Biomedical subjects

Martin Friedlander

Publications and source records attributed to Martin Friedlander.

27 records · Page 2Linked to original sources

PubMed2002

Co-translational targeting and translocation of the amino terminus of opsin across the endoplasmic membrane requires GTP but not ATP.

The tight coupling between ongoing translation and translocation across the mammalian endoplasmic reticulum has made it difficult to determine the requirements that are specific for translocation. We have developed an in vitro assay that faithfully mimics the co-translational targeting and translocation of the amino terminus of opsin without ongoing translation. Using this system we demonstrate that this post-translational targeting and translocation requires nucleotide triphosphates but not cytosolic proteins. The addition of GTP alone was sufficient to fully restore targeting. The addition of ATP was not specifically required, and non-hydrolyzable analogs of ATP that blocked 90% of the ATPase activity also had no inhibitory effect on translocation.

Adenosine Triphosphate↗

PubMed2002

Bone marrow-derived stem cells target retinal astrocytes and can promote or inhibit retinal angiogenesis.

Adult bone marrow (BM) contains cells capable of differentiating along hematopoietic (Lin(+)) or non-hematopoietic (Lin(-)) lineages. Lin(-) hematopoietic stem cells (HSCs) have recently been shown to contain a population of endothelial precursor cells (EPCs) capable of forming blood vessels. Here we show that intravitreally injected Lin(-) BM cells selectively target retinal astrocytes, cells that serve as a template for both developmental and injury-associated retinal angiogenesis. When Lin(-) BM cells were injected into neonatal mouse eyes, they extensively and stably incorporated into forming retinal vasculature. When EPC-enriched HSCs were injected into the eyes of neonatal rd/rd mice, whose vasculature ordinarily degenerates with age, they rescued and maintained a normal vasculature. In contrast, normal retinal angiogenesis was inhibited when EPCs expressing a potent angiostatic protein were injected. We have demonstrated that Lin(-) BM cells and astrocytes specifically interact with one another during normal angiogenesis and pathological vascular degeneration in the retina. Selective targeting with Lin(-) HSC may be a useful therapeutic approach for the treatment of many ocular diseases.

Animals↗

PubMed2002

The amino terminus of opsin translocates "posttranslationally" as efficiently as cotranslationally.

Opsin, a member of the G-protein-coupled receptor family, is a polytopic membrane protein that does not encode a cleaved amino-terminal signal sequence. The amino terminus of opsin precedes the first known targeting information, suggesting that it translocates across the endoplasmic reticulum (ER) membrane after synthesis, uncoupled from translation. However, translocation across the mammalian ER is believed to be coupled to protein synthesis. In this study we show that opsin, within a range of nascent peptide lengths, targets and translocates equally efficiently co- and posttranslationally. Longer nascent opsin peptides have a lower efficiency of cotranslational translocation but an even lower efficiency of posttranslational translocation. We also show that SRP is required for both co- and posttranslational targeting.

Animals↗

PubMed2002

Insulin-like growth factor 2 and potential regulators of hemangioma growth and involution identified by large-scale expression analysis.

Hemangiomas are benign tumors of the vascular endothelium and are the most common tumors of infancy. These tumors are characterized by an initial phase of rapid proliferation, which is followed, in most cases, by spontaneous involution. Although most lesions resolve without complication, there are some cases in which hemangiomas can be life threatening when occurring near a vital structure. Treatment for these aggressive tumors represents an unmet clinical need. In addition, this characteristic progression of hemangiomas through distinct phases provides a unique opportunity for studying endothelial cell biology and angiogenesis. Using DNA microarrays representing approximately 10,000 human genes, we identified insulin-like growth factor 2 (IGF-2) as a potentially important regulator of hemangioma growth. IGF-2 was highly expressed during the proliferative phase and substantially decreased during involution. This finding was confirmed at the message level by quantitative reverse transcription-PCR and at the protein level by immunohistochemistry. IGF-2 protein was localized primarily to tumor vessels or vascular channels. Using a human hemangioma explant model, we show that IGF-2 promotes sprouting from intact hemangioma tissue. In addition, several angiogenesis-related factors, including integrins alpha(v)beta3 and alpha5beta1, are present in proliferating hemangiomas. During the involuting phase, an increase in several IFN-induced genes was observed. These studies identify potential regulators of hemangioma growth and involution and provide a foundation on which to build further mechanistic investigations into angiogenesis, using hemangiomas as a model.

Cell Division↗

PubMed2002

Loss of p53 compensates for alpha v-integrin function in retinal neovascularization.

alpha(v)-Integrin antagonists block neovascularization in various species, whereas 20% of alpha(v)-integrin null mice are born with many normal looking blood vessels. Given that blockade of alpha(v)-integrins during angiogenesis induces p53 activity, we utilized p53 null mice to elucidate whether loss of p53 can compensate for alpha(v)-integrin function in neovascularization of the retina. Murine retinal vascularization was inhibited by systemic administration of an alpha(v)-integrin antagonist. In contrast, mice lacking p53 were refractory to this treatment, indicating that neovascularization in normal mice depends on alpha(v)-integrin-mediated suppression of p53. Blockade of alpha(v)-integrins during neovascularization resulted in an induction of p21(CIP1) in wild type and, surprisingly, in p53 null retinas, indicating that alpha(v)-integrin ligation regulates p21(CIP1) levels in a p53-independent manner. In conclusion, we demonstrate for the first time an in vivo intracellular mechanism for compensation of integrin function and that p53 and alpha(v)-integrins act in concert during retinal neovascularization.

Animals↗

PubMed2002

A fragment of human TrpRS as a potent antagonist of ocular angiogenesis.

Pathological angiogenesis contributes directly to profound loss of vision associated with many diseases of the eye. Recent work suggests that human tyrosyl- and tryptophanyl-tRNA synthetases (TrpRS) link protein synthesis to signal transduction pathways including angiogenesis. In this study, we show that a recombinant form of a COOH-terminal fragment of TrpRS is a potent antagonist of vascular endothelial growth factor-induced angiogenesis in a mouse model and of naturally occurring retinal angiogenesis in the neonatal mouse. The angiostatic activity is dose-dependent in both systems. The recombinant fragment is similar in size to one generated naturally by alternative splicing and can be produced by proteolysis of the full-length protein. In contrast, the full-length protein is inactive as an antagonist of angiogenesis. These results suggest that fragments of TrpRS, as naturally occurring and potentially nonimmunogenic anti-angiogenics, can be used for the treatment of neovascular eye diseases.

Alternative Splicing↗

PubMed2002

A human aminoacyl-tRNA synthetase as a regulator of angiogenesis.

Aminoacyl-tRNA synthetases catalyze the first step of protein synthesis. It was shown recently that human tyrosyl-tRNA synthetase (TyrRS) can be split into two fragments having distinct cytokine activities, thereby linking protein synthesis to cytokine signaling pathways. Tryptophanyl-tRNA synthetase (TrpRS) is a close homologue of TyrRS. A natural fragment, herein designated as mini TrpRS, was shown by others to be produced by alternative splicing. Production of this fragment is reported to be stimulated by IFN-gamma, a cytokine that also stimulates production of angiostatic factors. Mini TrpRS is shown here to be angiostatic in a mammalian cell culture system, the chicken embryo, and two independent angiogenesis assays in the mouse. The full-length enzyme is inactive in the same assays. Thus, protein synthesis may be linked to the regulation of angiogenesis by a natural fragment of TrpRS.

Animals↗

PubMed2002

Retinal vascular development is mediated by endothelial filopodia, a preexisting astrocytic template and specific R-cadherin adhesion.

PURPOSE: A neonatal mouse retina developmental model was used to study endothelial cell guidance and subsequent formation of vascular patterns. Since most diseases that cause catastrophic loss of vision do so as a result of abnormal ocular angiogenesis, a better understanding of events regulating normal retinal vascular growth may provide insight into pathologic angiogenesis. METHODS: Development of the retinal vasculature at various postnatal and embryonic time points was analyzed by collagen IV immunohistochemistry and staining with isolectin Griffonia simplicifolia. GFAP-GFP transgenic mice were used to evaluate the relationship between developing vessels and retinal glial cells. Immunolocalization of R-cadherin and intravitreous injection of R-cadherin-specific antibodies was performed to determine the role of R-cadherin during patterning of the superficial and deep retinal vascular plexuses. RESULTS: The characteristic honeycomb pattern of vessel formation observed in the superficial layer is a result of endothelial cell migration over a preexisting astrocytic template. Filopodial extensions associate with underlying astrocytes by protruding from the tips of endothelial cells at the migrating vascular front. Branching of vessels in the primary vascular plexus, as well as appropriate localization of the deep vascular network is mediated by R-cadherin, an adhesion molecule known to be involved in neuronal cell guidance. Injection of antibodies directed against R-cadherin prevents the normally extensive collateralization observed during formation of the superficial network. Injection of anti-R cadherin antibodies also dramatically affects vessels of the deep network. These vessels migrate beyond the normal turning point, penetrating into the deeper photoreceptor layer. CONCLUSIONS: . These studies suggest that angiogenesis and formation of vascular patterns in the retina may use many of the same developmental cues used by neurons in both the central and peripheral nervous systems. Furthermore, retinal vascular endothelial cell guidance mediated by filopodial extensions and neuronal guidance cues may represent a novel conceptual framework within which to study the establishment of vascular patterns in a variety of angiogenic systems.

Animals↗

PubMedDate not supplied

Retinal vascular regeneration.

We discuss the potential use of stem cells for therapeutic angiogenesis in the treatment of retinal diseases. We demonstrate that the clinical utility of these EPC may be not limited in the treatment of ischemic retinal diseases but may also have application for the treatment of retinal degenerative disorders and for a form of cell-based gene therapy. One of the greatest potential benefits of bone marrow derived EPC therapy is the possible use of autologous grafts. Nonetheless, potential toxicities and unregulated cell growth will need to be carefully evaluated before this approach is brought to the clinics.

Animals↗