Publications by authors named "Mirja Koch"

8 Publications

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The cGMP-Dependent Protein Kinase 2 Contributes to Cone Photoreceptor Degeneration in the -Deficient Mouse Model of Achromatopsia.

Int J Mol Sci 2020 Dec 23;22(1). Epub 2020 Dec 23.

Department of Pharmacy-Center for Drug Research, Ludwig-Maximilians-University, 81377 Munich, Germany.

Mutations in the gene, which encodes the A subunit of the cyclic guanosine monophosphate (cGMP)-gated cation channel in cone photoreceptor outer segments, cause total colour blindness, also referred to as achromatopsia. Cones lacking this channel protein are non-functional, accumulate high levels of the second messenger cGMP and degenerate over time after induction of ER stress. The cell death mechanisms that lead to loss of affected cones are only partially understood. Here, we explored the disease mechanisms in the knockout (KO) mouse model of achromatopsia. We found that another important effector of cGMP, the cGMP-dependent protein kinase 2 (Prkg2) is crucially involved in cGMP cytotoxicity of cones in KO mice. Virus-mediated knockdown or genetic ablation of in KO mice counteracted degeneration and preserved the number of cones. Analysis of markers of endoplasmic reticulum stress and unfolded protein response confirmed that induction of these processes in KO cones also depends on Prkg2. In conclusion, we identified Prkg2 as a novel key mediator of cone photoreceptor degeneration in achromatopsia. Our data suggest that this cGMP mediator could be a novel pharmacological target for future neuroprotective therapies.
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http://dx.doi.org/10.3390/ijms22010052DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7793084PMC
December 2020

ORCA study: real-world versus reading centre assessment of disease activity of neovascular age-related macular degeneration (nAMD).

Br J Ophthalmol 2020 11 17;104(11):1573-1578. Epub 2020 Feb 17.

Department of Ophthalmology, Rheinische Friedrich-Wilhelms-Universitat Bonn, Bonn, Germany.

Background/aims: The prospective, non-interventional ORCA module of the OCEAN study (Observation of Treatment Patterns with Lucentis in Approved Indications) evaluated the qualiy of spectral domain-optical coherence tomography (SD-OCT) image interpretation and treatment decisions by clinicians in Germany and the impact on visual outcomes over 24 months in patients with neovascular age-related macular degeneration (nAMD).

Methods: 2286 SD-OCT scans of 205 eyes were independently evaluated by clinicians and reading centres (RCs) regarding signs of choroidal neovascularisation (CNV) activity, including presence of intraretinal fluid, subretinal fluid, and/or increase in pigment epithelial detachments. Agreement between clinicians and RCs was calculated. Treatment decisions by clinicians and the impact on treatment outcomes were evaluated.

Results: CNV activity was detected by RCs on 1578 scans (69.0%) and by clinicians on 1392 scans (60.9%), with agreement in 74.9% of cases. Of the 1578 scans with RC detected CNV activity, anti-vascular endothelial growth factor injections were performed by clinicians in only 35.5% (560/1578). In 19.7% of cases (311/1578), lack of treatment was justified by patients request, termination criteria or chronic cystoid spaces without other signs for CNV activity. In 44.8% of cases (707/1578) with RC detected CNV activity, clinicians claimed no treatment was necessary despite having correctly detected CNV activity in about 2/3 of these cases. In 34% of cases with presumed undertreatment, visual acuity declined in the following visit.

Conclusion: Although broad agreement on CNV activity parameters was observed between clinicians and RCs, correct identification of CNV activity did not always lead to the initiation of (re-)treatment. To preserve vision over time, correct interpretation of SD-OCT scans and careful retreatment decisions are required.

Trial Registration Number: NCT02194803.
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http://dx.doi.org/10.1136/bjophthalmol-2019-315717DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7587226PMC
November 2020

A microRNA signature of toxic extrasynaptic N-methyl-D-aspartate (NMDA) receptor signaling.

Mol Brain 2020 01 10;13(1). Epub 2020 Jan 10.

Department of Neurobiology, Interdisciplinary Center for Neurosciences, Heidelberg University, 69120, Heidelberg, Germany.

The cellular consequences of N-Methyl-D-Aspartate receptor (NMDAR) stimulation depend on the receptors' subcellular localization. Synaptic NMDARs promote plasticity and survival whereas extrasynaptic NMDARs mediate excitotoxicity and contribute to cell death in neurodegenerative diseases. The mechanisms that couple activation of extrasynaptic NMDARs to cell death remain incompletely understood. We here show that activation of extrasynaptic NMDARs by bath application of NMDA or L-glutamate leads to the upregulation of a group of 19 microRNAs in cultured mouse hippocampal neurons. In contrast, none of these microRNAs is induced upon stimulation of synaptic activity. Increased microRNA expression depends on the pri-miRNA processing enzyme Drosha, but not on de novo gene transcription. These findings suggest that toxic NMDAR signaling involves changes in the expression levels of particular microRNAs.
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http://dx.doi.org/10.1186/s13041-020-0546-0DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6954508PMC
January 2020

Real-World Data: Ranibizumab Treatment For Retinal Vein Occlusion In The OCEAN Study.

Clin Ophthalmol 2019 7;13:2167-2179. Epub 2019 Nov 7.

Augenzentrum Am St. Franziskus Hospital, Muenster, Germany.

Purpose: The non-interventional OCEAN study (NCT02194803) evaluated frequency and monitoring of ranibizumab injections for retinal vein occlusion (RVO) in routine practice in Germany.

Methods: RVO patients (including branch and central RVO (BRVO/CRVO)) receiving ranibizumab were included. Best-corrected visual acuity (BCVA) testing, imaging and treatment were performed at the investigators' discretion and documented over 24 months.

Results: Overall, 744 RVO patients (27% BRVO, 16% CRVO, remaining unspecified RVO) were included. For 74% of patients, data were available for the 12-month visit and for 56% for the 24-month visit. Mean baseline BCVA was 52.0 Early Treatment for Diabetic Retinopathy Study (ETDRS) letters (BRVO: 55.9, CRVO: 43.9). BCVA improved rapidly within the first 3 months, reaching 64.3 letters at 12 months and 64.7 at 24 months. CRVO patients showed less improvement than those with BRVO. Patients received a median of 4 (5) injections over 12 (24) months, with 100% of patients receiving injections at baseline, 70% at Month 1 and 81% at Month 2. Overall, 40% of patients demonstrated a ≥15 letter increase within the first 3 months (42% BRVO, 46% CRVO). Patients with low initial BCVA (<50 letters) showed greater improvement than patients with higher baseline BCVA. Due to considerable loss to follow-up, the number of injections and optical coherence tomography (OCT) examinations were not associated with the change in BCVA.

Conclusion: Patients with RVO in routine practice in Germany received fewer injections and fewer OCT examinations than in clinical trials. CRVO patients showed less and later improvement compared to BRVO patients.
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http://dx.doi.org/10.2147/OPTH.S209253DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6847987PMC
November 2019

Intravitreal Ranibizumab Therapy for Diabetic Macular Edema in Routine Practice: Two-Year Real-Life Data from a Non-interventional, Multicenter Study in Germany.

Diabetes Ther 2018 Dec 4;9(6):2271-2289. Epub 2018 Oct 4.

Augenzentrum am St. Franziskus Hospital, Muenster, Germany.

Introduction: The prospective, non-interventional OCEAN study examined the use of intravitreal ranibizumab injections for the treatment of diabetic macular oedema (DME) in a real-world setting in Germany.

Methods: Adults with DME receiving ≥ 1 ranibizumab (0.5 mg) injections were recruited by 250 ophthalmologists. Best-corrected visual acuity (VA) testing, imaging and treatments were performed according to the investigators' routine practice and documented over 24 months.

Results: The full analysis set included 1226 participants. Mean baseline VA was 60.6 [95% CI: 59.7; 61.5] Early Treatment Diabetic Retinopathy Study letters. VA improved by ≥ 15 letters in 21.5% and 23.5% of the participants at 12 months and 24 months, respectively. They received a mean number of 4.42 [95% CI: 4.30; 4.54] injections in the first year and 5.52 [95% CI: 5.32; 5.73] injections over 24 months, which was markedly lower than in clinical trials. Only 33.4% of the participants received an upload with four initial monthly injections as recommended by the German ophthalmologic societies. Time-to-event analyses that account for missing data inherent to a non-interventional study design demonstrated that participants receiving ≥ 7 injections in the first year had a faster response, but the duration of the response was shorter compared to the subgroups receiving 1-3 and 4-6 injections. Serious adverse events were reported for 143/1250 (11.4%) participants in the safety population.

Conclusion: Under-treatment is a major problem of DME anti- vascular endothelial growth factor therapy under real life conditions. Despite fewer injections given compared to randomised controlled trials with a consequently reduced overall mean visual gain, a profound functional improvement (≥ 15 letters) was achieved over 2 years in 23.5% of eyes with DME.

Trial Registration Number: NCT02194803, ClinicalTrials.gov.

Funding: Novartis Pharma GmbH, Nuremberg, Germany.
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http://dx.doi.org/10.1007/s13300-018-0513-2DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6250630PMC
December 2018

Early Microglia Activation Precedes Photoreceptor Degeneration in a Mouse Model of CNGB1-Linked Retinitis Pigmentosa.

Front Immunol 2017 5;8:1930. Epub 2018 Jan 5.

Center for Integrated Protein Science Munich CiPSM and Department of Pharmacy, Center for Drug Research, Ludwig-Maximilians-Universität München, Munich, Germany.

Retinitis pigmentosa (RP) denotes a family of inherited blinding eye diseases characterized by progressive degeneration of rod and cone photoreceptors in the retina. In most cases, a rod-specific genetic defect results in early functional loss and degeneration of rods, which is followed by degeneration of cones and loss of daylight vision at later stages. Microglial cells, the immune cells of the central nervous system, are activated in retinas of RP patients and in several RP mouse models. However, it is still a matter of debate whether activated microglial cells may be responsible for the amplification of the typical degenerative processes. Here, we used mice, which represent a slow degenerative mouse model of RP, to investigate the extent of microglia activation in retinal degeneration. With a combination of FACS analysis, immunohistochemistry and gene expression analysis we established that microglia in the retina were already activated in an early, predegenerative stage of the disease. The evidence available so far suggests that early retinal microglia activation represents a first step in RP, which might initiate or accelerate photoreceptor degeneration.
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http://dx.doi.org/10.3389/fimmu.2017.01930DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5760536PMC
January 2018

In Vivo Analysis of Disease-Associated Point Mutations Unveils Profound Differences in mRNA Splicing of Peripherin-2 in Rod and Cone Photoreceptors.

PLoS Genet 2016 Jan 21;12(1):e1005811. Epub 2016 Jan 21.

Munich Center for Integrated Protein Science CIPSM, Ludwig-Maximilians-Universität München, München, Germany.

Point mutations in peripherin-2 (PRPH2) are associated with severe retinal degenerative disorders affecting rod and/or cone photoreceptors. Various disease-causing mutations have been identified, but the exact contribution of a given mutation to the clinical phenotype remains unclear. Exonic point mutations are usually assumed to alter single amino acids, thereby influencing specific protein characteristics; however, they can also affect mRNA splicing. To examine the effects of distinct PRPH2 point mutations on mRNA splicing and protein expression in vivo, we designed PRPH2 minigenes containing the three coding exons and relevant intronic regions of human PRPH2. Minigenes carrying wild type PRPH2 or PRPH2 exon 2 mutations associated with rod or cone disorders were expressed in murine photoreceptors using recombinant adeno-associated virus (rAAV) vectors. We detect three PRPH2 splice isoforms in rods and cones: correctly spliced, intron 1 retention, and unspliced. In addition, we show that only the correctly spliced isoform results in detectable protein expression. Surprisingly, compared to rods, differential splicing leads to lower expression of correctly spliced and higher expression of unspliced PRPH2 in cones. These results were confirmed in qRT-PCR experiments from FAC-sorted murine rods and cones. Strikingly, three out of five cone disease-causing PRPH2 mutations profoundly enhanced correct splicing of PRPH2, which correlated with strong upregulation of mutant PRPH2 protein expression in cones. By contrast, four out of six PRPH2 mutants associated with rod disorders gave rise to a reduced PRPH2 protein expression via different mechanisms. These mechanisms include aberrant mRNA splicing, protein mislocalization, and protein degradation. Our data suggest that upregulation of PRPH2 levels in combination with defects in the PRPH2 function caused by the mutation might be an important mechanism leading to cone degeneration. By contrast, the pathology of rod-specific PRPH2 mutations is rather characterized by PRPH2 downregulation and impaired protein localization.
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http://dx.doi.org/10.1371/journal.pgen.1005811DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4722987PMC
January 2016

Quick and reliable method for retina dissociation and separation of rod photoreceptor perikarya from adult mice.

MethodsX 2015 15;2:39-46. Epub 2015 Jan 15.

Department of Biology II, Center for Integrated Protein Science Munich (CIPSM), Ludwig Maximilians University Munich, Grosshadernerstrasse 2, 82152 Planegg-Martinsried, Germany.

A pure and abundant population of adult rod perikarya can be exploited in different studies concerning nuclear functions such as gene expression analyses which aim at elucidating the relationship between cell type and disease [1]. Sorting is based either on specific cell-surface markers or fluorescently labeled reporter proteins. Here, we describe a simple and reliable method for separation of rod photoreceptor perikarya without the use of staining procedures or transgenic mice. This method is limited, however, to sorting rod photoreceptors from adult mouse retina. Mature rods possess an inverted nuclear architecture which is determined by the optical functions of these nuclei [2]. The high backscatter of heterochromatin in the core of the nucleus can be used as a selection criterion for FAC-sorting by forward and sideward scatter. •The procedure for retina dissociation using the Papain Dissociation System (Wothington Biochemical Corporation) was optimized.•An easy to follow step-by-step protocol for retina dissociation was devised.•Rod perikarya were FAC-sorted by forward and sideward scatter based solely on the high backscatter of heterochromatin in their nuclei.
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http://dx.doi.org/10.1016/j.mex.2015.01.002DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4487332PMC
July 2015