The effects of proliferation and DNA damage on hematopoietic stem cell function determine aging

Multimodal Tracking of Hematopoietic Stem Cells from Young and Old Mice Labeled with Magnetic-Fluorescent Nanoparticles and Their Grafting by Bioluminescence in a Bone Marrow Transplant Model

This study proposes an innovative way to evaluate the homing and tracking of hematopoietic stem cells from young and old mice labeled with SPION_NIRF-Rh conjugated with two types of fluorophores (NIRF and Rhodamine), and their grafting by bioluminescence (BLI) in a bone marrow transplant (BMT) model. In an in vitro study, we isolated bone marrow mononuclear cells (BM-MNC) from young and old mice, and analyzed the physical-chemical characteristics of SPION_NIRF-Rh, their internalization, cell viability, and the iron quantification by NIRF, ICP-MS, and MRI. The in vivo study was performed in a BMT model to evaluate the homing, tracking, and grafting of young and old BM-MNC labeled with SPION_NIRF-Rh by NIRF and BLI, as well as the hematological reconstitution for 120 days. 5FU influenced the number of cells isolated mainly in young cells. SPION_NIRF-Rh had adequate characteristics for efficient internalization into BM-MNC. The iron load quantification by NIRF, ICP-MS, and MRI was in the order of 10⁴ SPION_NIRF-Rh/BM-MNC. In the in vivo study, the acute NIRF evaluation showed higher signal intensity in the spinal cord and abdominal region, and the BLI evaluation allowed follow-up (11-120 days), achieving a peak of intensity at 30 days, which remained stable around 10⁸ photons/s until the end. The hematologic evaluation showed similar behavior until 30 days and the histological results confirm that iron is present in almost all tissue evaluated. Our results on BM-MNC homing and tracking in the BMT model did not show a difference in migration or grafting of cells from young or old mice, with the hemogram analysis trending to differentiation towards the myeloid lineage in mice that received cells from old animals. The cell homing by NIRF and long term cell follow-up by BLI highlighted the relevance of the multimodal nanoparticles and combined techniques for evaluation.

The Periostin/Integrin-αv Axis Regulates the Size of Hematopoietic Stem Cell Pool in the Fetal Liver

We earlier showed that outside-in integrin signaling through POSTN-ITGAV interaction plays an important role in regulating adult hematopoietic stem cell (HSC) quiescence. Here, we show that Itgav deletion results in increased frequency of phenotypic HSCs in fetal liver (FL) due to faster proliferation. Systemic deletion of Postn led to increased proliferation of FL HSCs, albeit without any loss of stemness, unlike Vav-Itgav^−/− HSCs. Based on RNA sequencing analysis of FL and bone marrow HSCs, we predicted the involvement of DNA damage response pathways in this dichotomy. Indeed, proliferative HSCs from Postn-deficient FL tissues showed increased levels of DNA repair, resulting in lesser double-strand breaks. Thus POSTN, with its expression majorly localized in the vascular endothelium of FL tissue, acts as a regulator of stem cell pool size during development. Overall, we demonstrate that the duality of response to proliferation in HSCs is developmental stage dependent and can be correlated with DNA damage responses.

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Interruption of POSTN-ITGAV interaction leads to HSC expansion in fetal liver

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HSC from fetal liver in comparison with adult BM excel in their DNA damage responses

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POSTN is a potential component of the vascular niche for HSCs in the fetal liver

Biosystem Analysis of the Hypoxia Inducible Domain Family Member 2A: Implications in Cancer Biology

The expression of HIGD2A is dependent on oxygen levels, glucose concentration, and cell cycle progression. This gene encodes for protein HIG2A, found in mitochondria and the nucleus, promoting cell survival in hypoxic conditions. The genomic location of HIGD2A is in chromosome 5q35.2, where several chromosomal abnormalities are related to numerous cancers. The analysis of high definition expression profiles of HIGD2A suggests a role for HIG2A in cancer biology. Accordingly, the research objective was to perform a molecular biosystem analysis of HIGD2A aiming to discover HIG2A implications in cancer biology. For this purpose, public databases such as SWISS-MODEL protein structure homology-modelling server, Catalogue of Somatic Mutations in Cancer (COSMIC), Gene Expression Omnibus (GEO), MethHC: a database of DNA methylation and gene expression in human cancer, and microRNA-target interactions database (miRTarBase) were accessed. We also evaluated, by using Real-Time Quantitative Reverse Transcription Polymerase Chain Reaction (qRT-PCR), the expression of Higd2a gene in healthy bone marrow-liver-spleen tissues of mice after quercetin (50 mg/kg) treatment. Thus, among the structural features of HIG2A protein that may participate in HIG2A translocation to the nucleus are an importin α-dependent nuclear localization signal (NLS), a motif of DNA binding residues and a probable SUMOylating residue. HIGD2A gene is not implicated in cancer via mutation. In addition, DNA methylation and mRNA expression of HIGD2A gene present significant alterations in several cancers; HIGD2A gene showed significant higher expression in Diffuse Large B-cell Lymphoma (DLBCL). Hypoxic tissues characterize the “bone marrow-liver-spleen” DLBCL type. The relative quantification, by using qRT-PCR, showed that Higd2a expression is higher in bone marrow than in the liver or spleen. In addition, it was observed that quercetin modulated the expression of Higd2a gene in mice. As an assembly factor of mitochondrial respirasomes, HIG2A might be unexpectedly involved in the change of cellular energetics happening in cancer. As a result, it is worth continuing to explore the role of HIGD2A in cancer biology.

The OXPHOS supercomplex assembly factor HIG2A responds to changes in energetic metabolism and cell cycle

HIG2A promotes cell survival under hypoxia and mediates the assembly of complex III and complex IV into respiratory chain supercomplexes. In the present study, we show that human HIGD2A and mouse Higd2a gene expressions are regulated by hypoxia, glucose, and the cell cycle-related transcription factor E2F1. The latter was found to bind the promoter region of HIGD2A. Differential expression of the HIGD2A gene was found in C57BL/6 mice in relation to tissue and age. Besides, the silencing of HIGD2A evidenced the modulation of mitochondrial dynamics proteins namely, OPA1 as a fusion protein increases, while FIS1, a fission protein, decreases. Besides, the mitochondrial membrane potential (ΔΨm) increased. The protein HIG2A is localized in the mitochondria and nucleus. Moreover, we observed that the HIG2A protein interacts with OPA1. Changes in oxygen concentration, glucose availability, and cell cycle regulate HIGD2A expression. Alterations in HIGD2A expression are associated with changes in mitochondrial physiology.

Hair Follicle Stem Cell Faith Is Dependent on Chromatin Remodeling Capacity Following Low-Dose Radiation

The main function of the skin, to protect against the environment, is supported by the activity of different stem cell populations. The main focus of this study was elucidating the coping mechanisms of stem cells against the stimulation of constant exposure to genotoxic stresses, both endogenous and exogenous, to ensure long-term function. Investigation of various mouse strains, differing in their DNA repair capacity, enables us to clarify fractionated low-dose irradiation (LDR)-induced consequences for different stem cell populations of the murine hair follicle (HF) in their physiological stem cell niche. Using microscopic techniques combined with flow cytometry, we could show that LDR induces accumulation of persisting; pKu70-independent 53BP1-foci ("chromatin-alterations") in heterochromatic regions of the HF stem cells (HFSCs). These remaining chromatin-alterations result in varying stem cell consequences. CD34-positive HFSCs react by ataxia telangiectasia mutated-dependent, premature senescence, which correlates with global chromatin compaction, whereby apoptosis is prevented by the activity of DNA-dependent protein kinase catalytic subunit. However, distinctively highly damaged HFSCs seem to be sorted out of the niche by differentiation, transferring their chromatin-alterations to more proliferative G protein-coupled receptor 5-positive stem cells. Consequentially, the loss of basal HFSCs is compensated by increased proliferation within the stem cell pool. Despite the initial success of these mechanisms in stem cell population maintenance, the combined effect of the chromatin-alterations and the modification in stem cell pool composition may lead to downstream long-term functional loss of tissue or organs. Stem Cells 2018;36:574-588.

Outside-in integrin signalling regulates haematopoietic stem cell function via Periostin-Itgav axis

Integrins play an important role in haematopoietic stem cell (HSC) maintenance in the bone marrow niche. Here, we demonstrate that Periostin (Postn) via interaction with Integrin-αv (Itgav) regulates HSC proliferation. Systemic deletion of Postn results in peripheral blood (PB) anaemia, myelomonocytosis and lymphopenia, while the number of phenotypic HSCs increases in the bone marrow. Postn^−/− mice recover faster from radiation injury with concomitant loss of primitive HSCs. HSCs from Postn^−/− mice show accumulation of DNA damage generally associated with aged HSCs. Itgav deletion in the haematopoietic system leads to a similar PB phenotype and HSC-intrinsic repopulation defects. Unaffected by Postn, Vav-Itgav^−/− HSCs proliferate faster in vitro, illustrating the importance of Postn-Itgav interaction. Finally, the Postn-Itgav interaction inhibits the FAK/PI3K/AKT pathway in HSCs, leading to increase in p27Kip1 expression resulting in improved maintenance of quiescent HSCs. Together, we demonstrate a role for Itgav-mediated outside-in signalling in regulation of HSC proliferation and stemness.

Integrins regulate haematopoietic stem cell (HSC) homeostasis and engraftment into the bone marrow (BM) niche upon transplantation. Here, the authors show that HSC quiescence and function in the BM is regulated by the interaction of PERIOSTIN and INTEGRIN αv and subsequent increase in p27Kip1.