Vascular pathology: Cause or effect in Alzheimer disease? / Patología vascular: ¿causa o efecto en la enfermedad de Alzheimer?

INTRODUCTION: Alzheimer disease (AD) is the main cortical neurodegenerative disease. The incidence of this disease increases with age, causing significant medical, social and economic problems, especially in countries with ageing populations. OBJECTIVE: This review aims to highlight existing evidence of how vascular dysfunction may contribute to cognitive impairment in AD, as well as the therapeutic possibilities that might arise from this evidence. DEVELOPMENT: The vascular hypothesis emerged as an alternative to the amyloid cascade hypothesis as an explanation for the pathophysiology of AD. This hypothesis locates blood vessels as the origin for a variety of pathogenic pathways that lead to neuronal damage and dementia. Destruction of the organisation of the blood brain barrier, decreased cerebral blood flow, and the establishment of an inflammatory context would thus be responsible for any subsequent neuronal damage since these factors promote aggregation of ß-amyloid peptide in the brain. The link between neurodegeneration and vascular dysfunction pathways has provided new drug targets and therapeutic approaches that will add to the treatments for AD. CONCLUSIONS: It is difficult to determine whether the vascular component in AD is the cause or the effect of the disease, but there is no doubt that vascular pathology has an important relationship with AD. Vascular dysfunction is likely to act synergistically with neurodegenerative changes in a cycle that exacerbates the cognitive impairment found in AD.

Signaling by type I and II cytokine receptors: ten years after.

Discovered during the past ten years, Janus kinases and signal transducers and activators of transcription have emerged as critical elements in cytokine signaling and immunoregulation. Recently, knockout mice for all the members of these families have been generated, with remarkably specific outcomes. Equally exciting is the discovery of a new class of inhibitors, the suppressor of cytokine signaling family. The phenotypes of mice deficient in these molecules are also striking, underscoring the importance of negative regulation in cytokine signaling.

Inhibition of HMGI-C protein synthesis suppresses retrovirally induced neoplastic transformation of rat thyroid cells.

Elevated expression of the three high-mobility group I (HMGI) proteins (HMGI, HMGY, and HMGI-C) has previously been correlated with the presence of a highly malignant phenotype in epithelial and fibroblastic rat thyroid cells and in experimental thyroid, lung, mammary, and skin carcinomas. Northern (RNA) blot and run-on analyses demonstrated that the induction of HMGI genes in transformed thyroid cells occurs at the transcriptional level. An antisense methodology to block HMGI-C protein synthesis was then used to analyze the role of this protein in the process of thyroid cell transformation. Transfection of an antisense construct for the HMGI-C cDNA into normal thyroid cells, followed by infection with transforming myeloproliferative sarcoma virus or Kirsten murine sarcoma virus, generated cell lines that expressed significant levels of the retroviral transforming oncogenes v-mos or v-ras-Ki and removed the dependency on thyroid-stimulating hormones. However, in contrast with untransfected cells or cells transfected with the sense construct, those containing the antisense construct did not demonstrate the appearance of any malignant phenotypic markers (growth in soft agar and tumorigenicity in athymic mice). A great reduction of the HMGI-C protein levels and the absence of the HMGI(Y) proteins was observed in the HMGI-C antisense-transfected, virally infected cells. Therefore, the HMGI-C protein seems to play a key role in the transformation of these thyroid cells.

Rat protein tyrosine phosphatase eta suppresses the neoplastic phenotype of retrovirally transformed thyroid cells through the stabilization of p27(Kip1).

The r-PTPeta gene encodes a rat receptor-type protein tyrosine phosphatase whose expression is negatively regulated by neoplastic cell transformation. Here we first demonstrate a dramatic reduction in DEP-1/HPTPeta (the human homolog of r-PTPeta) expression in a panel of human thyroid carcinomas. Subsequently, we show that the reexpression of the r-PTPeta gene in highly malignant rat thyroid cells transformed by retroviruses carrying the v-mos and v-ras-Ki oncogenes suppresses their malignant phenotype. Cell cycle analysis demonstrated that r-PTPeta caused G(1) growth arrest and increased the cyclin-dependent kinase inhibitor p27(Kip1) protein level by reducing the proteasome-dependent degradation rate. We propose that the r-PTPeta tumor suppressor activity is mediated by p27(Kip1) protein stabilization, because suppression of p27(Kip1) protein synthesis using p27-specific antisense oligonucleotides blocked the growth-inhibitory effect induced by r-PTPeta. Furthermore, we provide evidence that in v-mos- or v-ras-Ki-transformed thyroid cells, the p27(Kip1) protein level was regulated by the mitogen-activated protein (MAP) kinase pathway and that r-PTPeta regulated p27(Kip1) stability by preventing v-mos- or v-ras-Ki-induced MAP kinase activation.

Increased in vivo phosphorylation of ret tyrosine 1062 is a potential pathogenetic mechanism of multiple endocrine neoplasia type 2B.

Mutations of the Ret receptor tyrosine kinase are responsible for inheritance of multiple endocrine neoplasia (MEN2A and MEN2B) and familial medullary thyroid carcinoma syndromes. Although several familial medullary thyroid carcinoma and most MEN2A mutations involve substitutions of extracellular cysteine residues, in most MEN2B cases there is a methionine-to-threonine substitution at position 918 (M918T) of the Ret kinase domain. The mechanism by which the MEN2B mutation converts Ret into a potent oncogene is poorly understood. Both MEN2A and MEN2B oncoproteins exert constitutive activation of the kinase. However, the highly aggressive MEN2B phenotype is not supported by higher levels of Ret-MEN2B kinase activity compared with Ret-MEN2A. It has been proposed that Ret-MEN2B is more than just an activated Ret kinase and that the M918T mutation, by targeting the kinase domain of Ret, might alter Ret substrate specificity, thus affecting Ret autophosphorylation sites and the ability of Ret to phosphorylate intracellular substrates. We show that the Ret-MEN2B mutation causes specific potentiated phosphorylation of tyrosine 1062 (Y1062) compared with Ret-MEN2A. Phosphorylated Y1062 is part of a Ret multiple effector docking site that mediates recruitment of the Shc adapter and of phosphatidylinositol-3 kinase (PI3K). Accordingly, we show that Ret-MEN2B is more active than Ret-MEN2A in associating with She and in causing constitutive activation of the Ras/mitogen-activated protein kinase and PI3K/Akt cascades. We conclude that the MEN2B mutation specifically potentiates the ability of Ret to autophosphorylate Y1062 and consequently to couple to the Ras/mitogen-activated protein kinase and the PI3K/Akt pathways. The more efficient triggering of these pathways may account for the difference between MEN2A and MEN2B syndromes.

Overexpression of the HIP gene coding for a heparin/heparan sulfate-binding protein in human thyroid carcinomas.

A subtractive library screening was performed to identify changes in gene expression that occur during the process of neoplastic transformation of thyroid cells. A cDNA library was constructed from a human thyroid papillary carcinoma cell line (NPA) subtracted with cDNAs from normal thyroid cells (HTC 2). The differential screening of this library lead to the isolation of 39 cDNA clones; six of them showed homology with a recently isolated gene, named HIP, that codes for a protein belonging to a novel class of heparin/heparan sulfate-binding proteins. Northern blot analysis revealed HIP gene overexpression in all of the human thyroid carcinoma cell lines analyzed, as compared to the HTC 2 cells. HIP expression was particularly abundant in the anaplastic carcinoma-derived cell lines. The analysis of surgically removed thyroid tumors showed overexpression of HIP gene in all of the carcinomas, independent of the histotype, although the largest increase in HIP expression was observed in the undifferentiated forms. In contrast, none of the benign adenomas or normal thyroid tissues showed HIP overexpression. To establish the role of HIP overexpression in cell transformation, the NPA cell line was transfected with an eukaryotic expression vector carrying the HIP gene in the antisense orientation. Stable transfectants expressed reduced HIP mRNA levels and showed morphological changes, such as becoming spindle-shaped and growing scattered. The growth rate of the antisense clones was greatly reduced compared to the NPA cells transfected with the backbone vector. Taken together, these results indicate that HIP gene overexpression is associated with thyroid carcinogenesis and strongly suggest its involvement in thyroid cell growth regulation.

Tyrosine 1062 of RET-MEN2A mediates activation of Akt (protein kinase B) and mitogen-activated protein kinase pathways leading to PC12 cell survival.

The RET tyrosine kinase is a functional receptor for neurotrophic ligands of the glial cell line-derived neurotrophic factor (GDNF) family. Loss of function of RET is associated with congenital megacolon or Hirschsprung's disease, whereas germ-line point mutations causing RET activation are responsible for multiple endocrine neoplasia type 2 (MEN2A, MEN2B, and familial medullary thyroid carcinoma) syndromes. Here we show that the expression of a constitutively active RET-MEN2A oncogene promotes survival of rat pheochromocytoma PC12 cells upon growth factor withdrawal. Moreover, we show that the RET-MEN2A-mediated survival depends on signals transduced by the phosphoinositide 3-kinase (PI3K) and mitogen-activated protein kinase (MAPK) cascades. Thus, in PC12 cells, RET-MEN2A associates with the PI3K regulatory subunit p85 and promotes activation of Akt (also referred to as protein kinase B) in a PI3K-dependent fashion; in addition, RET-MEN2A promotes MAPK activation. PI3K recruitment and Akt activation as well as MAPK activation depend on RET-MEN2A tyrosine residue 1062. As a result, tyrosine 1062 of RET-MEN2A is essential for RET-MEN2A-mediated survival of PC12 cells cultured in growth factor-depleted media.

Akt/protein kinase B promotes survival and hormone-independent proliferation of thyroid cells in the absence of dedifferentiating and transforming effects.

The Akt/protein kinase B serine/threonine kinase is a downstream effector of phosphoinositide 3-kinase (PI3K). Akt is an important component of mitogenic and antiapoptotic signaling pathways and is implicated in neoplastic transformation. Thyroid cells in culture retain a differentiated phenotype consisting of epithelial cell morphology and the expression of several tissue-specific genes. The survival and proliferation of these cells depend on thyrotropin and a mixture of five additional hormones that includes insulin. The regulation of proliferation and the expression of the thyroid differentiation program are intimately connected processes. As a result, oncogenes that induce hormone-independent proliferation invariably impair the expression of the thyroid-specific differentiation markers. Given that thyrotropin and insulin stimulate Akt activation in thyroid cells, we set out to determine the effects of Akt on thyroid cell proliferation, survival, and differentiation. To this end, we expressed constitutively active myristylated Akt (myrAkt) in PC Cl 3 thyroid cells. The myrAkt-expressing cells continued to proliferate, even in the absence of hormones, and they were resistant to programmed cell death induced by starvation. These effects were paralleled by the induction of the G1 cyclins D3 and E and by the inhibition of induction of the proapoptotic Fas, Fas ligand, and BAD genes in starved cells. However, in marked contrast with several other oncogenes, myrAkt did not interfere with the expression of thyroid differentiation functions. These results unveil the existence of an Akt-triggered thyroid cell pathway that modulates proliferation and survival without affecting the expression of the thyroid cell differentiated phenotype.

Ret-mediated mitogenesis requires Src kinase activity.

The proto-oncogene RET encodes a transmembrane growth neurotrophic receptor with tyrosine kinase (TK) activity. RET mutations are associated with several human neoplastic and nonneoplastic diseases, including thyroid papillary carcinoma, multiple endocrine neoplasia type 2 syndromes, and Hirschsprung's disease. Activation of receptor TKs results in the binding and activation of downstream signaling proteins, among which are nonreceptor TKs of the Src family. To test the involvement of c-Src in Ret-mediated signaling, we measured the levels of c-Src activity in NIH3T3 cells coexpressing Ret and the accessory GFR alpha-1 receptor or an epidermal growth factor receptor/Ret chimeric receptor when the cells were stimulated by glial cell line-derived neurotrophic factor or epidermal growth factor, respectively. Ret stimulation resulted in the activation of c-Src. We also measured the levels of Src kinase activity in cell lines expressing isoforms of the Ret receptor activated by different mutations. These cells showed higher Src kinase activity than the normal counterpart. Furthermore, we show that Ret is able to associate with the SH2 domain of Src in a phosphotyrosine-dependent fashion. Microinjection of a kinase inactive mutant of c-Src blocked Ret-mediated mitogenic effect. These experiments demonstrate that activated Ret is able to bind and stimulate c-Src kinase and that Src activation is essential for the mitogenic activity of Ret.

The RFG oligomerization domain mediates kinase activation and re-localization of the RET/PTC3 oncoprotein to the plasma membrane.

The RET/PTC3 oncogene arises from the fusion between the N-terminal encoding domain of the RFG gene and the tyrosine kinase encoding domain of RET receptor. RET/PTC3 is very frequent in papillary thyroid carcinomas, especially in children exposed to the Chernobyl accident. We have studied the functional consequences of the RFG-RET fusion. Here we show that the N-terminal coiled-coil domain of RGF mediates oligomerization and activation of the kinase and of the transforming capability of RET/PTC3. In addition, the RFG coiled-coil domain mediates a physical association between RET/PTC3 and RGF proteins, rendering RFG a bona fide substrate of RET/PTC3 kinase. Finally, we show that the coiled-coil domain of RGF is essential for the distribution of the RET/PTC3 protein at the membrane/particulate cell compartment level, where also most of the RFG protein is localized. We propose that fusion to the RFG coiled-coil domain provides RET kinase with a scaffold that mediates oligomerization and re-localization of the RET/PTC3 protein, a process that may be crucial for the signalling of this specific RET/PTC variant.

RET/PTC oncogene activation is an early event in thyroid carcinogenesis.

RET/PTC oncogene activation occurs in about 20% of human thyroid papillary carcinomas. However, it is not known yet whether it is an early or late event in the process of thyroid carcinogenesis. Here we demonstrate, by using a combined immunohistochemical and reverse transcriptase-polymerase chain reaction based approach, that RET/PTC activation is present in 11 out of 26 occult thyroid papillary carcinomas analysed. Therefore, we conclude that it represents an early event in the process of thyroid cell transformation.

High level expression of the HMGI (Y) gene during embryonic development.

The HMGI protein family includes three proteins, named HMG-I, HMG-Y and HMGI-C. The first two proteins are coded for by the same gene, HMGI (Y), through an alternative splicing mechanism. Their expression is elevated in neoplastic tissues and cells and this overexpression has a causal role in the process of cellular neoplastic transformation. We demonstrate that the HMGI (Y) gene is expressed at very low levels in normal adult tissues, whereas in embryonic tissues it is expressed at high levels comparable to those detected in neoplastic tissues. Specifically, a very high expression of the HMGI (Y) gene was detected in all embryonic tissues at 8.5 dpc. Then in the following days, even though the gene is expressed essentially in all tissues, an abundant gene expression was restricted to some tissues. These results indicate an important role of the HMGI (Y) gene in development.

The expression of the high mobility group HMGI (Y) proteins correlates with the malignant phenotype of human thyroid neoplasias.

High Mobility Group I (HMGI) proteins are nuclear proteins involved in the regulation of chromatin structure and function. Elevated expression of the HMGI proteins (HMGI, HMGY and HMGI-C) has been correlated with the presence of a highly malignant phenotype in epithelial and fibroblastic rat thyroid cells, and in several experimental carcinomas. Here, we demonstrate that HMGI and HMGY proteins are expressed in human thyroid carcinomas and thyroid carcinoma cell lines, but not in adenomas, goiters, normal thyroid tissues and cells. These results indicate a correlation between HMGI and HMGY expression and the malignant phenotype of thyroid neoplasias, suggesting that these proteins may be used as markers in thyroid cancer.

Expression of the neoplastic phenotype by human thyroid carcinoma cell lines requires NFkappaB p65 protein expression.

We have investigated the role of the NFkappaB complex in the process of thyroid carcinogenesis by analysing thyroid carcinoma cell lines. A significant increase in p65 NFkappaB mRNA and protein expression, compared to normal thyroid cultures or tissue, was found in all of the cancer cell lines. Conversely, only a modest increase in the p50 NFkappaB mRNA and protein was found in most, but not all carcinoma cell lines. The block of p65 protein synthesis with specific antisense oligonucleotides greatly reduced the ability of two undifferentiated carcinoma cell lines to form colonies in agar and reduced their growth rate. On the other hand, no effect was observed in the same cell lines when treated with p50 specific antisense oligonucleotides. These inhibitory effects seem to be mediated by the suppression of c-myc gene expression, since treatment with antisense oligonucleotides for p65 gene interfered negatively with c-myc gene expression. Our results indicate that activation of the NFkappaB complex by overexpression of p65 plays a critical role in the process of thyroid cell transformation.

Signalling of the Ret receptor tyrosine kinase through the c-Jun NH2-terminal protein kinases (JNKS): evidence for a divergence of the ERKs and JNKs pathways induced by Ret.

The RET proto-oncogene encodes a functional receptor tyrosine kinase (Ret) for the Glial cell line Derived Neurotrophic Factor (GDNF). RET is involved in several neoplastic and non-neoplastic human diseases. Oncogenic activation of RET is detected in human papillary thyroid tumours and in multiple endocrine neoplasia type 2 syndromes. Inactivating mutations of RET have been associated to the congenital megacolon, i.e. Hirschprung's disease. In order to identify pathways that are relevant for Ret signalling to the nucleus, we have investigated its ability to induce the c-Jun NH2-terminal protein kinases (JNK). Here we show that triggering the endogenous Ret, expressed in PC12 cells, induces JNK activity; moreover, Ret is able to activate JNK either when transiently transfected in COS-1 cells or when stably expressed in NIH3T3 fibroblasts or in PC Cl 3 epithelial thyroid cells. JNK activation is dependent on the Ret kinase function, as a kinase-deficient RET mutant, associated with Hirschsprung's disease, fails to activate JNK. The pathway leading to the activation of JNK by RET is clearly divergent from that leading to the activation of ERK: substitution of the tyrosine 1062 of Ret, the Shc binding site, for phenylalanine abrogates ERK but not JNK activation. Experiments conducted with dominant negative mutants or with negative regulators demonstrate that JNK activation by Ret is mediated by Rho/Rac related small GTPases and, particularly, by Cdc42.

Loss of fibula in mice overexpressing Hoxc11.

This study demonstrates severe malformations of the appendicular skeleton in mice overexpressing Hoxc11. Consistent with the endogenous expression pattern, the most conspicuous defect in Hoxc11 overexpressing neonates is aplasia/hypoplasia of the fibula. This is preceded at day 15.5 of embryonic development by marked reduction of chondrocyte proliferation, lack of PTHR expressing prehypertrophic cells, and the absence of hypertrophic and calcifying chondrocytes. Combined with the lack of an overt phenotype in the majority of Hoxc11 overexpressing embryos at day 13.5, the data suggest inhibition of chondrocyte differentiation during the elongation phase of the fibula bone as a primary effect of elevated Hoxc11 expression. This interpretation is further corroborated by Hoxc11 reporter gene expression in the joint areas at embryonic day 15.5, suggesting an involvement of the periarticular perichondrium in generating the mutant phenotype.

Block of c-myc expression by antisense oligonucleotides inhibits proliferation of human thyroid carcinoma cell lines.

Although elevated c-myc expression seems to be related to an unfavorable prognosis of human thyroid neoplasias, the role of c-myc overexpression in the process of thyroid carcinogenesis is still unknown. We analyzed c-myc expression in 7 human thyroid carcinoma cell lines, originating from different histotypes, and in 50 fresh thyroid tumors and found a higher level of c-myc mRNA in all the thyroid carcinoma cell lines and in several fresh thyroid tumors compared with normal thyroid. The highest increases occurred in the most malignant cell lines and in undifferentiated human thyroid carcinomas. The block of c-MYC protein synthesis with myc-specific antisense oligonucleotides reduced the growth rate of the thyroid carcinoma cell lines significantly. Our results indicate that c-myc overexpression plays a critical role in the growth of thyroid cancer cells, which supports the hypothesis that the myc proto-oncogene might be involved in the neoplastic progression of thyroid carcinogenesis.

The Fcp1-Wee1-Cdk1 axis affects spindle assembly checkpoint robustness and sensitivity to antimicrotubule cancer drugs.

To grant faithful chromosome segregation, the spindle assembly checkpoint (SAC) delays mitosis exit until mitotic spindle assembly. An exceedingly prolonged mitosis, however, promotes cell death and by this means antimicrotubule cancer drugs (AMCDs), that impair spindle assembly, are believed to kill cancer cells. Despite malformed spindles, cancer cells can, however, slip through SAC, exit mitosis prematurely and resist killing. We show here that the Fcp1 phosphatase and Wee1, the cyclin B-dependent kinase (cdk) 1 inhibitory kinase, play a role for this slippage/resistance mechanism. During AMCD-induced prolonged mitosis, Fcp1-dependent Wee1 reactivation lowered cdk1 activity, weakening SAC-dependent mitotic arrest and leading to mitosis exit and survival. Conversely, genetic or chemical Wee1 inhibition strengthened the SAC, further extended mitosis, reduced antiapoptotic protein Mcl-1 to a minimum and potentiated killing in several, AMCD-treated cancer cell lines and primary human adult lymphoblastic leukemia cells. Thus, the Fcp1-Wee1-Cdk1 (FWC) axis affects SAC robustness and AMCDs sensitivity.

Manipulation of cellular spheroid composition and the effects on vascular tissue fusion.

Cellular spheroids were investigated as tissue-engineered building blocks that can be fused to form functional tissue constructs. While spheroids can be assembled using passive contacts for the fusion of complex tissues, physical forces can be used to promote active contacts to improve tissue homogeneity and accelerate tissue fusion. Understanding the mechanisms affecting the fusion of spheroids is critical to fabricating tissues. Here, manipulation of the spheroid composition was used to accelerate the fusion process mediated by magnetic forces. The Janus structure of magnetic cellular spheroids spatially controls iron oxide magnetic nanoparticles (MNPs) to form two distinct domains: cells and extracellular MNPs. Studies were performed to evaluate the influence of extracellular matrix (ECM) content and cell number on the fusion of Janus magnetic cellular spheroids (JMCSs). Results showed that the integration of iron oxide MNPs into spheroids increased the production of collagen over time when compared to spheroids without MNPs. The results also showed that ring tissues composed of JMCSs with high ECM concentrations and high cell numbers fused together, but exhibited less contraction when compared to their lower concentration counterparts. Results from spheroid fusion in capillary tubes showed that low ECM concentrations and high cell numbers experienced more fusion and cellular intermixing over time when compared to their higher counterparts. These findings indicate that cell-cell and cell-matrix interactions play an important role in regulating fusion, and this understanding sets the rationale of spheroid composition to fabricate larger and more complex tissue-engineered constructs.

Oxidative stress triggers cytokinesis failure in hepatocytes upon isolation.

Primary hepatocytes are highly differentiated cells and proliferatively quiescent. However, the stress produced during liver digestion seems to activate cell cycle entry by proliferative/dedifferentiation programs that still remain unclear. The aim of this work was to assess whether the oxidative stress associated with hepatocyte isolation affects cell cycle and particularly cytokinesis, the final step of mitosis. Hepatocytes were isolated from C57BL/6 mice by collagenase perfusion in the absence and presence of N-acetyl cysteine (NAC). Polyploidy, cell cycle, and reactive oxygen species (ROS) were studied by flow cytometry (DNA, phospho-histone 3, and CellROX(®) Deep Red) and Western blotting (cyclins B1 and D1, and proliferating cell nuclear antigen). mRNA expression of cyclins A1, B1, B2, D1, and F by reverse transcription (RT)-PCR was also assessed. Glutathione levels were measured by mass spectrometry. Here we show that hepatocyte isolation enhanced cell cycle entry, increased hepatocyte binucleation, and caused marked glutathione oxidation. Addition of 5 mM NAC to the hepatocyte isolation media prevented glutathione depletion, partially blocked ROS production and cell cycle entry of hepatocytes, and avoided the blockade of mitosis progression, abrogating defective cytokinesis and diminishing the formation of binucleated hepatocytes during isolation. Therefore, addition of NAC to the isolation media decreased the generation of polyploid hepatocytes confirming that oxidative stress occurs during hepatocyte isolation and it is responsible, at least in part, for cytokinesis failure and hepatocyte binucleation.