Multiparametric Longitudinal Profiling of RCAS-tva-Induced PDGFB-Driven Experimental Glioma

Glioblastomas are incurable primary brain tumors harboring a heterogeneous landscape of genetic and metabolic alterations. Longitudinal imaging by MRI and [18F]FET-PET measurements enable us to visualize the features of evolving tumors in a dynamic manner. Yet, close-meshed longitudinal imaging time points for characterizing temporal and spatial metabolic alterations during tumor evolution in patients is not feasible because patients usually present with already established tumors. The replication-competent avian sarcoma-leukosis virus (RCAS)/tumor virus receptor-A (tva) system is a powerful preclinical glioma model offering a high grade of spatial and temporal control of somatic gene delivery in vivo. Consequently, here, we aimed at using MRI and [18F]FET-PET to identify typical neuroimaging characteristics of the platelet-derived growth factor B (PDGFB)-driven glioma model using the RCAS-tva system. Our study showed that this preclinical glioma model displays MRI and [18F]FET-PET features that highly resemble the corresponding established human disease, emphasizing the high translational relevance of this experimental model. Furthermore, our investigations unravel exponential growth dynamics and a model-specific tumor microenvironment, as assessed by histology and immunochemistry. Taken together, our study provides further insights into this preclinical model and advocates for the imaging-stratified design of preclinical therapeutic interventions.

Targeting CSF1R Alone or in Combination with PD1 in Experimental Glioma

Glioblastoma is an aggressive primary tumor of the central nervous system. Targeting the immunosuppressive glioblastoma-associated microenvironment is an interesting therapeutic approach. Tumor-associated macrophages represent an abundant population of tumor-infiltrating host cells with tumor-promoting features. The colony stimulating factor-1/ colony stimulating factor-1 receptor (CSF-1/CSF1R) axis plays an important role for macrophage differentiation and survival. We thus aimed at investigating the antiglioma activity of CSF1R inhibition alone or in combination with blockade of programmed death (PD) 1. We investigated combination treatments of anti-CSF1R alone or in combination with anti-PD1 antibodies in an orthotopic syngeneic glioma mouse model, evaluated post-treatment effects and assessed treatment-induced cytotoxicity in a coculture model of patient-derived microtumors (PDM) and autologous tumor-infiltrating lymphocytes (TILs) ex vivo. Anti-CSF1R monotherapy increased the latency until the onset of neurological symptoms. Combinations of anti-CSF1R and anti-PD1 antibodies led to longterm survivors in vivo. Furthermore, we observed treatment-induced cytotoxicity of combined anti-CSF1R and anti-PD1 treatment in the PDM/TILs cocultures ex vivo. Our results identify CSF1R as a promising therapeutic target for glioblastoma, potentially in combination with PD1 inhibition.

Accessory heterozygous mutations in cone photoreceptor CNGA3 exacerbate CNG channel-associated retinopathy

Mutations in CNGA3 and CNGB3, the genes encoding the subunits of the tetrameric cone photoreceptor cyclic nucleotide-gated ion channel, cause achromatopsia, a congenital retinal disorder characterized by loss of cone function. However, a small number of patients carrying the CNGB3/c.1208G>A;p.R403Q mutation present with a variable retinal phenotype ranging from complete and incomplete achromatopsia to moderate cone dysfunction or progressive cone dystrophy. By exploring a large patient cohort and published cases, we identified 16 unrelated individuals who were homozygous or (compound-)heterozygous for the CNGB3/c.1208G>A;p.R403Q mutation. In-depth genetic and clinical analysis revealed a co-occurrence of a mutant CNGA3 allele in a high proportion of these patients (10 of 16), likely contributing to the disease phenotype. To verify these findings, we generated a Cngb3R403Q/R403Q mouse model, which was crossbred with Cnga3-deficient (Cnga3-/-) mice to obtain triallelic Cnga3+/- Cngb3R403Q/R403Q mutants. As in human subjects, there was a striking genotype-phenotype correlation, since the presence of 1 Cnga3-null allele exacerbated the cone dystrophy phenotype in Cngb3R403Q/R403Q mice. These findings strongly suggest a digenic and triallelic inheritance pattern in a subset of patients with achromatopsia/severe cone dystrophy linked to the CNGB3/p.R403Q mutation, with important implications for diagnosis, prognosis, and genetic counseling.

Cystoid edema, neovascularization and inflammatory processes in the murine Norrin-deficient retina

Mutations in the Norrin (NDP) gene cause severe developmental blood vessel defects in the retina leading to congenital blindness. In the retina of Ndph-knockout mice only the superficial capillary network develops. Here, a detailed characterization of this mouse model at late stages of the disease using in vivo retinal imaging revealed cystoid structures that closely resemble the ovoid cysts in the inner nuclear layer of the human retina with cystoid macular edema (CME). In human CME an involvement of Müller glia cells is hypothesized. In Ndph-knockout retinae we could demonstrate that activated Müller cells were located around and within these cystoid spaces. In addition, we observed extensive activation of retinal microglia and development of neovascularization. Furthermore, ex vivo analyses detected extravasation of monocytic cells suggesting a breakdown of the blood retina barrier. Thus, we could demonstrate that also in the developmental retinal vascular pathology present in the Ndph-knockout mouse inflammatory processes are active and may contribute to further retinal degeneration. This observation delivers a new perspective for curative treatments of retinal vasculopathies. Modulation of inflammatory responses might reduce the symptoms and improve visual acuity in these diseases.

Gene Therapy Successfully Delays Degeneration in a Mouse Model of PDE6A-Linked Retinitis Pigmentosa (RP43)

Retinitis pigmentosa type 43 (RP43) is a blinding disease caused by mutations in the gene for rod phosphodiesterase 6 alpha (PDE6A). The disease process begins with a dysfunction of rod photoreceptors, subsequently followed by a currently untreatable progressive degeneration of the entire outer retina. Aiming at a curative approach via PDE6A gene supplementation, a novel adeno-associated viral (AAV) vector was developed for expression of the human PDE6A cDNA under control of the human rhodopsin promotor (rAAV8.PDE6A). This study assessed the therapeutic efficacy of rAAV8.PDE6A in the Pde6a^{nmf363/nmf363}-mutant mouse model of RP43. All mice included in this study were treated with sub-retinal injections of the vector at 2 weeks after birth. The therapeutic effect was monitored at 1 month and 6 months post injection. Biological function of the transgene was assessed in vivo by means of electroretinography. The degree of morphological rescue was investigated both in vivo using optical coherence tomography and ex vivo by immunohistological staining. It was found that the novel rAAV8.PDE6A vector resulted in a stable and efficient expression of PDE6A protein in rod photoreceptors of Pde6a^{nmf363/nmf363} mice following treatment at both the short- and long-term time points. The treatment led to a substantial morphological preservation of outer nuclear layer thickness, rod outer segment structure, and prolonged survival of cone photoreceptors for at least 6 months. Additionally, the ERG analysis confirmed a restoration of retinal function in a group of treated mice. Taken together, this study provides successful proof-of-concept for the cross-species efficacy of the rAAV8.PDE6A vector developed for use in human patients. Importantly, the data show stable expression and rescue effects for a prolonged period of time, raising hope for future translational studies based on this approach.

Murine Autoimmune Optic Neuritis Is Not Phenotypically Altered by the Retinal Degeneration 8 Mutation

Purpose

To investigate whether the presence of the retinal degeneration 8 (rd8) mutation in C57BL/6 mice alters the phenotype of autoimmune optic neuritis (AON).

Methods

C57BL/6J and C57BL/6N mice were genotyped for the rd8 mutation and fundus analyses and examination of retinal layer morphology were performed in vivo by scanning laser ophthalmoscopy and optical coherence tomography. Visual function was assessed by recording electroretinographs, and visual evoked potentials and retinae and optic nerves were assessed histopathologically. Retinal ganglion cell numbers were determined by retrograde labeling with fluorogold. Mice were then immunized with myelin oligodendrocyte glycoprotein 35-55 to induce AON before assessment of retinal ganglion cell degeneration, inflammatory infiltration of retinae and optic nerves, and demyelination. Furthermore, visual function was assessed by visual evoked potentials.

Results

All C57BL/6N mice were homozygous for the mutation (Crb1rd8/rd8) and had pathology typical of the rd8 mutation; however, this was not seen in the C57BL/6J (Crb1wt/wt) mice. Following induction of AON, no differences were seen between the Crb1rd8/rd8 and Crb1wt/wt mice regarding disease parameters nor regarding inner retinal degeneration either in the retina as a whole or in the inferior nasal quadrant.

Conclusions

The presence of the rd8 mutation in C57BL/6 mice does not affect the course of AON and should not provide a confounding factor in the interpretation of experimental results obtained in this model. However, it could be dangerous in other models of ocular pathology.

Long-term consequences of developmental vascular defects on retinal vessel homeostasis and function in a mouse model of Norrie disease

Loss of Norrin signalling due to mutations in the Norrie disease pseudoglioma gene causes severe vascular defects in the retina, leading to visual impairment and ultimately blindness. While the emphasis of experimental work so far was on the developmental period, we focus here on disease mechanisms that induce progression into severe adult disease. The goal of this study was the comprehensive analysis of the long-term effects of the absence of Norrin on vascular homeostasis and retinal function. In a mouse model of Norrie disease retinal vascular morphology and integrity were studied by means of in vivo angiography; the vascular constituents were assessed in detailed histological analyses using quantitative retinal morphometry. Finally, electroretinographic analyses were performed to assess the retinal function in adult Norrin deficient animals. We could show that the primary developmental defects not only persisted but developed into further vascular abnormalities and microangiopathies. In particular, the overall vessel homeostasis, the vascular integrity, and also the cellular constituents of the vascular wall were affected in the adult Norrin deficient retina. Moreover, functional analyses indicated to persistent hypoxia in the neural retina which was suggested as one of the major driving forces of disease progression. In summary, our data provide evidence that the key to adult Norrie disease are ongoing vascular modifications, driven by the persistent hypoxic conditions, which are ineffective to compensate for the primary Norrin-dependent defects.

AAV-Mediated Gene Supplementation Therapy in Achromatopsia Type 2: Preclinical Data on Therapeutic Time Window and Long-Term Effects

Achromatopsia type 2 (ACHM2) is a severe, inherited eye disease caused by mutations in the CNGA3 gene encoding the α subunit of the cone photoreceptor cyclic nucleotide-gated (CNG) channel. Patients suffer from strongly impaired daylight vision, photophobia, nystagmus, and lack of color discrimination. We have previously shown in the Cnga3 knockout (KO) mouse model of ACHM2 that gene supplementation therapy is effective in rescuing cone function and morphology and delaying cone degeneration. In our preclinical approach, we use recombinant adeno-associated virus (AAV) vector-mediated gene transfer to express the murine Cnga3 gene under control of the mouse blue opsin promoter. Here, we provide novel data on the efficiency and permanence of such gene supplementation therapy in Cnga3 KO mice. Specifically, we compare the influence of two different AAV vector capsids, AAV2/5 (Y719F) and AAV2/8 (Y733F), on restoration of cone function, and assess the effect of age at time of treatment on the long-term outcome. The evaluation included in vivo analysis of retinal function using electroretinography (ERG) and immunohistochemical analysis of vector-driven Cnga3 transgene expression. We found that both vector capsid serotypes led to a comparable rescue of cone function over the observation period between 4 weeks and 3 months post treatment. In addition, a clear therapeutic effect was present in mice treated at 2 weeks of age as well as in mice treated at 3 months of age at the first assessment at 4 weeks after treatment. Importantly, the effect extended in both cases over the entire observation period of 12 months post treatment. However, the average ERG amplitude levels differed between the two groups, suggesting a role of the absolute age, or possibly, the associated state of the degeneration, on the achievable outcome. In summary, we found that the therapeutic time window of opportunity for AAV-mediated Cnga3 gene supplementation therapy in the Cnga3 KO mouse model extends at least to an age of 3 months, but is presumably limited by the condition, number and topographical distribution of remaining cones at the time of treatment. No impact of the choice of capsid on the therapeutic success was detected.

Bivalent IAP antagonists, but not monovalent IAP antagonists, inhibit TNF-mediated NF-κB signaling by degrading TRAF2-associated cIAP1 in cancer cells

The inhibitor of apoptosis (IAP) proteins have pivotal roles in cell proliferation and differentiation, and antagonizing IAPs in certain cancer cell lines results in induction of cell death. A variety of IAP antagonist compounds targeting the baculovirus IAP protein repeat 3 (BIR3) domain of cIAP1have advanced into clinical trials. Here we sought to compare and contrast the biochemical activities of selected monovalent and bivalent IAP antagonists with the intent of identifying functional differences between these two classes of IAP antagonist drug candidates. The anti-cellular IAP1 (cIAP1) and pro-apoptotic activities of monovalent IAP antagonists were increased by using a single covalent bond to combine the monovalent moieties at the P4 position. In addition, regardless of drug concentration, treatment with monovalent compounds resulted in consistently higher levels of residual cIAP1 compared with that seen following bivalent compound treatment. We found that the remaining residual cIAP1 following monovalent compound treatment was predominantly tumor necrosis factor (TNF) receptor-associated factor 2 (TRAF2)-associated cIAP1. As a consequence, bivalent compounds were more effective at inhibiting TNF-induced activation of p65/NF-κB compared with monovalent compounds. Moreover, extension of the linker chain at the P4 position of bivalent compounds resulted in a decreased ability to degrade TRAF2-associated cIAP1 in a manner similar to monovalent compounds. This result implied that specific bivalent IAP antagonists but not monovalent compounds were capable of inducing formation of a cIAP1 E3 ubiquitin ligase complex with the capacity to effectively degrade TRAF2-associated cIAP1. These results further suggested that only certain bivalent IAP antagonists are preferred for the targeting of TNF-dependent signaling for the treatment of cancer or infectious diseases.

Retinitis pigmentosa: impact of different Pde6a point mutations on the disease phenotype

Mutations in the PDE6A gene can cause rod photoreceptors degeneration and the blinding disease retinitis pigmentosa (RP). While a number of pathogenic PDE6A mutations have been described, little is known about their impact on compound heterozygous situations and potential interactions of different disease-causing alleles. Here, we used a novel mouse model for the Pde6a R562W mutation in combination with an existing line carrying the V685M mutation to generate compound heterozygous Pde6a V685M/R562W animals, exactly homologous to a case of human RP. We compared the progression of photoreceptor degeneration in these compound heterozygous mice with the homozygous V685M and R562W mutants, and additionally with the D670G line that is known for a relatively mild phenotype. We investigated PDE6A expression, cyclic guanosine mono-phosphate accumulation, calpain and caspase activity, in vivo retinal function and morphology, as well as photoreceptor cell death and survival. This analysis confirms the severity of different Pde6a mutations and indicates that compound heterozygous mutants behave like intermediates of the respective homozygous situations. Specifically, the severity of the four different Pde6a situations may be categorized by the pace of photoreceptor degeneration: V685M (fastest) > V685M/R562W > R562W > D670G (slowest). While calpain activity was strongly increased in all four mutants, caspase activity was not. This points to the execution of non-apoptotic cell death and may lead to the identification of new targets for therapeutic interventions. For individual RP patients, our study may help to predict time-courses for Pde6a-related retinal degeneration and thereby facilitate the definition of a window-of-opportunity for clinical interventions.

Scale Adjustments to Facilitate Two-Dimensional Measurements in OCT Images

Purpose

To address the problem of unequal scales for the measurement of two-dimensional structures in OCT images, and demonstrate the use of intra¬ocular objects of known dimensions in the murine eye for the equal calibration of axes.

Methods

The first part of this work describes the mathematical foundation of major distortion effects introduced by X-Y scaling differences. Illustrations were generated with CorelGraph X3 software. The second part bases on image data obtained with a HRA2 Spectralis (Heidelberg Engineering) in SV129 wild-type mice. Subretinally and intravitreally implanted microbeads, alginate capsules with a diameter of 154±5 μm containing GFP-marked mesenchymal stem cells (CellBeads), were used as intraocular objects for calibration.

Results

The problems encountered with two-dimensional measurements in cases of unequal scales are demonstrated and an estimation of the resulting errors is provided. Commonly, the Y axis is reliably calibrated using outside standards like histology or manufacturer data. We show here that intraocular objects like dimensionally stable spherical alginate capsules allow for a two-dimensional calibration of the acquired OCT raw images by establishing a relation between X and Y axis data. For our setup, a correction factor of about 3.3 was determined using both epiretinally and subretinally positioned beads (3.350 ± 0.104 and 3.324 ± 0.083, respectively).

Conclusions

In this work, we highlight the distortion-related problems in OCT image analysis induced by unequal X and Y scales. As an exemplary case, we provide data for a two-dimensional in vivo OCT image calibration in mice using intraocular alginate capsules. Our results demonstrate the need for a proper two-dimensional calibration of OCT data, and we believe that equal scaling will certainly improve the efficiency of OCT image analysis.

Mutations in the unfolded protein response regulator ATF6 cause the cone dysfunction disorder achromatopsia

Achromatopsia (ACHM) is an autosomal recessive disorder characterized by color blindness, photophobia, nystagmus and severely reduced visual acuity. Using homozygosity mapping and whole-exome and candidate gene sequencing, we identified ten families carrying six homozygous and two compound-heterozygous mutations in the ATF6 gene (encoding activating transcription factor 6A), a key regulator of the unfolded protein response (UPR) and cellular endoplasmic reticulum (ER) homeostasis. Patients had evidence of foveal hypoplasia and disruption of the cone photoreceptor layer. The ACHM-associated ATF6 mutations attenuate ATF6 transcriptional activity in response to ER stress. Atf6(-/-) mice have normal retinal morphology and function at a young age but develop rod and cone dysfunction with increasing age. This new ACHM-related gene suggests a crucial and unexpected role for ATF6A in human foveal development and cone function and adds to the list of genes that, despite ubiquitous expression, when mutated can result in an isolated retinal photoreceptor phenotype.

Targeted ablation of the Pde6h gene in mice reveals cross-species differences in cone and rod phototransduction protein isoform inventory

Phosphodiesterase-6 (PDE6) is a multisubunit enzyme that plays a key role in the visual transduction cascade in rod and cone photoreceptors. Each type of photoreceptor utilizes discrete catalytic and inhibitory PDE6 subunits to fulfill its physiological tasks, i.e. the degradation of cyclic guanosine-3',5'-monophosphate at specifically tuned rates and kinetics. Recently, the human PDE6H gene was identified as a novel locus for autosomal recessive (incomplete) color blindness. However, the three different classes of cones were not affected to the same extent. Short wave cone function was more preserved than middle and long wave cone function indicating that some basic regulation of the PDE6 multisubunit enzyme was maintained albeit by a unknown mechanism. To study normal and disease-related functions of cone Pde6h in vivo, we generated Pde6h knock-out (Pde6h(-/-)) mice. Expression of PDE6H in murine eyes was restricted to both outer segments and synaptic terminals of short and long/middle cone photoreceptors, whereas Pde6h(-/-) retinae remained PDE6H-negative. Combined in vivo assessment of retinal morphology with histomorphological analyses revealed a normal overall integrity of the retinal organization and an unaltered distribution of the different cone photoreceptor subtypes upon Pde6h ablation. In contrast to human patients, our electroretinographic examinations of Pde6h(-/-) mice suggest no defects in cone/rod-driven retinal signaling and therefore preserved visual functions. To this end, we were able to demonstrate the presence of rod PDE6G in cones indicating functional substitution of PDE6. The disparities between human and murine phenotypes caused by mutant Pde6h/PDE6H suggest species-to-species differences in the vulnerability of biochemical and neurosensory pathways of the visual signal transduction system.

Elk3 deficiency causes transient impairment in post-natal retinal vascular development and formation of tortuous arteries in adult murine retinae

Serum Response Factor (SRF) fulfills essential roles in post-natal retinal angiogenesis and adult neovascularization. These functions have been attributed to the recruitment by SRF of the cofactors Myocardin-Related Transcription Factors MRTF-A and -B, but not the Ternary Complex Factors (TCFs) Elk1 and Elk4. The role of the third TCF, Elk3, remained unknown. We generated a new Elk3 knockout mouse line and showed that Elk3 had specific, non-redundant functions in the retinal vasculature. In Elk3(−/−) mice, post-natal retinal angiogenesis was transiently delayed until P8, after which it proceeded normally. Interestingly, tortuous arteries developed in Elk3(−/−) mice from the age of four weeks, and persisted into late adulthood. Tortuous vessels have been observed in human pathologies, e.g. in ROP and FEVR. These human disorders were linked to altered activities of vascular endothelial growth factor (VEGF) in the affected eyes. However, in Elk3(−/−) mice, we did not observe any changes in VEGF or several other potential confounding factors, including mural cell coverage and blood pressure. Instead, concurrent with the post-natal transient delay of radial outgrowth and the formation of adult tortuous arteries, Elk3-dependent effects on the expression of Angiopoietin/Tie-signalling components were observed. Moreover, in vitro microvessel sprouting and microtube formation from P10 and adult aortic ring explants were reduced. Collectively, these results indicate that Elk3 has distinct roles in maintaining retinal artery integrity. The Elk3 knockout mouse is presented as a new animal model to study retinal artery tortuousity in mice and human patients.

Towards a quantitative OCT image analysis

BACKGROUND

Optical coherence tomography (OCT) is an invaluable diagnostic tool for the detection and follow-up of retinal pathology in patients and experimental disease models. However, as morphological structures and layering in health as well as their alterations in disease are complex, segmentation procedures have not yet reached a satisfactory level of performance. Therefore, raw images and qualitative data are commonly used in clinical and scientific reports. Here, we assess the value of OCT reflectivity profiles as a basis for a quantitative characterization of the retinal status in a cross-species comparative study.

METHODS

Spectral-Domain Optical Coherence Tomography (OCT), confocal Scanning-Laser Ophthalmoscopy (SLO), and Fluorescein Angiography (FA) were performed in mice (Mus musculus), gerbils (Gerbillus perpadillus), and cynomolgus monkeys (Macaca fascicularis) using the Heidelberg Engineering Spectralis system, and additional SLOs and FAs were obtained with the HRA I (same manufacturer). Reflectivity profiles were extracted from 8-bit greyscale OCT images using the ImageJ software package (http://rsb.info.nih.gov/ij/).

RESULTS

Reflectivity profiles obtained from OCT scans of all three animal species correlated well with ex vivo histomorphometric data. Each of the retinal layers showed a typical pattern that varied in relative size and degree of reflectivity across species. In general, plexiform layers showed a higher level of reflectivity than nuclear layers. A comparison of reflectivity profiles from specialized retinal regions (e.g. visual streak in gerbils, fovea in non-human primates) with respective regions of human retina revealed multiple similarities. In a model of Retinitis Pigmentosa (RP), the value of reflectivity profiles for the follow-up of therapeutic interventions was demonstrated.

CONCLUSIONS

OCT reflectivity profiles provide a detailed, quantitative description of retinal layers and structures including specialized retinal regions. Our results highlight the potential of this approach in the long-term follow-up of therapeutic strategies.

Targeted ablation of Crb2 in photoreceptor cells induces retinitis pigmentosa

In humans, the Crumbs homolog-1 (CRB1) gene is mutated in autosomal recessive Leber congenital amaurosis and early-onset retinitis pigmentosa. In mammals, the Crumbs family is composed of: CRB1, CRB2, CRB3A and CRB3B. Recently, we showed that removal of mouse Crb2 from retinal progenitor cells, and consequent removal from Müller glial and photoreceptor cells, results in severe and progressive retinal degeneration with concomitant loss of retinal function that mimics retinitis pigmentosa due to mutations in the CRB1 gene. Here, we studied the effects of cell-type-specific loss of CRB2 from the developing mouse retina using targeted conditional deletion of Crb2 in photoreceptors or Müller cells. We analyzed the consequences of targeted loss of CRB2 in the adult mouse retina using adeno-associated viral vectors encoding Cre recombinase and short hairpin RNA against Crb2. In vivo retinal imaging by means of optical coherence tomography on retinas lacking CRB2 in photoreceptors showed progressive thinning of the photoreceptor layer and cellular mislocalization. Electroretinogram recordings under scotopic conditions showed severe attenuation of the a-wave, confirming the degeneration of photoreceptors. Retinas lacking CRB2 in developing photoreceptors showed early onset of abnormal lamination, whereas retinas lacking CRB2 in developing Müller cells showed late onset retinal disorganization. Our data suggest that in the developing retina, CRB2 has redundant functions in Müller glial cells, while CRB2 has essential functions in photoreceptors. Our data suggest that short-term loss of CRB2 in adult mouse photoreceptors, but not in Müller glial cells, causes sporadic loss of adhesion between photoreceptors and Müller cells.

Targeted ablation of CRB1 and CRB2 in retinal progenitor cells mimics Leber congenital amaurosis

Development in the central nervous system is highly dependent on the regulation of the switch from progenitor cell proliferation to differentiation, but the molecular and cellular events controlling this process remain poorly understood. Here, we report that ablation of Crb1 and Crb2 genes results in severe impairment of retinal function, abnormal lamination and thickening of the retina mimicking human Leber congenital amaurosis due to loss of CRB1 function. We show that the levels of CRB1 and CRB2 proteins are crucial for mouse retinal development, as they restrain the proliferation of retinal progenitor cells. The lack of these apical proteins results in altered cell cycle progression and increased number of mitotic cells leading to an increased number of late-born cell types such as rod photoreceptors, bipolar and Müller glia cells in postmitotic retinas. Loss of CRB1 and CRB2 in the retina results in dysregulation of target genes for the Notch1 and YAP/Hippo signaling pathways and increased levels of P120-catenin. Loss of CRB1 and CRB2 result in altered progenitor cell cycle distribution with a decrease in number of late progenitors in G1 and an increase in S and G2/M phase. These findings suggest that CRB1 and CRB2 suppress late progenitor pool expansion by regulating multiple proliferative signaling pathways.

Loss of CRB2 in the mouse retina mimics human retinitis pigmentosa due to mutations in the CRB1 gene

In humans, the Crumbs homolog-1 (CRB1) gene is mutated in progressive types of autosomal recessive retinitis pigmentosa and Leber congenital amaurosis. However, there is no clear genotype-phenotype correlation for CRB1 mutations, which suggests that other components of the CRB complex may influence the severity of retinal disease. Therefore, to understand the physiological role of the Crumbs complex proteins, we generated and analysed conditional knockout mice lacking CRB2 in the developing retina. Progressive disorganization was detected during late retinal development. Progressive thinning of the photoreceptor layer and sites of cellular mislocalization was detected throughout the CRB2-deficient retina by confocal scanning laser ophthalmoscopy and spectral domain optical coherence tomography. Under scotopic conditions using electroretinography, the attenuation of the a-wave was relatively stronger than that of the b-wave, suggesting progressive degeneration of photoreceptors in adult animals. Histological analysis of newborn mice showed abnormal lamination of immature rod photoreceptors and disruption of adherens junctions between photoreceptors, Müller glia and progenitor cells. The number of late-born progenitor cells, rod photoreceptors and Müller glia cells was increased, concomitant with programmed cell death of rod photoreceptors. The data suggest an essential role for CRB2 in proper lamination of the photoreceptor layer and suppression of proliferation of late-born retinal progenitor cells.

Gene therapy restores vision and delays degeneration in the CNGB1(-/-) mouse model of retinitis pigmentosa

Retinitis pigmentosa (RP) is a group of genetically heterogeneous, severe retinal diseases commonly leading to legal blindness. Mutations in the CNGB1a subunit of the rod cyclic nucleotide-gated (CNG) channel have been found to cause RP in patients. Here, we demonstrate the efficacy of gene therapy as a potential treatment for RP by means of recombinant adeno-associated viral (AAV) vectors in the CNGB1 knockout (CNGB1(-/-)) mouse model. To enable efficient packaging and rod-specific expression of the relatively large CNGB1a cDNA (~4 kb), we used an AAV expression cassette with a short rod-specific promoter and short regulatory elements. After injection of therapeutic AAVs into the subretinal space of 2-week-old CNGB1(-/-) mice, we assessed the restoration of the visual system by analyzing (i) CNG channel expression and localization, (ii) retinal function and morphology and (iii) vision-guided behavior. We found that the treatment not only led to expression of full-length CNGB1a, but also restored normal levels of the previously degraded CNGA1 subunit of the rod CNG channel. Both proteins co-localized in rod outer segments and formed regular CNG channel complexes within the treated area of the CNGB1(-/-) retina, leading to significant morphological preservation and a delay of retinal degeneration. In the electroretinographic analysis, we also observed restoration of rod-driven light responses. Finally, treated CNGB1(-/-) mice performed significantly better than untreated mice in a rod-dependent vision-guided behavior test. In summary, this work provides a proof-of-concept for the treatment of rod channelopathy-associated RP by AAV-mediated gene replacement.

Degeneration of the mouse retina upon dysregulated activity of serum response factor

PURPOSE

Our aim was to generate and phenotypically characterize a transgenic mouse line expressing a constitutively active variant of the transcription regulatory protein serum response factor (SRF), namely the SRF-VP16 protein. This new mouse strain has been registered under the designation Gt(ROSA)26Sor(tm1(SRF-VP16)Antu). We found phenotypic changes upon ectopic expression of SRF-VP16, especially in the mouse retina.

METHODS

Using homologous recombination, we integrated an SRF-VP16 conditional (i.e., "flox-STOP" repressed) expression transgene into the Rosa26 locus of murine embryonic stem (ES) cells. These engineered ES cells were used to derive the Gt(ROSA)26Sor(tm1(SRF-VP16)Antu) mouse strain. Semiquantitative real-time PCR was used to determine expression of the SRF-VP16 transgene at the mRNA level, both in young (P20 and P30) and adult (six months old) Gt(ROSA)26Sor(tm1(SRF-VP16)Antu) mice. We also investigated the transcript levels of endogenous Srf and several SRF target genes. Retinal function was tested by electroretinography in both young and adult mice. Morphological abnormalities could be visualized by hematoxylin and eosin staining of sectioned, paraffin-embedded eye tissue samples. Scanning-laser ophthalmoscopy was used to investigate retinal vascularization and degeneration in adult mice.

RESULTS

We show that the SRF-VP16 mRNA is expressed to a low but significant degree in the retinas of young and adult animals of the Gt(ROSA)26Sor(tm1(SRF-VP16)Antu) mouse strain, even in the absence of Cre-mediated deletion of the "flox-STOP" cassette. In the retinas of these transgenic mice, endogenous Srf displays elevated transcript levels. Ectopic retinal expression of constitutively active SRF-VP16 is correlated with the malfunction of retinal neurons in both heterozygous and homozygous animals of both age groups (P20 and adult). Additionally, mislamination of retinal cell layers and cellular rosette formations are found in retinas of both heterozygous and homozygous animals of young age. In homozygous individuals, however, the cellular rosettes are more widespread over the fundus. At adult age, retinas both from animals that are heterozygous and homozygous for the floxSTOP/SRF-VP16 transgene display severe degeneration, mainly of the photoreceptor cell layer. Wild-type age-matched littermates, however, do not show any degeneration. The severity of the observed effects correlates with dosage of the transgene.

CONCLUSIONS

This is the first report suggesting an influence of the transcription factor SRF on the development and function of the murine retina. Ectopic SRF-VP16 mRNA expression in the retinas of young animals is correlated with photoreceptor layer mislamination and impaired retinal function. At an advanced age of six months, degenerative processes are detected in SRF-VP16 transgenic retinas accompanied by impaired retinal function. The Gt(ROSA)26Sor(tm1(SRF-VP16)Antu) mouse strain represents a genetic SRF gain-of-function mouse model that will complement the current SRF loss-of-function models. It promises to provide new insight into the hitherto poorly defined role of SRF in retinal development and function, including potential contributions to ophthalmologic disorders. Furthermore, using conditional Cre-mediated activation of SRF-VP16, the described mouse strain will enable assessment of the impact of dysregulated SRF activity on the physiologic functions of various other organs.

Vax2 regulates retinoic acid distribution and cone opsin expression in the vertebrate eye

Vax2 is an eye-specific homeobox gene, the inactivation of which in mouse leads to alterations in the establishment of a proper dorsoventral eye axis during embryonic development. To dissect the molecular pathways in which Vax2 is involved, we performed a transcriptome analysis of Vax2(-/-) mice throughout the main stages of eye development. We found that some of the enzymes involved in retinoic acid (RA) metabolism in the eye show significant variations of their expression levels in mutant mice. In particular, we detected an expansion of the expression domains of the RA-catabolizing enzymes Cyp26a1 and Cyp26c1, and a downregulation of the RA-synthesizing enzyme Raldh3. These changes determine a significant expansion of the RA-free zone towards the ventral part of the eye. At postnatal stages of eye development, Vax2 inactivation led to alterations of the regional expression of the cone photoreceptor genes Opn1sw (S-Opsin) and Opn1mw (M-Opsin), which were significantly rescued after RA administration. We confirmed the above described alterations of gene expression in the Oryzias latipes (medaka fish) model system using both Vax2 gain- and loss-of-function assays. Finally, a detailed morphological and functional analysis of the adult retina in mutant mice revealed that Vax2 is necessary for intraretinal pathfinding of retinal ganglion cells in mammals. These data demonstrate for the first time that Vax2 is both necessary and sufficient for the control of intraretinal RA metabolism, which in turn contributes to the appropriate expression of cone opsins in the vertebrate eye.

Novel rodent models for macular research

Background

Many disabling human retinal disorders involve the central retina, particularly the macula. However, the commonly used rodent models in research, mouse and rat, do not possess a macula. The purpose of this study was to identify small laboratory rodents with a significant central region as potential new models for macular research.

Methodology/Principal Findings

Gerbillus perpallidus, Meriones unguiculatus and Phodopus campbelli, laboratory rodents less commonly used in retinal research, were subjected to confocal scanning laser ophthalmoscopy (cSLO), fluorescein and indocyanine green angiography, and spectral-domain optical coherence tomography (SD-OCT) using standard equipment (Heidelberg Engineering HRA1 and Spectralis™) adapted to small rodent eyes. The existence of a visual streak-like pattern was assessed on the basis of vascular topography, retinal thickness, and the topography of retinal ganglion cells and cone photoreceptors. All three species examined showed evidence of a significant horizontal streak-like specialization. cSLO angiography and retinal wholemounts revealed that superficial retinal blood vessels typically ramify and narrow into a sparse capillary net at the border of the respective area located dorsal to the optic nerve. Similar to the macular region, there was an absence of larger blood vessels in the streak region. Furthermore, the thickness of the photoreceptor layer and the population density of neurons in the ganglion cell layer were markedly increased in the visual streak region.

Conclusions/Significance

The retinal specializations of Gerbillus perpallidus, Meriones unguiculatus and Phodopus campbelli resemble features of the primate macula. Hence, the rodents reported here may serve to study aspects of macular development and diseases like age-related macular degeneration and diabetic macular edema, and the preclinical assessment of therapeutic strategies.

Cone loss is delayed relative to rod loss during induced retinal degeneration in the diurnal cone-rich rodent Arvicanthis ansorgei

Cone photoreceptor breakdown underlies functional vision loss in many blinding diseases. Cone loss is often secondary to that of rods, but little experimental data are available on the relationship between the two populations. Because of its high cone numbers, we used the diurnal rodent Arvicanthis ansorgei to explore changes in rod and cone survival and function during chemically-induced retinal degeneration. Adult animals received intraperitoneal injections of N-methyl-N-nitrosourea (MNU), and changes in retinal fundus appearance, histology, phenotype, apoptosis (TUNEL staining) and functionality (scotopic and photopic electroretinography) were monitored as a function of post-treatment time and retinal topography. Relative to control animals injected with vehicle only, MNU-injected animals showed time-, region- and population-specific changes as measured by morphological and immunochemical criteria. Histological (gradual thinning of photoreceptor layer) and phenotypical (reduced immunostaining of rhodopsin and rod transducin, and mid wavelength cone opsin and cone arrestin) modifications were first observed in superior central retina at 11 days post-injection. These degenerative changes spread into the superior peripheral and inferior hemisphere during the following 10 days. Rod loss preceded that of cones as visualized by differential immunolabelling and presence of apoptotic cells in rod but not cone cells. By 3 months post-injection, degeneration of the photoreceptor layer was complete in the superior hemisphere, but only partial in the inferior hemisphere. Despite the persistence of cone photoreceptors, scotopic and photopic electroretinography performed at 90 days post-treatment showed that both rod and cone function were severely compromised. In conclusion, MNU-induced retinal degeneration in Arvicanthis follows a predictable spatial and temporal pattern allowing clear separation of rod- and cone-specific pathogenic mechanisms. Compared to other rodents in which MNU has been used, Arvicanthis ansorgei demonstrates pronounced resistance to photoreceptor cell loss.

In vivo assessment of retinal vascular wall dimensions

PURPOSE

Retinal blood vessel diameter and arteriovenous ratio (AVR) are commonly used diagnostic parameters. Because vascular walls are typically not visible in funduscopy, clinical AVR estimation is based on the lumen rather than the entire vessel diameter. Here the authors used a transgenic mouse model to quantify AVR in vivo based on total vessel dimensions (wall and lumen).

METHODS

Confocal scanning laser ophthalmoscopy (cSLO) and indocyanine green angiography of the retinal vasculature were performed in wild-type and transgenic mice expressing green fluorescent protein (GFP) under the transcriptional control of the smooth muscle type α-actin (αSMA) promoter. Spectral-domain-OCT and ERG were performed to control for integrity of retinal structure and function in vivo and histology to demonstrate the location of GFP expression.

RESULTS

Native cSLO imaging and angiography yielded only inner vessel diameters similar to those observed through clinical funduscopy. In αSMA-GFP mice, autofluorescence imaging of the GFP-marked vascular walls also allowed the determination of outer vessel diameters. The mean AVR based on either inner diameter (AVR(id) = 0.72 ± 0.08) or outer diameter (AVR(od) = 0.97 ± 0.09) measurements were significantly different (P < 0.01).

CONCLUSIONS

Transgenic αSMA-GFP expression in murine vessel wall components allowed quantification of retinal vessel outer diameters in vivo. Although arterioles and venules differ in lumen and vessel wall width, they share a common outer diameter, leading to an AVR(od) close to unity. Because vessel walls are primary targets in common hypertensive and metabolic diseases, αSMA-GFP transgenic mice may prove valuable in the detailed assessment of such disorders in vivo.

Noninvasive, in vivo assessment of mouse retinal structure using optical coherence tomography

Background

Optical coherence tomography (OCT) is a novel method of retinal in vivo imaging. In this study, we assessed the potential of OCT to yield histology-analogue sections in mouse models of retinal degeneration.

Methodology/Principal Findings

We achieved to adapt a commercial 3^rd generation OCT system to obtain and quantify high-resolution morphological sections of the mouse retina which so far required in vitro histology. OCT and histology were compared in models with developmental defects, light damage, and inherited retinal degenerations. In conditional knockout mice deficient in retinal retinoblastoma protein Rb, the gradient of Cre expression from center to periphery, leading to a gradual reduction of retinal thickness, was clearly visible and well topographically quantifiable. In Nrl knockout mice, the layer involvement in the formation of rosette-like structures was similarly clear as in histology. OCT examination of focal light damage, well demarcated by the autofluorescence pattern, revealed a practically complete loss of photoreceptors with preservation of inner retinal layers, but also more subtle changes like edema formation. In Crb1 knockout mice (a model for Leber's congenital amaurosis), retinal vessels slipping through the outer nuclear layer towards the retinal pigment epithelium (RPE) due to the lack of adhesion in the subapical region of the photoreceptor inner segments could be well identified.

Conclusions/Significance

We found that with the OCT we were able to detect and analyze a wide range of mouse retinal pathology, and the results compared well to histological sections. In addition, the technique allows to follow individual animals over time, thereby reducing the numbers of study animals needed, and to assess dynamic processes like edema formation. The results clearly indicate that OCT has the potential to revolutionize the future design of respective short- and long-term studies, as well as the preclinical assessment of therapeutic strategies.

In vivo analysis of cone survival in mice

PURPOSE

To identify individual cone photoreceptors in a transgenic mouse line in vivo based on selective expression of green fluorescent protein (GFP) using cSLO (confocal scanning laser ophthalmoscopy) and to use this approach to monitor cone cell fate in mouse models of retinal degeneration.

METHODS

Transgenic mice expressing GFP under the control of a red-green opsin promoter (RG-GFP mice) were analyzed in vivo with respect to GFP expression in cone cells using cSLO and functional integrity using electroretinography (ERG). Histology was performed to correlate the pattern of GFP expression with light microscopic data. Longitudinal monitoring of cone survival was evaluated in crossbreds of RG-GFP mice with cpfl1 and Rpe65(-/-) mutant mice, respectively.

RESULTS

The authors found that RG-GFP transgenic mice had a stable GFP expression that did not interfere with retinal function up to at least 3 months of age. Thus, a longitudinal analysis of cone degeneration in individual RG cpfl1 and RG Rpe65(-/-) cross-bred mice in vivo was successfully performed and demonstrated distinct time frames of cone survival in the particular mouse model.

CONCLUSIONS

Monitoring GFP expression in cone photoreceptor cells, such as in the RG-GFP mouse, is a promising in vivo approach for the analysis of cone survival in mice.

Spectral domain optical coherence tomography in mouse models of retinal degeneration

PURPOSE

Spectral domain optical coherence tomography (SD-OCT) allows cross-sectional visualization of retinal structures in vivo. Here, the authors report the efficacy of a commercially available SD-OCT device to study mouse models of retinal degeneration.

METHODS

C57BL/6 and BALB/c wild-type mice and three different mouse models of hereditary retinal degeneration (Rho(-/-), rd1, RPE65(-/-)) were investigated using confocal scanning laser ophthalmoscopy (cSLO) for en face visualization and SD-OCT for cross-sectional imaging of retinal structures. Histology was performed to correlate structural findings in SD-OCT with light microscopic data.

RESULTS

In C57BL/6 and BALB/c mice, cSLO and SD-OCT imaging provided structural details of frequently used control animals (central retinal thickness, CRT(C57BL/6) = 237 +/- 2 microm and CRT(BALB/c) = 211 +/- 10 microm). RPE65(-/-) mice at 11 months of age showed a significant reduction of retinal thickness (CRT(RPE65) = 193 +/- 2 microm) with thinning of the outer nuclear layer. Rho(-/-) mice at P28 demonstrated degenerative changes mainly in the outer retinal layers (CRT(Rho) = 193 +/- 2 microm). Examining rd1 animals before and after the onset of retinal degeneration allowed monitoring of disease progression (CRT(rd1 P11) = 246 +/- 4 microm, CRT(rd1 P28) = 143 +/- 4 microm). Correlation of CRT assessed by histology and SD-OCT was high (r(2) = 0.897).

CONCLUSIONS

The authors demonstrated cross-sectional visualization of retinal structures in wild-type mice and mouse models for retinal degeneration in vivo using a commercially available SD-OCT device. This method will help to reduce numbers of animals needed per study by allowing longitudinal study designs and will facilitate characterization of disease dynamics and evaluation of putative therapeutic effects after experimental interventions.

Study of gene-targeted mouse models of splicing factor gene Prpf31 implicated in human autosomal dominant retinitis pigmentosa (RP)

PURPOSE

Pre-mRNA processing factor 31 (PRPF31) is a ubiquitous protein needed for the assembly of the pre-mRNA splicing machinery. It has been shown that mutations in this gene cause autosomal dominant retinitis pigmentosa 11 (RP11), which is characterized by rod-cell degeneration. Interestingly, mutations in this ubiquitously expressed gene do not lead to phenotypes other than retinal malfunction. Furthermore, the dominant inheritance pattern has shown incomplete penetrance, which poses interesting questions about the disease mechanism of RP11.

METHODS

To characterize PRPF31 function in the rod cells, two animal models have been generated. One was a heterozygous knock-in mouse (Prpf31(A216P/+)) carrying a point mutation p.A216P, which has previously been identified in RP11 patients. The second was a heterozygous knockout mouse (Prpf31(+/-)). Retinal degeneration in RP11 mouse models was monitored by electroretinography and histology.

RESULTS

Generation of the mouse models is presented, as are results of ERGs and retinal morphology. No degenerative phenotype on fundus examination was found in Prpf31(A216P/+) and Prpf31(+/-) mice. Prpf31(A216P/A216P) and Prpf31(-/-) genotypes were embryonic lethal.

CONCLUSIONS

The results imply that Prpf31 is necessary for survival, and there is no compensation mechanism in mouse for the lack of this splicing factor. The authors suggest that p.A216P mutation in Prpf31 does not exert a dominant negative effect and that one Prpf31 wild-type allele is sufficient for maintenance of the healthy retina in mice.

Retinal degenerative and hypoxic ischemic disease

A broad spectrum of retinal diseases affects both the retinal vasculature and the neural retina, including photoreceptor and postreceptor layers. The accepted clinical hallmarks of acute retinopathy of prematurity (ROP) are dilation and tortuosity of the retinal vasculature. Additionally, significant early and persistent effects on photoreceptor and postreceptor neural structures and function are demonstrated in ROP. In this paper, we focus on the results of longitudinal studies of electroretinographic (ERG) and vascular features in rats with induced retinopathies that model the gamut of human ROP, mild to severe. Two potential targets for pharmaceutical interventions emerge from the observations. The first target is immature photoreceptors because the status of the photoreceptors at an early age predicts later vascular outcome; this approach is appealing as it holds promise to prevent ROP. The second target is the interplay of the neural and vascular retinal networks, which develop cooperatively. Beneficial pharmaceutical interventions may be measured in improved visual outcome as well as lessening of the vascular abnormalities.

Crb1 is a determinant of retinal apical Müller glia cell features

Mutations in the human Crumbs homologue-1 (CRB1) gene cause retinal blinding diseases, such as Leber congenital amaurosis and retinitis pigmentosa. In the previous studies we have shown that Crb1 resides in retinal Müller glia cells and that loss of Crb1 results in retinal degeneration (particularly in the inferior temporal quadrant of the mouse eye). Degeneration is increased by exposure to white light. Here, we studied the role of light and aging to gain a better understanding of the factors involved in the progress of retinal disease. Our data reveal that light is neither sufficient nor required to induce retinal disorganization and degeneration in young Crb1(-/-) mutant mice, suggesting that it rather modulates the retinal phenotype. Gene expression profiling showed that expression of five genes is altered in light-exposed Crb1(-/-) mutant retinas. Three of the five genes are involved in chromosome stabilization (Pituitary tumor transforming gene 1 or Pttg1, Establishment of cohesion 1 homolog 1 or Esco1, and a gene similar to histone H2B). In aged retinas, degeneration of photoreceptors, inner retinal neurons, and retinal pigment epithelium was practically limited to the inferior temporal quadrant. Loss of Crb1 in Müller glia cells resulted in an irregular number and size of their apical villi. We propose that Crb1 is required to regulate number and size of these Müller glia cell villi. The subsequent loss of retinal integrity resulted in neovascularization, in which blood vessels of the choroid protruded into the neural retina.

No evidence for prooxidative effects of homocysteine in vascular endothelial cells

Many epidemiological studies predict a role for homocysteine (HCys) in cardiovascular disease occurrence, progression, and risk factors. In vitro studies demonstrated that HCys is an atherogenic determinant that promotes oxidant stress, inflammation, endothelial dysfunction and cell proliferation. This study originally attempted to examine the mechanism by which exposure of endothelial cells to HCys (0-250 microM) initiates inflammatory reaction and oxidative stress, by (i) investigating whether physiological and pathophysiological concentrations of HCys exhibit a prooxidative activity in vitro, (ii) examining the interaction of monocyte adhesion (Mono Mac 6) to monolayers of human microvascular endothelial cells (HMEC-1) exposed to different HCys concentrations, and (iii) examining if adherent monocytes increase reactive oxygen species either in endothelial cells or in monocytes themselves. However, our results demonstrate that HCys had neither prooxidative nor cytotoxic effects on endothelial cells. Only a moderate time- and concentration-dependent increase in monocyte adhesion up to 28.3 +/- 5.5% was achieved relative to control after 4 h of HCys stimulation. This effect was accompanied by an increased VCAM and ICAM-1 mRNA expression. This "proinflammatory" effect appeared also when HMEC-1 cells were incubated with cysteine or glutathione at the concentration range 0-250 microM, demonstrating a non-specific rather than a specific HCys effect. In addition, adherent monocytes did not increase ROS formation neither in endothelial cells nor in monocytes themselves, indicating no direct or indirect cytotoxic or prooxidative effects of HCys.

A splice site mutation in the murine Opa1 gene features pathology of autosomal dominant optic atrophy

Autosomal dominant optic atrophy (adOA) is a juvenile onset, progressive ocular disorder characterized by bilateral loss of vision, central visual field defects, colour vision disturbances, and optic disc pallor. adOA is most frequently associated with mutations in OPA1 encoding a dynamin-related large GTPase that localizes to mitochondria. Histopathological studies in adOA patients have shown a degeneration of retinal ganglion cells (RGCs) and a loss of axons in the optic nerve. However little is known about the molecular mechanism and pathophysiology of adOA due to the lack of appropriate in vivo models. Here we report a first mouse model carrying a splice site mutation (c.1065 + 5G --> A) in the Opa1 gene. The mutation induces a skipping of exon 10 during transcript processing and leads to an in-frame deletion of 27 amino acid residues in the GTPase domain. Western blot analysis showed no evidence of a shortened mutant protein but a approximately 50% reduced OPA1 protein level supporting haploinsufficiency as a major disease mechanism in adOA. Homozygous mutant mice die in utero during embryogenesis with first notable developmental delay at E8.5 as detected by magnetic resonance imaging (MRI). Heterozygous mutants are viable and of normal habitus but exhibit an age-dependent loss of RGCs that eventually progresses to a severe degeneration of the ganglion cell and nerve fibre layer. In addition optic nerves of mutant mice showed a reduced number of axons, and a swelling and abnormal shape of the remaining axons. Mitochondria in these axons showed disorganized cristae structures. All these defects recapitulate crucial features of adOA in humans and therefore document the validity and importance of this model for future research.

Mpp4 recruits Psd95 and Veli3 towards the photoreceptor synapse

Membrane-associated guanylate kinase (MAGUK) proteins function as scaffold proteins contributing to cell polarity and organizing signal transducers at the neuronal synapse membrane. The MAGUK protein Mpp4 is located in the retinal outer plexiform layer (OPL) at the presynaptic plasma membrane and presynaptic vesicles of photoreceptors. Additionally, it is located at the outer limiting membrane (OLM) where it might be involved in OLM integrity. In Mpp4 knockout mice, loss of Mpp4 function only sporadically causes photoreceptor displacement, without changing the Crumbs (Crb) protein complex at the OLM, adherens junctions or synapse structure. Scanning laser ophthalmology revealed no retinal degeneration. The minor morphological effects suggest that Mpp4 is a candidate gene for mild retinopathies only. At the OPL, Mpp4 is essential for correct localization of Psd95 and Veli3 at the presynaptic photoreceptor membrane. Psd95 labeling is absent of presynaptic membranes in both rods and cones but still present in cone basal contacts and dendritic contacts. Total retinal Psd95 protein levels are significantly reduced which suggests Mpp4 to be involved in Psd95 turnover, whereas Veli3 proteins levels are not changed. These protein changes in the photoreceptor synapse did not result in an altered electroretinograph. These findings suggest that Mpp4 coordinates Psd95/Veli3 assembly and maintenance at synaptic membranes. Mpp4 is a critical recruitment factor to organize scaffolds at the photoreceptor synapse and is likely to be associated with synaptic plasticity and protein complex transport.

In vivo confocal imaging of the retina in animal models using scanning laser ophthalmoscopy

Scanning-laser ophthalmoscopy is a technique for confocal imaging of the eye in vivo. The use of lasers of different wavelengths allows to obtain information about specific tissues and layers due to their reflection and transmission characteristics. In addition, fluorescent dyes excitable in the blue and infrared range offer a unique access to the vascular structures associated with each layer. In animal models, a further enhancement in specificity can be obtained by GFP expression under control of tissue-specific promotors. Important fields of application are studies in retinal degenerations and the follow-up of therapeutic intervention.

An extragalactic supernebula confined by gravity

Little is known about the origins of globular clusters, which contain hundreds of thousands of stars in a volume only a few light years across. Radiation pressure and winds from luminous young stars should disperse the star-forming gas and disrupt the formation of the cluster. Globular clusters in our Galaxy cannot provide answers; they are billions of years old. Here we report the measurement of infrared hydrogen recombination lines from a young, forming super star cluster in the dwarf galaxy NGC5253. The lines arise in gas heated by a cluster of about one million stars, including 4,000-6,000 massive, hot 'O' stars. It is so young that it is still enshrouded in gas and dust, hidden from optical view. The gases within the cluster seem bound by gravity, which may explain why the windy and luminous O stars have not yet blown away those gases. Young clusters in 'starbursting' galaxies in the local and distant Universe may also be gravitationally confined and cloaked from view.

IgA1 protease from Neisseria gonorrhoeae inhibits TNFalpha-mediated apoptosis of human monocytic cells

The modulation of programmed cell death is a common theme in the patho-physiology of inflammation and infectious disease. The synthesis and secretion of an IgA1 protease is strictly associated with virulence of the Neisseria species. Here, we report on the inhibition of tumor necrosis factor alpha (TNFalpha)-mediated apoptosis of the human myelo-monocytic cell line U937 by highly purified IgA1 protease. Apoptosis was verified by the cell surface exposure of phosphatidyl serine and by terminal transferase mediated end-labeling of fragmented DNA. Interestingly, IgA1 protease specifically cleaved the TNF receptor II (TNF-RII) on the surface of intact cells whereas TNF-RI was not affected by the enzyme. Therefore, inhibition of TNFalpha-mediated apoptosis might be correlated to specific cleavage of the TNF-RII by neisserial IgA1 protease.

The Radio Supernebula in NGC 5253

We present 1.3 cm and 2 cm subarcsecond resolution VLA images of the dwarf galaxy NGC 5253. Within the central starburst, we detect high-brightness [Tb&parl0;2 cm&parr0; approximately 100-12,000 K] radio continuum sources. These appear to be very dense, "compact" H ii regions. The dominant radio source is a nebula approximately 1-2 pc in size, requiring several thousand O stars within the volume to maintain its ionization. This nebula has no obvious optical counterpart. The number of ionizing photons we find for this cluster is nearly 2 orders of magnitude larger than indicated by Halpha fluxes, and the deduced stellar content accounts for a significant fraction of the total infrared luminosity of the galaxy. This cluster is a strong candidate for a globular cluster in the process of formation, perhaps the youngest globular cluster known.

Biochemical but not clinical vitamin A deficiency results from mutations in the gene for retinol binding protein

BACKGROUND

Two German sisters aged 14 and 17 y were admitted to the Tübingen eye hospital with a history of night blindness. In both siblings, plasma retinol binding protein (RBP) concentrations were below the limit of detection (<0.6 micromol/L) and plasma retinol concentrations were extremely low (0.19 micromol/L). Interestingly, intestinal absorption of retinyl esters was normal. In addition, other factors associated with low retinol concentrations (eg, low plasma transthyretin or zinc concentrations or mutations in the transthyretin gene) were not present. Neither sibling had a history of systemic disease.

OBJECTIVE

Our aim was to investigate the cause of the retinol deficiency in these 2 siblings.

DESIGN

The 2 siblings and their mother were examined clinically, including administration of the relative-dose-response test, DNA sequencing of the RBP gene, and routine laboratory testing.

RESULTS

Genomic DNA sequence analysis revealed 2 point mutations in the RBP gene: a T-to-A substitution at nucleotide 1282 of exon 3 and a G-to-A substitution at nucleotide 1549 of exon 4. These mutations resulted in amino acid substitutions of asparagine for isoleucine at position 41 (Ile41-->Asn) and of aspartate for glycine at position 74 (Gly74-->Asp). Sequence analysis of cloned polymerase chain reaction products spanning exons 3 and 4 showed that these mutations were localized on different alleles. The genetic defect induced severe biochemical vitamin A deficiency but only mild clinical symptoms (night blindness and a modest retinal dystrophy without effects on growth).

CONCLUSIONS

We conclude that the cellular supply of vitamin A to target tissues might be bypassed in these siblings via circulating retinyl esters, beta-carotene, or retinoic acid, thereby maintaining the health of peripheral tissues.

Multilineage potential of adult human mesenchymal stem cells

Human mesenchymal stem cells are thought to be multipotent cells, which are present in adult marrow, that can replicate as undifferentiated cells and that have the potential to differentiate to lineages of mesenchymal tissues, including bone, cartilage, fat, tendon, muscle, and marrow stroma. Cells that have the characteristics of human mesenchymal stem cells were isolated from marrow aspirates of volunteer donors. These cells displayed a stable phenotype and remained as a monolayer in vitro. These adult stem cells could be induced to differentiate exclusively into the adipocytic, chondrocytic, or osteocytic lineages. Individual stem cells were identified that, when expanded to colonies, retained their multilineage potential.

Chondrogenic differentiation of cultured human mesenchymal stem cells from marrow

In the adult human, mesenchymal stem cells (MSCs) resident in bone marrow retain the capacity to proliferate and differentiate along multiple connective tissue lineages, including cartilage. In this study, culture-expanded human MSCs (hMSCs) of 60 human donors were induced to express the morphology and gene products of chondrocytes. Chondrogenesis was induced by culturing hMSCs in micromass pellets in the presence of a defined medium that included 100 nM dexamethasone and 10 ng/ml transforming growth factor-beta(3) (TGF-beta(3)). Within 14 days, cells secreted an extracellular matrix incorporating type II collagen, aggrecan, and anionic proteoglycans. hMSCs could be further differentiated to the hypertrophic state by the addition of 50 nM thyroxine, the withdrawal of TGF-beta(3), and the reduction of dexamethasone concentration to 1 nM. Increased understanding of the induction of chondrogenic differentiation should lead to further progress in defining the mechanisms responsible for the generation of cartilaginous tissues, their maintenance, and their regeneration.

Mitogenic and adhesive effects of tenascin-C on human hematopoietic cells are mediated by various functional domains

In the adult organism, the extracellular matrix molecule tenascin-C is prominently expressed in the bone marrow. Bone marrow mononuclear cells can adhere to plastic-immobilized tenascin-C, and in the present study we have used bacterial expression proteins to map the domains of tenascin-C responsible for binding of hematopoietic cells. A strong binding site was found to be located within the fibrinogen-like domain, and this binding could be inhibited by heparin, suggesting interactions with membrane-bound heparan sulfate proteoglycans. A second strong binding site was identified within the fibronectin type III-like repeats 6-8, and was also inhibitable by heparin. Adhesion to both attachment sites could not be blocked by various anti-integrin antibodies. A third hematopoietic cell binding site is located in the fibronectin type III-like repeats 1-5, which harbor an RGD sequence in the third fibronectin type III-like repeat. Binding to this domain, however, seems to be RGD-independent, since RGD-containing peptides could not inhibit cell binding; the addition of heparin also did not block adhesion to this domain. Since contradictory results had been reported on a proliferative effect of soluble tenascin-C, we also analyzed its activity on hematopoietic cells. The heterogeneous bone marrow mononuclear cells show a striking proliferative response in the presence of tenascin-C which is concentration-dependent. This result indicates a strong mitogenic activity of tenascin-C on primary hematopoietic cells. Using recombinant fragments of human tenascin-C, we identified several mitogenic domains within the tenascin-C molecule. These adhesive and mitogenic effects of tenascin-C suggest a direct functional association with proliferation and differentiation of hematopoietic cells within the bone marrow microenvironment.

Distinct expression of heat shock and acute phase genes during regional hepatic ischemia-reperfusion

The hepatic response to injury is orchestrated by the expression of different gene groups (i.e., heat shock and acute phase). In the present study, the expression of heat shock and acute phase genes was analyzed in the context of a localized injury, regional hepatic ischemia-reperfusion. Left and median liver lobes were subjected to 1 h of ischemia, whereas blood flow was maintained to the remainder of the organ. After the period of ischemia, the organ was reperfused, and samples of the ischemic and nonischemic liver were obtained at different time points during reperfusion. Expression of the heat shock gene, HSP 72, was detected only in the ischemic liver, whereas expression of the acute phase gene, beta-fibrinogen, and the interleukin-6-inducible gene, metallothionein, was maximally induced in the nonischemic liver and attenuated in the ischemic liver. To determine how the heat shock and acute phase responses were reprioritized during stress, expression of beta-fibronogen and HSP 72 was induced simultaneously in the same animal by administration of endotoxin and total body hyperthermia, respectively. Administration of endotoxin did not impede the expression of HSP 72; however, heat shock attenuated, but did not eliminate, the endotoxin-induced expression of beta-fibronogen. These observations suggest that the heat shock and acute phase responses are not mutually exclusive.

Uptake and nuclear transport of Neisseria IgA1 protease-associated alpha-proteins in human cells

Pathogenic Neisseria species, the causative agents of gonorrhoea and bacterial meningitis, encode a family of polymorphic exo-proteins which are autoproteolytically processed into several distinct extracellular components, including an IgA1 protease and an alpha-protein. IgA1 protease, a putative virulence determinant, is a sequence-specific endopeptidase known to cleave human IgA1, but additional target proteins have been postulated. The physical linkage of IgA1 protease and alpha-protein suggests a functional relationship of both precursor components. Previous work has shown that alpha-protein is essential neither for extracellular transport nor for the proteolytic activity of IgA1 protease. Intriguingly, alpha-proteins carry amino acid sequences reminiscent of nuclear location signals of viral and eukaryotic proteins. Here we demonstrate the functionality of these nuclear location signal sequences in transfected eukaryotic cells. Chimeric alpha-proteins show nuclear transport and selectively associate with nucleolar structures. More importantly, native purified alpha-proteins are capable of entering certain human primary cells from the exterior via an endocytotic route and accumulate in the nuclei. The neisserial alpha-proteins share several features with eukaryotic transcription factors, such as the formation of dimers via a heptad repeat sequence. We propose a role for alpha-proteins in the regulation of host-cell functions. As the alpha-proteins are covalently connected with IgA1 protease they may also serve as carries for the IgA1 protease into human cells where additional proteolytic targets may exist. Neisseria meningitidis, which locally colonizes the nasopharyngeal mucosa of many human individuals without apparently causing symptoms, secretes this nucleus-targeted factor in large quantities.

Depressed expression of the inducible form of HSP 70 (HSP 72) in brain and heart after in vivo heat shock

The heat shock gene expression plays a role in the protection of cells from injury. In the present study, we have analyzed the expression of heat shock protein (HSP) 72 (the major inducible form of the HSP 70 family) in different rat organs after a total body hyperthermia. The content of HSP 72 was greatest in liver and colon. In contrast, accumulation of HSP 72 was low in heart and brain (3-5% and < 1% of the amount in liver, respectively). This low expression of HSP 72 in heart and brain could not be explained by a difference in the actual temperature within these organs. Analysis of cells in culture that resemble hepatocytes, myoblast, and neurons showed a pattern of HSP 72 expression similar to that observed in liver, heart, and brain in vivo after heat shock. These results suggest that this disparate expression of HSP 72 is due to intrinsic characteristics of the cell types rather than to physiological or environmental conditions. The differential expression of HSP 72 among different cell lines could be correlated with the different levels of protein synthesis protection.

Induction of heat shock gene expression in colonic epithelial cells after incubation with Escherichia coli or endotoxin

OBJECTIVE

The universal cellular response to stress is the expression of a family of genes known as heat shock or stress proteins. We investigated whether bacteria or bacterial products (endotoxin) can induce heat shock protein expression in human enterocytes.

DESIGN

Controlled, in vitro study.

SETTING

Cell culture laboratory.

SUBJECTS

Human Caco-2 enterocyte cell line.

MEASUREMENTS AND MAIN RESULTS

Incubation of confluent monolayers of Caco-2 cells with Escherichia coli C25 (1 x 10(9) bacteria/mL) for 1 hr at 37 degrees C was found to induce the expression of the 72-kilodalton molecular weight heat shock protein gene (heat shock protein-72), the major inducible form of the 70-kilodalton molecular weight heat shock protein family of stress proteins, as detected by Western blot analysis. The level of heat shock protein-72 induction after incubation with E. coli was similar to the response of Caco-2 cells to heat shock at 43 degrees C for 1 hr. The induction of heat shock protein-72 gene expression by E. coli was not purely due to the process of phagocytosis, since incubation of Caco-2 cells with latex beads (1 micron) failed to induce heat shock gene expression. To elucidate the possible mechanism of heat shock protein-72 induction mediated by bacteria, Caco-2 cells were incubated with E. coli endotoxin (200 micrograms/mL) for 1 hr at 37 degrees C. Such treatment was also found to induce the synthesis of heat shock protein-72.

CONCLUSIONS

These results demonstrate that bacteria and/or bacterial products induce the heat shock gene expression in Caco-2 cells. Since intestinal epithelial cells are constantly in contact with bacteria and bacterial products, we speculate that the heat shock gene expression may be part of the natural mechanism of protection for these cells in the potentially harmful environment that may be present in the intestinal tract.

Presence of the stress-inducible form of hsp-70 (hsp-72) in normal rat colon

The expression of heat shock proteins (hsp) is probably one of the most primitive mechanisms of cellular protection from stress. Pathogens such as viruses and bacteria have recently been found to induce the heat shock gene expression. In the present study hsp-72, the stress-inducible form of hsp-70, was detected by Western blotting in samples from rat distal colon (DC), proximal colon (PC), and terminal ileum (TI), but was not found in proximal small bowel (PSB) or other organs (liver, kidney, spleen, heart, and brain) of unstressed animals. The signal intensity of hsp-72 in colon (DC > PC > TI > PSB) correlates qualitatively with the presence of normal gut microflora. hsp-72 was also observed in DC, to a lesser extent in PC, but not in TI or PSB of bacteria-free or antibiotic-treated rats. Inflammatory states induced by the intravenous administration of endotoxin (1 mg/kg), the subcutaneous injection of zymosan (1 g/kg) or by cecal ligation and puncture (sepsis) failed to increase the hsp-72 levels in rat colon or other organs. These results demonstrate that hsp-72 is expressed in normal rat colon. However, the induction of hsp-72 expression may not be due solely to the presence of resident bacteria in the gut, but instead, may be the result of a more complex process.