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 À/À ) have altered numbers of ECs and CARs that produce less hematopoietic factors. HSCs co-cultured in vitro with HO-1 À/À mesenchymal stromal cells expand, but have altered kinetic of growth and differentiation of derived colonies. HSCs from young HO-1 À/À animals have reduced quiescence and regenerative potential. Young HO-1 À/À HSCs exhibit features of premature exhaustion on the transcriptional and functional level. HO-1 +/+ HSCs transplanted into HO-1 À/À recipients exhaust their regenerative potential early and do not reconstitute secondary recipients. In turn, transplantation of HO-1 À/À HSCs to the HO-1 +/+ recipients recovers the regenerative potential of HO-1 À/À 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.EMBO Reports (2020) 21: e47895 Until now, the mechanisms found to contribute to the aging of HSCs have been mostly intrinsic to the HSCs [6,15]. These include age-related accumulation of mutations and cell-autonomous changes in the transcriptome and epigenome of HSCs [6,7,[16][17][18][19].Although HSC-extrinsic factors from the local bone marrow (BM) environment of HSCs-the HSC niche-or systemic factors are critical for HSC maintenance [20][21][22], little is known about their contribution to HSC aging.Recent findings indicate that HSCs occupy a perivascular niche and localize in direct proximity to endothelial cells (ECs) and mesenchymal stromal cells (MSCs) surrounding vessels [23,24]. Among the many cell types in the HSC niche, the ECs and MSCs constitute the main source of stromal cell-derived factor 1a (SDF-1a) and stem cell factor (SCF)-extrinsic factors critical for HSC maintenance [25][26][27][28]. Specific deletion of either Sdf1a or Scf in either ECs or MSCs causes hematopoietic collapse or triggers overactivation of HSCs and their release from the niche [22,[25][26][27]. J endomucin CD31 HO-1 Figure 1. ª 2019 The Authors EMBO reports 21: e47895 | 2020 ****P < 0.0001. Data are shown as mean AE SEM. IECs and CARs from middle-aged animals (11-12 months) express lower levels of HO-1 protein. Two independent experiments, n = 5-10/group. Data are shown as mean AE SEM. *P < 0.05, ***P < 0.001, two-tailed unpaired t-test. JMiddle-aged animals have lower frequency of ECs. Two independent experiments, n = 10-11/group. Data are shown as mean AE SEM. **P < 0.01, two-tailed unpaired t-test. The control staining of HO-1 on HO-1 À/À bone marrow section is provided in Appendix Fig S1. 4 of 21 EMBO reports 21: e47895 | 2020 ª 2019 The Authors H Only 1 out of 267 DEGs identified in non-tran...

Chemerin is a chemoattractant protein with adipokine properties encoded by the retinoic acid receptor responder 2 (RARRES2) gene. it has gained more attention in the past few years due to its multilevel impact on metabolism and immune responses. However, mechanisms controlling the constitutive and regulated expression of RARRES2 in a variety of cell types remain obscure. To our knowledge, this report is the first to show that DNA methylation plays an important role in the cell-specific expression of RARRES2 in adipocytes, hepatocytes, and B lymphocytes. Using luciferase reporter assays, we determined the proximal fragment of the RARRES2 gene promoter, located from − 252 to + 258 bp, to be a key regulator of transcription. Moreover, we showed that chemerin expression is regulated in murine adipocytes by acute-phase cytokines, interleukin 1β and oncostatin M. in contrast with adipocytes, these cytokines exerted a weak, if any, response in mouse hepatocytes, suggesting that the effects of IL-1β and OSM on chemerin expression is specific to fat tissue. Together, our findings highlight previously uncharacterized mediators and mechanisms that control chemerin expression. Chemerin is a small (18 kDa) multifunctional protein capable of regulating different biological processes, including immune cell migration, adipogenesis, osteoblastogenesis, angiogenesis, myogenesis, and glucose homeostasis 1. Moreover, it shows broad-spectrum antimicrobial activity in both human and mouse epidermis, suggesting it plays a role in maintaining skin-barrier homeostasis 2,3. Chemerin-induced signaling is mediated predominantly through chemokine-like receptor 1 (CMKLR1), which is expressed by many cells including plasmacytoid dendritic cells (pDCs), macrophages, natural killer (NK) cells, adipocytes, hepatocytes, and keratinocytes 2,4-9. Chemerin is secreted as pro-chemerin and circulates in plasma as an inactive precursor protein (Chem163S) that can subsequently be activated through posttranslational carboxyl-terminal processing by a variety of proteinases 10,11. The gene encoding chemerin is known as retinoic acid receptor responder 2 (RARRES2) 12 , or as tazaroteneinduced gene 2 (TIG2) given it was first discovered in tazarotene-treated psoriatic skin lesions 13,14. Liver and adipose tissue are reported to be the major sites of chemerin production; nonetheless, RARRES2 mRNA is detectable in many other tissues, including the adrenal glands, ovaries, pancreas, lungs, kidney, and skin 2,15. Chemerin

Hematopoietic stem cells (HSCs) give rise to all types of blood cells and self‐renew their own population. The regeneration potential of HSCs has already been successfully translated into clinical applications. However, recent studies on the biology of HSCs may further extend their clinical use in future. The roles of HSCs in native hematopoiesis and in transplantation settings may differ. Furthermore, the heterogenic pool of HSCs dynamically changes during aging. These changes also involve the complex interactions of HSCs with the bone marrow niche. Here, we review the opportunities and challenges of these findings to improve the clinical use of HSCs. We describe new methods of HSCs mobilization and conditioning for the transplantation of HSCs. Finally, we highlight the research findings that may lead to overcoming the current limitations of HSC transplantation and broaden the patient group that can benefit from the clinical potential of HSCs.

Chemerin is a chemoattractant protein with adipokine properties encoded by the retinoic acid receptor responder 2 (RARRES2) gene. It has gained more attention over the past few years due to its multilevel impact on metabolism and immune responses. The pleiotropic actions of chemerin include chemotaxis of dendritic cells, macrophages and natural killers (NK) subsets, bactericidal activity as well as regulation of adipogenesis and glucose metabolism. Therefore, reflecting the pleiotropic actions of chemerin, expression of RARRES2 is regulated by a variety of inflammatory and metabolic mediators.However, for most cell types, the molecular mechanisms controlling constitutive and regulated chemerin expression are poorly characterized. Here we show that RARRES2 mRNA levels in murine adipocytes are upregulated in vitro and in vivo by acute-phase cytokines, IL-1 and OSM. In contrast to adipocytes, these cytokines exerted a weak, if any, response in mouse hepatocytes, suggesting that the effect of IL-1 and OSM on chemerin expression is specific to fat tissue. Moreover, we show that DNA methylation controls the constitutive expression of chemerin. Bisulfite sequencing analysis showed low methylation levels within -735 to +258 bp of the murine RARRES2 gene promoter in unstimulated adipocytes and hepatocytes. In contrast to these cells, the RARRES2 promoter is highly methylated in B lymphocytes, cells that do not produce chemerin. Together, our findings reveal previously uncharacterized mediators and mechanisms controlling chemerin expression in various cells.

Background Chemerin is a chemoattractant protein with adipokine and antimicrobial properties encoded by the retinoic acid receptor responder 2 (RARRES2) gene. Chemerin bioactivity largely depends on carboxyl-terminal proteolytic processing that generates chemerin isoforms with different chemotactic, regulatory, and antimicrobial potentials. While these mechanisms are relatively well known, the role of alternative splicing in generating isoform diversity remains obscure. Methods and results Using rapid amplification of cDNA ends (RACE) PCR, we determined RARRES2 transcript variants present in mouse and human tissues and identified novel transcript variant 4 of mouse Rarres2 encoding mChem153K. Moreover, analyses of real-time quantitative PCR (RT-qPCR) and publicly-available next-generation RNA sequencing (RNA-seq) datasets showed that different alternatively spliced variants of mouse Rarres2 are present in mouse tissues and their expression patterns were unaffected by inflammatory and infectious stimuli except brown adipose tissue. However, only one transcript variant of human RARRES2 was present in liver and adipose tissue. Conclusion Our findings indicate a limited role for alternative splicing in generating chemerin isoform diversity under all tested conditions.