Mutational analysis of Aedes aegypti Dicer 2 provides insights into the biogenesis of antiviral exogenous small interfering RNAs

The exogenous small interfering RNA (exo-siRNA) pathway is a key antiviral mechanism in the Aedes aegypti mosquito, a widely distributed vector of human-pathogenic arboviruses. This pathway is induced by virus-derived double-stranded RNAs (dsRNA) that are cleaved by the ribonuclease Dicer 2 (Dcr2) into predominantly 21 nucleotide (nt) virus-derived small interfering RNAs (vsiRNAs). These vsiRNAs are used by the effector protein Argonaute 2 within the RNA-induced silencing complex to cleave target viral RNA. Dcr2 contains several domains crucial for its activities, including helicase and RNase III domains. In Drosophila melanogaster Dcr2, the helicase domain has been associated with binding to dsRNA with blunt-ended termini and a processive siRNA production mechanism, while the platform-PAZ domains bind dsRNA with 3’ overhangs and subsequent distributive siRNA production. Here we analyzed the contributions of the helicase and RNase III domains in Ae. aegypti Dcr2 to antiviral activity and to the exo-siRNA pathway. Conserved amino acids in the helicase and RNase III domains were identified to investigate Dcr2 antiviral activity in an Ae. aegypti-derived Dcr2 knockout cell line by reporter assays and infection with mosquito-borne Semliki Forest virus (Togaviridae, Alphavirus). Functionally relevant amino acids were found to be conserved in haplotype Dcr2 sequences from field-derived Ae. aegypti across different continents. The helicase and RNase III domains were critical for silencing activity and 21 nt vsiRNA production, with RNase III domain activity alone determined to be insufficient for antiviral activity. Analysis of 21 nt vsiRNA sequences (produced by functional Dcr2) to assess the distribution and phasing along the viral genome revealed diverse yet highly consistent vsiRNA pools, with predominantly short or long sequence overlaps including 19 nt overlaps (the latter representing most likely true Dcr2 cleavage products). Combined with the importance of the Dcr2 helicase domain, this suggests that the majority of 21 nt vsiRNAs originate by processive cleavage. This study sheds new light on Ae. aegypti Dcr2 functions and properties in this important arbovirus vector species.

Aedes aegypti mosquitoes that transmit human-pathogenic viruses rely on the exogenous small interfering RNA (exo-siRNA) pathway as part of antiviral responses. This pathway is triggered by virus-derived double-stranded RNA (dsRNA) produced during viral replication that is then cleaved by Dicer 2 (Dcr2) into virus-derived small interfering RNAs (vsiRNAs). These vsiRNAs target viral RNA, leading to suppression of viral replication. The importance of Dcr2 in this pathway has been intensely studied in the Drosophila melanogaster model but is largely lacking in mosquitoes. Here, we have identified conserved and functionally relevant amino acids in the helicase and RNase III domains of Ae. aegypti Dcr2 that are important in its silencing activity and antiviral responses against Semliki Forest virus (SFV). Small RNA sequencing of SFV-infected mosquito cells with functional or mutated Dcr2 gave new insights into the nature and origin of vsiRNAs. The findings of this study, together with the different molecular tools we have previously developed to investigate the exo-siRNA pathway of mosquito cells, have started to uncover important properties of Dcr2 that could be valuable in understanding mosquito-arbovirus interactions and potentially in developing or assisting vector control strategies.

Energy metabolism in human retinal Müller cells

PURPOSE

To measure selected parameters of energy metabolism and adenosine triphosphate (ATP) production in passaged monolayer cultures of human retinal glial (Müller) cells to assess the effects of varying substrate and oxygen availability on the biochemistry and histologic integrity of these cells.

METHODS

Confluent Müller cell cultures were incubated for up to 4 hours at 37 degrees C in a modified minimal essential medium (no serum) under aerobic or mitochondrial-inhibited conditions in the presence and absence of 5 mM glucose or in the presence of lactate, pyruvate, glutamate, or glutamine. Cellular ATP levels, lactic acid production, and (14)CO(2) production from labeled glucose or glutamate were measured along with an examination of cellular morphology. Immunohistochemistry with antibodies to glial cell-specific proteins was also performed. Cells were positive for vimentin, but negative for glial fibrillary acidic protein and glutamine synthetase.

RESULTS

Human Müller cells maintained ATP content aerobically at the same level for 4 hours in the presence and absence of glucose. ATP content was also maintained anaerobically at a value equal to that found aerobically, but only in the presence of glucose. ATP content in human Müller cells declined to a very low level when glycolysis was blocked by iodoacetate, and inclusion of lactate, pyruvate, glutamate, or glutamine did not restore the level of ATP. Aerobically, lactic acid production accounted for 99% of the total glucose used, whereas the oxidation of glucose by the mitochondria accounted for only 1%. When mitochondria were inhibited with antimycin A, there was only a modest (1.3-fold) increase in the rate of lactic acid production. No significant differences were found in the histologic appearance of the cells after mitochondrial blockade, but there was massive death of cells after inhibition of glycolysis with iodoacetate.

CONCLUSIONS

These results suggest that, in the presence of glucose and oxygen, cultured Müller cells obtain their ATP principally from glycolysis and have a low rate of oxygen consumption. This metabolic pattern may spare oxygen for retinal neurons, particularly in the inner nuclear and ganglion cell layers under normal physiological conditions. Furthermore, retinal Müller cells in culture are resistant to anoxia or absence of glucose, which provides a basis for understanding why Müller cells are less susceptible than neurons to ischemia or hypoglycemia.

Effects of inhibiting glutamine synthetase and blocking glutamate uptake on b-wave generation in the isolated rat retina

The purpose of the present experiments was to evaluate the contribution of the glutamate-glutamine cycle in retinal glial (Müller) cells to photoreceptor cell synaptic transmission. Dark-adapted isolated rat retinas were superfused with oxygenated bicarbonate-buffered media. Recordings were made of the b-wave of the electroretinogram as a measure of light-induced photoreceptor to ON-bipolar neuron transmission. L-methionine sulfoximine (1-10 mM) was added to superfusion media to inhibit glutamine synthetase, a Müller cell specific enzyme, by more than 99% within 5-10 min, thereby disrupting the conversion of glutamate to glutamine in the Müller cells. Threo-hydroxyaspartic acid and D-aspartate were used to block glutamate transporters. The amplitude of the b-wave was well maintained for 1-2 h provided 0.25 mM glutamate or 0.25 mM glutamine was included in the media. Without exogenous glutamate or glutamine the amplitude of the b-wave declined by about 70% within 1 h. Inhibition of glutamate transporters led to a rapid (2-5 min) reversible loss of the b-wave in the presence and absence of the amino acids. In contrast, inhibition of glutamine synthetase did not alter significantly either the amplitude of the b-wave in the presence of glutamate or glutamine or the rate of decline of the b-wave found in the absence of these amino acids. Excellent recovery of the b-wave was found when 0.25 mM glutamate was resupplied to L-methionine sulfoximine-treated retinas. The results suggest that in the isolated rat retina uptake of released glutamate into photoreceptors plays a more important role in transmitter recycling than does uptake of glutamate into Müller cells and its subsequent conversion to glutamine.

Glucose dependence of glycolysis, hexose monophosphate shunt activity, energy status, and the polyol pathway in retinas isolated from normal (nondiabetic) rats

PURPOSE

To measure glucose-dependent metabolic activities and selected parameters of the polyol pathway in retinas isolated from normal rats to test the hypothesis recently proposed by Van den Enden et al that incubation of whole retinas for 2 hours with elevated concentrations of glucose results in activation of the polyol pathway, which is the cause of a redox imbalance, as measured by an increase in the retinal cytosolic lactate-pyruvate ratio and a diabetic-like state.

METHODS

Retinas obtained from nondiabetic rats and separated from other ocular tissues were incubated for several hours in incubation medium containing glucose at concentrations ranging from 5 to 30 mM. Measurements were made under aerobic and anaerobic conditions of lactic acid production, retinal adenosine triphosphate (ATP), lactic acid content, the hexose monophosphate shunt pathway, aldose reductase activity, and levels of sorbitol and galactitol. Morphology was examined by light microscopy at the end of the incubations.

RESULTS

Incubation of isolated rat retinas with 20 mM glucose increased lactic acid production by approximately 25% in comparison to the rate observed in 5mM glucose under aerobic and anaerobic conditions. The content of ATP and lactate in the retinas after a 2-hour incubation in the presence of oxygen and 20 mM glucose was equal to the amounts found in fresh tissues, whereas these metabolites declined, respectively, by 25% and 45% when 5 mM glucose was used. The activity of the hexose monophosphate shunt pathway in isolated rat retinas was not increased increased significantly when the concentration of glucose was raised from 5 to 30 mM. Aldose reductase activity and polyols were below our limits of detection, 0.5 nmol/minute.mg protein and 3.5 nmol/retina, respectively, under all conditions tested. The morphologic appearance of the retina was similar in the presence of normal and high concentrations of glucose.

CONCLUSIONS

These results show that incubation of isolated rat retinas, obtained from nondiabetic rats, with elevated concentrations of glucose for 2 hours leads to increases in glycolysis and a higher tissue content of lactic acid and ATP in comparison to values obtained with 5 mM glucose. However, the magnitude of the glucose-dependent increase in the retinal level of lactate in the current study and in that of Van den Enden et al is six to seven times greater than the calculated flux of glucose through the polyol pathway. These results, therefore, do not support the hypothesis of Van den Enden et al. Rather, it is suggested that supranormal concentrations of glucose yield more lactate and ATP in a whole retina because they optimize the supply of this essential nutrient to cells throughout the tissue by overcoming diffusional limitations that result when the retina is separated from its normal choroidal and intraretinal blood supplies.

Breast health. Challenges and promises

There has been significant improvement in breast health care in the United States over the past few decades primarily due to advances in health research by diverse teams of basic scientists, physicians, pharmacists, industries, nurses, and social workers. This research has involved inquiries about fundamental biological alterations in breast cancer, differences in diagnostic modalities, and treatment options and various outcome studies. Increase in public awareness of breast cancer, an interest in women's health issues, advances in radiologic imaging, development of new chemotherapeutic agents and the availability of molecular genetic testings have brought remarkable opportunities to a new insight in breast cancer. These efforts have resulted in earlier detection and prolonged disease-free intervals, however, the overall survival time has remained the same. This is mainly attributable to the wide range of individual therapy for breast cancer, which responds to a range of disease curable by surgery alone to one refractory to treatment and marked by rapid metastatic progression. Challenges remain in fostering adequate funding for biomedical, as well as behavioral and social research. Attempts should also be made to promote clinical and population-based studies and to emphasize the value of effective delivery of health-care services to all women with benign, high risk, premalignant and malignant breast disease.

Hypertension and determinants of blood pressure with special reference to socioeconomic status in a rural south Indian community

OBJECTIVES

The objective of the study was to establish the prevalence of hypertension and to assess determinants of blood pressure with special reference to socioeconomic status in a rural south Indian community.

DESIGN

This was a door to door, cross sectional survey.

SETTING

A rural south Indian community, KV Kuppam panchayat, North Arcot District, Tamil Nadu.

SUBJECTS

The area has a total population of 3500 people. Those aged over 20 years who were available at the time of measurement were asked to participate (mean age 39.5 years). This convenience sample totalled 1027 (456 men, 571 women). Out of 697 families, 487 were visited; 15 people refused to participate.

MEASUREMENTS AND MAIN RESULTS

The following potential determinants of blood pressure were assessed: age, body weight, pulse rate, salt intake, meat intake, and socioeconomic class. The prevalence of hypertension was 12.5%. Using multiple linear regression analysis, the most important positive determinants of high blood pressure seemed to be age, body weight, and pulse rate. Salt and meat intake were not significantly associated with hypertension. The prevalence of hypertension in the highest socioeconomic group (22.5%) was more than twice that in the lowest socioeconomic group (8.8%). When adjusted for body weight, the mean (SEM) difference in systolic blood pressure between the highest and lowest socioeconomic classes was 5.83 mmHg (1.63).

CONCLUSION

Hypertension is not yet as important a health problem in rural southern India as it is in westernised societies. Those particularly at risk of hypertension, however, are the elderly and overweight people of high socioeconomic class.

Q angle: effects of isometric quadriceps contraction and body position

The quadriceps femoral angle (Q angle) has been linked with several knee disorders, but Q-angle measurement procedures have not been standardized. The purpose of this study was to examine the effects of isometric quadriceps contraction in the standing and supine positions on the Q angle. The Q angles of the right knees of 30 men and 30 women were measured goniometrically during four test conditions: 1) quadriceps relaxed in standing, 2) quadriceps contracted in standing, 3) quadriceps relaxed in supine, and 4) quadriceps contracted in supine. The pelvic widths were also measured as the distance between the anterior superior iliac spines in standing and supine. A two-way multivariate analysis of variance showed a significant difference between genders (p < 0.001) and among the four test conditions (p < 0.001) (N = 60). Separate one-way analyses of variance (ANOVAs) with two grouping factors (contraction and position) showed significant effects of contraction (p < 0.001) for both men and women, but no significant effect of positions. A dependent t-test showed that the pelvic width differed between standing and supine for both men and women (p < 0.001). The results showed that isometric quadriceps contraction affects the Q angle with the subjects standing or supine, even though the pelvic width differed significantly between the two positions. Clinicians and researchers should consider the results of this study in order to standardize procedures for measuring the Q angle.

Accuracy and safety of transvaginal sonographic placental localization

Transvaginal sonographic localization of the placenta was performed in 100 patients suspected of having placenta previa. Except in one patient, the diagnosis was confirmed at cesarean delivery in all cases of placenta previa found by sonography before delivery, resulting in a 93.3% predictive value of a positive test. The predictive value of a negative test was 97.6%; in two patients a low-insertion placenta diagnosed by sonography was found to be a placenta previa at delivery. The sensitivity and specificity of the technique were 87.5 and 98.8%, respectively. Although in some instances transvaginal sonography was performed during vaginal hemorrhage, aggravation of bleeding was never observed. Transvaginal sonographic localization of the placenta proved to be an accurate and safe diagnostic procedure.

Salivary gland neoplasms as a late consequence of head and neck irradiation

An increased occurrence of salivary tumors was observed in 1922 patients who received radiation to the tonsils and nasopharynx. Twenty-seven tumors, 19 benign and eight malignant, were found in this group as compared with an expected 0.2 malignant and less than 1 benign tumor. The latent period between the initial radiation treatment and diagnosis ranged from 7 to 32 years. After the first 15 years the incidence (77 cases/10(5) subjects/year) has remained constant and shows no indication of declining. Continued observation for salivary gland tumors is therefore indicated for subjects who received childhood irradiation.

Plasma thyroglobulin in detecting thyroid carcinoma after childhood head and neck irradiation

The level of thyroglobulin in plasma was measured in 904 subjects with a history of head and neck irradiation during childhood to evaluate its potential value in screening for and differentiating thyroid neoplasms. Mean plasma thyroglobulin level was significantly elevated in subjects with nodular thyroid disease versus those without evidence of nodules (49.8 versus 27.0 ng/ml). However, the overlap with normal subjects does not allow thyroglobulin assays to serve as the only screening procedure. The mean levels in subjects with benign and malignant thyroid nodules were indistinguishable (48.8 versus 53.9 ng/ml). Thirteen percent of otherwise normal-appearing subjects had elevated values that may represent clinically inapparent thyroid disease. It is concluded that in screening large numbers of persons at risk for thyroid neoplasia, thyroglobulin assays are useful in combination with other modes of evaluation. The assay is without value in distinguishing benign from malignant disease.

Thyroid cancer occurring as a late consequence of head-and-neck irradiation. Evaluation of 1056 patients

From January 1 to September 30, 1974, we examined 1056 of 5266 subjects (20.1%) who had received therapeutic irradiation primarily for infections and inflammatory disease of the upper respiratory tract at our institution during the 1940's and 1950's. The tonsillar and nasopharyngeal region was the treatment site in 85% of those examined. Palpable nodular thyroid disease was found in 16.5%, and nonpalpable lesions were detected by 99m Tc pertechnetate thyroid imaging in an additional 10.7%, for a prevalence of nodular disease of 27.2%. Operation on 71% with nodular disease revealed thyroid cancer in 33% (60 of 182). Preliminary analysis for potential risk factors suggests a correlation between radiation exposure and the presence of thyroid nodules (P less than 0.001). These findings indicate that nodular thyroid disease, both benign and malignant, continues as a major health problem for at least 35 years in exposed subjects.