Height is known as an index that reflects the environment of the fetal, childhood, and adolescent periods, which affect adult health. This study was conducted to elucidate whether height is associated with cognitive impairment in community-dwelling elders in Korea.
The study subjects were recruited among community dwelling elderly individuals aged 65 or over who participated in the 2004 Hallym Aging Study. They were invited to a general hospital and were evaluated for socioeconomic status, smoking history, and various clinical measures. Cognitive function measurement was performed using the Korean-Mini Mental State Examination. Logistic regression was used to evaluate the association between height and cognitive function.
After adjusting for potential covariates such as age and education, the smallest group was associated with higher risk of cognitive impairment compared with the tallest group among elderly men (odds ratio [OR], 4.20; 95% confidence interval [CI], 1.02-17.36), but not among elderly women (OR,1.65; 95% CI, 0.62-4.40).
The reason for this difference according to sex may be explained by the differential effects of education on cognitive function by sex. A larger population-based prospective cohort study is needed to examine the association between height and cognitive function according to sex.
Body height; Cognition; Hallym Aging Study
Anisotropic electrical properties can be found in biological tissues
such as muscles and nerves. Conductivity tensor is a simplified model to
express the effective electrical anisotropic information and depends on the imaging
resolution. The determination of the conductivity tensor should be based on
Ohm's law. In other words, the measurement of partial information of current
density and the electric fields should be made. Since the direct measurements of
the electric field and the current density are difficult, we use MRI to measure their
partial information such as B1 map; it measures circulating current density and
circulating electric field. In this work, the ratio of the two circulating fields, termed
circulating admittivity, is proposed as measures of the conductivity anisotropy at
Larmor frequency. Given eigenvectors of the conductivity tensor, quantitative
measurement of the eigenvalues can be achieved from circulating admittivity for
special tissue models. Without eigenvectors, qualitative information of anisotropy
still can be acquired from circulating admittivity. The limitation of the circulating
admittivity is that at least two components of the magnetic fields should be
measured to capture anisotropic information.
Low grip strength is associated with decline in bone mineral density (BMD) and increased risk of spine fracture among the elderly. Smoking, a major factor determining BMD, is also known to have an indirect effect on bone loss. This study investigated whether smoking is associated with grip strength in the community-dwelling elderly in Korea.
This study was an outcome of the second of three waves of the Hallym Aging Study from January to May 2007, a population-based study of Koreans aged 45 years and upwards dwelling in Chuncheon. Its 218 subjects comprised men aged 65 years or over. They were evaluated at a general hospital for socioeconomic status, smoking history, and various clinical measures including grip strength.
Grip strength was higher in non-, ex-, and current smokers (33.7 kg, 30.6 kg, and 29.3 kg, respectively). Current smoking was found to increase the risk of decreased grip strength (adjusted odds ratio [aOR], 4.58; 95% confidence interval [CI],1.31 to 16.04) compared with non-smoking, after adjustment for potential covariates including socioeconomic status. After adjustment for smoking effect, education of fewer than six years and monthly income of fewer than 500,000 Korean won increased the risk of decreased grip strength compared with education of more than six years (aOR, 2.88; 95% CI, 1.08 to 7.66) and monthly income of more than 1,500,000 Korean won (aOR, 2.86; 95% CI, 1.08 to 7.54).
These results showed that current smoking, low education and low income were independent risk factors for decreased grip strength among elderly men in Korea.
Elderly men; Hand strength; Smoking; Socioeconomic
Gross hematuria secondary to vesical varices is an unusual presentation. We report such a case recurrent gross hematuria in a male patient who had a history of bladder substitution with ileal segments that had been treated by balloon-occluded percutaneous transhepatic obliteration of vesical varices.
Hematuria; Vesical varix; Percutaneous transhepatic obliteration
AIM: To understand the neuroprotective mechanism of human umbilical cord blood-derived mesenchymal stem cells (hUCB-MSCs) against amyloid-β42 (Aβ42) exposed rat primary neurons.
METHODS: To evaluate the neuroprotective effect of hUCB-MSCs, the cells were co-cultured with Aβ42-exposed rat primary neuronal cells in a Transwell apparatus. To assess the involvement of soluble factors released from hUCB-MSCs in neuroprotection, an antibody-based array using co-cultured media was conducted. The neuroprotective roles of the identified hUCB-MSC proteins was assessed by treating recombinant proteins or specific small interfering RNAs (siRNAs) for each candidate protein in a co-culture system.
RESULTS: The hUCB-MSCs secreted elevated levels of decorin and progranulin when co-cultured with rat primary neuronal cells exposed to Aβ42. Treatment with recombinant decorin and progranulin protected from Aβ42-neurotoxicity in vitro. In addition, siRNA-mediated knock-down of decorin and progranulin production in hUCB-MSCs reduced the anti-apoptotic effects of hUCB-MSC in the co-culture system.
CONCLUSION: Decorin and progranulin may be involved in anti-apoptotic activity of hUCB-MSCs exposed to Aβ42.
Human umbilical cord blood-derived mesenchymal stem cells; Decorin; Progranulin; Aβ42; Anti-apoptosis
Spectroscopic imaging applications outside of the brain can suffer from artifacts due to inherent long scan times and susceptibility to motion. A fast spectroscopic imaging sequence has been devised with reduced sensitivity to motion. The sequence uses oscillating readout gradients and acquires k-space data in a spiral out–in fashion, which allows fast k-space coverage. We show that a spiral out–in readout acquisition is characterized by small gradient moments, reducing sensitivity to motion-induced artifacts. Data are acquired comparing the sequence to normal phase encoded spectroscopic imaging and conventional spiral spectroscopic imaging protocols. In addition, in vivo data are acquired from the liver, demonstrating potential usage as a multivoxel fat/water spectroscopic imaging tool. Results indicate that in the presence of motion, ghosting effects are reduced while metabolite signal increases of approximately 10% can be achieved.
MRSI motion; gradient nulling
The purpose of this study was to assess the clinical and radiographic results of a total hip arthroplasty with the double tapered Mallory-Head system.
The clinical and radiographic results of a consecutive series of 81 total hip replacements in 75 patients were reviewed 10–15 years (average 11.4 years) postoperatively. The patients’ underlying conditions were avascular necrosis in 46 hips (57 %), osteoarthritis in 12 hips (15 %), RA in nine hips (11 %), and others. Clinical results were evaluated based on the modified Harris hip score and modified Merle d’Aubigné-Postel score. A radiographic analysis was performed.
The average modified Harris hip score improved from a preoperative score of 56 points to a postoperative 92 points. The average modified Merle d’Aubigné-Postel score was 15 points at the latest follow up, and 55 hips (68 %) were classified as the clinical grades of excellent or good results. One acetabular component was revised because of loosening, and one was revised for recurrent dislocation.
The clinical and radiological evaluations of the total hip replacements using the Mallory-Head system showed good results.
The utility of multi-voxel two-dimensional chemical shift imaging in the clinical environment will ultimately be determined by the imaging time and the metabolite peaks that can be detected. Different k-space sampling schemes can be characterized by their minimum required imaging time. The use of spiral-based readout gradients effectively reduces this minimum scan time due to simultaneous data acquisition in three k-space dimensions (kx, ky, and kf2). A 3T spiral-based multi-voxel two-dimensional spectroscopic imaging sequence using the PRESS excitation scheme was implemented. Good performance was demonstrated by acquiring preliminary in vivo data for applications including brain glutamate imaging, metabolite T2 quantification, and high spatial resolution prostate spectroscopic imaging. All protocols were designed to acquire the data within a 17 minute scan time at a field strength of 3T.
magnetic resonance spectroscopic imaging; spiral readout gradients; 2D J-resolved spectroscopy
Photothermal ablation is a minimally invasive approach, which typically involves delivery of photothermal sensitizers to targeted tissues. The purpose of our study was to demonstrate that gold nanoparticles are phagocytosed by pancreatic cancer cells, thus permitting magnetic resonance imaging (MRI) of sensitizer delivery and photothermal ablation.
Patients and methods
Iron-oxide core/gold-shell nanoparticles (GoldMag®, 30 nm diameter; Xi’an GoldMag Biotechnology Co, Xi’an, People’s Republic of China) were used. In a 96-well plate, 3 × 104 PANC-1 (human pancreatic cancer cell line) cells were placed. GoldMag (0, 25, or 50 μg/mL) was added to each well and 24 hours allowed for cellular uptake. Samples were then divided into two groups: one treated with photothermal ablation (7.9 W/cm2) for 5 minutes, the other not treated. Photothermal ablation was performed using laser system (BWF5; B&W Tek, Inc, Newark, DE, USA). Intraprocedural temperature changes were measured using a fiber optic temperature probe (FTP-LN2; Photon Control Inc, Burnaby, BC, Canada). After 24 hours, the remaining number of viable cells was counted using trypan blue staining; cell proliferation percentage was calculated based on the total number of viable cells after treatment compared with control. MRI of GoldMag uptake was performed using a 7.0T ClinScan system (Bruker BioSpin, Ettlingen, Germany).
Temperature curves demonstrated that with increased GoldMag uptake, laser irradiation produced higher temperature elevations in the corresponding samples; temperature elevations of 12.89°C, 35.16°C, and 79.51°C were achieved for 0, 25, and 50 μg/mL GoldMag. Without photothermal ablation, the cell proliferation percentage changed from 100% to 71.3% and 47.0% for cells treated with 25 and 50 μg/mL GoldMag. Photothermal ablation of PANC-1 cells demonstrated an effective treatment response, specifically a reduction to only 61%, 21.9%, and 2.3% cell proliferation for cells treated with 0, 25, and 50 μg/mL GoldMag. MRI was able to visualize GoldMag uptake within PANC-1 cells.
Our findings suggest that photothermal ablation may be effective in the treatment of pancreatic cancer. GoldMag nanoparticles could serve as photothermal sensitizers, and MRI is feasible to quantify delivery.
photothermal ablation therapy; hybrid nanoparticles; magnetic resonance imaging
The optimal treatment of advanced maxillary sinus cancer has been challenging for several decades. Intra-arterial chemotherapy (IAC) for head and neck cancer has been controversial. We have analyzed the long-term outcome of neoadjuvant IAC followed by radiation therapy (RT) and surgery.
Materials and Methods
Twenty-seven patients with advanced maxillary sinus cancer were treated between 1989 and 2002. Five-fluorouracil (5-FU, 500 mg/m2) was infused intra-arterially, and followed by RT (total 50.4 Gy/28 fractions). A planned surgery was performed 3 to 4 weeks after completion of IAC and RT.
At a median follow-up of 77 months (range, 12 to 169 months), the 5-year rates of overall survival in all patients were 63%. The 5-year rates of overall survival of stage T3/T4 patients were 70.0% and 58.8%, respectively. Seven of fourteen patients with disease recurrence had a local recurrence alone. The 5-year actuarial local control rates in patients with stage T3/T4, and in all patients were 20.0%, 32.3%, and 27.4%, respectively. Overall response rate after the completion of IAC and RT was 70.3%. During the follow-up, seven patients (25.9%) showed mild to moderate late complications. The tumor extent (i.e., the involvement of either orbit and/or base of skull) appeared to be related with local recurrence.
Neoadjuvant IAC with 5-FU followed by RT and surgery may be effective to improve local tumor control in the patients with advanced maxillary sinus cancer. However, local failure was still the major cause of death. Further investigations are required to determine the optimal treatment schedule, radiotherapy techniques and chemotherapy regimens.
Maxillary sinus neoplasms; Intra-arterial infusion; Radiation therapy; Surgery
To identify novel genetic factors for colorectal cancer (CRC), we conducted a genome-wide association study in East Asians. By analyzing genome-wide data in 2,098 cases and 5,749 controls, we selected 64 promising SNPs for replication in an independent set of samples including up to 5,358 cases and 5,922 controls. We identified four SNPs with a P-value of 8.58 × 10−7 to 3.77 × 10−10 in the combined analysis of all East Asian samples. Three of the four SNPs were replicated in a study conducted among 26,060 European descendants with a combined P-value of 1.22 × 10−10 for rs647161 (5q31.1), 6.64 × 10−9 for rs2423279 (20p12.3), and 3.06 × 10−8 for rs10774214 (12p13.32 near the CCND2 gene), respectively, derived from the meta-analysis of data from both East Asian and European populations. This study identified three new CRC susceptibility loci and provides additional insight into the genetics and biology of CRC.
A reproducibility study of proton magnetic resonance spectroscopic imaging (1H-MRSI) of the human brain was conducted to evaluate the reliability of an automated 3D in vivo spectroscopic imaging acquisition and associated quantification algorithm. A PRESS-based pulse sequence was implemented using dualband spectral-spatial RF pulses designed to fully excite the singlet resonances of choline (Cho), creatine (Cre) and N-acetyl aspartate (NAA) while simultaneously suppressing water and lipids. 1% of the water signal was left to be used as a reference signal for robust data processing, and additional lipid suppression was obtained using adiabatic inversion recovery. Spiral k-space trajectories were used for fast spectral and spatial encoding yielding high-quality spectra from 1 cc voxels throughout the brain with a 13 minute acquisition time. Data were acquired with an 8-channel phased-array coil and optimal SNR for the combined signals was achieved using a weighting based on the residual water signal. Automated quantification of the spectrum of each voxel was performed using LCModel. The complete study consisted of 8 healthy adult subjects to assess inter-subject variations and two subjects scanned six times each to assess intra-subject variations. The results demonstrate that reproducible whole-brain 1H-MRSI data can be robustly obtained with the proposed methods.
magnetic resonance spectroscopic imaging; metabolite maps; region of interest; reproducibility
SAMHD1 is a newly identified anti-HIV host factor that has a dNTP triphosphohydrolase activity and depletes intracellular dNTP pools in non-dividing myeloid cells. Since DNA viruses utilize cellular dNTPs, we investigated whether SAMHD1 limits the replication of DNA viruses in non-dividing myeloid target cells. Indeed, two double stranded DNA viruses, vaccinia and herpes simplex virus type 1, are subject to SAMHD1 restriction in non-dividing target cells in a dNTP dependent manner. Using a thymidine kinase deficient strain of vaccinia virus, we demonstrate a greater restriction of viral replication in non-dividing cells expressing SAMHD1. Therefore, this study suggests that SAMHD1 is a potential innate anti-viral player that suppresses the replication of a wide range of DNA viruses, as well as retroviruses, which infect non-dividing myeloid cells.
Various viral pathogens such as HIV-1, herpes simplex virus (HSV) and vaccinia virus infect terminally-differentiated/non-dividing macrophages during the course of viral pathogenesis. Unlike dividing cells, non-dividing cells lack chromosomal DNA replication, do not enter the cell cycle, and harbor very low levels of cellular dNTPs, which are substrates of viral DNA polymerases. A series of recent studies revealed that the host protein SAMHD1 is dNTP triphosphohydrolase, which contributes to the poor dNTP abundance in non-dividing myeloid cells, and restricts proviral DNA synthesis of HIV-1 and other lentiviruses in macrophages, dendritic cells, and resting T cells. In this report, we demonstrate that SAMHD1 also controls the replication of large dsDNA viruses: vaccinia virus and HSV-1, in primary human monocyte-derived macrophages. SAMHD1 suppresses the replication of these DNA viruses to an even greater extent in the absence of viral genes that are involved in dNTP metabolism such as thymidine kinase. Therefore, this study supports that dsDNA viruses evolved to express enzymes necessary to increase the levels of dNTPs as a mechanism to overcome the restriction induced by SAMHD1 in myeloid cells.
Patho-physiological conditions with high oxidative stress, such as conditions associated with increased denatured heme-proteins, are associated with enhanced adipogenic response. This effect predominantly manifests as adipocyte hypertrophy characterized by dysfunctional, pro-inflammatory adipocytes exhibiting reduced expression of anti-inflammatory hormone, adiponectin. To understand how increased levels of cellular heme, a pro-oxidant molecule, modulates adipogenesis; the following study was designed to evaluate effects of heme on adipogenesis in human mesenchymal stem cells (hMSCs) and mouse pre-adipocytes (3T3L1). Experiments were conducted in the absence and in the presence of a superoxide dismutase mimetic (tempol, 100μM). Heme (10μM) increased (p<0.05) adipogenesis in hMSCs and mouse pre-adipocytes, where tempol alone (100μmol/l) attenuated adipogenesis in these cells (p<0.05). Tempol also reversed heme-induced increase in adipogenesis in both hMSCs and mouse pre-adipocytes (p<0.05). In addition, heme exposed 3T3L1 exhibited reduced (p<0.05) expression of transcriptional regulator–sirtuin 1 (Sirt1), along with, increased (p<0.05) expression of adipogenic markers PPARγ, C/EBPα and aP2. These effects of heme were rescued (p<0.05) in cells concurrently treated with heme and tempol (p<0.05) and prevented in cells over-expressing Sirt1. Taken together, our results indicate that heme-induced oxidative stress inhibits Sirt1, thus un-inhibiting adipogenic regulators such as PPARγ and C/EBPα; which in turn induce increased adipogenesis along with adipocyte hypertrophy in pre-adipocytes. Anti-oxidant induced offsetting of these effects of heme supports the role of heme-dependent oxidative stress in mediating such events.
Adipogenesis; Heme; Oxidative stress; Tempol; 3T3L1
In vivo tracking of gene therapy vectors challenges the investigation and improvement of biodistribution of these agents in the brain, a key feature for their targeting of infiltrative malignant gliomas. The glioma-targeting Ad5/3-cRGD gene therapy vector was covalently bound to super-paramagnetic iron oxide (Fe3O4) nanoparticles (SPION) to monitor its distribution by MRI. Transduction of labeled and unlabeled vectors was assessed on the U87 glioma cell line and normal human astrocytes (NHA), and was higher in U87 compared to NHA, but was similar between labeled and unlabeled virus. An in vivo study was performed by intracranial subcortical injection of labeled-Ad5/3-cRGD particles into a pig brain. The labeled vector appeared in vivo as a T2-weighted hyperintensity and a T2-gradient echo signal at the injection site, persisting up to 72 hours post-injection. We describe a glioma-targeting vector that is labeled with SPION, thereby allowing for MRI detection with no change in transduction capability.
Adenovirus; Gene therapy; Nanoparticle
Authors evaluated pulmonary tuberculosis (PTB) history as a risk factor for lung cancer in current male smokers in a prospective, population-based cohort study. The subjects were the 7,009 males among the participants in the Seoul Male Cancer Cohort Study for whom there was full information on PTB history and smoking habits. With a 16-yr follow-up, 93 cases of lung cancer occurred over the 99,965 person-years of the study. The estimated relative risk (RR) of PTB history of current smokers in lung cancer after adjusting for three confounders - intake of coffee and tomatoes, and age at entry - was 1.85 (95% CI: 1.08-3.19). The observed joint RRs and attributable risks (ARs) across strata of three confounders were greater than the expected, indicating a positive interaction. Thus a history of PTB in current smokers may be another risk factor for lung cancer. Based on a synergic interaction, a heavy male smoker with a PTB history would be expected to belong to the group at high risk of lung cancer.
Lung Neoplasms; Cancer Incidence; Tuberculosis, Pulmonary; Smoking; Effect Modifier; Cohort Studies
To investigate the effect of gastrocnemius muscle fatigue on postural control ability in elderly people.
Twenty-four healthy elderly people participated in this study. The postural control ability of single leg standing was evaluated with Health Improvement & Management System (HIMS) posturography before and after fatiguing exercises. After evaluating initial postural control ability, the maximal voluntary contraction (MVC) of ankle plantarflexion was assessed using a surface electromyogram from the medial belly of the gastrocnemius muscle. After a 5-minute resting period, subjects began submaximal isometric ankle plantarflexion (40% MVC) until 40% of MVC was dropped below 95% for 5 seconds, or subject couldn't continue working out due to muscle fatigue. And postural control ability was assessed after fatiguing exercise. The mean deviation of center of pressure (COP), length of COP movement, occupied area of COP were measured, and analyzed by paired t-test.
Mediolateral deviation, length of COP movement, and area of COP occupied were increased after fatiguing exercise of the gastrocnemius muscle. Anteroposterior deviation and length of COP movement were also increased, but had low statistical significance.
These findings suggest that the gastrocnemius muscle fatigue affects mediolateral stability and accuracy during single leg standing in elderly people. Therefore muscle endurance training is necessary to prevent falls in elderly people.
Balance; Posture; Elderly; Fatigue; Ankle
In vitro culture methods underpin many experimental approaches to biology and drug discovery. The modification of established cell culture methods to make them more biologically relevant or to optimize growth is traditionally a laborious task. Emerging metabolomic technology enables the rapid evaluation of intra- and extracellular metabolites and can be applied to the rational development of cell culture media. In this study, untargeted semiquantitative and targeted quantitative metabolomic analyses of fresh and spent media revealed the major nutritional requirements for the growth of bloodstream form Trypanosoma brucei. The standard culture medium (HMI11) contained unnecessarily high concentrations of 32 nutrients that were subsequently removed to make the concentrations more closely resemble those normally found in blood. Our new medium, Creek's minimal medium (CMM), supports in vitro growth equivalent to that in HMI11 and causes no significant perturbation of metabolite levels for 94% of the detected metabolome (<3-fold change; α = 0.05). Importantly, improved sensitivity was observed for drug activity studies in whole-cell phenotypic screenings and in the metabolomic mode of action assays. Four-hundred-fold 50% inhibitory concentration decreases were observed for pentamidine and methotrexate, suggesting inhibition of activity by nutrients present in HMI11. CMM is suitable for routine cell culture and offers important advantages for metabolomic studies and drug activity screening.
Iron deficiency remains a very common nutritional problem despite the improvement in nutrition and increased understanding of methods for its prevention. Thus, we try to create a new method for screening iron nutrition through infant nutrition history.
Among the children who visited Inha University Hospital from March 2006 to July 2012, 181 children with iron deficiency anemia (IDA) and 52 children without IDA ranging from 6 to 36 months of age were reviewed in this study. We used the age when they began to wean food, the type of sort weaning foods, the time required for successful weaning, iron content in weaning foods, and the duration of breastfeeding for scoring infant nutrition history based on a questionnaire.
The mean score of the IDA group was 7.8±2.6 points, which was significantly higher than that of the control group (5.6±2.1) (p=0.000). If we set up the cutoff value at 6 points, this screening has 86.8% sensitivity and 36% specificity. In addition, as the IDA score increased, there was a falling trend of hemoglobin.
The IDA score does not have high specificity or high sensitivity. However, this study conveys that those patients who record a high score have low hemoglobin. Therefore, we suggest this score system for screening more IDA patients via nonpainful techniques.
Iron-deficiency anemia; Weaning; Breast feeding; Diet; Nutrition
Diabetes mellitus and the metabolic syndrome are becoming leading causes of death in the world. Identifying the etiology of diabetes is key to prevention. Despite the similarity in their structures, fructose and glucose are metabolized in different ways. Uric acid, a byproduct of uncontrolled fructose metabolism is known risk factor for hypertension. In the liver, fructose bypasses the two highly regulated steps in glycolysis, glucokinase and phosphofructokinase, both of which are inhibited by increasing concentrations of their byproducts. Fructose is metabolized by fructokinase (KHK). KHK has no negative feedback system, and ATP is used for phosphorylation. This results in intracellular phosphate depletion and the rapid generation of uric acid due to activation of AMP deaminase. Uric acid, a byproduct of this reaction, has been linked to endothelial dysfunction, insulin resistance, and hypertension. We present possible mechanisms by which fructose causes insulin resistance and suggest actions based on this association that have therapeutic implications.
Microglia are resident immune cells in the central nervous system. They play a role in normal brain development and neuronal recovery. However, overactivation of microglia causes neuronal death, which is associated with neurodegenerative diseases, such as Parkinson’s disease and Alzheimer’s disease. Therefore, controlling microglial activation has been suggested as an important target for treatment of neurodegenerative diseases. In the present study, we investigated the anti-inflammatory effect of ginsenoside Rg5 in lipopolysaccharide (LPS)-stimulated BV2 microglial cells and rat primary microglia. The data showed that Rg5 suppressed LPS-induced nitric oxide (NO) production and proinflammatory TNF-α secretion. In addition, Rg5 inhibited the mRNA expressions of iNOS, TNF-α, IL-1β, COX-2 and MMP-9 induced by LPS. Further mechanistic studies revealed that Rg5 inhibited the phophorylations of PI3K/Akt and MAPKs and the DNA binding activities of NF-κB and AP-1, which are upstream molecules controlling inflammatory reactions. Moreover, Rg5 suppressed ROS production with upregulation of hemeoxygenase-1 (HO-1) expression in LPS-stimulated BV2 cells. Overall, microglial inactivation by ginsenoside Rg5 may provide a therapeutic potential for various neuroinflammatory disorders.
ginsenoside Rg5; microglia; neuroinflammation; iNOS; cytokine; signaling pathway
Cell division is positively regulated by cyclin-dependent kinases (CDKs) partnered with cyclins and negatively regulated by CDK inhibitors. In the frog, Xenopus laevis, three types of CDK inhibitors have been described: p27Xic1 (Xic1) which shares sequence homology with both p21Cip1 and p27Kip1 from mammals, p16Xic2 (Xic2) which shares sequence homology with p21Cip1, and p17Xic3 (Xic3) which shares sequence homology with p27Kip1. While past studies have demonstrated that during DNA polymerase switching, Xic1 is targeted for protein turnover dependent upon DNA, Proliferating Cell Nuclear Antigen (PCNA), and the ubiquitin ligase CRL4Cdt2, little is known about the processes that regulate Xic2 or Xic3.
We used the Xenopus interphase egg extract as a model system to examine the regulation of Xic2 by proteolysis and phosphorylation.
Our studies indicated that following primer synthesis during the initiation of DNA replication, Xic2 is targeted for DNA- and PCNA-dependent ubiquitin-mediated proteolysis and that Cdt2 can promote Xic2 turnover. Additionally, during interphase, Xic2 is phosphorylated by CDK2 at Ser-98 and Ser-131 in a DNA-independent manner, inhibiting Xic2 turnover. In the presence of double-stranded DNA ends, Xic2 is also phosphorylated at Ser-78 and Ser-81 by a caffeine-sensitive kinase, but this phosphorylation does not alter Xic2 turnover. Conversely, in the presence or absence of DNA, Xic3 was stable in the Xenopus interphase egg extract and did not exhibit a shift indicative of phosphorylation.
During interphase, Xic2 is targeted for DNA- and PCNA-dependent proteolysis that is negatively regulated by CDK2 phosphorylation. During a response to DNA damage, Xic2 may be alternatively regulated by phosphorylation by a caffeine-sensitive kinase. Our studies suggest that the three types of Xenopus CDK inhibitors, Xic1, Xic2, and Xic3 appear to be uniquely regulated which may reflect their specialized roles during cell division or early development in the frog.
Xic2; Xenopus; PCNA; Phosphorylation; Proteolysis; CDK inhibitor
Available evidence strongly suggests that the γ-aminobutyric acid type A (GABAA) receptor has a crucial role in memory retrieval. However, the signaling mechanisms underlying the role of GABAA receptor modulation in memory retrieval are unclear. We conducted one-trial passive avoidance task with pre-retention trial drug administration in the hippocampus to test the effects of GABAA receptor modulation on memory retrieval. We further tested the co-involvement of signaling molecules: extracellular signal-regulated kinase (ERK), Ca2+/calmodulin-dependent protein kinase II (CaMKII), and cAMP responsive element-binding protein (CREB). First, we observed that the phosphorylation of hippocampal ERK was required for memory retrieval during the task. Accordingly, to investigate whether GABAA receptor activation or inhibition induces ERK phosphorylation during memory retrieval, drugs that target the GABAA receptor were administered into the hippocampus before the retention trial. Muscimol, a GABAA receptor agonist, and diazepam, an agonist to benzodiazepine-binding site of GABAA receptor, blocked retention trial-induced ERK phosphorylation and impaired memory retrieval. Furthermore, co-treatment with sub-effective dose of U0126, a mitogen-activated protein kinase inhibitor, blocked the upregulation of ERK phosphorylation and impaired memory retrieval, and bicuculline methiodide (BMI), a GABAA receptor antagonist, increased ERK phosphorylation induced by the retention trial and facilitated memory retrieval. Finally, the effects of BMI were blocked by the co-application of a sub-effective dose of U0126. These results suggest that GABAA receptor-mediated memory retrieval is closely related to ERK activity.
memory retrieval; GABAA receptor; extracellular signal-regulated kinase; one-trial passive avoidance task; GABA; behavioral science; biological psychiatry; learning & memory; memory retrieval; GABAA receptor; extracellular signal-regulated kinase; one-trial passive avoidance task