V(D)J recombination process and the Pre-B to immature B-cells transition are altered in Fanca-/- mice.

B-lymphocytes in the bone marrow (BM) must generate a functional B-cell receptor and overcome the negative selection induced by reactivity with autoantigens. Two rounds of DNA recombination are required for the production of functional immunoglobulin heavy (Ig-HCs) and light (LCs) chains necessary for the continuation of B-lymphocyte development in the BM. Both rounds depend on the joint action of recombination activating gene-1 (RAG-1) and RAG-2 endonucleases with the DNA non-homologous end-joining pathway. Loss of the FANC gene leads to the chromosome breakage and cancer predisposition syndrome Fanconi anemia. Because the FANC proteins are involved in certain aspects of the recombination process, we sought to determine the impact of the FANC pathway on the Ig diversification process using Fanca-/- mice. In this work we demonstrated that Fanca-/- animals have a mild B-cell differentiation defect characterized by a specific alteration of the IgM- to IgM+ transition of the B220low B-cell population. Pre-B cells from Fanca-/- mice show evidence of impaired kLC rearrangement at the level of the Vk-Jk junction. Furthermore, Fanca-/- mice showed a skewed Vκ gene usage during formation of the LCs Vk-Jk junctions. Therefore, the Fanca protein appears as a yet unidentified factor involved in the primary diversification of Ig.

Heme oxygenase-1 and anti-inflammatory M2 macrophages.

Heme oxygenase-1 (HO-1) catalyzes the first and rate-limiting enzymatic step of heme degradation and produces carbon monoxide, free iron, and biliverdin. HO-1, a stress-inducible protein, is induced by various oxidative and inflammatory signals. Consequently, HO-1 expression has been regarded as an adaptive cellular response against inflammatory response and oxidative injury. Although several transcriptional factors and signaling cascades are involved in HO-1 regulation, the two main pathways of Nrf2/Bach1 system and IL-10/HO-1 axis exist in monocyte/macrophage. Macrophages are broadly divisible into two groups: pro-inflammatory M1 macrophages and anti-inflammatory M2 macrophages. More recently, several novel macrophage subsets have been identified including Mhem, Mox, and M4 macrophages. Of these, M2 macrophages, Mhem, and Mox are HO-1 highly expressing macrophages. HO-1 has been recognized as having major immunomodulatory and anti-inflammatory properties, which have been demonstrated in HO-1 deficient mice and human cases of genetic HO-1 deficiency. However, the mechanism underlying the immunomodulatory actions of HO-1 remains poorly defined. This review specifically addresses macrophage polarization. The present current evidence indicates that HO-1 induction mediated by multiple pathways can drive the phenotypic shift to M2 macrophages and suggests that HO-1 induction in macrophages is a potential therapeutic approach to immunomodulation in widely diverse human diseases.

TNF-α signaling in Fanconi anemia.

Tumor necrosis factor-alpha (TNF-α) is a major pro-inflammatory cytokine involved in systemic inflammation and the acute phase reaction. Dysregulation of TNF production has been implicated in a variety of human diseases including Fanconi anemia (FA). FA is a genomic instability syndrome characterized by progressive bone marrow failure and cancer susceptibility. The patients with FA are often found overproducing TNF-α, which may directly affect hematopoietic stem cell (HSC) function by impairing HSC survival, homing and proliferation, or indirectly change the bone marrow microenvironment critical for HSC homeostasis and function, therefore contributing to disease progression in FA. In this brief review, we discuss the link between TNF-α signaling and FA pathway with emphasis on the implication of inflammation in the pathophysiology and abnormal hematopoiesis in FA.