Hemoglobin E distribution in ten endogamous population groups of Assam, India

Previous studies have reported a high incidence of hemoglobin E (HbE) in Northeast Indian populations. In the present study 10 endogamous populations of Assam belonging to two racial groups, Caucasoid and Mongoloid, were examined. The frequency of HbE gene (Hb beta E) in the Caucasoid caste populations is around 0.1, whereas the gene is highly prevalent in the Mongoloid populations, frequencies ranging between 0.2 and 0.6. Predominance of Hb beta E in the Tibeto-Burman speakers is contrary to observations made in Southeast Asia, where an association between Austro-Asiatic speakers and high prevalence of HbE exist. The highest occurrence of the gene in this area, which is on the far end of the proposed centre of distribution in Northern Kampuchea and Northeast Thailand, is also a deviation from the expected pattern of gene distribution. It is speculated that Hb beta E in the Tibeto-Burman populations of Assam arose by an independent mutation which contributed to the high frequencies of Hb beta E in the Northeast Indian populations.     

Reversible HuR‐microRNA binding controls extracellular export of miR‐122 and augments stress response

microRNAs (miRNAs), the tiny but stable regulatory RNAs in metazoan cells, can undergo selective turnover in presence of specific internal and external cues to control cellular response against the changing environment. We have observed reduction in cellular miR‐122 content, due to their accelerated extracellular export in human hepatic cells starved for small metabolites including amino acids. In this context, a new role of human ELAV protein HuR has been identified. HuR, a negative regulator of miRNA function, accelerates extracellular vesicle (EV)‐mediated export of miRNAs in human cells. In stressed cells, HuR replaces miRNPs from target messages and is both necessary and sufficient for the extracellular export of corresponding miRNAs. HuR could reversibly bind miRNAs to replace them from Ago2 and subsequently itself gets freed from bound miRNAs upon ubiquitination. The ubiquitinated form of HuR is predominantly associated with multivesicular bodies (MVB) where HuR‐unbound miRNAs also reside. These MVB‐associated pool of miRNAs get exported out via EVs thereby delimiting cellular miR‐122 level during starvation. Therefore, by modulating extracellular export of miR‐122, HuR could control stress response in starved human hepatic cells.     

Directed discovery of bivalent peptide ligands to an SH3 domain

The Caenorhabditis elegans SEM-5 SH3 domains recognize proline-rich peptide segments with modest affinity. We developed a bivalent peptide ligand that contains a naturally occurring proline-rich binding sequence, tethered by a glycine linker to a disulfide-closed loop segment containing six variable residues. The glycine linker allows the loop segment to explore regions of greatest diversity in sequence and structure of the SH3 domain: the RT and n-Src loops. The bivalent ligand was optimized using phage display, leading to a peptide (PP-G(4)-L) with 1000-fold increased affinity for the SEM-5 C-terminal SH3 domain over that of a natural ligand. NMR analysis of the complex confirms that the peptide loop segment is targeted to the RT and n-Src loops and parts of the beta-sheet scaffold of this SH3 domain. This binding region is comparable to that targeted by a natural non-PXXP peptide to the p67(phox) SH3 domain, a region not known to be targeted in the Grb2 SH3 domain family. PP-G(4)-L may aid in the discovery of additional binding partners of Grb2 family SH3 domains.     

Structural basis for sequential displacement of Ca(2+) by Yb(3+) in a protozoan EF-hand calcium binding protein

We have studied the displacement of Ca(2+)by the trivalent lanthanide ions (Yb(3+)) in a protozoan (Entamoeba histolytica) Ca(2+)-binding protein (EhCaBP), by NMR and thermodynamics. We have demonstrated, for the first time, how one can use in a combined fashion the utility of NMR and thermodynamics to have an insight to the relative binding specificities/affinity between Ca(2+) and Yb(3+). As revealed by the titration experiments, Yb(3+) displaces Ca(2+) from the four metal binding sites present in EhCaBP in a sequential manner. The study provides a structural origin for such a sequential Ca(2+) displacement by Yb(3+) in EhCaBP.     

Phytoestrogenic effects of black tea extract (Camellia sinensis) in an oophorectomized rat (Rattus norvegicus) model of osteoporosis

The adverse side effects of currently available anti-osteoporotic agents warrant the search for compounds with less toxic effects. In this study, we assessed the phytoestrogenic potentiality of whole aqueous extract of black tea (BTE) in a bilaterally oophorectomized rat model (2.5%, 1 ml/100 g body weight/day for 28 days). Although the supplementation was given for 28 days but, sign of revival of copulation period (estrous stage) from non-receptive diestrous stage was first noticed after 21 days of BTE supplementation in bilaterally oophorectomized rats. This was accompanied by a significant increase in serum estradiol level. To test whether this increase in serum estradiol level could have an influence upon the oophorectomy-induced damage of bone, we assessed marker parameters of bone resorption and osteoclastic activity (tartrate-resistant acid phosphatase), collagen degradation (urinary hydroxyproline), bone loss (bone ash mineral content) and bone breaking strength (bone density). Results indicated that increase in serum estradiol level after BTE supplementation could significantly diminish oophorectomy-induced decaying changes in bone. This study proposes that aqueous BTE may be assessed as a phytoestrogenic compound for prevention against estrogen deficiency-related osteoporotic damages.     

The adipocyte as an important target cell for Trypanosoma cruzi infection

Adipose tissue plays an active role in normal metabolic homeostasis as well as in the development of human disease. Beyond its obvious role as a depot for triglycerides, adipose tissue controls energy expenditure through secretion of several factors. Little attention has been given to the role of adipocytes in the pathogenesis of Chagas disease and the associated metabolic alterations. Our previous studies have indicated that hyperglycemia significantly increases parasitemia and mortality in mice infected with Trypanosoma cruzi. We determined the consequences of adipocyte infection in vitro and in vivo. Cultured 3T3-L1 adipocytes can be infected with high efficiency. Electron micrographs of infected cells revealed a large number of intracellular parasites that cluster around lipid droplets. Furthermore, infected adipocytes exhibited changes in expression levels of a number of different adipocyte-specific or adipocyte-enriched proteins. The adipocyte is therefore an important target cell during acute Chagas disease. Infection of adipocytes by T. cruzi profoundly influences the pattern of adipokines. During chronic infection, adipocytes may represent an important long-term reservoir for parasites from which relapse of infection can occur. We have demonstrated that acute infection has a unique metabolic profile with a high degree of local inflammation in adipose tissue, hypoadiponectinemia, hypoglycemia, and hypoinsulinemia but with relatively normal glucose disposal during an oral glucose tolerance test.     

Monitoring the organization and dynamics of bovine hippocampal membranes utilizing Laurdan generalized polarization

Organization and dynamics of cellular membranes in the nervous system are crucial for the function of neuronal membrane receptors. The lipid composition of neuronal cells is unique and has been correlated with the increased complexity in the organization of the nervous system during evolution. Previous work from our laboratory has established bovine hippocampal membranes as a convenient natural source for studying neuronal receptors such as the G-protein coupled serotonin_1A receptor. In this paper, we have explored the organization and dynamics of bovine hippocampal membranes using the amphiphilic environment-sensitive fluorescent probe Laurdan. Our results show that the emission spectra of Laurdan display an additional red shifted peak as a function of increasing temperature in native as well as cholesterol-depleted membranes and liposomes made from lipid extracts of the native membrane. Interestingly, wavelength dependence of Laurdan generalized polarization (GP) in native membranes indicates the presence of an ordered gel-like phase at low temperatures, whereas characteristics of the liquid-ordered phase are observed at high temperatures. Similar experiments performed using cholesterol-depleted membranes show fluidization of the membrane with increasing cholesterol depletion. In addition, results from fluorescence polarization of DPH indicate that the hippocampal membrane is fairly ordered even at physiological temperature. The temperature dependence of Laurdan excitation GP provides a measure of the apparent thermal transition temperature and extent of cooperativity in these membranes. Analysis of time-resolved fluorescence measurements of Laurdan shows reduction in mean fluorescence lifetime with increasing temperature due to change in environmental polarity. These results constitute novel information on the dynamics of hippocampal membranes and its modulation by cholesterol depletion monitored using Laurdan fluorescence.