transforming-growth-factor-beta and Purpura--Thrombotic-Thrombocytopenic

The glomerular capillary endothelium is highly specialized to support the selective filtration of massive volumes of plasma. Filtration is driven by Starling forces acting across the glomerular capillary wall, and depends on its large surface area and extremely high water permeability. Glomerular endothelial cells are extremely flat and perforated by dense arrays of trans-cellular pores, the fenestrae. This phenotype is critical for the high glomerular water permeability and depends on podocyte-derived VEGF, as well as TGF-beta. Endothelial cell-derived PDGFB, in turn, is necessary for the establishment of mesangial cells, which sculpt the glomerular loop structure that underlies the large filtration surface area. In pre-eclampsia, inhibition of the VEGF- and TGF-beta signaling pathways leads to endothelial swelling and loss of fenestrae, reducing the glomerular filtration rate. Similarly, in the thrombotic microangiopathies, glomerular endothelial cell injury coupled with inappropriate VWF activation leads to intracapillary platelet aggregation and loss of the flat, fenestrated phenotype, thus reducing the glomerular filtration rate. Normally, a remarkably small fraction of albumin and other large plasma proteins passes across the glomerular capillary wall despite the massive filtration of water and small solutes. An elaborate glycocalyx, which covers glomerular endothelial cells and their fenestrae forms an impressive barrier that, together with other components of the glomerular capillary wall, prevents loss of plasma proteins into the urine. Indeed, microalbuminuria is a marker for endothelial glycocalyx disruption, and most forms of glomerular endothelial cell injury including pre-eclampsia and thrombotic microangiopaties can cause proteinuria.

Topics: Albuminuria; Animals; Endothelium, Vascular; Glomerular Filtration Rate; Humans; Kidney Glomerulus; Permeability; Proteinuria; Purpura, Thrombotic Thrombocytopenic; Transforming Growth Factor beta

Primary human microvascular endothelial cells (MVEC) of restricted lineage undergo apoptosis when exposed to plasma from patients with thrombotic thrombocytopenic purpura (TTP) and sporadic hemolytic-uremic syndrome (HUS). This reflects the pathology and tissue distribution of lesions in vivo. As extracellular matrix (ECM) is critical to MVEC survival, and cytokines which regulate ECM, such as transforming growth factor (TGF)-beta1, have been reported anecdotally to be altered in TTP/HUS, we examined the role of TGF-beta1 and two ECM proteins, fibronectin and thrombospondin (TSP), in these disorders. Levels of active TGF-beta1 were elevated in acute but not convalescent phases of TTP/sporadic HUS, as well as TTP associated with human immunodeficiency virus infection and use of the anti-platelet drug ticlopidine. MVEC from tissues susceptible to TTP-mediated apoptosis showed little active TGF-beta1 production when exposed to TTP plasmas. In contrast, pulmonary MVEC and large-vessel EC, which are resistant to TTP-linked pathology, showed marked induction of TGF-beta1 following TTP plasma exposure. Exogenous TGF-beta1 suppressed TTP plasma-mediated apoptosis in susceptible MVEC in association with blockade of cell entry into S phase. Soluble TSP, devoid of detectable bound TGF-beta1, had a similar effect, which paralleled its ability to induce TGF-beta1 production in MVEC. In vivo, TSP deposition was diminished markedly in involved tissues of TTP patients. These data highlight the role of TGF-beta1 and ECM in TTP and suggest that differential production of TGF-beta1 by MVEC may play a role in their sensitivity or resistance to TTP/sporadic HUS-mediated apoptosis in vitro and in vivo.

Topics: Apoptosis; Cell Cycle; Cell Lineage; Cells, Cultured; Coronary Vessels; Culture Media, Serum-Free; Endothelium, Vascular; Extracellular Matrix Proteins; Fibronectins; Hemolytic-Uremic Syndrome; HIV Infections; Humans; Liver; Organ Specificity; Palatine Tonsil; Platelet Aggregation Inhibitors; Platelet Count; Purpura, Thrombotic Thrombocytopenic; RNA, Messenger; Skin; Tetradecanoylphorbol Acetate; Thrombospondins; Ticlopidine; Transforming Growth Factor beta; Transforming Growth Factor beta1; Tumor Necrosis Factor-alpha

In this study we evaluated the effect of serum collected from seven thrombotic thrombocytopenic purpura (TTP) patients, either in the acute phase of the disease or in clinical remission, on the in vitro growth of bone marrow haematopoietic progenitor cells, obtained from the same TTP patients in clinical remission and from normal donors. The addition to the cultures of autologous sera collected from TTP patients in acute phase of the disease showed a clear-cut dose-dependent inhibition of immature haematopoietic progenitor cells (BFU-E, CFU-meg and 14th day CFU-GM). On the other hand, no inhibitory effects were observed on more mature 7th day CFU-GM. Interestingly, also sera collected from TTP patients in clinical remission still maintained some inhibitory activity on the growth of immature progenitor cells. A similar inhibitory activity was noticed when TTP sera were tested on normal bone marrow haematopoietic progenitor cells. Such inhibitory activity was significantly reduced in blocking experiments by the addition of a polyclonal neutralizing anti-TGF-beta 1 antibody and the presence of increased levels of both bioactive and latent TGF-beta 1 in TTP sera was confirmed in a bioassay on CCL64 cells. These data contribute to explain the lack of a clear compensatory haematopoiesis observed in some patients with active TTP and add further evidence to the notion of the existence of a state of latent platelet activation in TTP patients in clinical remission.

Topics: Acute Disease; Adult; Bone Marrow; Cell Division; Cells, Cultured; Female; Hematopoiesis; Hematopoietic Stem Cells; Humans; Male; Purpura, Thrombotic Thrombocytopenic; Transforming Growth Factor beta