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Biomedical subjects

David Stern

Publications and source records attributed to David Stern.

18 recordsLinked to original sources
PubMed2006

Mitochondrial dysfunction and Alzheimer's disease.

Mitochondrial dysfunction has been implicated in causing metabolic abnormalities in Alzheimer's disease (AD). The searches for mitochondrial DNA variants associated with AD susceptibility have generated conflicting results. The age-related accumulation of somatic mitochondrial DNA deletion has been suggested to play a pathogenic role in the development of AD. Recent studies have demonstrated that amyloid-beta peptide (Abeta) progressively accumulates in mitochndrial matrix, as demonstrated in both transgenic mice over-expressing mutant amyloid precursor protein (APP) and autopsy brain from AD patients. Abeta-mediated mitochondrial stress was evidenced by impaired oxygen consumption and decreased respiratory chain complexes III and IV activities in brains from AD patients and AD-type transgenic mouse model. Furthermore, our studies indicated that interaction of intramitochondrial Abeta with a mitochondrial enzyme, amyloid binding alcohol dehydrogenase (ABAD), inhibits its enzyme activity, enhances generation of reactive oxygen species (ROS), impairs energy metabolism, and exaggerates Abeta-induced spatial learning/memory deficits and neuropathological changes in transgenic AD-type mouse model. Interception of ABAD-Abeta interaction may be a potential therapeutic strategy for Alzheimer's disease.

Alzheimer Disease↗
PubMed2005

Mitochondrial Abeta: a potential focal point for neuronal metabolic dysfunction in Alzheimer's disease.

Although amyloid-beta peptide (Abeta) is the neurotoxic species implicated in the pathogenesis of Alzheimer's disease (AD), mechanisms through which intracellular Abeta impairs cellular properties, resulting in neuronal dysfunction, remain to be clarified. Here we demonstrate that intracellular Abeta is present in mitochondria from brains of transgenic mice with targeted neuronal overexpression of mutant human amyloid precursor protein and AD patients. Abeta progressively accumulates in mitochondria and is associated with diminished enzymatic activity of respiratory chain complexes (III and IV) and a reduction in the rate of oxygen consumption. Importantly, mitochondria-associated Abeta, principally Abeta42, was detected as early as 4 months, before extensive extracellular Abeta deposits. Our studies delineate a new means through which Abeta potentially impairs neuronal energetics, contributing to cellular dysfunction in AD.

Alzheimer Disease↗
PubMed2005

RAGE and amyloid beta interactions: atomic force microscopy and molecular modeling.

In the AD brain, there are elevated amounts of soluble and insoluble Abeta peptides which enhance the expression of membrane bound and soluble receptor for advanced glycation end products (RAGE). The binding of soluble Abeta to soluble RAGE inhibits further aggregation of Abeta peptides, while membrane bound RAGE-Abeta interactions elicit activation of the NF-kappaB transcription factor promoting sustained chronic neuroinflammation. Atomic force microscopy observations demonstrated that the N-terminal domain of RAGE, by interacting with Abeta, is a powerful inhibitor of Abeta polymerization even at prolonged periods of incubation. Hence, the potential RAGE-Abeta structural interactions were further explored utilizing a series of computational chemistry algorithms. Our modeling suggests that a soluble dimeric RAGE assembly creates a positively charged well into which the negative charges of the N-terminal domain of dimeric Abeta dock.

Alzheimer Disease↗
PubMed2005

Transcriptional maps of 10 human chromosomes at 5-nucleotide resolution.

Sites of transcription of polyadenylated and nonpolyadenylated RNAs for 10 human chromosomes were mapped at 5-base pair resolution in eight cell lines. Unannotated, nonpolyadenylated transcripts comprise the major proportion of the transcriptional output of the human genome. Of all transcribed sequences, 19.4, 43.7, and 36.9% were observed to be polyadenylated, nonpolyadenylated, and bimorphic, respectively. Half of all transcribed sequences are found only in the nucleus and for the most part are unannotated. Overall, the transcribed portions of the human genome are predominantly composed of interlaced networks of both poly A+ and poly A- annotated transcripts and unannotated transcripts of unknown function. This organization has important implications for interpreting genotype-phenotype associations, regulation of gene expression, and the definition of a gene.

Cell Line↗
PubMed2005

The nature of qualitative comments in evaluating professionalism.

INTRODUCTION: We analysed written comments on clerkship evaluation forms to determine if they furthered our understanding of students' professional behaviour. METHODS: We transcribed all written comments related to professional behaviour for 1 medical school class in 4 major clerkships, then categorised the comments. Comments were coded into categories by two raters. They were also coded as positive, negative or equivocal. The 3 types of comments were each correlated with a Likert-type score for professionalism for each student in these same clerkships. RESULTS: Most comments covered initiative, working well with others, patient skills and working hard. Of the 1845 comments, 1721 were positive, 106 were negative and 18 were equivocal, neither wholly positive nor wholly negative. The total number of positive comments correlated with the students' numerical professionalism score (r = 0.29, P < 0.001); negative comments correlated negatively with the numerical professionalism score (r = -0.44, P < 0.001). Equivocal comments were significantly negative (r = -0.25, P = 0.002). Qualitative analysis revealed that equivocal comments were focused on maturity, initiative and teamwork. CONCLUSIONS: Written comments contain unique indicators of students' professional behaviour and are largely positive in nature; negative comments stand out by their rarity and intensity. There is a set of negative comments masked by evaluators in language that appears neutral or even partly positive that statistically resemble negative comments and should be regarded as such by students who receive this type of comments. Evaluators should be encouraged and trained to express their qualitative views of students.

Clinical Clerkship↗
PubMed2004

Blockade of late stages of autoimmune diabetes by inhibition of the receptor for advanced glycation end products.

Ligation of the receptor for advanced glycation end products (RAGE) occurs during inflammation. Engagement of RAGE results in enhanced expression of addressins and it is therefore, not surprising that previous studies have shown a role of RAGE/ligand interactions in immune responses including cell/cell contact but the role of RAGE in spontaneous autoimmunity has not been clearly defined. To study the role of RAGE/ligand interactions in autoimmune diabetes, we tested the ability of soluble RAGE, a scavenger of RAGE ligands, in late stages of diabetes development in the NOD mouse-disease transferred with diabetogenic T cells and recurrent disease in NOD/scid recipients of syngeneic islet transplants. RAGE expression was detected on CD4(+), CD8(+), and B cells from diabetic mice and transferred to NOD/scid recipients. RAGE and its ligand, S100B, were found in the islets of NOD/scid mice that developed diabetes. Treatment of recipient NOD/scid mice with soluble RAGE prevented transfer of diabetes and delayed recurrent disease in syngeneic islet transplants. RAGE blockade was associated with increased expression of IL-10 and TGF-beta in the islets from protected mice. RAGE blockade reduced the transfer of disease with enriched T cells, but had no effect when diabetes was transferred with the activated CD4(+) T cell clone, BDC2.5. We conclude that RAGE/ligand interactions are involved in the differentiation of T cells to a mature pathogenic phenotype during the late stages of the development of diabetes.

Animals↗
PubMed2004

ABAD directly links Abeta to mitochondrial toxicity in Alzheimer's disease.

Mitochondrial dysfunction is a hallmark of beta-amyloid (Abeta)-induced neuronal toxicity in Alzheimer's disease (AD). Here, we demonstrate that Abeta-binding alcohol dehydrogenase (ABAD) is a direct molecular link from Abeta to mitochondrial toxicity. Abeta interacts with ABAD in the mitochondria of AD patients and transgenic mice. The crystal structure of Abeta-bound ABAD shows substantial deformation of the active site that prevents nicotinamide adenine dinucleotide (NAD) binding. An ABAD peptide specifically inhibits ABAD-Abeta interaction and suppresses Abeta-induced apoptosis and free-radical generation in neurons. Transgenic mice overexpressing ABAD in an Abeta-rich environment manifest exaggerated neuronal oxidative stress and impaired memory. These data suggest that the ABAD-Abeta interaction may be a therapeutic target in AD.

3-Hydroxyacyl CoA Dehydrogenases↗
PubMed2003

Body-size control: how an insect knows it has grown enough.

Insulin signaling controls organ growth and final body size in insects. Recent results have begun to clarify how insulin signaling drives organ growth to match nutrient levels, but have not yet elucidated how insulin signaling controls final body size.

Animal Nutritional Physiological Phenomena↗
PubMed2003

RAGE mediates amyloid-beta peptide transport across the blood-brain barrier and accumulation in brain.

Amyloid-beta peptide (Abeta) interacts with the vasculature to influence Abeta levels in the brain and cerebral blood flow, providing a means of amplifying the Abeta-induced cellular stress underlying neuronal dysfunction and dementia. Systemic Abeta infusion and studies in genetically manipulated mice show that Abeta interaction with receptor for advanced glycation end products (RAGE)-bearing cells in the vessel wall results in transport of Abeta across the blood-brain barrier (BBB) and expression of proinflammatory cytokines and endothelin-1 (ET-1), the latter mediating Abeta-induced vasoconstriction. Inhibition of RAGE-ligand interaction suppresses accumulation of Abeta in brain parenchyma in a mouse transgenic model. These findings suggest that vascular RAGE is a target for inhibiting pathogenic consequences of Abeta-vascular interactions, including development of cerebral amyloidosis.

Aged↗
PubMed2002

Receptor for advanced glycation endproducts: a multiligand receptor magnifying cell stress in diverse pathologic settings.

Receptor for Advanced Glycation Endproducts (RAGE) is a member of the immunoglobulin superfamily of cell surface molecules capable of interacting with a broad spectrum of ligands, including advanced glycation endproducts (AGEs), amyloid fibrils, S100/calgranulins and amphoterin. The biology of RAGE is dictated by the accumulation of these ligands at pathologic sites, leading to upregulation of the receptor and sustained RAGE-dependent cell activation eventuating in cellular dysfunction. Although RAGE is not central to the initial pathogenesis of disorders in which it ultimately appears to be involved, such as diabetes, amyloidoses, inflammatory conditions and tumors (each of these conditions leading to accumulation of RAGE ligands), the receptor functions as a progression factor driving cellular dysfunction and exaggerating the host response towards tissue destruction, rather than restitution of homeostasis. These observations suggest that RAGE might represent a therapeutic target in a diverse group of seemingly unrelated disorders linked only by a multiligand receptor with an unusually wide and diverse repertoire of ligands, namely, RAGE.

Animals↗
PubMed2002

Evidence for in vivo modulation of chloroplast RNA stability by 3'-UTR homopolymeric tails in Chlamydomonas reinhardtii.

Polyadenylation of synthetic RNAs stimulates rapid degradation in vitro by using either Chlamydomonas or spinach chloroplast extracts. Here, we used Chlamydomonas chloroplast transformation to test the effects of mRNA homopolymer tails in vivo, with either the endogenous atpB gene or a version of green fluorescent protein developed for chloroplast expression as reporters. Strains were created in which, after transcription of atpB or gfp, RNase P cleavage occurred upstream of an ectopic tRNA(Glu) moiety, thereby exposing A(28), U(25)A(3), [A+U](26), or A(3) tails. Analysis of these strains showed that, as expected, polyadenylated transcripts failed to accumulate, with RNA being undetectable either by filter hybridization or reverse transcriptase-PCR. In accordance, neither the ATPase beta-subunit nor green fluorescent protein could be detected. However, a U(25)A(3) tail also strongly reduced RNA accumulation relative to a control, whereas the [A+U] tail did not, which is suggestive of a degradation mechanism that does not specifically recognize poly(A), or that multiple mechanisms exist. With an A(3) tail, RNA levels decreased relative to a control with no added tail, but some RNA and protein accumulation was observed. We took advantage of the fact that the strain carrying a modified atpB gene producing an A(28) tail is an obligate heterotroph to obtain photoautotrophic revertants. Each revertant exhibited restored atpB mRNA accumulation and translation, and seemed to act by preventing poly(A) tail exposure. This suggests that the poly(A) tail is only recognized as an instability determinant when exposed at the 3' end of a message.

3' Untranslated Regions↗
PubMed2002

The anatomy of the professional lapse: bridging the gap between traditional frameworks and students' perceptions.

PURPOSE: To support students' developing professionalism, it is necessary to understand the professional challenges and dilemmas they perceive in the clinical setting. This study systematically documented and catalogued students' reports of professional lapses. METHOD: Six focus groups were conducted with senior medical students (n = 29) at three universities. Using a grounded-theory approach, three researchers analyzed the students' reports of specific lapses in professionalism for recurrent themes. The resulting coding structure was applied using NVivo qualitative data analysis software. RESULTS: A total of 120 pages of text yielded 48 specific incidents of professional lapses, which were analyzed by three researchers using grounded theory. Most incidents were witnessed (n = 34) or known about (n = 4), as opposed to self-reported (n = 10). Six critical "issues" emerged: communicative violations (to or about patients or other health care professionals); role resistance (individuals chafing against constraints or expectations of their perceived roles); objectification of patients (ignoring patients or treating patients as vehicles for learning); accountability (to colleagues or patients, including avoiding patients, failing to disclose information, or failing to treat appropriately); physical harm (to patients or others); and crossfire (being put in the middle of a struggle between superiors). CONCLUSIONS: This study explored how students experienced and operationalized professionalism in clinical settings at a variety of universities. Interestingly, the critical issues they reported as salient did not map easily onto standard, abstract definitions of professionalism. This incongruence suggested that the development of effective curricula in this domain must bridge the gap between traditional taxonomies and students' perceptions of professionalism.

Canada↗
PubMed2002

Effect of endothelial cell polarity on beta-amyloid-induced migration of monocytes across normal and AD endothelium.

During normal aging and amyloid beta-peptide (Abeta) disorders such as Alzheimer's disease (AD), one finds increased deposition of Abeta and activated monocytes/microglial cells in the brain. Our previous studies show that Abeta interaction with a monolayer of normal human brain microvascular endothelial cells results in increased adherence and transmigration of monocytes. Relatively little is known of the role of Abeta accumulated in the AD brain in mediating trafficking of peripheral blood monocytes (PBM) across the blood-brain barrier (BBB) and concomitant accumulation of monocytes/microglia in the AD brain. In this study, we showed that interaction of Abeta(1--40) with apical surface of monolayer of brain endothelial cells (BEC), derived either from normal or AD individuals, resulted in increased transendothelial migration of monocytic cells (HL-60 and THP-1) and PBM. However, transmigration of monocytes across the BEC monolayer cultivated in a Transwell chamber was increased 2.5-fold when Abeta was added to the basolateral side of AD compared with normal individual BEC. The Abeta-induced transmigration of monocytes was inhibited in both normal and AD-BEC by antibodies to the putative Abeta receptor, receptor for advanced glycation end products (RAGE), and to the endothelial cell junction molecule, platelet-endothelial cell adhesion molecule-1 (PECAM-1). We conclude that interaction of Abeta with the basolateral surface of AD-BEC induces cellular signaling, promoting transmigration of monocytes from the apical to basolateral direction. We suggest that Abeta in the AD brain parenchyma or cerebrovasculature initiates cellular signaling that induces PBM to transmigrate across the BBB and accumulate in the brain.

Aged↗
PubMed2002

Activation of tubular epithelial cells in diabetic nephropathy.

Previous studies have shown that renal function in type 2 diabetes correlates better with tubular changes than with glomerular pathology. Since advanced glycation end products (AGEs; AGE-albumin) and in particular carboxymethyllysine (CML) are known to play a central role in diabetic nephropathy, we studied the activation of nuclear factor kappaB (NF-kappaB) in tubular epithelial cells in vivo and in vitro by AGE-albumin and CML. Urine samples from healthy control subjects (n = 50) and type 2 diabetic patients (n = 100) were collected and tested for excretion of CML and the presence of proximal tubular epithelial cells (pTECs). CML excretion was significantly higher in diabetic patients than in healthy control subjects (P < 0.0001) and correlated with the degree of albuminuria (r = 0.7, P < 0.0001), while there was no correlation between CML excretion and HbA(1c) (r = 0.03, P = 0.76). Urine sediments from 20 of 100 patients contained pTECs, evidenced by cytokeratin 18 positivity, while healthy control subjects (n = 50) showed none (P < 0.0001). Activated NF-kappaB could be detected in the nuclear region of excreted pTECs in 8 of 20 patients with pTECs in the urine sediment (40%). Five of eight NF-kappaBp65 antigen-positive cells stained positive for interleukin-6 (IL-6) antigen (62%), while only one of the NF-kappaB-negative cells showed IL-6 positivity. pTECs in the urine sediment correlated positively with albuminuria (r = 0.57, P < 0.0001) and CML excretion (r = 0.55, P < 0.0001). Immunohistochemistry in diabetic rat kidneys and a human diabetic kidney confirmed strong expression of NF-kappaB in tubular cells. To further prove an AGE/CML-induced NF-kappaB activation in pTECs, NF-kappaB activation was studied in cultured human pTECs by electrophoretic mobility shift assays (EMSAs) and Western blot. Stimulation of NF-kappaB binding activity was dose dependent and was one-half maximal at 250 nmol/l AGE-albumin or CML and time dependent at a maximum of activation after 4 days. Functional relevance of the observed NF-kappaB activation was demonstrated in pTECs transfected with a NF-kappaB-driven luciferase reporter plasmid and was associated with an increased release of IL-6 into the supernatant. The AGE- and CML-dependent activation of NF-kappaBp65 and NF-kappaB-dependent IL-6 expression could be inhibited using the soluble form of the receptor for AGEs (RAGE) (soluble RAGE [sRAGE]), RAGE-specific antibody, or the antioxidant thioctic acid. In addition transcriptional activity and IL-6 release from transfected cells could be inhibited by overexpression of the NF-kappaB-specific inhibitor kappaBalpha. The findings that excreted pTECs demonstrate activated NF-kappaB and IL-6 antigen and that AGE-albumin and CML lead to a perpetuated activation of NF-kappaB in vitro infer that a perpetuated increase in proinflammtory gene products, such as IL-6, plays a role in damaging the renal tubule.

Animals↗
PubMed2000

Expression of advanced glycation end products and their cellular receptor RAGE in diabetic nephropathy and nondiabetic renal disease.

Advanced glycation end products (AGE) contribute to diabetic tissue injury by two major mechanisms, i.e., the alteration of extracellular matrix architecture through nonenzymatic glycation, with formation of protein crosslinks, and the modulation of cellular functions through interactions with specific cell surface receptors, the best characterized of which is the receptor for AGE (RAGE). Recent evidence suggests that the AGE-RAGE interaction may also be promoted by inflammatory processes and oxidative cellular injury. To characterize the distributions of AGE and RAGE in diabetic kidneys and to determine their specificity for diabetic nephropathy, an immunohistochemical analysis of renal biopsies from patients with diabetic nephropathy (n = 26), hypertensive nephrosclerosis (n = 7), idiopathic focal segmental glomerulosclerosis (n = 11), focal sclerosis secondary to obesity (n = 7), and lupus nephritis (n = 11) and from normal control subjects (n = 2) was performed, using affinity-purified antibodies raised to RAGE and two subclasses of AGE, i.e., N(epsilon)-(carboxymethyl)-lysine (CML) and pentosidine (PENT). AGE were detected equally in diffuse and nodular diabetic nephropathy. CML was the major AGE detected in diabetic mesangium (96%), glomerular basement membranes (GBM) (42%), tubular basement membranes (85%), and vessel walls (96%). In diabetic nephropathy, PENT was preferentially located in interstitial collagen (90%) and was less consistently observed in vessel walls (54%), mesangium (77%), GBM (4%), and tubular basement membranes (31%). RAGE was expressed on normal podocytes and was upregulated in diabetic nephropathy. The restriction of RAGE mRNA expression to glomeruli was confirmed by reverse transcription-PCR analysis of microdissected renal tissue compartments. The extent of mesangial and GBM immunoreactivity for CML, but not PENT, was correlated with the severity of diabetic glomerulosclerosis, as assessed pathologically. CML and PENT were also identified in areas of glomerulosclerosis and arteriosclerosis in idiopathic and secondary focal segmental glomerulosclerosis, hypertensive nephrosclerosis, and lupus nephritis. In active lupus nephritis, CML and PENT were detected in the proliferative glomerular tufts and crescents. In conclusion, CML is a major AGE in renal basement membranes in diabetic nephropathy, and its accumulation involves upregulation of RAGE on podocytes. AGE are also accumulated in acute inflammatory glomerulonephritis secondary to systemic lupus erythematosus, possibly via enzymatic oxidation of glomerular matrix proteins.

Adult↗