Smac, a mitochondrial protein that promotes cytochrome c-dependent caspase activation by eliminating IAP inhibition

We report here the identification of a novel protein, Smac, which promotes caspase activation in the cytochrome c/Apaf-1/caspase-9 pathway. Smac promotes caspase-9 activation by binding to inhibitor of apoptosis proteins, IAPs, and removing their inhibitory activity. Smac is normally a mitochondrial protein but is released into the cytosol when cells undergo apoptosis. Mitochondrial import and cleavage of its signal peptide are required for Smac to gain its apoptotic activity. Overexpression of Smac increases cells' sensitivity to apoptotic stimuli. Smac is the second mitochondrial protein, along with cytochrome c, that promotes apoptosis by activating caspases.

Role of LXRs in control of lipogenesis

The discovery of oxysterols as the endogenous liver X receptor (LXR) ligands and subsequent gene targeting studies in mice provided strong evidence that LXR plays a central role in cholesterol metabolism. The identification here of a synthetic, nonsteroidal LXR-selective agonist series represented by T0314407 and T0901317 revealed a novel physiological role of LXR. Oral administration of T0901317 to mice and hamsters showed that LXR activated the coordinate expression of major fatty acid biosynthetic genes (lipogenesis) and increased plasma triglyceride and phospholipid levels in both species. Complementary studies in cell culture and animals suggested that the increase in plasma lipids occurs via LXR-mediated induction of the sterol regulatory element-binding protein 1 (SREBP-1) lipogenic program.

Regulation of absorption and ABC1-mediated efflux of cholesterol by RXR heterodimers

Several nuclear hormone receptors involved in lipid metabolism form obligate heterodimers with retinoid X receptors (RXRs) and are activated by RXR agonists such as rexinoids. Animals treated with rexinoids exhibited marked changes in cholesterol balance, including inhibition of cholesterol absorption and repressed bile acid synthesis. Studies with receptor-selective agonists revealed that oxysterol receptors (LXRs) and the bile acid receptor (FXR) are the RXR heterodimeric partners that mediate these effects by regulating expression of the reverse cholesterol transporter, ABC1, and the rate-limiting enzyme of bile acid synthesis, CYP7A1, respectively. Thus, these RXR heterodimers serve as key regulators of cholesterol homeostasis by governing reverse cholesterol transport from peripheral tissues, bile acid synthesis in liver, and cholesterol absorption in intestine.

Alagille syndrome is caused by mutations in human Jagged1, which encodes a ligand for Notch1

Alagille syndrome is an autosomal dominant disorder characterized by abnormal development of liver, heart, skeleton, eye, face and, less frequently, kidney. Analyses of many patients with cytogenetic deletions or rearrangements have mapped the gene to chromosome 20p12, although deletions are found in a relatively small proportion of patients (< 7%). We have mapped the human Jagged1 gene (JAG1), encoding a ligand for the developmentally important Notch transmembrane receptor, to the Alagille syndrome critical region within 20p12. The Notch intercellular signalling pathway has been shown to mediate cell fate decisions during development in invertebrates and vertebrates. We demonstrate four distinct coding mutations in JAG1 from four Alagille syndrome families, providing evidence that it is the causal gene for Alagille syndrome. All four mutations lie within conserved regions of the gene and cause translational frameshifts, resulting in gross alterations of the protein product Patients with cytogenetically detectable deletions including JAG1 have Alagille syndrome, supporting the hypothesis that haploinsufficiency for this gene is one of the mechanisms causing the Alagille syndrome phenotype.

Activin receptor-like kinase 1 modulates transforming growth factor-beta 1 signaling in the regulation of angiogenesis

The activin receptor-like kinase 1 (ALK1) is a type I receptor for transforming growth factor-beta (TGF-beta) family proteins. Expression of ALK1 in blood vessels and mutations of the ALK1 gene in human type II hereditary hemorrhagic telangiectasia patients suggest that ALK1 may have an important role during vascular development. To define the function of ALK1 during development, we inactivated the ALK1 gene in mice by gene targeting. The ALK1 homozygous embryos die at midgestation, exhibiting severe vascular abnormalities characterized by excessive fusion of capillary plexes into cavernous vessels and hyperdilation of large vessels. These vascular defects are associated with enhanced expression of angiogenic factors and proteases and are characterized by deficient differentiation and recruitment of vascular smooth muscle cells. The blood vessel defects in ALK1-deficient mice are reminiscent of mice lacking TGF-beta1, TGF-beta type II receptor (TbetaR-II), or endoglin, suggesting that ALK1 may mediate TGF-beta1 signal in endothelial cells. Consistent with this hypothesis, we demonstrate that ALK1 in endothelial cells binds to TGF-beta1 and TbetaR-II. Furthermore, the ALK1 signaling pathway can inhibit TGF-beta1-dependent transcriptional activation mediated by the known TGF-beta1 type I receptor, ALK5. Taken together, our results suggest that the balance between the ALK1 and ALK5 signaling pathways in endothelial cells plays a crucial role in determining vascular endothelial properties during angiogenesis.

Texture analysis of medical images

The analysis of texture parameters is a useful way of increasing the information obtainable from medical images. It is an ongoing field of research, with applications ranging from the segmentation of specific anatomical structures and the detection of lesions, to differentiation between pathological and healthy tissue in different organs. Texture analysis uses radiological images obtained in routine diagnostic practice, but involves an ensemble of mathematical computations performed with the data contained within the images. In this article we clarify the principles of texture analysis and give examples of its applications, reviewing studies of the technique.

Low-density lipoprotein receptor-related protein-5 binds to Axin and regulates the canonical Wnt signaling pathway

To understand how the Wnt coreceptor LRP-5 is involved in transducing the canonical Wnt signals, we identified Axin as a protein that interacts with the intracellular domain of LRP-5. LRP-5, when expressed in fibroblast cells, showed no effect on the canonical Wnt signaling pathway by itself, but acted synergistically with Wnt. In contrast, LRP-5 mutants lacking the extracellular domain functioned as constitutively active forms that bind Axin and that induce LEF-1 activation by destabilizing Axin and stabilizing beta-catenin. Addition of Wnt caused the translocation of Axin to the membrane and enhanced the interaction between Axin and LRP-5. In addition, the LRP-5 sequences involved in interactions with Axin are required for LEF-1 activation. Thus, we conclude that the binding of Axin to LRP-5 is an important part of the Wnt signal transduction pathway.

Reconstruction of damaged corneas by transplantation of autologous limbal epithelial cells

BACKGROUND

Stevens-Johnson syndrome, ocular pemphigoid, and thermal or chemical burns can cause scarring and opacification of the cornea and loss of vision. Transplantation of epithelial cells from the limbus of the contralateral cornea can restore useful vision. However, this procedure requires a large limbal graft from the healthy eye and is not possible in patients who have bilateral lesions.

METHODS

We took specimens of limbal epithelial cells from the healthy contralateral eyes of six patients with severe unilateral corneal disease. The epithelial cells were cultured and expanded on amniotic membrane. The amniotic membrane, together with the sheet of limbal epithelial cells, was transplanted to the denuded corneal surface of the damaged eye after superficial keratectomy to remove fibrovascular ingrowth. The mean (+/-SD) follow-up period was 15+/-2 months.

RESULTS

Complete reepithelialization of the corneal surface occurred within two to four days of transplantation in all six eyes receiving transplants. By one month, the ocular surface was covered with corneal epithelium, and the clarity of the cornea was improved. In five of the six eyes receiving transplants (83 percent), the mean visual acuity improved from 20/112 to 20/45. In one patient with a chemical burn who had total opacification of the cornea, the acuity improved from the ability to count fingers at 40 cm to 20/200. No patient had recurrent neovascularization or inflammation in the transplanted area during the follow-up period.

CONCLUSIONS

Transplantation of autologous limbal epithelial cells cultured on amniotic membrane is a simple and effective method of reconstructing the corneal surface and restoring useful vision in patients with unilateral deficiency of limbal epithelial cells.

Prism adaptation to a rightward optical deviation rehabilitates left hemispatial neglect

A large proportion of right-hemisphere stroke patients show hemispatial neglect-a neurological deficit of perception, attention, representation, and/or performing actions within their left-sided space, inducing many functional debilitating effects on everyday life, and responsible for poor functional recovery and ability to benefit from treatment. The frequent parietal locus of the lesion producing neglect reflects the impairment of coordinate transformation used by the nervous system to represent extrapersonal space. Given that adaptation to a visual distortion can provide an efficient way to stimulate neural structures responsible for the transformation of sensorimotor coordinates, the aim of our study was to investigate the effect of prism adaptation on various neglect symptoms, including the pathological shift of the subjective midline to the right. All patients exposed to the optical shift of the visual field to the right were improved on their manual body-midline demonstration and on classical neuropsychological tests. Unlike other physiological manipulations used to improve neglect, this improvement lasted for at least two hours after prism removal and thus could be useful in rehabilitation programmes. The positive effect found for both sensorimotor and more cognitive spatial functions suggests that they share or depend on a common level of space representation linked to multisensory integration.

Volumetry of hippocampus and amygdala with high-resolution MRI and three-dimensional analysis software: minimizing the discrepancies between laboratories

Within the medial temporal lobe, both the hippocampus and amygdala are frequently targeted by researchers and clinicians for volumetric analysis based on magnetic resonance imaging (MRI). However, different data acquisition techniques, analysis software and anatomical boundaries have in the past made it difficult to compare results of MRI studies from different laboratories. In order to reduce these differences, a segmentation protocol was established with 40 healthy normal control subjects recently scanned in our laboratory. Data acquisition was performed with a three-dimensional gradient echo technique, and scans were corrected for non-uniformity and registered into standard stereotaxic space prior to segmentation. Volumetric analysis was performed manually using three-dimensional software that allows simultaneous analysis of sagittal, coronal and horizontal images. Intra- and inter-rater coefficients yielded correlation coefficients comparable with other protocols. The hippocampal volume was larger in the right hemisphere (3324 versus 3208 mm(3)), while no interhemispheric differences for the amygdala (1154 versus 1160 mm(3)) could be observed. Most importantly, results from recent segmentation protocols for hippocampus and amygdala seem to approach each other with regard to mean volumes and interhemispheric differences. This indicates that the advances in scanning technique, volume preparation and segmentation protocols allow a more precise definition of medial temporal lobe structures with MRI, and that results for mean volumes for hippocampus and amygdala from different laboratories will eventually become comparable.

Arrhythmogenesis and contractile dysfunction in heart failure: Roles of sodium-calcium exchange, inward rectifier potassium current, and residual beta-adrenergic responsiveness

Ventricular arrhythmias and contractile dysfunction are the main causes of death in human heart failure (HF). In a rabbit HF model reproducing these same aspects of human HF, we demonstrate that a 2-fold functional upregulation of Na(+)-Ca(2+) exchange (NaCaX) unloads sarcoplasmic reticulum (SR) Ca(2+) stores, reducing Ca(2+) transients and contractile function. Whereas beta-adrenergic receptors (beta-ARs) are progressively downregulated in HF, residual beta-AR responsiveness at this critical HF stage allows SR Ca(2+) load to increase, causing spontaneous SR Ca(2+) release and transient inward current carried by NaCaX. A given Ca(2+) release produces greater arrhythmogenic inward current in HF (as a result of NaCaX upregulation), and approximately 50% less Ca(2+) release is required to trigger an action potential in HF. The inward rectifier potassium current (I(K1)) is reduced by 49% in HF, and this allows greater depolarization for a given NaCaX current. Partially blocking I(K1) in control cells with barium mimics the greater depolarization for a given current injection seen in HF. Thus, we present data to support a novel paradigm in which changes in NaCaX and I(K1), and residual beta-AR responsiveness, conspire to greatly increase the propensity for triggered arrhythmias in HF. In addition, NaCaX upregulation appears to be a critical link between contractile dysfunction and arrhythmogenesis.

Developing motor neurons rescued from programmed and axotomy-induced cell death by GDNF

During normal development of the vertebrate nervous system, large numbers of neurons in the central and peripheral nervous system undergo naturally occurring cell death. For example, about half of all spinal motor neurons die over a period of a few days in developing avian, rat and mouse embryos. Previous studies have shown that extracts from muscle and brain, secreted factors from glia, as well as several growth factors and neurotrophic agents, including muscle-derived factors, can promote the survival of developing motor neurons in vitro and in vivo. But because neurotrophins and other known trophic agents administered alone or in combination are insufficient to rescue all developing motor neurons from cell death, other neurotrophic molecules are probably essential for the survival and differentiation of motor neurons. Here we report that glial-cell-line-derived neurotrophic factor (GDNF), a potent neurotrophic factor that enhances survival of mammalian midbrain dopaminergic neurons, rescues developing avian motor neurons from natural programmed cell death in vivo and promotes the survival of enriched populations of cultured motor neurons. Furthermore, treatment with this agent in vivo also prevents the induced death and atrophy of both avian and mouse spinal motor neurons following peripheral axotomy.

The FET3 gene of S. cerevisiae encodes a multicopper oxidase required for ferrous iron uptake

S. cerevisiae accumulate iron by a process requiring a ferrireductase and a ferrous transporter. We have isolated a mutant, fet3, defective for high affinity Fe(II) uptake. The wild-type FET3 gene was isolated by complementation of the mutant defect. Sequence analysis of the gene revealed the presence of an open reading frame coding for a protein with strong similarity to the family of blue multicopper oxidoreductases. Consistent with the role of copper in iron transport, growth of wild-type cells in copper-deficient media resulted in decreased ferrous iron transport. Addition of copper, but not other transition metals (manganese or zinc), to the assay media resulted in the recovery of Fe(II) transporter activity. We suggest that the catalytic activity of the Fet3 protein is required for cellular iron accumulation.

Akt activation preserves cardiac function and prevents injury after transient cardiac ischemia in vivo

BACKGROUND

The serine-threonine kinase Akt is activated by several ligand-receptor systems previously shown to be cardioprotective. Akt activation reduces cardiomyocyte apoptosis in models of transient ischemia. Its role in cardiac dysfunction or infarction, however, remains unclear.

METHODS AND RESULTS

We examined the effects of a constitutively active Akt mutant (myr-Akt) in a rat model of cardiac ischemia-reperfusion injury. In vivo gene transfer of myr-Akt reduced infarct size by 64% and the number of apoptotic cells by 84% (P<0.005 for each). Ischemia-reperfusion injury decreased regional cardiac wall thickening as well as the maximal rate of left ventricular pressure rise and fall (+dP/dt and -dP/dt). Akt activation restored regional wall thickening and +dP/dt and -dP/dt to levels seen in sham-operated rats. To better understand this benefit, we examined the effects of myr-Akt on hypoxic cardiomyocyte dysfunction in vitro. myr-Akt prevented hypoxia-induced abnormalities in cardiomyocyte calcium transients and shortening. Akt activation also enhanced sarcolemmal expression of Glut-4 in vivo and increased glucose uptake in vitro to the level seen with insulin treatment.

CONCLUSIONS

Akt activation exerts a powerful cardioprotective effect after transient ischemia that probably reflects its ability to both inhibit cardiomyocyte death and improve function of surviving cardiomyocytes. Akt may represent an important nodal target for therapy in ischemic and other heart disease.

A neural mechanism for working and recognition memory in inferior temporal cortex

Inferior temporal (IT) cortex is critical for visual memory, but it is not known how IT neurons retain memories while new information is streaming into the visual system. Single neurons were therefore recorded from IT cortex of two rhesus monkeys performing tasks that required them to hold items in memory while concurrently viewing other items. The neuronal response to an incoming visual stimulus was attenuated if it matched a stimulus actively held in working memory, even when several other stimuli intervened. The neuronal response to novel stimuli declined as the stimuli became familiar to the animal. IT neurons appear to function as adaptive mnemonic "filters" that preferentially pass information about new, unexpected, or not recently seen stimuli.

A dynamical systems approach to lower extremity running injuries

In this paper, we are presenting an alternative approach to the investigation of lower extremity coupling referred to as a dynamical systems approach. In this approach, we calculate the phase angle of each segment and joint angle. Pairing the key segment/joint motions, we use phase angles to determine the continuous relative phase and the variability of the continuous relative phase. Data from two studies illustrate the efficacy of the dynamical systems approach. Individuals who were asymptomatic, even though they may have anatomical aberrant structural problems (i.e. high Q-angle vs low Q-angle) showed no differences in the pattern of the continuous relative phase or in the variability of the continuous phase. However, differences in the variability of the continuous relative phase were apparent in comparing individuals who were symptomatic with patellofemoral pain with non-injured individuals. Patellofemoral pain individuals showed less variability in the continuous relative phase of the lower extremity couplings than did the healthy subjects. We hypothesize that the lower variability of the couplings in the symptomatic individuals indicates repeatable joint actions within a very narrow range.

RELEVANCE

We claim that the traditional view of the variability of disordered movement is not tenable and suggest that there is a functional role for variability in lower extremity segment coupling during locomotion. While the methods described in this paper cannot determine a cause of the injury, they may be useful in the detection and treatment of running injuries.

Chinese SF-36 Health Survey: translation, cultural adaptation, validation, and normalisation

STUDY OBJECTIVE

To develop a self administered Chinese (mainland) version of the Short-Form Health Survey (SF-36) for use in health related quality of life measurements in China.

DESIGN

A three stage protocol was followed including translation, tests of scaling construction and scoring assumptions, validation, and normalisation.

SETTING

1000 households in 18 communities of Hangzhou.

PARTICIPANTS

1688 respondents recruited by multi-stage mixed sampling.

MAIN RESULTS

The assumption of equal intervals was violated for the vitality and mental health scales. The recoded item values were used to calculate scale scores. The clustering and ordering of item means was the same as that of the source and other two Chinese versions. The items in each scale had similar standard deviations except those in the physical functioning, boduily pain, social functioning scales. The item hypothesised scale correlations were identical for all except the social functioning and vitality scales. Convergent validity and discriminant validity were satisfactory for all except the social functioning scale. Cronbach's alpha coefficients ranged from 0.72 to 0.88 except 0.39 for the social functioning scale and 0.66 for the vitality scale. Two weeks test-retest reliability coefficients ranged from 0.66 to 0.94. Factor analysis identified two principal components explaining 56.3% of the total variance. The Chinese SF-36 could distinguish known groups.

CONCLUSIONS

This study suggested that the Chinese (mainland) version of the SF-36 functioned in the general population of Hangzhou, China quite similarly to the original American population tested. Caution is recommended in the interpretation of the social functioning and vitality scales pending further studies.

From ab initio quantum mechanics to molecular neurobiology: a cation-pi binding site in the nicotinic receptor

The nicotinic acetylcholine receptor is the prototype ligand-gated ion channel. A number of aromatic amino acids have been identified as contributing to the agonist binding site, suggesting that cation-pi interactions may be involved in binding the quaternary ammonium group of the agonist, acetylcholine. Here we show a compelling correlation between: (i) ab initio quantum mechanical predictions of cation-pi binding abilities and (ii) EC50 values for acetylcholine at the receptor for a series of tryptophan derivatives that were incorporated into the receptor by using the in vivo nonsense-suppression method for unnatural amino acid incorporation. Such a correlation is seen at one, and only one, of the aromatic residues-tryptophan-149 of the alpha subunit. This finding indicates that, on binding, the cationic, quaternary ammonium group of acetylcholine makes van der Waals contact with the indole side chain of alpha tryptophan-149, providing the most precise structural information to date on this receptor. Consistent with this model, a tethered quaternary ammonium group emanating from position alpha149 produces a constitutively active receptor.

Mutations of tau protein in frontotemporal dementia promote aggregation of paired helical filaments by enhancing local beta-structure

The microtubule-associated protein tau is a natively unfolded protein in solution, yet it is able to polymerize into the ordered paired helical filaments (PHF) of Alzheimer's disease. In the splice isoforms lacking exon 10, this process is facilitated by the formation of beta-structure around the hexapeptide motif PHF6 ((306)VQIVYK(311)) encoded by exon 11. We have investigated the structural requirements for PHF polymerization in the context of adult tau isoforms containing four repeats (including exon 10). In addition to the PHF6 motif there exists a related PHF6* motif ((275)VQIINK(280)) in the repeat encoded by the alternatively spliced exon 10. We show that this PHF6* motif also promotes aggregation by the formation of beta-structure and that there is a cross-talk between the two hexapeptide motifs during PHF aggregation. We also show that two of the tau mutations found in hereditary frontotemporal dementias, DeltaK280 and P301L, have a much stronger tendency for PHF aggregation which correlates with their high propensity for beta-structure around the hexapeptide motifs.

The representation of stimulus familiarity in anterior inferior temporal cortex

1. The inferior temporal (IT) cortex plays an important role in both short- and long-term memory for visual patterns. Most previous studies of IT neurons have tested their responses in recency memory tasks, which require that the memory lasts only the length of a single behavioral trial, which may be < 1 s. To determine the role of IT neurons in longer lasting memories, we measured their responses to initially novel stimuli as the stimuli gradually became familiar to the animal. 2. Two rhesus monkeys were trained on a delayed matching to sample (DMS) task with several intervening stimuli between the sample and the final matching stimulus on each trial. The purpose of the task was to ensure that the animal attended to the stimuli and held them in memory, at least temporarily. Unlike in several previous studies, the focus was not on within-trial effects but rather on the incidental memories that built up across trials as the stimuli became familiar. Each cell was tested with a set of 20 novel stimuli (digitized pictures of objects) that the monkey had not seen before. These stimuli were used in a fixed order over the course of an hour-long recording session, and the number of intervening trials between repetitions of a given sample stimulus was varied. 3. The responses of about one-third of the cells recorded in anterior-ventral IT cortex declined systematically as the novel stimuli became familiar. After six to eight repetitions, responses reached a plateau that was approximately 40% of the peak response. Virtually all of these cells also showed selectivity for particular visual stimuli and thus were not "novelty detectors" in the sense of cells that respond to any novel stimulus. Rather, the responses of these cells were a joint function of familiarity and specific object features such as shape and color. A few cells showed increasing responses with repetition over the recording session, but these changes were accompanied by changes in baseline firing rate, suggesting that they were caused by nonspecific effects. 4. The decrement in response with familiarity was stimulus specific and bridged > 150 presentations of other stimuli, the maximum tested. For some cells the maximum decrement in response occurred for those stimuli that initially elicited the largest response. There was no significant change in response to stimuli that were already familiar. 5. The same cells that showed familiarity effects also showed reduced responses to the matching stimuli at the end of each trial, compared with the responses to the samples.(ABSTRACT TRUNCATED AT 400 WORDS)