Antagonizing Retinoic Acid Receptors Increases Myeloid Cell Production by Cultured Human Hematopoietic Stem Cells

Abstract

Activities of the retinoic acid receptor (RAR)α and RARγ are important to hematopoiesis. Here, we have investigated the effects of receptor selective agonists and antagonists on the primitive human hematopoietic cell lines KG1 and NB-4 and purified normal human hematopoietic stem cells (HSCs). Agonizing RARα (by AGN195183) was effective in driving neutrophil differentiation of NB-4 cells and this agonist synergized with a low amount (10 nM) of 1α,25-dihydroxyvitamin D3 to drive monocyte differentiation of NB-4 and KG1 cells. Treatment of cultures of human HSCs (supplemented with stem cell factor ± interleukin 3) with an antagonist of all RARs (AGN194310) or of RARα (AGN196996) prolonged the lifespan of cultures, up to 55 days, and increased the production of neutrophils and monocytes. Slowing down of cell differentiation was not observed, and instead, hematopoietic stem and progenitor cells had expanded in number. Antagonism of RARγ (by AGN205728) did not affect cultures of HSCs. Studies of CV-1 and LNCaP cells transfected with RAR expression vectors and a reporter vector revealed that RARγ and RARβ are activated by sub-nM all-trans retinoic acid (EC50–0.3 nM): ~50-fold more is required for activation of RARα (EC50–16 nM). These findings further support the notion that the balance of expression and activity of RARα and RARγ are important to hematopoietic stem and progenitor cell expansion and differentiation.

Retinoic Acid, Leaky Gut, and Autoimmune Diseases

“…On the other hand, RARγ hinders hematopoietic stem cell (HSC) differentiation in favor of their self-renewal and proliferation [ 70 ]. Recent findings suggest that the expression and activities of both RARs coordinate to derive the differentiation lineages of HSCs, and that this is largely dependent on the bioavailability of RA [ 71 ]. Therefore, different doses of RA can determine different cellular lineage specificities.…”

Role of Vitamin A/Retinoic Acid in Regulation of Embryonic and Adult Hematopoiesis

“…Treatment with retinoids and vitamin D abolishes this effect [ 63 ]. However, when human HSC are cultured with RARα antagonists, the lifespan of the cultures, the number of the progenitors and also the production of monocytes and neutrophils increase, while antagonists of RARγ do not affect the cultures [ 64 ]. This specific role of RARα for human HSC would be different to that above described in mice.…”

“…Treatment of hematopoietic stem cells or some leukemia cell lines with the active form of the vitamin D leads to increased monocyte/macrophage differentiation [ 92 , 119 , 120 ], an effect which is not detected in VDR knock-out mice [ 114 , 119 ]. As stated above, when cultured HSC are treated with RA signaling inhibitors, their differentiation is blocked, but retinoids and vitamin D treatment counteract this effect [ 64 ]. Since RARα receptor activation induces granulopoiesis, it has been suggested that VDR and RARα can compete for RXR heterodimerization.…”

“…Since vitamin D3 induces monocytic differentiation of some lines of leukemic cells, vitamin D analogs could represent a therapeutic option [ 115 , 119 , 121 ]. Synergy between vitamin D and RA signaling is demonstrated by the enhanced neutrophil differentiation of NB4 cells when a RARα agonist (AGN195183) is used in combination with a low concentration (10 nM) of vitamin D3 [ 64 ]. The differentiation effect of the RA/vitamin D3 combination is variable in different AML cell lines [ 122 ], and this is probably due to the regulation of the VDR transcription by RARα.…”

Enhancing human cord blood hematopoietic stem cell engraftment by targeting nuclear hormone receptors

“…Mechanistically, once binding with LG1506, the RXR-RAR complex recruits silencing mediator of retinoic acid and thyroid hormone receptor (SMRT) corepressors to promoters of target genes such as CD38 , thus inhibiting differentiation of HSCs [46]. Recently, it was found that RARα antagonist increases myeloid cell production and promotes expansion of human HSCs, while RARγ antagonist had no effect due to different sensitivity to ATRA [47]. RXR forms heterodimers with other NRs, including liver X receptor (LXR), thyroid hormone receptor (THR), vitamin D receptor (VDR), peroxisome proliferator-activated receptors (PPARs).…”