Biomedical subjects

David M Stern

Publications and source records attributed to David M Stern.

At least 19 recordsLinked to original sources

PubMed2006

Pael receptor induces death of dopaminergic neurons in the substantia nigra via endoplasmic reticulum stress and dopamine toxicity, which is enhanced under condition of parkin inactivation.

Selective loss of dopaminergic neurons is the final common pathway in Parkinson's disease. Expression of Parkin associated endothelin-receptor like receptor (Pael-R) in mouse brain was achieved by injecting adenoviral vectors carrying a modified neuron-specific promoter and Cre recombinase into the striatum. Upregulation of Pael-R in the substantia nigra pars compacta of mice by retrograde infection induced endoplasmic reticulum (ER) stress leads to death of dopaminergic neurons. The role of ER stress in dopaminergic neuronal vulnerability was highlighted by their decreased survival in mice deficient in the ubiquitin-protein ligase Parkin and the ER chaperone ORP150 (150 kDa oxygen-regulated protein). Dopamine-related toxicity was also a key factor, as a dopamine synthesis inhibitor blocked neuronal death in parkin null mice. These data suggest a model in which ER- and dopamine-related stress are major contributors to decreased viability of dopaminergic neurons in a setting relevant to Parkinson's disease.

Adenoviridae↗

PubMed2006

A rat model of human FENIB (familial encephalopathy with neuroserpin inclusion bodies).

FENIB (familial encephalopathy with neuroserpin inclusion bodies) is caused by intracellular accumulation/polymerization of mutant neuroserpins in the endoplasmic reticulum (ER). Transgenic rats overexpressing megsin (Tg meg), a newly identified serine protease inhibitor (serpin), demonstrated intraneuronal periodic-acid Schiff (PAS)-positive inclusions distributed throughout deeper layers of cerebral cortex, CA1 of the hippocampus, and substantia nigra. Hippocampal extracts from Tg meg rats showed increased expression of ER stress proteins, and activation of caspases-12 and -3, associated with decreased neuronal density. Enhanced ER stress was also observed in dopaminergic neurons in the substantia nigra, in parallel with decreased neuronal viability and motor coordination. In each case, PAS-positive inclusions were also positive for megsin. These data suggest that overexpression of megsin results in ER stress, eventuating in the formation of PAS-positive inclusions. Tg meg rats provide a novel model of FENIB, where accumulation of serpins in the ER induces selective dysfunction/loss of specific neuronal populations.

Animals↗

PubMed2006

Regulation of osteoclast function and bone mass by RAGE.

The receptor for advanced glycation end products (RAGE) is a member of the immunoglobulin superfamily that has multiple ligands and is implicated in the pathogenesis of various diseases, including diabetic complications, neurodegenerative disorders, and inflammatory responses. However, the role of RAGE in normal physiology is largely undefined. Here, we present evidence for a role of RAGE in osteoclast maturation and function, which has consequences for bone remodeling. Mice lacking RAGE had increased bone mass and bone mineral density and decreased bone resorptive activity in vivo. In vitro-differentiated RAGE-deficient osteoclasts exhibited disrupted actin ring and sealing zone structures, impaired maturation, and reduced bone resorptive activity. Impaired signaling downstream of alphavbeta3 integrin was observed in RAGE(-/-) bone marrow macrophages and precursors of OCs. These results demonstrate a role for RAGE in osteoclast actin cytoskeletal reorganization, adhesion, and function, and suggest that the osteosclerotic-like phenotype observed in RAGE knockout mice is due to a defect in osteoclast function.

Actins↗

PubMed2006

Effect of simvastatin on high glucose- and angiotensin II-induced activation of the JAK/STAT pathway in mesangial cells.

In the current study, we investigated the effect of simvastatin on the ability of high glucose (HG) and ANG II to activate the JAK2-STAT signaling cascade and induce glomerular mesangial cell (GMC) growth. We found that pretreatment with simvastatin significantly inhibited HG- and ANG II-induced collagen IV production, JAK2 activation, and phosphorylation of STAT1 and STAT3 in GMC. We also found that the activation of JAK2 by HG and ANG II was dependent on the Rho family of GTPases. Consistent with these in vitro results, both albumin protein excretion and phosphorylation of JAK2, STAT1, and STAT3 were attenuated in renal glomeruli by administration of simvastatin in a streptozotocin-induced rat model of HG diabetes. This study demonstrates that simvastatin blocks ANG II-induced activation of the JAK/STAT pathway in the diabetic environment, in vitro and in vivo, and, thereby, provides new insights into the molecular mechanisms underlying early diabetic nephropathy.

Angiotensin II↗

PubMed2006

Deletion of SERP1/RAMP4, a component of the endoplasmic reticulum (ER) translocation sites, leads to ER stress.

Stress-associated endoplasmic reticulum (ER) protein 1 (SERP1), also known as ribosome-associated membrane protein 4 (RAMP4), is a Sec61-associated polypeptide that is induced by ER stress. SERP1-/- mice, made by targeted gene disruption, demonstrated growth retardation, increased mortality, and impaired glucose tolerance. Consistent with high levels of SERP1 expression in pancreas, pancreatic islets from SERP1-/- mice failed to rapidly synthesize proinsulin in response to a glucose load. In addition, reduced size and enhanced ER stress were observed in the anterior pituitary of SERP1-/- mice, and growth hormone production was slowed in SERP1-/- pituitary after insulin stimulation. Experiments using pancreatic microsomes revealed aberrant association of ribosomes and the Sec61 complex and enhanced ER stress in SERP1-/- pancreas. In basal conditions, the Sec61 complex in SERP1-/- microsomes was more cofractionated with ribosomes, compared with SERP1+/+ counterparts, in high-salt conditions. In contrast, after glucose stimulation, the complex showed less cofractionation at an early phase (45 min) but more at a later phase (120 min). Although intracellular insulin/proinsulin levels were not significantly changed in both genotypes, these results suggest that subtle changes in translocation efficiency play an important role in the regulation of ER stress and rapid polypeptide synthesis.

Animals↗

PubMed2006

Role of the JAK/STAT signaling pathway in diabetic nephropathy.

Excessive cellular growth is a major contributor to pathological changes associated with diabetic nephropathy. In particular, high glucose-induced growth of glomerular mesangial cells is a characteristic feature of diabetes-induced renal complications. Glomerular mesangial cells respond to traditional growth factors, although in diabetes this occurs in the context of an environment enriched in both circulating vasoactive mediators and high glucose. For example, the vasoactive peptide ANG II has been implicated in the pathogenesis of diabetic renal disease, and recent findings suggest that high glucose and ANG II activate intracellular signaling processes, including the polyol pathway and generation of reactive oxygen species. These pathways activate the Janus kinase (JAK)/signal transducers and activators of transcription (STAT) signaling cascades in glomerular mesangial cells. Activation of the JAK/STAT signaling cascade can stimulate excessive proliferation and growth of glomerular mesangial cells, contributing to diabetic nephropathy. This review focuses on some of the key elements in the diabetic microenvironment, especially high glucose and the accumulation of advanced glycoxidation end products and considers their impact on ANG II and other vasoactive peptide-mediated signaling events in vitro and in vivo.

Angiotensin II↗

PubMed2006

Posttranslationally modified proteins as mediators of sustained intestinal inflammation.

Oxidative and carbonyl stress leads to generation of N(epsilon)-carboxymethyllysine-modified proteins (CML-mps), which are known to bind the receptor for advanced glycation end products (RAGE) and induce nuclear factor (NF)-kappaB-dependent proinflammatory gene expression. To determine the impact of CML-mps in vivo, RAGE-dependent sustained NF-kappaB activation was studied in resection gut specimens from patients with inflammatory bowel disease. Inflamed gut biopsy tissue demonstrated a significant up-regulation of RAGE and increased NF-kappaB activation. Protein extracts from the inflamed zones, but not from noninflamed resection borders, caused perpetuated NF-kappaB activation in cultured endothelial cells, which was mediated by CML-mps including CML-modified S100 proteins. The resulting NF-kappaB activation, lasting 5 days, was primarily inhibited by either depletion of CML-mps or by the addition of sRAGE, p44/42 and p38 MAPKinase-specific inhibitors. Consistently, CML-mps isolated from inflamed gut areas and rectally applied into mice caused NF-kappaB activation, increased proinflammatory gene expression, and histologically detectable inflammation in wild-type mice, but not in RAGE-/- mice. A comparable up-regulation of NF-kappaB and inflammation on rectal application of CML-mps was observed in IL-10-/- mice. Thus, CML-mps generated in inflammatory lesions have the capacity to elicit a RAGE-dependent intestinal inflammatory response.

Adult↗

PubMed2006

Mitochondrial amyloid-beta peptide: pathogenesis or late-phase development?

Mitochondrial and metabolic dysfunction have been linked to Alzheimer's disease for some time. Key questions regarding this association concern the nature and mechanisms of mitochondrial dysfunction, and whether such changes in metabolic properties are pathogenic or secondary, with respect to neuronal degeneration. In terms of mitochondria and Alzheimer's, altered function could reflect intrinsic properties of this organelle, potentially due to mutations in mitochondrial DNA, or extrinsic changes secondary to signal transduction mechanisms activated in the cytosol. This review presents data relevant to these questions, and considers the implication of recent findings demonstrating the presence of amyloid-beta peptide in mitochondria, as well as intra-mitochondrial molecular targets with which it can interact. Regardless of the underlying mechanism(s), it is likely that mitochondrial dysfunction contributes to oxidant stress which is commonly observed in brains of patients with Alzheimer's and transgenic models of Alzheimer's-like pathology.

Alzheimer Disease↗

PubMed2006

RAGE in inflammation: a new therapeutic target?

High-molecular group box 1-protein, S100/calgranulins, advanced glycation end products (AGEs), amyloid-beta peptides and the family of beta-sheet fibrils contribute to a number of inflammatory conditions by promoting cellular dysfunction and breaking immune tolerance. The receptor of AGE (RAGE) is a multiligand receptor of the immunoglobulin superfamily of cell surface molecules that acts as a pattern recognition receptor. Besides binding ligands actively participating in inflammation and immune responses, RAGE serves as an endothelial adhesion receptor for leukocyte integrins and promotes leukocyte recruitment and extravasation of infiltrating cells. Engagement of RAGE subsequently converts transient cellular stimulation into sustained cellular dysfunction driven by long-term activation of the proinflammatory nuclear factor-kappaB. Deletion of RAGE and pharmacological interventions targeting interruption of RAGE-ligand interaction suppresses inflammation and dampens tissue damage in experimental models of inflammatory disorders, thus delineating RAGE as a potential therapeutic target in inflammation.

Animals↗

PubMed2006

A new protocol for quantifying CD34(+) cells in peripheral blood of patients with cardiovascular disease.

Increasing evidence points to a role for circulating CD34-positive (CD34(+)) cells in vascular maintenance and neovascularization. Although there are established methods for evaluating absolute numbers of CD34(+) cells in bone marrow or mobilized peripheral blood, there is no convenient and highly reproducible method for quantifying low numbers of CD34(+) cells in blood samples, such as those from the peripheral blood of patients with cardiovascular disease. With current commonly used methods, the mean percentage of CD34(+) cells in leukocyte fractions from such patients was only 0.02%, and the cumulative intra-assay coefficient of variation was approximately 30%. With use of the protocol described herein, actual counts of CD34(+) cells increased approximately 5-fold and cumulative intra-assay coefficients of variation were reduced to approximately 7%. The new method is useful to precisely measure low numbers of CD34(+) cells in samples, and it has potential as a screening tool to evaluate cardiovascular risk in large patient populations.

Aged↗

PubMed2005

Disordered osteoclast formation in RAGE-deficient mouse establishes an essential role for RAGE in diabetes related bone loss.

The mechanisms underlying diabetes-mediated bone loss are not well defined. It has been reported that the advanced glycation endproducts (AGEs) and receptor for AGEs (RAGEs) are involved in diabetic complications. Here, mice deficient in RAGE were used as a model for investigating the effects of RAGE on bone mass. We found that RAGE-/- mice have a significantly increased bone mass and bone biomechanical strength and a decreased number of osteoclasts compared to wild-type mice. The serum levels of IL-6 and bone breakdown marker pyridinoline were significantly decreased in RAGE-/- mice. RAGE-/- mice maintain bone mass following ovariectomy, whereas wild-type mice lose bone mass. Furthermore, osteoclast-like cells do express RAGE mRNA. Our data therefore indicate that RAGE serves as a positive factor to regulate the osteoclast formation, directly implicates a role for RAGE in diabetes-promoted bone destruction, and documents that the AGE-RAGE interaction may account for diabetes associated bone loss.

Animals↗

PubMed2005

Hyperglycemia and reactive oxygen species mediate apoptosis in aortic endothelial cells through Janus kinase 2.

The generation of reactive oxygen species (ROS) has been implicated in the perturbation of endothelial function and cell death. However, the specific signaling pathways which mediate and modifying this response have not been fully elucidated. Therefore, in this study we tested the hypothesis that activation of JAK2 is involved in the aortic endothelial cell (EC) response to ROS. When ECs were exposed to HG (25 mM) for 6 h or ROS (i.e., H(2)O(2) (100 microM)) for 1 h and returned to normal medium we found a decrease in cell density and morphologic signs of apoptosis. Furthermore, incubation of ECs with HG and H(2)O(2) also resulted in the tyrosine phosphorylation of JAK2. In addition, pretreatment of ECs with AG-490, an inhibitor of JAK2, prevented nuclear fragmentation, whereas inhibitors of Jun kinase (SP 600125), MAP kinase (PD 98059), Src kinase (PP2) or PI-3 kinase (wortmannin) were without effect. Finally, immunoblot analysis of caspase-3 and PARP cleavage confirmed a role for activation of JAK2 in both HG- or ROS-induced apoptosis, based on inhibition by either AG-490 or adenoviral transfection with a dominant-negative JAK2 mutant. In conclusion the activation of JAK2 plays a pivotal role in oxidant stress-induced commitment of ECs to apoptosis, based on studies with HG and H(2)O(2).

Adenoviridae↗

PubMed2005

Understanding RAGE, the receptor for advanced glycation end products.

Advanced glycation end products (AGEs), S100/calgranulins, HMGB1-proteins, amyloid-beta peptides, and the family of beta-sheet fibrils have been shown to contribute to a number of chronic diseases such as diabetes, amyloidoses, inflammatory conditions, and tumors by promoting cellular dysfunction via binding to cellular surface receptors. The receptor for AGEs (RAGE) is a multiligand receptor of the immunoglobulin superfamily of cell surface molecules acting as counter-receptor for these diverse molecules. Engagement of RAGE converts a brief pulse of cellular activation to sustained cellular dysfunction and tissue destruction. The involvement of RAGE in pathophysiologic processes has been demonstrated in murine models of chronic disease using either a receptor decoy such as soluble RAGE (sRAGE), RAGE neutralizing antibodies, or a dominant-negative form of the receptor. Studies with RAGE-/- mice confirmed that RAGE contributes, at least in part, to the development of late diabetic complications, such as neuropathy and nephropathy, macrovascular disease, and chronic inflammation. Furthermore, deletion of RAGE provided protection from the lethal effects of septic shock caused by cecal ligation and puncture (CLP). In contrast, deletion of RAGE had no effect on the host response in delayed-type hypersensitivity (DTH). Despite the lack of effect seen in adaptive immunity by the deletion of RAGE, administration of the receptor decoy, sRAGE, still afforded a protective effect in RAGE-/- mice. Thus, sRAGE is likely to sequester ligands, thereby preventing their interaction with other receptors in addition to RAGE. These data suggest that, just as RAGE is a multiligand receptor, its ligands are also likely to recognize several receptors in mediating their biologic effects.

Animals↗

PubMed2005

The N-terminal domain of thrombomodulin sequesters high-mobility group-B1 protein, a novel antiinflammatory mechanism.

Thrombomodulin (TM) is an endothelial anticoagulant cofactor that promotes thrombin-mediated formation of activated protein C (APC). We have found that the N-terminal lectin-like domain (D1) of TM has unique antiinflammatory properties. TM, via D1, binds high-mobility group-B1 DNA-binding protein (HMGB1), a factor closely associated with necrotic cell damage following its release from the nucleus, thereby preventing in vitro leukocyte activation, in vivo UV irradiation-induced cutaneous inflammation, and in vivo lipopolysaccharide-induced lethality. Our data also demonstrate antiinflammatory properties of a peptide spanning D1 of TM and suggest its therapeutic potential. These findings highlight a novel mechanism, i.e., sequestration of mediators, through which an endothelial cofactor, TM, suppresses inflammation quite distinctly from its anticoagulant cofactor activity, thereby preventing the interaction of these mediators with cell surface receptors on effector cells in the vasculature.

Animals↗

PubMed2005

Mitochondrial dysfunction, endoplasmic reticulum stress, and apoptosis in Alzheimer's disease.

Alzheimer's disease (AD) is the most common neurodegenerative disorder of late life characterized by insidious, chronic, and progressive memory impairment in association with the accumulation of senile plaques, neurofibrillary tangles, and massive loss of neurons. Apoptosis is believed to be an important contributor to progression and pathology of neurodegeneration in AD. There is considerable evidence that amyloid beta-peptide, a major component of senile plaques, has the capacity to activate intracellular apoptosis pathways leading to neuronal cell death. AD-related mutations in genes coding presenilins are also shown to cause neuronal apoptosis, by directly and indirectly regulating apoptotic signaling cascades. Recent evidence suggests that two intrinsic pathways, mitochondrial dysfunction and endoplasmic reticulum stress, are central in the execution of apoptosis in AD. This review summarizes recent progress of research in this field focused on the molecular mechanisms involved in neuronal apoptosis mediated by organelle dysfunction.

Alzheimer Disease↗

PubMed2005

ABAD enhances Abeta-induced cell stress via mitochondrial dysfunction.

Amyloid-beta peptide (Abeta) binding alcohol dehydrogenase (ABAD), an enzyme present in neuronal mitochondria, is a cofactor facilitating Abeta-induced cell stress. We hypothesized that ABAD provides a direct link between Abeta and cytotoxicity via mitochondrial oxidant stress. Neurons cultured from transgenic (Tg) mice with targeted overexpression of a mutant form of amyloid precursor protein and ABAD (Tg mAPP/ABAD) displayed spontaneous generation of hydrogen peroxide and superoxide anion, and decreased ATP, as well as subsequent release of cytochrome c from mitochondria and induction of caspase-3-like activity followed by DNA fragmentation and loss of cell viability. Generation of reactive oxygen species (ROS) was associated with dysfunction at the level of mitochondrial complex IV (cytochrome c oxidase, or COX). In neurons cultured from Tg mAPP/ABAD mice, COX activity was selectively decreased, and cyanide, an inhibitor of complex IV, exacerbated leakage of ROS, induction of caspase-3-like activity, and DNA fragmentation. In vivo, Tg mAPP/ABAD mice displayed reduced levels of brain ATP and COX activity, diminished glucose utilization, as well as electrophysiological abnormalities in hippocampal slices compared with Tg mAPP mice. In contrast, neither Tg ABAD mice nor nontransgenic (non-TG) littermates showed similar changes in ATP, COX activity, glucose utilization or electrophysiological properties. Each of the genotypes (Tg ABAD, Tg mAPP and Tg mAPP/ABAD mice, and non-TG littermates) displayed normal reproductive fitness, development and lifespan (1) These findings link ABAD-induced oxidant stress to critical aspects of Alzheimer's disease (AD)-associated cellular dysfunction, suggesting a pivotal role for this enzyme in the pathogenesis of AD.

3-Hydroxyacyl CoA Dehydrogenases↗

PubMed2005

Atherosclerosis and restenosis: is there a role for RAGE?

Diabetic vascular complications are a major cause of morbidity and mortality. Furthermore, such vascular disease is only incompletely explained by "traditional" risk factors in the nondiabetic complications. This situation has prompted the search for factors contributing to the pathogenesis of accelerated and more severe vascular disease in patients with diabetes. We review evidence that receptor for advanced glycation end products (RAGE), via its interaction with ligands, serves as a cofactor exacerbating diabetic vascular disease. RAGE is a member of the immunoglobulin superfamily of cell surface molecules with a diverse repertoire of ligands reminiscent of pattern recognition receptors. In the diabetic milieu, two classes of RAGE ligands, products of nonenzymatic glycoxidation and S100 proteins, appear to drive receptor-mediated cellular activation and, potentially, acceleration of vascular disease.

Arteriosclerosis↗

PubMed2005

The marriage of glucose and blood vessels: it isn't all that sweet.

The secondary complications of diabetes are the major factors limiting quality of life and longevity in diabetic patients. Among these complications, cardiovascular disease is the major cause of morbidity and mortality. Based on a recent paper by Vikramadithyan et al. (2005), this preview addresses the role of aldose reductase as a contributor to the pathogenesis of diabetic macrovascular disease.

Aldehyde Reductase↗