Several platelet-derived growth factor (PDGF) and vascular endothelial growth factor (VEGF) family members display C-terminal protein motifs that confer retention of the secreted factors within the pericellular space. To address the role of PDGF-B retention in vivo, we deleted the retention motif by gene targeting in mice. This resulted in defective investment of pericytes in the microvessel wall and delayed formation of the renal glomerulus mesangium. Long-term effects of lack of PDGF-B retention included severe retinal deterioration, glomerulosclerosis, and proteinuria. We conclude that retention of PDGF-B in microvessels is essential for proper recruitment and organization of pericytes and for renal and retinal function in adult mice. Received April 3, 2003; revised version accepted May 23, 2003. The control of cell migration and the formation of specific patterns during embryonic development are believed to depend, at least in part, on the precise spatial distribution of secreted growth and differentiation factors (GDFs). This is achieved by strictly localized and regulated synthesis and secretion of GDFs, but also by binding of the secreted GDFs to cell surface-and extracellular matrix molecules. One type of molecule strongly implicated in the regulation of GDF activities in vivo is the heparan sulphate proteoglycans ( Certain isoforms of platelet-derived growth factor (PDGF) and vascular endothelial growth factor (VEGF) family members display positively charged stretches of amino acids residues at the C terminus. These stretches are included or excluded depending on alternative splicing or proteolytic processing (Eriksson and Alitalo 1999; Heldin and Westermark 1999). For VEGF-A, the long splice isoforms, which carry HSPG-binding domains, accumulate on the cell surface or in the extracellular matrix, whereas short VEGF-A is diffusible following cellular release (Park et al. 1993). The developmental role of HSPG binding of VEGF-A was recently addressed using mice in which the long VEGF-A splice isoforms were selectively ablated (Carmeliet et al. 1999;Ruhrberg et al. 2002;Stalmans et al. 2002). In these mice, extracellular VEGF-A distribution becomes more widespread, leading to changes in endothelial sprouting and branching, and to the formation of abnormal vascular patterns (Ruhrberg et al. 2002). In PDGF-A and PDGF-B, the HSPGbinding motifs do not affect receptor binding or biological activity of the recombinant proteins (Östman et al. 1989). However, in transfected cells, these motifs confer retention of the secreted growth factor to the surface of the producing cells. Conversely, absence of the retention motif leads to increased secretion of a diffusible protein that readily accumulates in the cell culture medium (LaRochelle et al. 1991;Östman et al. 1991;Raines and Ross 1992;Andersson et al. 1994). The retention motif also appears to limit the action range of PDGF-B in vivo, as suggested from experiments with transplanted keratinocytes transfected with PDGF-B expression vectors (Eming et al. 1999). ...

Loss of pericytes from the capillary wall is a hallmark of diabetic retinopathy, however, the pathogenic signi®cance of this phenomenon is unclear. In previous mouse gene knockout models leading to pericyte de®-ciency, prenatal lethality has so far precluded analysis of postnatal consequences in the retina. We now report that endothelium-restricted ablation of platelet-derived growth factor-B generates viable mice with extensive inter-and intra-individual variation in the density of pericytes throughout the CNS. We found a strong inverse correlation between pericyte density and the formation of a range of retinal microvascular abnormalities strongly reminiscent of those seen in diabetic humans. Proliferative retinopathy invariably developed when pericyte density was <50% of normal. Our data suggest that a reduction of the pericyte density is suf®cient to cause retinopathy in mice, implying that pericyte loss may also be a causal pathogenic event in human diabetic retinopathy.

Platelet-derived growth factor-B (PDGFB) is necessary for normal cardiovascular development, but the relative importance of different cellular sources of PDGFB has not been established. Using Cre-lox techniques, we show here that genetic ablation of Pdgfb in endothelial cells leads to impaired recruitment of pericytes to blood vessels. The endothelium-restricted Pdgfb knockout mutants also developed organ defects including cardiac, placental and renal abnormalities. These defects were similar to those observed in Pdgfb null mice. However, in marked contrast to the embryonic lethality of Pdgfb null mutants, the endothelium-specific mutants survived into adulthood with persistent pathological changes, including brain microhemorrhages, focal astrogliosis, and kidney glomerulus abnormalities. This spectrum of pathological changes is reminiscent of diabetic microangiopathy, suggesting that the endothelium-restricted Pdgfb knockouts may serve as models for some of the pathogenic events of vascular complications to diabetes.

Interleukin-1 (IL-1) is a major mediator of inflammation that exerts its biological activities through the IL-1 type I receptor (IL-1RI). The body weights of IL-1RI؊/؊ mice of both sexes started to deviate from those of wild-type mice at 5-6 months of age and were 20% higher at 9 months of age. Visceral and subcutaneous fat mass, measured by dual-energy X-ray absorptiometry and magnetic resonance imaging, was markedly (1.5-to 2.5-fold) increased. Lean body mass and crown-rump length were also slightly (11 and 5%, respectively) increased, as was serum IGF-I. Obese IL-1RI؊/؊ mice were insulin resistant, as evidenced by hyperinsulinemia, decreased glucose tolerance, and insulin sensitivity. To elucidate the mechanisms for the development of obesity, young preobese IL-1RI ؊/؊ mice were investigated. They showed decreased suppression of body weight and food intake in response to systemic leptin treatment. The decreased leptin responsiveness was even more pronounced in older obese animals. Moreover, spontaneous locomotor activity and fat utilization, as measured by respiratory quotient, were decreased in preobese IL-1RI ؊/؊ mice. In conclusion, lack of IL-1RI-mediated biological activity causes mature-onset obesity. This obese phenotype is preceded by decreased leptin sensitivity, fat utilization, and locomotor activity. Diabetes 55: [1205][1206][1207][1208][1209][1210][1211][1212][1213] 2006 T he prevalence of obesity is growing rapidly in many parts of the world and reaching epidemic proportions in several developed countries (1). Overweight and obesity are associated with increased risk of metabolic disorders, such as type 2 diabetes and hyperlipidemia, and thereby increased risk of cardiovascular mortality. Although the regulation of body weight and body composition involves input from lifestyle and environment, compelling scientific evidence indicates that propensity to develop obesity is in large part attributable to genetic factors. Over the last decade, the study of different transgenic and knockout mouse models has contributed to the identification of new factors involved in the complex mechanisms regulating energy balance and to the clarification of the contribution of genetics to obesity (2,3). Moreover, a number of human genes have been identified in which major missense or nonsense mutations as well as genetic variations are associated with obesityrelated phenotypes. Many of these genetic variants have occurred in molecules identical or similar to those identified as a cause of obesity in rodents, supporting their involvement in the regulation of body weight homeostasis also in humans (4).Interleukin-1 (IL-1) is a major mediator of inflammation and exerts effects on the neuro-immuno-endocrine system (5). Infection, injury, and inflammation are associated with negative energy balance, characterized by reduced food intake, weight loss, increased thermogenesis, and fever. IL-1 could be of importance for these effects, as peripheral or central injection of IL-1 induces a marked rise in body temperature (f...

BackgroundSepsis is a potentially deadly disease that often is caused by gram-positive bacteria, in particular Staphylococcus aureus (S. aureus). As there are few effective therapies for sepsis, increased basic knowledge about factors predisposing is needed.Methodology/Principal FindingsThe purpose of this study was to study the effect of Western diet on mortality induced by intravenous S. aureus inoculation and the immune functions before and after bacterial inoculation. Here we show that C57Bl/6 mice on high-fat diet (HFD) for 8 weeks, like genetically obese Ob/Ob mice on low-fat diet (LFD), have increased mortality during S. aureus-induced sepsis compared with LFD-fed C57Bl/6 controls. Bacterial load in the kidneys 5–7 days after inoculation was increased 10-fold in HFD-fed compared with LFD-fed mice. At that time, HFD-fed mice had increased serum levels and fat mRNA expression of the immune suppressing cytokines interleukin-1 receptor antagonist (IL-1Ra) and IL-10 compared with LFD-fed mice. In addition, HFD-fed mice had increased serum levels of the pro-inflammatory IL-1β. Also, HFD-fed mice with and without infection had increased levels of macrophages in fat. The proportion and function of phagocytosing granulocytes, and the production of reactive oxygen species (ROS) by peritoneal lavage cells were decreased in HFD-fed compared with LFD-fed mice.ConclusionsOur findings imply that chronic HFD disturb several innate immune functions in mice, and impairs the ability to clear S. aureus and survive sepsis.