2. Academic Validation
  3. β2M Signals Monocytes Through Non-Canonical TGFβ Receptor Signal Transduction

β2M Signals Monocytes Through Non-Canonical TGFβ Receptor Signal Transduction

  • Circ Res. 2021 Mar 5;128(5):655-669. doi: 10.1161/CIRCRESAHA.120.317119.
Zachary T Hilt 1 2,  Preeti Maurya 1,  Laura Tesoro 1 3,  Daphne N Pariser 1,  Sara K Ture 1,  Simon J Cleary 4,  Mark R Looney 4,  Kathleen E McGrath 5,  Craig N Morrell 1 6
Affiliations

Affiliations

  • 1 Aab Cardiovascular Research Institute (Z.T.H., P.M., L.T., D.N.P., S.K.T., C.N.M.), University of Rochester School of Medicine, NY.
  • 2 Department of Microbiology and Immunology, Cornell University, Ithaca, NY (Z.T.H.).
  • 3 Cardiology Department, University Francisco de Vitoria/Hospital Ramón y Cajal Research Unit (IRYCIS), CIBERCV, Madrid, Spain (L.T.).
  • 4 Department of Medicine, UCSF, San Francisco (S.J.C., M.R.L.).
  • 5 Center for Pediatric Biomedical Research, Department of Pediatrics (K.E.M.), University of Rochester School of Medicine, NY.
  • 6 Departments of Medicine, Microbiology and Immunology and Pathology (C.N.M.).
PMID: 33508948 DOI: 10.1161/CIRCRESAHA.120.317119
Abstract

Rationale: Circulating monocytes can have proinflammatory or proreparative phenotypes. The endogenous signaling molecules and pathways that regulate monocyte polarization in vivo are poorly understood. We have shown that platelet-derived β2M (β-2 microglobulin) and TGF-β (transforming growth factor β) have opposing effects on monocytes by inducing inflammatory and reparative phenotypes, respectively, but each bind and signal through the same receptor. We now define the signaling pathways involved.

Objective: To determine the molecular mechanisms and signal transduction pathways by which β2M and TGF-β regulate monocyte responses both in vitro and in vivo.

Methods and results: Wild-type- (WT) and platelet-specific β2M knockout mice were treated intravenously with either β2M or TGF-β to increase plasma concentrations to those in cardiovascular diseases. Elevated plasma β2M increased proinflammatory monocytes, while increased plasma TGFβ increased proreparative monocytes. TGF-βR (TGF-β Receptor) inhibition blunted monocyte responses to both β2M and TGF-β in vivo. Using imaging flow cytometry, we found that β2M decreased monocyte SMAD2/3 nuclear localization, while TGF-β promoted SMAD nuclear translocation but decreased noncanonical/inflammatory (JNK [jun kinase] and NF-κB [nuclear factor-κB] nuclear localization). This was confirmed in vitro using both imaging flow cytometry and immunoblots. β2M, but not TGF-β, promoted ubiquitination of SMAD3 and SMAD4, that inhibited their nuclear trafficking. Inhibition of ubiquitin Ligase activity blocked noncanonical SMAD-independent monocyte signaling and skewed monocytes towards a proreparative monocyte response.

Conclusions: Our findings indicate that elevated plasma β2M and TGF-β dichotomously polarize monocytes. Furthermore, these immune molecules share a common receptor but induce SMAD-dependent canonical signaling (TGF-β) versus noncanonical SMAD-independent signaling (β2M) in a ubiquitin Ligase dependent manner. This work has broad implications as β2M is increased in several inflammatory conditions, while TGF-β is increased in fibrotic diseases. Graphic Abstract: A graphic abstract is available for this article.

Keywords

cytokines; inflammation; monocytes; platelets; transforming growth factors.

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