Heme oxygenase 1 affects granulopoiesis in mice through control of myelocyte proliferation

Xanthohumol Attenuated Inflammation and ECM Degradation by Mediating HO-1/C/EBPβ Pathway in Osteoarthritis Chondrocytes

Osteoarthritis (OA) is the most frequent and disabling disease in developed countries. The progressive degeneration of articular cartilage characterized as thinner and erosive. Inflammation is well-known to be involved in OA development. However, there are no effective therapeutic strategies to cure it. Xanthohumol (XH) is a natural prenylflavonoid isolated from hops and beer. The protective activity of XH against OA chondrocytes inflammation and ECM degradation is unclear. In this article, we found that XH significantly inhibited inflammatory responses, attenuated catabolic enzymes expression, and ameliorated ECM degradation, as showed by decreased production of NO, PGE2, TNFα, and IL-6, decreased expression of MMP-3/-13 and ADAMTS-4/-5, and increased expression of collagen-II and aggrecan. In addition, XH activated HO-1 signaling and attenuated IL-1β-induced C/EBPβ. XH promoted the interaction between HO-1 and C/EBPβ, inhibiting the nuclear translocation of C/EBPβ. HO-1 knockdown could abrogate the protective effects of XH in IL-1β-treated chondrocytes. Collectively, XH attenuated inflammatory responses and ECM degradation by mediating HO-1 and C/EBPβ signaling pathways in osteoarthritis chondrocytes.

The role of heme oxygenase-1 in hematopoietic system and its microenvironment

Hematopoietic system transports all necessary nutrients to the whole organism and provides the immunological protection. Blood cells have high turnover, therefore, this system must be dynamically controlled and must have broad regeneration potential. In this review, we summarize how this complex system is regulated by the heme oxygenase-1 (HO-1)-an enzyme, which degrades heme to biliverdin, ferrous ion and carbon monoxide. First, we discuss how HO-1 influences hematopoietic stem cells (HSC) self-renewal, aging and differentiation. We also describe a critical role of HO-1 in endothelial cells and mesenchymal stromal cells that constitute the specialized bone marrow niche of HSC. We further discuss the molecular and cellular mechanisms by which HO-1 modulates innate and adaptive immune responses. Finally, we highlight how modulation of HO-1 activity regulates the mobilization of bone marrow hematopoietic cells to peripheral blood. We critically discuss the issue of metalloporphyrins, commonly used pharmacological modulators of HO-1 activity, and raise the issue of their important HO-1-independent activities.

Role of HMOX1 Promoter Genetic Variants in Chemoresistance and Chemotherapy Induced Neutropenia in Children with Acute Lymphoblastic Leukemia

Whilst the survival rates of childhood acute lymphoblastic leukemia (ALL) have increased remarkably over the last decades, the therapy resistance and toxicity are still the major causes of treatment failure. It was shown that overexpression of heme oxygenase-1 (HO-1) promotes proliferation and chemoresistance of cancer cells. In humans, the HO-1 gene (HMOX1) expression is modulated by two polymorphisms in the promoter region: (GT)n-length polymorphism and single-nucleotide polymorphism (SNP) A(−413)T, with short GT repeat sequences and 413-A variants linked to an increased HO-1 inducibility. We found that the short alleles are significantly more frequent in ALL patients in comparison to the control group, and that their presence may be associated with a higher risk of treatment failure, reflecting the role of HO-1 in chemoresistance. We also observed that the presence of short alleles may predispose to develop chemotherapy-induced neutropenia. In case of SNP, the 413-T variant co-segregated with short or long alleles, while 413-A almost selectively co-segregated with long alleles, hence it is not possible to determine if SNPs are actually of phenotypic significance. Our results suggest that HO-1 can be a potential target to overcome the treatment failure in ALL patients.

Heme oxygenase-1 deficiency triggers exhaustion of hematopoietic stem cells

While intrinsic changes in aging hematopoietic stem cells (HSCs) are well characterized, it remains unclear how extrinsic factors affect HSC aging. Here, we demonstrate that cells in the niche-endothelial cells (ECs) and CXCL12-abundant reticular cells (CARs)-highly express the heme-degrading enzyme, heme oxygenase 1 (HO-1), but then decrease its expression with age. HO-1-deficient animals (HO-1-/- ) have altered numbers of ECs and CARs that produce less hematopoietic factors. HSCs co-cultured in vitro with HO-1-/- mesenchymal stromal cells expand, but have altered kinetic of growth and differentiation of derived colonies. HSCs from young HO-1-/- animals have reduced quiescence and regenerative potential. Young HO-1-/- HSCs exhibit features of premature exhaustion on the transcriptional and functional level. HO-1+/+ HSCs transplanted into HO-1-/- recipients exhaust their regenerative potential early and do not reconstitute secondary recipients. In turn, transplantation of HO-1-/- HSCs to the HO-1+/+ recipients recovers the regenerative potential of HO-1-/- HSCs and reverses their transcriptional alterations. Thus, HSC-extrinsic activity of HO-1 prevents HSCs from premature exhaustion and may restore the function of aged HSCs.

Cobalt protoporphyrin IX increases endogenous G-CSF and mobilizes HSC and granulocytes to the blood

Granulocyte colony‐stimulating factor (G‐CSF) is used in clinical practice to mobilize cells from the bone marrow to the blood; however, it is not always effective. We show that cobalt protoporphyrin IX (CoPP) increases plasma concentrations of G‐CSF, IL‐6, and MCP‐1 in mice, triggering the mobilization of granulocytes and hematopoietic stem and progenitor cells (HSPC). Compared with recombinant G‐CSF, CoPP mobilizes higher number of HSPC and mature granulocytes. In contrast to G‐CSF, CoPP does not increase the number of circulating T cells. Transplantation of CoPP‐mobilized peripheral blood mononuclear cells (PBMC) results in higher chimerism and faster hematopoietic reconstitution than transplantation of PBMC mobilized by G‐CSF. Although CoPP is used to activate Nrf2/HO‐1 axis, the observed effects are Nrf2/HO‐1 independent. Concluding, CoPP increases expression of mobilization‐related cytokines and has superior mobilizing efficiency compared with recombinant G‐CSF. This observation could lead to the development of new strategies for the treatment of neutropenia and HSPC transplantation.

The CCAAT/Enhancer-Binding Protein Family: Its Roles in MDSC Expansion and Function

Immunosuppressive cells have been highlighted in research due to their roles in tumor progression and treatment failure. Myeloid-derived suppressor cells (MDSCs) are among the major immunosuppressive cell populations in the tumor microenvironment, and transcription factors (TFs) are likely involved in MDSC expansion and activation. As key regulatory TFs, members of the CCAAT/enhancer-binding protein (C/EBP) family possibly modulate many biological processes, including cell growth, differentiation, metabolism, and death. Current evidence suggests that C/EBPs maintain critical regulation of MDSCs and are involved in the differentiation and function of MDSCs within the tumor microenvironment. To better understand the MDSC-associated transcriptional network and identify new therapy targets, we herein review recent findings about the C/EBP family regarding their participation in the expansion and function of MDSCs.

Modulation of the monocyte/macrophage system in heart failure by targeting heme oxygenase-1

Upon myocardial infarction (MI) immune system becomes activated by extensive necrosis of cardiomyocytes releasing intracellular molecules called damage-associated molecular patterns. Overactive and prolonged immune responses are likely to be responsible for heart failure development and progression in patients surviving the ischemic episode. Heme oxygenase-1 (HO-1) plays a crucial role in heme degradation and in this way releases carbon monoxide, free iron, and biliverdin. This stress-inducible enzyme is induced by various oxidative and inflammatory signals. Consequently, biological actions of HO-1 are not limited to degradation of a toxic heme released from hemoproteins, but also provide an adaptive cellular response against chronic inflammation and oxidative injury. Indeed, the immunomodulatory and anti-inflammatory properties of HO-1 were demonstrated in several experimental studies, as well as in human cases of genetic HO-1 deficiency. HO-1 was shown to suppress the production, myocardial infiltration and inflammatory properties of monocytes and macrophages what resulted in limitation of post-MI cardiac damage. This review specifically addresses the role of HO-1, heme and its degradation products in macrophage biology and post-ischemic cardiac repair. A more complete understanding of these mechanisms is essential to develop new therapeutic approaches.