PDGF receptor-{beta} modulates metanephric mesenchyme chemotaxis induced by PDGF AA

Computational modelling of nephron progenitor cell movement and aggregation during kidney organogenesis

During early kidney organogenesis, nephron progenitor (NP) cells move from the tip to the corner region of the ureteric bud (UB) branches in order to form the pretubular aggregate, the early structure giving rise to nephron formation. NP cells derive from metanephric mesenchymal cells and physically interact with them during the movement. Chemotaxis and cell-cell adhesion differences are believed to drive the cell patterning during this critical period of organogenesis. However, the effect of these forces to the cell patterns and their respective movements are known in limited details. We applied a Cellular Potts Model to explore how these forces and organizations contribute to directed cell movement and aggregation. Model parameters were estimated based on fitting to experimental data obtained in ex vivo kidney explant and dissociation-reaggregation organoid culture studies. Our simulations indicated that optimal enrichment and aggregation of NP cells in the UB corner niche requires chemoattractant secretion from both the UB epithelial cells and the NP cells themselves, as well as differences in cell-cell adhesion energies. Furthermore, NP cells were observed, both experimentally and by modelling, to move at higher speed in the UB corner as compared to the tip region where they originated. The existence of different cell speed domains along the UB was confirmed using self-organizing map analysis. In summary, we saw faster NP cell movements near aggregation. The applicability of Cellular Potts Model approach to simulate cell movement and patterning was found to be good during for this early nephrogenesis process. Further refinement of the model should allow us to recapitulate the effects of developmental changes of cell phenotypes and molecular crosstalk during further organ development.

Mouse Metanephric Mesenchymal Cell-Derived Angioblasts Undergo Vasculogenesis in Three-Dimensional Culture

In vitro models for the investigation of renal vascular development are limited. We previously showed that isolated metanephric mesenchymal (MM) and ureteric bud (UB) cells grown in three-dimensional (3D) matrices formed organoids that consisted of primitive vascular structures surrounding a polarized epithelium. Here, we examined the potential of two principal effectors of vasculogenesis, vascular endothelial growth factor A (VEGF-A), and platelet-derived growth factor B chain (PDGF-BB), to stimulate MM cell differentiation. The results showed that MM cells possess angioblast characteristics by expressing phenotypic markers for endothelial and mesenchymal cells. UB cells synthesize VEGF-A and PDGF-BB proteins and RNA, whereas the MM cells express the respective cognate receptors, supporting their role in directional induction of vasculogenesis. VEGF-A stimulated proliferation of MM cells in monolayer and in 3D sponges but did not affect MM cell migration, organization, or vasculogenesis. However, PDGF-BB stimulated MM cell proliferation, migration, and vasculogenesis in monolayer and organization of the cells into primitive capillary-like assemblies in 3D sea sponge scaffolds in vitro. A role for PDGF-BB in vasculogenesis in the 3D MM/UB co-culture system was validated by direct interference with PDGF-BB or PDGF receptor-β cell interactions to implicate PDGF-BB as a primary effector of MM cell vasculogenesis. Thus, MM cells resemble early renal angioblasts that may provide an ideal platform for the investigation of renal vasculogenesis in vitro.

Pericytes, integral components of adult hematopoietic stem cell niches

The interest in perivascular cells as a niche for adult hematopoietic stem cells (HSCs) is significantly growing. In the adult bone marrow (BM), perivascular cells and HSCs cohabit. Among perivascular cells, pericytes are precursors of mesenchymal stem/stromal cells (MSCs) that are capable of differentiating into osteoblasts, adipocytes and chondrocytes. In situ, pericytes are recognised by their localisation to the abluminal side of the blood vessel wall and closely associated with endothelial cells, in combination with the expression of markers such as CD146, neural glial 2 (NG2), platelet derived growth factor receptor β (PDGFRβ), α-smooth muscle actin (α-SMA), nestin (Nes) and/or leptin receptor (LepR). However, not all pericytes share a common phenotype: different immunophenotypes can be associated with distinct mesenchymal features, including hematopoietic support. In adult BM, arteriolar and sinusoidal pericytes control HSC behaviour, maintenance, quiescence and trafficking through paracrine effects. Different groups identified and characterized hematopoietic supportive pericyte subpopulations using various markers and mouse models. In this review, we summarize recent work performed by others to understand the role of the perivascular niche in the biology of HSCs in adults, as well as their importance in the development of therapies.

Bioinformatics Analysis of Proteome Changes in Calu-3 Cell Infected by Influenza A Virus (H5N1)

<b><i>Aim:</i></b> This paper aimed to identify the differentially expressed proteins (DEPs) in Calu-3 cells infected by influenza A virus (IAV) subtype H5N1. <b><i>Methods:</i></b> We downloaded proteome data (BTO: 0000762) from the Proteomics Identifications database and identified the DEPs in the IAV-infected Calu-3 cells. Then we constructed a protein-protein interaction network and a transcriptional regulatory network of the proteins. Finally, we performed gene ontology (GO) analysis to study the IAV infection at a functional level. <b><i>Results:</i></b> A total of 4 protein groups between the normal cells and the Calu-3 cells infected by IAV, severe acute respiratory syndrome or swine influenza were identified. In the networks, we found 5 significant proteins including FAN, CPSF2, AGO1, AGO2 and PAX5. In addition, we demonstrated those proteins were associated with GO terms such as phosphate metabolic process, calcium ion transport, cell division and regulation of cell motion. STAT1, NS2, CD5, NCKX6 and PDGFB were significant DEPs in these GO terms. <b><i>Conclusions:</i></b> By referring to the previous studies, we suggest that proteins including FAN, CPSF2, AGO1, AGO2, PAX5, STAT1 and PDGFB can be used as therapeutic targets of IAV infection.

PDGF and the progression of renal disease

Progressive renal diseases represent a global medical problem, in part because we currently lack effective treatment strategies. Inhibition of platelet-derived growth factors (PDGFs) might represent one such novel strategy. PDGFs are required for normal kidney development by the recruitment of mesenchymal cells to both glomeruli and the interstitium. PDGFs are expressed in renal mesenchymal cells and, upon injury, in epithelial and infiltrating cells. They exert autocrine and paracrine effects on PDGF receptor-bearing mesenchymal cells, i.e. mesangial cells, fibroblasts and vascular smooth-muscle cells, which are crucially involved in progressive renal diseases. Proliferation but also migration and activation of these mesenchymal cells are the major effects mediated by PDGFs. These actions predefine the major roles of PDGFs in renal pathology, particularly in mesangioproliferative glomerulonephritis and interstitial fibrosis. Whereas for the former, the role of PDGFs is very well described and established, the latter is increasingly better documented as well. An involvement of PDGFs in other renal diseases, e.g. acute kidney injury, vascular injury and hypertensive as well as diabetic nephropathy, is less well established or presently unknown. Nevertheless, PDGFs represent a promising therapeutic option for progressive renal diseases, especially those characterized by mesangial cell proliferation and interstitial fibrosis. Clinical studies are eagerly awaited, in particular, since several drugs inhibiting PDGF signalling are available for clinical testing.

Src tyrosine kinase mediates platelet-derived growth factor BB-induced and redox-dependent migration in metanephric mesenchymal cells

The adult kidney is derived from the interaction between the metanephric blastema and the ureteric bud. Platelet-derived growth factor (PDGF) receptor β is essential for the development of the mature glomerular tuft, as mice deficient for this receptor lack mesangial cells. This study investigated the role of Src tyrosine kinase in PDGF-mediated reactive oxygen species (ROS) generation and migration of metanephric mesenchymal cells (MMCs). Cultured embryonic MMCs from wild-type and PDGF receptor-deficient embryos were established. Migration was determined via wound-healing assay. Unlike PDGF AA, PDGF BB-induced greater migration in MMCs with respect to control. This was abrogated by neutralizing an antibody to PDGF BB. Phosphatidylinositol 3-kinase (PI3K) inhibitors suppressed PDGF BB-induced migration. Conversely, mitogen-activated protein kinase/extracellular signal-regulated kinase (MEK) inhibitors had no effect. Src inhibitors inhibited PDGF-induced cell migration, PI3K activity, and Akt phosphorylation. Adenoviral dominant negative Src (AD DN Src) abrogated PDGF BB-induced Akt phosphorylation. Hydrogen peroxide stimulated cell migration. PDGF BB-induced wound closure was inhibited by the antioxidants N-acetyl-l-cysteine, tiron, and the flavoprotein inhibitor diphenyleneiodonium. These cells express the NADPH oxidase homolog Nox4. Inhibiting Nox4 with antisense oligonucleotides or small interfering RNA (siRNA) suppressed PDGF-induced wound closure. Inhibition of Src with siRNA reduced PDGF BB-induced ROS generation as assessed by 2',7'-dichlorodihydrofluorescein diacetate fluorescence. Furthermore, PDGF BB-stimulated ROS generation and migration were similarly suppressed by Ad DN Src. In MMCs, PDGF BB-induced migration is mediated by PI3K and Src in a redox-dependent manner involving Nox4. Src may be upstream to PI3K and Nox4.

Nephrogenic systemic fibrosis: evidence for oxidative stress and bone marrow-derived fibrocytes in skin, liver, and heart lesions using a 5/6 nephrectomy rodent model

Nephrogenic systemic fibrosis (NSF) is associated with gadolinium-based magnetic resonance imaging (MRI) contrast exposure in the setting of acute or chronic renal compromise. It has been proposed that circulating fibrocytes mediate the disease. A study was conducted to determine whether bone marrow-derived fibroblast precursors are involved in contributing to organ fibrosis in MRI contrast-treated rodents with renal insufficiency. Rats status post 5/6 nephrectomy underwent bone marrow transplant from human placental alkaline phosphatase (hPAP)-expressing donors. After engraftment, animals were treated with gadolinium-based MRI contrast (2.5 mmol/kg IP), during weekdays for 4 weeks, or an equivalent volume of normal saline. Dermal cellularity in the contrast-treated group was fourfold that of control. Skin cells from the contrast-treated group demonstrated greater hPAP expression with co-expression of pro-collagen I and α-smooth muscle actin-positive stress fibers. Donor and host cells expressed CD34. Dihydroethidium staining of skin was greater in the contrast-treated animals, indicating oxidative stress. This was abrogated when the animals were co-administered the superoxide dismutase mimetic tempol. In conclusion, a bone marrow-derived cell population is increased in the dermis of MRI contrast-treated rodents. The cell markers are consistent with fibrocytes mediating the disease. These changes correlate with oxidative stress and expression of Nox4, suggestive of a novel therapeutic target. Elucidation of the mechanisms of MRI contrast-induced fibrosis may aid in discovering therapies to this devastating disease.

NADPH-oxidase 4 protects against kidney fibrosis during chronic renal injury

NADPH oxidases synthesize reactive oxygen species that may participate in fibrosis progression. NOX4 and NOX2 are NADPH oxidases expressed in the kidneys, with the former being the major renal isoform, but their contribution to renal disease is not well understood. Here, we used the unilateral urinary obstruction model of chronic renal injury to decipher the role of these enzymes using wild-type, NOX4-, NOX2-, and NOX4/NOX2-deficient mice. Compared with wild-type mice, NOX4-deficient mice exhibited more interstitial fibrosis and tubular apoptosis after obstruction, with lower interstitial capillary density and reduced expression of hypoxia-inducible factor-1α and vascular endothelial growth factor in obstructed kidneys. Furthermore, NOX4-deficient kidneys exhibited increased oxidative stress. With NOX4 deficiency, renal expression of other NOX isoforms was not altered but NRF2 protein expression was reduced under both basal and obstructed conditions. Concomitant deficiency of NOX2 did not modify the phenotype exhibited by NOX4-deficient mice after obstruction. NOX4 silencing in a mouse collecting duct (mCCD(cl1)) cell line increased TGF-β1-induced apoptosis and decreased NRF2 protein along with expression of its target genes. In addition, NOX4 silencing decreased hypoxia-inducible factor-1α and expression of its target genes in response to hypoxia. In summary, these results demonstrate that the absence of NOX4 promotes kidney fibrosis, independent of NOX2, through enhanced tubular cell apoptosis, decreased microvascularization, and enhanced oxidative stress. Thus, NOX4 is crucial for the survival of kidney tubular cells under injurious conditions.

In vivo tracking of mesechymal stem cells using fluorescent nanoparticles in an osteochondral repair model

We devised and tested an in vivo system to monitor the migration of mesenchymal stem cells (MSCs) within the marrow cavity. In vitro studies confirmed that platelet-derived growth factor (PDGF)-AA had the most potent chemotactic effect of the tested factors, and possessed the greatest number of receptors in MSCs. MSCs were labeled with fluorescent nanoparticles and injected into the marrow cavity of nude rats through osteochondral defects created in the distal femur. The defects were sealed with HCF (heparin-conjugated fibrin) or PDGF-AA-loaded HCF. In the HCF-only group, the nanoparticle-labeled MSCs dispersed outside the marrow cavity within 3 days after injection. In the PDGF-AA-loaded HCF group, the labeled cells moved time-dependently for 14 days toward the osteochondral defect. HCF-PDGF in low dose (LD; 8.5 ng/µl) was more effective than HCF-PDGF in high dose (HD; 17 ng/µl) in recruiting the MSCs to the osteochondral defect. After 21 days, the defects treated with PDGF and transforming growth factor (TGF)-β1-loaded HCF showed excellent cartilage repair compared with other groups. Further studies confirmed that this in vivo osteochondral MSCs tracking system (IOMTS) worked for other chemoattractants (chemokine (C-C motif) ligand 2 (CCL2) and PDGF-BB). IOMTS can provide a useful tool to examine the effect of growth factors or chemokines on endogenous cartilage repair.

Platelet-derived growth factor and renal disease

PURPOSE OF REVIEW

This review focuses on the recent advances in our understanding of the role of platelet-derived growth factor (PDGF) in glomerular disease.

RECENT FINDINGS

Accumulating evidence indicates a critical involvement of PDGF receptor-β (PDGFR-β) signaling in glomerular disease. Augmented signaling via PDGFR-β is involved in the pathogenesis of IgA nephropathy. Therefore, targeting PDGFR-β signaling is a viable therapeutic strategy for glomerular diseases. However, current PDGFR-β antagonists are nonspecific, and their long-term effects remain to be elucidated. To develop effective intervention therapies targeting PDGF signaling, it is necessary to clarify the specific involvement of PDGF in the pathogenesis of glomerular disease. A novel PDGFR-β targeting mouse model has provided new insight into the postnatal role of PDGFR-β in aging-related mesangial sclerosis and the glomerular remodeling after nephrectomy. Furthermore, the same study indicated the redundancy of growth factor signals underlying glomerular remodeling. In this context, other studies have suggested a role for PDGFR-α signaling and collaborating growth factors to compensate for PDGFR-β in the kidney glomerulus.

SUMMARY

Intervention in growth factor signaling could be a valuable therapeutic strategy for kidney glomerular diseases. Further studies are required to characterize the pathogenesis of these diseases for the successful development of such a therapy.

Emerging roles of PDGF-D signaling pathway in tumor development and progression

Platelet-derived growth factor-D (PDGF-D) can regulate many cellular processes, including cell proliferation, apoptosis, transformation, migration, invasion, angiogenesis and metastasis. Therefore PDGF-D signaling has been considered to be important in human malignancies, and thus PDGF-D signaling may represent a novel therapeutic target, and as such suggests that the development of agents that will target PDGF-D signaling is likely to have a significant therapeutic impact on human cancers. This mini-review describes the mechanisms of signal transduction associated with PDGF-D signaling to support the role of PDGF-D in the carcinogenesis. Moreover, we summarize data on several PDGF-D inhibitors especially naturally occurring "chemopreventive agent" such an indole compound, which we believe could serve as a novel agent for the prevention of tumor progression and/or treatment of human malignancies by targeted inactivation of PDGF-D signaling.