TIMP3 is Regulated by Pericytes upon Shear Stress Detection Leading to a Modified Endothelial Cell Response.

OBJECTIVES: Atherosclerosis is a hallmark of cardiovascular disease. Shear stress on endothelial cells has been linked to atherogenesis and to fibrous cap thinning and rupture. Pericytes reside in the sub-endothelial space of vessels and have vasoprotective effects. They are subjected to shear stress when endothelial cell integrity is disrupted. The aim was to investigate the susceptibility and response of pericytes to shear stress. METHODS: Endothelial cells and pericytes were seeded in two dimensional monocultures and co-cultures, and in a novel three dimensional co-culture system and were subjected to no, low and high shear stress (0, 10, 30 dyne/cm2) for 48 h. The morphological response to flow was assessed by histology and the expression of extracellular matrix proteins was analysed using quantitative polymerase chain reaction, immunoblotting, and ELISA. RESULTS: While endothelial cells aligned into flow direction, pericytes aligned perpendicularly (p < .001), indicating that they must be capable of sensing flow. When pericytes were embedded into a 3D matrix they showed similar alignment and pericytes built long processes towards the lumen. Under shear stress endothelial cells upregulated "a disintegrin and metalloproteinase with thrombospondin motif 1" (ADAMTS-1) (p < .01) and pericytes upregulated "tissue inhibitor of matrix metalloproteinase" (TIMP) 3 (p < .05), an inhibitor of ADAMTS-1, meanwhile differential expression of extracellular matrix (ECM) proteins could be detected in co-cultures of both cells. For TIMP3 expression direct cell-cell contact between endothelial cells and pericytes was required. CONCLUSION: The experiments highlight that pericytes are able to sense direct flow thereby regulating ECM proteins known to be involved in vascular remodelling. Furthermore, pericytes counter-regulate endothelial ADAMTS-1 by protective TIMP3 expression to prevent matrix degradation and maintain vascular stability. For this protective effect direct cell contact was necessary. This observation might represent an adaptive, protective mechanism of pericytes to counteract endothelial damage in the onset of atherosclerosis.

Kidney pericytes: a novel therapeutic target in interstitial fibrosis.

Chronic Kidney Disease affects approximately 8% of the population and contributes considerably to premature morbidity and mortality. Recently reported studies have highlighted an important role for resident microvascular pericytes in the pathogenesis of kidney fibrosis. Pericytes are emerging as the predominant source of the activated, matrix depositing, stromal cell population seen in progressive fibrosis. Further, pericyte activation leads to their detachment from the vasculature, triggers unstable microvasculature and leads to rarefaction. Strategies to modulate pericyte function in these processes are therefore therapeutically attractive. In this review we will first describe our current understanding of the structure and function of the pericyte and the role these cells play in angiogenesis and the pathogenesis of renal fibrosis. Novel therapeutic approaches targeting pericytes in murine models of renal disease will then be considered.

Renal stem cells in recovery from acute kidney injury.

The kidney has a dramatic capacity to regenerate after injury. Whether stem cells are the source of the epithelial progenitors replacing injured and dying tubular epithelium is currently an area of intense investigation. Studies from our laboratory and others have supported a model whereby many surviving renal epithelial cells after injury become dedifferentiated and take on mesenchymal characteristics. These cells proliferate to restore the integrity of the denuded basement membrane, and subsequently redifferentiate into a functional epithelium. An alternative possibility is that a minority of surviving intratubular cells possess stem cell properties and selectively proliferate after damage to neighboring cells. Some evidence exists to support this hypothesis but it has not yet been rigorously evaluated. A third hypothesis is that extratubular cells contribute to repair of damaged epithelium. Bone marrow-derived stem cells have been proposed to contribute to this process but our work and work of others indicates that the vast majority of tubular cells derive from an intrarenal source. Recent evidence suggests that interstitial cells may represent another extratubular stem cell niche. The fundamental unanswered questions in this field include whether renal stem cells exist in the adult, and if they do where are they located (interstitium, tubule, cortex, medulla) and what markers can be relied upon for the isolation and purification of these putative renal stem cells. In this review we focus on our current understanding of the potential role of renal and extrarenal stem cells in repair of the adult kidney and highlight some of the controversies in this field.

Suppression by apoptotic cells defines tumor necrosis factor-mediated induction of glomerular mesangial cell apoptosis by activated macrophages.

Activated macrophages (M(phi)) isolated from inflamed glomeruli or generated by interferon-gamma and lipopolysaccharide treatment in vitro induce glomerular mesangial cell apoptosis by hitherto incompletely understood mechanisms. In this report we demonstrate that nitric oxide-independent killing of co-cultured mesangial cells by interferon-gamma/lipopolysaccharide-activated M(phi) is suppressed by binding/ingestion of apoptotic cells and is mediated by tumor necrosis factor (TNF). Thus, soluble TNF receptor-1 significantly inhibited induction of mesangial cell apoptosis by 1) rodent M(phi) in the presence of nitric oxide synthase inhibitors or 2) human M(phi), both situations in which nitric oxide release was minimal. Furthermore, murine TNF knockout M(phi) were completely unable to induce mesangial cell apoptosis in the presence of nitric oxide synthase inhibitors. We conclude that TNF-restricted M(phi)-directed apoptosis of glomerular mesangial cells can be down-regulated by M(phi) binding/ingestion of apoptotic cells, suggesting a new mechanism for negative feedback regulation of M(phi) controls on resident cell number at inflamed sites.

Activated macrophages direct apoptosis and suppress mitosis of mesangial cells.

During inflammation in the glomerulus, the complement of resident myofibroblast-like mesangial cells is regulated by mitosis and apoptosis, but the cellular mechanisms controlling the size of mesangial cell populations have remained obscure. Prompted by studies of development, we sought evidence that macrophages regulate mesangial cell number. Rat bone marrow-derived macrophages primed with IFN-gamma then further activated in coculture with LPS or TNF-alpha elicited a 10-fold induction of rat mesangial cell apoptosis and complete suppression of mitosis, effects inhibitable by the NO synthase inhibitors L-monomethyl arginine and L-N(6)-(1-iminoethyl) lysine dihydrochloride. Complete dependence upon macrophage-derived NO was observed in comparable experiments employing activated bone marrow macrophages from wild-type and NO synthase 2(-/-) mice. Nevertheless, when mesangial cells were primed with IFN-gamma plus TNF-alpha, increased induction by activated macrophages of mesangial apoptosis exhibited a NO-independent element. The use of gld/gld macrophages excluded a role for Fas ligand in this residual kill, despite increased expression of Fas and increased susceptibility to soluble Fas ligand exhibited by cytokine-primed mesangial cells. Finally, activated macrophages isolated from the glomeruli of rats with nephrotoxic nephritis also induced apoptosis and suppressed mitosis in mesangial cells by an L-monomethyl arginine-inhibitable mechanism. These data demonstrate that activated macrophages, via the release of NO and other mediators, regulate mesangial cell populations in vitro and may therefore control the mesangial cell complement at inflamed sites.

Patterns in acute referral to hospital.

This retrospective observational study aimed to assess factors affecting acute referral and subsequent admission to hospital by general practitioners. Data concerning 2,303 consecutive acute referrals to hospital from all GPs in a defined study area were collected over one month. Fund holding practices cared for 13% of the population referred 13% of all referrals resulting in 14% of admissions. Referral through the A&E resulted in significantly more patients being discharged upon initial assessment (p < 0.001). A telephone call accompanying referral dramatically increased the chance of hospital admission (p < 0.001). Referral to hospital was more likely the more socially deprived the patient (p < 0.001) but had no subsequent bearing on admission.

Increasing incidence of tuberculosis in the young and the elderly in Scotland.

BACKGROUND: Since 1987 there has been an arrest in the previously established decline of tuberculosis notifications in Scotland. A study was undertaken to determine whether age contributed to this phenomenon. METHODS: Notifications of tuberculosis in Scotland were quantified by year and age group for the years 1981-92 from national statistics supplied by the Information and Statistics Division. Population data were obtained from the 1981 and 1991 national censuses. RESULTS: Age group analysis of pulmonary tuberculosis notifications showed that, in the 0-14 age group, incidence (per 10(5) population) decreased from 7.4 in 1981 to 2.6 in 1987, rising by an estimated 12.6% per annum to 3.7 in 1992. In the 65+ age group incidence declined from 30.1 in 1981 to 17.3 in 1988, and rose by an estimated 4.1% per annum to 22.2 in 1992. In the age groups 15-44 and 45-64 a continuous decrease in notification rate was seen over the period of the study. CONCLUSIONS: The plateauing of the incidence of tuberculosis in Scotland is associated with significant increases since 1987 of tuberculosis in the young and elderly. Contributions from ethnic minorities and those infected with HIV are negligible. An ageing population over the decade, with the highest tuberculosis rates seen in the older age group, may explain these findings.

Pure alexia without agraphia: a classical cortical syndrome revisited.

A patient who developed pure alexia without agraphia following a stroke is described. An infarction of the left occipital pole was demonstrated by Magnetic Resonance Imaging (MRI). The literature on this rare syndrome is reviewed, and the localisation of damage in relation to the clinical findings discussed.