Protective Role for B-1b B Cells and IgM in Obesity-Associated Inflammation, Glucose Intolerance, and Insulin Resistance.

OBJECTIVE: Little is known about the role(s) B cells play in obesity-induced metabolic dysfunction. This study used a mouse with B-cell-specific deletion of Id3 (Id3(Bcell KO)) to identify B-cell functions involved in the metabolic consequences of obesity. APPROACH AND RESULTS: Diet-induced obese Id3(Bcell KO) mice demonstrated attenuated inflammation and insulin resistance in visceral adipose tissue (VAT), and improved systemic glucose tolerance. VAT in Id3(Bcell KO) mice had increased B-1b B cells and elevated IgM natural antibodies to oxidation-specific epitopes. B-1b B cells reduced cytokine production in VAT M1 macrophages, and adoptively transferred B-1b B cells trafficked to VAT and produced natural antibodies for the duration of 13-week studies. B-1b B cells null for Id3 demonstrated increased proliferation, established larger populations in Rag1(-/-) VAT, and attenuated diet-induced glucose intolerance and VAT insulin resistance in Rag1(-/-) hosts. However, transfer of B-1b B cells unable to secrete IgM had no effect on glucose tolerance. In an obese human population, results provided the first evidence that B-1 cells are enriched in human VAT and IgM antibodies to oxidation-specific epitopes inversely correlated with inflammation and insulin resistance. CONCLUSIONS: NAb-producing B-1b B cells are increased in Id3(Bcell KO) mice and attenuate adipose tissue inflammation and glucose intolerance in diet-induced obese mice. Additional findings are the first to identify VAT as a reservoir for human B-1 cells and to link anti-inflammatory IgM antibodies with reduced inflammation and improved metabolic phenotype in obese humans.

B-cell aortic homing and atheroprotection depend on Id3.

RATIONALE: B cells are abundant in the adventitia of normal and diseased vessels. Yet, the molecular and cellular mechanisms mediating homing of B cells to the vessel wall and B-cell effects on atherosclerosis are poorly understood. Inhibitor of differentiation-3 (Id3) is important for atheroprotection in mice and polymorphism in the human ID3 gene has been implicated as a potential risk marker of atherosclerosis in humans. Yet, the role of Id3 in B-cell regulation of atherosclerosis is unknown. OBJECTIVE: To determine if Id3 regulates B-cell homing to the aorta and atheroprotection and identify molecular and cellular mechanisms mediating this effect. METHODS AND RESULTS: Loss of Id3 in Apoe(-/-) mice resulted in early and increased atherosclerosis. Flow cytometry revealed a defect in Id3(-/-) Apoe(-/-) mice in the number of B cells in the aorta but not the spleen, lymph nodes, and circulation. Similarly, B cells transferred from Id3(-/-) Apoe(-/-) mice into B-cell-deficient mice reconstituted spleen, lymph node, and blood similarly to B cells from Id3(+/+) Apoe(-/-) mice, but aortic reconstitution and B-cell-mediated inhibition of diet-induced atherosclerosis was significantly impaired. In addition to retarding initiation of atherosclerosis, B cells homed to regions of existing atherosclerosis, reduced macrophage content in plaque, and attenuated progression of disease. The chemokine receptor CCR6 was identified as an important Id3 target mediating aortic homing and atheroprotection. CONCLUSIONS: Together, these results are the first to identify the Id3-CCR6 pathway in B cells and demonstrate its role in aortic B-cell homing and B-cell-mediated protection from early atherosclerosis.

Helix-loop-helix factor inhibitor of differentiation 3 regulates interleukin-5 expression and B-1a B cell proliferation.

OBJECTIVE: Natural immunity is emerging as an important mediator of protection from atherogenesis. Natural IgM antibodies that recognize oxidation-specific epitopes on low-density lipoprotein or phospholipids and the B-1a B cells that produce them attenuate atherosclerosis. We previously demonstrated that Apoe(-/-) mice globally deficient in the helix-loop-helix protein inhibitor of differentiation 3 (Id3) develop early diet-induced atherosclerosis. Furthermore, B cell-mediated attenuation of atherosclerosis in B cell-deficient mice was dependent on Id3. Here, we sought to determine whether Id3 regulates B-1a B cells and the natural antibodies that they produce and identify mechanisms mediating these effects. APPROACH AND RESULTS: Mice lacking Id3 had significantly fewer B-1a B cells in the spleen and peritoneal cavity and reduced serum levels of the natural antibody E06. B cell-specific deletion of Id3 revealed that this effect was not because of the loss of Id3 in B cells. Interleukin (IL)-33 induced abundant, Id3-dependent IL-5 production in the recently identified innate lymphoid cell, the natural helper (NH) cell, but not Th2 or mast cells. In addition, delivery of IL-5 to Id3-deficient mice restored B-1a B cell proliferation. B-1a B cells were present in aortic samples also containing NH cells. Aortic NH cells produced IL-5, a B-1a B cell mitogen in response to IL-33 stimulation. CONCLUSIONS: These studies are the first to identify NH and B-1a B cells in the aorta and provide evidence that Id3 is a key regulator of NH cell IL-5 production and B-1a B cell homeostasis.

Inhibitor of differentiation-3 mediates high fat diet-induced visceral fat expansion.

OBJECTIVE: Inhibitor of differentiation-3 (Id3) has been implicated in promoting angiogenesis, a key determinant of high-fat diet (HFD)-induced visceral adiposity. Yet the role of Id3 in HFD-induced angiogenesis and visceral adipose expansion is unknown. METHODS AND RESULTS: Id3(-/-) mice demonstrated a significant attenuation of HFD-induced visceral fat depot expansion compared to wild type littermate controls. Importantly, unlike other Id proteins, loss of Id3 did not affect adipose depot size in young mice fed chow diet or differentiation of adipocytes in vitro or in vivo. Contrast enhanced ultrasound revealed a significant attenuation of visceral fat microvascular blood volume in HFD-fed mice null for Id3 compared to wild type controls. HFD induced Id3 and VEGFA expression in the visceral stromal vascular fraction and Id3(-/-) mice had significantly lower levels of VEGFA protein in visceral adipose tissue compared to wild type. Furthermore, HFD-induced VEGFA expression in visceral adipose tissue was completely abolished by loss of Id3. Consistent with this effect, Id3 abolished E12-mediated repression of VEGFA promoter activity. CONCLUSIONS: Results identify Id3 as an important regulator of HFD-induced visceral adipose VEGFA expression, microvascular blood volume, and depot expansion. Inhibition of Id3 may have potential as a therapeutic strategy to limit visceral adiposity.

Loss of Id3 increases VCAM-1 expression, macrophage accumulation, and atherogenesis in Ldlr-/- mice.

OBJECTIVE: Inhibitor of differention-3 (Id3) promotes B cells homing to the aorta and atheroprotection in Apoe(-/-) mice. We sought to determine the impact of loss of Id3 in the Ldlr((-/-)) mouse model of diet-induced atherosclerosis and identify novel Id3 targets in the vessel wall. METHODS AND RESULTS: Ex vivo optical imaging confirmed that Id3((-/-)) Ldlr((-/-)) mice have significantly fewer aortic B cells than Id3((+/+)) Ldlr(-/-) mice. After 8 and 16 weeks of Western diet, Id3((-/-)) Ldlr((-/-)) mice developed significantly more atherosclerosis than Id3((+/+)) Ldlr((-/-)) mice, with Id3(+/-) Ldlr(-/-) mice demonstrating an intermediate phenotype. There were no differences in serum lipid levels between genotypes. Immunostaining demonstrated that aortas from Id3((-/-)) Ldlr((-/-)) mice had greater intimal macrophage density and C-C chemokine ligand 20 and vascular cell adhesion molecule 1 (VCAM-1) expression compared with Id3((+/+)) Ldlr(-/-) mice. Real-time polymerase chain reaction demonstrated increased VCAM-1 mRNA levels in the aortas of Id3(-/-) Ldlr(-/-) mice. Primary vascular smooth muscle cells from Id3((-/-)) mice expressed greater amounts of VCAM-1 protein compared with control. Gain and loss of function studies in primary vascular smooth muscle cells identified a role for Id3 in repressing VCAM-1 promoter activation. Chromatin immunoprecipitation demonstrated interaction of E12 with the VCAM-1 promoter, which is inhibited by Id3. CONCLUSIONS: Id3 is an atheroprotective transcription regulator with targets in both B cells and vessel wall cells leading to reduced macrophage accumulation and reduced atherosclerosis formation.

Id3 is a novel atheroprotective factor containing a functionally significant single-nucleotide polymorphism associated with intima-media thickness in humans.

RATIONALE: The gene encoding the helix-loop-helix transcription factor Id3 (inhibitor of differentiation-3) is located within atherosclerosis susceptibility loci of both mice and humans, yet its influence on atherosclerosis is not known. OBJECTIVE: The present study sought to determine whether polymorphisms in the ID3 gene were associated with indices of atherosclerosis in humans and if loss of Id3 function modulated atherogenesis in mice. METHODS AND RESULTS: Six tagging single-nucleotide polymorphisms (SNPs) (tagSNPs) in the human ID3 gene were assessed in participants of the Diabetes Heart Study. One tagSNP, rs11574, was independently associated with carotid intima-media thickness (IMT). The human ID3 variant at rs11574 results in an alanine to threonine substitution in the C terminus. To determine the effect of this polymorphism on the basic function of Id3, site-directed mutagenesis of the human ID3 gene at rs11574 was performed. Results demonstrated a significant reduction in coimmunoprecipitation of the known E-protein partner, E12, with Id3 when it contains the sequence encoded by the risk allele (Id3105T). Further, Id3105T had an attenuated ability to modulate E12-mediated transcriptional activation compared to Id3 containing the ancestral allele (Id3105A). Microarray analysis of vascular smooth muscle cells from WT and Id3(-/-) mice revealed significant modulation of multiple gene pathways implicated in atherogenesis. Moreover, Id3(-/-)ApoE(-/-) mice developed significantly more atherosclerosis in response to 32 weeks of Chow or Western diet feeding than Id3(+/+)ApoE(-/-) mice. CONCLUSIONS: Taken together, results provide novel evidence that Id3 is an atheroprotective factor and link a common SNP in the human ID3 gene to loss of Id3 function and increased IMT.

Increased 12/15-lipoxygenase enhances cell growth, fibronectin deposition, and neointimal formation in response to carotid injury.

OBJECTIVE: To determine whether increased 12/15-lipoxygenase (12/15LO) expression in vivo enhances neointimal formation in response to injury. METHODS AND RESULTS: 12/15LO expression in the vessel wall is increased in animal models of metabolic syndrome and diabetes mellitus. Increased expression of 12/15LO enhances cultured vascular smooth muscle cell (VSMC) proliferation, an effect mediated by the helix-loop-helix factor inhibitor of differentiation 3 (Id3). Carotid endothelial denudation was performed on apolipoprotein (Apo) E(-/-), ApoE(-/-)/12/15LO(-/-), C57BL/6, and 12/15LO-overexpressing transgenic mice. ApoE(-/-)/12/15LO(-/-) mice had attenuated and 12/15LO-overexpressing transgenic mice had enhanced neointimal formation compared with control mice. 12/15LO-overexpressing transgenic mice had greater postinjury carotid Id3 and Ki-67 expression, cell number, and fibronectin deposition compared with C57BL/6 mice. Loss of 12/15LO attenuated proliferation of cultured ApoE(-/-) VSMCs, whereas 12/15LO overexpression induced VSMC proliferation. Loss of Id3 enhanced immunoglobulin trascription factor (ITF)-2b binding to and activation of the p21(cip1) promoter and abrogated 12/15LO-induced VSMC proliferation. CONCLUSIONS: To our knowledge, these data are the first demonstration that increased expression of 12/15LO in the vessel wall enhances Id3-dependent cell proliferation, fibronectin deposition, and neointimal formation in response to injury. Results identify p21(cip1) as a potential target of the 12/15LO-Id3 pathway and suggest that modulation of this pathway may have therapeutic implications for targeting the increased risk of restenosis in patients with diabetes.

The helix-loop-helix factors Id3 and E47 are novel regulators of adiponectin.

Adiponectin is an adipocyte-derived cytokine with beneficial effects on insulin sensitivity and the development of atherosclerosis. Id3 is a helix-loop-helix factor that binds to E-proteins such as E47 and inhibits their binding to DNA. Although the helix-loop-helix factor sterol regulatory element binding protein (SREBP)-1c is a known activator of adiponectin transcription, this study provides the first evidence of a role for Id3 and E47 in adiponectin expression. Decreased Id3 in differentiating adipocytes correlates with increased adiponectin expression and forced expression of Id3 inhibits adiponectin expression. Moreover, Id3-null mice have increased adiponectin expression in visceral fat tissue and in serum. We demonstrate that E47 potentiates SREBP-1c-mediated adiponectin promoter activation and that Id3 can dose-dependently inhibit this action via interaction with E47. Mutation of a consensus E47 binding site results in nearly complete loss of promoter activation. Furthermore, we demonstrate E47 binding to the endogenous adiponectin promoter both in vitro and in vivo by chromatin immunoprecipitation analysis. Binding is not detected in undifferentiated cells which express Id3 but peaks during differentiation in parallel with Id3 decline. This promoter binding can be completely abolished by the overexpression of Id3 and is enhanced in adipose tissue null for Id3. These data establish Id3 and E47 as novel regulators of SREBP-1c-mediated adiponectin expression in differentiating adipocytes and provide evidence that Id3 regulates adiponectin expression in vivo.

Adipocyte progenitor cells initiate monocyte chemoattractant protein-1-mediated macrophage accumulation in visceral adipose tissue.

OBJECTIVE: Macrophages are important producers of obesity-induced MCP-1; however, initial obesity-induced increases in MCP-1 production precede M1 macrophage accumulation in visceral adipose tissue (VAT). The initial cellular source of obesity-induced MCP-1 in vivo is currently unknown. Preliminary reports based on in vitro studies of preadipocyte cell lines and adherent stroma-vascular fraction cells suggest that resident stromal cells express MCP-1. In the past several years, elegant methods of identifying adipocyte progenitor cells (AdPCs) have become available, making it possible to study these cells in vivo. We have previously published that global deletion of transcription factor Inhibitor of Differentiation 3 (Id3) attenuates high fat diet-induced obesity, but it is unclear if Id3 plays a role in diet-induced MCP-1 production. We sought to determine the initial cellular source of MCP-1 and identify molecular regulators mediating MCP-1 production. METHODS: Id3 (+/+) and Id3 (-/-) mice were fed either a standard chow or HFD for varying lengths of time. Flow cytometry, semi-quantitative real-time PCR, ELISAs and adoptive transfers were used to assess the importance of AdPCs during diet-induced obesity. Flow cytometry was also performed on a cohort of 14 patients undergoing bariatric surgery. RESULTS: Flow cytometry identified committed CD45(-)CD31 (-) Ter119(-)CD29(+)CD34(+)Sca-1(+)CD24(-) adipocyte progenitor cells as producers of high levels of MCP-1 in VAT. High-fat diet increased AdPC numbers, an effect dependent on Id3. Loss of Id3 increased p21(Cip1) levels and attenuated AdPC proliferation, resulting in reduced MCP-1 and M1 macrophage accumulation in VAT, compared to Id3 (+/+) littermate controls. AdPC rescue by adoptive transfer of 50,000 Id3 (+/+) AdPCs into Id3 (-/-) recipient mice increased MCP-1 levels and M1 macrophage number in VAT. Additionally, flow cytometry identified MCP-1-producing CD45(-)CD31(-)CD34(+)CD44(+)CD90(+) AdPCs in human omental and subcutaneous adipose tissue, with a higher percentage in omental adipose. Furthermore, high surface expression of CD44 marked abundant MCP-1 producers, only in visceral adipose tissue. CONCLUSIONS: This study provides the first in vivo evidence, to our knowledge, that committed AdPCs in VAT are the initial source of obesity-induced MCP-1 and identifies the helix-loop-helix transcription factor Id3 as a critical regulator of p21(Cip1) expression, AdPC proliferation, MCP-1 expression and M1 macrophage accumulation in VAT. Inhibition of Id3 and AdPC expansion, as well as CD44 expression in human AdPCs, may serve as unique therapeutic targets for the regulation of adipose tissue inflammation.