Biomedical subjects

Frans C S Ramaekers

Publications and source records attributed to Frans C S Ramaekers.

At least 19 recordsLinked to original sources

PubMed2007

Nucleoplasmic LAP2alpha-lamin A complexes are required to maintain a proliferative state in human fibroblasts.

In human diploid fibroblasts (HDFs), expression of lamina-associated polypeptide 2 alpha (LAP2alpha) upon entry and exit from G(0) is tightly correlated with phosphorylation and subnuclear localization of retinoblastoma protein (Rb). Phosphoisoforms of Rb and LAP2alpha are down-regulated in G(0). Although RbS780 phosphoform and LAP2alpha are up-regulated upon reentry into G(1) and colocalize in the nucleoplasm, RbS795 migrates between nucleoplasmic and speckle compartments. In HDFs, which are null for lamins A/C, LAP2alpha is mislocalized within nuclear aggregates, and this is correlated with cell cycle arrest and accumulation of Rb within speckles. Nuclear retention of nucleoplasmic Rb during G(1) phase but not of speckle-associated Rb depends on lamin A/C. siRNA knock down of LAP2alpha or lamin A/C in HDFs leads to accumulation of Rb in speckles and G(1) arrest, probably because of activation of a cell cycle checkpoint. Our results suggest that LAP2alpha and lamin A/C are involved in controlling Rb localization and phosphorylation, and a lack or mislocalization of either protein leads to cell cycle arrest in HDFs.

Cell Cycle↗

PubMed2006

The inner nuclear membrane protein emerin regulates beta-catenin activity by restricting its accumulation in the nucleus.

Emerin is a type II inner nuclear membrane (INM) protein of unknown function. Emerin function is likely to be important because, when it is mutated, emerin promotes both skeletal muscle and heart defects. Here we show that one function of Emerin is to regulate the flux of beta-catenin, an important transcription coactivator, into the nucleus. Emerin interacts with beta-catenin through a conserved adenomatous polyposis coli (APC)-like domain. When GFP-emerin is expressed in HEK293 cells, beta-catenin is restricted to the cytoplasm and beta-catenin activity is inhibited. In contrast, expression of an emerin mutant, lacking its APC-like domain (GFP-emerinDelta), dominantly stimulates beta-catenin activity and increases nuclear accumulation of beta-catenin. Human fibroblasts that are null for emerin have an autostimulatory growth phenotype. This unusual growth phenotype arises through enhanced nuclear accumulation and activity of beta-catenin and can be replicated in wild-type fibroblasts by transfection with constitutively active beta-catenin. Our results support recent findings that suggest that INM proteins can influence signalling pathways by restricting access of transcription coactivators to the nucleus.

Cell Line↗

PubMed2006

Compound heterozygosity for mutations in LMNA causes a progeria syndrome without prelamin A accumulation.

LMNA-associated progeroid syndromes have been reported with both recessive and dominant inheritance. We report a 2-year-old boy with an apparently typical Hutchinson-Gilford progeria syndrome (HGPS) due to compound heterozygous missense mutations (p.T528M and p.M540T) in LMNA. Both mutations affect a conserved region within the C-terminal globular domain of A-type lamins, defining a progeria hot spot. The nuclei of the patient showed no prelamin A accumulation. In general, the nuclear phenotype did not correspond to that previously described for HGPS. Instead, honeycomb figures predominated and nuclear blebs with reduced/absent expression of B-type lamins could be detected. The healthy heterozygous parents showed similar nuclear changes, although in a smaller percentage of nuclei. Treatment with a farnesylation inhibitor resulted in accumulation of prelamin A at the nuclear periphery, in annular nuclear membrane plaques and in intra/trans-nuclear membrane invaginations. In conclusion, these findings suggest a critical role for the C-terminal globular lamin A/C region in nuclear structure and support a major contribution of abnormal assembly to the progeroid phenotype. In contrast to earlier suggestions, we show that prelamin A accumulation is not the major determinant of the progeroid phenotype.

Adult↗

PubMed2006

Gene expression of tumor angiogenesis dissected: specific targeting of colon cancer angiogenic vasculature.

Crucial to designing angiostatic and vascular targeting agents is the identification of target molecules. Because angiogenesis is not limited to pathologic conditions, careful evaluation of putative therapeutic targets is warranted to prevent adverse effects associated with impaired physiologic angiogenesis. To identify tumor-specific angiogenesis markers, we compared transcriptional profiles of angiogenic endothelial cells isolated from malignant and nonmalignant tissues with those of resting endothelial cells. We identified 17 genes that showed specific overexpression in tumor endothelium but not in angiogenic endothelium of normal tissues, creating a therapeutic window for tumor vasculature-specific targeting. Antibody targeting of 4 cell-surface-expressed or secreted products (vimentin, CD59, HMGB1, IGFBP7) inhibited angiogenesis in vitro and in vivo. Finally, targeting endothelial vimentin in a mouse tumor model significantly inhibited tumor growth and reduced microvessel density. Our results demonstrate the usefulness of the identification and subsequent targeting of specific tumor endothelial markers for anticancer therapy.

Animals↗

PubMed2006

Dietary plant sterols accumulate in the brain.

Dietary plant sterols and cholesterol have a comparable chemical structure. It is generally assumed that cholesterol and plant sterols do not cross the blood-brain barrier, but quantitative data are lacking. Here, we report that mice deficient for ATP-binding cassette transporter G5 (Abcg5) or Abcg8, with strongly elevated serum plant sterol levels, display dramatically increased (7- to 16-fold) plant sterol levels in the brain. Apolipoprotein E (ApoE)-deficient mice also displayed elevated serum plant sterol levels, which was however not associated with significant changes in brain plant sterol levels. Abcg5- and Abcg8-deficient mice were found to carry circulating plant sterols predominantly in high-density lipoprotein (HDL)-particles, whereas ApoE-deficient mice accommodated most of their serum plant sterols in very low-density lipoprotein (VLDL)-particles. This suggests an important role for HDL and/or ApoE in the transfer of plant sterols into the brain. Moreover, sitosterol upregulated apoE mRNA and protein levels in astrocytoma, but not in neuroblastoma cells, to a higher extend than cholesterol. In conclusion, dietary plant sterols pass the blood-brain barrier and accumulate in the brain, where they may exert brain cell type-specific effects.

ATP Binding Cassette Transporter, Subfamily G, Mem↗

PubMed2006

24(S)-hydroxycholesterol participates in a liver X receptor-controlled pathway in astrocytes that regulates apolipoprotein E-mediated cholesterol efflux.

Both apolipoprotein E (apoE) and 24(S)-hydroxycholesterol are involved in the pathogenesis of Alzheimer disease (AD). It has been hypothesized that apoE affects AD development via isoform-specific effects on lipid trafficking between astrocytes and neurons. However, the regulation of the cholesterol supply of neurons via apoE-containing high density lipoproteins remains to be clarified. We show for the first time that the brain-specific metabolite of cholesterol produced by neurons, i.e. 24(S)-hydroxycholesterol, induces apoE transcription, protein synthesis, and secretion in a dose- and time-dependent manner in cells of astrocytic but not of neuronal origin. Moreover, 24(S)-hydroxycholesterol primes astrocytoma, but not neuroblastoma cells, to mediate cholesterol efflux to apoE. Similar results were obtained using the synthetic liver X receptor (LXR) agonist GW683965A, suggesting involvement of an LXR-controlled signaling pathway. A 10-20-fold higher basal LXRalpha and -beta expression level in astrocytoma compared with neuroblastoma cells may underlie these differential effects. Furthermore, apoE-mediated cholesterol efflux from astrocytoma cells may be controlled by the ATP binding cassette transporters ABCA1 and ABCG1, since their expression was also up-regulated by both compounds. In contrast, ABCG4 seems not to be involved, because its expression was induced only in neuronal cells. The expression of sterol regulatory element-binding protein (SREBP-2), low density lipoprotein receptor, 3-hydroxy-3-methylglutaryl-CoA reductase, and SREBP-1c was transiently up-regulated by GW683965A in astrocytes but down-regulated by 24(S)-hydroxycholesterol, suggesting that cholesterol efflux and synthesis are regulated independently. In conclusion, evidence is provided that 24(S)-hydroxycholesterol induces apoE-mediated efflux of cholesterol in astrocytes via an LXR-controlled pathway, which may be relevant for chronic and acute neurological diseases.

ATP Binding Cassette Transporter, Subfamily G↗

PubMed2006

DEDD association with cytokeratin filaments correlates with sensitivity to apoptosis.

The cytokeratin 8/18 (CK8/18) cytoskeleton network is an early target for caspase cleavage during apoptosis. Recent reports suggest that the highly conserved and ubiquitous death effector domain containing DNA binding protein (DEDD) plays a role in the recruitment of procaspase-9 and -3 at this CK8/18 scaffold. DEDD interacts with both the CK8/18 intermediate filament network and procaspase-3 and -9. It is suggested that the CK8/18 fibrils may provide a scaffold for the proximity-induced autocleavage and activation of procaspase-9 in close association with caspase-3.We addressed this issue by investigating DEDD staining patterns in various cell lines and by correlating these expression patterns with the sensitivity of these cell lines for roscovitine-induced apoptosis. We showed that in some cell lines DEDD revealed a bright filamentous staining pattern in others DEDD staining was weak and diffusely distributed in the cytoplasm of the cells. The difference in staining patterns was irrespective of the phosphorylation status of the cytokeratin filaments. In cells showing a filamentous staining pattern, DEDD was strongly associated with the CK8/18 cytokeratin filaments as evidenced by double immunofluorescence and its resistance to extraction with Triton X-100. Subcellular fractionation indicates that DEDD co-purifies with CK18, which corroborates a strong association of DEDD and the cytokeratin network. DEDD was either mono- or diubiquinated. Cells showing a filamentous DEDD distribution are more apoptosis-prone as evidenced by the rapid appearance of M30 CytoDeath-positive cells after induction of apoptosis. The sensitivity towards apoptosis is irrespective of the procaspase-3 content of the cells. Our data support the notion that DEDD-mediated accumulation of procaspases at the cytokeratin scaffold leads to an increase in the local concentration, which renders cells more apoptosis-prone.

Apoptosis↗

PubMed2006

Effects of mistletoe (Viscum album L.) extracts Iscador on cell cycle and survival of tumor cells.

The molecular and cellular mechanisms by which mistletoe (Viscum album L.) extracts exert cytotoxic and immunomodulatory anti-tumoral effects are largely unknown. In this study the hypothesis that Iscador preparations induce tumor regression by cell cycle inhibition and/or interference with apoptotic signaling pathways in cancer cells was investigated. Also a possible effect on angiogenesis, which is a prerequisite for tumor growth in vivo, is studied in endothelial cell cultures. Furthermore, it was examined which apoptotic signaling route(s) is (are) activated by Iscador by studying specific pro-apoptotic proteins in cultured cells. To characterize these properties, 9 human cancer cell lines of different origin, one epidermis derived cell line and 2 endothelial cell cultures were incubated with different concentrations of Iscador Quercus Spezial and Iscador Malus Spezial. Cell cycle kinetic parameters were measured by bromodeoxyuridine (BrdU) pulse labeling and tubulin staining. Apoptotic responses were detected by M30 Cyto-Death or Annexin V/propidium iodide assays. Characterization of the apoptotic pathway(s) was performed by staining cells for amongst others active caspase 3 and cytochrome C (mitochondrial pathway), as well as active caspase 8 (death receptor pathway). The sensitivity to Iscador treatment varies strongly between different cell lines and also ing those derived from small cell lung cancer, and adenocarcinoma of the lung and breast, as well as endothelial cell cultures, Iscador caused early cell cycle inhibition followed by apoptosis in a dose dependent manner. Amongst the low responders are cell lines derived from colorectal carcinoma. In general Iscador Malus exerted a stronger response than Iscador Quercus. Apoptosis was induced by activating the mitochondrial but not the death receptor dependent pathway, at least in case of Iscador Quercus. Iscador Malus also seemed to induce apoptosis via the death receptor route, which may explain the higher sensitivity of cancer and endothelial cells to this preparation.

Annexin A5↗

PubMed2006

Structural adaptation in adult rabbit ventricular myocytes: influence of dynamic physical interaction with fibroblasts.

The mechanism of induction of cardiomyocyte (CM) dedifferentiation, as seen in chronic hibernating myocardium, is largely unknown. Recently, a cellular model was proposed consisting of long-term cocultures of adult rabbit CMs and cardiac fibroblasts in which typical structural characteristics of hibernation-like dedifferentiation could be induced. Only CMs in close contact with fibroblasts underwent these changes. In this study, we further investigated the characteristics of the fibroblast-CM interaction to seek for triggers and phenomena involved in CM dedifferentiation. Adult rabbit CMs were cocultured with cardiac or 3T3 fibroblasts. Heterocellular interactions and the structural adaptation of the CMs were quantified and studied with vital microscopy and electron microscopy. Immunocytochemical analysis of several adhesion molecules, i.e., N-cadherin, vinculin, beta1-integrin, and desmoplakin, were examined. Upon contact with CMs, fibroblasts attached firmly and pulled the former cells, resulting in anisotropic stretch. Quantification of the attachment sites revealed a predominant binding of the fibroblast to the distal ends of the CM in d 1 cocultures and a shift towards the lateral sides of the CMs on d 2 of coculture, suggesting a redistribution of CM membrane proteins. Immunocytochemical analysis of cell adhesion proteins showed that these were upregulated at the heterocellular contact sites. Addition of autologous and nonautologous fibroblasts to the CM culture similarly induced a progressive and accelerated structural adaptation of the CM. Dynamic passive stretch invoked by the fibroblasts and/or intercellular communication involving cell adhesion molecule expression at the interaction sites may play an important role in the induction of hibernation-like dedifferentiation of the cocultured adult rabbit CMs.

Adaptation, Physiological↗

PubMed2005

Partial cell fusion: a newly recognized type of communication between dedifferentiating cardiomyocytes and fibroblasts.

OBJECTIVE: Fibroblasts have been shown to couple to neonatal cardiomyocytes in heterocellular cultures through functional gap junctions. Our objective was to provide evidence for an additional type of heterocellular communication between fibroblasts and adult cardiomyocytes in vitro and in vivo. METHODS: The contact areas in heterocellular co-cultures were evaluated by specific labeling and the intercellular communication was studied using preloading of fibroblasts with tracer molecules. Heterocellular fibroblast-cardiomyocyte contacts present in the in vitro setting and in the border zone of a rabbit myocardial infarction in vivo were further examined by electron microscopy. RESULTS: Addition of fibroblasts preloaded with the fluorescent low molecular weight tracer calcein-AM to cultured myocytes indicated early dye transfer via connexin 43 functional gap junctions. At a later time-period after co-culturing, dye transfer of fibroblasts preloaded with the high molecular weight tracer dextran 10,000 suggested partial cell fusion. The membrane continuity giving rise to this partial cell fusion was confirmed by electron microscopy, clearly showing areas of intercytoplasmic contacts between fibroblasts and phenotypically adapted (dedifferentiated) cardiomyocytes. Fluorescein-labeled annexin V affinity studies revealed transient exposure of phosphatidylserine at the contact sites, suggesting that phosphatidylserine mediates the fusion process. Close contacts between cardiac fibroblasts and dedifferentiated cardiomyocytes accompanied by disruption of the basal lamina were observed in the border zone of a rabbit myocardial infarction in vivo. CONCLUSION: Our results suggest that the partial cell fusion-type of heterocellular communication in our co-culture model and the contacts observed in vivo may lead to new insights in cardiovascular disease.

Animals↗

PubMed2005

HPV in situ hybridization: impact of different protocols on the detection of integrated HPV.

Although there is consensus that HPV integration is common in invasive cervical carcinomas and uncommon or absent in low-grade uterine cervical intraepithelial neoplasia (CIN I), estimates for HPV integration in CIN II/III range from 5 to 100% using different PCR-based and in situ hybridization (ISH) approaches. It has been suggested that HPV integration can be identified using ISH by scoring of punctate signals. The increased sensitivity of fluorescence ISH (FISH) methods, allowing the detection of single copies of HPV, complicates the distinction between integrated and episomal HPV. Recently it has been suggested that, in such assays, the signals originating from integrated virus can be hidden in a background of episomal HPV. We therefore compared 2 different FISH protocols for the detection of integrated HPV in a series of CIN II/III lesions: 1) a mild protocol in which episomal HPV and RNA is retained and 2) a harsh protocol that extensively extracts proteins and RNA, and which promotes the partial loss of episomal HPV but not integrated HPV. A series of 28 HPV 16/18 positive CIN II/III lesions (17 solitary lesions and 11 lesions adjacent to microinvasive carcinoma) were studied. A punctate signal pattern was identified in 7 of these lesions with both protocols. Punctate signal was also present in control samples from lesions that are known to be associated with HPV integration (invasive squamous cell carcinoma (n = 3), adenocarcinoma in situ (n = 3), and invasive adenocarcinoma (n = 1). HPV RNA contributed significantly to the intensity of punctate FISH signal, especially when applying the mild protocol, as shown by omitting DNA denaturation, including RNase pretreatment steps and measuring the fluorescence signal intensity. Also, HPV RNA was frequently detected in addition to episomal/integrated HPV DNA in the majority of the other 21 CIN II/III lesions; this resulted in intense granular/diffuse FISH signals throughout the epithelium. However, in 7 of these lesions, the harsh protocol gave a more consistent punctate pattern in cells throughout the full thickness of the epithelium. This supports the hypothesis that the harsh protocol unmasks integrated HPV more efficiently by extracting RNA and episomal HPV. Overall, with this harsh protocol, a clonally expanded population of cells containing punctate HPV signals was found in 5 of 17 (29%) solitary CIN II/III lesions and in 9 of 11 (88%) CIN II/III lesions associated with microinvasive carcinoma. Combining these data with the results from our previous study, with the harsh protocol in 7 of 40 (18%) solitary CIN II/III lesions and 19/21 (90%) CIN II/III lesions associated with microinvasive carcinoma (p < 0.001), this pattern was found. This indicates that, when robustly defined, a punctate HPV pattern in CIN II/III lesions is associated with the presence of an invasive carcinoma.

Adenocarcinoma↗

PubMed2004

Decreased mechanical stiffness in LMNA-/- cells is caused by defective nucleo-cytoskeletal integrity: implications for the development of laminopathies.

Laminopathies comprise a group of inherited diseases with variable clinical phenotypes, caused by mutations in the lamin A/C gene (LMNA). A prominent feature in several of these diseases is muscle wasting, as seen in Emery-Dreifuss muscle dystrophy, dilated cardiomyopathy and limb-girdle muscular dystrophy. Although the mechanisms underlying this phenotype remain largely obscure, two major working hypotheses are currently being investigated, namely, defects in gene regulation and/or abnormalities in nuclear architecture causing cellular fragility. In this study, using a newly developed cell compression device we have tested the latter hypothesis. The device allows controlled application of mechanical load onto single living cells, with simultaneous visualization of cellular deformation and quantitation of resistance. With the device, we have compared wild-type (MEF+/+) and LMNA knockout (MEF-/-) mouse embryonic fibroblasts (MEFs), and found that MEF-/- cells show a significantly decreased mechanical stiffness and a significantly lower bursting force. Partial rescue of the phenotype by transfection with either lamin A or lamin C prevented gross nuclear disruption, as seen in MEF-/- cells, but was unable to fully restore mechanical stiffness in these cells. Our studies show a direct correlation between absence of LMNA proteins and nuclear fragility in living cells. Simultaneous recordings by confocal microscopy revealed that the nuclei in MEF-/- cells, in contrast to MEF+/+ cells, exhibited an isotropic deformation upon indentation, despite an anisotropic deformation of the cell as a whole. This nuclear behaviour is indicative for a loss of interaction of the disturbed nucleus with the surrounding cytoskeleton. In addition, careful investigation of the three-dimensional organization of actin-, vimentin- and tubulin-based filaments showed a disturbed interaction of these structures in MEF-/- cells. Therefore, we suggest that in addition to the loss of nuclear stiffness, the loss of a physical interaction between nuclear structures (i.e. lamins) and the cytoskeleton is causing more general cellular weakness and emphasizes a potential key function for lamins in maintaining cellular tensegrity.

Actins↗

PubMed2004

Keratin 8/18 breakdown and reorganization during apoptosis.

Monoclonal antibodies that specifically recognize caspase cleaved K18 fragments or specific (phospho)epitopes on intact K8 and K18 were used for a detailed investigation of the temporal and causal relationship of proteolysis and phosphorylation in the collapse of the keratin cytoskeleton during apoptosis. Caspases involved in the specific proteolysis of keratins were analyzed biochemically using recombinant caspases and specific caspase inhibitors. Finally, the fate of the keratin aggregates was analyzed using the M30-ApoptoSense trade mark Elisa kit to measure shedding of caspase cleaved fragments into the supernatant of apoptotic cell cultures. From our studies, we conclude that C-terminal K18 cleavage at the (393)DALD/S site is an early event during apoptosis for which caspase 9 is responsible, both directly and indirectly by activating downstream caspases 3 and 7. Cleavage of the L1-2 linker region of the central alpha-helical rod domain is responsible for the final collapse of the keratin scaffold into large aggregates. Phosphorylation facilitates formation of these aggregates, but is not crucial. K8 and K18 remain associated in heteropolymeric aggregates during apoptosis. At later stages of the apoptotic process, that is, when the integrity of the cytoplasmic membrane becomes compromised, keratin aggregates are shed from the cells.

Apoptosis↗

PubMed2004

10q25.3 (DMBT1) copy number changes in astrocytoma grades II and IV.

In the literature, it has been suggested that loss of the 10q25-26 region, including the DMBT1 gene (10q25.3), is correlated with initiation and/or malignant progression of astrocytomas, although the results of the studies on the loss of heterozygosity that led to this assumption are not unequivocal. For this reason, using double-target fluorescence in situ hybridization, we compared copy number changes of 10q25.3 to those of the pericentromeric region (10q12) in 10 cases each of astrocytoma grades II and IV. The same specimens were analyzed for copy number changes of chromosome 1, as a marker for polyploidy, and chromosome 7, which is often gained in astrocytomas of all grades. Our results show that selective loss of the 10q25.3 region was present in 2 of 10 specimens in both astrocytoma grade II and grade IV, occurring only in tumors with polysomy for 10q12. Furthermore, astrocytoma grade II often showed polyploidy for chromosomes 1, 7, and 10 (8 of 10 specimens). In addition, astrocytoma grade IV frequently exhibited losses of chromosome 10 in a high percentage of nuclei. Although based on a small number of cases, the results clearly show that loss of the 10q25.3 region is uncommon in astrocytoma grade II and mostly coincident with loss of chromosome 10 in grade IV tumors. These data indicate that selective loss of the 10q25.3 region, including the DMBT1 gene, is not an initiating event in the genesis of astrocytoma grade II.

Adult↗

PubMed2004

Transition of high-grade cervical intraepithelial neoplasia to micro-invasive carcinoma is characterized by integration of HPV 16/18 and numerical chromosome abnormalities.

Cervical intraepithelial neoplasia (CIN I, II, and III) and cases of CIN III associated with micro-invasive cervical carcinoma (CIN III & mCA) were analysed for evidence of episomal or integrated human papillomavirus (HPV) 16/18 DNA by fluorescence in situ hybridization (FISH). In parallel, numerical aberrations of chromosomes 1, 17, and X were determined in these lesions as indicators of genomic instability. HPV 16/18 DNA was present in 2 of 12 CIN I, 19 of 23 CIN II/III, and 10 of 12 CIN III & mCA. None of the CIN I and only two of the 19 HPV 16/18-positive solitary CIN II/III showed an integrated HPV pattern. However, all ten cases of HPV-positive CIN III & mCA showed this pattern. Transition of CIN II/III to CIN III & mCA therefore correlates strongly with viral integration (p<0.001). Chromosomal aberrations were detected in 23 of 31 HPV 16/18-positive lesions (14 solitary CIN I-III and nine CIN III & mCA) and 5 of 16 HPV-negative lesions. Nine of 21 HPV 16/18-positive solitary CIN I-III showed tetrasomy for all chromosomes tested, while trisomies for a single chromosome were seen in a further five of these HPV-positive lesions. In eight of ten HPV-positive CIN III & mCA, predominantly aneusomies and/or polysomies were detected. A significant correlation (p<0.02) was found between the chromosome copy number and the physical status of HPV, indicating that in its episomal form HPV induces genomic changes such as tetrasomies and single trisomies, while HPV integration correlates with aneusomies and polysomies, predominantly detected in CIN III & mCA. These data indicate that integration of HPV 16/18 DNA is a pivotal step in the transition of CIN to micro-invasive carcinoma.

Adult↗

PubMed2004

Laminopathies.

Nuclear lamins form a fibrous nucleoskeletal network of intermediate-sized filaments that underlies the inner nuclear membrane. It associates with this membrane through interactions with specific integral nuclear membrane proteins, while within this flattened lamin lattice the nuclear pore complexes are embedded. Next to this peripheral network, the lamins can form intranuclear structures. The lamins are the evolutionary progenitors of the cytoplasmic intermediate filament proteins and have profound influences on nuclear structure and function. These influences require that lamins have dynamic properties and dual identities as structural building blocks on the one hand, and transcription regulators on the other. Which of these identities underlies the laminopathies, a myriad of genetic diseases caused by mutations in lamins or lamin-associated proteins, is a topic of intense debate.

Adipose Tissue↗

PubMed2004

The cytoskeleton and disease.

Cytoskeletal research in recent years has revolutionized cell biology and biomedicine. The cytoskeleton spans the cytoplasm and interconnects the cell nucleus with the extracellular matrix, thereby forming a structural link between molecules involved in cell communication on the one hand, and gene expression on the other. Since the cytoskeleton is involved in virtually all cellular processes, abnormalities in this essential cellular component frequently result in disease. In this introduction, the basic structure of the cytoskeleton is briefly outlined. Furthermore, the disease processes in which the cytoskeleton plays a decisive role, and which are reviewed in detail in the papers in this issue, are briefly introduced. The advances in our understanding of the cytoskeleton and its function in disease will lead to new diagnostic and therapeutic applications in the foreseeable future.

Actins↗

PubMed2004

Low-density lipoprotein receptor-knockout mice display impaired spatial memory associated with a decreased synaptic density in the hippocampus.

The low-density lipoprotein receptor (LDLR) is the first described receptor for apolipoprotein E (apoE). We hypothesize that the absence of the LDLR, similar to the absence of apoE, results in impaired learning and memory processes. Six-month-old homozygous Ldlr-/- and wild-type littermates (Ldlr+/+), maintained on a standard lab chow diet, were used. Unlike humans, Ldlr-/- mice, under these conditions, do not develop atherosclerosis. The results of the Morris water escape task revealed an impaired spatial memory in the Ldlr-/- mice in comparison with Ldlr+/+ mice. Also in a T-maze task, the working memory performance of the Ldlr-/- mice was impaired. Furthermore, Ldlr-/- mice, in comparison with Ldlr+/+ mice, display a decreased number of synaptophysin-immunoreactive presynaptic boutons in the hippocampus CA1. In conclusion, the results show in mice deficiency for the LDLR results in impaired hippocampal-dependent memory functions. A decrease in the number of presynaptic boutons may underlay these behavioral alterations. Therefore, the LDLR may be an important receptor for apoE in the central nervous system.

Animals↗