Inhibition Of Platelet-derived Growth Factor Signaling Research Articles

Contribution of platelet-derived growth factor signaling to retina regeneration in zebrafish

Accumulated evidence indicates that platelet-derived growth factor (PDGF) contributes to various types of tissue regeneration. However, the effects and mechanisms of PDGF signaling for retina regeneration have not been sufficiently investigated. To clarify this, we investigated the role of PDGF signaling in retina regeneration process after needle puncture in zebrafish. Time-course analysis showed a spike peak of pdgf-a at 6 h after injury and a broad peak of pdgf-b during 6–96 h after injury. Inhibition of PDGF signaling with AG1295 suppressed BrdU-positive proliferative cell numbers at 4 days after injury. At the same time, retina regeneration-associated transcription factors, ascl1a and pax6b, were down-regulated by AG1295 treatment. Intravitreal injection of human recombinant PDGF-AA or -BB into intact zebrafish induced the cell proliferation. PDGF-BB injection induced the Müller glia-derived neurogenic cluster; PDGF-AA increased the 4C4-positive microglia. These findings indicate that PDGF signaling contributes to retina regeneration in zebrafish and causes different types of cell proliferation, depending on each subtype of PDGF. (160 words)

Exclusive inhibition of PI3K/Akt/mTOR signaling is not sufficient to prevent PDGF-mediated effects on glycolysis and proliferation in colorectal cancer.

Platelet-derived growth factor (PDGF) and signaling via its receptors plays a crucial role in tumor cell proliferation and thus may represent an attractive target besides VEGF/EGFR-based antibody therapies. In this study we analyzed the influence of PDGF in colorectal cancer. PDGF was expressed intensively in early and even more intensively in late stage primary CRCs. Like VEGF, PDGF enhanced human colon cancer proliferation, and increased oxidative glycolytic activity, and activated HIF1α and c-Myc in vitro. PDGF activated the PI3K/Akt/mTOR pathway while leaving MAPK signaling untouched. Further dissection showed that inhibition of Akt strongly impeded cancer cell growth while inhibition of PI3K did not. MAPK analysis suggested an inhibitory crosstalk between both pathways, thus explaining the different effects of the Akt and PI3K inhibitors on cancer cell proliferation. PDGF stimulates colon cancer cell proliferation, and prevents inhibitor induced apoptosis, resulting in tumor growth. Therefore inhibition of PDGF signaling seems to be a promising target in colorectal cancer therapy. However, due to the multifaceted nature of the intracellular PDGF signaling, careful intervention strategies are needed when looking into specific signaling pathways like PI3K/Akt/mTOR and MAPK.

Abstract 5663: Imatinib Inhibits Proliferation and Migration and Induces Apoptosis in Pulmonary Artery Smooth Muscle Cells From Patients With Idiopathic Pulmonary Arterial Hypertension

Background : Idiopathic pulmonary arterial hypertension (IPAH) is characterized by inappropriate increase of pulmonary artery smooth muscle cells (PASMCs). We assessed the inhibitory effects of imatinib, a platelet-derived growth factor (PDGF)-receptor tyrosine kinase inhibitor, on PDGF-induced proliferation and migration of PASMCs obtained from patients with IPAH, and investigated whether imatinib induces apoptosis of PASMCs. Methods and Results : PASMCs were obtained from 7 patients with IPAH undergoing lung transplantation. PDGF (10 ng/mL) stimulation caused a higher growth rate of PASMCs from patients with IPAH than that of normal control PASMCs (n=6) as assessed by 3 H-thymidine incorporation (normal: 179±45 vs. IPAH: 310±31 % of counts before PDGF, P <0.05). After treatment with imatinib (0.1 and 1 μ g/mL), PDGF-induced cell proliferation of PASMCs from IPAH patients decreased by 51% and 90 % respectively (PDGF vs PDGF+imatinib (0.1 and 1 μ g/mL): P <0.001). Western blot analysis revealed that imatinib (1 μ g/mL) increased the expression of cyclin-dependent kinase inhibitor p27 in IPAH-PASMCs compared with treatment with PDGF (53%; PDGF vs. PDGF+imatinib, P <0.005). A time-lapse system revealed that PDGF increased the migration distance of IPAH-PASMCs compared to that of normal PASMCs ( P <0.0001), and imatinib (1 μ g/mL) inhibited PDGF-induced migration ( P <0.0001). TUNEL assay revealed that imatinib (1 μ g/mL) alone did not induce apoptosis in IPAH-PASMCs, but combination of imatinib and PDGF increased apoptotic cells (Figure ). Conclusions: Inhibition of PDGF signaling by imatinib may become a useful molecular-targeted therapy for IPAH. Figure. Effect of imatinib on apoptosis of PASMICs in Tunnel assay.

Activation of PKC-δ and SHP-1 by hyperglycemia causes vascular cell apoptosis and diabetic retinopathy

Cellular apoptosis induced by hyperglycemia occurs in many vascular cells and is crucial for the initiation of diabetic pathologies. In the retina, pericyte apoptosis and the formation of acellular capillaries, the most specific vascular pathologies attributed to hyperglycemia, is linked to the loss of platelet-derived growth factor (PDGF)-mediated survival actions owing to unknown mechanisms. Here we show that hyperglycemia persistently activates protein kinase C-delta (PKC-delta, encoded by Prkcd) and p38alpha mitogen-activated protein kinase (MAPK) to increase the expression of a previously unknown target of PKC-delta signaling, Src homology-2 domain-containing phosphatase-1 (SHP-1), a protein tyrosine phosphatase. This signaling cascade leads to PDGF receptor-beta dephosphorylation and a reduction in downstream signaling from this receptor, resulting in pericyte apoptosis independently of nuclear factor-kappaB (NF-kappaB) signaling. We observed increased PKC-delta activity and an increase in the number of acellular capillaries in diabetic mouse retinas, which were not reversible with insulin treatment that achieved normoglycemia. Unlike diabetic age-matched wild-type mice, diabetic Prkcd(-/-) mice did not show activation of p38alpha MAPK or SHP-1, inhibition of PDGF signaling in vascular cells or the presence of acellular capillaries. We also observed PKC-delta, p38alpha MAPK and SHP-1 activation in brain pericytes and in the renal cortex of diabetic mice. These findings elucidate a new signaling pathway by which hyperglycemia can induce PDGF resistance and increase vascular cell apoptosis to cause diabetic vascular complications.

Amelioration of autoimmune nephritis by imatinib in MRL/lpr mice

To examine whether the platelet-derived growth factor (PDGF) receptor antagonist imatinib ameliorates glomerulonephritis in MRL/lpr mice, a condition that is similar to severe lupus nephritis in humans. Sixteen-week-old MRL/lpr female mice having an advanced stage of glomerulonephritis were divided into 3 groups according to treatment: 1) 50 mg/kg or 2) 10 mg/kg of imatinib (administered orally 4 times a week up to 24 weeks of age) or 3) vehicle solution (untreated group). The histopathologic condition of the kidneys and salivary glands of each mouse as well as the cumulative survival rates, extent of lymphadenopathy and splenomegaly, and serum chemistry and immunologic values were assessed. In mice treated with 50 mg/kg imatinib, neither proliferation of glomerular cells nor crescent formation occurred. A drastic decrease in mesangial matrix was noted. Mice treated with 50 mg/kg imatinib had a prolonged life span compared with mice treated with 10 mg/kg imatinib and untreated mice. Expression of PDGF receptor and transforming growth factor beta messenger RNA in the kidneys was significantly reduced in the 50 mg/kg imatinib-treated mice compared with that in the 10 mg/kg imatinib-treated mice (P < 0.05) and the untreated mice (P < 0.01). Intriguingly, lymphadenopathy and salivary gland inflammation were also attenuated in imatinib-treated mice, in a dose-dependent manner. Serum levels of IgG and anti-double-stranded DNA antibodies were also reduced in the imatinib-treated mice. These findings indicate that imatinib has a pleiotropic therapeutic effect, namely, the inhibition of PDGF signaling and immunosuppression, on the glomerulonephritis of MRL/lpr mice, which suggests a potential application of this drug in the treatment of human lupus nephritis.

Culture-Expanded Human Bone Marrow Stromal Stem Cells Organize Functional Bone Marrow Niches In Vivo.

Bone marrow stromal stem cells (BMSSCs) are mesenchymal stem cells that are capable of differentiating into osteoblasts, chondrocytes, adipocytes, muscle cells and neural cells. Upon in vivo transplantation, BMSSCs form bone and associated hematopoietic marrow elements. However, the functional role of BMSSC-associated bone marrow is still unknown. In this study, we demonstrated that human BMSSCs organized ectopic bone marrow niche microarchitecture that contained hematopoietic progenitors and multiple lineages of cells including myeloid, lymphoid, erythroid and megakaryocytic cells originated from recipients. Significantly, transplantation of the ectopically generated bone marrow cells can rescue lethally irradiated mice with successful hematopoietic engraftment, suggesting a therapeutic potentiality of human BMSSC-organized hematopoietic progenitor cells. In addition, systemically administrated bone marrow cells derived from long bones of donor mice homed to BMSSC-associated ectopic bone marrow niche microenvironments. These data demonstrate that BMSSC-organized ectopic bone marrow has functional analogy to physiological bone marrow. Mechanistically, platelet-derived growth factor (PDGF)-BB was found to promote hematopoiesis in the BMSSC transplants through an up-regulated expression of β-catenin. Conversely, inhibition of PDGF signaling in BMSSCs by PDGF receptor β siRNA blocked hematopoiesis and osteogenesis in the BMSSC transplants. Moreover, the BMSSC-organized ectopic bone/marrow structure could be utilized as an organ to be re-transplanted into secondary recipient mice to deliver hematopoietic cells in the recipient's circulation system, implying a therapeutic potential of transplanting bone/marrow organ system containing hematopoietic stem cell niches. In summary, these evidences demonstrate that regeneration of BMSSC-organized functional bone marrow niches contain hematopoietic progenitor/stem cells and therefore provide promise for clinical therapy.