MicroRNAs (miRNAs) can regulate hematopoietic stem/progenitor cells (HSPC) by modulation of intrinsic cell components such as transcription factors and receptors. In addition, miRNAs could play a role in the microenvironment were HSPC host and consequently affect HSPC via extrinsic factors, which to our knowledge is an hypothesis that has not been tested. Since the chemokine stromal derived factor 1alpha (SDF-1alpha) is essential for both homing and retention of HSPC in the bone marrow, we tested if miRNAs expressed by human bone marrow-derived mesenchymal stem cells (MSC; a key source of SDF-1alpha), could potentially inhibit SDF-1alpha expression. In deed, using luciferase reporter-systems we show specific binding of miR-23a to the 3′UTR of SDF-1alpha. Consequently, transfection of MSCs with a precursor miR-23a (pre-miR-23a) leads to a 30% reduction of SDF-1alpha at both mRNA and protein levels. In contrast, inhibition of endogenous miR-23a with anti-sense oligonucleotides (anti-miR-23a), leads to a significant increase of SDF-1alpha also at both mRNA (30%) and protein (10%) levels as compared to controls (scramble pre-/anti-miR). As a result, migration of CD34+ HSPC in transwell assays is strongly affected upon overexpression or inhibition of miR-23a in MSCs (with pre-miR-23a 35% less migration; with anti-miR-23a 20% more migration, as compared to respective controls). Interestingly, transforming growth factor beta 1 (TGF-beta1) inhibits SDF-1alpha expression in MSCs in a concentration dependent manner, while miR-23a is increased under same experimental settings. Even more, silencing endogenous miR-23a significantly reduces the effect of TGF-beta1 on SDF-1alpha mRNA and protein levels, suggesting that at least in part TGF-beta1 inhibits SDF-1alpha expression via increasing miR-23a levels. This is to our knowledge the first established connection between miRNA biology and HSPC-niche related factors.

Disclosures: No relevant conflicts of interest to declare.

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