Role of Lefty in the anti tumor activity of human adult liver stem cells.

Recent studies demonstrated that factors derived from embryonic stem cells inhibit the tumorigenicity of a variety of cancer cell lines. Embryonic stem cell-secreted Lefty, an inhibitor of Nodal-signalling pathway, was implicated in reprogramming cancer cells. Whether adult stem cells exhibited similar properties has not been explored. The aim of the present study was to investigate whether the conditioned medium (CM) derived from adult stem cells influence in vitro and in vivo tumor growth by a Nodal-dependent pathway. In particular we compared the anti-tumor effect of CM from human liver stem cells (HLSC) with that of bone marrow-derived mesenchymal stem cells (MSC). We found that HLSC-CM inhibited the in vitro growth and promoted apoptosis in HepG2 cells that expressed a deregulated Nodal pathway. The effect of HLSC-CM was related to the presence of Lefty A in the CM of HLSC. Silencing Lefty A in HLSC or Lefty A blockade with a blocking peptide abrogated the anti-proliferative and pro-apoptotic effect of HLSC-CM. Moreover, the administration of human recombinant Lefty A protein mimicked the effect of HLSC-CM indicating that Nodal pathway is critical for the growth of HepG2. At variance of HLSC, bone marrow-derived MSC did not express and release Lefty A and the MSC-CM did not exhibited an anti-tumor activity in vitro, but rather stimulated proliferation of HepG2. In addition, the intra-tumor administration of HLSC-CM was able to inhibit the in vivo growth of HepG2 hepatoma cells implanted subcutaneously in SCID mice. At variance, HLSC-CM derived from Lefty A silenced HLSC was unable to inhibit tumor growth. In conclusion, the results of present study suggest that Lefty A may account for the tumor suppressive activity of HLSC as a result of an inhibition of the Nodal-signalling pathway by a mechanism similar to that described for embryonic stem cells.

Human liver stem cell-derived microvesicles accelerate hepatic regeneration in hepatectomized rats.

Several studies indicate that adult stem cells may improve the recovery from acute tissue injury. It has been suggested that they may contribute to tissue regeneration by the release of paracrine factors promoting proliferation of tissue resident cells. However, the factors involved remain unknown. In the present study we found that microvesicles (MVs) derived from human liver stem cells (HLSC) induced in vitro proliferation and apoptosis resistance of human and rat hepatocytes. These effects required internalization of MVs in the hepatocytes by an alpha(4)-integrin-dependent mechanism. However, MVs pre-treated with RNase, even if internalized, were unable to induce hepatocyte proliferation and apoptosis resistance, suggesting an RNA-dependent effect. Microarray analysis and quantitative RT-PCR demonstrated that MVs were shuttling a specific subset of cellular mRNA, such as mRNA associated in the control of transcription, translation, proliferation and apoptosis. When administered in vivo, MVs accelerated the morphological and functional recovery of liver in a model of 70% hepatectomy in rats. This effect was associated with increase in hepatocyte proliferation and was abolished by RNase pre-treatment of MVs. Using human AGO2, as a reporter gene present in MVs, we found the expression of human AGO2 mRNA and protein in the liver of hepatectomized rats treated with MVs. These data suggested a translation of the MV shuttled mRNA into hepatocytes of treated rats. In conclusion, these results suggest that MVs derived from HLSC may activate a proliferative program in remnant hepatocytes after hepatectomy by a horizontal transfer of specific mRNA subsets.

Recent insights into the pathogenesis of severe sepsis.

OBJECTIVE: Severe sepsis remains the dominant challenge in the care of critically ill patients. Over the last 10 years a large body of research has modified our understanding of this condition. In this article, we review the evolution of our understanding of the molecular mechanisms responsible for the development of this clinical syndrome. DATA SOURCES: The authors undertook a critical review of the literature on the molecular basis of the pathogenesis of sepsis with particular emphasis on the role of cytokines, toll-like receptors, adhesion molecules, coagulation cascade molecules and the possible role of in-vitro experimental models of blood-endothelium interaction. SUMMARY OF REVIEW: Recent insights into the molecular mechanisms responsible for the pathogenesis of the severe sepsis syndrome suggest that pro- and anti- inflammatory pathways are simultaneously activated and interact in a dynamic way. Pro-inflammatory cytokines previously considered as targets for intervention have typically been already activated and de-activated by the time the clinical diagnosis is made and intervention is possible. Cellular activity involving white cell-endothelial interactions occur later, making them a more attractive option for therapeutic intervention. Immunological incompetence rather than over-activity may be the most common state of cell function in critically ill patients. CONCLUSIONS: Our understanding of the the pathogenesis of severe sepsis continues to grow. Expression of membrane surface molecules such as toll-like receptors, adhesion molecules and cytokine receptors induce a high degree of redundancy and amplification. Cell responsiveness is reduced in an attempt to circumvent the amplification loop. However, the ensuing interaction between the host and the pathogen(s) may lead to an immune deficiency, leaving the field open to further invasion by the original bacteria or to superimposed infection agents. Endothelium-white cell interactions might be an appropriate target for future interventions.