Aaron Avivi - Academia.edu (original) (raw)

Papers by Aaron Avivi

Scientific Reports, 2017

The blind subterranean mole rat Spalax shows a remarkable tolerance to hypoxia, cancer-resistance... more The blind subterranean mole rat Spalax shows a remarkable tolerance to hypoxia, cancer-resistance and longevity. Unravelling the genomic basis of these adaptations will be important for biomedical applications. RNA-Seq gene expression data were obtained from normoxic and hypoxic Spalax and rat liver tissue. Hypoxic Spalax broadly downregulates genes from major liver function pathways. This energy-saving response is likely a crucial adaptation to low oxygen levels. In contrast, the hypoxia-sensitive rat shows massive upregulation of energy metabolism genes. Candidate genes with plausible connections to the mole rat’s phenotype, such as important key genes related to hypoxia-tolerance, DNA damage repair, tumourigenesis and ageing, are substantially higher expressed in Spalax than in rat. Comparative liver transcriptomics highlights the importance of molecular adaptations at the gene regulatory level in Spalax and pinpoints a variety of starting points for subsequent functional studies.

Frontiers in Neuroanatomy, 2016

The blind mole rat, Spalax ehrenbergi, can, despite severely degenerated eyes covered by fur, ent... more The blind mole rat, Spalax ehrenbergi, can, despite severely degenerated eyes covered by fur, entrain to the daily light/dark cycle and adapt to seasonal changes due to an intact circadian timing system. The present study demonstrates that the Spalax retina contains a photoreceptor layer, an outer nuclear layer (ONL), an outer plexiform layer (OPL), an inner nuclear layer (INL), an inner plexiform layer (IPL), and a ganglion cell layer (GCL). By immunohistochemistry, the number of melanopsin (mRGCs) and non-melanopsin bearing retinal ganglion cells was analyzed in detail. Using the ganglion cell marker RNA-binding protein with multiple splicing (RBPMS) it was shown that the Spalax eye contains 890 ± 62 RGCs. Of these, 87% (752 ± 40) contain melanopsin (cell density 788 melanopsin RGCs/mm 2). The remaining RGCs were shown to co-store Brn3a and calretinin. The melanopsin cells were located mainly in the GCL with projections forming two dendritic plexuses located in the inner part of the IPL and in the OPL. Few melanopsin dendrites were also found in the ONL. The Spalax retina is rich in rhodopsin and long/middle wave (L/M) cone opsin bearing photoreceptor cells. By using Ctbp2 as a marker for ribbon synapses, both rods and L/M cone ribbons containing pedicles in the OPL were found in close apposition with melanopsin dendrites in the outer plexus suggesting direct synaptic contact. A subset of cone bipolar cells and all photoreceptor cells contain recoverin while a subset of bipolar and amacrine cells contain calretinin. The calretinin expressing amacrine cells seemed to form synaptic contacts with rhodopsin containing photoreceptor cells in the OPL and contacts with melanopsin cell bodies and dendrites in the IPL. The study demonstrates the complex retinal circuitry used by the Spalax to detect light, and provides evidence for both melanopsin and non-melanopsin projecting pathways to the brain.

BMC Biology, 2013

Background: Subterranean blind mole rats (Spalax) are hypoxia tolerant (down to 3% O 2), long liv... more Background: Subterranean blind mole rats (Spalax) are hypoxia tolerant (down to 3% O 2), long lived (>20 years) rodents showing no clear signs of aging or aging related disorders. In 50 years of Spalax research, spontaneous tumors have never been recorded among thousands of individuals. Here we addressed the questions of (1) whether Spalax is resistant to chemically-induced tumorigenesis, and (2) whether normal fibroblasts isolated from Spalax possess tumor-suppressive activity. Results: Treating animals with 3-Methylcholantrene (3MCA) and 7,12-Dimethylbenz(a) anthracene/ 12-O-tetradecanoylphorbol-13-acetate (DMBA/TPA), two potent carcinogens, confirmed Spalax high resistance to chemically induced cancers. While all mice and rats developed the expected tumors following treatment with both carcinogens, among Spalax no tumors were observed after DMBA/TPA treatment, while 3MCA induced benign fibroblastic proliferation in 2 Spalax individuals out of12, and only a single animal from the advanced age group developed malignancy 18 months post-treatment. The remaining animals are still healthy 30 months post-treatment. In vitro experiments showed an extraordinary ability of normal Spalax cultured fibroblasts to restrict malignant behavior in a broad spectrum of human-derived and in newly isolated Spalax 3MCA-induced cancer cell lines. Growth of cancer cells was inhibited by either direct interaction with Spalax fibroblasts or with soluble factors released into culture media and soft agar. This was accompanied by decreased cancer cell viability, reduced colony formation in soft agar, disturbed cell cycle progression, chromatin condensation and mitochondrial fragmentation. Cells from another cancer resistant subterranean mammal, the naked mole rat, were also tested for direct effect on cancer cells and, similar to Spalax, demonstrated anti-cancer activity. No effect on cancer cells was observed using fibroblasts from mouse, rat or Acomys. Spalax fibroblast conditioned media had no effect on proliferation of noncancerous cells. Conclusions: This report provides pioneering evidence that Spalax is not only resistant to spontaneous cancer but also to experimentally induced cancer, and shows the unique ability of Spalax normal fibroblasts to inhibit growth and kill cancer cells, but not normal cells, either through direct fibroblast-cancer cell interaction or via soluble factors. Obviously, along with adaptation to hypoxia, Spalax has evolved efficient anti-cancer mechanisms yet to be elucidated. Exploring the molecular mechanisms allowing Spalax to survive in extreme environments and to escape cancer as well as to kill homologous and heterologous cancer cells may hold the key for understanding the molecular nature of host resistance to cancer and identify new anti-cancer strategies for treating humans.

Background: Subterranean blind mole rats (Spalax) are hypoxia tolerant (down to 3% O2), long live... more Background: Subterranean blind mole rats (Spalax) are hypoxia tolerant (down to 3% O2), long lived (>20 years) rodents showing no clear signs of aging or aging related disorders. In 50 years of Spalax research, spontaneous tumors have never been recorded among thousands of individuals. Here we addressed the questions of (1) whether Spalax is resistant to chemically-induced tumorigenesis, and (2) whether normal fibroblasts isolated from Spalax possess tumor-suppressive activity. Results: Treating animals with 3-Methylcholantrene (3MCA) and 7,12-Dimethylbenz(a) anthracene/ 12-O-tetradecanoylphorbol-13-acetate (DMBA/TPA), two potent carcinogens, confirmed Spalax high resistance to chemically induced cancers. While all mice and rats developed the expected tumors following treatment with both carcinogens, among Spalax no tumors were observed after DMBA/TPA treatment, while 3MCA induced benign fibroblastic proliferation in 2 Spalax individuals out of12, and only a single animal from th...

Nature Biotechnology

ABSTRACT In this review we summarize the current knowledge of polypeptide growth factors, their r... more ABSTRACT In this review we summarize the current knowledge of polypeptide growth factors, their receptors and oncogenes. Recent studies indicate that oncogenes are linked to growth factors and to growth factor receptors, suggesting that these molecules participate in the proliferation of normal and neoplastic cells.

The Quintessential NaturalistHonoring the Life and Legacy of Oliver P. Pearson, 2007

Fibroblast growth factors (FGF) are multifunctional, heparin binding polypeptides that share stru... more Fibroblast growth factors (FGF) are multifunctional, heparin binding polypeptides that share structural similarity, but differ in their target cell specificity and expression pattern. Here we describe the cloning and expression of the mouse homologue of FGF9, and the use of a panel of soluble FGF receptors and genetically engineered cells to study its receptor binding specificity. FGF9 is found to bind with high affinity (kd: 0.25 nM) to FGFR3, for which a specific ligand has not yet been identified. FGF9 can also bind, albeit with a lower affinity, to FGFR2 but does not bind FGFR1 or FGFR4. There is no significant binding to either FGFR3 or FGFR2, expressed either as soluble receptors or in heparin sulfate deficient cells, in the absence of heparin. Moreover, receptor binding of FGF9 requires heparin in a manner specific to the receptor type. In conclusion FGF9 presents a unique case of ligand-receptor specificity and fulfills the criteria as a high affinity, heparin-dependent ligand for FGFR3.

Journal of Biological Rhythms, Feb 1, 2004

The blind subterranean mole rat superspecies Spalax ehrenbergi is an extreme example of mammalian... more The blind subterranean mole rat superspecies Spalax ehrenbergi is an extreme example of mammalian adaptation to life underground. Though this rodent is totally visually blind, harboring a drastically degenerated subcutaneous rudimentary eye, its daily activity rhythm is entrainable to LD cycles. This indicates that it confers light information to the clock, as has been previously shown by the authors in behavioral studies as well as by molecular analyses of its Clock/MOP3 and its three Per genes. The Cryptochrome (Cry) genes found in animals and plants act both as photoreceptors and as essential components of the negative feedback mechanism of the biological clock. To further understand the circadian system of this unique mammal, the authors cloned and characterized the open reading frame of Spalax Cry1 and Cry2. The Spalax CRY1 protein is significantly closer to the human homolog than to the mice one, in contrast to the evolutionary expectations. They have found two isoforms of Cry2 in Spalax, which differ in their 5' end of the open reading frame and defined their expression in Spalax populations. They found a large and significant excess of heterozygotes of sCry2 (sCry2L/S genotype). Both sCry1 and sCry2 mRNAs were found in the SCN, the eye, the harderian gland, as well as in a wide range of peripheral tissues. Their expression pattern under different LD conditions has also been analyzed. As was already shown for other circadian genes, despite being blind and living in darkness, the Cry genes of Spalax behave in a similar, though not identical, pattern as in sighted animals. Once again, the results indicate that the uniquely hypertrophied harderian gland of Spalax plays a key role in its circadian system.

J Biol Chem, 2003

Cytoglobin is a recently discovered vertebrate globin distantly related to myoglobin, and its fun... more Cytoglobin is a recently discovered vertebrate globin distantly related to myoglobin, and its function is unknown. Here we present the first detailed analysis of the distribution and expression of cytoglobin. Northern and Western blotting experiments show the presence of cytoglobin mRNA and protein in a broad range of tissues. Quantitative PCR demonstrates an up-regulation of cytoglobin mRNA levels in rat heart and liver under hypoxic conditions (22 and 44 h of 9% oxygen). Immunofluorescence studies with three antibodies directed against different epitopes of the protein consistently show cytoglobin in connective tissue fibroblasts as well as in hepatic stellate cells. Cytoglobin is also present in chondroblasts and osteoblasts and shows a decreased level of expression upon differentiation to chondrocytes and osteocytes. Cytoglobin is located in the cytoplasm of these cell types. Evidence against an exclusively nuclear localization of cytoglobin, as recently proposed, is also provided by transfection assays with green fluorescent protein fusion constructs, which demonstrates the absence of an active nuclear import. The differential expression of cytoglobin argues against a general respiratory function of this molecule, but rather indicates a connective tissue-specific function. We hypothesize that cytoglobin may be involved in collagen synthesis. Cytoglobin expression was also observed in some neuronal subpopulations of the central and the peripheral nervous systems. Surprisingly, cytoglobin is localized in both the cytoplasm and nucleus of neurons, indicating a possible additional role of this protein in neuronal tissues.

Human Molecular Genetics, May 1, 2001

To explore the role of DCX in differentiation and signal transduction we overexpressed DCX in PC1... more To explore the role of DCX in differentiation and signal transduction we overexpressed DCX in PC12 cells. Our results indicate that DCX stabilizes microtubules and inhibits neurite outgrowth in nerve growth factor-induced differentiation. However, neurite length is increased when differentiation is induced by epidermal growth factor and forskolin or by dibutyryl-cAMP. Furthermore, CREB-mediated transcription is downregulated, supporting the notion that cytoskeletal regulatory proteins can affect the transcriptional state of a cell. Using different constructs and mutations we reach the conclusion that microtubule stabilization is a key factor, but not the only one, in controlling neurite extension. Overexpression of a mutation found in a lissencephaly patient (S47R), completely blocks neurite outgrowth. We propose that these functions are important during normal and abnormal brain development.

Gene, 2015

The Nrf2-Keap1 pathway is crucial for the cellular antioxidant and hypoxia response in vertebrate... more The Nrf2-Keap1 pathway is crucial for the cellular antioxidant and hypoxia response in vertebrates. Deciphering its modifications in hypoxia-adapted animals will help understand its functionality under environmental stress and possibly allow for knowledge transfer into biomedical research. The blind mole rat Spalax, a long-lived cancer-resistant rodent, lives in burrows underground and is adapted to severely hypoxic conditions. Here we have conducted a bioinformatical survey of Spalax core genes from the Nrf2-Keap1 pathway on the coding sequence level in comparison to other hypoxia-tolerant and -sensitive rodents. We find strong sequence conservation across all genes, illustrating the pathway&amp;#39;s importance. One of the central players however, Spalax Keap1, shows a non-conservative amino acid substitution from tyrosine to cysteine in its intervening region (IVR) domain. Cysteines in this location have been shown to be of high functional relevance to the binding and degradation of Nrf2. Therefore, this peculiar substitution could influence the cellular Nrf2 levels in Spalax and, thereby, downstream gene expression in the antioxidant pathway, contributing to the special adaptive phenotype of the blind mole rat.

Oncogene

Fibroblast growth factors (FGFs) and their receptors play an important role in cell growth, angio... more Fibroblast growth factors (FGFs) and their receptors play an important role in cell growth, angiogenesis and embryonal development. Four distinct genes encoding fibroblast growth factor receptors (FGFRs) were identified: flg, encoding FGFR1, bek encoding FGFR2, and the genes for FGFR3 and FGFR4. Both FGFR2 and keratinocyte growth factor receptor (KGFR) are encoded by the same gene, bek. To study the regulation of expression of the FGF receptors we analysed the DNA sequence flanking the 5' region of the cDNA of murine FGFR2 to seek elements that control its transcription. A 5-kbp fragment containing the 5' end of the cDNA was isolated from mouse genomic library and used to map the promoter region. We found that the sequence encoding the 5' non-translated region of the FGFR2/KGFR cDNA contains an intron located 210 bp upstream from the translation start site. Using RNAase protection and primer extension, we identified the mRNA start 37 bp upstream from the beginning of the...

Molecular and cellular biochemistry, 2001

The ATP-sensitive potassium (KATP) channel is thought to play an important role in the protection... more The ATP-sensitive potassium (KATP) channel is thought to play an important role in the protection of heart and brain against tissue hypoxia. The genetic regulation of the components of the channel by hypoxia has not been previously described. Here, we investigated the regulation of the two pore-forming channel proteins, Kir6.1 and Kir6.2, in response to hypoxia in vivo and in vitro. We find that these two structurally-related inwardly-rectifying potassium channel proteins are reciprocally regulated by hypoxia in vivo, with upregulation of Kir6.1 and down-regulation of Kir6.2, thereby resulting in a significant change in the composition of the channel complex in response to hypoxia. In vitro we describe neuronal and cardiac cell lines in which Kir6.1 is up-regulated by hypoxia, demonstrating that Kir6.1 is a hypoxia-inducible gene. We conclude that the heart and brain display genetic plasticity in response to hypoxic stress through specific genetic reprograming of cytoprotective chan...

Oncogene, 1991

Transmembrane tyrosine kinases are involved in the control of cell growth and differentiation by ... more Transmembrane tyrosine kinases are involved in the control of cell growth and differentiation by extracellular signals. To enable identification of new receptor tyrosine kinases we developed a method that selectively amplifies segments of receptor genes. The method is based on a combination of polymerase chain reaction (PCR) and hybridization screening and it employs three oligonucleotide primers derived from conserved domains of receptor tyrosine kinases. It yields amplification of receptors' genes and appears to ignore cytoplasmic tyrosine kinases. When applied to RNA from 12.5 days post coitum mouse placenta, this methodology resulted in the detection of several putative or established receptors. Molecular cloning of one of these genes, which is identical to the partially characterized bek gene, identified a transmembrane tyrosine kinase with three immunoglobulin-like domains in the extracellular portion, and a cytoplasmic tyrosine kinase sequence. The isolated cDNA shows rem...

Proceedings of the National Academy of Sciences, 2009

Heparanase is an endoglycosidase that degrades heparan sulfate (HS) at the cell surface and in th... more Heparanase is an endoglycosidase that degrades heparan sulfate (HS) at the cell surface and in the extracellular matrix. Heparanase is expressed mainly by cancer cells, and its expression is correlated with increased tumor aggressiveness, metastasis, and angiogenesis. Here, we report the cloning of a unique splice variant (splice 36) of heparanase from the subterranean blind mole rat (Spalax). This splice variant results from skipping part of exon 3, exons 4 and 5, and part of exon 6 and functions as a dominant negative to the wild-type enzyme. It inhibits HS degradation, suppresses glioma tumor growth, and decreases experimental B16 -BL6 lung colonization in a mouse model. Intriguingly, Spalax splice variant 7 of heparanase (which results from skipping of exon 7) is devoid of enzymatic activity, but unlike splice 36 it enhances tumor growth. Our results demonstrate that alternative splicing of heparanase regulates its enzymatic activity and might adapt the heparanase function to the fluctuating normoxic-hypoxic subterranean environment that Spalax experiences. Development of anticancer drugs designed to suppress tumor growth, angiogenesis, and metastasis is a major challenge, of which heparanase inhibition is a promising approach. We anticipate that the heparanase splicing model, evolved during 40 million years of Spalacid adaptation to underground life, would pave the way for the development of heparanase-based therapeutic modalities directed against angiogenesis, tumor growth, and metastasis. alternative splicing ͉ angiogenesis ͉ blind mole rat ͉ cancer ͉ heparan sulfate

Cell cycle (Georgetown, Tex.), Jan 15, 2010

The tumor suppressor gene, p53, in response to DNA damage/hypoxia, induces growth arrest and/or a... more The tumor suppressor gene, p53, in response to DNA damage/hypoxia, induces growth arrest and/or apoptosis. Inactivation of p53, by mutations and/or overexpression of the mdm2 gene, confers a selective advantage to tumor cells under hypoxic microenvironment during tumor progression. The mole rat, Spalax, spends its life underground at low-oxygen tensions and hence has developed a wide range of respiratory/molecular adaptations to hypoxic stress. We previously reported that the highly conserved p53 Arg(R)-174 is substituted by lysine (K) in Spalax, identical to a tumor-associated mutation. Functionality assays revealed that Spalax p53 and human R174K-mutated p53 were unable to induce human/Spalax apaf1, an apoptotic target gene, while over-activating the mdm2 gene. Moreover, cells transfected with human p53 underwent more extensive apoptosis (44.8%) as compared to Spalax p53 (23.2%) transfected cells. To support our hypothesis that the pattern of activity in Spalax is related to hypox...

Cardiovascular diabetology, Jan 18, 2003

Angiogenic therapy with vascular endothelial growth factor (VEGF) has been proposed as a treatmen... more Angiogenic therapy with vascular endothelial growth factor (VEGF) has been proposed as a treatment paradigm for patients suffering from an insufficiency of collateral vessels. Diabetes is associated with increase in the production of VEGF and therefore additional VEGF may not be beneficial. Accordingly, we sought to determine the efficacy of VEGF therapy to augment collateral formation and tissue perfusion in a diabetic mouse ischemic hindlimb model. Diabetic and non-diabetic mice were studied in parallel for the efficacy of VEGF administration. Diabetes was induced with streptozotocin. Hindlimb ischemia was produced by severing the left iliac artery. An outlet tube from an osmotic infusion pump with placebo/500 micrograms of plasmid-DNA encoding VEGF was fenestrated and tunneled into the left quadriceps muscle. VEGF induced more rapid and complete restoration of blood flow in normal mice. However, in the setting of diabetes there was no difference between VEGF vs. placebo in the ra...