Loss of endogenous bone morphogenetic protein-6 aggravates renal fibrosis.

Bone morphogenetic protein-6 (BMP-6) suppresses inflammatory genes in renal proximal tubular cells and regulates iron metabolism by inducing hepcidin. In diabetic patients, an increase of myofibroblast progenitor cells (MFPCs), also known as fibrocytes, was found to be associated with decreased BMP-6 expression. We hypothesized that loss of endogenous BMP-6 would aggravate renal injury and fibrosis. Wild type (WT) and BMP-6 null mice underwent unilateral ureteral obstruction. In WT mice, ureteral obstruction down-regulated BMP-6. Obstructed kidneys of BMP-6 null mice showed more casts (1.5-fold), epithelial necrosis (1.4-fold), and brush border loss (1.3-fold). This was associated with more inflammation (1.8-fold more CD45(+) cells) and more pronounced overexpression of profibrotic genes for αSMA (2.0-fold), collagen I (6.8-fold), fibronectin (4.3-fold), CTGF (1.8-fold), and PAI-1 (3.8-fold), despite similar BMP-7 expression. Also, 1.3-fold more MFPCs were obtained from BMP-6 null than from WT mononuclear cell cultures, but in vivo only very few MFPCs were observed in obstructed kidneys, irrespective of BMP-6 genotype. The obstructed kidneys of BMP-6 null mice showed 2.2-fold more iron deposition, in association with 3.3-fold higher expression of the oxidative stress marker HO-1. Thus, ureteral obstruction leads to down-regulation of BMP-6 expression, and BMP-6 deficiency aggravates tubulointerstitial damage and fibrosis independent of BMP-7. This process appears to involve loss of both direct anti-inflammatory and antifibrotic action and indirect suppressive effects on renal iron deposition, oxidative stress, and MFPCs.

Folic acid supplementation normalizes the endothelial progenitor cell transcriptome of patients with type 1 diabetes: a case-control pilot study.

BACKGROUND: Endothelial progenitor cells play an important role in vascular wall repair. Patients with type 1 diabetes have reduced levels of endothelial progenitor cells of which their functional capacity is impaired. Reduced nitric oxide bioavailability and increased oxidative stress play a role in endothelial progenitor cell dysfunction in these patients. Folic acid, a B-vitamin with anti-oxidant properties, may be able to improve endothelial progenitor cell function. In this study, we investigated the gene expression profiles of endothelial progenitor cells from patients with type 1 diabetes compared to endothelial progenitor cells from healthy subjects. Furthermore, we studied the effect of folic acid on gene expression profiles of endothelial progenitor cells from patients with type 1 diabetes. METHODS: We used microarray analysis to investigate the gene expression profiles of endothelial progenitor cells from type 1 diabetes patients before (n = 11) and after a four week period of folic acid supplementation (n = 10) compared to the gene expression profiles of endothelial progenitor cells from healthy subjects (n = 11). The probability of genes being differentially expressed among the classes was computed using a random-variance t-test. A multivariate permutation test was used to identify genes that were differentially expressed among the two classes. Functional classification of differentially expressed genes was performed using the biological process ontology in the Gene Ontology database. RESULTS: Type 1 diabetes significantly modulated the expression of 1591 genes compared to healthy controls. These genes were found to be involved in processes regulating development, cell communication, cell adhesion and localization. After folic acid treatment, endothelial progenitor cell gene expression profiles from diabetic patients were similar to those from healthy controls. Genes that were normalized by folic acid played a prominent role in development, such as the transcription factors ID1 and MAFF. Few oxidative-stress related genes were affected by folic acid. CONCLUSION: Folic acid normalizes endothelial progenitor cell gene expression profiles of patients with type 1 diabetes. Signaling pathways modulated by folic acid may be potential therapeutic targets to improve endothelial progenitor cell function.

Insights into mechanisms behind arteriogenesis: what does the future hold?

Arteriogenesis, the enlargement of collateral vessels, seems a promising new target to improve blood flow to ischemic regions in patients suffering from cardiovascular conditions. With the growing knowledge of the mechanisms involved in arteriogenesis and the factors that influence the process, an increasing number of clinical trials are being performed to stimulate arteriogenesis, providing more insight in therapeutic opportunities for arteriogenesis. The expression of growth factors and the cooperation of surrounding and infiltrating cells seem to be essential in orchestrating the complex processes during arteriogenesis. In this review, we will discuss the regulating mechanisms of arteriogenesis, including the role of growth factors and different cell types and their implementation in a clinical setting. Furthermore, individual differences in the arteriogenic response will be considered, in light of the effect this will have on the success of therapeutic strategies to improve blood flow to ischemic tissue.

Age-related changes in plaque composition: a study in patients suffering from carotid artery stenosis.

OBJECTIVE: The extent of atherosclerotic plaque burden and the incidence of atherosclerosis-related cardiovascular events accelerate with increasing age. The composition of the plaque is associated with plaque thrombosis and acute coronary occlusion. Surprisingly, however, the relation between advancing age and atherosclerotic plaque composition is still unclear. In the present study, we investigated the association between plaque characteristics and advancing age in a population of patients with haemodynamically significant carotid artery stenosis. METHODS: Patients (N=383), ages 39-89 years, underwent carotid endarterectomy (CEA). Morphometric analysis was performed on the dissected atherosclerotic plaques to study the prevalence of fibrous and atheromatous plaques. Picro sirius red, haematoxylin eosin, alfa actin and CD68 stainings were performed to investigate the extent of collagen, calcification, smooth muscle cells and macrophages in carotid plaques, respectively. The presence of metalloproteinases-2 and -9 was assessed by ELISA. RESULTS: With aging, a decrease in fibrous plaques and an increase in atheromatous plaques were observed. This was accompanied by an age-associated decrease in smooth muscle cell content in carotid plaques. Macrophage content slightly increased with age. In addition, total matrix metalloprotease (MMP)-2 was negatively and MMP-9 positively related with age. Differences in plaque phenotype were most prominent for the youngest age quartile compared with older age quartiles. CONCLUSIONS: With increasing age, the morphology of atherosclerotic plaques from patients with carotid artery stenosis changes. Plaques become more atheromatous and contain less smooth muscle cells with increasing age. Local inflammation and MMP-9 levels slightly increased with age in plaques obtained from patients suffering from haemodynamically significant advanced atherosclerotic lesions.

Leukocyte-derived interleukin 10 is required for protection against atherosclerosis in low-density lipoprotein receptor knockout mice.

BACKGROUND: Atherosclerosis is an immunoinflammatory disease. Here we examined the role of leukocyte-derived interleukin 10 (IL-10) on advanced atherosclerosis development in low-density lipoprotein receptor knockout (LDLr-/-) mice. METHODS AND RESULTS: Bone marrow cells harvested from C57BL/6 IL-10-/- and IL-10+/+ mice were transplanted into irradiated male LDLr-/- mice. Four weeks after transplantation, mice were fed a high-fat cholate-free diet for 14 weeks. Despite no differences in weights, serum total, and HDL-cholesterol levels between the 2 groups, IL-10 deficiency in leukocytes induced a >2-fold increase in lesion development in the thoracic aorta compared with controls. We also found a significant 35% increase in aortic root lesion area of IL-10-/- mice compared with IL-10+/+ mice. Furthermore, IL-10 deficiency led to a marked increase in lymphocyte and macrophage accumulation associated with a significant reduction in collagen accumulation. Finally, transfer of IL-10-/- splenocytes to LDLr-/- mice resulted in a 3-fold increase in lesion size in the aortic sinus compared with mice transplanted with IL-10+/+ splenocytes. CONCLUSIONS: IL-10 expressed by leukocytes prevents exaggerated advanced atherosclerosis development and plays a critical role in modulation of cellular and collagen plaque composition, at least in part, through a modulation of the systemic immune response.

Circulating endothelial progenitor cell levels are higher during childhood than in adult life.

Age-related vascular dysfunction contributes to the increased cardiovascular risk in elderly. Endothelial progenitor cells (EPC), a hematopoietic stem cell (HSC) subtype, can improve vascular repair. Therefore, it is hypothesized that a decrease in these circulating progenitor cells during aging plays a role in the enhanced cardiovascular risk. Until now, research has focused on EPC and HSC in the aging adult, but no studies have been conducted in children whereas animal studies specifically suggest a benefit of juvenile bone marrow. We investigated CD34(+)/KDR(+) EPC and CD34(+) HSC numbers by flow cytometry in healthy humans aged 1- to 81-years old. An inverse relation with age was observed for EPC counts [r=-0.37, p=0.007] as well as for HSC counts [r=-0.37, p=0.008]. During childhood significantly higher levels of EPC [p<0.0001] and HSC [p=0.001] were found compared to adults. These findings may have great clinical relevance since increasing circulating EPC levels is a promising therapeutic target to enhance the endogenous regenerative capacity. Better insight in the mechanisms underlying the higher EPC levels in children may provide options to increase EPC counts in adults, thereby potentiating endothelial repair mechanisms.

Smooth muscle progenitor cells: friend or foe in vascular disease?

The origin of vascular smooth muscle cells that accumulate in the neointima in vascular diseases such as transplant arteriosclerosis, atherosclerosis and restenosis remains subject to much debate. Smooth muscle cells are a highly heterogeneous cell population with different characteristics and markers, and distinct phenotypes in physiological and pathological conditions. Several studies have reported a role for bone marrow-derived progenitor cells in vascular maintenance and repair. Moreover, bone marrow-derived smooth muscle progenitor cells have been detected in human atherosclerotic tissue as well as in in vivo mouse models of vascular disease. However, it is not clear whether smooth muscle progenitor cells can be regarded as a 'friend' or 'foe' in neointima formation. In this review we will discuss the heterogeneity of smooth muscle cells, the role of smooth muscle progenitor cells in vascular disease, potential mechanisms that could regulate smooth muscle progenitor cell contribution and the implications this may have on designing novel therapeutic tools to prevent development and progression of vascular disease.

End-stage renal disease causes an imbalance between endothelial and smooth muscle progenitor cells.

Patients with end-stage renal disease (ESRD) on hemodialysis have an increased risk of cardiovascular disease (CVD). Circulating endothelial progenitor cells (EPC) contribute to vascular regeneration and repair, thereby protecting against CVD. However, circulating smooth muscle progenitor cells (SPC) may contribute to adverse vascular remodeling. We hypothesized that an imbalance occurs between EPC and SPC in ESRD patients and sampled progenitor cells from 45 ESRD patients receiving regular treatment. Our study is the first to show reduced numbers of CD34+KDR+ hematopoietic stem cell (HSC)-derived EPC (type I EPC). Furthermore, monocyte-derived EPC cultured from mononuclear cells (type II EPC) were reduced in number and had a reduced capacity to stimulate endothelial cell angiogenesis. In contrast, SPC outgrowth was unaffected. In vitro incubation with uremic serum impaired type II EPC outgrowth from healthy donor mononuclear cells and did not influence SPC outgrowth. The hemodialysis procedure itself induced HSC apoptosis and caused an acute depletion of circulating EPC. Taken together, the decreased number and impaired function of EPC are compatible with impaired endogenous vascular repair in hemodialysis patients, whereas the unaffected SPC numbers suggest that the potential of progenitor cells to contribute to adverse remodeling is retained. This EPC-SPC imbalance may contribute to the acceleration of CVD in ESRD patients and could offer novel therapeutic targets.