The obesity and inflammatory marker haptoglobin attracts monocytes via interaction with chemokine (C-C motif) receptor 2 (CCR2).
BACKGROUND
Obesity is a chronic low inflammatory state. In the obesity condition the white adipose tissue (WAT) is massively infiltrated with monocytes/macrophages, and the nature of the signals recruiting these inflammatory cells has yet to be fully elucidated. Haptoglobin (Hp) is an inflammatory marker and its expression is induced in the WAT of obese subjects. In an effort to elucidate the biological significance of Hp presence in the WAT and of its upregulation in obesity we formulated the hypothesis that Hp may serve as a macrophage chemoattractant.


RESULTS
We demonstrated by chemotaxis assay that Hp is able to attract chemokine (C-C motif) receptor 2 (CCR2)-transfected pre-B lymphocytes and monocytes in a dose-dependent manner. Moreover, Hp-mediated migration of monocytes is impaired by CCR2-specific inhibition or previous cell exposure to monocyte chemoattractant protein 1 (MCP1) (also known as CCR2 ligand or chemokine (C-C motif) ligand 2 (CCL2)). Downstream effects of Hp/CCR2 interaction were also investigated: flow cytometry proved that monocytes treated with Hp show reduced CCR2 expression on their surface; Hp interaction induces calcium release that is reduced upon pretreatment with CCR2 antagonist; extracellular signal-regulated kinase (ERK)1/2, a signal transducer activated by CCR2, is phosphorylated following Hp treatment and this phosphorylation is reduced when cells are pretreated with a specific CCR2 inhibitor. Consistently, blocking the ERK1/2 pathway with U0126, the selective inhibitor of the ERK upstream mitogen-activated protein (MAP)-ERK kinase (MEK), results in a dramatic reduction (by almost 100%) of the capability of Hp to induce monocyte migration.


CONCLUSIONS
Our data show that Hp is a novel monocyte chemoattractant and that its chemotactic potential is mediated, at least in part. by its interaction with CCR2.
Maffei
Margherita
M
Dulbecco Telethon Institute, CNR, Area della Ricerca di Pisa, Pisa, Italy. maffeim@immr.med.unipi.it
Funicello
Marcella
M
Vottari
Teresa
T
Gamucci
Olimpia
O
Costa
Mario
M
Lisi
Simonetta
S
Viegi
Alessandro
A
Ciampi
Osele
O
Bardi
Giuseppe
G
Vitti
Paolo
P
Pinchera
Aldo
A
Santini
Ferruccio
F
D000328:Adult; D001402:B-Lymphocytes / Q000187:drug effects / Q000502:physiology; D002070:Butadienes / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D002460:Cell Line; D002462:Cell Membrane / Q000187:drug effects / Q000502:physiology; D002465:Cell Movement / Q000187:drug effects / Q000502:physiology; D018932:Chemokine CCL2 / Q000378:metabolism; D002633:Chemotaxis / Q000187:drug effects / Q000502:physiology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006242:Haptoglobins / Q000378:metabolism*; D006801:Humans; D008297:Male; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D020929:Mitogen-Activated Protein Kinase Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D009000:Monocytes / Q000187:drug effects / Q000502:physiology*; D009570:Nitriles / Q000494:pharmacology; D010766:Phosphorylation / Q000187:drug effects; D054390:Receptors, CCR2 / Q000819:agonists / Q000037:antagonists & inhibitors / Q000378:metabolism*; D020298:U937 Cells; D055815:Young Adult
D002070:Butadienes; C111835:CCL2 protein, human; C515334:CCR2 protein, human; D018932:Chemokine CCL2; D004791:Enzyme Inhibitors; C485359:HP protein, human; D006242:Haptoglobins; D009570:Nitriles; D054390:Receptors, CCR2; C113580:U 0126; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020929:Mitogen-Activated Protein Kinase Kinases; D002118:Calcium