Non-oxidizable HMGB1 induces cardiac fibroblasts migration via CXCR4 in a CXCL12-independent manner and worsens tissue remodeling after myocardial infarction.

Myocardial infarction (MI) is a major health burden worldwide. Extracellular High mobility group box 1 (HMGB1) regulates tissue healing after injuries. The reduced form of HMGB1 (fr-HMGB1) exerts chemotactic activity by binding CXCL12 through CXCR4, while the disulfide form, (ds-HMGB1), induces cytokines expression by TLR4. Here, we assessed the role of HMGB1 redox forms and the non-oxidizable mutant (3S) on human cardiac fibroblast (hcFbs) functions and cardiac remodeling after infarction. Among HMGB1 receptors, hcFbs express CXCR4. Fr-HMGB1 and 3S, but not ds-HMGB1, promote hcFbs migration through Src activation, while none of HMGB1 redox forms induces proliferation or inflammatory mediators. 3S is more effective than fr-HMGB1 in stimulating hcFbs migration and Src phosphorylation being active at lower concentrations and in oxidizing conditions. Notably, chemotaxis toward both proteins is CXCR4-dependent but, in contrast to fr-HMGB1, 3S does not require CXCL12 since hcFbs migration persists in the presence of the CXCL12/CXCR4 inhibitor AMD3100 or an anti-CXCL12 antibody. Interestingly, 3S interacts with CXCR4 and induces a different receptor conformation than CXCL12. Mice undergoing MI and receiving 3S exhibit adverse LV remodeling owing to an excessive collagen deposition promoted by a higher number of myofibroblasts. On the contrary, fr-HMGB1 ameliorates cardiac performance enhancing neoangiogenesis and reducing the infarcted area and fibrosis. Altogether, our results demonstrate that non-oxidizable HMGB1 induce a sustained cardiac fibroblasts migration despite the redox state of the environment and by altering CXCL12/CXCR4 axis. This affects proper cardiac remodeling after an infarction.

Macrophage uptake and accumulation of folates are polarization-dependent in vitro and in vivo and are regulated by activin A.

Vitamin B9, commonly known as folate, is an essential cofactor for one-carbon metabolism that enters cells through three major specialized transporter molecules (RFC, FR, and PCFT), which differ in expression pattern, affinity for substrate, and ligand-binding pH dependency. We now report that the expression of the folate transporters differs between macrophage subtypes and explains the higher accumulation of 5-MTHF-the major folate form found in serum-in M2 macrophages in vitro and in vivo. M1 macrophages display a higher expression of RFC, whereas FRß and PCFT are preferentially expressed by anti-inflammatory and homeostatic M2 macrophages. These differences are also seen in macrophages from normal tissues involved in folate transit (placenta, liver, colon) and inflamed tissues (ulcerative colitis, RA), as M2-like macrophages from normal tissues express FRß and PCFT, whereas TNF-α-expressing M1 macrophages from inflamed tissues are RFC+. Besides, we provide evidences that activin A is a critical factor controlling the set of folate transporters in macrophages, as it down-regulates FRß, up-regulates RFC expression, and modulates 5-MTHF uptake. All of these experiments support the notion that folate handling is dependent on the stage of macrophage polarization.