muscle actin (αSMA) and fibronectin abundance upon dose-dependent stimulation with IL-13/IL-4. These fibrotic effects were lost in WAT lacking il4ra, which encodes for the underlying receptor controlling this process. Adipose tissue macrophages were found to play a key role in mediating IL-13/IL-4 effects in WAT fibrosis as their depletion through clodronate dramatically decreased the fibrotic phenotype. IL-4-induced WAT fibrosis was partly confirmed in mice injected intraperitoneally with IL-4. Furthermore, gene correlation analyses of human WAT samples revealed a strong positive correlation of fibrosis markers with IL-13/IL-4 receptors, whereas IL13 and IL4 correlations failed to confirm this association. In conclusion, IL-13 and IL-4 can induce WAT fibrosis ex vivo and partly in vivo, but their role in human WAT remains to be further elucidated.

Increased Fibrosis in White Adipose Tissue of Male and Female bGH Transgenic Mice Appears Independent of TGF-β Action.

Fibrosis is a pathological state caused by excess deposition of extracellular matrix proteins in a tissue. Male bovine growth hormone (bGH) transgenic mice experience metabolic dysfunction with a marked decrease in lifespan and with increased fibrosis in several tissues including white adipose tissue (WAT), which is more pronounced in the subcutaneous (Sc) depot. The current study expanded on these initial findings to evaluate WAT fibrosis in female bGH mice and the role of transforming growth factor (TGF)-β in the development of WAT fibrosis. Our findings established that female bGH mice, like males, experience a depot-dependent increase in WAT fibrosis, and bGH mice of both sexes have elevated circulating levels of several markers of collagen turnover. Using various methods, TGF-β signaling was found unchanged or decreased-as opposed to an expected increase-despite the marked fibrosis in WAT of bGH mice. However, acute GH treatments in vivo, in vitro, or ex vivo did elicit a modest increase in TGF-β signaling in some experimental systems. Finally, single nucleus RNA sequencing confirmed no perturbation in TGF-β or its receptor gene expression in any WAT cell subpopulations of Sc bGH WAT; however, a striking increase in B lymphocyte infiltration in bGH WAT was observed. Overall, these data suggest that bGH WAT fibrosis is independent of the action of TGF-β and reveals an intriguing shift in immune cells in bGH WAT that should be further explored considering the increasing importance of B cell-mediated WAT fibrosis and pathology.

Genetic ablation of diabetes-associated gene Ccdc92 reduces obesity and insulin resistance in mice

Multiple genome-wide association studies (GWAS) have identified specific genetic variants in the coiled-coil domain containing 92 (CCDC92) locus that is associated with obesity and type 2 diabetes in humans. However, the biological function of CCDC92 in obesity and insulin resistance remains to be explored. Utilizing wild-type (WT) and Ccdc92 whole-body knockout (KO) mice, we found that Ccdc92 KO reduced obesity and increased insulin sensitivity under high-fat diet (HFD) conditions. Ccdc92 KO inhibited macrophage infiltration and fibrosis in white adipose tissue (WAT), suggesting Ccdc92 ablation protects against adipose tissue dysfunction. Ccdc92 deletion also increased energy expenditure and further attenuated hepatic steatosis in mice on an HFD. Ccdc92 KO significantly inhibited the inflammatory response and suppressed the NLR Family Pyrin Domain Containing 3 (NLRP3) inflammasome in WAT. Altogether, we demonstrated the critical role of CCDC92 in metabolism, constituting a potential target for treating obesity and insulin resistance.

Nicotinamide riboside supplementation exerts an anti–obesity effect and prevents inflammation and fibrosis in white adipose tissue of female diet-induced obesity mice

Nicotinamide riboside (NR) is a nicotinamide adenine dinucleotide (NAD+) precursor. We previously reported that NR supplementation prevented the development of liver fibrosis in male mice. However, whether NR exerts a similar effect in females is unknown. Therefore, we determined whether NR supplementation can prevent obesity-induced inflammation and fibrosis in the liver and white adipose tissue (WAT) by providing NAD+ in obese female mice. Female C57BL/6J mice at the age of 8 weeks (young) and 16 weeks (old) were fed a high-fat/high-sucrose/high-cholesterol diet (HF) or HF diet supplemented with NR at 400 mg/kg/d for 20 weeks. While NR had minor effects in young female mice, it significantly reduced body weight gain, fat mass, glucose intolerance, and serum cholesterol levels compared to the HF group in old females. Hepatic NAD+ level tended toward an increase in the NR group (P=.054), but NR did not attenuate serum alanine aminotransferase levels, steatosis, and liver fibrosis in old female mice. However, NR decreased weight and adipocyte size in gonadal WAT (gWAT) of old females. NR also reduced the number of crown-like structures and the expression of inflammatory genes, along with decreases in fibrogenic gene expression and collagen accumulation in gWAT compared with the HF group. Also, old mice fed NR showed increased metabolic rates, physical activity, and energy expenditure compared with the HF. Thus, our results indicated that NR supplementation exerted an anti–obesity effect and prevented the development of inflammation and fibrosis in the WAT of old, but not young, female mice with diet-induced obesity.

An Experimental DUAL Model of Advanced Liver Damage.

Individuals exhibiting an intermediate alcohol drinking pattern in conjunction with signs of metabolic risk present clinical features of both alcohol‐associated and metabolic‐associated fatty liver diseases. However, such combination remains an unexplored area of great interest, given the increasing number of patients affected. In the present study, we aimed to develop a preclinical DUAL (alcohol‐associated liver disease plus metabolic‐associated fatty liver disease) model in mice. C57BL/6 mice received 10% vol/vol alcohol in sweetened drinking water in combination with a Western diet for 10, 23, and 52 weeks (DUAL model). Animals fed with DUAL diet elicited a significant increase in body mass index accompanied by a pronounced hypertrophy of adipocytes, hypercholesterolemia, and hyperglycemia. Significant liver damage was characterized by elevated plasma alanine aminotransferase and lactate dehydrogenase levels, extensive hepatomegaly, hepatocyte enlargement, ballooning, steatosis, hepatic cell death, and compensatory proliferation. Notably, DUAL animals developed lobular inflammation and advanced hepatic fibrosis. Sequentially, bridging cirrhotic changes were frequently observed after 12 months. Bulk RNA‐sequencing analysis indicated that dysregulated molecular pathways in DUAL mice were similar to those of patients with steatohepatitis. Conclusion: Our DUAL model is characterized by obesity, glucose intolerance, liver damage, prominent steatohepatitis and fibrosis, as well as inflammation and fibrosis in white adipose tissue. Altogether, the DUAL model mimics all histological, metabolic, and transcriptomic gene signatures of human advanced steatohepatitis, and therefore serves as a preclinical tool for the development of therapeutic targets.

1747-P: MicroRNA-30a Exerts Antifibrotic Effects in Subcutaneous White Adipose Tissue to Preserve Insulin Sensitivity in Obesity

White adipose tissue (WAT) is an endocrine organ that dynamically expands and contracts to meet the metabolic demands of the organism. However, prolonged excessive caloric intake overwhelms WAT depots, resulting in peripheral fat deposition, systemic glucose dysregulation, tissue fibrosis, insulin resistance, and type 2 diabetes mellitus. The chronic triggers that degrade WAT function remain undefined, hindering the development of effective strategies to treat obesity and prevent its co-morbidities. We have identified a microRNA, miR-30a, that potently stimulates subcutaneous adipose tissue metabolic flexibility and enhances systemic insulin sensitivity. In follow-up studies, we created a genetically engineered mouse model to conclusively show miR-30a expression in white adipocytes is antidiabetic. Obese mice modified to express miR-30a at elevated levels in adipose tissues maintain insulin sensitivity coupled with reduced hepatic steatosis. Proteomic profiling indicated that miR-30a targets Plasminogen Activator Inhibitor-1 (PAI-1) to limit pro-fibrotic programs that would otherwise restrict subcutaneous WAT expansion and decrease insulin sensitivity. While visceral WAT depots remain a site of significant fibrosis in mice, subcutaneous WAT fibrosis is epidemiologically linked to metabolic disease risk in adult humans. In obese humans, miR-30a expression negatively correlates with PAI-1 levels in subcutaneous WAT, supporting an anti-fibrotic role for miR-30a that ultimately defends insulin sensitivity. Collectively, our observations linking miR-30a expression to insulin sensitivity suggest a new method that restores WAT homeostasis. Disclosure N. Chernis: None. P. Saha: None. J.B. Felix: None. P.M. Masschelin: None. L. Lian: None. A. Cox: None. K. Kim: None. H. Wu: None. S.M. Hartig: None. Funding American Diabetes Association (1-18-IBS-105 to S.M.H.); National Institutes of Health (R01DK114356)

Loss of Histone Deacetylase 4 in Hepatocytes Increases De Novo Lipogenesis in Diet-Induced Obesity Mice

Abstract Objectives Evidence suggests that histone deacetylase 4 (HDAC4) is downregulated in adipose tissue of obese subjects. We determined the role of HDAC4 in the regulation of energy metabolism of metabolically active tissues, such as the liver and adipose tissue. Methods Hepatocyte-specific (Hdac4HKO) and adipocyte-specific (Hdac4AKO) Hdac4 knockout mice were generated by crossing homozygous Hdac4 floxed (Hdac4fl/fl) mice with mice expressing Cre recombinase under the control of the enhancer/promoter of Albumin or Adipoq gene, respectively. Hdac4fl/fl and Hdac4HKO mice were fed a high fat/high sucrose (HF/HS; 57%/28% energy from fat/sucrose) with 2% cholesterol (w/w) diet for 16 weeks. Hdac4fl/fl and Hdac4AKO mice were fed an obesogenic HF/HS diet for 16 weeks. The final serum was collected by cardiopuncture for blood analysis. Tissues were snap frozen for mRNA and protein analysis. Results Both Hdac4HKO and Hdac4AKO mice did not show differences in body weight compared to Hdac4fl/fl mice following the 16-week of experimental diet. However, loss of hepatic HDAC4 increased serum alanine transaminase levels, a marker for liver injury. Also, Hdac4HKO mice had exacerbated hepatic steatosis with higher liver weights and triglyceride levels than Hdac4fl/fl mice. Consistently, hepatic expression of genes for de novo lipogenesis, including Srebf1c and its target genes, fatty acid synthase and acetyl CoA carboxylase 1, was significantly higher in Hdac4HKO mice compared with control mice. Interestingly, the loss of hepatocyte HDAC4 aggravated inflammation and fibrosis in white adipose tissue. Serum cytokine array indicated increases in fibroblast growth factor 1, pentraxin 3, tissue inhibitor of metalloproteinases 1, and decrease in endocan, which may contribute to the crosstalk between the liver and adipose tissue in Hdac4HKO. On the other hand, the loss of adipocyte HDAC4 elicited minimal changes in mRNA levels of lipogenic, inflammatory, and fibrogenic genes in adipose tissue and the liver. Conclusions The lack of functional hepatocyte HDAC4 increased lipid accumulation in the liver of obesity mice via increasing hepatic de novo lipogenesis, and also aggravated adipose tissue inflammation and fibrosis. Further investigation is warranted to elucidate the crosstalk between the liver and adipose tissue in Hdac4HKO. Funding Sources This study was supported by NIH.

PS-134-Oral treatment with PBI-4547 promotes beta-oxidation and energy expenditure, and reverses liver damage and white adipose tissue fibrosis in high-fat diet and ob/ob mouse models of NAFLD.

PS-134-Oral treatment with PBI-4547 promotes beta-oxidation and energy expenditure, and reverses liver damage and white adipose tissue fibrosis in high-fat diet and ob/ob mouse models of NAFLD.

Adipocyte-Specific GH Receptor-Null (AdGHRKO) Mice Have Enhanced Insulin Sensitivity With Reduced Liver Triglycerides.

Global GH receptor-null or knockout (GHRKO) mice have been extensively studied owing to their unique phenotype (dwarf and obese but remarkably insulin sensitive and long-lived). To better understand the influence of adipose tissue (AT) on the GHRKO phenotype, we previously generated fat-specific GHRKO (FaGHRKO) mice using the adipocyte protein-2 (aP2) promoter driving Cre expression. Unlike global GHRKO mice, FaGHRKO mice are larger than control mice and have an increase in white AT (WAT) mass and adipocyte size as well as an increase in brown AT mass. FaGHRKO mice also have an unexpected increase in IGF-1, decrease in adiponectin, no change in insulin sensitivity or liver triglyceride content, and a decreased lifespan. Extensive analysis of the aP2 promoter/enhancer by multiple laboratories has revealed expression in nonadipose tissues, confounding interpretation of results. In the current study, we used the adiponectin promoter/enhancer to drive Cre expression, which better targets mature adipocytes, and generated a new line of adipocyte-specific GHRKO (AdGHRKO) mice. AdGHRKO mice have an increase in adipocyte size and WAT depot mass in all depots except male perigonadal, a WAT accumulation pattern similar to FaGHRKO mice. Likewise, adiponectin levels and WAT fibrosis are decreased in both tissue-specific mouse lines. However, unlike FaGHRKO mice, AdGHRKO mice have no change in IGF-1 levels, improved glucose homeostasis, and reduced liver triglycerides. Thus, AdGHRKO mice should be valuable for future studies assessing the contribution of adipocyte GHR signaling in long-term health and lifespan.

Sirt1 activator induces proangiogenic genes in preadipocytes to rescue insulin resistance in diet-induced obese mice

Sirt1 plays an important role in regulating glucose and lipid metabolism in obese animal models. Impaired adipose tissue angiogenesis in the obese state decreases adipogenesis and thereby contributes to glucose intolerance and lipid metabolism. However, the mechanism by which Sirt1 activation affects obesity-associated impairments in angiogenesis in the adipose tissue is not fully understood. Here, we show that SRT1720 treatment induces angiogenic genes in cultured 3T3-L1 preadipocytes and ex vivo preadipocytes. siRNA-mediated knockdown of Sirt1 in 3T3-L1 preadipocytes downregulated angiogenic genes in the preadipocytes. SRT1720 treatment upregulated metabolically favorable genes and reduced inflammatory gene expressions in the adipose tissue of diet-induced obese (DIO) mice. Collectively, these findings suggest a novel role of SRT1720-induced Sirt1 activation in the induction of angiogenic genes in preadipocytes, thereby reducing inflammation and fibrosis in white adipose tissue (WAT) and promoting insulin sensitivity.

Transgenic Mice Overexpressing SREBP-1a in Male ob/ob Mice Exhibit Lipodystrophy and Exacerbate Insulin Resistance.

Sterol regulatory element-binding protein (SREBP)-1a is a key transcription factor that activates the expression of genes involved in the synthesis of fatty acids, triglycerides (TGs), and cholesterol. Transgenic mice that overexpress the nuclear form of SREBP-1a under the control of the phosphoenolpyruvate carboxykinase promoter (Tg-1a) were previously shown to display a lipodystrophic phenotype characterized by enlarged and fatty livers, diminished peripheral white adipose tissue (WAT), and insulin resistance. In the current study, we crossed these Tg-1a mice with genetically obese (ob/ob) mice (Tg-1a;ob/ob) and examined change in fat distribution between liver and adipose tissues in severe obesity and mechanism underlying the lipodystrophic phenotype in mice with Tg-1a. Tg-1a;ob/ob mice developed more severe steatohepatitis but had reduced WAT mass and body weight compared with ob/ob mice. The reduction of WAT mass in Tg-1a and Tg-1a;ob/ob mice was accompanied by enhanced lipogenesis and lipid uptake in the liver, reduced plasma lipid levels, impaired adipocyte differentiation, reduced food intake, enhanced energy expenditure, and extended macrophage infiltration and fibrosis in WAT. Despite the improved glucose tolerance, Tg-1a;ob/ob mice showed severe peripheral insulin resistance. Adenoviral hepatic expression of SREBP-1a mimicked these phenotypes. The "fat steal"-like lipodystrophy phenotype of the Tg-1a;ob/ob model demonstrates that hepatic SREBP-1a activation has a strong impact on the partition of TG accumulation, resulting in adipose-tissue remodeling by inflammation and fibrosis and insulin resistance.

Dipeptidyl peptidase IV (DPP-IV) inhibition prevents fibrosis in adipose tissue of obese mice

BackgroundDuring the development of obesity the expansion of white adipose tissue (WAT) leads to a dysregulation and an excessive remodeling of extracellular matrix (ECM), leading to fibrosis formation. These ECM changes have high impact on WAT physiology and may change obesity progression. Blocking WAT fibrosis may have beneficial effects on the efficacy of diet regimen or therapeutical approaches in obesity. Since dipeptidyl peptidase IV (DPP-IV) inhibitors prevent fibrosis in tissues, such as heart, liver and kidney, the objective of this study was to assess whether vildagliptin, a DPP-IV inhibitor, prevents fibrosis in WAT in a mouse model of obesity, and to investigate the mechanisms underlying this effect. MethodsWe evaluated the inhibitory effect of vildagliptin on fibrosis markers on WAT of high-fat diet (HFD)-induced obese mice and on 3T3-L1 cell line of mouse adipocytes treated with a fibrosis inducer, transforming growth factor beta 1 (TGFβ1). ResultsVildagliptin prevents the increase of fibrosis markers in WAT of HFD-fed mice and reduces blood glucose, serum triglycerides, total cholesterol and leptin levels. In the in vitro study, the inhibition of DPP-IV with vildagliptin, neuropeptide Y (NPY) treatment and NPY Y1 receptor activation prevents ECM deposition and fibrosis markers increase induced by TGFβ1 treatment. ConclusionsVildagliptin prevents fibrosis formation in adipose tissue in obese mice, at least partially through NPY and NPY Y1 receptor activation. General significanceThis study highlights the importance of vildagliptin in the treatment of fibrosis that occur in obesity.

Adipose Tissue VEGF‐D Overexpression Increases Lymphatic Vessel Density and Protects Against Inflammation and Insulin Resistance in Obesity

Lymphatic vessels modulate tissue fluid balance and inflammation and provide a conduit for endocrine and lipid transport: all mechanisms that could potentially regulate adipose tissue physiology in obesity. The growth of new lymphatic vessels in is mediated through vascular endothelial growth factor receptor‐3 (VEGFR‐3) signaling. We took advantage of the unique binding of murine VEGF‐D to VEGFR‐3 and generated mice capable of inducible, tissue‐specific expression of murine VEGF‐D under a tightly‐controlled tetracycline response element (TRE) promoter to stimulate lymphangiogenesis. Crossed with adipocyte‐specific adiponectin‐rtTA mice (Adipo‐VD), VEGF‐D overexpression by adipocytes induced de novo lymphangiogenesis in murine white adipose tissue and a massive expansion of brown adipose tissue lymphatics. Upon removal of the doxycycline stimulus, VEGF‐D expression returned to normal and the expanded adipose tissue lymphatics regressed. The new white adipose lymphatic network provided a route for increased glycerol flux during lipolysis. As a chemokine, VEGF‐D expression recruited macrophages and caused fibrosis in white adipose tissue on chow diet, but no negative systemic metabolic consequences were identified. On high fat diet feeding, Adipo‐VD gained equivalent weight and adiposity as littermate controls, but were markedly more insulin sensitive. White adipose tissues in Adipo‐VD mice were full of lymphatics, but exhibited less fibrosis, contained fewer crown‐like structure macrophages, and displayed increased UCP‐1 RNA and protein. Infusion of CD45.1+ leukocytes into CD45.2+ Adipo‐VD mice identified fewer immune cells accumulating in the Adipo‐VD subcutaneous adipose with more trafficking out and into the inguinal lymph node. The increased lymphatic density thus reduces local inflammation in adipose tissue, manifesting as decreased liver triglyceride, increased insulin sensitivity, and overall healthier obesity highlighting the roles of lymphatic in regulating inflammatory pathologies and VEGFR‐3 signaling as a potential target in the metabolic syndrome.

Forecasting Fat Fibrosis

Excess ECM and fibrosis of white adipose tissue (WAT) is associated with tissue dysfunction and type 2 diabetes. In this issue of Cell Metabolism, Marcelin etal. (2017) elucidate a key mechanism behind WAT fibrosis in which the activation of PDGFRα on adipocyte precursors drives this population toward a fibrotic phenotype.

A PDGFRα-Mediated Switch toward CD9high Adipocyte Progenitors Controls Obesity-Induced Adipose Tissue Fibrosis

Obesity-induced white adipose tissue (WAT) fibrosis is believed to accelerate WAT dysfunction. However, the cellular origin of WAT fibrosis remains unclear. Here, we show that adipocyte platelet-derived growth factor receptor-α-positive (PDGFRα+) progenitors adopt a fibrogenic phenotype in obese mice prone to visceral WAT fibrosis. More specifically, a subset of PDGFRα+ cells with high CD9 expression (CD9high) originates pro-fibrotic cells whereas their CD9low counterparts, committed to adipogenesis, are almost completely lost in the fibrotic WAT. PDGFRα pathway activation promotes a phenotypic shift toward PDGFRα+CD9high fibrogenic cells, driving pathological remodeling and altering WAT function in obesity. These findings translated to human obesity as the frequency of CD9high progenitors in omental WAT (oWAT) correlates with oWAT fibrosis level, insulin-resistance severity, and type 2 diabetes. Collectively, our data demonstrate that in addition to representing a WAT adipogenic niche, different PDGFRα+ cell subsets modulate obesity-induced WAT fibrogenesis and are associated with loss of metabolic fitness.

Role for hepatic CEACAM1 in regulating fatty acid metabolism along the adipocyte-hepatocyte axis

Carcinoembryonic antigen-related cell adhesion molecule 1 (CEACAM1) regulates insulin sensitivity by promoting hepatic insulin clearance and mediating suppression of fatty acid synthase activity. Feeding C57BL/6J male mice with a high-fat (HF) diet for 3-4 weeks triggered a >60% decrease in hepatic CEACAM1 levels to subsequently impair insulin clearance and cause systemic insulin resistance and hepatic steatosis. This study aimed at investigating whether lipolysis drives reduction in hepatic CEACAM1 and whether this constitutes a key mechanism leading to diet-induced metabolic abnormalities. Blocking lipolysis with a daily intraperitoneal injection of nicotinic acid in the last two days of a 30-day HF feeding regimen demonstrated that white adipose tissue (WAT)-derived fatty acids repressed hepatic CEACAM1-dependent regulation of insulin and lipid metabolism in 3-month-old male C57BL/6J mice. Adenoviral-mediated CEACAM1 redelivery countered the adverse metabolic effect of the HF diet on insulin resistance, hepatic steatosis, visceral obesity, and energy expenditure. It also reversed the effect of HF diet on inflammation and fibrosis in WAT and liver. This assigns a causative role for lipolysis-driven decrease in hepatic CEACAM1 level and its regulation of insulin and lipid metabolism in sustaining systemic insulin resistance, hepatic steatosis, and other abnormalities associated with excessive energy supply.

High levels of CRP in morbid obesity: the central role of adipose tissue and lessons for clinical practice before and after bariatric surgery

BackgroundObesity, characterized by low-grade inflammation both in blood and white adipose tissue (WAT) is associated with increased C-reactive protein (CRP), a well-known acute phase protein. The aim of this study was to determine factors associated with high levels of CRP in obesity. MethodsIn 674 obese patients candidates to bariatric surgery (mean body mass index [BMI] = 47.4±7.4 kg/m²), we examined the relationships between CRP and a series of bioclinical markers and histologic features of subcutaneous and omental WAT (scWAT) and liver. We also compared the same parameters after separating patients with “high” inflammation (HI, CRP≥20 mg/L, n = 52) and with “low” inflammation (LI, CRP<20 mg/L, n = 622). ResultsMean CRP was 8.9±6.9 mg/L and positively correlated with fat mass (P<10–4). The HI group included predominantly women (92% versus 79%), of a younger age, with higher BMI (50.9±8.8 versus 47.1±7.2 kg/m2, P = .003), and fat mass (51.6 versus 48.8%, P<.001), higher prevalence of obstructive sleep apnea (OSA) (73% versus 57%, P = .02), and had increased number of HAM56+ immune cells in scWAT (20.8 versus 14.5%, P = .05). There was no difference in metabolic status, WAT fibrosis or liver histology findings between the groups. After 1 year of surgery-induced weight loss, 48 out of 52 patients with HI returned to CRP levels <20 mg/L. ConclusionOur results suggest that WAT inflammation is a major contributor to increased CRP in obesity. In obese patients presenting high CRP levels with no obvious explanation, age, gender, BMI, fat mass proportion, OSA, and WAT inflammation should be taken into account to decide to perform further additional medical investigations.

Human adipocyte function is impacted by mechanical cues

Fibrosis is a hallmark of human white adipose tissue (WAT) during obesity-induced chronic inflammation. The functional impact of increased interstitial fibrosis (peri-adipocyte fibrosis) on adjacent adipocytes remains unknown. Here we developed a novel in vitro 3D culture system in which human adipocytes and decellularized material of adipose tissue (dMAT) from obese subjects are embedded in a peptide hydrogel. When cultured with dMAT, adipocytes showed decreased lipolysis and adipokine secretion and increased expression/production of cytokines (IL-6, G-CSF) and fibrotic mediators (LOXL2 and the matricellular proteins THSB2 and CTGF). Moreover, some alterations including lipolytic activity and fibro-inflammation also occurred when the adipocyte/hydrogel culture was mechanically compressed. Notably, CTGF expression levels correlated with the amount of peri-adipocyte fibrosis in WAT from obese individuals. Moreover, dMAT-dependent CTGF promoter activity, which depends on β1-integrin/cytoskeleton pathways, was enhanced in the presence of YAP, a mechanosensitive co-activator of TEAD transcription factors. Mutation of TEAD binding sites abolished the dMAT-induced promoter activity. In conclusion, fibrosis may negatively affect human adipocyte function via mechanosensitive molecules, in part stimulated by cell deformation.