PDGF stimulation of Müller cell proliferation: Contributions of c-JNK and the PI3K/Akt pathway

Parallels between the Developing Vascular and Neural Systems: Signaling Pathways and Future Perspectives for Regenerative Medicine

Neurovascular disorders, which involve the vascular and nervous systems, are common. Research on such disorders usually focuses on either vascular or nervous components, without looking at how they interact. Adopting a neurovascular perspective is essential to improve current treatments. Therefore, comparing molecular processes known to be involved in both systems separately can provide insight into promising areas of future research. Since development and regeneration share many mechanisms, comparing signaling molecules involved in both the developing vascular and nervous systems and shedding light to those that they have in common can reveal processes, which have not yet been studied from a regenerative perspective, yet hold great potential. Hence, this review discusses and compares processes involved in the development of the vascular and nervous systems, in order to provide an overview of the molecular mechanisms, which are most promising with regards to treatment for neurovascular disorders. Vascular endothelial growth factor, semaphorins, and ephrins are found to hold the most potential, while fibroblast growth factor, bone morphogenic protein, slits, and sonic hedgehog are shown to participate in both the developing vascular and nervous systems, yet have not been studied at the neurovascular level, therefore being of special interest for future research.

PDGF as an Important Initiator for Neurite Outgrowth Associated with Fibrovascular Membranes in Proliferative Diabetic Retinopathy

PURPOSE

The formation of fibrovascular membranes (FVMs) is a serious sight-threatening complication of proliferative diabetic retinopathy (PDR) that may result in retinal detachment and eventual blindness. During the formation of these membranes, neurite/process outgrowth occurs in retinal neurons and glial cells, which may both serve as a scaffold and have guiding or regulatory roles. To further understand this process, we investigated whether previously identified candidate proteins, from vitreous of PDR patients with FVMs, could induce neurite outgrowth in an experimental setting.

MATERIALS AND METHODS

Retinal explants of C57BL6/N mouse pups on postnatal day 3 (P3) were cultured in poly-L-lysine- and laminin-coated dishes. Outgrowth stimulation experiments were performed with the addition of potential inducers of neurite outgrowth. Automated analysis of neurite outgrowth was performed by measuring β-tubulin-immunopositive neurites using Image J. Expression of PDGF receptors was quantified by RT-PCR in FVMs of PDR patients.

RESULTS

Platelet-derived growth factor (PDGF) induced neurite outgrowth in a concentration-dependent manner, whilst neuregulin 1 (NRG1) and connective tissue growth factor (CTGF) did not. When comparing three different PDGF dimers, treatment with PDGF-AB resulted in the highest neurite induction, followed by PDGF-AA and -BB. In addition, incubation of retinal explants with vitreous from PDR patients resulted in a significant induction of neurite outgrowth as compared to non-diabetic control vitreous from patients with macular holes, which could be prevented by addition of CP673451, a potent PDGF receptor (PDGFR) inhibitor. Abundant expression of PDGF receptors was detected in FVMs.

CONCLUSION

Our findings suggest that PDGF may be involved in the retinal neurite outgrowth, which is associated with the formation of FVMs in PDR.

Systematic Analysis of Long Noncoding RNA and mRNA in Granulosa Cells during the Hen Ovulatory Cycle

Simple Summary

Chicken is one of the most economically important farm poultry, and providing many food products, such as meat and eggs for human consumption. However, follicle transcriptome studies in chickens with timepoints relating to changes in luteinizing hormone level remain unknown. In this study, the largest preovulatory follicle of chicken underwent the early, middle, and terminal stages of ovulatory cycle. Our work provides a comprehensive analysis of lncRNAs and mRNAs in chicken granulosa cells during the ovulatory cycle. A total of 12,479 mRNAs and 7528 lncRNAs were identified among the three stages. Thousands of lncRNAs were annotated, and the most differentially abundant genes were detected in the luteinizing hormone surge stage. Functional features of the lncRNAs and mRNAs at each stage were revealed, which was also associated with the changes in serum luteinizing hormone level. Especially, genes related to oxidative stress, steroids regulation, and inflammatory process were enriched in the luteinizing hormone surge stage, The comprehensive data generated in this study provides the foundation for future investigations to improve the reproductive performance of chickens and explore the mechanisms responsible for female ovarian diseases.

Abstract

Long non-coding RNAs (lncRNAs) and mRNAs are temporally expressed during chicken follicle development. However, follicle transcriptome studies in chickens with timepoints relating to changes in luteinizing hormone (LH) levels are rare. In this study, gene expression in Rohman layers was investigated at three distinct stages of the ovulatory cycle: zeitgeber time 0 (ZT0, 9:00 a.m.), zeitgeber time 12 (ZT12, 9:00 p.m.), and zeitgeber time 20 (ZT20, 5:00 a.m.) representing the early, middle, and LH surge stages, respectively, of the ovulatory cycle. Gene expression profiles were explored during follicle development at ZT0, ZT12, and ZT20 using Ribo-Zero RNA sequencing. The three stages were separated into two major stages, including the pre-LH surge and the LH surge stages. A total of 12,479 mRNAs and 7528 lncRNAs were identified among the three stages, and 4531, 523 differentially expressed genes (DEGs) and 2367, 211 differentially expressed lncRNAs (DELs) were identified in the ZT20 vs. ZT12, and ZT12 vs. ZT0, comparisons. Functional enrichment analysis revealed that genes involved in cell proliferation and metabolism processes (lipid-related) were mainly enriched in the ZT0 and ZT12 stages, respectively, and genes related to oxidative stress, steroids regulation, and inflammatory process were enriched in the ZT20 stage. These findings provide the basis for further investigation of the specific genetic and molecular functions of follicle development in chickens.

[Proliferative vitreoretinopathy process-To heal or not to heal]

BACKGROUND

Proliferative vitreoretinopathy (PVR) is still an unsolved problem after half a century of research.

METHODS

This article provides a review of mechanisms leading to PVR in the context of wound healing research.

RESULTS

Wound healing is a physiological repair process that occurs in a similar way in all organs and may end in scar formation. The development of PVR is based on this wound healing mechanism. The localization and structures involved lead to specific characteristics and consequences. Up to now the pharmacotherapeutic strategies were not sufficiently effective. The growing understanding of the mechanisms of scar-free fetal wound healing, could however lead to a solution of the PVR problem.

CONCLUSION

The PVR is a physiological process with a pathological result. The complex steps involved in vitreoretinal wound healing are well understood. There is currently no therapeutic approach neither in ophthalmology nor in other medical disciplines that is able to restore the original function and structure of the involved tissue or organ but there is hope that this can succeed in the future.

Growth factors-based therapeutic strategies and their underlying signaling mechanisms for peripheral nerve regeneration

Peripheral nerve injury (PNI), one of the most common concerns following trauma, can result in a significant loss of sensory or motor function. Restoration of the injured nerves requires a complex cellular and molecular response to rebuild the functional axons so that they can accurately connect with their original targets. However, there is no optimized therapy for complete recovery after PNI. Supplementation with exogenous growth factors (GFs) is an emerging and versatile therapeutic strategy for promoting nerve regeneration and functional recovery. GFs activate the downstream targets of various signaling cascades through binding with their corresponding receptors to exert their multiple effects on neurorestoration and tissue regeneration. However, the simple administration of GFs is insufficient for reconstructing PNI due to their short half‑life and rapid deactivation in body fluids. To overcome these shortcomings, several nerve conduits derived from biological tissue or synthetic materials have been developed. Their good biocompatibility and biofunctionality made them a suitable vehicle for the delivery of multiple GFs to support peripheral nerve regeneration. After repairing nerve defects, the controlled release of GFs from the conduit structures is able to continuously improve axonal regeneration and functional outcome. Thus, therapies with growth factor (GF) delivery systems have received increasing attention in recent years. Here, we mainly review the therapeutic capacity of GFs and their incorporation into nerve guides for repairing PNI. In addition, the possible receptors and signaling mechanisms of the GF family exerting their biological effects are also emphasized.

Pirfenidone suppresses the abnormal activation of human Müller cells after platelet-derived growth factor-BB stimulation

AIM

To determine the effect of pirfenidone on the activated human Müller cells by platelet-derived growth factor-BB (PDGF-BB).

METHODS

The primary human Müller cells were separated from retinal tissues and established the pathogenic model by stimulated with PDGF-BB. The Müller cells behaviour of normal group and the model group was measured by MTT assay, Trypan blue assay, cell migration assay, and collagen contraction assay. The expression of transforming growth factor (TGF)-β1, -β2, and pigment epithelium-derived factor (PEDF) was estimated with real-time polymerase chain reaction (PCR), Western blot and immunofluorescence analyses.

RESULTS

A pathogenic/proliferative model of Müller cells was established by stimulating normal cultured Müller cells with 10 ng/mL PDGF-BB for 48h. After treated with 0.2 and 0.3 mg/mL pirfenidone, the proliferation, migration and collagen contraction was statistically significantly depressed in the model group compared with the normal groups. The expression levels of TGF-β1 and TGF-β2 were significantly down-regulated, while the PEDF expression was significantly up-regulated after treated with 0.2 and 0.3 mg/mL pirfenidone in the model group.

CONCLUSION

Pirfenidone effectively suppress the proliferation, migration and collagen contraction of the human Müller cells stimulated with PDGF-BB through down-regulation of TGF-β1/TGF-β2 and up-regulation of PEDF.

Purinergic signaling in the retina: From development to disease

Retinal injuries and diseases are major causes of human disability involving vision impairment by the progressive and permanent loss of retinal neurons. During development, assembly of this tissue entails a successive and overlapping, signal-regulated engagement of complex events that include proliferation of progenitors, neurogenesis, cell death, neurochemical differentiation and synaptogenesis. During retinal damage, several of these events are re-activated with both protective and detrimental consequences. Purines and pyrimidines, along with their metabolites are emerging as important molecules regulating both retinal development and the tissue's responses to damage. The present review provides an overview of the purinergic signaling in the developing and injured retina. Recent findings on the presence of vesicular and channel-mediated ATP release by retinal and retinal pigment epithelial cells, adenosine synthesis and release, expression of receptors and intracellular signaling pathways activated by purinergic signaling in retinal cells are reported. The pathways by which purinergic receptors modulate retinal cell proliferation, migration and death of retinal cells during development and injury are summarized. The contribution of nucleotides to the self-repair of the injured zebrafish retina is also discussed.

Platelet-derived growth factor receptor alpha (PDGFRα) is overexpressed in NK/T-cell lymphoma and mediates cell survival

Nasal-type natural killer/T-cell lymphoma (NKTCL) is a subtype of non-Hodgkin lymphoma (NHL) that is clinically aggressive and has a poor prognosis. Platelet-derived growth factor receptors (PDGFRs) and their ligands (PDGFs) play important roles in angiogenesis, cancer cell proliferation, survival, migration and poor prognosis in various tumours. However, the significance of PDGFRs in NKTCL remains unknown. Herein, the present study aimed to investigate the important role of PDGFRα in pathogenesis, progression and prognisis of NKTCL. Firstly, we performed immunohistochemical staining, qRT-PCR and western blotting to determine PDGFRα expression in formalin-fixed, paraffin-embedded tissue sections from 78 NKTCL cases and in cell lines. Secondly, correlations between PDGFRα expression and NKTCL clinical parameters and prognosis were analysed. Moreover, a biological assessment of PDGFRα blockade in two NKTCL cell lines was conducted through proliferation assay, cell-cycle evaluation and apoptosis detection by flow cytometry analyses. Furthermore, we detected in vivo activity of imatinib in mouse model of NKTCL. We found that the expression of PDGFRα was significantly higher in NKTCL tissues compared to the reactive lymphoid hyperplasia of the nasopharynx (P = 0.028). High PDGFRα expression was strongly associated with a high LDH level (P = 0.028) and III-IV stage (P = 0.013). NKTCL patients with high PDGFRα expression displayed a reduced median overall survival time and progression-free survival time when compared with those with low PDGFRα expression (P = 0.011, P = 0.005, respectively). Cox multivariate analysis showed that III-IV stage (P = 0.024) and high PDGFRα expression (P = 0.003) were independent prognostic factors in NKTCL patients. Biological assessment assays in two NKTCL cell lines revealed that a specific PDGFR antagonist, imatinib, inhibited cell viability, blocked cell cycle progression at G0/G1 stage and induced apoptosis. Similarly, the in vivo assay showed that imatinib delayed mouse model tumour growth. In conclusion, NKTCL tumour cells have prominent PDGFRα expression, which can serve as a candidate prognostic marker. PDGFR antagonists have significant biological effect on NKTCL and may be useful therapeutic agents for treatment of NKTCL.

Identification of proteins associated with clinical and pathological features of proliferative diabetic retinopathy in vitreous and fibrovascular membranes

Purpose

To identify the protein profiles in vitreous associated with retinal fibrosis, angiogenesis, and neurite formation in epiretinal fibrovascular membranes (FVMs) in patients with proliferative diabetic retinopathy (PDR).

Methods

Vitreous samples of 5 non-diabetic control patients with vitreous debris and 7 patients with PDR membranes were screened for 507 preselected proteins using the semi-quantitative RayBio® L-series 507 antibody array. From this array, 60 proteins were selected for a custom quantitative antibody array (Raybiotech, Human Quantibody® array), analyzing 7 control patients, 8 PDR patients with FVMs, and 5 PDR patients without FVMs. Additionally, mRNA levels of proteins of interest were measured in 10 PDR membranes and 11 idiopathic membranes and in retinal tissues and cells to identify possible sources of protein production.

Results

Of the 507 proteins screened, 21 were found to be significantly elevated in PDR patients, including neurogenic and angiogenic factors such as neuregulin 1 (NRG1), nerve growth factor receptor (NGFR), placental growth factor (PlGF) and platelet derived growth factor (PDGF). Angiopoietin-2 (Ang2) concentrations were strongly correlated to the degree of fibrosis and the presence of FVMs in patients with PDR. Protein correlation analysis showed PDGF to be extensively co-regulated with other proteins, including thrombospondin-1 and Ang2. mRNA levels of glial-derived and brain/derived neurotrophic factor (GDNF and BDNF) were elevated in PDR membranes. These results were validated in a second study of 52 vitreous samples of 32 PDR patients and 20 control patients.

Conclusions

This exploratory study reveals protein networks that potentially contribute to neurite outgrowth, angiogenesis and fibrosis in the formation of fibrovascular membranes in PDR. We identified a possible role of Ang2 in fibrosis and the formation of FVMs, and of the neurotrophic factors NRG1, PDGF and GDNF in neurite growth that occurs in all FVMs in PDR.

Mucins in neoplasms of pancreas, ampulla of Vater and biliary system

Tumors of the pancreas, the ampulla of Vater, and the extrahepatic and intrahepatic bile ducts have significant histological similarities due to the common embryonic origin of the pancreatobiliary system. This obviates the need for discovery of biomarkers with diagnostic and prognostic value for these tumors. Mucins, especially MUC-1, -2, -4 and -5AC, are important candidates for developing into such reliable biomarkers. Increased expression of MUC1 occurs in pancreatic ductal adenocarcinomas and is associated with increased degrees of dysplasia in pancreatic intraepithelial neoplasia (PanIN). Positive expression of MUC2 in intraductal papillary mucinus neoplasms (IPMN) of the intestinal type indicates high potential progression to invasive carcinoma with de novo expression of MUC1, while absence of MUC2 expression in IPMNs of gastric type implies low potential to malignant evolution. De novo MUC4 expression correlates to the severity of dysplasia in PanIN and is associated with a poor prognosis in patients with pancreatic ductal adenocarcinomas. In biliary intraepithelial neoplasia (BilIN), increased expression of MUC1 is associated with higher degrees of dysplasia. Intrahepatic cholangiocarcinomas (ICC) are characterized by increased expression of all glycoforms of MUC1. Positive MUC2 expression in intraductal papillary neoplasm of the bile ducts (IPNB) of the intestinal type indicates high malignant potential with de novo expression of MUC1 in the invasive element. Absent MUC2 expression in any degree of BilIN may prove useful in differentiating them from IPNB. De novo expression of MUC4 is associated with poor prognosis in patients with ICC or carcinoma of the extrahepatic bile ducts (EHBDC). High de novo expression of MUC5AC is found in all degrees of BilIN and all types of IPNB and ICC. The MUC5AC is useful in the detection of neoplastic lesions of the bile duct at an early stage. Increased expression of mucin MUC1 in carcinoma of the ampulla of Vater associated with unfavorable behavior of the tumor, such as lymph node metastasis, infiltration of the pancreas and duodenum, advanced TNM classification and worse prognosis. Patients with intra-ampullary papillary-tubular neoplasm (IAPN) of the pancreatobiliary immunophenotype did not show MUC2, while those of the intestinal immunophenotype are MUC2 positive. The expression of MUC4 is associated with poor prognosis in patients with carcinoma of the ampulla of Vater favoring metastasis and making them resistant to apoptosis. Moreover, it appears that MUC4 positivity correlates with recurrence of the tumor. Expression of MUC5AC is associated with the invasive potential of the tumor.

PI3K-mediated glioprotective effect of epidermal growth factor under oxidative stress conditions

AIM

To determine the effects of epidermal growth factor (EGF) on the proliferation and migration of Müller cell line Moorfields/Institute of Ophthalmology-Müller 1 (MIO-M1), and its related molecular mechanisms under normal and oxidative stress conditions.

METHODS

Müller cells were cultured with different concentrations of EGF in the presence or absence of varied amounts of H2O2 and glucose oxidase (GO) which induced oxidative stress. The proliferation and migration of Müller cells were examined by 5-Bromo-2-deoxyUridine (BrdU), MTT assay, Transwell assay and scratch wound healing assays. The cell viability was determined with the MTT assay. The secretion of EGF by Müller cells was evaluated by ELISA. Western blot was performed to detect the activation of extracellular regulated protein kinases (ERK)1/2 and Akt signal pathways.

RESULTS

EGF stimulated the proliferation and migration of Müller cells in a concentration-dependent manner in vitro. Under oxidative damage condition, 2h of pretreatment with 10-100 ng/mL EGF can mostly inhibit 50% lethal dose of 0.08 mmol/L H2O2-induced cell damage. The Western blot results showed that after Müller cells were exposed to varying EGF for 24h, Akt and ERK1/2 were phosphorylated in a dose-dependent manner. In the presence of the LY294002, the potent PI3K inhibitor, the p-Akt was significantly attenuated.

CONCLUSION

EGF may induce the proliferation and migration of human Müller cells through the Akt and the ERK1/2 signal pathways, and induce PI3K-mediated glioprotective effect under oxidative stress.

Platelet-derived growth factor BB mimics serum-induced dispersal of pancreatic epithelial cell clusters

We showed previously that proliferating human islet-derived de-differentiated cells (DIDs) exhibit many characteristics of mesenchymal stem cells. Dispersed DIDs can be induced by serum deprivation to undergo mesenchymal-to-epithelial transition and aggregate into epithelial cell clusters (ECCs). Conversely, ECCs can be induced to disperse and undergo epithelial-to-mesenchymal transition (EMT) by re-addition of mammalian sera. In this study, we show that platelet-derived growth factor BB (PDGF-BB) mimics and mediates serum-induced ECCs' dispersal accompanied by accumulation of cytoplasmic β-catenin and a decrease in the levels of insulin and glucagon mRNAs. Moreover, we show that PDGF-BB-induced dispersal of ECCs is a more general phenomenon that occurs also with bone marrow mesenchymal stem cells (BM-MSCs) and dermal fibroblasts (DFs). In DIDs, BM-MSCs, and DFs, PDGF decreased the levels of DKK1 mRNA, suggesting involvement of the Wnt signaling pathway. PDGF-BB stimulated a significant increase in S473 phosphorylation of Akt and the PI3K specific inhibitor (PIP828) partially inhibited PDGF-BB-induced ECC dispersal. Lastly, the PDGF-receptor (PDGF-R) antagonist JNJ-10198409 inhibited both PDGF-BB--and serum-induced ECC dispersal. Epidermal growth factor (EGF), which shares most of the PDGF signaling pathway, did not induce dispersal and only weakly stimulated Akt phosphorylation. Our data suggest that PDGF-BB mediates serum-induced DIDs dispersal, correlated with the activation of the PI3K-Akt pathway.

ATP-competitive mTOR kinase inhibitors delay plant growth by triggering early differentiation of meristematic cells but no developmental patterning change

The TOR (target of rapamycin) protein, a large phosphatidylinositol 3-kinase-like protein kinase (PIKK) that is conserved in eukaryotes and is a central regulator of growth and metabolism. The analysis of function of TOR in plant growth and development has been limited by the fact that plants are very poorly sensitive to rapamycin. As the kinase domain of TOR is highly conserved, this study analysed the dose-dependent effect of three sets of first- and second-generation ATP-competitive inhibitors (called asTORis for active-site TOR inhibitors) recently developed for the human TOR kinase on Arabidopsis thaliana growth. All six asTORis inhibited plant root growth in a dose-dependent manner, with 50% growth inhibitory doses (GI50) of <10 μM and <1 μM for the first- and second-generation inhibitors, respectively, similarly to the values in mammalian cells. A genetic approach further demonstrated that only asTORis inhibited root growth in an AtTOR gene-dosage-dependent manner. AsTORis decreased the length of: (i) the meristematic zone (MZ); (ii) the division zone in the MZ; (iii) epidermal cells in the elongation zone; and (iv) root hair cells. Whereas meristematic cells committed to early differentiation, the pattern of cell differentiation was not affected per se. AsTORis-induced root hair growth phenotype was shown to be specific by using other growth inhibitors blocking the cell cycle or translation. AsTORis dose-dependent inhibition of growth and root hairs was also observed in diverse groups of flowering plants, indicating that asTORis can be used to study the TOR pathway in other angiosperms, including crop plants.

Activation of c-Jun N-terminal kinase (JNK) during mitosis in retinal progenitor cells

Most studies of c-Jun N-terminal Kinase (JNK) activation in retinal tissue were done in the context of neurodegeneration. In this study, we investigated the behavior of JNK during mitosis of progenitor cells in the retina of newborn rats. Retinal explants from newborn rats were kept in vitro for 3 hours and under distinct treatments. Sections of retinal explants or freshly fixed retinal tissue were used to detect JNK phosphorylation by immunohistochemistry, and were examined through both fluorescence and confocal microscopy. Mitotic cells were identified by chromatin morphology, histone-H3 phosphorylation, and location in the retinal tissue. The subcellular localization of proteins was analyzed by double staining with both a DNA marker and an antibody to each protein. Phosphorylation of JNK was also examined by western blot. The results showed that in the retina of newborn rats (P1), JNK is phosphorylated during mitosis of progenitor cells, mainly during the early stages of mitosis. JNK1 and/or JNK2 were preferentially phosphorylated in mitotic cells. Inhibition of JNK induced cell cycle arrest, specifically in mitosis. Treatment with the JNK inhibitor decreased the number of cells in anaphase, but did not alter the number of cells in either prophase/prometaphase or metaphase. Moreover, cells with aberrant chromatin morphology were found after treatment with the JNK inhibitor. The data show, for the first time, that JNK is activated in mitotic progenitor cells of developing retinal tissue, suggesting a new role of JNK in the control of progenitor cell proliferation in the retina.

MUC1 regulates PDGFA expression during pancreatic cancer progression

Pancreatic Ductal Adenocarcinoma (PDA) has one of the worst prognoses of all cancers. Mucin 1 (MUC1), a transmembrane mucin glycoprotein, is a key modulator of several signaling pathways that affect oncogenesis, motility, and metastasis. Its expression is known to be associated with poor prognosis in patients. However, the precise mechanism remains elusive. We report a novel association of MUC1 with Platelet-Derived Growth Factor-A (PDGFA). PDGFA is one of the many drivers of tumor growth, angiogenesis, and metastasis in PDA. Using mouse PDA models as well as human samples, we show clear evidence that MUC1 regulates the expression and secretion of PDGFA. This, in turn, influences proliferation and invasion of pancreatic cancer cells leading to higher tumor burden in vivo. In addition, we reveal that MUC1 over expressing cells are heavily dependent on PDGFA both for proliferation and invasion while MUC1-null cells are not. Moreover, PDGFA and MUC1 are critical for translocation of βcatenin to the nucleus for oncogenesis to ensue. Finally, we elucidate the underlying mechanism by which MUC1 regulates PDGFA expression and secretion in pancreatic cancer cells. We show that MUC1 associates with Hif1-α, a known transcription factor involved in controlling PDGFA expression. Furthermore, MUC1 facilitates Hif1-α translocation to the nucleus. In summary, we have demonstrated that MUC1-induced invasion and proliferation occurs via increased exogenous production of PDGFA. Thus, impeding MUC1 regulation of PDGFA signaling may be therapeutically beneficial for patients with PDA.

Vitreous IGFBP-3 effects on Müller cell proliferation and tractional force generation

PURPOSE

Previous studies from this laboratory revealed that vitreous insulin-like growth factor binding protein-3 (IGFBP-3) is a biologically active fragment of the intact protein. The goal of this study was to characterize its effects on Müller cell proliferation and tractional force generation, activities relevant to proliferative diabetic retinopathy (PDR).

METHODS

Müller cells were isolated from normal porcine retina. The vitreous-type IGFBP-3 fragment was isolated from normal human plasma and compared with intact recombinant protein for the ability to modulate Müller cell proliferation and tractional force generation in tissue culture models.

RESULTS

Müller cells were stimulated to proliferate by serum and platelet-derived growth factor (PDGF), but not insulin-like growth factor (IGF)-I or IGF-II. The cells were similarly unresponsive to IGFBP-3 or the IGFBP-3 fragment alone or in combination with IGF-I or IGF-II. In contrast, Müller cells demonstrated robust extracellular matrix contraction in response to IGF-I, IGF-II, and PDGF. Intact IGFBP-3 attenuated extracellular matrix contraction in response to IGF-I and IGF-II while the IGFBP-3 fragment modulated cell responses to IGF-II only. Neither binding protein altered cell responses to PDGF.

CONCLUSIONS

Intact IGFBP-3 modulates Müller cell tractional force generation stimulated by IGF-I and IGF-II while the effects of the vitreous-type fragment are limited to IGF-II. Porcine Müller cells proliferate in response to PDGF, but not IGF-I or IGF-II. Both forms of IGFBP-3 are also without mitogenic effects alone or in combination with IGFs. It appears that Müller cell tractional force generation in PDR is driven by vitreous IGF activity and proliferation is stimulated by growth factors outside of the IGF system.

Involvement of the PI3K/AKT pathway in ATP-induced proliferation of developing retinal cells in culture

ATP induces the proliferation of chick retinal cells in culture through the activation of P2Y1 receptors, PKC and MAP kinases. Together with MAP kinases, the PI3K/AKT pathway has also been implicated as an important mediator in proliferative events during development. Here we investigated the participation of the PI3K/AKT signal pathway on ATP-induced proliferation of chick embryo retinal cells in culture. When retinal cultures obtained from 7-day-old embryos were cultivated for 1 day and treated with ATP, a transient and dose-dependent phosphorylation of both ERK and AKT was observed, an effect that could be mimicked by 500 microM ADP and blocked by 100 microM PPADS, a P2 receptor antagonist. Maximal stimulation of both enzymes was obtained with 100 microM ATP in 5 min, decreasing thereafter. Activation of these pathways by ATP seemed to be independent, since LY294002 and U0126, inhibitors of PI3K and MEK, did not block the activation of ERK and AKT, respectively, although each compound blocked its respective target. Moreover, when the cultures were incubated with ATP in the presence of LY294002, a decreased incorporation of [(3)H]-thymidine was observed, as compared to cultures treated only with ATP, a decline that was also obtained by incubating the cells with ATP plus 0.5 microM API-59CJ-Ome, an inhibitor of AKT. No decrease in cell viability was observed with this concentration of API-59CJ-Ome. An increase in cyclin D1 expression, that could be inhibited by 10 microM LY 294002 or 20 microM U0126, was observed when cells were incubated with 500 microM ADP. No effect of PI3K and MEK inhibitors was observed in the expression of p27kip1 in the cultures. These results suggest that, besides the involvement of the MAP kinases pathway, ATP-induced cell cycling of late developing retinal progenitors in culture also involves the activation of the PI3K/AKT pathway.