Adipocyte regulation of cancer stem cells

Cancer stem cells (CSCs) are a highly tumorigenic subpopulation of the cancer cells within a tumor that drive tumor initiation, progression, and therapy resistance. In general, stem cell niche provides a specific microenvironment in which stem cells are present in an undifferentiated and self-renewable state. CSC niche is a specialized tumor microenvironment for CSCs which provides cues for their maintenance and propagation. However, molecular mechanisms for the CSC-niche interaction remain to be elucidated. We have revealed that adipsin (complement factor D) and its downstream effector hepatocyte growth factor are secreted from adipocytes and enhance the CSC properties in breast cancers in which tumor initiation and progression are constantly associated with the surrounding adipose tissue. Considering that obesity, characterized by excess adipose tissue, is associated with an increased risk of multiple cancers, it is reasonably speculated that adipocyte-CSC interaction is similarly involved in many types of cancers, such as pancreas, colorectal, and ovarian cancers. In this review, various molecular mechanisms by which adipocytes regulate CSCs, including secretion of adipokines, extracellular matrix production, biosynthesis of estrogen, metabolism, and exosome, are discussed. Uncovering the roles of adipocytes in the CSC niche will propose novel strategies to treat cancers, especially those whose progression is linked to obesity.

The Role of Adipsin, Complement Factor D, in the Pathogenesis of Graves' Orbitopathy

Purpose

Graves' orbitopathy (GO) is an orbital manifestation of autoimmune Graves' disease, and orbital fibroblast is considered a target cell, producing pro-inflammatory cytokines and/or differentiating into adipocytes. Adipose tissue has been focused on as an endocrine and inflammatory organ secreting adipokines. We investigated the pathogenic role of a specific adipokine, adipsin, known as complement factor D in Graves' orbital fibroblasts.

Methods

The messenger RNA (mRNA) expression of multiple adipokines was investigated in adipose tissues harvested from GO and healthy subjects. Adipsin protein production was analyzed in primary cultured orbital fibroblasts under insulin growth factor (IGF)-1, CD40 ligand (CD40L) stimulation, and adipogenesis. The effect of blocking adipsin with small interfering RNA (siRNA) on pro-inflammatory cytokine production and adipogenesis was evaluated using quantitative real-time PCR, Western blot, and ELISA. Adipogenic differentiation was identified using Oil Red O staining.

Results

Adipsin gene expression was significantly elevated in GO tissue and increased after the stimulation of IGF-1 and CD40L, as well as adipocyte differentiation in GO cells. Silencing of adipsin suppressed IGF-1-induced IL-6, IL-8, COX2, ICAM-1, CCL2 gene expression, and IL-6 protein secretion. Adipsin suppression also attenuated adipocyte differentiation. Exogenous treatment of recombinant adipsin resulted in the activation of the Akt, ERK, p-38, and JNK signaling pathways.

Conclusions

Adipsin, secreted by orbital fibroblasts, may play a distinct role in the pathogenesis of GO. Inhibition of adipsin ameliorated the production of pro-inflammatory cytokines and adipogenesis in orbital fibroblasts. Our study provides an in vitro basis suggesting adipsin as a potential therapeutic target for GO treatment.

Increased Serum Adipsin Correlates with MAFLD and Metabolic Risk Abnormalities

PURPOSE

A panel of international experts proposed a new definition of fatty liver in 2020, namely metabolic dysfunction-associated fatty liver disease (MAFLD). As an adipokine, adipsin is closely related to metabolic-related diseases. In this study, we aimed to evaluate the relationship among MAFLD, serum adipsin, and metabolic risk abnormalities.

METHODS

Our study was a cross-sectional study based on the first follow-up of the Guangzhou Nutrition and Health Study (GNHS). A total of 908 patients with hepatic steatosis were involved in our study. Detailed data of patients were collected based upon questionnaire information, physical examination, and blood biochemical test.

RESULTS

Among the 908 patients, 789 patients were diagnosed with MAFLD. The levels of serum adipsin in the MAFLD group and non-MAFLD group were (3543.00 (3187.94-3972.50) ng/mL) and (3095.33 (2778.71-3354.77) ng/mL) (P < 0.001), respectively. After adjusting for potential confounders, adipsin levels were found to be associated with MAFLD. The OR was 3.46 (95% CI: 1.57-7.64) for adipsin when comparing subjects in the highest tertile with those in the lowest tertile. With the increase in the number of metabolic risk abnormalities, both the levels of serum adipsin and the proportion of moderate to severe fatty liver increased (all p-trend < 0.001).

CONCLUSION

Increased serum adipsin correlates with MAFLD. Both adipsin levels as well as fatty liver severity increase with higher numbers of metabolic risk abnormalities.

PPARγ Acetylation Orchestrates Adipose Plasticity and Metabolic Rhythms

Systemic glucose metabolism and insulin activity oscillate in response to diurnal rhythms and nutrient availability with the necessary involvement of adipose tissue to maintain metabolic homeostasis. However, the adipose-intrinsic regulatory mechanism remains elusive. Here, the dynamics of PPARγ acetylation in adipose tissue are shown to orchestrate metabolic oscillation in daily rhythms. Acetylation of PPARγ displays a diurnal rhythm in young healthy mice, with the peak at zeitgeber time 0 (ZT0) and the trough at ZT18. This rhythmic pattern is deranged in pathological conditions such as obesity, aging, and circadian disruption. The adipocyte-specific acetylation-mimetic mutation of PPARγ K293Q (aKQ) restrains adipose plasticity during calorie restriction and diet-induced obesity, associated with proteolysis of a core circadian component BMAL1. Consistently, the rhythmicity in glucose tolerance and insulin sensitivity is altered in aKQ and the complementary PPARγ deacetylation-mimetic K268R/K293R (2KR) mouse models. Furthermore, the PPARγ acetylation-sensitive downstream target adipsin is revealed as a novel diurnal factor that destabilizes BMAL1 and mediates metabolic rhythms. These findings collectively signify that PPARγ acetylation is a hinge connecting adipose plasticity and metabolic rhythms, the two determinants of metabolic health.

Exercise Promotes Bone Marrow Microenvironment by Inhibiting Adipsin in Diet-Induced Male Obese Mice

Obesity is a growing global epidemic linked to many diseases, including diabetes, cardiovascular diseases, and musculoskeletal disorders. Exercise can improve bone density and decrease excess bone marrow adipose tissue (BMAT) in obese individuals. However, the mechanism of exercise regulating bone marrow microenvironment remains unclear. This study examines how exercise induces bone marrow remodeling in diet-induced obesity. We employed unbiased RNA-Seq to investigate the effect of exercise on the bone marrow of diet-induced obese male mice. Bone mesenchymal stem cells (BMSCs) were isolated to explore the regulatory effects of exercise in vitro. Our data demonstrated that exercise could slow down the progression of obesity and improve trabecular bone density. RNA-seq data revealed that exercise inhibited secreted phosphoprotein 1 (Spp1), which was shown to mediate bone resorption through mechanosensing mechanisms. Interactome analysis of Spp1 using the HINT database showed that Spp1 interacted with the adipokine adipsin. Moreover, exercise decreased BMAT, which induced osteoclast differentiation and promoted bone loss. Our study reveals that exercise improves the bone marrow microenvironment by at least partially inhibiting the adipsin-Spp1 signaling pathway so as to inhibit the alternative complement system from activating osteoclasts in diet-induced obese mice.

Influence of eight weeks of combined training on adipsin and lipoprotein profile and possible relations with depression, anxiety and stress in women with multiple sclerosis

OBJECTIVES

Immobility and its physiological and psychological consequences are common problems in patients with multiple sclerosis. The aim of this study was to investigate the effect of 8 weeks of combined training on Adipsin and lipid profile and the possible relationship between these indicators and psychological function in women with multiple sclerosis.

METHODS

In this quasi-experimental study, 40 women with multiple sclerosis were selected by purposeful sampling method and randomly divided into two equal control and exercise groups (n=20). Exercise was performed for 8 weeks (two resistance sessions and one endurance session per week). Before and after the intervention, blood samples were taken and the DASS-21 questionnaire was completed to assess anxiety, depression and stress. Data were analyzed using analysis of covariance, t-test, Bonferroni post hoc test and Pearson correlation test at a significance level of p≤0.05.

RESULTS

In the exercise group, levels of Adipsin, total cholesterol, LDL, TG, weight, fat percentage, WHR, BMI, depression, anxiety and stress were significantly reduced and HDL levels were significantly increased after 8 weeks of combined exercise (p≤0.05). Also, BMI (p=0.01), fat percentage (p=0.01) and WHR (p=0.01) levels had significant positive correlation with Adipsin. There was a significant positive relationship between Total cholesterol level with depression index (p=0.04).

CONCLUSIONS

Performing combination exercises through improving body composition can increase the risk of obesity and cardiovascular risk factors and improve the psychological function of patients with multiple sclerosis. Specialists can use these exercises as an adjunct to drug therapy for MS patients.

Evaluation of Applicability of Novel Markers of Metabolic Syndrome in Adult Men

There is a continuous worldwide increase in incidences of metabolic syndrome (MetS) reaching about a quarter of the world’s population. Thus, studies that allow for a robust diagnosis of MetS are of paramount importance from an economic and medical point of view. This study was carried out in a group of men diagnosed with MetS using consensus definition criteria that included the definitions of the International Diabetes Foundation and Diabetes Federation and the American Heart Association/National Heart, Lung, and Blood Institute. The control group consisted of men for whom the parameters that define the MetS were in the norm. This study analyzed statistical differences between MetS and healthy men and the correlations between the set of 14 potential markers of MetS, that is, between body mass index, total cholesterol, high-density lipoprotein cholesterol, low-density lipoprotein, triglycerides, cortisol, adiponectin, monocyte chemotactic protein-1 (MCP-1), C-reactive protein (CRP), adipsin, leptin, resistin, and plasminogen activator inhibitor-1 (PAI)-1. This report revealed a significant difference between MetS and healthy men in most of the parameters studied. Furthermore, a strong positive correlation between cortisol levels and body mass index was demonstrated. Furthermore, MCP-1 levels in men with MetS were significantly higher than their levels in healthy men. Finally, a strong positive correlation was also observed between adiponectin and adipsin in Mets men. Thus, this study reveals the potential usefulness of adiponectin, MCP-1, adipsin, leptin, resistin, and PAI-1 as markers of MetS in adult men.

Complement Factor D Is a Novel Biomarker and Putative Therapeutic Target in Cutaneous Squamous Cell Carcinoma

Simple Summary

The incidence of the most common metastatic skin malignancy, cutaneous squamous cell carcinoma (cSCC), is growing worldwide, and the prognosis of the metastatic disease is poor. Presently, there are no biomarkers or therapeutic targets for high-risk cSCCs. Recent studies have demonstrated the essential role of autocrine complement synthesis in the progression of cSCC. Here, we have evaluated the role of complement Factor D (FD), the rate-limiting enzyme of the alternative complement pathway, in cSCC development. The results identify FD as a novel biomarker and putative therapeutic target for cSCC and propose the small-molecule FD inhibitor Danicopan as a highly specific drug candidate in the therapy of advanced cSCC. It is expected that the discovery of complement-associated molecular markers for cSCC progression would improve diagnosis, classification, prognostication, and targeted therapy of cSCC and its precursors in the future.

Abstract

Cutaneous squamous cell carcinoma (cSCC) is the most prevalent metastatic skin cancer. Previous studies have demonstrated the autocrine role of complement components in cSCC progression. We have investigated factor D (FD), the key enzyme of the alternative complement pathway, in the development of cSCC. RT-qPCR analysis of cSCC cell lines and normal human epidermal keratinocytes (NHEKs) demonstrated significant up-regulation of FD mRNA in cSCC cells compared to NHEKs. Western blot analysis also showed more abundant FD production by cSCC cell lines. Significantly higher FD mRNA levels were noted in cSCC tumors than in normal skin. Strong tumor cell-associated FD immunolabeling was detected in the invasive margin of human cSCC xenografts. More intense tumor cell-specific immunostaining for FD was seen in the tumor edge in primary and metastatic cSCCs, in metastases, and in recessive dystrophic epidermolysis bullosa-associated cSCCs, compared with cSCC in situ, actinic keratosis and normal skin. FD production by cSCC cells was dependent on p38 mitogen-activated protein kinase activity, and it was induced by interferon-γ and interleukin-1β. Blocking FD activity by Danicopan inhibited activation of extracellular signal-regulated kinase 1/2 and attenuated proliferation of cSCC cells. These results identify FD as a novel putative biomarker and therapeutic target for cSCC progression.

Elevated Adipsin and Reduced C5a Levels in the Maternal Serum and Follicular Fluid During Implantation Are Associated With Successful Pregnancy in Obese Women

INTRODUCTION

Complement factors mediate the recruitment and activation of immune cells and are associated with metabolic changes during pregnancy. The aim of this study was to determine whether complement factors in the maternal serum and follicular fluid (FF) are associated with in vitro fertilization (IVF) outcomes in overweight/obese women.

METHODS

Forty overweight/obese (BMI = 30.8 ± 5.2 kg/m²) female patients, 33.6 ± 6.3 years old, undergoing IVF treatment for unexplained infertility were recruited. Baseline demographic information, including biochemical hormonal, metabolic, and inflammatory markers, and pregnancy outcome, was collected. Levels of 14 complement markers (C2, C4b, C5, C5a, C9, adipsin, mannose-binding lectin, C1q, C3, C3b/iC3b, C4, factor B, factor H, and properdin) were assessed in the serum and FF and compared to IVF outcome, inflammatory, and metabolic markers using multivariate and univariate models.

RESULTS

Out of 40 IVF cycles, 14 (35%) resulted in pregnancy. Compared to women with failed pregnancies, women with successful pregnancies had higher levels of adipsin in the serum and FF (p = 0.01) but lower C5a levels (p = 0.05). Serum adipsin levels were positively correlated with circulating levels of vitamin D (R = 0.5, p = 0.02), glucagon (R = 0.4, p = 0.03), leptin (R = 0.4, p = 0.01), resistin (R = 0.4, p = 0.02), and visfatin (R = 0.4, p = 0.02), but negatively correlated with total protein (R = -0.5, p = 0.03). Higher numbers of top-quality embryos were associated with increased levels of C3, properdin, C1q, factors H and B, C4, and adipsin, but with reduced C2 and C5a levels (p ≤ 0.01).

CONCLUSIONS

Higher adipsin and lower C5a levels in the maternal serum during implantation are potential markers of successful outcome in obese women undergoing IVF-assisted pregnancies.

[Changes in adipokines in the blood of patients with the first episode of schizophrenia during treatment with haloperidol and risperidone]

OBJECTIVE

To study plasma adipokines (adiponectin, leptin, adipsin) in patients with the first episode of schizophrenia treated with haloperidol and risperidone.

MATERIAL AND METHODS

Two hundred and twelve patients with the first episode of paranoid schizophrenia (F20.09) were examined. Patients were divided into the haloperidol group (n=107) and the risperidone group (n=105). The control group included 132 healthy people. Body mass index was recorded at baseline and in 2, 4, 6, 8 week of treatment. Adiponectin, adipsin and leptin were determined by the multiplex analysis. Blood test was conducted prior to therapy and after 8 weeks of treatment.

RESULTS

An increase in body mass index is recorded in both clinical groups, with no statistically significant differences between groups. Before treatment with antipsychotics, the levels of adiponectin and adipsin increase in both clinical groups. In the course of therapy, the levels of adiponectin and adipsin significantly increase in the haloperidol group and the levels of adiponectin and leptin in the risperidone group.

CONCLUSION

The increase in body weight is not the only mechanism of changes in adipokines in blood during treatment with antipsychotics. Further studies on the relationship between the levels of adipokines and pharmacogenic metabolic disorders are required.

Adipsin of the Alternative Complement Pathway Is a Potential Predictor for Preeclampsia in Early Pregnancy

Objective

The concentrations of complement proteins (adipsin, C3a, and C5a) and soluble endoglin (sENG) in the plasma were measured in this study, and their value as early-pregnancy predictors and potential diagnostic marker of preeclampsia was assessed, respectively.

Experimental Design

Plasma samples were obtained from healthy and preeclampsia pregnant women before delivery for a cross-sectional study. Plasma samples were collected from healthy and preeclampsia pregnant women throughout pregnancy and postpartum for a follow-up study. Enzyme-linked immunosorbent assays were used to detect plasma levels of several complement proteins (adipsin, C3a, and C5a) and sENG.

Results

The plasma levels of adipsin, C5a, and sENG were significantly increased before delivery in pregnant women with preeclampsia. During pregnancy, the plasma adipsin, C5a, and sENG levels were increased from the third trimester in healthy pregnant women; plasma adipsin levels remained stable after delivery, while C3a levels increased in the second trimester and remained stable afterward. Furthermore, levels of adipsin, C5a, and sENG were higher in preeclampsia patients at different stages of pregnancy; the C3a level presents a similar change and no difference was found in the third trimester. In the first trimester, receiver-operating curve (ROC) curve analysis showed that adipsin (AUC, 0.83 ± 0.06, P=0.001) and sENG (AUC, 0.74 ± 0.09, P=0.021) presented high value as predictors of early pregnancy.

Conclusions

Adipsin is likely a novel plasma biomarker to monitor the increased risk of preeclampsia in early pregnancy. Moreover, the increased plasma levels of adipsin, C5a, and sENG before delivery may be associated with preeclampsia.

Adipsin-Dependent Secretion of Hepatocyte Growth Factor Regulates the Adipocyte-Cancer Stem Cell Interaction

Simple Summary

Obesity, which is characterized by the excess of adipose tissue, is associated with an increased risk of multiple cancers. We have previously reported that adipsin, a secreted factor from adipocytes, enhances cancer cell proliferation and stem cell properties. In this study, we found that adipsin affected adipocytes themselves and enhanced their secretion of hepatocyte growth factor (HGF). We found that HGF enhanced the adipocyte-cancer cell interactions as a downstream effector of adipsin. Understanding the adipocyte-cancer cell interaction will provide a novel strategy to treat cancers whose initiation, invasion, and metastatic progression are associated with adipose tissues.

Abstract

Adipose tissue is a component of the tumor microenvironment and is involved in tumor progression. We have previously shown that adipokine adipsin (CFD) functions as an enhancer of tumor proliferation and cancer stem cell (CSC) properties in breast cancers. We established the Cfd-knockout (KO) mice and the mammary adipose tissue-derived stem cells (mADSCs) from them. Cfd-KO in mADSCs significantly reduced their ability to enhance tumorsphere formation of breast cancer patient-derived xenograft (PDX) cells, which was restored by the addition of Cfd in the culture medium. Hepatocyte growth factor (HGF) was expressed and secreted from mADSCs in a Cfd-dependent manner. HGF rescued the reduced ability of Cfd-KO mADSCs to promote tumorsphere formation in vitro and tumor formation in vivo by breast cancer PDX cells. These results suggest that HGF is a downstream effector of Cfd in mADSCs that enhances the CSC properties in breast cancers.

Complement Factor D (adipsin) Levels Are Elevated in Acquired Partial Lipodystrophy (Barraquer-Simons syndrome)

Complement overactivation has been reported in most patients with Barraquer-Simons syndrome (BSS), a rare form of acquired partial lipodystrophy. Complement Factor D (FD) is a serine protease with a crucial role in the activation of the alternative pathway of the complement system, which is mainly synthesized by adipose tissue. However, its role in the pathogenesis of BSS has not been addressed. In this study, plasma FD concentration was measured in 13 patients with BSS, 20 patients with acquired generalized lipodystrophy, 22 patients with C3 glomerulopathy (C3G), and 50 healthy controls. Gene expression and immunohistochemistry studies were assayed using atrophied adipose tissue from a patient with BSS. We found significantly elevated FD levels in BSS cases compared with the remaining cohorts (p < 0.001). There were no significant differences in FD levels between sexes but FD was strongly and directly associated with age in BSS (r = 0.7593, p = 0.0036). A positive correlation between FD and C3 was seen in patients with C3G, characterized by decreased FD levels due to chronic C3 consumption, but no correlation was detected for BSS. Following mRNA quantification in the patient's adipose tissue, we observed decreased CFD and C3 but elevated C5 transcript levels. In contrast, the increased FD staining detected in the atrophied areas reflects the effects of persistent tissue damage on the adipose tissue, thus providing information on the ongoing pathogenic process. Our results suggest that FD could be a reliable diagnostic biomarker involved in the pathophysiology of BSS by promoting unrestrained local complement system activation in the adipose tissue environment.

Adiposity Measurements and Metabolic Syndrome Are Linked Through Circulating Neuregulin 4 and Adipsin Levels in Obese Adults

Background

Adiposity and adipokines are associated with metabolic disorders, but little is known regarding that whether adiposity measurements link metabolic syndrome (MetS) through circulating neuregulin 4 (Nrg4) and adipsin levels.

Materials and Methods

A total of 1212 subjects with a waist circumference greater than 90 cm for men or 80 cm for women were enrolled from a Chinese community. Circulating Nrg4 and adipsin levels were measured using commercial kits. Mediation analyses of circulating Nrg4 and adipsin were performed in the study using linear and logistic regression.

Results

Subjects with MetS had higher waist circumference, visceral fat level, and circulating adipsin level, and lower levels of circulating Nrg4 and muscle mass to visceral fat (MVF) ratio (all P < 0.05). In multivariable logistic regression analyses, after adjusting for confounding variables, per standard deviation (SD) increase in waist circumference and visceral fat level were significantly associated with increased odds of MetS [OR (95% CI), 1.42 (1.22–1.64); 2.20 (1.62–2.99); respectively]; and per SD reduction in MVF ratio was significantly associated with reduced odds of MetS [OR (95% CI), 0.65 (0.55–0.77)]. In the mediation analyses, both circulating Nrg4 and adipsin levels mediated the association between waist circumference (8.31% and 18.35%, respectively), visceral fat level (7.50% and 9.98%, respectively), and MVF ratio (5.80% and 9.86%, respectively) and MetS after adjustments.

Conclusion

These findings indicate that adiposity measurements and MetS are linked through circulating Nrg4 and adipsin levels in obese adults, suggesting that circulating Nrg4 and adipsin levels might be potential predictors for management of MetS.

Fli1 deficiency induces endothelial adipsin expression, contributing to the onset of pulmonary arterial hypertension in systemic sclerosis

OBJECTIVES

Adipsin, or complement factor D, is a serine proteinase catalysing complement factor C3 breakdown, leading to the production of opsonin (C3b), membrane attack complex (C5b-C9) and anaphylatoxins (C3a and C5a). Since adipsin is potentially associated with pulmonary arterial hypertension in SSc, we investigated adipsin expression in dermal small vessels of SSc-involved skin, the mechanism regulating adipsin expression in endothelial cells, and the correlation of serum adipsin levels with SSc clinical symptoms.

METHODS

Adipsin expression was assessed by immunohistochemistry with skin sections of SSc and healthy subjects. mRNA levels of target genes and transcription factor binding to the ADIPSIN promoter were evaluated by quantitative reverse transcription PCR and chromatin immunoprecipitation, respectively. Serum adipsin levels were determined by enzyme-linked immunosorbent assay.

RESULTS

Adipsin expression was remarkably increased in dermal small vessels of SSc-involved skin as compared with those of healthy control skin. Consistent with the notion that Fli1 deficiency induces SSc-like phenotypes in various types of cells, FLI1 siRNA enhanced adipsin expression at protein and mRNA levels and Fli1 bound to the ADIPSIN promoter in human dermal microvascular endothelial cells. Serum adipsin levels were significantly lower in diffuse cutaneous SSc patients than in limited cutaneous SSc patients and healthy controls, and were associated positively with elevated right ventricular systolic pressure and inversely with interstitial lung disease by multivariate regression analysis.

CONCLUSION

Adipsin is up-regulated at least partially by Fli1 deficiency in endothelial cells, potentially contributing to the development of pulmonary vascular involvement in SSc.

Adipsin promotes bone marrow adiposity by priming mesenchymal stem cells

Background

Marrow adipose tissue (MAT) has been shown to be vital for regulating metabolism and maintaining skeletal homeostasis in the bone marrow (BM) niche. As a reflection of BM remodeling, MAT is highly responsive to nutrient fluctuations, hormonal changes, and metabolic disturbances such as obesity and diabetes mellitus. Expansion of MAT has also been strongly associated with bone loss in mice and humans. However, the regulation of BM plasticity remains poorly understood, as does the mechanism that links changes in marrow adiposity with bone remodeling.

Methods

We studied deletion of Adipsin, and its downstream effector, C3, in C57BL/6 mice as well as the bone-protected PPARγ constitutive deacetylation 2KR mice to assess BM plasticity. The mice were challenged with thiazolidinedione treatment, calorie restriction, or aging to induce bone loss and MAT expansion. Analysis of bone mineral density and marrow adiposity was performed using a μCT scanner and by RNA analysis to assess adipocyte and osteoblast markers. For in vitro studies, primary bone marrow stromal cells were isolated and subjected to osteoblastogenic or adipogenic differentiation or chemical treatment followed by morphological and molecular analyses. Clinical data was obtained from samples of a previous clinical trial of fasting and high-calorie diet in healthy human volunteers.

Results

We show that Adipsin is the most upregulated adipokine during MAT expansion in mice and humans in a PPARγ acetylation-dependent manner. Genetic ablation of Adipsin in mice specifically inhibited MAT expansion but not peripheral adipose depots, and improved bone mass during calorie restriction, thiazolidinedione treatment, and aging. These effects were mediated through its downstream effector, complement component C3, to prime common progenitor cells toward adipogenesis rather than osteoblastogenesis through inhibiting Wnt/β-catenin signaling.

Conclusions

Adipsin promotes new adipocyte formation and affects skeletal remodeling in the BM niche. Our study reveals a novel mechanism whereby the BM sustains its own plasticity through paracrine and endocrine actions of a unique adipokine.

Funding

This work was supported by the National Institutes of Health T32DK007328 (NA), F31DK124926 (NA), R01DK121140 (JCL), R01AR068970 (BZ), R01AR071463 (BZ), R01DK112943 (LQ), R24DK092759 (CJR), and P01HL087123 (LQ).

Adipsin deficiency does not impact atherosclerosis development in Ldlr-/- mice

Obesity is a potent risk factor for atherosclerotic morbidity and mortality. Cytokines secreted from adipose tissue, namely, adipokines, have been suggested to be actively involved in atherosclerosis. One of the most abundant adipokines, adipsin, is downregulated in obesity. It catalyzes the rate-limiting step of alternative complement activation, which is one of the three complement pathways potentially involved in inflammation in atherosclerosis. Interestingly, adipsin has been identified as a novel biomarker in human coronary artery disease. However, its role in the development of atherosclerosis remains unexplored. We crossed adipsin^-/- mice onto an Ldlr^-/- background [double-knockout (DKO) mice] and induced atherogenesis by high-fat and high-cholesterol feeding. Metabolic profiles were systemically characterized, and atherosclerotic plaques were measured at both aortic root and arch regions. Western blotting was conducted to assess adipsin level and complement activity. The DKO mice exhibited similar sizes of atherosclerotic lesions as Ldlr^-/- control mice at both the aortic root and arch regions. Accordingly, they displayed comparable metabolic parameters, including body weight, insulin sensitivity, and lipid profiles, along with compensated complement activity. Adipsin deficiency does not impact the development of atherosclerosis in Ldlr^-/- mice despite its crucial function in alternative complement activation. Therefore, it is unlikely to play an important role in mediating the risk of atherosclerotic complications in obesity.NEW & NOTEWORTHY Adipsin deficiency does not impact the development of atherosclerosis in Ldlr^-/- mice despite its crucial function in alternative complement activation. Therefore, it is unlikely to play an important role in mediating the risk of atherosclerotic complications in obesity.

Predictors of HbA1c among Adipocytokine Biomarkers in African-American Men with Varied Glucose Tolerance

This study explored adipocytokine associations with acute and chronic hyperglycemia in African-American men (AAM). Fourteen adipocytokines were measured from men with normal glucose tolerance (NGT) or type 2 diabetes (T2D, drug-naïve MF(-) or using metformin MF(+)). Acute and chronic hyperglycemia were evaluated by 120 min oral glucose tolerance test (OGTT) and glycohemoglobin A1c (HbA1c). AAM with T2D (n = 21) compared to NGT (n = 20) were older, had higher BMI and slightly higher glucose and insulin. In the fasted state, TNF-α, IL-6, PAI-1, IL-13, adiponectin, adipsin, and lipocalin were lower in T2D vs. NGT. At 120 min post-glucose load, TNF-α, IL-6, IL-13, IL-8, PAI-1, adiponectin, adipsin, lipocalin, and resistin were lower in T2D vs. NGT. There were no statistical differences for GM-CSF, IL-7, IL-10, IP-10, and MCP-1. Regression analysis showed that fasting IL-8, TNF-α, adiponectin, lipocalin, resistin, adipsin, and PAI-1 were associated with HbA1c. After adjusting for age, BMI, glucose tolerance, and metformin use, only adipsin remained significantly associated with HbA1c (p = 0.021). The model including adipsin, TNF-α, age, BMI, and group designation (i.e., NGT, MF(-), MF(+)) explained 86% of HbA1c variability. The data suggested that adipsin could be associated with HbA1c in AAM with varied glucose tolerance.

Fat-Produced Adipsin Regulates Inflammatory Arthritis

We explored the relationship of obesity and inflammatory arthritis (IA) by selectively expressing diphtheria toxin in adipose tissue yielding "fat-free" (FF) mice completely lacking white and brown fat. FF mice exhibit systemic neutrophilia and elevated serum acute phase proteins suggesting a predisposition to severe IA. Surprisingly, FF mice are resistant to K/BxN serum-induced IA and attendant bone destruction. Despite robust systemic basal neutrophilia, neutrophil infiltration into joints of FF mice does not occur when challenged with K/BxN serum. Absence of adiponectin, leptin, or both has no effect on joint disease, but deletion of the adipokine adipsin (complement factor D) completely prevents serum-induced IA. Confirming that fat-expressed adipsin modulates the disorder, transplantation of wild-type (WT) adipose tissue into FF mice restores susceptibility to IA, whereas recipients of adipsin-deficient fat remain resistant. Thus, adipose tissue regulates development of IA through a pathway in which adipocytes modify neutrophil responses in distant tissues by producing adipsin.

Plasma Adipsin as a Biomarker and Its Implication in Type 2 Diabetes Mellitus

Diabetes mellitus (DM) is a worldwide health threat affecting millions of people, which is associated with different micro- and macro-vascular complications. Type 2 diabetes mellitus (T2DM) is one of the different types of DM caused by insulin resistance and/or reduced secretion of insulin from the pancreas. A validated novel biomarker is required to enhance the accuracy of disease prediction, provide novel insights into pathophysiology and contribute to future prevention of T2DM. Various newer diagnostic methods have been developed by targeting endogenous proteins among which Adipsin is one of the promising target. Therefore, this review discusses Adipsin as a potential biomarker and its implication in T2DM. Adipsin is one of the adipokines secreted by adipose tissues which is involved in maintaining adipose tissue homeostasis and increasing insulin secretion in response to glucose. According to different experimental and clinical studies, plasma Adipsin concentrations are low in animals and patients with DM which support its use as a biomarker in combination to the other diagnostic modalities for DM. Additionally, the existence of Adipsin could be important in improving hyperglycemia by preserving β-cell mass through improving β-cell survival and maintaining their transcriptional identity.

Regulation of Adipsin Expression by Endoplasmic Reticulum Stress in Adipocytes

Adpsin is an adipokine that stimulates insulin secretion from β-cells and improves glucose tolerance. Its expression has been found to be markedly reduced in obese animals. However, it remains unclear what factors lead to downregulation of adipsin in the context of obesity. Endoplasmic reticulum (ER) stress response is activated in various tissues under obesity-related conditions and can induce transcriptional reprogramming. Therefore, we aimed to investigate the relationship between adipsin expression and ER stress in adipose tissues during obesity. We observed that obese mice exhibited decreased levels of adipsin in adipose tissues and serum and increased ER stress markers in adipose tissues compared to lean mice. We also found that ER stress suppressed adipsin expression via adipocytes-intrinsic mechanisms. Moreover, the ER stress-mediated downregulation of adipsin was at least partially attributed to decreased expression of peroxisome proliferator-activated receptor γ (PPARγ), a key transcription factor in the regulation of adipocyte function. Finally, treatment with chemical chaperones recovered the ER stress-mediated downregulation of adipsin and PPARγ in vivo and in vitro. Our findings suggest that activated ER stress in adipose tissues is an important cause of the suppression of adipsin expression in the context of obesity.

In vivo protective effect of adipsin-deficiency on spontaneous knee osteoarthritis in aging mice

The adipokine adipsin is an emerging mediator of human osteoarthritis (OA) progression. Here, we investigated its in vivo role in the development of spontaneous OA in aging mice. We compared articular knee joint morphology, histology in knee cartilage, synovial membrane, subchondral bone, meniscus, and anterior cruciate ligament (ACL); and chondrogenesis in the ACL from adipsin-deficient (Df^-/-) and wild-type (Df^+/+) 20-week- and 20-month-old mice. Serum levels of a panel of adipokines, inflammatory factors, and metalloproteases known to be implicated in OA were investigated. Data first revealed that the early manifestation of OA appeared in the ACL of 20-week-old mice, progressing to severe alterations in the 20 month-old wild-type mice. Further results demonstrated that adipsin-deficiency protected the articular tissues from spontaneous OA progression and triggered significantly higher serum levels of the adipokines adiponectin and FGF-21 while lowering levels of the inflammatory factor interleukin 6 (IL-6) in both young and old mice. This work further underlines the clinical relevance of adipsin as a novel therapeutic approach of human OA. Moreover, this study shows the potential beneficial effect of the adipokine FGF-21 against OA, and provides support for this factor to be a new biomarker and/or target of primary OA therapeutic avenues.

CITED2 mediates the mechanical loading-induced suppression of adipokines in the infrapatellar fat pad

Adipokines secreted from the infrapatellar fat pad (IPFP), such as adipsin and adiponectin, have been implicated in osteoarthritis pathogenesis. CITED2, a mechanosensitive transcriptional regulator with chondroprotective activity, may modulate their expression. Cited2 haploinsufficient mice (Cited2^+/- ) on a high-fat diet (HFD) exhibited increased body weight and increased IPFP area compared to wild-type (WT) mice on an HFD. While an exercise regimen of moderate treadmill running induced the expression of CITED2, as well as PGC-1α, and reduced the expression of adipsin and adiponectin in the IPFP of WT mice on an HFD, Cited2 haploinsufficiency abolished the loading-induced expression of PGC-1α and loading-induced suppression of adipsin and adiponectin. Furthermore, knocking down or knocking out CITED2 in adipose stem cells (ASCs)/preadipocytes derived from the IPFP in vitro led to the increased expression of adipsin and adiponectin and reduced PGC-1α, and abolished the loading-induced suppression of adipsin and adiponectin and loading-induced expression of PGC-1α. Overexpression of PGC-1α in these ASC/preadipocytes reversed the effects caused by CITED2 deficiency. The current data suggest that CITED2 is a critical regulator in physiologic loading-induced chondroprotection in the context of an HFD and PGC-1α is required for the inhibitory effects of CITED2 on the expression of adipokines such as adipsin and adiponectin in the IPFP.

Analysis of a lectin microarray identifies altered sialylation of mouse serum glycoproteins induced by whole-body radiation exposure

Microarrays containing 45 different lectins were analyzed to identify global changes in the glycosylation of serum glycoproteins from mice exposed to whole-body γ-radiation. The results showed that radiation exposure increased and decreased the relative amounts of α-2,3- and α-2,6-sialic acids, respectively. The expression of α-2,3- and α-2,6-sialyltransferase genes in the liver was analyzed to determine whether changes in their expression were responsible for the sialic acid changes. The increase in α-2,3-sialic acid correlated with St3gal5 upregulation after radiation exposure; however, a decrease in St6gal1 expression was not observed. Analysis of a PCR array of genes expressed in irradiated mouse livers revealed that irradiation did not alter the expression of most of the included genes. These results suggest that glycomic screening of serum glycoproteins using lectin microarrays can be a powerful tool for identifying radiation-induced changes in the post-translational addition of sugar moieties to proteins. In addition, the results indicate that altered sialylation of glycoproteins may be an initial response to acute radiation exposure.

Association Between Serum Adipsin Levels and Insulin Resistance in Subjects With Various Degrees of Glucose Intolerance

Context

The association between adipsin and glucose metabolism in human subjects remains unclear.

Objective

We investigated the associations between adipsin and insulin resistance/β-cell function in subjects with various degrees of glucose intolerance.

Design

Fasting blood samples were collected for measurements of fasting plasma glucose (FPG), insulin, and adipsin. An oral glucose tolerance test was conducted in subjects with no history of diabetes.

Setting

This study was conducted at a medical center.

Patients

We enrolled 240 subjects with no history of diabetes and 80 patients with known type 2 diabetes (T2D) on diet control or metformin monotherapy.

Main Outcome Measure

β-cell function and insulin resistance were assessed using the homeostasis model assessment (HOMA-β and HOMA-IR, respectively).

Results

Levels of serum adipsin were higher in subjects with normal glucose tolerance (4.0 ± 1.1 µg/mL) or prediabetes (4.0 ± 1.5 µg/mL) compared with subjects with newly diagnosed diabetes (3.8 ± 1.1 µg/mL) or with known T2D on diet control (3.4 ± 1.0 µg/mL) or metformin monotherapy (3.0 ± 1.0 µg/mL, P < 0.001). There was no significant association between adipsin and HOMA-β. In contrast, there was an independent negative association between adipsin and HOMA-IR (β coefficient −0.414, 95% CI −0.720 to −0.109, P = 0.008). The association was more prominent in subjects with a body mass index (BMI) ≥25 kg/m² or an FPG ≥100 mg/dL (P interaction < 0.001 and 0.014, respectively).

Conclusions

Serum adipsin levels were negatively associated with insulin resistance, especially in subjects with a BMI ≥25 kg/m² or an FPG ≥100 mg/dL.

Quercetin Impacts Expression of Metabolism- and Obesity-Associated Genes in SGBS Adipocytes

Obesity is characterized by the rapid expansion of visceral adipose tissue, resulting in a hypoxic environment in adipose tissue which leads to a profound change of gene expression in adipocytes. As a consequence, there is a dysregulation of metabolism and adipokine secretion in adipose tissue leading to the development of systemic inflammation and finally resulting in the onset of metabolic diseases. The flavonoid quercetin as well as other secondary plant metabolites also referred to as phytochemicals have anti-oxidant, anti-inflammatory, and anti-diabetic effects known to be protective in view of obesity-related-diseases. Nevertheless, its underlying molecular mechanism is still obscure and thus the focus of this study was to explore the influence of quercetin on human SGBS (Simpson Golabi Behmel Syndrome) adipocytes’ gene expression. We revealed for the first time that quercetin significantly changed expression of adipokine (Angptl4, adipsin, irisin and PAI-1) and glycolysis-involved (ENO2, PFKP and PFKFB4) genes, and that this effect not only antagonized but in part even overcompensated the effect mediated by hypoxia in adipocytes. Thus, these results are explained by the recently proposed hypothesis that the protective effect of quercetin is not solely due to its free radical-scavenging activity but also to a direct effect on mitochondrial processes, and they demonstrate that quercetin might have the potential to counteract the development of obesity-associated complications.