In vitro evidence for a dual role of tumor necrosis factor-α in human immunodeficiency virus type 1 encephalopathy

Microglial cell activation, myelin alteration, and abundant tumor necrosis factor (TNF)-α message have been observed in the brains of some human immunodeficiency virus type 1 (HIV - 1)vinfected and demented patients. We therefore used cultures of purified human microglia and oligodendrocytes derived from adult human brain to examine the role of TNF-α in HIV-1 encephalopathy. Human microglia synthesize TNF-α message and protein in vitro. When these cells were infected with HIV-1 JrFL and maintained in the presence of TNF-α antibodies, soluble TNF-α receptors, or the TNF-α inhibitor pentoxifylline, viral replication was delayed or strongly inhibited. Both human microglia and oligodendrocytes express the two TNF receptors, TNF-Rl, which has been implicated in cytotoxicity, and TNF-R2. While TNF-α may enhance HIV-1 replication in an autocrine manner, it is not toxic for microglia. In contrast, recombinant human TNF-α causes oligodendrocyte death in a dose-dependent manner. In situ detection of DNA fragmentation in some cells indicated that oligodendrocyte death may occur by apoptosis. Addition of live microglia or medium conditioned by these cells also resulted in 30 to 40% oligodendrocyte death, which was largely prevented by TNF-α inhibitors. We propose that TNF-α plays a dual role in HIV-1 encephalopathy, enhancing viral replication by activated microglia and damaging oligodendrocytes. Thus, TNF-α inhibitors may alleviate some ofthe neurological manifestations of acquired immunodeficiency syndrome.     

Tumor necrosis factor (TNF)-mediated activation of the p55 TNF receptor negatively regulates maintenance of cycling reconstituting human hematopoietic stem cells

Hematopoietic stem cell (HSC) fate decisions between self-renewal and commitment toward differentiation are tightly regulated in vivo. Recent developments in HSC culture and improvements of human HSC assays have facilitated studies of these processes in vitro. Through such studies stimulatory cytokines critically involved in HSC maintenance in vivo have been demonstrated to also promote HSC self-renewing divisions in vitro. Evidence for negative regulators of HSC self-renewal is, however, lacking. Tumor necrosis factor (TNF), if overexpressed, has been implicated to mediate bone marrow suppression. However, whether and how TNF might affect the function of HSC with a combined myeloid and lymphoid reconstitution potential has not been investigated. In the present studies in vitro conditions recently demonstrated to promote HSC self-renewing divisions in vitro were used to study the effect of TNF on human HSCs capable of reconstituting myelopoiesis and lymphopoiesis in nonobese diabetic-severe combined immunodeficient (NOD-SCID) mice. Although all cord blood and adult bone marrow CD34(+)CD38(-) cells were capable of undergoing cell divisions in the presence of TNF, cycling HSCs exposed to TNF in vitro and in vivo were severely compromised in their ability to reconstitute NOD-SCID mice and long-term cultures. The negative effect of TNF was not dependent on the Fas pathway, and a similar effect could be observed using a mutant TNF exclusively targeting the p55 TNF receptor. TNF did not appear to enhance apoptosis or affect cell-cycle distribution of cultured progenitors, but rather promoted myeloid differentiation. Thus, TNF might regulate HSC fate by promoting their differentiation rather than self-renewal.     

Tumor necrosis factor-alpha inhibits stem cell factor-induced proliferation of human bone marrow progenitor cells in vitro. Role of p55 and p75 tumor necrosis factor receptors.

Stem cell factor (SCF), a key regulator of hematopoiesis, potently synergizes with a number of hematopoietic growth factors. However, little is known about growth factors capable of inhibiting the actions of SCF. TNF-alpha has been shown to act as a bidirectional regulator of myeloid cell proliferation and differentiation. This study was designed to examine interactions between TNF-alpha and SCF. Here, we demonstrate that TNF-alpha potently and directly inhibits SCF-stimulated proliferation of CD34+ hematopoietic progenitor cells. Furthermore, TNF-alpha blocked all colony formation stimulated by SCF in combination with granulocyte colony-stimulating factor (CSF) or CSF-1. The synergistic effect of SCF observed in combination with GM-CSF or IL-3 was also inhibited by TNF-alpha, resulting in colony numbers similar to those obtained in the absence of SCF. These effects of TNF-alpha were mediated through the p55 TNF receptor, whereas little or no inhibition was signaled through the p75 TNF receptor. Finally, TNF-alpha downregulated c-kit cell-surface expression on CD34+ bone marrow cells, and this was predominantly a p55 TNF receptor-mediated event as well.     

Ibuprofen plus codeine, ibuprofen, and placebo in a single- and multidose cross-over comparison for coxarthrosis pain

The analgesic efficacy of 200 mg ibuprofen plus 30 mg codeine, 200 mg ibuprofen and placebo was investigated in a new analgesic evaluation model using single- and repeated-dose administration. The study was a double-blind randomized cross-over investigation in 26 coxarthrosis patients with persistent pain. After a washout period of at least 2 days with paracetamol available as rescue analgesic, each of the 3 treatments was administered in a total of 6 doses during 24 h. The hourly pain intensity was recorded on a 100-mm visual analogue scale (VAS) for 8 h after the 1st and the 6th dose. The pretreatment VAS score was 31–37 mm. After the 1st dose the 8-h mean pain intensity values were 25, 27, and 26 mm after ibuprofen plus codeine, ibuprofen, and placebo, respectively. Following another 5 doses every 4 h the corresponding values were 10, 17 and 29 mm. Repeated administration of both active drugs reduced the pain intensity significantly. The analgesic efficacy of ibuprofen plus codeine was significantly superior to that of ibuprofen which was, in turn, superior to that of placebo. In conclusion, analgesic efficacy was better differentiated after repeated-dose than after single-dose administration. The present study design was able to differentiate between 200 mg ibuprofen plus 30 mg codeine and 200 mg ibuprofen alone in a relatively small number of patients.     

All-trans retinoic acid directly inhibits granulocyte colony- stimulating factor-induced proliferation of CD34+ human hematopoietic progenitor cells

In this study we examine the effects of retinoids on purified CD34+ human hematopoietic progenitor cells. All-trans retinoic acid inhibited granulocyte colony-stimulating factor (G-CSF)-induced proliferation of CD34+ cells in short-term liquid cultures in a dose-dependent fashion with maximal inhibition of 72% at a concentration of retinoic acid of 1 mumol/L. Although no significant effects were observed on granulocyte- macrophage CSF (GM-CSF)--interleukin-3--or stem cell factor (SCF)- induced proliferation, the combinations of G-CSF and each of these cytokines were all inhibited. Moreover, retinol (3 mumol/L) and chylomicron remnant retinyl esters (0.1 mumol/L) in concentrations normally found in human plasma also had inhibitory effects. Single-cell experiments showed that the effects of retinoic acid were directly mediated. Retinoids also significantly inhibited G-CSF-induced colony formation in semisolid medium, with 88% inhibition observed at a concentration of retinoic acid of 1 mumol/L. However, we did not observe any effects of retinoic acid on G-CSF-induced differentiation as assessed by morphology and flowcytometry. Similar to previous findings using total bone marrow mononuclear cells, we observed a stimulation of GM-CSF-induced colony formation after 14 days. We also observed a stimulatory effect of low doses of retinoic acid (30 nmol/L) on blast-cell colony formation on stromal cell layers. Taken together, the data indicate that vitamin A present in human plasma has inhibitory as well as stimulatory effects on myelopoiesis.     

Role of the 75-kDa tumor necrosis factor receptor: inhibition of early hematopoiesis.

Biological effects of tumor necrosis factor alpha (TNF-alpha) are mediated through two cell surface receptors, the 55-kDa TNF receptor and the 75-kDa TNF receptor. The present study investigated the relative roles of the two TNF receptors in normal hematopoiesis. Using agonists (antibodies) specific for the 55- and 75-kDa TNF receptors, we demonstrate differential roles of the two TNF receptors in hematopoiesis in that only the 55-kDa TNF receptor mediates antiproliferative effects of TNF-alpha on mature Lin- hematopoietic progenitor cells responding to granulocyte colony-stimulating factor or interleukin 3 alone. In contrast, the 75-kDa TNF receptor is essential in mediating inhibition of primitive Lin-Sca-1+ high-proliferative-potential colony-forming cells and inhibition of the total number of proliferative clones of individually cultured Lin-Sca-1+Rh123lo and Lin-Sca-1+Rh123hi cells.     

Aberrant receptor signaling and trafficking as mechanisms in oncogenesis

Intracellular signaling pathways activated through cell surface receptors are essential for cell proliferation, differentiation, survival, and migration. Dysregulation of such signaling through mutations, chromosome rearrangements, aberrant gene expression, or epigenetic changes is a key factor in oncogenesis. Prominent examples of receptor signaling pathways that are dysregulated in cancers include those initiated by receptor tyrosine kinases, WNT, TGFbeta, and Notch receptors. In this review we will discuss these signaling pathways and how their dysfunction may contribute to oncogenesis. We will also highlight the important role of endocytic membrane trafficking in receptor signaling and tumor suppression.