[Advances in the research of application of three-dimensional bioprinting in skin tissue engineering]

Deep skin wounds require skin grafts for coverage. Current treatments such as tissue engineered skin or skin substitutes can not meet the needs of clinical application due to the technical problems involving preservation, transportation, and a lengthy preparation process. In comparison with traditional methods such as freeze-drying, three-dimensional bioprinting can precisely dispense living cells, nucleic acid, growth factor, and phase-changing hydrogels according to the wound form, while maintaining high cell viability. Besides, it has excellent performance in high resolution, flexibility, reproducibility, and high throughput, showing great potential in the fabrication of tissue engineered skin. This review mainly introduces the common techniques of three-dimensional bioprinting, and their application in skin tissue engineering, focusing on the latest research progress, and summarizes the current challenges and future development of three-dimensional skin printing.

Severe hypoglycemia and hip fracture in patients with type 2 diabetes: a nationwide population-based cohort study

Hypoglycemia is a major concern in glycemic control. Using the Taiwan National Health Insurance Research Database, we found that the risk of hip fracture was associated with emergency or hospitalization visits of severe hypoglycemia in patients with type 2 diabetes; greater visits were associated with higher incidence of hip fracture.

INTRODUCTION

The objective of the study was to assess the risk of hip fracture among patients with type 2 diabetes mellitus (T2DM) and severe hypoglycemia.

METHODS

Using the National Health Insurance Research database in Taiwan, we identified 2588 patients with T2DM who had developed severe hypoglycemia from 2001 to 2009. A comparison cohort who had never developed severe hypoglycemia was frequency matched at a ratio of approximately 1:2. Multivariate Cox proportional hazard regression analysis was used to evaluate the risk of hip fracture.

RESULTS

During a median follow-up period of 3.9 years, there were 219 hip fracture events in 5173 comparison cohorts and 148 hip fracture events in 2588 hypoglycemia cohorts. The incidence of hip fracture was higher in patients with severe hypoglycemia than without severe hypoglycemia (17.19 vs. 8.83 per 1000 person-years; adjusted HR 1.71, 95% CI = 1.35-2.16). Approximately half of the individuals developed hip fracture within 2 years from the first occurrence of severe hypoglycemia. There was a significant associated trend towards increased hip fracture risk with increasing average visit of severe hypoglycemia per year (p for trend <0.001). Medication analysis showed that patients taking sulfonylurea alone, insulin alone, and insulin secretagogues combined with insulin had a higher associated risk to develop hip fracture.

CONCLUSIONS

Severe hypoglycemia was associated with a higher risk to develop hip fracture. The more the visits of severe hypoglycemia per year indicated the higher associated risk in patients with T2DM. Fall is likely an important reason for severe hypoglycemia in relation to increased risk of hip fracture.

A phase III randomised controlled trial of erlotinib vs gefitinib in advanced non-small cell lung cancer with EGFR mutations

Background:

A phase III trial was conducted to compare the safety and efficacy of erlotinib with that of gefitinib in advanced non-small cell lung cancer harbouring epidermal growth factor receptor mutations in exon 19 or 21.

Methods:

Eligible patients were randomised to receive erlotinib (150 mg per day) or gefitinib (250 mg per day) orally until disease progression or unacceptable toxicity. We aimed to determine whether erlotinib is superior to gefitinib in efficacy. The primary end point was progression-free survival.

Results:

A total of 256 patients were randomised to receive erlotinib (N=128) or gefitinib (N=128). Median progression-free survival was not better with erlotinib than with gefitinib (13.0 vs 10.4 months, 95% confidence interval (CI) 0.62–1.05, P=0.108). The corresponding response rates and median overall survival were 56.3% vs 52.3% (P=0.530) and 22.9 vs 20.1 months (95% CI 0.63–1.13, P=0.250), respectively. There were no significant differences in grade 3/4 toxicities between the two arms (P=0.172).

Conclusions:

The primary end point was not met. Erlotinib was not significantly superior to gefitinib in terms of efficacy in advanced non-small cell lung cancer with epidermal growth factor receptor mutations in exon 19 or 21, and the two treatments had similar toxicities.

Successful transvaginal aspiration of interstitial pregnancy after failed methotrexate treatment

Interstitial pregnancy is an uncommon condition that is challenging, not only in making an accurate diagnosis, but also in the choice of treatment. Systemic methotrexate (MTX) treatment has been favored to prevent scarring of the uterus. Nevertheless, surgery is generally indicated when this treatment fails. Transvaginal aspiration of the gestational tissue has been proposed as an alternative to surgery. The authors present a case of interstitial pregnancy in which the patient failed to respond to multidose MTX treatment and was successfully treated with transvaginal sonography-guided transvaginal aspiration of the gestational tissue, thereby bypassing the risk associated with undergoing major surgery. Transvaginal aspiration of conceptive tissue may be a novel treatment for patients with unruptured interstitial pregnancy.

Magnetically induced forward scattering at visible wavelengths in silicon nanosphere oligomers

Electromagnetically induced transparency is a type of quantum interference that induces near-zero reflection and near-perfect transmission. As a classical analogy, metal nanostructure plasmonic ‘molecules' produce plasmon-induced transparency conventionally. Herein, an electromagnetically induced transparency interaction is demonstrated in silicon nanosphere oligomers, wherein the strong magnetic resonance couples with the electric gap mode effectively to markedly suppress reflection. As a result, a narrow-band transparency window created at visible wavelengths, called magnetically induced transparency, is easily realized in nearly touching silicon nanospheres, exhibiting low dependence on the number of spheres and aggregate states compared with plasmon induced transparency. A hybridization mechanism between magnetic and electric modes is proposed to pursue the physical origin, which is crucial to build all-dielectric metamaterials. Remarkably, magnetic induced transparency effect exhibiting near-zero reflection and near-perfect transmission causes light to propagate with no extra phase change. This makes silicon nanosphere oligomers promising as a unit cell in epsilon-near-zero metamaterials.

A weak and narrow electric dipole has limited the use of silicon nanospheres in nanophotonic applications requiring strong interaction between electric and magnetic modes. Here, Yan et al. demonstrate effective coupling between the magnetic resonance and the electric gap mode in nearly touching silicon nanospheres.

In situ investigation of the surface morphology evolution of the bulk ceramic Y2Mo3O12 during crystal water release

The surface morphology evolution of the bulk ceramic Y2Mo3O12 during the release of crystal water is followed in situ for the first time using atomic force microscopy. It is found that both the shape and size of individual grains and the integration morphology of the sample exhibit dynamic changes with increasing temperature. We believe that the surface morphology evolution of the sample with increasing temperature is closely correlated with the forces induced by the contraction and expansion of the lattice during crystal water release in two different stages.

Human placenta-derived adherent cells improve cardiac performance in mice with chronic heart failure

Human placenta-derived adherent cells (PDACs) are a culture-expanded, undifferentiated mesenchymal-like population derived from full-term placental tissue, with immunomodulatory, anti-inflammatory, angiogenic, and neuroprotective properties. PDA-001 (cenplacel-L), an intravenous formulation of PDAC cells, is in clinical development for the treatment of autoimmune and inflammatory diseases. We tested the therapeutic effects of PDA-001 in mice with chronic heart failure (CHF). Three weeks after transaortic constriction surgery to induce CHF, the mice underwent direct intramyocardial (IM) or i.v. injection of PDA-001 at a high (0.5 × 10(6) cells per mouse), medium (0.5 × 10(5) cells per mouse), or low (0.5 × 10(4) cells per mouse) dose. The mice were sacrificed 4 weeks after treatment. Echocardiography and ventricular catheterization showed that IM injection of PDA-001 significantly improved left ventricular systolic and diastolic function compared with injection of vehicle or i.v. injection of PDA-001. IM injection of PDA-001 also decreased cardiac fibrosis, shown by trichrome staining in the vicinity of the injection sites. Low-dose treatment showed the best improvement in cardiac performance compared with the medium- and high-dose groups. In another independent study to determine the mechanism of action with bromodeoxyuridine labeling, the proliferation rates of endothelial cells and cardiomyocytes were significantly increased by low or medium IM dose PDA-001. However, no surviving PDA-001 cells were detected in the heart 1 month after injection. In vivo real-time imaging consistently revealed that the PDA-001 cells were detectable only within 2 days after IM injection of luciferase-expressing PDA-001. Together, these results have demonstrated the cardiac therapeutic potential of PDA-001, likely through a paracrine effect.

Enhanced repair of a critical-sized segmental bone defect in rabbit femur by surface microstructured porous titanium

Repair of load-bearing bone defects remains a challenge in the field of orthopaedic surgery. In the current study, a surface microstructured porous titanium (STPT) successively treated with H2O2/TaCl5 solution and simulated body fluid was used to repair the critical-sized segmental bone defects in rabbit femur, and non-treated porous titanium (NTPT) and porous biphasic calcium phosphate ceramics (PBCP) were used as control, respectively. A 15 mm long implant was positioned in the femoral defect and stabilized by a plate and screws fixation. After implantation into the body for 1, 3 and 6 months, X-ray observation confirmed that porous titanium groups (NTPT and STPT) provided better mechanical support than PBCP group at the early stage. However, there was no obvious difference in the formed bony callus between PBCP and STPT groups in the later stage, and they both showed better shape of bony callus than NTPT group. Micro-CT and histomorphometric analysis for the samples of 6-month implantation demonstrated that more new bone formed in the inner pores of PBCP and STPT groups than that in NTPT group. Moreover, the biomechanical tests revealed that STPT group could bear larger compressive load than NTPT and PBCP groups, almost reaching the level of the normal rabbit femur. STPT exhibited the enhanced repairing effect on the critical-sized segmental bone defect in rabbit femur, meaning that it could be an ideal material for the repair of large bone defect in load-bearing site.

Human placenta-derived adherent cells induce tolerogenic immune responses

Human placenta-derived adherent cells (PDAC cells) are a culture expanded, undifferentiated mesenchymal-like population derived from full-term placental tissue, with immunomodulatory and anti-inflammatory properties. PDA-001 (cenplacel-L), an intravenous formulation of PDAC cells, is in clinical development for the treatment of autoimmune and inflammatory diseases. To elucidate the mechanisms underlying the immunoregulatory properties of PDAC cells, we investigated their effects on immune cell populations, including T cells and dendritic cells (DC) in vitro and in vivo. PDAC cells suppressed T-cell proliferation in an OT-II T-cell adoptive transfer model, reduced the severity of myelin oligodendrocyte glycoprotein peptide-induced experimental autoimmune encephalomyelitis and ameliorated inflammation in a delayed type hypersensitivity response model. In vitro, PDAC cells suppressed T-cell proliferation and inhibited Th1 and Th17 differentiation. Analysis of tissues derived from PDAC cell-treated animals revealed diminished CD86 expression on splenic DC, suggesting that they can also modulate DC populations. Furthermore, PDAC cells modulate the differentiation and maturation of mouse bone marrow-derived DC. Similarly, human DC differentiated from CD14(+) monocytes in the presence of PDAC cells acquired a tolerogenic phenotype. These tolerogenic DC failed to induce allogeneic T-cell proliferation and differentiation toward Th1, but skewed T-cell differentiation toward Th2. Inhibition of cyclo-oxygenase-2 activity resulted in a significant, but not complete, abrogation of PDAC cells' effects on DC phenotype and function, implying a role for prostaglandin E2 in PDAC-mediated immunomodulation. This study identifies modulation of DC differentiation toward immune tolerance as a key mechanism underlying the immunomodulatory activities of PDAC cells.

Response of discharge, TSS, and E. coli to rainfall events in urban, suburban, and rural watersheds

Understanding dominant processes influencing microorganism responses to storm events aids in the development of effective management controls on pathogen contamination in surface water so that they are suitable for water supply, recreation, and aquatic habitat. Despite the urgent needs at present, numerous facets of microbial transport and fate are still poorly understood. Using correlation and multiple regression combined with spatial analyses, this paper evaluates the relationship between antecedent precipitation and discharge, TSS, and E. coli concentrations, and examines correlations between E. coli and TSS, as well as whether and how those relationships change along an urban and rural gradient. The urban watershed exhibited a faster and stronger response of streamflow, TSS, and E. coli to precipitation mainly due to its higher degree of imperviousness. In general, TSS was significantly correlated with E. coli concentrations, which linearly decreased as % developed area increased, with large variation in regions with a high percentage of development, implying the more complex stormwater infrastructure and more variable pollutant sources of E. coli in the urban watershed. Seasonal differences for E. coli were noted. Specifically, summer showed a higher level of E. coli, which might be attributed to the higher temperature since E. coli is more likely to persist and grow in a warmer environment. Further multiple linear regression analyses showed the best E. coli prediction result for the largest, suburban watershed, using antecedent precipitation, TSS, and temperature as independent variables. The models are capable of explaining 60% and 50% of the variability in the E. coli concentration for the dry and wet season, respectively. The study not only provides more detailed and accurate characterization of the storm-period response of E. coli across an urban and rural gradient, but also lays a foundation for predicting the concentration of E. coli in practice, potentially suggesting effective watershed management decisions.

Perianal necrotizing fasciitis treated with a loose-seton technique

AIM

The study evaluated the effect of a loose-seton technique for perianal necrotizing fasciitis.

METHOD

The medical records of seven patients with perianal necrotizing fasciitis treated by the loose-seton technique between December 2005 and June 2010 were reviewed. Age, gender, status of diabetes mellitus, duration of symptoms, the length of hospital stay and number of debridements were investigated.

RESULTS

Five of the patients were men. The mean age was 53 years and the range was 43-79 years. All seven patients had a past history of acute perianal abscess. Six (85.7%) patients had diabetes mellitus. The mean time for removal of the seton was 24 (14-32) days and the mean hospitalization time was 31 (23-45) days. All patients had primary wound healing. There was no mortality. At a median follow-up 18 (6-60) months one patient required inpatient treatment with cutting-seton for complex anal fistula after 11 months. All patients had normal faecal continence and none of them required a reconstructive procedure during the follow-up.

CONCLUSION

The loose-seton technique is an effective treatment for perianal necrotizing fasciitis. The advantages include inhibiting the spread of inflammation, reducing the frequency of debridements, decreasing the area of the wound and limiting extensive scar formation.

Including climate change in pest risk assessment: the peach fruit fly, Bactrocera zonata (Diptera: Tephritidae)

Bactrocera zonata (Saunders) is one of the most harmful species of Tephritidae. It causes extensive damage in Asia and threatens many countries located along or near the Mediterranean Sea. The climate mapping program, CLIMEX 3.0, and the GIS software, ArcGIS 9.3, were used to model the current and future potential geographical distribution of B. zonata. The model predicts that, under current climatic conditions, B. zonata will be able to establish itself throughout much of the tropics and subtropics, including some parts of the USA, southern China, southeastern Australia and northern New Zealand. Climate change scenarios for the 2070s indicate that the potential distribution of B. zonata will expand poleward into areas which are currently too cold. The main factors limiting the pest's range expansion are cold, hot and dry stress. The model's predictions of the numbers of generations produced annually by B. zonata were consistent with values previously recorded for the pest's occurrence in Egypt. The ROC curve and the AUC (an AUC of 0.912) were obtained to evaluate the performance of the CLIMEX model in this study. The analysis of this information indicated a high degree of accuracy for the CLIMEX model. The significant increases in the potential distribution of B. zonata projected under the climate change scenarios considered in this study suggest that biosecurity authorities should consider the effects of climate change when undertaking pest risk assessments. To prevent the introduction and spread of B. zonata, enhanced quarantine and monitoring measures should be implemented in areas that are projected to be suitable for the establishment of the pest under current and future climatic conditions.

Flow density of a reversible ratchet

By defining "flow density" in a reversible ratchet, a kind of Brownian motor that runs four processes in a two-dimensional parameter space to complete a cycle, we analytically investigate the behavior of the motor's integrated flow in terms of the magnitude and location of the density maximum. It turns out that flow density gives information that can serve as a guide for obtaining the most suitable integrated flow important in the design of reversible ratchets.

Apparent diffusion and fractional anisotropy of diffuse intrinsic brain stem gliomas

BACKGROUND AND PURPOSE

DIBSGs have the worst prognosis among pediatric brain tumors with no improvement of outcome for several decades. In this study, we determined whether diffusion imaging could improve patient stratification and our understanding of the impact of therapies.

MATERIALS AND METHODS

Nine baseline and 24 follow-up DTI studies performed in 9 patients on a 1.5T clinical MR imaging scanner were reviewed. ADC and FA were measured for the whole lesion and at 5 anatomic levels: the rostral medulla, caudal pons, midpons, rostral pons, and caudal midbrain. Reference data were obtained from 8 controls with normal brain stem, 6 patients with medulloblastoma, and 7 patients with pilocytic astrocytoma.

RESULTS

ADC was higher in untreated DIBSG than in normal brain stem and medulloblastoma (1.14 ± 0.18 [×10⁻³ mm²/s] versus 0.75 ± 0.06 and 0.56 ± 0.05, both P < .001). FA was lower in DIBSG than in normal brain stem (0.24 ± 0.04 versus 0.43 ± 0.02, P < .001) but was higher than that in pilocytic astrocytoma (0.17 ± 0.05, P < .05). Lower baseline ADC and higher FA correlated with a worse clinical course. Correlations were more significant at the caudal midbrain than in other regions. ADC decreased and FA increased after RT. Changes of FA after RT at the caudal midbrain correlated with event-free survival.

CONCLUSIONS

Baseline ADC and FA of DIBSG revealed hypocellular tumors with extensive edema. Diffusion changes after therapy implied reduced edema but did not support a significant response to therapy. The significance of diffusion properties varied with anatomic locations, the caudal midbrain being particularly important.

Clinical characteristics and outcomes of patients with obstructive sleep apnoea requiring intensive care

We reviewed the clinical characteristics, required intervention and short- and long-term outcomes in obstructive sleep apnoea (OSA) patients requiring intensive care. A retrospective, single-centre, observational cohort study was undertaken in a multidisciplinary teaching medical and surgical intensive care unit. Adult patients with OSA (apnoea-hypopnoea index of 5 or higher) requiring intensive care from January 2000 to January 2005 were included. Thirty-seven OSA patients (age: 58 +/- 14 years, male:female 27:10) were admitted due to respiratory (n=12, 32%), cerebrovascular (n=8, 22%), cardiovascular (n=16, 43%) and infectious events (n=1, 2.7%). Comparing the clinical features, polysomnographic data and outcome among these groups, we found that OSA patients admitted due to respiratory events had significantly higher Acute Physiology and Chronic Health Evaluation II scores, lower arterial blood gas pH, higher PaCO2, a higher incidence of respiratory failure (92%) and required non-invasive ventilation after extubation (73%), and higher intensive care unit readmission rates than patients admitted due to cerebrovascular events and cardiovascular events (P < 0.05). No difference was found in the in-hospital and long-term mortality rate. The most common reason for intensive care unit admission in critically ill OSA patients was a cardiovascular event, followed by respiratory and cerebrovascular events. The baseline polysomnographic data of the OSA patients were not correlated with their clinical features and outcomes in the intensive care unit. A more complicated clinical course and higher intensive care unit readmission rate were encountered in OSA patients admitted due to respiratory events. Further studies would be required to evaluate the efficacy of non-invasive ventilation for facilitation of extubation in OSA patients presenting with hypercapnic respiratory failure.

Toluidine blue O photodynamic inactivation on multidrug-resistant Pseudomonas aeruginosa

BACKGROUND AND OBJECTIVES

Multidrug-resistant (MDR) Pseudomonas aeruginosa infection is becoming a critical problem worldwide. Currently, only limited therapeutic options are available for the treatment of infections caused by MDR P. aeruginosa, therefore, the development of new alternative treatments is needed. Toluidine blue O (TBO) is an effective antibacterial photosensitizing agent against various bacteria. However, reports on antibacterial photosensitization of MDR bacteria are limited. This study aims to determine the in vitro photobactericidal activity of TBO against MDR P. aeruginosa.

STUDY DESIGN/MATERIALS AND METHODS

The efficacy of antibacterial photodynamic inactivation, DNA fragmentation and protein carbonylation of three MDR P. aeruginosa strains and one susceptible strain was compared using TBO as the photosensitizer followed by red light irradiation (630 nm, 90 J/cm(2)) from a light-emitting diode light source. Subsequently, the efficacy of TBO photodynamic inactivation (TBO-PDI) on 60 MDR strains, including 11 with the efflux pump phenotype and 49 with no pump activity, was tested using the minimum lethal drug concentration (MLC) assay.

RESULTS

TBO-PDI caused similar bactericidal effect (6-7 logs of killing effect), DNA fragmentation and protein carbonylation in three MDR and one susceptible P. aeruginosa strains. Although the TBO accumulation assay indicated that TBO is a substrate for the efflux pump, TBO-PDI produce similar photobactericidal activity against 60 MDR P. aeruginosa strains, either with or without efflux-pump phenotype, and 19 susceptible strains.

CONCLUSION

MDR did not affect the susceptibility of P. aeruginosa strains to TBO-PDI. The efflux pump played an insignificant role in TBO-PDI of MDR P. aeruginosa.

Resveratrol reduces endothelial progenitor cells senescence through augmentation of telomerase activity by Akt-dependent mechanisms

BACKGROUND AND PURPOSE

Recent studies have shown that resveratrol increased endothelial progenitor cells (EPCs) numbers and functional activity. However, the mechanisms remain to be determined. Previous studies have demonstrated that increased EPC numbers and activity were associated with the inhibition of EPC senescence, which involves activation of telomerase. Therefore, we investigated whether resveratrol inhibits the onset of EPC senescence through telomerase activation, leading to potentiation of cellular activity.

EXPERIMENTAL APPROACH

After prolonged in vitro cultivation, EPCs were incubated with or without resveratrol. The senescence of EPCs were determined by acidic beta-galactosidase staining. The bromo-deoxyuridine incorporation assay or a modified Boyden chamber assay were employed to assess proliferative or migratory capacity, respectively. To further examine the underlying mechanisms of these effects, we measured telomerase activity and the phosphorylation of Akt by western blotting.

KEY RESULTS

Resveratrol dose dependently prevented the onset of EPCs senescence and increased the proliferation and migration of EPCs. The effect of resveratrol on senescence could not be abolished by eNOS inhibitor or by an oestrogenic receptor antagonist. Resveratrol significantly increased telomerase activity and Akt phosphorylation. Pre-treatment with the PI3K inhibitor, LY294002, significantly attenuated resveratrol-induced telomerase activity.

CONCLUSIONS AND IMPLICATIONS

Resveratrol delayed the onset of EPC senescence and this effect was accompanied by activation of telomerase through the PI3K-Akt signalling pathway. The inhibition of EPCs senescence by resveratrol might protect EPCs against dysfunction induced by pathological factors in vivo and improve EPC functional activities in a way that may be important for cell therapy.

3-D shape measurement by composite pattern projection and hybrid processing

This article presents a projection system with a novel composite pattern for one-shot acquisition of 3D surface shape. The pattern is composed of color encoded stripes and cosinoidal intensity fringes, with parallel arrangement. The stripe edges offer absolute height phases with high accuracy, and the cosinoidal fringes provide abundant relative phases involved in the intensity distribution. Wavelet transform is utilized to obtain the relative phase distribution of the fringe pattern, and the absolute height phases measured by triangulation are combined to calibrate the phase data in unwrapping, so as to eliminate the initial and noise errors and to reduce the accumulation and approximation errors. Numerical simulations are performed to prove the new unwrapping algorithms and actual experiments are carried out to show the validity of the proposed technique for accurate 3- D shape measurement.

Long term follow-up results of dorsal root entry zone lesions for intractable pain after brachial plexus avulsion injuries

Brachial plexus avulsion injury is one of the major complications after traffic, especially motorcycle accidents and machine injuries. Intractable pain and paralysis of the affected limbs are the major neurological deficits. During the past 18 years, we have encountered and treated more than 500 cases with brachial plexus avulsion injuries. Dorsal root entry zone lesions (DREZ) made by thermocoagulation were performed for intractable pain in 60 cases. Forty cases were under regular follow-up for 5-18 years. In early postoperative stage, the pain relief rate was excellent or good in 32 cases (80%). The pain relief rate dropped to 60% in 5 year follow-up period and only 9 cases (50%) had excellent or good result in 10 year follow-up. Reconstructive procedures were performed in almost all patients in the last 10 years. Dorsal root entry zone lesion is an effective procedure for pain control after brachial plexus avulsion injuries.

SynGAP regulates spine formation

SynGAP is a brain-specific ras GTPase-activating protein that is an abundant component of the signaling complex associated with the NMDA-type glutamate receptor. We generated mutant mice lacking synGAP to study its physiological role. Homozygous mutant mice die in the first few days after birth; however, neurons from mutant embryos can be maintained in culture. Here, we report that spine and synapse formation are accelerated in cultured mutant neurons, and the spines of mature mutant neurons are significantly larger than those of wild type. Clusters of PSD-95 and subunits of AMPA-type and NMDA-type glutamate receptors accumulate in spines of mutant neurons by day 10 in vitro, whereas in wild-type neurons they are still mostly located in dendritic shafts. The frequency and amplitude of miniature EPSCs are larger in mutant neurons at day 10 in vitro, confirming that they have more functional synapses. At day 21 in vitro, the spines of mutant neurons remain significantly larger than those of wild type. The mutant phenotype at day 10 in vitro can be rescued by introduction of recombinant wild-type synGAP on day 9. In contrast, introduction of mutant synGAP with a mutated GAP domain or lacking the terminal domain that binds to PSD-95 does not rescue the mutant phenotype, indicating that both domains play a role in control of spine formation. Thus, the GAP activity of synGAP and its association with PSD-95 are important for normal regulation of spine and synapse formation in hippocampal neurons.

A role for synGAP in regulating neuronal apoptosis

The brain-specific Ras/Rap GTPase-activating protein synGAP is a major component of the postsynaptic density at glutamatergic synapses. It is a target for phosphorylation by Ca(2+)/calmodulin-dependent protein kinase II, which up-regulates its GTPase-activating activity. Thus, SynGAP may play an important role in coupling N-methyl-D-aspartate-type glutamate receptor activation to signaling pathways downstream of Ras or Rap. Homozygous deletion of synGAP is lethal within the first few days after birth. Therefore, to study the functions of synGAP, we used the cre/loxP recombination system to produce conditional mice mutants in which gradual loss of synGAP begins at approximately 1 week, and usually becomes maximal by 3 weeks, after birth. The resulting phenotypes fall into two groups. In a small group, the level of synGAP protein is reduced to 20-25% of wild type, and they die at 2-3 weeks of age. In a larger group, the levels remain higher than approximately 40% of wild type, and they survive and remain healthy. In all mutants, however, an abnormally high number of neurons in the hippocampus and cortex undergo apoptosis, as detected by caspase-3 activation. The effect is cell autonomous, occurring only in neuronal types in which the synGAP gene is eliminated. The level of caspase-3 activation in neurons correlates inversely with the level of synGAP protein measured at 2 and 8 weeks after birth, indicating that neuronal apoptosis is enhanced by reduction of synGAP. These data show that synGAP plays a role in regulation of the onset of apoptotic neuronal death.

A role for synGAP in regulating neuronal apoptosis

The brain-specific Ras/Rap GTPase-activating protein synGAP is a major component of the postsynaptic density at glutamatergic synapses. It is a target for phosphorylation by Ca(2+)/calmodulin-dependent protein kinase II, which up-regulates its GTPase-activating activity. Thus, SynGAP may play an important role in coupling N-methyl-D-aspartate-type glutamate receptor activation to signaling pathways downstream of Ras or Rap. Homozygous deletion of synGAP is lethal within the first few days after birth. Therefore, to study the functions of synGAP, we used the cre/loxP recombination system to produce conditional mice mutants in which gradual loss of synGAP begins at approximately 1 week, and usually becomes maximal by 3 weeks, after birth. The resulting phenotypes fall into two groups. In a small group, the level of synGAP protein is reduced to 20-25% of wild type, and they die at 2-3 weeks of age. In a larger group, the levels remain higher than approximately 40% of wild type, and they survive and remain healthy. In all mutants, however, an abnormally high number of neurons in the hippocampus and cortex undergo apoptosis, as detected by caspase-3 activation. The effect is cell autonomous, occurring only in neuronal types in which the synGAP gene is eliminated. The level of caspase-3 activation in neurons correlates inversely with the level of synGAP protein measured at 2 and 8 weeks after birth, indicating that neuronal apoptosis is enhanced by reduction of synGAP. These data show that synGAP plays a role in regulation of the onset of apoptotic neuronal death.