Local Growth Factor Concentrations Research Articles

Growth-factor-mediated coupling between lineage size and cell fate choice underlies robustness of mammalian development.

Precise control and maintenance of population size is fundamental for organismal development and homeostasis. The three cell types of the mammalian blastocyst are generated in precise proportions over a short time, suggesting a mechanism to ensure a reproducible outcome. We developed a minimal mathematical model demonstrating growth factor signaling is sufficient to guarantee this robustness and which anticipates an embryo's response to perturbations in lineage composition. Addition of lineage-restricted cells both in vivo and in silico, causes a shift of the fate of progenitors away from the supernumerary cell type, while eliminating cells using laser ablation biases the specification of progenitors toward the targeted cell type. Finally, FGF4 couples fate decisions to lineage composition through changes in local growth factor concentration, providing a basis for the regulative abilities of the early mammalian embryo whereby fate decisions are coordinated at the population level to robustly generate tissues in the right proportions.

Bayesian inference of agent-based models: a tool for studying kidney branching morphogenesis

The adult mammalian kidney has a complex, highly-branched collecting duct epithelium that arises as a ureteric bud sidebranch from an epithelial tube known as the nephric duct. Subsequent branching of the ureteric bud to form the collecting duct tree is regulated by subcellular interactions between the epithelium and a population of mesenchymal cells that surround the tips of outgrowing branches. The mesenchymal cells produce glial cell-line derived neurotrophic factor (GDNF), that binds with RET receptors on the surface of the epithelial cells to stimulate several subcellular pathways in the epithelium. Such interactions are known to be a prerequisite for normal branching development, although competing theories exist for their role in morphogenesis. Here we introduce the first agent-based model of ex vivo kidney uretic branching. Through comparison with experimental data, we show that growth factor-regulated growth mechanisms can explain early epithelial cell branching, but only if epithelial cell division depends in a switch-like way on the local growth factor concentration; cell division occurring only if the driving growth factor level exceeds a threshold. We also show how a recently-developed method, “Approximate Approximate Bayesian Computation”, can be used to infer key model parameters, and reveal the dependency between the parameters controlling a growth factor-dependent growth switch. These results are consistent with a requirement for signals controlling proliferation and chemotaxis, both of which are previously identified roles for GDNF.

Do Postoperative Platelet-Rich Plasma Injections Accelerate Early Tendon Healing and Functional Recovery After Arthroscopic Supraspinatus Repair? A Randomized Controlled Trial

After arthroscopic supraspinatus tendon repair, ultrasound guided PRP injections on two occasions to the tendon repair site do not improve early tendon bone healing or accelerate functional recovery. Establishing early tendon bone healing is critical for subsequent rehabilitation and optimal functional outcome after rotator cuff repair. Biological therapies that elevate local growth-factor concentrations may promote early rotator cuff healing after surgery. The aim of this study was to determine whether postoperative and repeated application of platelet-rich plasma (PRP) to the tendon repair site resulted in improved early tendon healing and enhanced early functional recovery after double-row arthroscopic supraspinatus repair. A total of 60 patients underwent arthroscopic double-row supraspinatus tendon repair. Thirty patients were randomised to receive two ultrasound-guided injections of PRP to the tendon repair site at postoperative days 7 and 14. The control group did not receive placebo injections. Early structural healing of the tendon repair was assessed with MRI at 16 weeks post surgery by a blinded musculoskeletal radiologist, and cuff appearances were graded according to the Sugaya classification. Functional scores were recorded with the Oxford Shoulder Score, quick DASH, and visual analogue scale for pain; and were measured preoperatively and at postoperative weeks 6, 12, and 16. Isokinetic strength and active range of motion were measured in both operated and non-operated shoulders at 16 weeks post surgery. All patients complied with the study protocol and no patients were lost to followup. There were no differences in MRI structural integrity of the supraspinatus repair between the PRP group (0% full-thickness retear; 23% partial tear; 77% intact) and the control group (7% full-thickness retear; 23% partial tear; 70% intact) at 16 weeks postoperatively (p = 0.35). Significant improvements in clinical function and VAS pain scores were observed in both PRP and control groups at 12 weeks and 16 weeks post surgery (p<0.01). However PRP treatment did not result in superior functional scores, range of motion, shoulder strength or pain scores compared to the control group. After arthroscopic supraspinatus tendon repair, image-guided PRP treatment on two occasions does not improve early tendon-bone healing or functional recovery.

Do Postoperative Platelet-Rich Plasma Injections Accelerate Early Tendon Healing and Functional Recovery After Arthroscopic Supraspinatus Repair?

Background: Tendon-bone healing after rotator cuff repair directly correlates with a successful outcome. Biological therapies that elevate local growth-factor concentrations may potentiate healing after surgery. Purpose: To ascertain whether postoperative and repeated application of platelet-rich plasma (PRP) to the tendon repair site improves early tendon healing and enhances early functional recovery after double-row arthroscopic supraspinatus repair. Study Design: Randomized controlled trial; Level of evidence, 1. Methods: A total of 60 patients underwent arthroscopic double-row supraspinatus tendon repair. After randomization, half the patients received 2 ultrasound-guided injections of PRP to the repair site at postoperative days 7 and 14. Early structural healing was assessed with MRI at 16 weeks, and cuff appearances were graded according to the Sugaya classification. Functional scores were recorded with the Oxford Shoulder Score; Quick Disability of the Arm, Shoulder and Hand; visual analog scale for pain; and Short Form–12 quality-of-life score both preoperatively and at postoperative weeks 6, 12, and 16; isokinetic strength and active range of motion were measured at 16 weeks. Results: PRP treatment did not improve early functional recovery, range of motion, or strength or influence pain scores at any time point after arthroscopic supraspinatus repair. There was no difference in structural integrity of the supraspinatus repair on MRI between the PRP group (0% full-thickness retear; 23% partial tear; 77% intact) and the control group (7% full-thickness retear; 23% partial tear; 70% intact) at 16 weeks postoperatively (P = .35). Conclusion: After arthroscopic supraspinatus tendon repair, image-guided PRP treatment on 2 occasions does not improve early tendon-bone healing or functional recovery.

Cartilage oligomeric matrix protein enhances osteogenesis by directly binding and activating bone morphogenetic protein-2

Bone morphogenetic proteins (BMPs) are effective for bone regeneration, and are used clinically. However, supraphysiological doses are required, which limits their use. Cartilage oligomeric matrix protein is an extracellular matrix protein, which we have previously shown can bind to growth factors of the TGFs family, suggesting that COMP may also bind to BMP-2. Rather than being a passive component of the matrix, COMP may serve as an “instructive matrix” component capable of increasing local growth factor concentration, slowing the diffusion of growth factors, and promoting their biological activity. The purpose of this investigation was to determine whether COMP binds to BMP-2, and whether it promotes the biological activity of BMP-2 with respect to osteogenesis. We found that COMP binds BMP-2, and characterized the biochemical nature of the binding interaction. COMP binding enhanced BMP-2-induced intracellular signaling through Smad proteins, increased the levels of BMP receptors, and up-regulated the luciferase activity from a BMP-2-responsive reporter construct. COMP binding enhanced BMP-2-dependent osteogenesis in vitro, in the C2C12 cell line and in primary human bone mesenchymal stem cells, as measured by alkaline phosphatase activity, matrix mineralization, and gene expression. Finally, we found that COMP enhanced BMP-2-dependent ectopic bone formation in a rat model assessed histologically, by alkaline phosphatase activity, gene expression, and micro-CT. In summary, this study demonstrates that COMP enhances the osteogenic activity of BMP-2, both in-vitro and in-vivo.

In vitro and in vivo evaluation of acellular diaphragmatic matrices seeded with muscle precursors cells and coated with VEGF silica gels to repair muscle defect of the diaphragm

In this work, a bioartificial system consisting of VEGF-loaded porous silica gel and myoblasts cultured on acellular diaphragmatic matrix (ADM) has been implanted to repair a surgically created diaphragmatic defect in Lewis rats. ADMs exerted a strong angiogenic response on chorio-allantoic membrane. Cytotoxicity, VEGF release and matrix erodibility in vitro tests demonstrated that the silica support was nontoxic and that the VEGF bioactivity was maintained after matrix entrapment and it was released within a timeframe that can be modulated by synthesis parameters. Different grafts composed by ADMs with and without autologous male myoblasts or/and VEGF-loaded porous silica gel have been implanted to repair previously created diaphragmatic defects in female Lewis rats. Patches composed of ADMs and myoblasts appeared well preserved until 8 weeks, and contained multinucleated cells and cholinergic fibers. At 8 weeks, the implanted cells were still present inside the patches. The disappointing results obtained when VEGF was delivered by porous silica gel were probably due to an abnormal angiogenic response following an excess of local growth factor concentration. Taken together, these results confirmed that our matrices contained biologically active angiogenic factors which were per se sufficient to induce neo-vessels formation, thus allowing the survival of implanted myoblasts.

Angiogenesis in bone fracture healing: A bioregulatory model

The process of fracture healing involves the action and interaction of many cells, regulated by biochemical and mechanical signals. Vital to a successful healing process is the restoration of a good vascular network. In this paper, a continuous mathematical model is presented that describes the different fracture healing stages and their response to biochemical stimuli only (a bioregulatory model); mechanoregulatory effects are excluded here. The model consists of a system of nonlinear partial differential equations describing the spatiotemporal evolution of concentrations and densities of the cell types, extracellular matrix types and growth factors indispensable to the healing process. The model starts after the inflammation phase, when the fracture callus has already been formed. Cell migration is described using not only haptokinetic, but also chemotactic and haptotactic influences. Cell differentiation is controlled by the presence of growth factors and sufficient vascularisation. Matrix synthesis and growth factor production are controlled by the local cell and matrix densities and by the local growth factor concentrations. Numerical simulations of the system, using parameter values based on experimental data obtained from literature, are presented. The simulation results are corroborated by comparison with experimental data from a standardised rodent fracture model. The results of sensitivity analyses on the parameter values as well as on the boundary and initial conditions are discussed. Numerical simulations of compromised healing situations showed that the establishment of a vascular network in response to angiogenic growth factors is a key factor in the healing process. Furthermore, a correct description of cell migration is also shown to be essential to the prediction of realistic spatiotemporal tissue distribution patterns in the fracture callus. The mathematical framework presented in this paper can be an important tool in furthering the understanding of the mechanisms causing compromised healing and can be applied in the design of future fracture healing experiments.

Simulation of angiogenesis, remodeling and pruning in microvascular networks

In the microcirculation, vessel formation (angiogenesis), structural adaptation (remodeling), and regression (pruning) redistribute flow in response to varying demands. Here, previously developed theoretical models for remodeling in response to pressure, shear stress and local oxygen level (PO2) are extended to include vessel sprouting, interconnection and pruning. A diffusible growth factor (GF) is assumed to be produced in hypoxic tissue. For given network geometry, the blood flow distribution and the resulting PO2 and GF fields are computed. The probability of sprout formation depends on local GF concentration, and the direction of sprout growth depends on GF gradient. Pruning occurs when diameter drops below 3 μm. In simulations starting with a sparse network and tissue hypoxia, vascular density first increased, with many non-flowing segments. Redundant vessels then dropped out, yielding stable and efficient network structures with little or no hypoxia, resembling structures observed in the rat mesentery. Both remodeling and pruning were found to be necessary for formation of functional and efficient networks. Supported by NIH HL034555.

Significance of heparin-binding growth factor expression on cells of solid pediatric tumors

Background: The heparin-binding growth factors pleiotrophin (PTN), midkine (MK), vascular endothelial growth factor (VEGF), and basic fibroblast growth factor (bFGF) stimulate tumor cell proliferation and angiogenesis. In this study the authors wanted to know if these growth factors are expressed by cell lines and tumor tissue of solid pediatric tumors, growth factor expression is influenced by proinflammatory cytokines, and local growth factor concentration has an influence on experimental tumor growth. Methods: Growth factor mRNA expression was analyzed by reverse transcriptase polymerase chain reaction (RT-PCR) and protein secretion by enzyme-linked immunosorbent assay (ELISA). Neuroblastoma cells were suspended in solutions containing different growth factor concentrations before injection into the nude mice, which were given pentosan polysulfate (PPS) for antagonism. Results: The analyzed growth factors were expressed by most cells of solid malignant pediatric tumors. Their expression was not influenced by proinflammatory cytokines. The inhibition of tumor growth by PPS in the nude mouse model was dependent on the local growth factor concentration. High concentration excluded significant tumor suppression. Conclusions: Because of the redundancy of growth factor expression and the abolishment of PPS efficacy by a high local growth factor concentration, the authors conclude that overall targeting of growth factors is a promising approach to cancer therapy in childhood.

Role of epidermal growth factor in the acquisition of ovarian steroid hormone responsiveness in the normal mouse mammary gland.

The purpose of the present studies was to investigate the role of epidermal growth factor (EGF) in the acquisition of estrogen (E) and progestin (P) responsiveness in the mouse mammary gland in vivo. Using the Elvax 40P implant technique to introduce bioactive molecules directly into the mammary gland to produce a localized effect, we have made the novel observation that EGF implanted into glands of pubertal mice followed by E treatment resulted in the precocious acquisition of E-inducible progesterone receptors (PR). In sexually mature mice, EGF implants alone were able to increase PR. A neutralizing antibody specific for EGF blocked E-dependent stimulation of end-bud development and PR induction. Furthermore, the antiestrogen ICI 182,780 blocked the EGF-induced stimulation end-buds and PR induction, indicating that these EGF effects are mediated via estrogen receptors (ER). Immunohistochemical analysis showed that the endogenous EGF content of mammary glands of mature mice was higher than pubertal mice, that E implants caused a localized increase in mammary gland EGF content in both pubertal and mature mice, and that in mature mice E caused an increase in stromal cell EGF content. We have previously shown that the acquisition of E-inducible PR can be modulated by mammary stroma, and the present results indicate that mammary stroma could modulate hormonal responsiveness through control of local growth factor concentration. Taken together, these results provide evidence that E-dependent responses of mouse mammary gland in vivo, such as end-bud proliferation and PR regulation, may be mediated by EGF through an ER-dependent mechanism.

Megakaryocytes and fibroblasts—Interactions as determined in normal human bone marrow specimens

An in vitro study was performed to investigate possible interactions between megakaryocytes and bone marrow fibroblasts, both obtained from healthy donors. We were able to demonstrate that the proliferation of fibroblasts increased significantly by co-culturing these cells with megakaryocytes for 6 days. Addition of neutralizing antibodies for PDGF and TGF β 1 caused a significant reduction of fibroblast growth. Inhibition of cell to cell contacts via tissue culture inserts generated a conspicuous impairment of fibroblast proliferation compared with megakaryocyte-fibroblast co-cultures, where contact was allowed. Hence, our findings suggest that a close spatial relationship between megakaryocytes and fibroblasts is needed for the activation of growth in normal human bone marrow. Neighbouring of megakaryocytes and fibroblasts seems to be necessary in order to achieve a certain threshold of local growth factor concentration. Our results are in keeping with the assumption that PDGF and IGF β 1 are secreted by normal human megakaryocytes in very low concentrations and promote significantly fibroblast proliferation.