Th17 cells at the crossroads of autoimmunity, inflammation, and atherosclerosis.

The connection between inflammation, autoimmunity, and atherosclerosis is long established. In this issue of Immunity, Lim et al. (2014) demonstrate that oxidized low-density lipoprotein is one of the key environmental factors driving the development of inflammatory T helper 17 cells in atherosclerosis.

Interleukin-22 alleviates metabolic disorders and restores mucosal immunity in diabetes.

The connection between an altered gut microbiota and metabolic disorders such as obesity, diabetes, and cardiovascular disease is well established. Defects in preserving the integrity of the mucosal barriers can result in systemic endotoxaemia that contributes to chronic low-grade inflammation, which further promotes the development of metabolic syndrome. Interleukin (IL)-22 exerts essential roles in eliciting antimicrobial immunity and maintaining mucosal barrier integrity within the intestine. Here we investigate the connection between IL-22 and metabolic disorders. We find that the induction of IL-22 from innate lymphoid cells and CD4(+) T cells is impaired in obese mice under various immune challenges, especially in the colon during infection with Citrobacter rodentium. While innate lymphoid cell populations are largely intact in obese mice, the upregulation of IL-23, a cytokine upstream of IL-22, is compromised during the infection. Consequently, these mice are susceptible to C. rodentium infection, and both exogenous IL-22 and IL-23 are able to restore the mucosal host defence. Importantly, we further unveil unexpected functions of IL-22 in regulating metabolism. Mice deficient in IL-22 receptor and fed with high-fat diet are prone to developing metabolic disorders. Strikingly, administration of exogenous IL-22 in genetically obese leptin-receptor-deficient (db/db) mice and mice fed with high-fat diet reverses many of the metabolic symptoms, including hyperglycaemia and insulin resistance. IL-22 shows diverse metabolic benefits, as it improves insulin sensitivity, preserves gut mucosal barrier and endocrine functions, decreases endotoxaemia and chronic inflammation, and regulates lipid metabolism in liver and adipose tissues. In summary, we identify the IL-22 pathway as a novel target for therapeutic intervention in metabolic diseases.

Anti-inflammatory strategies for plaque stabilization after acute coronary syndromes.

Despite dramatic advances in standard of care, the risk of recurrent myocardial infarction early after an acute coronary syndrome (ACS) remains high. This period of elevated risk after a cardiovascular event is associated with an acute inflammatory response. While post-ACS inflammation correlates with the risk for recurrent events and is likely to play a causal role in this period, the precise pathophysiologic mechanisms have been unclear. Recent studies have proposed that the cardiac event itself activates the sympathetic nervous system to directly mobilize hematopoietic stem cells to differentiate into inflammatory monocytes, acutely infiltrate plaque, and lead to recurrent plaque rupture. Here, we summarize the existing and emerging evidence implicating post-ACS activation of systemic inflammation in the progression of atherosclerosis, and identify possible targets for therapeutic intervention. We highlight experimental therapies and ongoing clinical studies that will validate these targets.

Bv8 regulates myeloid-cell-dependent tumour angiogenesis.

Bone-marrow-derived cells facilitate tumour angiogenesis, but the molecular mechanisms of this facilitation are incompletely understood. We have previously shown that the related EG-VEGF and Bv8 proteins, also known as prokineticin 1 (Prok1) and prokineticin 2 (Prok2), promote both tissue-specific angiogenesis and haematopoietic cell mobilization. Unlike EG-VEGF, Bv8 is expressed in the bone marrow. Here we show that implantation of tumour cells in mice resulted in upregulation of Bv8 in CD11b+Gr1+ myeloid cells. We identified granulocyte colony-stimulating factor as a major positive regulator of Bv8 expression. Anti-Bv8 antibodies reduced CD11b+Gr1+ cell mobilization elicited by granulocyte colony-stimulating factor. Adenoviral delivery of Bv8 into tumours was shown to promote angiogenesis. Anti-Bv8 antibodies inhibited growth of several tumours in mice and suppressed angiogenesis. Anti-Bv8 treatment also reduced CD11b+Gr1+ cells, both in peripheral blood and in tumours. The effects of anti-Bv8 antibodies were additive to those of anti-Vegf antibodies or cytotoxic chemotherapy. Thus, Bv8 modulates mobilization of CD11b+Gr1+ cells from the bone marrow during tumour development and also promotes angiogenesis locally.

Granulocyte-colony stimulating factor promotes lung metastasis through mobilization of Ly6G+Ly6C+ granulocytes.

Priming of the organ-specific premetastatic sites is thought to be an important yet incompletely understood step during metastasis. In this study, we show that the metastatic tumors we examined overexpress granulocyte-colony stimulating factor (G-CSF), which expands and mobilizes Ly6G+Ly6C+ granulocytes and facilitates their subsequent homing at distant organs even before the arrival of tumor cells. Moreover, G-CSF-mobilized Ly6G+Ly6C+ cells produce the Bv8 protein, which has been implicated in angiogenesis and mobilization of myeloid cells. Anti-G-CSF or anti-Bv8 antibodies significantly reduced lung metastasis. Transplantation of Bv8 null fetal liver cells into lethally irradiated hosts also reduced metastasis. We identified an unexpected role for Bv8: the ability to stimulate tumor cell migration through activation of one of the Bv8 receptors, prokineticin receptor (PKR)-1. Finally, we show that administration of recombinant G-CSF is sufficient to increase the numbers of Ly6G+Ly6C+ cells in organ-specific metastatic sites and results in enhanced metastatic ability of several tumors.

Erratum to: Ungersma SE, Pacheco G, Ho C, Yee SF, Ross J, van Bruggen N, Peale FV Jr, Ross S, Carano RA. Vessel imaging with viable tumor analysis for quantification of tumor angiogenesis. Magn Reson Med 2010;63:1637­1647.

Imaging of tumor microvasculature has become an important tool for studying angiogenesis and monitoring antiangiogenic therapies. Ultrasmall paramagnetic iron oxide contrast agents for indirect imaging of vasculature offer a method for quantitative measurements of vascular biomarkers such as vessel size index, blood volume, and vessel density (Q). Here, this technique is validated with direct comparisons to ex vivo micro-computed tomography angiography and histologic vessel measurements, showing significant correlations between in vivo vascular MRI measurements and ex vivo structural vessel measurements. The sensitivity of the MRI vascular parameters is also demonstrated, in combination with a multispectral analysis technique for segmenting tumor tissue to restrict the analysis to viable tumor tissue and exclude regions of necrosis. It is shown that this viable tumor segmentation increases sensitivity for detection of significant effects on blood volume and Q by two antiangiogenic therapeutics [anti-vascular endothelial growth factor (anti-VEGF) and anti-neuropilin-1] on an HM7 colorectal tumor model. Anti-vascular endothelial growth factor reduced blood volume by 36±3% (p<0.0001) and Q by 52±3% (p<0.0001) at 48 h post-treatment; the effects of anti-neuropilin-1 were roughly half as strong with a reduction in blood volume of 18±6% (p<0.05) and a reduction in Q of 33±5% (p<0.05) at 48 h post-treatment.

New imaging paradigms in drug development: the PET imaging approach.

Molecular imaging is becoming an indispensable part of clinical drug development. The presented review highlights few state-of-the-art examples that serve to illustrate specific points and discuss future directions of the use of positron emission tomography (PET) imaging in various phases of clinical drug development.:

Noncompartmental kinetic analysis of DCE-MRI data from malignant tumors: Application to glioblastoma treated with bevacizumab.

Dynamic contrast enhanced MRI contrast agent kinetics in malignant tumors are typically complex, requiring multicompartment tumor models for adequate description. For consistent comparisons among tumors or among successive studies of the same tumor, we propose to estimate the total contrast agent-accessible volume fraction of tumor, including blood plasma, v(pe), and an average transfer rate constant across all tumor compartments, K(trans.av), by fitting a three-compartment tumor model and then calculating the area under the tumor impulse-response function (= v(pe)) and the ratio area under the tumor impulse response function over mean residence time in tumor (= K(trans.av)). If the duration of dynamic contrast enhanced MRI was too short to extrapolate the tumor impulse-response function to infinity with any confidence, then conditional parameters v(pe)(*) and K(trans.av*) should be calculated from the available incomplete impulse response function. Median decreases of 33% were found for both v(pe)(*) and K(trans.av*) in glioblastoma patients (n = 16) 24 hours after the administration of bevacizumab (P < 0.001). Median total contrast-enhancing tumor volume was reduced by 18% (P < 0.0001). The combined changes of tumor volume, v(pe)(*), and K(trans.av*) suggest a reduction of true v(pe), possibly accompanied by a reduction of true K(trans.av). The proposed method provides estimates of a scale and a shape parameter to describe contrast agent kinetics of varying complexity in a uniform way.

Vessel imaging with viable tumor analysis for quantification of tumor angiogenesis.

Imaging of tumor microvasculature has become an important tool for studying angiogenesis and monitoring antiangiogenic therapies. Ultrasmall paramagnetic iron oxide contrast agents for indirect imaging of vasculature offer a method for quantitative measurements of vascular biomarkers such as vessel size index, blood volume, and vessel density. Here, this technique is validated with direct comparisons to ex vivo micro-CT angiography and histologic vessel measurements, showing significant correlations between in vivo vascular MRI measurements and ex vivo structural vessel measurements. The sensitivity of the MRI vascular parameters is also demonstrated, in combination with a multispectral analysis technique for segmenting tumor tissue to restrict the analysis to viable tumor tissue and exclude regions of necrosis. It is shown that this viable tumor segmentation increases sensitivity for detection of significant effects on blood volume and vessel density by two antiangiogenic therapeutics (anti-VEGF and anti-neuropilin-1) on an HM7 colorectal tumor model. Anti-VEGF reduced blood volume by 36 +/- 3% (P < 0.0001) and vessel density by 52 +/- 3% (P < 0.0001) at 48 h posttreatment; the effects of anti-neuropilin-1 were roughly half as strong with a reduction in blood volume of 18 +/- 6% (P < 0.05) and a reduction in vessel density of 33 +/- 5% (P < 0.05) at 48 h posttreatment.

Preclinical evaluation of carcinoembryonic cell adhesion molecule (CEACAM) 6 as potential therapy target for pancreatic adenocarcinoma.

Despite the availability of new targeted therapies, ductal pancreatic adenocarcinoma continues to carry a poor prognosis. Carcinoembryonic antigen-related cell adhesion molecule (CEACAM)6 has been reported as a potential biomarker and therapy target for this malignancy. We have evaluated CEACAM6 as a potential therapy target, using an antibody-drug conjugate (ADC). Expression of CEACAM6 in pancreatic adenocarcinomas was determined using immunohistochemistry on tissue microarrays. The expression pattern in granulocytes and granulocytic precursors was measured by flow cytometry. Murine xenograft and non-human primate models served to evaluate efficacy and safety, respectively. Robust expression of CEACAM6 was found in > 90% of invasive pancreatic adenocarcinomas as well as in intraepithelial neoplastic lesions. In the granulocytic lineage, CEACAM6 was expressed at all stages of granulocytic maturation except for the early lineage-committed precursor cell. The anti-CEACAM6 ADC showed efficacy against established CEACAM6-expressing tumours. In non-human primates, antigen-dependent toxicity of the ADC consisted of dose-dependent and reversible depletion of granulocytes and their precursors. This was associated with preferential and rapid localization of the antibody in bone marrow, as determined by sequential in vivo PET imaging of the radiolabelled anti-CEACAM6. Localization of the radiolabelled tracer could be attenuated by predosing with unlabelled antibody confirming specific accumulation in this compartment. Based on the expression pattern in normal and malignant pancreatic tissues, efficacy against established tumours and limited and reversible bone marrow toxicity, we propose that CEACAM6 should be considered for an ADC-based therapy approach against pancreatic adenocarcinomas and possibly other CEACAM6-positive neoplasms.

PET of glial metabolism using 2-18F-fluoroacetate.

UNLABELLED: Imaging of the glial activation that occurs in response to central nervous system trauma and inflammation could become a powerful technique for the assessment of several neuropathologies. The selective uptake and metabolism of 2-(18)F-fluoroacetate ((18)F-FAC) in glia may represent an attractive strategy for imaging glial metabolism. METHODS: We have evaluated the use of (18)F-FAC as a specific PET tracer of glial cell metabolism in rodent models of glioblastoma, stroke, and ischemia-hypoxia. RESULTS: Enhanced uptake of (18)F-FAC was observed (6.98 +/- 0.43 percentage injected dose per gram [%ID/g]; tumor-to-normal ratio, 1.40) in orthotopic U87 xenografts, compared with healthy brain tissue. The lesion extent determined by (18)F-FAC PET correlated with that determined by MRI (R(2) = 0.934, P = 0.007). After transient middle cerebral artery occlusion in the rat brain, elevated uptake of (18)F-FAC (1.00 +/- 0.03 %ID/g; lesion-to-normal ratio, 1.90) depicted the ischemic territory and correlated with infarct volumes as determined by 2,3,5-triphenyltetrazolium chloride staining (R(2) = 0.692, P = 0.010) and with the presence of activated astrocytes detected by anti-glial fibrillary acidic protein. Ischemia-hypoxia, induced by permanent ligation of the common carotid artery with transient hypoxia, resulted in persistent elevation of (18)F-FAC uptake within 30 min of the induction of hypoxia. CONCLUSION: Our data support the further evaluation of (18)F-FAC PET for the assessment of glial cell metabolism associated with neuroinflammation.

Blocking vascular endothelial growth factor-A inhibits the growth of pituitary adenomas and lowers serum prolactin level in a mouse model of multiple endocrine neoplasia type 1.

PURPOSE: Multiple endocrine neoplasia type 1 (MEN1) is defined clinically by the combined occurrence of multiple tumors, typically of the parathyroid glands, pancreatic islet cells, and anterior pituitary gland. A mouse model with a heterozygous deletion of the Men1 gene recapitulates the tumorigenesis of MEN1. We wished to determine the role of vascular endothelial growth factor (VEGF)-A in the vascularization and growth of MEN1-associated tumors, with an emphasis on pituitary adenomas. EXPERIMENTAL DESIGN: To investigate whether tumor growth in Men1(+/-) mice is mediated by VEGF-A dependent angiogenesis, we carried out a monotherapy with the anti-VEGF-A monoclonal antibody (mAb) G6-31. We evaluated tumor growth by magnetic resonance imaging and assessed vascular density in tissue sections. We also measured hormone levels in the serum. RESULTS: During the treatment with mAb G6-31, a significant inhibition of the pituitary adenoma growth was observed, leading to an increased mean tumor doubling-free survival compared with mice treated with a control antibody. Similarly, the growth of s.c. pituitary adenoma transplants was effectively inhibited by administration of anti-VEGF-A mAb. Serum prolactin was lowered by mAb G6-31 treatment but not by control antibody, potentially providing a new therapeutic approach for treating the hormonal excess in MEN1 patients. Additionally, the vascular density in pancreatic islet tumors was significantly reduced by the treatment. CONCLUSIONS: These results suggest that VEGF-A blockade may represent a nonsurgical treatment for benign tumors of the endocrine system.

MANF regulates metabolic and immune homeostasis in ageing and protects against liver damage.

Aging is accompanied by altered intercellular communication, deregulated metabolic function, and inflammation. Interventions that restore a youthful state delay or reverse these processes, prompting the search for systemic regulators of metabolic and immune homeostasis. Here we identify MANF, a secreted stress-response protein with immune modulatory properties, as an evolutionarily conserved regulator of systemic and in particular liver metabolic homeostasis. We show that MANF levels decline with age in flies, mice and humans, and MANF overexpression extends lifespan in flies. MANF deficient flies exhibit enhanced inflammation and shorter lifespans, and MANF heterozygous mice exhibit inflammatory phenotypes in various tissues, as well as progressive liver damage, fibrosis, and steatosis. We show that immune cell-derived MANF protects against liver inflammation and fibrosis, while hepatocyte-derived MANF prevents hepatosteatosis. Liver rejuvenation by heterochronic parabiosis in mice further depends on MANF, while MANF supplementation ameliorates several hallmarks of liver aging, prevents hepatosteatosis induced by diet, and improves age-related metabolic dysfunction. Our findings identify MANF as a systemic regulator of homeostasis in young animals, suggesting a therapeutic application for MANF in age-related metabolic diseases.

Sustained Brown Fat Stimulation and Insulin Sensitization by a Humanized Bispecific Antibody Agonist for Fibroblast Growth Factor Receptor 1/ßKlotho Complex.

Dissipating excess calories as heat through therapeutic stimulation of brown adipose tissues (BAT) has been proposed as a potential treatment for obesity-linked disorders. Here, we describe the generation of a humanized effector-less bispecific antibody that activates fibroblast growth factor receptor (FGFR) 1/ßKlotho complex, a common receptor for FGF21 and FGF19. Using this molecule, we show that antibody-mediated activation of FGFR1/ßKlotho complex in mice induces sustained energy expenditure in BAT, browning of white adipose tissue, weight loss, and improvements in obesity-associated metabolic derangements including insulin resistance, hyperglycemia, dyslipidemia and hepatosteatosis. In mice and cynomolgus monkeys, FGFR1/ßKlotho activation increased serum high-molecular-weight adiponectin, which appears to contribute over time by enhancing the amplitude of the metabolic benefits. At the same time, insulin sensitization by FGFR1/ßKlotho activation occurs even before the onset of weight loss in a manner that is independent of adiponectin. Together, selective activation of FGFR1/ßKlotho complex with a long acting therapeutic antibody represents an attractive approach for the treatment of type 2 diabetes and other obesity-linked disorders through enhanced energy expenditure, insulin sensitization and induction of high-molecular-weight adiponectin.

Systemic VEGF-A neutralization ameliorates diet-induced metabolic dysfunction.

The vascular endothelial growth factor (VEGF) family of cytokines are important regulators of angiogenesis that have emerged as important targets for the treatment of obesity. While serum VEGF levels rise during obesity, recent studies using genetic models provide conflicting evidence as to whether VEGF prevents or accelerates metabolic dysfunction during obesity. In the current study, we sought to identify the effects of VEGF-A neutralization on parameters of glucose metabolism and insulin action in a dietary mouse model of obesity. Within only 72 h of administration of the VEGF-A-neutralizing monoclonal antibody B.20-4.1, we observed almost complete reversal of high-fat diet-induced insulin resistance principally due to improved insulin sensitivity in the liver and in adipose tissue. These effects were independent of changes in whole-body adiposity or insulin signaling. These findings show an important and unexpected role for VEGF in liver insulin resistance, opening up a potentially novel therapeutic avenue for obesity-related metabolic disease.

Inhibition of VEGF-C modulates distal lymphatic remodeling and secondary metastasis.

Tumor-associated lymphatics are postulated to provide a transit route for disseminating metastatic cells. This notion is supported by preclinical findings that inhibition of pro-lymphangiogenic signaling during tumor development reduces cell spread to sentinel lymph nodes (SLNs). However, it is unclear how lymphatics downstream of SLNs contribute to metastatic spread into distal organs, or if modulating distal lymph transport impacts disease progression. Utilizing murine models of metastasis, longitudinal in vivo imaging of lymph transport, and function blocking antibodies against two VEGF family members, we provide evidence that distal lymphatics undergo disease course-dependent up-regulation of lymph transport coincidental with structural remodeling. Inhibition of VEGF-C activity with antibodies against VEGF-C or NRP2 prevented these disease-associated changes. Furthermore, utilizing a novel model of adjuvant treatment, we demonstrate that antagonism of VEGF-C or NRP2 decreases post SLN metastasis. These data support a potential therapeutic strategy for inhibiting distant metastatic dissemination via targeting tumor-associated lymphatic remodeling.

Mapping in vivo tumor oxygenation within viable tumor by 19F-MRI and multispectral analysis.

Quantifying oxygenation in viable tumor remains a major obstacle toward a better understanding of the tumor micro-environment and improving treatment strategies. Current techniques are often complicated by tumor heterogeneity. Herein, a novel in vivo approach that combines (19)F magnetic resonance imaging ((19)F-MRI) R 1 mapping with diffusion-based multispectral (MS) analysis is introduced. This approach restricts the partial pressure of oxygen (pO2) measurements to viable tumor, the tissue of therapeutic interest. The technique exhibited sufficient sensitivity to detect a breathing gas challenge in a xenograft tumor model, and the hypoxic region measured by MS (19)F-MRI was strongly correlated with histologic estimates of hypoxia. This approach was then applied to address the effects of antivascular agents on tumor oxygenation, which is a research question that is still under debate. The technique was used to monitor longitudinal pO2 changes in response to an antibody to vascular endothelial growth factor (B20.4.1.1) and a selective dual phosphoinositide 3-kinase/mammalian target of rapamycin inhibitor (GDC-0980). GDC-0980 reduced viable tumor pO2 during a 3-day treatment period, and a significant reduction was also produced by B20.4.1.1. Overall, this method provides an unprecedented view of viable tumor pO2 and contributes to a greater understanding of the effects of antivascular therapies on the tumor's microenvironment.

Targeting oxidized LDL improves insulin sensitivity and immune cell function in obese Rhesus macaques.

Oxidation of LDL (oxLDL) is a crucial step in the development of cardiovascular disease. Treatment with antibodies directed against oxLDL can reduce atherosclerosis in rodent models through unknown mechanisms. We demonstrate that through a novel mechanism of immune complex formation and Fc-γ receptor (FcγR) engagement, antibodies targeting oxLDL (MLDL1278a) are anti-inflammatory on innate immune cells via modulation of Syk, p38 MAPK phosphorylation and NFκB activity. Subsequent administration of MLDL1278a in diet-induced obese (DIO) nonhuman primates (NHP) resulted in a significant decrease in pro-inflammatory cytokines and improved overall immune cell function. Importantly, MLDL1278a treatment improved insulin sensitivity independent of body weight change. This study demonstrates a novel mechanism by which an anti-oxLDL antibody improves immune function and insulin sensitivity independent of internalization of oxLDL. This identifies MLDL1278a as a potential therapy for reducing vascular inflammation in diabetic conditions.

FDG-PET is a good biomarker of both early response and acquired resistance in BRAFV600 mutant melanomas treated with vemurafenib and the MEK inhibitor GDC-0973.

BACKGROUND: The BRAF inhibitor, vemurafenib, has recently been approved for the treatment of metastatic melanoma in patients harboring BRAFV600 mutations. Currently, dual BRAF and MEK inhibition are ongoing in clinical trials with the goal of overcoming the acquired resistance that has unfortunately developed in some vemurafenib patients. FDG-PET measures of metabolic activity are increasingly employed as a pharmacodynamic biomarker for guiding single-agent or combination therapies by gauging initial drug response and monitoring disease progression. However, since tumors are inherently heterogeneous, investigating the effects of BRAF and MEK inhibition on FDG uptake in a panel of different melanomas could help interpret imaging outcomes. METHODS: 18 F-FDG uptake was measured in vitro in cells with wild-type and mutant (V600) BRAF, and in melanoma cells with an acquired resistance to vemurafenib. We treated the cells with vemurafenib alone or in combination with MEK inhibitor GDC-0973. PET imaging was used in mice to measure FDG uptake in A375 melanoma xenografts and in A375 R1, a vemurafenib-resistant derivative. Histological and biochemical studies of glucose transporters, the MAPK and glycolytic pathways were also undertaken. RESULTS: We demonstrate that vemurafenib is equally effective at reducing FDG uptake in cell lines harboring either heterozygous or homozygous BRAFV600 but ineffective in cells with acquired resistance or having WT BRAF status. However, combination with GDC-0973 results in a highly significant increase of efficacy and inhibition of FDG uptake across all twenty lines. Drug-induced changes in FDG uptake were associated with altered levels of membrane GLUT-1, and cell lines harboring RAS mutations displayed enhanced FDG uptake upon exposure to vemurafenib. Interestingly, we found that vemurafenib treatment in mice bearing drug-resistant A375 xenografts also induced increased FDG tumor uptake, accompanied by increases in Hif-1α, Sp1 and Ksr protein levels. Vemurafenib and GDC-0973 combination efficacy was associated with decreased levels of hexokinase II, c-RAF, Ksr and p-MEK protein. CONCLUSIONS: We have demonstrated that 18 F-FDG-PET imaging reflects vemurafenib and GDC-0973 action across a wide range of metastatic melanomas. A delayed post-treatment increase in tumor FDG uptake should be considered carefully as it may well be an indication of acquired drug resistance. TRIAL REGISTRATION: ClinicalTrials.gov NCT01271803.

Amelioration of type 2 diabetes by antibody-mediated activation of fibroblast growth factor receptor 1.

Clinical use of recombinant fibroblast growth factor 21 (FGF21) for the treatment of type 2 diabetes and other disorders linked to obesity has been proposed; however, its clinical development has been challenging owing to its poor pharmacokinetics. Here, we describe an alternative antidiabetic strategy using agonistic anti-FGFR1 (FGF receptor 1) antibodies (R1MAbs) that mimic the metabolic effects of FGF21. A single injection of R1MAb into obese diabetic mice induced acute and sustained amelioration of hyperglycemia, along with marked improvement in hyperinsulinemia, hyperlipidemia, and hepatosteatosis. R1MAb activated the mitogen-activated protein kinase pathway in adipose tissues, but not in liver, and neither FGF21 nor R1MAb improved glucose clearance in lipoatrophic mice, which suggests that adipose tissues played a central role in the observed metabolic effects. In brown adipose tissues, both FGF21 and R1MAb induced phosphorylation of CREB (cyclic adenosine 5'-monophosphate response element-binding protein), and mRNA expression of PGC-1α (peroxisome proliferator-activated receptor-γ coactivator 1α) and the downstream genes associated with oxidative metabolism. Collectively, we propose FGFR1 in adipose tissues as a major functional receptor for FGF21, as an upstream regulator of PGC-1α, and as a compelling target for antibody-based therapy for type 2 diabetes and other obesity-associated disorders.