scholarly journals Aryl Hydrocarbon Receptor-Null Allele Mice Have Hematopoietic Stem/Progenitor Cells with Abnormal Characteristics and Functions

2011 ◽  
Vol 20 (5) ◽  
pp. 769-784 ◽  
Author(s):  
Kameshwar P. Singh ◽  
Russell W. Garrett ◽  
Fanny L. Casado ◽  
Thomas A. Gasiewicz
Keyword(s):  
Aryl Hydrocarbon Receptor ◽  
Progenitor Cells ◽  
Null Allele ◽  
Hematopoietic Stem ◽  
Aryl Hydrocarbon

The Aryl Hydrocarbon Receptor Influences Multiple Stages of Megakaryocyte Differentiation

Blood ◽  
2011 ◽  
Vol 118 (21) ◽  
pp. 1298-1298
Author(s):  
Stephan C. Lindsey ◽  
Eleftherios T. Papoutsakis
Keyword(s):  
Bone Marrow ◽  
Aryl Hydrocarbon Receptor ◽  
Progenitor Cells ◽  
Platelet Function ◽  
Ex Vivo ◽  
Ex Vivo Expansion ◽  
Current Work ◽  
Hematopoietic Stem ◽  
Aryl Hydrocarbon ◽  
Inside Out

Abstract 1298 Previous microarray analyses (n=3) uncovered evidence that aryl hydrocarbon receptor (AHR) mRNA increased 4–6 fold during megakaryocytic (Mk) differentiation as compared to isogenic granulocytic cultures (Lindsey et al. Blood, 2010) and identified AHR as a novel regulator of Mk polyploidization and differentiation (Lindsey et al. Brit J of Haem, 2011). Best known as a mediator of toxicological signals, we now provide unpublished data suggesting AHR impacts several additional aspects of Mk differentiation, including the initial “decision” of hematopoietic stem cells (HSCs) to differentiate toward the Mk lineage, as well as platelet function. In our current work, we first investigated if the absence of AHR signaling within the bone marrow results in Mk polyploidization defects. We found that after 7 days of ex vivo expansion, AHR-null mice had 59.5% fewer Mks ≥128n compared to WT littermates (n=3; p=0.011). In separate experiments, treatment of murine progenitor cells (n=4) with 10 nM TCDD (Dioxin, a prototypic AHR ligand) generated polyploid CD41-expressing cells within 1 day of ex vivo expansion, indicating that AHR ligands can stimulate ex vivo expansion toward the Mk lineage in the absence of cytokines such as thrombopoietin (TPO). As one might expect, TCDD is not as effective as TPO; 18.5% of the Mks treated with TCDD were polyploid by day 7, as compared to 31.5% of the Mks treated with TPO (n=3, p=0.004). Adding TCDD (n=3) did not significantly enhance Mk differentiation in response to TPO (35.4% vs 31.5%; p=0.377). Ex vivo expanding murine progenitor cells with 10 mM of the AHR inhibitor 6',2',4'-trimethoxyflavone (TMF) resulted in 37% fewer highly polyploid (≥32n) Mks by day 7 (n=3, p=0.017), effectively blocking the effects of TPO on Mk differentiation and suggesting that AHR activation is downstream of TPO signaling. Further underscoring a role for AHR during the initial differentiation “decisions” of HSCs, AHR antagonists promote HSC expansion (Boitano et al. Science, 2010) and treatments with AHR agonists deplete the HSC pool within the bone marrow (Singh et al. Carcinogenesis, 2009). HSCs reside in hypoxic niches within the bone marrow and move toward areas of increasing oxygen tension as the differentiate (Laluppa et al. Exp Hematol, 1998), suggesting to many that HSCs prefer areas of hypoxia and that HIF-1α may play a role in this process. Preliminary data shows a 3.1-fold decrease in AHR protein level under hypoxic conditions at a time when HIF-1α expression increases by 2.1-fold. AHR and HIF-1α expression is mediated by the same nuclear chaperone, HIF-1β, suggesting AHR and HIF-1α competition for HIF-1β may serve as a molecular switch by which hematopoietic cells respond to differences in oxygen levels. AHR-null mice bleed 5.3 times longer and lose three times as much blood volume than WT mice in bleeding time assays. While AHR-null mice had 9% fewer platelets and 10.4% fewer reticulated, young RNA-containing platelets than WT mice, we felt that this was not enough to explain the drastic bleeding phenotype in AHR-null mice. In agreement with our hypothesis that AHR impacts platelet function, others have suggested AHR is critical for blood clotting during Oryzias latipes embryogenesis (Kawamura et al. Zoolog Sci, 2002). Platelet function is mediated by both outside-in and inside-out signaling; defects in one or both of these signaling cascades result in bleeding disorders. In the current study, platelets from AHR-null mice bind fibrinogen as well or better than WT platelets (n=3), suggesting that AHR is not involved in inside-out platelet signaling. Based on these findings and work that shows AHR regulates vav2, a critical mediator of platelet outside-in signaling (Pearce et al. JBC, 2004), we pursued the possibility that AHR mediates platelet outside-in signaling. In agreement with a role in outside-in signaling, platelets from AHR-null mice demonstrate defective aggregation in response to collagen as compared to WT platelets. Current work seeks to further investigate the role of AHR in outside-in signaling using spreading assays. Ideally, new therapeutic approaches for Mk/platelet diseases should target specific biological events such as the initial “decisions” leading to Mk expansion from HSCs, Mk polyploidization, or platelet function. By impacting all of these processes, AHR is quickly becoming a very interesting therapeutic target and definitely warrants further investigation. Disclosures: No relevant conflicts of interest to declare.

Aryl Hydrocarbon Receptor Blocks Aging-Induced Senescence in the Liver and Fibroblast Cells

2021 ◽  
Author(s):  
Ana Nacarino-Palma ◽  
Eva M. Rico-Leo ◽  
Judith Campisi ◽  
Arvind Ramanathan ◽  
Jaime M. Merino ◽  
...  
Keyword(s):  
Aryl Hydrocarbon Receptor ◽  
Progenitor Cells ◽  
Chromatin Immunoprecipitation ◽  
Tissue Homeostasis ◽  
Fibroblast Cells ◽  
Aryl Hydrocarbon ◽  
Basal Expression ◽  
Repressive Effect ◽  
Secretory Phenotype ◽  
Mouse Lungs

ABSTRACTAging induces progressive organ degeneration and worsening of tissue homeostasis leading to multiple pathologies. Yet, little is known about the mechanisms and molecular intermediates involved. Here, we report that aged aryl hydrocarbon receptor-null mice (AhR-/-) had exacerbated senescence and larger numbers of liver progenitor cells. Senescence-associated markers β-galactosidase (SA-β-Gal), p16Ink4a and p21Cip1 and genes of the senescence-associated secretory phenotype (SASP) TNF and IL1 were overexpressed in aged AhR-/- livers. AhR binding to the promoter of those genes, as shown by chromatin immunoprecipitation, likely had a repressive effect maintaining their physiological levels in AhR+/+ livers. Furthermore, factors secreted by senescent cells MCP-2, MMP12 and FGF were also produced at higher levels in aged AhR-null livers. Supporting the linkage between senescence and stemness, liver progenitor cells were more abundant in AhR-/- mice, which could probably contribute to their increased hepatocarcinoma burden. These roles of AhR are not liver-specific since adult and embryonic AhR-null fibroblasts acquired cellular senescence upon culturing with overexpression of SA-β-Gal, p16Ink4a and p21Cip1. Notably, depletion of senescent cells with the senolytic agent navitoclax restored basal expression of senescent markers in AhR-/- fibroblasts. Oppositely, senescence promoter palbociclib induced an AhR-null like phenotype in AhR+/+ fibroblasts. Moreover, doxycycline-induced senescence reduced AhR levels while depletion of p16Ink4a-expressing senescent cells restored basal AhR levels in mouse lungs. Thus, AhR is needed to restrict age-induced senescence, and such activity seems to correlate with a more differentiated phenotype and with increased resistance to liver tumorigenesis.

scholarly journals Selective Autophagy Maintains the Aryl Hydrocarbon Receptor Levels in HeLa Cells: A Mechanism That Is Dependent on the p23 Co-Chaperone

2020 ◽  
Vol 21 (10) ◽  
pp. 3449
Author(s):  
Yujie Yang ◽  
William K. Chan
Keyword(s):  
Aryl Hydrocarbon Receptor ◽  
Hela Cells ◽  
Stem Cell Differentiation ◽  
26S Proteasome ◽  
Chemical Agent ◽  
Physical Interaction ◽  
Hematopoietic Stem ◽  
Selective Autophagy ◽  
Protein Levels ◽  
Aryl Hydrocarbon

The aryl hydrocarbon receptor (AHR) is an environmental sensing molecule which impacts diverse cellular functions such as immune responses, cell growth, respiratory function, and hematopoietic stem cell differentiation. It is widely accepted that the degradation of AHR by 26S proteasome occurs after ligand activation. Recently, we discovered that HeLa cells can modulate the AHR levels via protein degradation without exogenous treatment of a ligand, and this degradation is particularly apparent when the p23 content is down-regulated. Inhibition of autophagy by a chemical agent (such as chloroquine, bafilomycin A1, or 3-methyladenine) increases the AHR protein levels in HeLa cells whereas activation of autophagy by short-term nutrition deprivation reduces its levels. Treatment of chloroquine retards the degradation of AHR and triggers physical interaction between AHR and LC3B. Knockdown of LC3B suppresses the chloroquine-mediated increase of AHR. Down-regulation of p23 promotes AHR degradation via autophagy with no change of the autophagy-related gene expression. Although most data in this study were derived from HeLa cells, human lung (A549), liver (Hep3B), and breast (T-47D and MDA-MB-468) cells also exhibit AHR levels sensitive to chloroquine treatment and AHR–p62/LC3 interactions. Here we provide evidence supporting that AHR undergoes the p62/LC3-mediated selective autophagy in HeLa cells.

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