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Secondary bile acids (SBAs) with high hydrophobicity are abundant in the colonic lumen. However, both aggravating and protective roles of SBAs have been proposed in the pathogenesis of inflammatory bowel diseases (IBDs). We observed that oral administration of hyodeoxycholic acid (HDCA), a hydrophilic bile acid, prevented the development of dextran sulfate sodium (DSS)-induced colitis in mice. We then examined the individual effects of DSS and HDCA as well as their combined effects on fecal bile acid profile in mice. HDCA treatment increased the levels of most of fecal bile acids, whereas DSS treatment had limited effects on the levels of fecal bile acids. The combined treatment with DSS and HDCA synergistically increased the levels of fecal chenodeoxycholic acid (CDCA) and deoxycholic acid (DCA) in feces, which are potent activators of the farnesoid X receptor (FXR) and Takeda G-protein-coupled receptor 5 (TGR5). The overall hydrophobicity of fecal bile acids was not modified by any treatments. Our data suggest that the preventive effect of HDCA on DSS-induced colitis in mice is due to the synergism between DSS and HDCA in increasing the levels of the fecal bile acids with potencies to activate FXR and TGR5.

BACKGROUND Distal pancreatectomy with en bloc celiac artery resection (DP-CAR) is a curative surgical method for locally advanced pancreatic body cancer; however, arterial reconstruction remains controversial in this procedure. This report presents the case of a 47-year-old man with advanced distal pancreatic carcinoma and initial partial response to chemotherapy who required celiac axis reconstruction of the common hepatic artery and left gastric artery. CASE REPORT A 47-year-old man had loss of appetite. He had a 40-mm hypovascular tumor extending from the pancreatic body to the tail, invading around the celiac artery, common hepatic artery, left gastric artery, and splenic artery. We initiated chemotherapy concurrent with chemo-radiotherapy with S-1 administration. After chemo-radiotherapy, computed tomography (CT) showed tumor shrinkage, indicating partial response, but soft tissue CT density surrounding the celiac axis arteries persisted. We conducted conversion surgery. When the common hepatic artery was clamped during surgery, the intrahepatic arterial blood flow reduced; thus, we reconstructed the middle hepatic artery to the common hepatic artery. The left gastric artery was also reconstructed using the second jejunal artery to prevent ischemic gastropathy. Histopathologic examination showed no tumor cells in the specimen; thus, R0 resection was achieved. CONCLUSIONS Arterial reconstruction can be an option for R0 resection in DP-CAR when hepatic arterial blood flow is reduced due to an intraoperative common hepatic artery clamping test.

A 72-year-old woman was diagnosed with rheumatoid arthritis (RA) 6 years ago and was referred to our hospital for the management of RA. She achieved remission with methotrexate, and her arthritis w...

Arteriovenous malformation (AVM) in the pancreas rarely causes acute pancreatitis. However, even when it does cause pancreatitis, the pathogenesis is unclear. A 61-year-old man was admitted to our hospital for acute pancreatitis. The findings of computed abdominal tomography, magnetic resonance imaging, and endoscopic ultrasonography revealed pancreatic AVM and hematoma in the tail of the pancreas. These lesions were suspected to be associated with pancreatitis. Although endoscopic retrograde pancreatography could not confirm hemosuccus pancreaticus, distal pancreatectomy was performed because of repeated pancreatitis. The histopathological findings of the resected specimen revealed rupture of the AVM vessels into the main pancreatic ducts. Finally, we considered that intermittent bleeding due to AVM rupture and hematoma formation in the main pancreatic duct caused the repeated pancreatitis.

Pancreatic cancer is a malignant neoplasm with high invasiveness and poor prognosis. In a previous study, a highly invasive pancreatic cancer cell line was established and found to feature enhanced interleukin-32 (IL-32) expression. However, whether IL-32 promotes the invasiveness by enhancing or suppressing the expression of IL-32 through regulating downstream molecules was unclear. To investigate the effect of IL-32, cells were established with high levels of expression or downregulated IL-32; their invasive ability was measured using a real-time measurement system and the expression of some candidate downstream molecules involved in invasion was evaluated in the two cell types. The morphological changes in both cell types and the localization of IL-32 expression in pancreatic cancer tissues were studied using immunohistochemistry. Among the several splice variants of IL-32, cells transfected with the ε isoform had increased invasiveness, whereas the IL-32-suppressed cells had reduced invasiveness. Several downstream molecules, whose expression was changed in the two cell types, were monitored. Notably, changes of E-cadherin, CLDN1, CD44, CTGF and Wnt were documented. The morphologies of the two cell types differed from the original cell line. Immunohistochemically, the expression of IL-32 was observed only in tumor cells and not in normal pancreatic cells. In conclusion, IL-32 was found to promote the invasiveness of pancreatic cancer cells by regulating downstream molecules.

Muscle regeneration requires the coordination of muscle stem cells, mesenchymal fibro-adipogenic progenitors (FAPs), and macrophages. How macrophages regulate the paracrine secretion of FAPs during the recovery process remains elusive. Herein, we systemically investigated the communication between CD206

Intraosseous mucoepidermoid carcinoma of the jaw is a rare lesion that has been suggested to originate from the odontogenic epithelium. We report an unusual case of central mucoepidermoid carcinoma in an 18‐year‐old Japanese man with an odontogenic cyst., This report describes the clinical and histologic features of this extremely rare case of central mucoepidermoid carcinoma admixed with a calcifying odontogenic cyst.

Lenvatinib is a first-line standard treatment for advanced hepatocellular carcinoma (HCC) with better anti-tumor effects than sorafenib, as shown by greater inhibition of the kinases of fibroblast growth factor receptor and vascular endothelial growth factor (VEGF) receptor. This report describes a patient with advanced HCC who experienced perforation of the small intestine 1 month after starting the treatment with lenvatinib. This patient likely had partial necrosis of a metastasis to the small intestine before starting lenvatinib treatment, with subsequent ischemic changes leading to perforation of the small intestine. Although metastasis of HCC to the small intestine is rare, patients with these metastases should be regarded as being at risk for perforation during lenvatinib treatment.

Background Skeletal muscle is mainly responsible for insulin‐stimulated glucose disposal. Dysfunction in skeletal muscle metabolism especially during obesity contributes to the insulin resistance. Astaxanthin (AX), a natural antioxidant, has been shown to ameliorate hepatic insulin resistance in obese mice. However, its effects in skeletal muscle are poorly understood. The current study aimed to investigate the molecular target of AX in ameliorating skeletal muscle insulin resistance. Methods We fed 6‐week‐old male C57BL/6J mice with normal chow (NC) or NC supplemented with AX (NC+AX) and high‐fat‐diet (HFD) or HFD supplemented with AX for 24 weeks. We determined the effect of AX on various parameters including insulin sensitivity, glucose uptake, inflammation, kinase signaling, gene expression, and mitochondrial function in muscle. We also determined energy metabolism in intact C2C12 cells treated with AX using the Seahorse XFe96 Extracellular Flux Analyzer and assessed the effect of AX on mitochondrial oxidative phosphorylation and mitochondrial biogenesis. Results AX‐treated HFD mice showed improved metabolic status with significant reduction in blood glucose, serum total triglycerides, and cholesterol (p< 0.05). AX‐treated HFD mice also showed improved glucose metabolism by enhancing glucose incorporation into peripheral target tissues, such as the skeletal muscle, rather than by suppressing gluconeogenesis in the liver as shown by hyperinsulinemic–euglycemic clamp study. AX activated AMPK in the skeletal muscle of the HFD mice and upregulated the expressions of transcriptional factors and coactivator, thereby inducing mitochondrial remodeling, including increased mitochondrial oxidative phosphorylation component and free fatty acid metabolism. We also assessed the effects of AX on mitochondrial biogenesis in the siRNA‐mediated AMPK‐depleted C2C12 cells and showed that the effect of AX was lost in the genetically AMPK‐depleted C2C12 cells. Collectively, AX treatment (i) significantly ameliorated insulin resistance and glucose intolerance through regulation of AMPK activation in the muscle, (ii) stimulated mitochondrial biogenesis in the muscle, (iii) enhanced exercise tolerance and exercise‐induced fatty acid metabolism, and (iv) exerted antiinflammatory effects via its antioxidant activity in adipose tissue. Conclusions We concluded that AX treatment stimulated mitochondrial biogenesis and significantly ameliorated insulin resistance through activation of AMPK pathway in the skeletal muscle.

To investigate the overexpression of genes in sebaceous gland carcinoma (SGC) of the eyelid compared to sebaceous adenoma of the eyelid in order to elucidate the molecular mechanism underlying pathogenesis. We performed histopathological examination of eyelid tissues surgically removed from four patients diagnosed with SGC (cases 1–3) and sebaceous adenoma (case 4) of the eyelid. Next, we performed global gene expression analysis of surgical tissue samples using a GeneChip® system and the Ingenuity Pathways Knowledge Base. The results of the GeneChip® analysis were explored with quantitative real-time polymerase chain reaction (qRT-PCR) analysis. In the SGC samples, we found that 211, 199, and 199 genes, respectively, showed ≥ 2.0-fold higher expression than those in the sebaceous adenoma sample (case 4); 194 genes were common to all three SGC samples. For the 194 genes with upregulated expression, functional category analysis showed that SGC of the eyelid employed a unique gene network, including cyclin-dependent kinase inhibitor 2A (CDKN2A), cyclin-dependent kinase 1 (CDK1), and cyclin E1 (CCNE1), which are related to cell cycle progression, incidence of tumor, and cell viability. Furthermore, qRT-PCR analysis showed that the expression levels of CDKN2A, CDK1, and CCNE1 were significantly upregulated in all SGC cases compared to those in the sebaceous adenoma case. These data were similar to the results of microarray analysis. Overexpression of cell cycle-related genes CDKN2A, CDK1, CCNE1, and their gene network may help elucidate the pathogenic pathway of SGC of the eyelid at the molecular level.

BACKGROUND/AIM This study aimed to obtain accurate differential diagnosis (DDx) of multicentric carcinogenesis (MC) and intrahepatic metastasis (IM) in recurrent lesions of hepatocellular carcinoma. MATERIALS AND METHODS A total of 79 patients who underwent re-hepatectomy (2000-2013) were examined. PCR was used to analyze 13 chromosomal microsatellite loci by PCR. On the basis of this genetic analysis, the recurrent lesions were diagnosed as IM, MC or not determined (ND). Subsequently, DDx was compared with types of resection and outcome. RESULTS The recurrent lesions were diagnosed as IM in 33 patients, MC in 44, and ND in 2. The anatomical resection group included 14 IM lesions (28%) and 36 MC lesions (72%), while the non-anatomical resection group included 19 IM lesions (70%) and 8 MC lesions (30%) (p

Atopic dermatitis is a chronic inflammatory skin disease with persistent pruritus. To clarify its molecular mechanism, it is important to establish a mouse model similar to the phenotypes of atopic dermatitis patients, particularly in exhibiting scratching behavior. Ikk2, a component of the IκB kinase complex, exerts pro-inflammatory responses, whereas its deficiency in keratinocytes paradoxically causes skin inflammation. In this study, we sought to generate a mouse model exhibiting skin inflammation by which dermal fibroblasts lack Ikk2 expression and evaluate whether cutaneous inflammatory phenotypes are similar to those of atopic dermatitis patients. To generate Ikk2-deficient mice (Nestincre;Ikk2FL/FL) in which Ikk2 is deleted in dermal fibroblasts, we crossed female Ikk2FL/FL mice to male Nestincre;Ikk2FL/+mice. These mice spontaneously developed skin inflammation limited to the face, with the appearance of Ikk2-deficient fibroblasts in the facial skin. These mice showed phenotypes similar to those of atopic dermatitis patients, including scratching behaviors, which are resistant to immunosuppressive or molecularly targeted drugs. These findings suggest that the Nestincre;Ikk2FL/FL mouse is an atopic dermatitis model that will be useful in clarifying atopic dermatitis pathogenesis and in developing a novel therapeutic agent for atopic dermatitis symptoms.

BackgroundOvarian tumors are predominantly of epithelial origin and are currently divided into three groups: Adenoma, borderline tumor, and adenocarcinoma by the presence or absence of invasion and cellular atypia. However, it is difficult to assess invasion, so a more objective biomarker would be desirable. Laminin-5 (Lam5) is a protein that constitutes the extracellular matrix of the basement membrane, and it is composed of three short-chain subunits. One of them, the Lam5γ2 chain (Lam5γ2), has been reported to be expressed in some malignant tumors and is suggested to be related to tumor cell invasion. Against this background, we investigated immunohistologically whether the Lam5γ2 would be useful as a marker to predict invasion in ovarian serous and mucinous tumors.MethodsImmunohistochemistry for Lam5γ2 was performed on a total of 80 cases of serous and mucinous tumor adenomas, borderline tumors, and adenocarcinomas, and the differences in the localization of Lam5γ2 expression were observed.ResultsThe basement membrane expression of Lam5γ2 tended to be preserved or had disappeared in half of the adenomas and borderline serous tumors. In all cases of adenocarcinoma, the expression on the basement membrane had disappeared. The frequency of expression in tumor cells increased in the order of adenoma, borderline tumor, adenocarcinoma. In particular, in most adenocarcinoma cases a cytoplasmic expression was observed. The same tendency was noted in mucinous tumors, and the basement membrane expression tended to disappear in the order of adenoma, borderline tumor and adenocarcinoma. Many cases of adenocarcinoma were observed among the tumor cells. In adenocarcinoma cases of both types of tumor, many tumor cells showed prominent cytoplasmic expression particularly in the microinvasive foci and in the invasive front.ConclusionsThe disappearance of Lam5γ2 from the basement membrane and its aberrant expression in serous and mucinous tumor cells may serve as a phenotype for invasiveness.

AIMS This study investigated the relationship between the differentiation of tumour cells into crypts, which is determined by cell differentiation into Paneth and neuroendocrine cells, and tumour infiltration in gastric dysplasia. METHODS AND RESULTS The lesions were endoscopically biopsied low-grade dysplasia (LGD), endoscopically resected high-grade dysplasia (HGD), or cancer with submucosal invasion. LGD (n = 32) displayed crypt differentiation across the entire width of the tumour in all cases. Crypt differentiation was identified as a characteristic of tumours with low biological malignancy. HGD (n = 40) included tumours with a mixture of areas with and without crypt differentiation (n = 25) and tumours with crypt differentiation throughout the entire width (n = 15). Of the cancers with submucosal invasion (n = 30), the morphological progression of HGD area with crypt differentiation, HGD area without crypt differentiation and invasive cancer without crypt differentiation was confirmed for 23 samples. In two lesions, invasive cancer without crypt differentiation developed from HGD without crypt differentiation throughout the tumour width. In five samples, well-differentiated tubular adenocarcinoma with crypt differentiation developed from HGD with crypt differentiation and invaded with lamina propria-like stroma. CONCLUSIONS Loss of crypt differentiation could be an objective indicator of infiltration in the progression of HGD to invasive cancer. The invasive potential of dysplasia depends on the presence or absence of crypt differentiation.

Background Melanotic oncocytic metaplasia is a rare non-neoplastic lesion. It has been described as a phenomenon in which cells change their morphology to adapt to various stimuli. The incidence of melanotic oncocytic metaplasia is higher in middle-aged Asian males and smokers. The nasopharynx is the most common site of occurrence. Clinically, it is necessary to distinguish this lesion from malignant melanoma. Case The patient was a man in his sixties and a heavy smoker. Brownish lesions were observed at bilateral pharyngeal openings of the eustachian tube through nasopharyngoscopy. Histopathologically, oncocytic cells without atypia having abundant granular cytoplasm and brownish pigmented granules were observed in the biopsy specimen obtained from the lesion. Immunohistochemically, most of these cells showed positive reaction for anti-mitochondria, S100, and Melan A, but not for HMB45. Discussion The characteristic histological finding of this lesion was the presence of abundant mitochondria and melanin pigments in the cytoplasm. The former may be the result of a mitochondrial response to various stimuli, while the latter may be transported from dendritic cells mixed in the surrounding mucosal epithelium. Conclusion It is important that otolaryngologists understand the features of this lesion, perform thorough observations, and reach a diagnosis through biopsy.

Antigen modification and denaturation are recognized causes of false negatives in immunostaining. Specimens that have been stored for an extended period at room temperature show decreased immunoreactivity and may mislead the diagnosis. Studies of the molecular targeting of drugs often involve immunostaining of previous samples and, in some situations, only unstained specimens can be used. The present study aimed to develop an effective staining method to recover antigen activation in unstained specimens stored for an extended period by using ethylene-diamine-tetraacetic acid (EDTA) buffer solution with boric acid. We compared several commonly used antigen retrieval solutions and found that Tris-borate-EDTA (TBE) buffer solution with a pH ≥8.3 provided sufficient antigen retrieval. However, pH values higher than 8.3 (9.0, 10.0, and 11.0) frequently caused severe tissue damage. Thus, TBE with pH 8.3 was the most suitable antigen retrieval solution for recovering the antigenicity of specimens stored for an extended period. This procedure may allow useful immunohistochemical information, even from sections that have been stored for an extended period.

Endoscopic ultrasound-guided fine-needle biopsy (EUS-FNB) enables easy and accurate pathological assessment. Here, we compared and assessed the area of samples on glass slides for three needle types: a 19-gauge Franseen needle (Acquire, Boston Scientific, Natick, MA, USA), a 22-gauge Franseen needle, and a 19-gauge fine-needle aspiration (FNA) needle (EZ Shot 3 Plus, Olympus, Tokyo, Japan). Among patients with suspected pancreatic cancer, with a ≥20 mm tumor located in the pancreatic body and tail, and who underwent EUS-FNA or FNB between June 2018 and March 2020, 10 were randomly selected to test each needle. The areas of histological tissue and blood clot samples were measured using the BZ-X800 imaging software (Keyence Corporation, Osaka, Japan). Baseline patient characteristics and pathological sample data showed no significant differences among the needles. The 19-gauge Franseen needle obtained significantly more histological tissue samples than the 19-gauge conventional needle (p = 0.010) and 22-gauge Franseen needle (p = 0.008). Conversely, there was no significant difference between the 19-gauge conventional needle and 22-gauge Franseen needle (p = 0.838) in this regard. The 19-gauge Franseen needle could collect more samples than the other needles, contributing to giving a more precise pathological diagnosis and more information, including genomic profiling.

OBJECTIVES Measurement of the macroscopic visible core (MVC) length during macroscopic on-site quality evaluation (MOSE) may allow estimation of sample adequacy for next-generation sequencing (NGS), and prediction of correct diagnosis in endoscopic ultrasound-guided tissue acquisition (EUS-TA) of pancreatic masses. METHODS This multicenter prospective study included consecutive patients who underwent EUS-TA for pancreatic masses using a 22-G Franseen needle. MVC length and pathological samples obtained from two needle passes were analyzed on a per-pass basis. Outcome measures included respective correlations of MVC length with histological sample quantity and diagnostic yields. RESULTS The analysis included 204 passes from 102 EUS-TAs. MVC length correlated positively with histological sample quantity (P

Background: Cetuximab is a powerful anti-neoplastic agent that can inhibit cell growth in oral squamous cell carcinomas (OSCCs). Unfortunately, there are cases with unfavorable outcomes. Because few studies have focused on the combined effects of cetuximab and histone deacetylase (HDAC) inhibitors, we aimed to evaluate the antitumor effect of cetuximab in combination with HDAC inhibitors in human OSCC cell lines, and investigate the mechanism of apoptosis enhancing activity thereof.Methods: We used human OSCC cell lines treated with cetuximab (500 mg/ml) and several HDAC inhibitors. The WST assay and ApoToxGlo™ Triplex Assay determined cell survival. We employed the TdT-mediated dUTP-biotin nick end labeling method to detect apoptosis. We used western blotting to examine the histone acetylation status, ER stress markers, and epidermal growth factor receptor (EGFR) signaling pathways.Results: Cetuximab in combination with 4-phenyl butyric acid (4-PBA) remarkably decreases cell growth in vitro. In addition, the combined treatment resulted in increased EGFR mRNA expression, and it promoted the activation of ERK. The combination treatment induced apoptosis at a significantly higher frequency than did either agent alone.Conclusions: The combination of cetuximab and 4-PBA is more effective against human OSCC cells than either agent alone, suggesting a potential clinical applicability of combination treatment in OSCC therapies.

Histoplasmosis is a fungal infection caused by Histoplasma capsulatum (HC), which can occasionally be aggressive resulting in the formation of granulomatous lesions. These are usually located in the lungs; however, immunocompromised patients may occasionally develop disseminated lesions in other organs as well. Human immunodeficiency virus (HIV) primarily infects cells of the immune system expressing CD4 molecules. Not only does HIV multiply within these cells, but it can also kill them or otherwise cause loss of cellular function, leading to an immunocompromised state. As a result, in an immunocompromised patient, infection with HC can have serious implications, often the development of visceral histoplasmosis in different organs. Although several types of lesions are formed in HC-infected organs, it may be difficult to distinguish the causative organism from other pathogens based on morphology alone. The present case report describes the case of a 57-year-old woman, from South America, who may have been infected with HC >20 years previously, remaining asymptomatic over the years. She later developed a lesion in the duodenum associated with immunodeficiency caused by HIV infection. The differential diagnosis of this case was made on the basis of several specific morphological findings using histopathological analysis and molecular pathological techniques. The pathogenesis of characteristic lesions caused by HC in the presence of HIV infection was also reviewed.

Background Benign and malignant cells need to be distinguished in any cytological examination of bile. Here, we report an original scoring system to improve the diagnostic accuracy of bile cytology. Methods The study used 158 bile aspiration samples obtained for cytological examination. Fourteen cytological findings were used to differentiate benign and malignant samples. Statistical significance tests and multivariate analysis were used to determine and quantify significant findings and develop a scoring system. Results Four cytological findings were significant in discriminating between benign and malignant cells: abnormal chromatin, irregularly arranged nuclei, irregularly overlapped nuclei, and irregular cluster margins. Our newly developed scoring system based on these four cytological findings yielded excellent results with a sensitivity of 87%, specificity of 98%, and an odds ratio of 329. Conclusions The use of our new scoring system is expected to contribute to the diagnostic accuracy of cytological evaluations of bile samples.

Beige adipocytes are an inducible form of thermogenic adipocytes that become interspersed within white adipose tissue (WAT) depots in response to cold exposure. Previous studies have shown that type 2 cytokines and M2 macrophages induce cold-induced browning in inguinal WAT (ingWAT) by producing catecholamines. Exactly how the conditional and partial depletion of CD206+ M2-like macrophages regulates the cold-induced browning of ingWAT, however, remains unknown. We examined the role of CD206+ M2-like macrophages in the cold-induced browning of WAT using genetically engineered CD206DTR mice, in which CD206+ M2-like macrophages were conditionally depleted. The partial depletion of CD206+ M2-like enhanced UCP1 expression in ingWAT, as shown by immunostaining, and also upregulated the expression of Ucp1 and other browning-related marker genes in ingWAT after cold exposure. A flow cytometry analysis showed that the partial depletion of CD206+ M2-like macrophages caused an increase in the number of beige progenitors in ingWAT in response to cold. Thus, we concluded that CD206+ M2-like macrophages inhibit the proliferation of beige progenitors and that the partial depletion of CD206+ M2-like macrophages releases this inhibition, thereby enhancing browning and insulin sensitivity.

Objectives Our goal was to evaluate whether endothlin-1 (ET-1) plays an important role in the Fontan circulation. Methods Thirteen patients with single-ventricle physiology (Glenn circulation, n = 7; Fontan circulation, n = 6) were evaluated using lung histopathological and immunohistochemical studies and then compared with the normal autopsied controls without congenital heart disease (n = 13). We evaluated the medial thickness of the small pulmonary arteries. For 10 of these patients, quantitative real-time polymerase chain reaction analyses of ET-1, endothelin receptors Type A and Type B, endothelin-converting enzyme-1 and endothelial nitric oxide synthase were performed. Results The medial thickness of the small pulmonary arteries in patients with single-ventricle physiology was greater than that of those in the control group (P = 0.0341). Severe medial hypertrophy of the pulmonary arteries was observed in patients who had poor outcomes. Immunohistochemical studies revealed that the marked expression of ET-1 was observed in the endothelium and media of their pulmonary arteries. In these patients, the messenger RNA expression of ET-1 was also increased. Two patients showed high levels of expression of ETAR and ETBR, although these 2 cases maintain good Fontan circulation. Conclusions Medial hypertrophy and the overexpression of ET-1 in the pulmonary arteries were observed in some patients in whom the Fontan circulation failed. Our data suggest that ET-1 may play an important role in maintaining the Fontan circulation.

Adipose tissue resident macrophages have important roles in the maintenance of tissue homeostasis and regulate insulin sensitivity for example by secreting pro-inflammatory or anti-inflammatory cytokines. Here, we show that M2-like macrophages in adipose tissue regulate systemic glucose homeostasis by inhibiting adipocyte progenitor proliferation via the CD206/TGFβ signaling pathway. We show that adipose tissue CD206+ cells are primarily M2-like macrophages, and ablation of CD206+ M2-like macrophages improves systemic insulin sensitivity, which was associated with an increased number of smaller adipocytes. Mice genetically engineered to have reduced numbers of CD206+ M2-like macrophages show a down-regulation of TGFβ signaling in adipose tissue, together with up-regulated proliferation and differentiation of adipocyte progenitors. Our findings indicate that CD206+ M2-like macrophages in adipose tissues create a microenvironment that inhibits growth and differentiation of adipocyte progenitors and, thereby, control adiposity and systemic insulin sensitivity. Adipose tissue contains macrophages that can influence both local and systemic metabolism via the secretion of cytokines. Here, Nawaz et al. report that M2-like macrophages, present in adipose tissue, create a microenvironment that inhibits proliferation of adipocyte progenitors due to the secretion of TGF-β1