Background: Irradiation disrupts the vascular niche where hematopoietic stem cells (HSCs) reside, causing delayed hematopoietic reconstruction. The subsequent recovery of sinusoidal vessels is key to vascular niche regeneration and a prerequisite for hematopoietic reconstruction. We hypothesize that resident bone marrow macrophages (BM-Mφs) are responsible for repairing the HSC niche upon irradiation injury.

Bone marrow mesenchymal stem cells (BMSCs), the important component and regulator of bone marrow microenvironment, give rise to hematopoietic-supporting stromal cells and form hematopoietic niches for hematopoietic stem cells (HSCs). However, how BMSC differentiation affects hematopoiesis is poorly understood. In this review, we focus on the role of BMSC differentiation in hematopoiesis. We discussed the role of BMSCs and their progeny in hematopoiesis. We also examine the mechanisms that cause differentiation bias of BMSCs in stress conditions including aging, irradiation, and chemotherapy. Moreover, the differentiation balance of BMSCs is crucial to hematopoiesis. We highlight the negative effects of differentiation bias of BMSCs on hematopoietic recovery after bone marrow transplantation. Keeping the differentiation balance of BMSCs is critical for hematopoietic recovery. This review summarises current understanding about how BMSC differentiation affects hematopoiesis and its potential application in improving hematopoietic recovery after bone marrow transplantation.

Background: DNA double-strand break (DSB) induction and repair are important events for determining cell survival and the outcome of cancer radiotherapy. The DNA-dependent protein kinase (DNA-PK) complex functions at the apex of DSBs repair, and its assembly and activity are strictly regulated by post-translation modifications (PTMs)-associated interactions. However, the PTMs of the catalytic subunit DNA-PKcs and how they affect DNA-PKcs’s functions are not fully understood. Methods: Mass spectrometry analyses were performed to identify the crotonylation sites of DNA-PKcs in response to γ-ray irradiation. Co-immunoprecipitation (Co-IP), western blotting, in vitro crotonylation assays, laser microirradiation assays, in vitro DNA binding assays, in vitro DNA-PK assembly assays and IF assays were employed to confirm the crotonylation, identify the crotonylase and decrotonylase, and elucidate how crotonylation regulates the activity and function of DNA-PKcs. Subcutaneous xenografts of human HeLa GCN5 WT or HeLa GCN5 siRNA cells in BALB/c nude mice were generated and utilized to assess tumor proliferation in vivo after radiotherapy. Results: Here, we reveal that K525 is an important site of DNA-PKcs for crotonylation, and whose level is sharply increased by irradiation. The histone acetyltransferase GCN5 functions as the crotonylase for K525-Kcr, while HDAC3 serves as its dedicated decrotonylase. K525 crotonylation enhances DNA binding activity of DNA-PKcs, and facilitates assembly of the DNA-PK complex. Furthermore, GCN5-mediated K525 crotonylation is indispensable for DNA-PKcs autophosphorylation and the repair of double-strand breaks in the NHEJ pathway. GCN5 suppression significantly sensitizes xenograft tumors of mice to radiotherapy. Conclusions: Our study defines K525 crotonylation of DNA-PKcs is important for the DNA-PK complex assembly and DSBs repair activity via NHEJ pathway. Targeting GCN5-mediated K525 Kcr of DNA-PKcs may be a promising therapeutic strategy for improving the outcome of cancer radiotherapy.

Macrophages are widely distributed in tissues and function in homeostasis. During cancer development, tumor-associated macrophages (TAMs) dominatingly support disease progression and resistance to therapy by promoting tumor proliferation, angiogenesis, metastasis, and immunosuppression, thereby making TAMs a target for tumor immunotherapy. Here, we started with evidence that TAMs are highly plastic and heterogeneous in phenotype and function in response to microenvironmental cues. We pointed out that efforts to tear off the heterogeneous “camouflage” in TAMs conduce to target de facto protumoral TAMs efficiently. In particular, several fate-mapping models suggest that most tissue-resident macrophages (TRMs) are generated from embryonic progenitors, and new paradigms uncover the ontogeny of TAMs. First, TAMs from embryonic modeling of TRMs and circulating monocytes have distinct transcriptional profiling and function, suggesting that the ontogeny of TAMs is responsible for the functional heterogeneity of TAMs, in addition to microenvironmental cues. Second, metabolic remodeling helps determine the mechanism of phenotypic and functional characteristics in TAMs, including metabolic bias from macrophages’ ontogeny in macrophages’ functional plasticity under physiological and pathological conditions. Both models aim at dissecting the ontogeny-related metabolic regulation in the phenotypic and functional heterogeneity in TAMs. We argue that gleaning from the single-cell transcriptomics on subclonal TAMs’ origins may help understand the classification of TAMs’ population in subclonal evolution and their distinct roles in tumor development. We envision that TAM-subclone-specific metabolic reprogramming may round-up with future cancer therapies.

The high mortality associated with pancytopenia and multi-organ failure resulting from hematopoietic disorders of acute radiation syndrome (h-ARS) creates an urgent need for developing more effective treatment strategies. Here, we showed that bone marrow multipotent mesenchymal stromal cells (BMMSCs) effectively regulate oxidative stress following radiative injury, which might be on account of irradiation-induced elevation of protein levels of CR6-interacting factor 1(CRIF1) and nuclear factor E2-related factor 2(NRF2). Crif1-knockdown BMMSCs presented increased oxidative stress and apoptosis after irradiation, which were partially due to a suppressed antioxidant response mediated by decreased NRF2 nuclear translocation. Co-immunoprecipitation (Co-IP) experiments indicated that CRIF1 interacted with protein kinase C-δ (PKC-δ). NRF2 Ser40 phosphorylation was inhibited in Crif1-deficient BMMSCs even in the presence of three kinds of PKC agonists, suggesting that CRIF1 might co-activate PKC-δ to phosphorylate NRF2 Ser40. After radiative injury, the supporting effect of BMMSCs for the colony forming ability of HSCs in vitro was reduced, and the deficiency of CRIF1 aggravated such damage. Thus, CRIF1 plays an essential role in PKC-δ/NRF2 pathway modulation to alleviate oxidative stress in BMMSCs after irradiative injury, and at some level it may maintain the HSCs-supporting effect of BMMSCs after radiative injuries.

Background: With the increasing risk of nuclear exposure, more attention has been paid to the prevention and treatment of acute radiation syndrome (ARS). Although amino acids are key nutrients involved in hematopoietic regulation, the impacts of amino acids on bone marrow hematopoiesis following irradiation and the associated mechanisms have not been fully elucidated. Hence, it is of paramount importance to study the changes in amino acid metabolism after irradiation and their effects on hematopoiesis as well as the related mechanisms. Methods: The content of serum amino acids was analyzed using metabolomic sequencing. The survival rate and body weight of the irradiated mice were detected after altering the methionine content in the diet. Extracellular matrix (ECM) protein analysis was performed via proteomics analysis. Inflammatory factors were examined by enzyme-linked immunosorbent assay (ELISA). Flow cytometry, Western blotting, and immunofluorescence were employed to determine the mechanism by which S100 calcium-binding protein A4 (S100A4) regulates macrophage polarization. Results: The survival time of irradiated mice was significantly associated with alterations in multiple amino acids, particularly methionine. A high methionine diet promoted irradiation tolerance, especially in the recovery of bone marrow hematopoiesis, yet with dose limitations. Folate metabolism could partially alleviate the dose bottleneck by reducing the accumulation of homocysteine. Mechanistically, high methionine levels maintained the abundance of ECM components, including collagens and glycoproteins, in the bone marrow post-irradiation, among which the level of S100A4 was significantly changed. S100A4 regulated macrophage polarization via the STAT3 pathway, inhibited bone marrow inflammation and facilitated the proliferation and differentiation of hematopoietic stem/progenitor cells. Conclusions: We have demonstrated that an appropriate elevation in dietary methionine enhances irradiation tolerance in mice and explains the mechanism by which methionine regulates bone marrow hematopoiesis after irradiation.