Stromal-Derived Factor-1 and Its Receptor, CXCR4, Are Constitutively Expressed by Mouse Liver Sinusoidal Endothelial Cells: Implications for the Regulation of Hematopoietic Cell Migration to the Liver During Extramedullary Hematopoiesis

Abstract

Stromal-derived factor (SDF)-1 is the main regulating factor for trafficking/homing of hematopoietic stem cells (HSC) to the bone marrow (BM). It is possible that this chemokine may also play a fundamental role in regulating the migration of HSC to several organs during extramedullary hematopoiesis. Because liver sinusoidal endothelial cells (LSEC) constitute an extramedullary niche for HSC, it is possible that these cells represent one of the main cellular sources of SDF-1 at the liver. Here, we show that LSEC express SDF-1 at the mRNA and protein level. Biological assays showed that conditioned medium from LSEC (LSEC-CM) stimulated the migration of BM progenitor lineage-negative (BM/Lin -) cells. This effect was significantly reduced by AMD3100, indicating that the SDF-1/CXCR4 axis is involved in the stimulatory migrating effect induced by LSEC-CM. Early localization of HSC in SDF-1-expressing LSEC microenvironment together with increased levels of this chemokine in hepatic homogenates was found in an experimental model of liver extramedullary hematopoiesis. Flow cytometry studies showed that LSEC express the CXCR4 receptor. Functional assays showed that activation of this receptor by SDF-1 stimulated the migration of LSEC and increased the expression of PECAM-1. Our findings suggest that LSEC through the production of SDF-1 may constitute a fundamental niche for regulation of HSC migration to the liver. To our knowledge, this is the first report showing that LSEC not only express and secrete SDF-1, but also its receptor CXCR4.

Role of SDF-1 (CXCL12) in regulating hematopoietic stem and progenitor cells traffic into the liver during extramedullary hematopoiesis induced by G-CSF, AMD3100 and PHZ

“…2A and B). Low c-kit expression was evidenced in liver sinusoids from territories on LSEC from control animals, as we have previously reported [22] (Fig. 2B).…”

“…We evaluated cell migration as previously [22]. Briefly, 5-FU BM cells (1 Â 10 4 cells; 100 ll serum-free medium) were placed into the top of semi-porous polyester membrane (Transwell Ò , 24 well cell clusters; Corning, Inc., Corning, NY) of 5 lm pore sizes.…”

“…The supernatants were collected and passed through a 0.2 mm filter before use. Serum, liver and bone marrow homogenates were analyzed by ELISA for murine SDF-1 (R&D Systems) as previously described [22]. Cytokine levels were corrected for total protein content per sample using the Lowry's method.…”

“…SDF-1) by liver cells may promote the homing of circulating HSPCs to this organ. Recent evidence has shown that the liver sinusoidal endothelial cells (LSECs) express SDF-1, and that conditioned media from these cells induce migration of HSPCs [22]. Based on these results, it is possible that migration and homing of HSPCs from BM to the liver, during EMH, could be regulated by the expression of SDF-1 by LSEC.…”

“…There is evidence showing that mobilizing agents, such as G-CSF, induce not only mobilization of HSPCs from BM to the blood, but also migration of these cells to other extramedullary organs, such as the liver [22]. Regarding the liver, the mechanisms involved in regulating migration and homing of HSPCs to this organ during extramedullary hematopoiesis (EMH) are not well known.…”