Search PubMed⌕ Search

Biomedical subjects

George M Martin

Publications and source records attributed to George M Martin.

At least 19 recordsLinked to original sources
PubMed2006

Collagen expression in fibroblasts with a novel LMNA mutation.

Laminopathies are a group of genetic disorders caused by LMNA mutations; they include muscular dystrophies, lipodystrophies, and progeroid syndromes. We identified a novel heterozygous LMNA mutation, L59R, in a patient with the general appearance of mandibuloacral dysplasia and progeroid features. Examination of the nuclei of dermal fibroblasts revealed the irregular morphology characteristic of LMNA mutant cells. The nuclear morphological abnormalities of LMNA mutant lymphoblastoid cell lines were less prominent compared to those of primary fibroblasts. Since it has been reported that progeroid features are associated with increased extracellular matrix in dermal tissues, we compared a subset of these components in fibroblast cultures from LMNA mutants with those of control fibroblasts. There was no evidence of intracellular accumulation or altered mobility of collagen chains, or altered conversion of procollagen to collagen, suggesting that skin fibroblast-mediated matrix production may not play a significant role in the pathogenesis of this particular laminopathy.

Adolescent↗
PubMed2006

The genetics and epigenetics of altered proliferative homeostasis in ageing and cancer.

Ageing mammals are subject to an amazing array of aberrations in proliferative homeostasis. These are of two basic types: the post-maturational failure to adequately replace effete somatic cells (atrophies) and excessive proliferations of somatic cells (hyperplasias). To a surprising degree, these occur side by side within the same tissues and are features of numerous mammalian geriatric disorders. Atrophy is the likely usual initial event, the proliferative response perhaps developing as a secondary, compensatory, initially adaptive reaction. We have little understanding of why this putative compensatory reaction so often fails to be appropriately regulated in ageing mammals, leading to such pathologies as chronic inflammation, fibrosis, metaplasia and neoplasia. Advances in formal genetic analysis, mutagenesis, stem cell biology and epigenetics are likely to provide major new understanding. Stochastic epigenetic shifts in gene expression are of growing interest, particularly in explaining intra-specific variations on rates and patterns of ageing. Nature may well have evolved such random fluctuations in gene expression as a type of group-selectionist adaptive strategy to cope with diverse stochastic environmental challenges. Alternatively, such background "noise" in transcription and translation may simply reflect a type of informational entropy.

Aging↗
PubMed2006

SAGE lessons.

Explore the source record for details and available documents.

Aging↗
PubMed2006

Keynote lecture: an update on the what, why and how questions of ageing.

In this keynote address, we briefly consider three global questions on the biology of ageing. What is it? While it is certainly the case that development has a major impact upon ageing, gerontologists characterize ageing as gradual, insidious, post-maturational declines in the structure and function of multiple organ systems, certainly to include reproduction. This is accompanied by increasing rates of mortality within populations. Comprehensive, longitudinal physiological assessments are not commonly pursued in their experiments, however; this deficiency limits one's ability to interpret the results of putative interventions. Why does it happen? Although subject to recent challenges, the most satisfying explanation for inter-specific variations in longevity is given by the evolutionary biological theory of ageing. Life history parameters, including longevity, are molded by the ecological forces in which the species evolves. How does it happen? To gain insight into fundamental mechanisms of ageing, we have focused upon classes of gene actions that, according to the evolutionary theory, can escape the forces of natural selection.

Aged↗
PubMed2006

The spectrum of WRN mutations in Werner syndrome patients.

The International Registry of Werner syndrome (www.wernersyndrome.org) has been providing molecular diagnosis of the Werner syndrome (WS) for the past decade. The present communication summarizes, from among 99 WS subjects, the spectrum of 50 distinct mutations discovered by our group and by others since the WRN gene (also called RECQL2 or REQ3) was first cloned in 1996; 25 of these have not previously been published. All WRN mutations reported thus far have resulted in the elimination of the nuclear localization signal at the C-terminus of the protein, precluding functional interactions in the nucleus; thus, all could be classified as null mutations. We now report two new mutations in the N-terminus that result in instability of the WRN protein. Clinical data confirm that the most penetrant phenotype is bilateral ocular cataracts. Other cardinal signs were seen in more than 95% of the cases. The median age of death, previously reported to be in the range of 46-48 years, is 54 years. Lymphoblastoid cell lines (LCLs) have been cryopreserved from the majority of our index cases, including material from nuclear pedigrees. These, as well as inducible and complemented hTERT (catalytic subunit of human telomerase) immortalized skin fibroblast cell lines are available to qualified investigators.

Adult↗
PubMed2006

A novel tricyclic pyrone compound ameliorates cell death associated with intracellular amyloid-beta oligomeric complexes.

The neurotoxicity of amyloid-beta protein (Abeta) is widely regarded as one of the fundamental causes of neurodegeneration in Alzheimer's disease (AD). This toxicity is related to Abeta aggregation into oligomers, protofibrils and fibrils. Recent studies suggest that intracellular Abeta, which causes profound toxicity, could be one of the primary therapeutic targets in AD. So far, no compounds targeting intracellular Abeta have been identified. We have investigated the toxicity induced by intracellular Abeta in a neuroblastoma MC65 line and found that it was closely related to intracellular accumulation of oligomeric complexes of Abeta (Abeta-OCs). We further identified a cell-permeable tricyclic pyrone named CP2 that ameliorates this toxicity and significantly reduces the levels of Abeta-OCs. In aqueous solution, CP2 attenuates Abeta oligomerization and prevents the oligomer-induced death of primary cortical neurons. CP2 analogs represent a new class of promising compounds for the amelioration of Abeta toxicities within both intracellular and extracellular sites.

Amyloid beta-Peptides↗
PubMed2005

A dominant role for FE65 (APBB1) in nuclear signaling.

FE65 has been described as an adaptor protein; its partners include the beta-amyloid precursor protein (APP) and Tip60 (a histone acetyltransferase). Recent evidence suggests that APP may function in a nuclear signaling pathway via formation of APP-FE65-Tip60 complexes. The evidence is largely based on experiments in which APP/Tip60 is fused to the DNA binding domain of a yeast transcriptional factor Gal4 (Gal4DB) that can activate a reporter gene only when FE65 is coexpressed. One interpretation of published experiments has not yet been tested; however, there is the possibility that FE65 itself is the dominant transcriptional activator, whereas APP and Tip60 serve merely as positive/negative modulators or bridges for connecting FE65 to Gal4DB. To test this possibility, we fused Gal4DB directly to either end of FE65 and assessed their nuclear signaling in the presence or absence of exogenous APP/Tip60 or after knockdown of endogenous APP/Tip60. We found that FE65-Gal4DB by itself was able to trigger robust reporter activities. Increasing levels of APP could not further augment the reporter activity, but knocking down endogenous APP or interrupting FE65-APP binding reduced the signaling by up to 2-fold. The magnitudes of the reporter activities did not correlate with relative FE65 affinities for APP. Both overexpression and knockdown experiments showed that Tip60 plays a negative role. The results are consistent with the notion that FE65 is the key agent of Gal4DB-mediated transcriptional transactivation, whereas Tip60 is an FE65-associated repressor. Although APP may have modest stimulating effects, apparently there is no absolute requirement for that molecule for the nuclear signaling pathway.

Acetyltransferases↗
PubMed2005

Correction of cellular phenotypes of Hutchinson-Gilford Progeria cells by RNA interference.

The great majority of cases of the Hutchinson-Gilford progeroid syndrome (HGPS) ("Progeria of Childhood'') are caused by a single nucleotide mutation (1824 C->T) in the LMNA gene which encodes lamin A and C, nuclear intermediate filaments that are important components of the nuclear lamina. The resultant mutant protein (Delta50 lamin A) is thought to act in a dominant fashion. We exploited RNA interference technology to suppress Delta50 lamin A expression, with the long range goal of intervening in the pathogenesis of the coronary artery atherosclerosis that typically leads to the death of HGPS patients. Short hairpin RNA (shRNA) constructs were designed to target the mutated pre-spliced or mature LMNA mRNAs, and were expressed in HGPS fibroblasts carrying the 1824 C->T mutations using lentiviruses. One of the shRNAs targeted to the mutated mRNA reduced the expression levels of Delta50 lamin A to 26% or lower. The reduced expression was associated with amelioration of abnormal nuclear morphology, improvement of proliferative potential, and reduction in the numbers of senescent cells. These findings provide a rationale for potential gene therapy.

Cell Culture Techniques↗
PubMed2005

Extension of murine life span by overexpression of catalase targeted to mitochondria.

To determine the role of reactive oxygen species in mammalian longevity, we generated transgenic mice that overexpress human catalase localized to the peroxisome, the nucleus, or mitochondria (MCAT). Median and maximum life spans were maximally increased (averages of 5 months and 5.5 months, respectively) in MCAT animals. Cardiac pathology and cataract development were delayed, oxidative damage was reduced, H2O2 production and H2O2-induced aconitase inactivation were attenuated, and the development of mitochondrial deletions was reduced. These results support the free radical theory of aging and reinforce the importance of mitochondria as a source of these radicals.

8-Hydroxy-2'-Deoxyguanosine↗
PubMed2005

Genetic modulation of senescent phenotypes in Homo sapiens.

Single-gene mutations can produce human progeroid syndromes--phenotypes that mimic usual or "normative" aging. These can be divided into two classes--those that have their impacts upon multiple organs and tissues (segmental progeroid syndromes) and those that have their major impacts upon a single organ or tissue (unimodal progeroid syndromes). The prototypic example of the former is the Werner syndrome, a condition caused by mutations of the RecQ family of DNA helicases. Research on the Werner syndrome and a surprising number of other progeroid syndromes support the importance of the maintenance of genomic stability as a partial antidote to aging. The prototypic examples of the latter are Alzheimer type dementias. The three gene products that cause rare autosomal-dominant early-onset varieties of these disorders all participate in the modulation of the beta amyloid precursor protein. They thus support the importance of the maintenance of proper protein processing and folding as a partial antidote to aging.

Aging↗
PubMed2005

Endoproteolytic cleavage of FE65 converts the adaptor protein to a potent suppressor of the sAPPalpha pathway in primates.

Adaptor protein FE65 (APBB1) specifically binds to the intracellular tail of the type I transmembrane protein, beta-amyloid precursor protein (APP). The formation of this complex may be important for modulation of the processing and function of APP. APP is proteolytically cleaved at multiple sites. The cleavages and their regulation are of central importance in the pathogenesis of dementias of the Alzheimer type. In cell cultures and perhaps in vivo, secretion of the alpha-cleaved APP ectodomain (sAPPalpha) is the major pathway in the most cells. Regulation of the process may require extracellular/intracellular cues. Neither extracellular ligands nor intracellular mediators have been identified, however. Here, we show novel evidence that the major isoform of FE65 (97-kDa FE65, p97FE65) can be converted to a 65-kDa N-terminally truncated C-terminal fragment (p65FE65) via endoproteolysis. The cleavage region locates immediately after an acidic residue cluster but before the three major protein-protein binding domains. The cleavage activity is particularly high in human and non-human primate cells and low in rodent cells; the activity appears to be triggered/enhanced by high cell density, presumably via cell-cell/cell-substrate contact cues. As a result, p65FE65 exhibits extraordinarily high affinity for APP (up to 40-fold higher than p97FE65) and potent suppression (up to 90%) of secretion of sAPPalpha. Strong p65FE65-APP binding is required for the suppression. The results suggest that p65FE65 may be an intracellular mediator in a signaling cascade regulating alpha-secretion of APP, particularly in primates.

Aged↗
PubMed2005

Age-related cataract progression in five mouse models for anti-oxidant protection or hormonal influence.

Five mouse models with known alterations of resistance to oxidative damage were compared by slit lamp examination for the presence and degree of advancement of age-related cataract in young adult and old animals along with wild type controls. A group of young and old normal C57BL/6Jax mice were examined first to constitute a standard, and they were found to exhibit age-related cataract development. Following this, four models on the C57BL/6 background with imposed genetic alterations affecting anti-oxidant enzyme presence or activity, and one outbred model in which a deletion blocked the growth hormone/IGF-1 axis, were similarly examined. There was no evidence of foetal or juvenile cataract development in any of these models, and an age-related severity for lens opacities was shown between young adult and old mice in all groups. Model 1, mice null for the anti-oxidant gene glutathione peroxidase-1 (GPX1) had significantly advanced cataracts in older mice vs. same age controls. In mouse model 2 hemizygous knockout of SOD2 (MnSOD) did not affect age-related cataract development. In model 3 combining the GPX1 and SOD2 deficiencies in the same animal did not advance cataract development beyond that of the GPX1 null alone. In model 4 the addition of anti-oxidant protection in the lens by transfection of human catalase targeted only to the mitochondria resulted in a significant delay in cataract development. The 5th model, growth hormone receptor knockout (GHR-/-) mice, also demonstrated a significant reduction in age-related cataract development, as well as dwarfism. These findings, in general, support the oxidative theory of age-related cataract development. The exception, the partial deletion of SOD2 in the hemizygous KO model, probably did not represent a sufficiently severe deprivation of anti-oxidant protection to produce pathologic changes in the lens.

Aging↗
PubMed2005

Genetic engineering of mice to test the oxidative damage theory of aging.

The laboratory mouse Mus musculus domesticus provides the best current mammalian models for the genetic analysis of aging. We give a brief overview of the use of transgenic manipulations to test the oxidative damage theory of aging. These manipulations are of two types: The first approach engineers mice that exhibit increased sensitivities to oxidative damage and thus produces mice that are likely to be short-lived. The second approach engineers mice to be more resistant to such injuries, and thus may produce mice that exhibit enhanced longevities, something that is much harder to engineer. The latter result is thus more meaningful, with the caveat that it may result from some special vulnerability of a particular lab strain or lab strains in general. The first approach, most elegantly carried out by Arlan Richardson's laboratory, provides evidence against the oxidative damage theory. My colleagues and I have been engaged in the second approach and have accumulated evidence supporting the theory. These conventional transgenic experiments, however, should be supplemented by alternative genetic approaches. One that is surprisingly neglected takes advantage of the pleuripotency of embryonic stem cells and the power of somatic cell genetics. A cautionary note is that interventions that minimize oxidative stress may be complicated by unwanted compromises of physiologically adaptive actions such as superoxide signaling and the possible protective effects of certain oxidatively modified proteins.

Aging↗
PubMed2004

A knowledgebase system to enhance scientific discovery: Telemakus.

BACKGROUND: With the rapid expansion of scientific research, the ability to effectively find or integrate new domain knowledge in the sciences is proving increasingly difficult. Efforts to improve and speed up scientific discovery are being explored on a number of fronts. However, much of this work is based on traditional search and retrieval approaches and the bibliographic citation presentation format remains unchanged. METHODS: Case study. RESULTS: The Telemakus KnowledgeBase System provides flexible new tools for creating knowledgebases to facilitate retrieval and review of scientific research reports. In formalizing the representation of the research methods and results of scientific reports, Telemakus offers a potential strategy to enhance the scientific discovery process. While other research has demonstrated that aggregating and analyzing research findings across domains augments knowledge discovery, the Telemakus system is unique in combining document surrogates with interactive concept maps of linked relationships across groups of research reports. CONCLUSION: Based on how scientists conduct research and read the literature, the Telemakus KnowledgeBase System brings together three innovations in analyzing, displaying and summarizing research reports across a domain: (1) research report schema, a document surrogate of extracted research methods and findings presented in a consistent and structured schema format which mimics the research process itself and provides a high-level surrogate to facilitate searching and rapid review of retrieved documents; (2) research findings, used to index the documents, allowing searchers to request, for example, research studies which have studied the relationship between neoplasms and vitamin E; and (3) visual exploration interface of linked relationships for interactive querying of research findings across the knowledgebase and graphical displays of what is known as well as, through gaps in the map, what is yet to be tested. The rationale and system architecture are described and plans for the future are discussed.

Journal Article↗