Decreased TNF Levels and Improved Retinal Ganglion Cell Survival in MMP-2 Null Mice Suggest a Role for MMP-2 as TNF Sheddase

Candidate SNP Markers Significantly Altering the Affinity of the TATA-Binding Protein for the Promoters of Human Genes Associated with Primary Open-Angle Glaucoma

Primary open-angle glaucoma (POAG) is the most common form of glaucoma. This condition leads to optic nerve degeneration and eventually to blindness. Tobacco smoking, alcohol consumption, fast-food diets, obesity, heavy weight lifting, high-intensity physical exercises, and many other bad habits are lifestyle-related risk factors for POAG. By contrast, moderate-intensity aerobic exercise and the Mediterranean diet can alleviate POAG. In this work, we for the first time estimated the phylostratigraphic age indices (PAIs) of all 153 POAG-related human genes in the NCBI Gene Database. This allowed us to separate them into two groups: POAG-related genes that appeared before and after the phylum Chordata, that is, ophthalmologically speaking, before and after the camera-type eye evolved. Next, in the POAG-related genes' promoters, we in silico predicted all 3835 candidate SNP markers that significantly change the TATA-binding protein (TBP) affinity for these promoters and, through this molecular mechanism, the expression levels of these genes. Finally, we verified our results against five independent web services-PANTHER, DAVID, STRING, MetaScape, and GeneMANIA-as well as the ClinVar database. It was concluded that POAG is likely to be a symptom of the human self-domestication syndrome, a downside of being civilized.

NLRP3 and autophagy in retinal ganglion cell inflammation in age-related macular degeneration: potential therapeutic implications

Retinal degenerative diseases were a large group of diseases characterized by the primary death of retinal ganglion cells (RGCs). Recent studies had shown an interaction between autophagy and nucleotide-binding oligomerization domain-like receptor 3 (NLRP3) inflammasomes, which may affect RGCs in retinal degenerative diseases. The NLRP3 inflammasome was a protein complex that, upon activation, produces caspase-1, mediating the apoptosis of retinal cells and promoting the occurrence and development of retinal degenerative diseases. Upregulated autophagy could inhibit NLRP3 inflammasome activation, while inhibited autophagy can promote NLRP3 inflammasome activation, which leaded to the accelerated emergence of drusen and lipofuscin deposition under the neurosensory retina. The activated NLRP3 inflammasome could further inhibit autophagy, thus forming a vicious cycle that accelerated the damage and death of RGCs. This review discussed the relationship between NLRP3 inflammasome and autophagy and its effects on RGCs in age-related macular degeneration, providing a new perspective and direction for the treatment of retinal diseases.

Association between elevated serum matrix metalloproteinase-2 and tumor necrosis factor-α, and clinical symptoms in male patients with treatment-resistant and chronic medicated schizophrenia

BACKGROUND

Inflammation has an important role in the pathogenesis of schizophrenia. The aim of this study was to investigate the levels of tumor necrosis factor (TNF) and matrix metalloproteinase-2 (MMP-2) in male patients with treatment-resistant schizophrenia (TRS) and chronic medicated schizophrenia (CMS), and the relationship with psychopathology.

METHODS

The study enrolled 31 TRS and 49 cm male patients, and 53 healthy controls. Serum MMP-2 and TNF-α levels were measured by the Luminex liquid suspension chip detection method. Positive and Negative Syndrome Scale (PANSS) scores were used to evaluate symptom severity and Repeatable Battery for the Assessment of Neuropsychological Status was used to assess cognitive function.

RESULTS

Serum TNF-α and MMP-2 levels differed significantly between TRS, CMS and healthy control patients (F = 4.289, P = 0.016; F = 4.682, P = 0.011, respectively). Bonferroni correction demonstrated that serum TNF-α levels were significantly elevated in CMS patients (P = 0.022) and MMP-2 levels were significantly higher in TRS patients (P = 0.014) compared to healthy controls. In TRS patients, TNF-α was negatively correlated with age (r=-0.435, P = 0.015) and age of onset (r=-0.409, P = 0.022). In CMS patients, MMP-2 and TNF-α were negatively correlated with PANSS negative and total scores, and TNF-α was negatively correlated with PANSS general psychopathology scores (all P < 0.05). MMP-2 levels were positively correlated with TNF-α levels (P < 0.05), but not with cognitive function (P > 0.05).

CONCLUSION

The results indicate the involvement of inflammation in the etiology of TRS and CMS. Further studies are warranted.

Genetic Variants Associated with Acne Vulgaris

Acne vulgaris (AV) ranks among the common chronic inflammatory disorders that impact the sebaceous components of hair follicles. Acne vulgaris is characterised by cardinal manifestations such as the presence of pimples, nodules, pustules, and cysts, which have the potential to lead to the development of acne scarring and pigmentation. The phenomenon is influenced by polygenic inheritance or can be ascribed to the interplay between multiple genes and environmental factors. In recent years, some researchers have found that some genes (such as IL, TNF, RETN, CYP family, MMPs and TIMPs genes et al) are associated with acne vulgaris and may affect the progression and prognosis of the disease. The number of reviews addressing acne-associated genetic variants, however, is limited. In that case, we have compiled a list of prevalent genes associated with acne in recent times. This helps us understand acne's genetic basis and lets us step in early for people prone to severe acne, lowering the chance of acne scars.

Activation of retinal glial cells contributes to the degeneration of ganglion cells in experimental glaucoma

Elevation of intraocular pressure (IOP) is a major risk factor for neurodegeneration in glaucoma. Glial cells, which play an important role in normal functioning of retinal neurons, are well involved into retinal ganglion cell (RGC) degeneration in experimental glaucoma animal models generated by elevated IOP. In response to elevated IOP, mGluR I is first activated and Kir4.1 channels are subsequently inhibited, which leads to the activation of Müller cells. Müller cell activation is followed by a complex process, including proliferation, release of inflammatory and growth factors (gliosis). Gliosis is further regulated by several factors. Activated Müller cells contribute to RGC degeneration through generating glutamate receptor-mediated excitotoxicity, releasing cytotoxic factors and inducing microglia activation. Elevated IOP activates microglia, and following morphological and functional changes, these cells, as resident immune cells in the retina, show adaptive immune responses, including an enhanced release of pro-inflammatory factors (tumor neurosis factor-α, interleukins, etc.). These ATP and Toll-like receptor-mediated responses are further regulated by heat shock proteins, CD200R, chemokine receptors, and metabotropic purinergic receptors, may aggravate RGC loss. In the optic nerve head, astrogliosis is initiated and regulated by a complex reaction process, including purines, transmitters, chemokines, growth factors and cytokines, which contributes to RGC axon injury through releasing pro-inflammatory factors and changing extracellular matrix in glaucoma. The effects of activated glial cells on RGCs are further modified by the interplay among different types of glial cells. This review is concluded by presenting an in-depth discussion of possible research directions in this field in the future.

The Role of Metalloproteinases and Their Tissue Inhibitors on Ocular Diseases: Focusing on Potential Mechanisms

Eye diseases are associated with visual impairment, reduced quality of life, and may even lead to vision loss. The efficacy of available treatment of eye diseases is not satisfactory. The unique environment of the eye related to anatomical and physiological barriers and constraints limits the bioavailability of existing agents. In turn, complex ethiopathogenesis of ocular disorders that used drugs generally are non-disease specific and do not act causally. Therefore, there is a need for the development of a new therapeutic and preventive approach. It seems that matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs) have a significant role in the development and progression of eye diseases and could be used in the therapy of these disorders as pharmacological targets. MMPs and TIMPs play an important role in the angiogenesis, epithelial-mesenchymal transition, cell invasion, and migration, which occur in ocular diseases. In this review, we aim to describe the participation of MMPs and TIMPs in the eye diseases, such as age-related macular degeneration, cataract, diabetic retinopathy, dry eye syndrome, glaucoma, and ocular cancers, posterior capsule opacification focusing on potential mechanisms.

Soluble tumor necrosis factor-alpha-induced hyperexcitability contributes to retinal ganglion cell apoptosis by enhancing Nav1.6 in experimental glaucoma

BACKGROUND

Neuroinflammation plays an important role in the pathogenesis of glaucoma. Tumor necrosis factor-alpha (TNF-α) is a major pro-inflammatory cytokine released from activated retinal glial cells in glaucoma. Here, we investigated how TNF-α induces retinal ganglion cell (RGC) hyperexcitability and injury.

METHODS

Whole-cell patch-clamp techniques were performed to explore changes in spontaneous firing and evoked action potentials, and Na+ currents in RGCs. Both intravitreal injection of TNF-α and chronic ocular hypertension (COH) models were used. Western blotting, immunofluorescence, quantitative real-time polymerase chain reaction (q-PCR), and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) techniques were employed to investigate the molecular mechanisms of TNF-α effects on RGCs.

RESULTS

Intravitreal injection of soluble TNF-α significantly increased the spontaneous firing frequencies of RGCs in retinal slices. When the synaptic transmissions were blocked, more than 90% of RGCs still showed spontaneous firing; both the percentage of cells and firing frequency were higher than the controls. Furthermore, the frequency of evoked action potentials was also higher than the controls. Co-injection of the TNF-α receptor 1 (TNFR1) inhibitor R7050 eliminated the TNF-α-induced effects, suggesting that TNF-α may directly act on RGCs to induce cell hyperexcitability through activating TNFR1. In RGCs acutely isolated from TNF-α-injected retinas, Na+ current densities were upregulated. Perfusing TNF-α in RGCs of normal rats mimicked this effect, and the activation curve of Na+ currents shifted toward hyperpolarization direction, which was mediated through p38 MAPK and STAT3 signaling pathways. Further analysis revealed that TNF-α selectively upregulated Nav1.6 subtype of Na+ currents in RGCs. Similar to observations in retinas of rats with COH, intravitreal injection of TNF-α upregulated the expression of Nav1.6 proteins in both total cell and membrane components, which was reversed by the NF-κB inhibitor BAY 11-7082. Inhibition of TNFR1 blocked TNF-α-induced RGC apoptosis.

CONCLUSIONS

TNF-α/TNFR1 signaling induces RGC hyperexcitability by selectively upregulating Nav1.6 Na+ channels, thus contributing to RGC apoptosis in glaucoma.

Inflammation in Glaucoma: From the back to the front of the eye, and beyond

The pathophysiology of glaucoma is complex, multifactorial and not completely understood. Elevated intraocular pressure (IOP) and/or impaired retinal blood flow may cause initial optic nerve damage. In addition, age-related oxidative stress in the retina concurrently with chronic mechanical and vascular stress is crucial for the initiation of retinal neurodegeneration. Oxidative stress is closely related to cell senescence, mitochondrial dysfunction, excitotoxicity, and neuroinflammation, which are involved in glaucoma progression. Accumulating evidence from animal glaucoma models and from human ocular samples suggests a dysfunction of the para-inflammation in the retinal ganglion cell layer and the optic nerve head. Moreover, quite similar mechanisms in the anterior chamber could explain the trabecular meshwork dysfunction and the elevated IOP in primary open-angle glaucoma. On the other hand, ocular surface disease due to topical interventions is the most prominent and visible consequence of inflammation in glaucoma, with a negative impact on filtering surgery failure, topical treatment efficacy, and possibly on inflammation in the anterior segment. Consequently, glaucoma appears as an outstanding eye disease where inflammatory changes may be present to various extents and consequences along the eye structure, from the ocular surface to the posterior segment, and the visual pathway. Here we reviewed the inflammatory processes in all ocular structures in glaucoma from the back to the front of the eye and beyond. Our approach was to explain how para-inflammation is necessary to maintain homoeostasis, and to describe abnormal inflammatory findings observed in glaucomatous patients or in animal glaucoma models, supporting the hypothesis of a dysregulation of the inflammatory balance toward a pro-inflammatory phenotype. Possible anti-inflammatory therapeutic approaches in glaucoma are also discussed.

Systemic and Intravitreal Antagonism of the TNFR1 Signaling Pathway Delays Axotomy-Induced Retinal Ganglion Cell Loss

Here, we have blocked the signaling pathway of tumor necrosis factor α (TNFα) in a mouse model of traumatic neuropathy using a small cell permeable molecule (R7050) that inhibits TNFα/TNF receptor 1 (TNFR1) complex internalization. Adult pigmented mice were subjected to intraorbital optic nerve crush (ONC). Animals received daily intraperitoneal injections of R7050, and/or a single intravitreal administration the day of the surgery. Some animals received a combinatorial treatment with R7050 (systemic or local) and a single intravitreal injection of brain derived neurotrophic factor (BDNF). As controls, untreated animals were used. Retinas were analyzed for RGC survival 5 and 14 days after the lesion i.e., during the quick and slow phase of axotomy-induced RGC death. qPCR analyses were done to verify that Tnfr1 and TNFα were up-regulated after ONC. At 5 days post-lesion, R7050 intravitreal or systemic treatment neuroprotected RGCs as much as BDNF alone. At 14 days, RGC rescue by systemic or intravitreal administration of R7050 was similar. At this time point, intravitreal treatment with BDNF was significantly better than intravitreal R7050. Combinatory treatment was not better than BDNF alone, although at both time points, the mean number of surviving RGCs was higher. In conclusion, antagonism of the extrinsic pathway of apoptosis rescues axotomized RGCs as it does the activation of survival pathways by BDNF. However, manipulation of both pathways at the same time, does not improve RGC survival.

Role of MMP-2(-1306 C/T) and TIMP-2(-418G/C) Polymorphism in Chinese Han Patients with Acne Vulgaris

Acne is the most common chronic inflammatory skin diseases. Multiple factors, such as hormonal, environmental, immunological, and genetic factors, are thought to be involved in acne. However, genetic studies have yet to elucidate the full mechanism of acne. The aim of this study was to investigate the association of MMP-2 (-1306C/T) and TIMP-2 (-418G/C) polymorphisms with the risk of acne vulgaris in a Chinese Han population. We also analyzed the correlation of clinical parameters and family history in patients with acne vulgaris. This study included 251 acne patients and 121 age- and sex-matched healthy controls. Genomic DNA was extracted from peripheral blood, and genotyping was performed by PCR and DNA sequencing techniques. There is a significant correlation between the MMP-2 (-1306C/T) polymorphism and the acne vulgaris (P<0.001). Although no association was found between the TIMP-2 (-418G/C) polymorphism and the acne vulgaris, patients with the MMP-2 CT/TIMP-2 GG or GC allele are at higher risk of acne vulgaris. There is also a significant difference in the severity of the disease between acne vulgaris patients with and without family history (P<0.001). This study indicated that the MMP-2 (-1306C/T) polymorphism, in combination with the TIMP-2 (-418G/C) polymorphism, contributes to acne vulgaris susceptibility in the Chinese Han population.

Involvement of matrix metalloproteinases in capillary degeneration following NMDA-induced neurotoxicity in the neonatal rat retina

Interactions between neuronal cells and vascular cells in the retina are critical for maintaining retinal tissue homeostasis. Impairment of cellular interactions contributes to development and progression of retinal diseases. Previous studies demonstrated that neuronal cell damage leads to capillary degeneration in an N-methyl-D-aspartic acid (NMDA)-induced retinal degeneration model. However, the mechanisms underlying this phenomenon are not fully understood. In this study, we examined the possible role of matrix metalloproteinase (MMP)-9 in neuronal cell loss and capillary degeneration in NMDA-treated retinas of neonatal rats. Intravitreal injection of NMDA (50 or 200 nmol) was performed on postnatal day (P) 7 and morphological changes in retinal neurons and vasculature were examined on P14. The MMP inhibitor CP101537 (100 nmol) or vehicle (dimethyl sulfoxide) was intravitreally injected simultaneously with, or 2 days after, NMDA injection. CP101537 protected against neurovascular degeneration in a time-dependent manner as follows: 1) simultaneous injection of CP101537 with NMDA prevented morphological changes in retinal neurons induced by NMDA (50 nmol); and 2) reduction in capillary density and number of vertical sprouts induced by NMDA (200 nmol) was prevented when CP101537 was injected 2 days after NMDA injection. Gelatin zymography and western blot analyses indicated that activity and protein levels of MMP-9 were enhanced from 4 h to 2 days after NMDA injection. Increased activity and protein levels of MMP-9 were suppressed by MMP inhibitors (CP101537 and GM6001). In situ zymography revealed that MMP activity was enhanced throughout the retinal vasculature in NMDA-treated retinas. These results indicate that MMP-9 plays an important role in neurovascular degeneration in the injured retina. Inhibition of MMP-9 may be an effective strategy for preventing and reducing neurovascular degeneration.

Colorectal Cancer and Mitochondrial Dysfunctions of the Adjunct Adipose Tissues: A Case Study

Excess body weight has been causally linked to an increased risk of different cancer types, including colorectal cancer (CRC) but the mechanisms underlying this association are practically unknown. We investigate redox state-superoxide (SO) generation rate, activity of complex I in electron transport chain (ETC) of mitochondria and of dinitrosyl iron complexes by electron paramagnetic resonance; activity of matrix metalloproteinase (gelatinase) MMP-2 and MMP-9 by gel zymography of adipose tissues (AT) from 46 patients (64.0 ± 1.6 y.o.) with CRC (II-III stages, pT2-3N0-2M0) in the AT adjacent to tumor (ATAT) and at a distance of 3 cm from the tumor (ATD) to follow the connection of the AT redox state with some of the tumor microenvironment indicators. We have incubated the AT species with the tumor necrosis factor α (TNF-α) to follow its influence on the measured values. As a control, normal AT (NAT) obtained during the liposuction is used. Tumor-induced changes in mitochondrial ETC of ATAT, particularly for Complex I, lead to the enhanced SO generation and consequent oxidative modifications of DNA in ATAT (up to 6.1 times higher than that in NAT and 3.7 times higher than that in ATD, p < 0.05). Gelatinase activity in ATAT is significantly higher than in ATD. A considerable effect of TNF-α on ATAT and ATD (but not on NAT, i.e., only on the tissues where the reprogramming of metabolism has already occurred under the influence of tumor) manifested in increase of cellular hypoxia, gelatinase activity, and SO generation rate is observed. The results can be used for better understanding the mechanism(s) of metabolic symbiosis of tumor and AT as well as serving as a basis for new therapeutic approaches.

Theissenolactone C Exhibited Ocular Protection of Endotoxin-Induced Uveitis by Attenuating Ocular Inflammatory Responses and Glial Activation

The aim of this study was to investigate the effects of a natural component, theissenolactone C (LC53), on the ocular inflammation of experimental endotoxin-induced uveitis (EIU) and its related mechanisms in microglia. Evaluation of the severity of anterior uveitis indicated that LC53 treatment significantly decreased iridal hyperemia and restored the clinical scores. Additionally, the deficient retina functions of electroretinography were improved by LC53. LC53 significantly reduced levels of tumor necrosis factor (TNF)-α, monocyte chemoattractant protein-1, protein leakage and activation of matrix metalloproteinases in the anterior section during EIU. Moreover, LC53 treatment decreased the oxidative stress as well as neuroinflammatory reactivities of GFAP and Iba-1 in the posterior section. Furthermore, LC53 decreased the phosphorylation of p65, expression of HSP90, Bax, and cleaved-caspase-3 in EIU. According to the microglia studies, LC53 significantly abrogated the productions of TNF-α, PGE₂, NO and ROS, as well as inducible NO synthase and cyclooxygenase-2 expression in LPS-stimulated microglial BV2 cells. The microglial activation of IKKβ, p65 phosphorylation and nuclear phosphorylated p65 translocation were strongly attenuated by LC53. On the other hand, LC53 exhibited the inhibitory effects on JNK and ERK MAPKs activation. Our findings indicated that LC53 exerted the ocular-protective effect through its inhibition on neuroinflammation, glial activation, and apoptosis in EIU, suggesting a therapeutic potential with down-regulation of the NF-κB signaling for uveitis and retinal inflammatory diseases.

Assessment of intrinsic and extrinsic signaling pathway in excitotoxic retinal ganglion cell death

Excitotoxicity leads to the activation of a cytotoxic cascade that causes neuronal death. In the retina, retinal ganglion cells (RGCs) die after an excitotoxic insult. Multiple pathways have been proposed to contribute to RGC death after an excitotoxic insult, including TNF signaling, JNK activation, and ER stress. To test the importance of these pathways in RGC death after excitotoxic injury, the excitotoxin N-methyl-D-aspartate (NMDA) was intravitreally injected into mice deficient in components of these pathways. Absence of Tnf or its canonical downstream mediator, Bid, did not confer short- or long-term protection to RGCs. Despite known activation in RGCs and a prominent role in mediating RGC death after other insults, attenuating JNK signaling did not prevent RGC death after excitotoxic insult. Additionally, deficiency of the ER stress protein DDIT3 (CHOP), which has been shown to be involved in RGC death, did not lessen NMDA induced RGC death. Furthermore, absence of both Jun (JNK’s canonical target) and Ddit3, which together provide robust, long-term protection to RGC somas after axonal insult, did not lessen RGC death. Collectively, these results indicate that the drivers of excitotoxic injury remain to be identified and/or multiple cell death pathways are activated in response to injury.

Epigenetic intervention with a BET inhibitor ameliorates acute retinal ganglion cell death in mice

PURPOSE

The bromo and extraterminal (BET) epigenetic "reader" family is becoming an appealing new therapeutic target for several common diseases, yet little is known of its role in retinal neurodegeneration. We explored the potential of BET inhibition in the protection of retinal ganglion cells (RGCs).

METHODS

To test the therapeutic effect of JQ1, an inhibitor highly selective for the BET family of proteins, we used an acute RGC damage model induced by N-methyl-D-aspartic acid (NMDA) excitotoxicity. Adult C57BL/6 mice received an intravitreal injection of NMDA with (or without) JQ1 in one eye and vehicle control in the contralateral eye; RGC loss was assessed on retinal sections and whole mounts. Gene expression and apoptosis were analyzed by quantitative real time (RT)-PCR and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL), respectively. For counting RGCs, immunostaining of the marker protein BRN3A was performed on whole mounts.

RESULTS

NMDA treatment eliminated RGCs (day 7 and day 14 post injection) and diminished the expression (mRNAs) of RGC-selective genes, including Thy1, Nrn1, Sncg, and Nfl (day 3 and day 7). In contrast, co-injection with JQ1 maintained the number and gene expression of RGCs at ~2 fold of the control (NMDA only, no JQ1), and it decreased NMDA-induced TUNEL-positive cells in the RGC layer by 35%. While NMDA treatment dramatically upregulated mRNAs of inflammatory cytokines (TNFα, IL-1β, MCP-1, RANTES) in retinal homogenates, co-injection with JQ1 suppressed their upregulation by ~50%.

CONCLUSIONS

Intravitreal injection of a BET inhibitor (JQ1) ameliorates NMDA-induced RGC death, revealing the RGC-protective potential of pharmacological blockage of the BET family. This new strategy of epigenetic intervention may be extended to other retinal degenerative conditions.

Neutralization of MMP-2 protects Staphylococcus aureus infection induced septic arthritis in mice and regulates the levels of cytokines

Matrix metalloproteinases (MMPs) are crucial players in Staphylococcus aureus mediated synovial tissue destruction in the pathogenesis of septic arthritis. Bacterial insult increases proteolytic matrix fragments by activated chondrocytes and synovial fibroblasts leading to induction of matrix metalloproteinases. Tissue destruction via MMPs induced by bacterial products, necrotic tissues and proinflammatory cytokines have been reported. Cytokines like TNF-α, IL-1β released from host cells in response to S. aureus infection promote cartilage degradation by stimulating the production of MMPs. Antibiotic treatment can eradicate invading bacteria but elevated levels of cytokines and cytokines induced MMPs activation lead to progressive and devastating bone and cartilage destruction even after bacterial clearance. Like other MMPs, MMP-2 also contributes to extracellular matrix degradation in different types of arthritis. Release of certain pro inflammatory cytokines can also be regulated by MMP-2 activation leading to further tissue destruction. The role of MMP-2 in the pathogenesis of S. aureus infection induced septic arthritis and its influence on cytokines regulation needs further investigation. Whether neutralization of MMP-2 provides protection against Staphylococcus aureus infection induced septic arthritis in mice is an obvious question. Here we reported that neutralization of MMP-2 during S. aureus infection induced septic arthritis might be beneficial for preventing infection induced extracellular matrix destruction thereby decreasing bacterial burden in synovial tissues and regulating inflammatory cytokines in arthritic mice.

A freely available semi-automated method for quantifying retinal ganglion cells in entire retinal flatmounts

Glaucomatous optic neuropathies are characterized by progressive loss of retinal ganglion cells (RGCs), the neurons that connect the eye to the brain. Quantification of these RGCs is a cornerstone in experimental optic neuropathy research and commonly performed via manually quantifying parts of the retina. However, this is a time-consuming process subject to inter- and intra-observer variability. Here we present a freely available ImageJ script to semi-automatically quantify RGCs in entire retinal flatmounts after immunostaining for the RGC-specific transcription factor Brn3a. The blob-like signal of Brn3a-immunopositive RGCs is enhanced via eigenvalues of the Hessian matrix and the resulting local maxima are counted as RGCs. After the user has outlined the retinal flatmount area, the total RGC number and retinal area are reported and an isodensity map, showing the RGC density distribution across the retina, is created. The semi-automated quantification shows a very strong correlation (Pearson's r ≥ 0.99) with manual counts for both widefield and confocal images, thereby validating the data generated via the developed script. Moreover, application of this method in established glaucomatous optic neuropathy models such as N-methyl-D-aspartate-induced excitotoxicity, optic nerve crush and laser-induced ocular hypertension revealed RGC loss conform with literature. Compared to manual counting, the described automated quantification method is faster and shows user-independent consistency. Furthermore, as the script detects the RGC number in entire retinal flatmounts, the method allows detection of regional differences in RGC density. As such, it can help advance research investigating the degenerative mechanisms of glaucomatous optic neuropathies and the effectiveness of new neuroprotective treatments. Because the script is flexible and easy to optimize due to a low number of critical parameters, it can potentially be applied in combination with other tissues or alternative labeling protocols.

Matrix metalloproteinases in the mouse retina: a comparative study of expression patterns and MMP antibodies

BACKGROUND

Matrix metalloproteinases (MMPs), a family of Zn(2+)-dependent endoproteases, have been shown to act as fine regulators of both health and disease. Limited research revealed that they are essential to maintaining ocular physiology and inordinate MMP activities have been linked to several neurodegenerative disorders of the retina, including age-related macular degeneration, proliferative diabetic retinopathy and glaucomatous optic neuropathies (GONs). Nevertheless, a clear definition of their pathology-exacerbating and/or -resolving actions is lacking, especially in the context of GONs, as most studies thus far merely focused on expression profiling in human patients. Therefore, in an initial step towards an improved understanding of MMP functions in the retina, we studied the spatial expression pattern of MMP-2, -3, -9 and MT1-MMP in the healthy mouse retina.

METHODS

The spatial expression pattern of MMP-2, -3, -9 and MT1-MMP was studied in the healthy mouse retina via immunohistochemical stainings, and immunoreactivity profiles were compared to existing literature. Moreover, we considered sensitivity and specificity issues with commercially available MMP antibodies via Western blot.

RESULTS

Basal expression of MMP-2,-3, -9 and MT1-MMP was found in the retina of healthy, adult mice. MMP-2 expression was seen in Müller glia, predominantly in their end feet, which is in line with available literature. MMP-3 expression was described for the first time in the retina, and was observed in vesicle-like structures along the radial fibers of Müller glia. MMP-9 expression, about which still discords exists, was seen in microglia and in a sparse subset of (apoptosing) RGCs. MT1-MMP localization was for the first time studied in adult mice and was found in RGC axons and Müller glia, mimicking the MT1-MMP expression pattern seen in rabbits and neonatal mice. Moreover, one antibody was selected for each MMP, based on its staining pattern in Western blot.

CONCLUSIONS

The present MMP immunoreactivity profiles in the mouse retina and validation of MMP antibodies, can be instrumental to study MMP expression in mouse models of ocular pathologies and to compare these expression profiles to observations from clinical studies, which would be a first step in the disentanglement of the exact role MMPs in ocular/retinal diseases.