S156C mutation in tissue inhibitor of metalloproteinases-3 induces increased angiogenesis

Engineering metalloproteinase inhibitors: tissue inhibitors of metalloproteinases or antibodies, that is the question

Targeting metalloproteinases (MPs) has been the center of attention for developing therapeutics due to their contribution to a wide range of diseases, including cancer, cardiovascular, neurodegenerative disease, and preterm labor. Protein-based MP inhibitors offer higher stability and selectivity, which is critical for developing efficient therapeutics with low off-target effects. Tissue inhibitors of metalloproteinases (TIMPs), natural inhibitors of MPs, and antibodies provide excellent protein scaffolds for engineering selective or multispecific MP inhibitors. Advances in protein engineering and design techniques, such as rational design and directed evolution using yeast display to develop potent MP inhibitors, are discussed, including but not limited to loop grafting, swapping, and counterselective selection.

Review: Mechanisms of TIMP-3 accumulation and pathogenesis in Sorsby fundus dystrophy

Sorsby fundus dystrophy (SFD) is a rare, inherited form of macular degeneration caused by mutations in the gene encoding tissue inhibitor of metalloproteinases 3 (TIMP-3). There are 21 mutations currently associated with SFD, with some variants (e.g., Ser179Cys, Tyr191Cys, and Ser204Cys) having been studied much more than others. We review what is currently known about the identified SFD variants in terms of their dimerization, metalloproteinase inhibition, and impact on angiogenesis, with a focus on disparities between reports and areas requiring further study. We also explore the potential molecular mechanisms leading to the accumulation of extracellular TIMP-3 in SFD and consider how accumulated TIMP-3 causes macular damage. Recent reports have identified extraocular pathologies in a small number of SFD patients. We discuss these intriguing findings and consider the apparent discrepancy between the widespread expression of TIMP-3 and the primarily retinal manifestations of SFD. The potential benefits of novel experimental approaches (e.g., metabolomics and stem cell models) in terms of investigating SFD pathology are presented. The review thus highlights gaps in our current molecular understanding of SFD and suggests ways to support the development of novel therapies.

Deglycosylation Increases the Aggregation and Angiogenic Properties of Mutant Tissue Inhibitor of Metalloproteinase 3 Protein: Implications for Sorsby Fundus Dystrophy

Sorsby fundus dystrophy (SFD) is an autosomal dominant macular disorder caused by mutations in tissue Inhibitor of the metalloproteinase-3 (TIMP3) gene with the onset of symptoms including choroidal neovascularization as early as the second decade of life. We have previously reported that wild-type TIMP3 is an endogenous angiogenesis inhibitor that inhibits Vascular Endothelial Growth Factor (VEGF)-mediated signaling in endothelial cells. In contrast, SFD-related S179C-TIMP3 when expressed in endothelial cells, does not have angiogenesis-inhibitory properties. To evaluate if this is a common feature of TIMP3 mutants associated with SFD, we examined and compared endothelial cells expressing S179C, Y191C and S204C TIMP3 mutants for their angiogenesis-inhibitory function. Western blot analysis, zymography and reverse zymography and migration assays were utilized to evaluate TIMP3 protein, Matrix Metalloproteinase (MMP) and MMP inhibitory activity, VEGF signaling and in vitro migration in endothelial cells expressing (VEGF receptor-2 (VEGFR-2) and wild-type TIMP3 or mutant-TIMP3. We demonstrate that mutant S179C, Y191C- and S204C-TIMP3 all show increased glycosylation and multimerization/aggregation of the TIMP3 protein. In addition, endothelial cells expressing TIMP3 mutations show increased angiogenic activities and elevated VEGFR-2. Removal of N-glycosylation by mutation of Asn¹⁸⁴, the only potential N-glycosylation site in mutant TIMP3, resulted in increased aggregation of TIMP3, further upregulation of VEGFR-2, VEGF-induced phosphorylation of VEGFR2 and VEGF-mediated migration concomitant with reduced MMP inhibitory activity. These results suggest that even though mutant TIMP3 proteins are more glycosylated, post-translational deglycosylation may play a critical role in the aggregation of mutant TIMP3 and contribute to the pathogenesis of SFD. The identification of factors that might contribute to changes in the glycome of patients with SFD will be useful. Future studies will evaluate whether variations in the glycosylation of mutant TIMP3 proteins are contributing to the severity of the disease.

Potential CRISPR Base Editing Therapeutic Options in a Sorsby Fundus Dystrophy Patient

TIMP3 mutations are associated with early-onset macular choroidal neovascularisation for which no treatment currently exists. CRISPR base editing, with its ability to irreversibly correct point mutations by chemical modification of nucleobases at DNA level, may be a therapeutic option. We report a bioinformatic analysis of potential therapeutic options in a patient presenting with Sorsby fundus dystrophy. Genetic testing in a 35-year-old gentleman with bilateral macular choroidal neovascularisation revealed the patient to be heterozygous for a TIMP3 variant c.610A>T, p.(Ser204Cys). Using a glycosylase base editor (GBE), another DNA-edit could be introduced that would revert the variant back to wild-type on amino acid level. Alternatively, the mutated residue could be changed to another amino acid that would be better tolerated, and for that, an available 'NG'-PAM site was found to be available for the SpCas9-based adenine base editor (ABE) that would introduce p.(Ser204Arg). In silico analyses predicted this variant to be non-pathogenic; however, a bystander edit, p.Ile205Thr, would be introduced. This case report highlights the importance of considering genetic testing in young patients with choroidal neovascularisation, particularly within the context of a strong family history of presumed wet age-related macular degeneration, and describes potential therapeutic options.

Sorsby fundus dystrophy (SFD): A narrative review

Sorsby fundus dystrophy (SFD) is a rare autosomal dominant disorder with complete penetrance affecting the macula. This is caused by a mutation in the TIMP-3. This objective narrative review aims to provide an overview of the pathophysiology, current treatment modalities, and future perspectives. A literature search was performed using "PubMed," "Web of Science," "Scopus," "ScienceDirect," "Google Scholar," "medRxiv," and "bioRxiv." The molecular mechanisms underlying SFD are not completely understood. Novel advancements in cell culture techniques, including induced pluripotent stem cells, may enable more reliable modeling of SFD. These cell culture techniques aim to shed more light on the pathophysiology of SFD, and hopefully, this may lead to the future development of treatment strategies for SFD. Currently, no gene therapy is available. The main treatment is the use of anti-vascular endothelial growth factors (anti-VEGF) to treat secondary choroidal neovascular membrane (CNV), which is a major complication observed in this condition. If CNV is detected and treated promptly, patients with SFD have a good chance of maintaining a functional central vision. Other treatment modalities have been tried but have shown limited benefit, and therefore, have not managed to be more widely accepted. In summary, although there is no definitive cure yet, the use of anti-VEGF treatment for secondary CNV has provided the opportunity to maintain functional vision in individuals with SFD, provided CNV is detected and treated early.

Extracellular matrix dysfunction in Sorsby patient-derived retinal pigment epithelium

Sorsby Fundus Dystrophy (SFD) is a rare form of macular degeneration that is clinically similar to age-related macular degeneration (AMD), and a histologic hallmark of SFD is a thick layer of extracellular deposits beneath the retinal pigment epithelium (RPE). Previous studies of SFD patient-induced pluripotent stem cell (iPSC) derived RPE differ as to whether these cultures recapitulate this key clinical feature by forming increased drusenoid deposits. The primary purpose of this study is to examine whether SFD patient-derived iPSC-RPE form basal deposits similar to what is found in affected family member SFD globes and to determine whether SFD iPSC RPE may be more oxidatively stressed. We performed a careful comparison of iPSC RPE from three control individuals, multiple iPSC clones from two SFD patients' iPSC RPE, and post-mortem eyes of affected SFD family members. We also examined the effect of CRISPR-Cas9 gene correction of the S204C TIMP3 mutation on RPE phenotype. Finally, targeted metabolomics with liquid chromatography and mass spectrometry analysis and stable isotope-labeled metabolite analysis were performed to determine whether SFD RPE are more oxidatively stressed. We found that SFD iPSC-RPE formed significantly more sub-RPE deposits (∼6-90 μm in height) compared to control RPE at 8 weeks. These deposits were similar in composition to the thick layer of sub-RPE deposits found in SFD family member globes by immunofluorescence staining and TEM imaging. S204C TIMP3 correction by CRISPR-Cas9 gene editing in SFD iPSC RPE cells resulted in significantly reduced basal laminar and sub-RPE calcium deposits. We detected a ∼18-fold increase in TIMP3 accumulation in the extracellular matrix (ECM) of SFD RPE, and targeted metabolomics showed that intracellular 4-hydroxyproline, a major breakdown product of collagen, is significantly elevated in SFD RPE, suggesting increased ECM turnover. Finally, SFD RPE cells have decreased intracellular reduced glutathione and were found to be more vulnerable to oxidative stress. Our findings suggest that elements of SFD pathology can be demonstrated in culture which may lead to insights into disease mechanisms.

Tissue Inhibitor of Metalloproteinase-3 Ameliorates Diabetes-Induced Retinal Inflammation

Purpose: Endogenous tissue inhibitor of matrix metalloproteinase-3 (TIMP-3) has powerful regulatory effects on inflammation and angiogenesis. In this study, we investigated the role of TIMP-3 in regulating inflammation in the diabetic retina.

Methods: Vitreous samples from patients with proliferative diabetic retinopathy (PDR) and non-diabetic patients were subjected to Western blot analysis. Streptozotocin-treated rats were used as a preclinical diabetic retinopathy (DR) model. Blood-retinal barrier (BRB) breakdown was assessed with fluorescein isothiocyanate (FITC)-conjugated dextran. Rat retinas, human retinal microvascular endothelial cells (HRMECs) and human retinal Müller glial cells were studied by Western blot analysis and ELISA. Adherence of human monocytes to HRMECs was assessed and in vitro angiogenesis assays were performed.

Results: Tissue inhibitor of matrix metalloproteinase-3 in vitreous samples was largely glycosylated. Intravitreal injection of TIMP-3 attenuated diabetes-induced BRB breakdown. This effect was associated with downregulation of diabetes-induced upregulation of the p65 subunit of NF-κB, intercellular adhesion molecule-1 (ICAM-1), and vascular endothelial growth factor (VEGF), whereas phospho-ERK1/2 levels were not altered. In Müller cell cultures, TIMP-3 significantly attenuated VEGF upregulation induced by high-glucose (HG), the hypoxia mimetic agent cobalt chloride (CoCl₂) and TNF-α and attenuated MCP-1 upregulation induced by CoCl₂ and TNF-α, but not by HG. TIMP-3 attenuated HG-induced upregulation of phospho-ERK1/2, caspase-3 and the mature form of ADAM17, but not the levels of the p65 subunit of NF-κB and the proform of ADAM17 in Müller cells. TIMP-3 significantly downregulated TNF-α-induced upregulation of ICAM-1 and VCAM-1 in HRMECs. Accordingly, TIMP-3 significantly decreased spontaneous and TNF-α- and VEGF-induced adherence of monocytes to HRMECs. Finally, TIMP-3 significantly attenuated VEGF-induced migration, chemotaxis and proliferation of HRMECs.

Conclusion:In vitro and in vivo data point to anti-inflammatory and anti-angiogenic effects of TIMP-3 and support further studies for its applications in the treatment of DR.

Targeting Lipid Metabolism for the Treatment of Age-Related Macular Degeneration: Insights from Preclinical Mouse Models

Age-related macular degeneration (AMD) is a major leading cause of irreversible visual impairment in the world with limited therapeutic interventions. Histological, biochemical, genetic, and epidemiological studies strongly implicate dysregulated lipid metabolism in the retinal pigmented epithelium (RPE) in AMD pathobiology. However, effective therapies targeting lipid metabolism still need to be identified and developed for this blinding disease. To test lipid metabolism-targeting therapies, preclinical AMD mouse models are needed to establish therapeutic efficacy and the role of lipid metabolism in the development of AMD-like pathology. In this review, we provide a comprehensive overview of current AMD mouse models available to researchers that could be used to provide preclinical evidence supporting therapies targeting lipid metabolism for AMD. Based on previous studies of AMD mouse models, we discuss strategies to modulate lipid metabolism as well as examples of studies evaluating lipid-targeting therapeutics to restore lipid processing in the RPE. The use of AMD mouse models may lead to worthy lipid-targeting candidate therapies for clinical trials to prevent the blindness caused by AMD.

The retinal pigment epithelium in Sorsby Fundus Dystrophy shows increased sensitivity to oxidative stress-induced degeneration

Sorsby Fundus Dystrophy (SFD) is a rare inherited autosomal dominant macular degeneration caused by specific mutations in TIMP3. Patients with SFD present with pathophysiology similar to the more common Age-related Macular Degeneration (AMD) and loss of vision due to both choroidal neovascularization and geographic atrophy. Previously, it has been shown that RPE degeneration in AMD is due in part to oxidative stress. We hypothesized that similar mechanisms may be at play in SFD. The objective of this study was to evaluate whether mice carrying the S179C-Timp3 mutation, a variant commonly observed in SFD, showed increased sensitivity to oxidative stress. Antioxidant genes are increased at baseline in the RPE in SFD mouse models, but not in the retina. This suggests the presence of a pro-oxidant environment in the RPE in the presence of Timp3 mutations. To determine if the RPE of Timp3 mutant mice is more susceptible to degeneration when exposed to low levels of oxidative stress, mice were injected with low doses of sodium iodate. The RPE and photoreceptors in Timp3 mutant mice degenerated at low doses of sodium iodate, which had no effect in wildtype control mice. These studies suggest that TIMP3 mutations may result in a dysregulation of pro-oxidant-antioxidant homeostasis in the RPE, leading to RPE degeneration in SFD.

MAb NJ001 inhibits lung adenocarcinoma invasiveness by directly regulating TIMP-3 promoter activity via FOXP1 binding sites

Background

Previously, we developed a monoclonal antibody (mAb) NJ001 that binds to the antigen SP70 in human non‐small cell lung cancer (NSCLC) cells and showed it could inhibit lung adenocarcinoma (AD) growth. Here, we investigated the effect and mechanisms of NJ001 in lung AD metastasis.

Methods

Human lung AD cells (SPC‐A1 and A549) were treated with different concentrations of mAb NJ001, and the effects of NJ001 on cell migration and invasive activity were investigated using wound‐healing and Matrigel assays, respectively. The molecular mechanism of this inhibition was explored by microarrays, qRT‐PCR, western blot, luciferase assays and electrophoretic mobility shift assays (EMSA).

Results

MAb NJ001 markedly suppressed lung AD cell migration; and the invasiveness of SPC‐A1 and A549 cells treated with mAb NJ001 was diminished by 65%. Tissue inhibitor of matrix metalloproteinase‐3 (TIMP‐3) was highly expressed in SPC‐A1 cells treated with mAb NJ001, whereas knockdown of TIMP‐3 by shRNA significantly increased SPC‐A1 and A549 invasiveness. MAb NJ001 affects lung AD by inhibiting TIMP‐3 through direct transcriptional regulation of FOXP1 binding sites in the TIMP‐3 promoter region, as shown in luciferase assays and EMSA.

Conclusions

MAb NJ001 inhibits invasiveness and metastasis in lung AD through the FOXP1 binding sites in the TIMP‐3 promoter region. It may have clinical applications in preventing and treating metastatic lung AD.

In vitro stem cell modelling demonstrates a proof-of-concept for excess functional mutant TIMP3 as the cause of Sorsby fundus dystrophy

Sorsby fundus dystrophy (SFD) is a rare autosomal dominant disease of the macula that leads to bilateral loss of central vision and is caused by mutations in the TIMP3 gene. However, the mechanisms by which TIMP3 mutations cause SFD are poorly understood. Here, we generated human induced pluripotent stem cell-derived retinal pigmented epithelial (hiPSC-RPE) cells from three SFD patients carrying TIMP3 p.(Ser204Cys) and three non-affected controls to study disease-related structural and functional differences in the RPE. SFD-hiPSC-RPE exhibited characteristic RPE structure and physiology but showed significantly reduced transepithelial electrical resistance associated with enriched expression of cytoskeletal remodelling proteins. SFD-hiPSC-RPE exhibited basolateral accumulation of TIMP3 monomers, despite no change in TIMP3 gene expression. TIMP3 dimers were observed in both SFD and control hiPSC-RPE, suggesting that mutant TIMP3 dimerisation does not drive SFD pathology. Furthermore, mutant TIMP3 retained matrix metalloproteinase activity. Proteomic profiling showed increased expression of ECM proteins, endothelial cell interactions and angiogenesis-related pathways in SFD-hiPSC-RPE. By contrast, there were no changes in VEGF secretion. However, SFD-hiPSC-RPE secreted higher levels of monocyte chemoattractant protein 1, PDGF and angiogenin. Our findings provide a proof-of-concept that SFD patient-derived hiPSC-RPE mimic mature RPE cells and support the hypothesis that excess accumulation of mutant TIMP3, rather than an absence or deficiency of functional TIMP3, drives ECM and angiogenesis-related changes in SFD. © 2020 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Biology of Tissue Inhibitor of Metalloproteinase 3 (TIMP3), and Its Therapeutic Implications in Cardiovascular Pathology

Tissue inhibitor of metalloproteinase 3 (TIMP3) is unique among the four TIMPs due to its extracellular matrix (ECM)-binding property and broad range of inhibitory substrates that includes matrix metalloproteinases (MMPs), a disintegrin and metalloproteinases (ADAMs), and ADAM with thrombospondin motifs (ADAMTSs). In addition to its metalloproteinase-inhibitory function, TIMP3 can interact with proteins in the extracellular space resulting in its multifarious functions. TIMP3 mRNA has a long 3' untranslated region (UTR) which is a target for numerous microRNAs. TIMP3 levels are reduced in various cardiovascular diseases, and studies have shown that TIMP3 replenishment ameliorates the disease, suggesting a therapeutic potential for TIMP3 in cardiovascular diseases. While significant efforts have been made in identifying the effector targets of TIMP3, the regulatory mechanism for the expression of this multi-functional TIMP has been less explored. Here, we provide an overview of TIMP3 gene structure, transcriptional and post-transcriptional regulators (transcription factors and microRNAs), protein structure and partners, its role in cardiovascular pathology and its application as therapy, while also drawing reference from TIMP3 function in other diseases.

Role of FGF and Hyaluronan in Choroidal Neovascularization in Sorsby Fundus Dystrophy

Sorsby's fundus dystrophy (SFD) is an inherited blinding disorder caused by mutations in the tissue inhibitor of metalloproteinase-3 (TIMP3) gene. The SFD pathology of macular degeneration with subretinal deposits and choroidal neovascularization (CNV) closely resembles that of the more common age-related macular degeneration (AMD). The objective of this study was to gain further insight into the molecular mechanism(s) by which mutant TIMP3 induces CNV. In this study we demonstrate that hyaluronan (HA), a large glycosaminoglycan, is elevated in the plasma and retinal pigment epithelium (RPE)/choroid of patients with AMD. Mice carrying the S179C-TIMP3 mutation also showed increased plasma levels of HA as well as accumulation of HA around the RPE in the retina. Human RPE cells expressing the S179C-TIMP3 mutation accumulated HA apically, intracellularly and basally when cultured long-term compared with cells expressing wildtype TIMP3. We recently reported that RPE cells carrying the S179C-TIMP3 mutation have the propensity to induce angiogenesis via basic fibroblast growth factor (FGF-2). We now demonstrate that FGF-2 induces accumulation of HA in RPE cells. These results suggest that the TIMP3-MMP-FGF-2-HA axis may have an important role in the pathogenesis of CNV in SFD and possibly AMD.

The Diverse Roles of TIMP-3: Insights into Degenerative Diseases of the Senescent Retina and Brain

Tissue inhibitor of metalloproteinase-3 (TIMP-3) is a component of the extracellular environment, where it mediates diverse processes including matrix regulation/turnover, inflammation and angiogenesis. Rare TIMP-3 risk alleles and mutations are directly linked with retinopathies such as age-related macular degeneration (AMD) and Sorsby fundus dystrophy, and potentially, through indirect mechanisms, with Alzheimer's disease. Insights into TIMP-3 activities may be gleaned from studying Sorsby-linked mutations. However, recent findings do not fully support the prevailing hypothesis that a gain of function through the dimerisation of mutated TIMP-3 is responsible for retinopathy. Findings from Alzheimer's patients suggest a hitherto poorly studied relationship between TIMP-3 and the Alzheimer's-linked amyloid-beta (A) proteins that warrant further scrutiny. This may also have implications for understanding AMD as aged/diseased retinae contain high levels of A. Findings from TIMP-3 knockout and mutant knock-in mice have not led to new treatments, particularly as the latter does not satisfactorily recapitulate the Sorsby phenotype. However, recent advances in stem cell and in vitro approaches offer novel insights into understanding TIMP-3 pathology in the retina-brain axis, which has so far not been collectively examined. We propose that TIMP-3 activities could extend beyond its hitherto supposed functions to cause age-related changes and disease in these organs.

Sorsby Fundus Dystrophy Mutation in Tissue Inhibitor of Metalloproteinase 3 (TIMP3) promotes Choroidal Neovascularization via a Fibroblast Growth Factor-dependent Mechanism

Choroidal neovascularization (CNV) leads to loss of vision in patients with Sorsby Fundus Dystrophy (SFD), an inherited, macular degenerative disorder, caused by mutations in the Tissue Inhibitor of Metalloproteinase-3 (TIMP3) gene. SFD closely resembles age-related macular degeneration (AMD), which is the leading cause of blindness in the elderly population of the Western hemisphere. Variants in TIMP3 gene have recently been identified in patients with AMD. A majority of patients with AMD also lose vision as a consequence of choroidal neovascularization (CNV). Thus, understanding the molecular mechanisms that contribute to CNV as a consequence of TIMP-3 mutations will provide insight into the pathophysiology in SFD and likely the neovascular component of the more commonly seen AMD. While the role of VEGF in CNV has been studied extensively, it is becoming increasingly clear that other factors likely play a significant role. The objective of this study was to test the hypothesis that basic Fibroblast Growth Factor (bFGF) regulates SFD-related CNV. In this study we demonstrate that mice expressing mutant TIMP3 (Timp3S179C/S179C) showed reduced MMP inhibitory activity with an increase in MMP2 activity and bFGF levels, as well as accentuated CNV leakage when subjected to laser injury. S179C mutant-TIMP3 in retinal pigment epithelial (RPE) cells showed increased secretion of bFGF and conditioned medium from these cells induced increased angiogenesis in endothelial cells. These studies suggest that S179C-TIMP3 may promote angiogenesis and CNV via a FGFR-1-dependent pathway by increasing bFGF release and activity.

Interactions of the choroid, Bruch's membrane, retinal pigment epithelium, and neurosensory retina collaborate to form the outer blood-retinal-barrier

The three interacting components of the outer blood-retinal barrier are the retinal pigment epithelium (RPE), choriocapillaris, and Bruch's membrane, the extracellular matrix that lies between them. Although previously reviewed independently, this review integrates these components into a more wholistic view of the barrier and discusses reconstitution models to explore the interactions among them. After updating our understanding of each component's contribution to barrier function, we discuss recent efforts to examine how the components interact. Recent studies demonstrate that claudin-19 regulates multiple aspects of RPE's barrier function and identifies a barrier function whereby mutations of claudin-19 affect retinal development. Co-culture approaches to reconstitute components of the outer blood-retinal barrier are beginning to reveal two-way interactions between the RPE and choriocapillaris. These interactions affect barrier function and the composition of the intervening Bruch's membrane. Normal or disease models of Bruch's membrane, reconstituted with healthy or diseased RPE, demonstrate adverse effects of diseased matrix on RPE metabolism. A stumbling block for reconstitution studies is the substrates typically used to culture cells are inadequate substitutes for Bruch's membrane. Together with human stem cells, the alternative substrates that have been designed offer an opportunity to engineer second-generation culture models of the outer blood-retinal barrier.

Single-cell transcriptomic atlas of the human retina identifies cell types associated with age-related macular degeneration

Genome-wide association studies (GWAS) have identified genetic variants associated with age-related macular degeneration (AMD), one of the leading causes of blindness in the elderly. However, it has been challenging to identify the cell types associated with AMD given the genetic complexity of the disease. Here we perform massively parallel single-cell RNA sequencing (scRNA-seq) of human retinas using two independent platforms, and report the first single-cell transcriptomic atlas of the human retina. Using a multi-resolution network-based analysis, we identify all major retinal cell types, and their corresponding gene expression signatures. Heterogeneity is observed within macroglia, suggesting that human retinal glia are more diverse than previously thought. Finally, GWAS-based enrichment analysis identifies glia, vascular cells, and cone photoreceptors to be associated with the risk of AMD. These data provide a detailed analysis of the human retina, and show how scRNA-seq can provide insight into cell types involved in complex, inflammatory genetic diseases.

The N-terminal p.(Ser38Cys) TIMP3 mutation underlying Sorsby fundus dystrophy is a founder mutation disrupting an intramolecular disulfide bond

Sorsby fundus dystrophy (SFD) is a macular degeneration caused by mutations in TIMP3, the majority of which introduce a novel cysteine. However, the exact molecular mechanisms underlying SFD remain unknown. We aimed to provide novel insights into the functional consequences of a distinct N-terminal mutation. Haplotype reconstruction in three SFD families revealed that the identified c.113C>G, p.(Ser38Cys) mutation is a founder in Belgian and northern French families with a late-onset SFD phenotype. Functional consequences of the p.(Ser38Cys) mutation were investigated by high-resolution Western blot analysis of wild type and mutant TIMP3 using patient fibroblasts and in vitro generated proteins, and by molecular modeling of TIMP3 and its interaction partners. We could not confirm a previous hypothesis on dimerization of mutant TIMP3 proteins. However, we identified aberrant intramolecular disulfide bonding. Our data provide evidence for disruption of the established Cys36-Cys143 disulfide bond and formation of a novel Cys36-Cys38 bond, possibly associated with increased glycosylation of the protein. In conclusion, we propose a novel pathogenetic mechanism underlying the p.(Ser38Cys) TIMP3 founder mutation involving intramolecular disulfide bonding. These results provide new insights into the pathogenesis of SFD and other retinopathies linked to mutations in TIMP3, such as age-related macular degeneration.

Imbalances in tissue inhibitors of metalloproteinases differentiate choroidal neovascularization from geographic atrophy

PURPOSE

Tissue inhibitor of metalloproteinase (TIMP) is known to play a role in age-related macular degeneration (AMD). We wished to investigate alterations in different late stages of AMD: neovascular AMD and geographic atrophy (GA).

METHODS

This was a prospective case-control study. A total of 125 participants were included consecutively during a period of 18 months. We included 46 patients with neovascular AMD, 46 patients with GA without any sign of choroidal neovascularization in either eye, and 33 healthy aged controls. Patients with immune-affecting disorders were not included. Commercial immunoassay kits were used to quantify levels of TIMP-1, TIMP-3, MMP-2 and MMP-9 in blood plasma.

RESULTS

We found that patients with neovascular AMD had lower plasma concentration of TIMP-3 (p = 0.028) than healthy controls. Patients with GA had higher plasma levels of TIMP-1 (p < 0.001) and MMP-9 (p = 0.022) compared to healthy controls. Also, we found that TIMP-1 levels in patients with GA increased with age (Spearman's rho = 0.04, p = 0.006).

CONCLUSION

Matrix metalloproteinases (MMPs) and TIMPs, which are known to be involved in age-related changes in Bruch's membrane, are significantly altered systemically, suggesting the presence of an imbalance in the homeostasis of the extracellular matrix. These imbalances may explain differences in the clinical manifestation of late AMD.

Sorsby fundus dystrophy: Insights from the past and looking to the future

Sorsby fundus dystrophy (SFD), an autosomal dominant, fully penetrant, degenerative disease of the macula, is manifested by symptoms of night blindness or sudden loss of visual acuity, usually in the third to fourth decades of life due to choroidal neovascularization (CNV). SFD is caused by specific mutations in the Tissue Inhibitor of Metalloproteinase-3, (TIMP3) gene. The predominant histo-pathological feature in the eyes of patients with SFD are confluent 20-30 m thick, amorphous deposits found between the basement membrane of the retinal pigment epithelium (RPE) and the inner collagenous layer of Bruch's membrane. SFD is a rare disease but it has generated significant interest because it closely resembles the exudative or "wet" form of the more common age-related macular degeneration (AMD). In addition, in both SFD and AMD donor eyes, sub-retinal deposits have been shown to accumulate TIMP3 protein. Understanding the molecular functions of wild-type and mutant TIMP3 will provide significant insights into the patho-physiology of SFD and perhaps AMD. This review summarizes the current knowledge on TIMP3 and how mutations in TIMP3 cause SFD to provide insights into how we can study this disease going forward. Findings from these studies could have potential therapeutic implications for both SFD and AMD.

Drusen in patient-derived hiPSC-RPE models of macular dystrophies

Age-related macular degeneration (AMD) and related macular dystrophies (MDs) are a major cause of vision loss. However, the mechanisms underlying their progression remain ill-defined. This is partly due to the lack of disease models recapitulating the human pathology. Furthermore, in vivo studies have yielded limited understanding of the role of specific cell types in the eye vs. systemic influences (e.g., serum) on the disease pathology. Here, we use human induced pluripotent stem cell-retinal pigment epithelium (hiPSC-RPE) derived from patients with three dominant MDs, Sorsby's fundus dystrophy (SFD), Doyne honeycomb retinal dystrophy/malattia Leventinese (DHRD), and autosomal dominant radial drusen (ADRD), and demonstrate that dysfunction of RPE cells alone is sufficient for the initiation of sub-RPE lipoproteinaceous deposit (drusen) formation and extracellular matrix (ECM) alteration in these diseases. Consistent with clinical studies, sub-RPE basal deposits were present beneath both control (unaffected) and patient hiPSC-RPE cells. Importantly basal deposits in patient hiPSC-RPE cultures were more abundant and displayed a lipid- and protein-rich "drusen-like" composition. Furthermore, increased accumulation of COL4 was observed in ECM isolated from control vs. patient hiPSC-RPE cultures. Interestingly, RPE-specific up-regulation in the expression of several complement genes was also seen in patient hiPSC-RPE cultures of all three MDs (SFD, DHRD, and ADRD). Finally, although serum exposure was not necessary for drusen formation, COL4 accumulation in ECM, and complement pathway gene alteration, it impacted the composition of drusen-like deposits in patient hiPSC-RPE cultures. Together, the drusen model(s) of MDs described here provide fundamental insights into the unique biology of maculopathies affecting the RPE-ECM interface.

Sorsby fundus dystrophy - A review of pathology and disease mechanisms

Sorsby fundus dystrophy (SFD) is an autosomal dominant macular dystrophy with an estimated prevalence of 1 in 220,000 and an onset of disease around the 4th to 6th decade of life. Similar to age-related macular degeneration (AMD), ophthalmoscopy reveals accumulation of protein/lipid deposits under the retinal pigment epithelium (RPE), referred to as drusen, in the eyes of patients with SFD. SFD is caused by variants in the gene for tissue inhibitor of metalloproteinases-3 (TIMP3), which has been found in drusen-like deposits of SFD patients. TIMP3 is constitutively expressed by RPE cells and, in healthy eyes, resides in Bruch's membrane. Most SFD-associated TIMP3 variants involve the gain or loss of a cysteine residue. This suggests the protein aberrantly forms intermolecular disulphide bonds, resulting in the formation of TIMP3 dimers. It has been demonstrated that SFD-associated TIMP3 variants are more resistant to turnover, which is thought to be a result of dimerisation and thought to explain the accumulation of TIMP3 in drusen-like deposits at the level of Bruch's membrane. An important function of TIMP3 within the outer retina is to regulate the thickness of Bruch's membrane. TIMP3 performs this function by inhibiting the activity of matrix metalloproteinases (MMPs), which have the function of catalysing breakdown of the extracellular matrix. TIMP3 has an additional function to inhibit vascular endothelial growth factor (VEGF) signalling and thereby to inhibit angiogenesis. However, it is unclear whether SFD-associated TIMP3 variant proteins retain these functions. In this review, we discuss the current understanding of the potential mechanisms underlying development of SFD and summarise all known SFD-associated TIMP3 variants. Cell culture models provide an invaluable way to study disease and identify potential treatments. These allow a greater understanding of RPE physiology and pathophysiology, including the ability to study the blood-retinal barrier as well as other RPE functions such as phagocytosis of photoreceptor outer segments. This review describes some examples of such recent in vitro studies and how they might provide new insights into degenerative diseases like SFD. Thus far, most studies on SFD have been performed using ARPE-19 cells or other, less suitable, cell-types. Now, induced pluripotent stem cell (iPSC) technologies allow the possibility to non-invasively collect somatic cells, such as dermal fibroblast cells and reprogram those to produce iPSCs. Subsequent differentiation of iPSCs can generate patient-derived RPE cells that carry the same disease-associated variant as RPE cells in the eyes of the patient. Use of these patient-derived RPE cells in novel cell culture systems should increase our understanding of how SFD and similar macular dystrophies develop.

Glycosylation of matrix metalloproteases and tissue inhibitors: present state, challenges and opportunities

Current knowledge about the glycosylation of matrix metalloproteinases (MMPs) and the inhibitors of metalloproteinases (TIMPs) is reviewed. Whereas structural and functional aspects of the glycobiology of many MMPs is unknown, research on MMP-9 and MMP-14 glycosylation reveals important functional implications, such as altered inhibitor binding and cellular localization. This, together with the fact that MMPs contain conserved and many potential attachment sites for N-linked and O-linked oligosaccharides, proves the need for further studies on MMP glycobiology.

Matrix metalloproteases (MMPs) are crucial components of a complex and dynamic network of proteases. With a wide range of potential substrates, their production and activity are tightly controlled by a combination of signalling events, zymogen activation, post-translational modifications and extracellular inhibition. Slight imbalances may result in the initiation or progression of specific disease states, such as cancer and pathological inflammation. As glycosylation modifies the structures and functions of glycoproteins and many MMPs contain N- or O-linked oligosaccharides, we examine, compare and evaluate the evidence for whether glycosylation affects MMP catalytic activity and other functions. It is interesting that the catalytic sites of MMPs do not contain O-linked glycans, but instead possess a conserved N-linked glycosylation site. Both N- and O-linked oligosaccharides, attached to specific protein domains, endow these domains with novel functions such as the binding to lectins, cell-surface receptors and tissue inhibitors of metalloproteases (TIMPs). Validated glycobiological data on N- and O-linked oligosaccharides of gelatinase B/MMP-9 and on O-linked structures of membrane-type 1 MMP/MMP-14 indicate that in-depth research of other MMPs may yield important insights, e.g. about subcellular localizations and functions within macromolecular complexes.

A new autosomal dominant eye and lung syndrome linked to mutations in TIMP3 gene

To revisit the autosomal dominant Sorsby fundus dystrophy (SFD) as a syndromic condition including late-onset pulmonary disease. We report clinical and imaging data of ten affected individuals from 2 unrelated families with SFD and carrying heterozygous TIMP3 mutations (c.572A > G, p.Y191C, exon 5, in family 1 and c.113C > G, p.S38C, exon 1, in family 2). In family 1, all SFD patients older than 50 (two generations) had also a severe emphysema, despite no history of smoking or asthma. In the preceding generation, the mother died of pulmonary emphysema and she was blind after the age of 50. Her two great-grandsons (<20 years), had abnormal Bruch Membrane thickness, a sign of eye disease. In family 2, eye and lung diseases were also associated in two generations, both occurred later, and lung disease was moderate (bronchiectasis). This is the first report of a syndromic SFD in line with the mouse model uncovering the role of TIMP3 in human lung morphogenesis and functions. The TIMP3 gene should be screened in familial pulmonary diseases with bronchiectasis, associated with a medical history of visual loss. In addition, SFD patients should be advised to avoid tobacco consumption, to practice sports, and to undergo regular pulmonary examinations.

Tissue inhibitor of metalloproteinase-3 (TIMP3) promotes endothelial apoptosis via a caspase-independent mechanism

Tissue inhibitor of metalloproteinases-3 (TIMP3) is a tumor suppressor and a potent inhibitor of angiogenesis. TIMP3 exerts its anti-angiogenic effect via a direct interaction with vascular endothelial growth factor (VEGF) receptor-2 (KDR) and inhibition of proliferation, migration and tube formation of endothelial cells (ECs). TIMP3 has also been shown to induce apoptosis in some cancer cells and vascular smooth muscle cells via MMP inhibition and caspase-dependent mechanisms. In this study, we examined the molecular mechanisms of TIMP3-mediated apoptosis in endothelial cells. We have previously demonstrated that mice developed smaller tumors with decreased vascularity when injected with breast carcinoma cells overexpressing TIMP3, than with control breast carcinoma cells. TIMP3 overexpression resulted in increased apoptosis in human breast carcinoma (MDA-MB435) in vivo but not in vitro. However, TIMP3 could induce apoptosis in ECs in vitro. The apoptotic activity of TIMP3 in ECs appears to be independent of MMP inhibitory activity. Furthermore, the equivalent expression of functional TIMP3 promoted apoptosis and caspase activation in ECs expressing KDR (PAE/KDR), but not in ECs expressing PDGF beta-receptor (PAE/β-R). Surprisingly, the apoptotic activity of TIMP3 appears to be independent of caspases. TIMP3 inhibited matrix-induced focal adhesion kinase (FAK) tyrosine phosphorylation and association with paxillin and disrupted the incorporation of β3 integrin, FAK and paxillin into focal adhesion contacts on the matrix, which were not affected by caspase inhibitors. Thus, TIMP3 may induce apoptosis in ECs by triggering a caspase-independent cell death pathway and targeting a FAK-dependent survival pathway.

Choroidal neovascularization secondary to sorsby fundus dystrophy treated with intravitreal bevacizumab

PURPOSE

To report a case of extrafoveal choroidal neovascularization secondary to Sorsby fundus dystrophy that maintained 20/20 visual acuity over 14 months with intravitreal bevacizumab therapy.

METHODS

Interventional case report of as-needed treatment with intravitreal bevacizumab of a 38-year-old lady with choroidal neovascularization from Sorsby fundus dystrophy.

RESULTS

Three injections of intravitreal bevacizumab were given over 14.5 months, maintaining visual acuity at 20/20.

CONCLUSION

Intravitreal bevacizumab therapy appears to maintain vision in patients with choroidal neovascularization from Sorsby fundus dystrophy.

Normalization of the tumor microenvironment: evidence for tissue inhibitor of metalloproteinase-2 as a cancer therapeutic

Matrix metalloproteinases (MMPs) are members of the Metzincin family of proteases responsible for degrading the extracellular matrix (ECM). In early studies, MMP degradation of the sub-epithelial basement membrane was thought to be tumor cell autonomous and contribute to the invasive behavior of malignant cells. It is now recognized that MMPs have multiple roles that can either promote or inhibit tumor progression and metastasis. The endogenous inhibitors of the MMPs are the tissue inhibitors of metalloproteinases (TIMPs). Early studies on the tumor microenvironment revealed TIMP function to be principally through the inhibition of MMPs, thereby blocking tumor cell migration and invasion. However, data from a number of laboratories are now reporting that TIMPs have direct cellular functions, independent of their MMP inhibitory activity. The TIMPs can modulate normal tissue physiology and development, as well as pathology and progression in a variety of acute and chronic disease states. In this review, we briefly describe the role of MMPs and TIMPs in ECM turnover and formation of the tumor microenvironment. Based on the evidence presented, we postulate that TIMP-2 and other soluble components of the normal ECM may provide a novel therapeutic approach to cancer treatment through "normalization" of the tumor microenvironment.

Integrin α7 binds tissue inhibitor of metalloproteinase 3 to suppress growth of prostate cancer cells

Integrin α7 (ITGA7) is a tumor-suppressor gene that is critical for suppressing the growth of malignant tumors; however, the mechanisms allowing ITGA7 to suppress the growth of cancer cells remain unclear. Herein, we show that ITGA7 binds to tissue inhibitor of metalloproteinase 3 (TIMP3) in prostate cancer cells. The ITGA7-TIMP3 binding led to a decreased protein level of tumor necrosis factor α, cytoplasmic translocation of NF-κB, and down-regulation of cyclin D1. These changes led to an accumulation of cells in G0/G1 and a dramatic suppression of cell growth. Knocking down TIMP3 or ITGA7/TIMP3 binding interference largely abrogated the signaling changes induced by ITGA7, whereas a mutant ITGA7 lacking TIMP3 binding activity had no tumor-suppressor activity. Interestingly, knocking down ITGA7 ligand laminin β1 enhanced ITGA7-TIMP3 signaling and the downstream tumor-suppressor activity, suggesting the existence of a counterbalancing role between extracellular matrix and integrin signaling. As a result, this report demonstrates a novel and critical signaling mechanism of ITGA7, through the TIMP3/NF-κB/cyclin D1 pathway.

Tissue inhibitor of metalloproteinases-3 peptides inhibit angiogenesis and choroidal neovascularization in mice

Tissue inhibitors of metalloproteinases (TIMPs) while originally characterized as inhibitors of matrix metalloproteinases (MMPs) have recently been shown to have a wide range of functions that are independent of their MMP inhibitory properties. Tissue inhibitor of metalloproteinases-3 (TIMP-3) is a potent inhibitor of VEGF-mediated angiogenesis and neovascularization through its ability to block the binding of VEGF to its receptor VEGFR-2. To identify and characterize the anti-angiogenic domain of TIMP-3, structure function analyses and synthetic peptide studies were performed using VEGF-mediated receptor binding, signaling, migration and proliferation. In addition, the ability of TIMP-3 peptides to inhibit CNV in a mouse model was evaluated. We demonstrate that the anti-angiogenic property resides in the COOH-terminal domain of TIMP-3 protein which can block the binding of VEGF specifically to its receptor VEGFR-2, but not to VEGFR-1 similar to the full-length wild-type protein. Synthetic peptides corresponding to putative loop 6 and tail region of TIMP-3 have anti-angiogenic properties as determined by inhibition of VEGF binding to VEGFR-2, VEGF-induced phosphorylation of VEGFR-2 and downstream signaling pathways as well as endothelial cell proliferation and migration in response to VEGF. In addition, we show that intravitreal administration of TIMP-3 peptide could inhibit the size of laser-induced choroidal neovascularization lesions in mice. Thus, we have identified TIMP-3 peptides to be efficient inhibitors of angiogenesis and have a potential to be used therapeutically in diseases with increased neovascularization.

Ranibizumab for choroidal neovascular membrane in a rare case of Bietti's crystalline dystrophy: a case report

We report a rare case of Bietti's crystalline dystrophy presenting with choroidal neovascular membrane (CNVM) which was treated with three injections of intravitreal ranibizumab. The CNVM underwent scarring after the injections with stabilization of visual acuity at a follow-up period of 12 months suggesting that intravitreal ranibizumab may have a role in the management of CNVM in these rare cases.

Pericyte TIMP3 and ADAMTS1 modulate vascular stability after kidney injury

Kidney pericytes are progenitors of scar-forming interstitial myofibroblasts that appear after injury. The function of kidney pericytes as microvascular cells and how these cells detach from peritubular capillaries and migrate to the interstitial space, however, are poorly understood. Here, we used an unbiased approach to identify genes in kidney pericytes relevant to detachment and differentiation in response to injury in vivo, with a particular focus on genes regulating proteolytic activity and angiogenesis. Kidney pericytes rapidly activated expression of a disintegrin and metalloprotease with thrombospondin motifs-1 (ADAMTS1) and downregulated its inhibitor, tissue inhibitor of metalloproteinase 3 (TIMP3) in response to injury. Similarly to brain pericytes, kidney pericytes bound to and stabilized capillary tube networks in three-dimensional gels and inhibited metalloproteolytic activity and angiogenic signaling in endothelial cells. In contrast, myofibroblasts did not have these vascular stabilizing functions despite their derivation from kidney pericytes. Pericyte-derived TIMP3 stabilized and ADAMTS1 destabilized the capillary tubular networks. Furthermore, mice deficient in Timp3 had a spontaneous microvascular phenotype in the kidney resulting from overactivated pericytes and were more susceptible to injury-stimulated microvascular rarefaction with an exuberant fibrotic response. Taken together, these data support functions for kidney pericytes in microvascular stability, highlight central roles for regulators of extracellular proteolytic activity in capillary homoeostasis, and identify ADAMTS1 as a marker of activation of kidney pericytes.

An rs9621532 variant near the TIMP3 gene is not associated with neovascular age-related macular degeneration and polypoidal choroidal vasculopathy in a Chinese Han population

BACKGROUND

Recently, two genome-wide association studies with large cohorts both identified rs9621532, a new single nucleotide polymorphism (SNP) that is associated with advanced age-related macular degeneration (AMD) and located near the TIMP3 gene. Previous studies have demonstrated that AMD and polypoidal choroidal vasculopathy (PCV) share some common genetic background and that the incidence of PCV is higher in Asian populations than Caucasian populations. In this study, we aimed to investigate whether the rs9621532 SNP is associated with neovascular AMD (nAMD) and PCV in a Chinese Han population.

METHODS

We performed a case-control study in a Chinese Han population. The rs9621532 SNP was genotyped in 136 patients with nAMD, 195 patients with PCV, and 181 control individuals using the Multiplex SNaPshot system and the direct DNA sequencing technique. Rs9621532 genotypes and allele frequencies in the nAMD, PCV and control groups were evaluated using PLINK software.

RESULTS

In the nAMD, PCV, and control groups, the minor allele frequencies of the rs9621532 variant were 0.05147, 0.02564, and 0.03039, respectively. The rs9621532 SNP was not significantly associated with susceptibility to nAMD (p = 0.1773) or PCV (p = 0.6933). None of the p-values for the additive or dominant models were found to be statistically significant in the nAMD or PCV groups. No recessive homozygotes were genotyped in any of the three groups.

CONCLUSIONS

No evidence was found to support an association between the rs9621532 variant and susceptibility to either nAMD or PCV in a Chinese Han population.

An alternate perspective on the roles of TIMPs and MMPs in pathology

Tissue inhibitors of metalloproteinases (TIMPs) are pleiotropic extracellular proteins. TIMPs are recognized as endogenous regulators of matrix metalloproteinases (MMPs), a large family of extracellular enzymes with proteolytic activities that participate in cellular homeostasis, adaptation, and tissue remodeling. In addition to their roles as endogenous potent MMP inhibitors, accumulating evidence indicates important physiological roles for TIMPs that are independent of their ability to block MMP activities. For instance, MMP-independent actions of TIMP-1 in the central nervous system have been implicated in synaptic plasticity, neuroprotection, oncogenesis, and oligodendrocyte differentiation. Expression of TIMP-1 is dramatically increased in response to a variety of injurious and inflammatory insults. In the context of disease pathogenesis, MMP and TIMP expression are interpreted with respect to the proteolytic consequences of increased MMP/TIMP ratios. Here, we provide an alternative perspective on the homeostatic balance of TIMP and MMP proteins, whereby consideration is given to the possible role of MMPs as cognate inhibitors of the signaling functions of TIMPs. Thus, MMPs may regulate the receptor-mediated actions of TIMPs, inasmuch as TIMPs are themselves inhibitors of MMP-mediated proteolytic activities. This broader view reflects our emerging understanding that TIMP signaling and MMP inhibition represent two important functions of TIMPs that have the potential to affect tissue pathology.

Molecular screening of the CYP4V2 gene in Bietti crystalline dystrophy that is associated with choroidal neovascularization

PURPOSE

Bietti crystalline dystrophy (BCD) is an autosomal recessive disease characterized by intraretinal deposits of multiple small crystals, with or without associated crystal deposits in the cornea. The disease is caused by mutation in the cytochrome p450, family 4, subfamily v, polypeptide 2 (CYP4V2) gene. Choroidal neovascularization (CNV) is a rare event in BCD. We report two cases of BCD associated with CNV. CYP4V2 and exon 5 of tissue inhibitor of metalloproteinase 3 (TIMP3) were screened in both cases. A patient with BCD, but without CNV, was also screened to identify pathogenic variations.

METHODS

Three BCD families of Asian Indian origin were recruited after a comprehensive ophthalmic examination. Genomic DNA was isolated from blood leukocytes, and coding exons and flanking introns of CYP4V2 and exon 5 of TIMP3 were amplified via polymerase chain reaction (PCR) and were sequenced. Family segregation, control screening, and bioinformatics tools were used to assess the pathogenicity of the novel variations.

RESULTS

Of the three BCD patients, two had parafoveal CNV. The patient with BCD, but without CNV had novel single base-pair duplication (c.1062_1063dupA). This mutation results in a structurally defective and unstable protein with impaired protein function. Four novel benign variations (three in exons and one in an intron) were observed in the cohort. Screening of exon 5 of TIMP3 did not reveal any variation in these families.

CONCLUSIONS

A novel mutation was found in a patient with BCD but without CNV, while patients with BCD and CNV did not show any pathogenic variation. The modifier role of TIMP3 in the pathogenesis of CNV in BCD was partly ruled out, as no variation was observed in exon 5 of the gene. A larger BCD cohort with CNV needs to be studied and screened to understand the genetics of CNV in BCD.

Genome-wide association study of advanced age-related macular degeneration identifies a role of the hepatic lipase gene (LIPC)

Advanced age-related macular degeneration (AMD) is the leading cause of late onset blindness. We present results of a genome-wide association study of 979 advanced AMD cases and 1,709 controls using the Affymetrix 6.0 platform with replication in seven additional cohorts (totaling 5,789 unrelated cases and 4,234 unrelated controls). We also present a comprehensive analysis of copy-number variations and polymorphisms for AMD. Our discovery data implicated the association between AMD and a variant in the hepatic lipase gene (LIPC) in the high-density lipoprotein cholesterol (HDL) pathway (discovery P = 4.53e-05 for rs493258). Our LIPC association was strongest for a functional promoter variant, rs10468017, (P = 1.34e-08), that influences LIPC expression and serum HDL levels with a protective effect of the minor T allele (HDL increasing) for advanced wet and dry AMD. The association we found with LIPC was corroborated by the Michigan/Penn/Mayo genome-wide association study; the locus near the tissue inhibitor of metalloproteinase 3 was corroborated by our replication cohort for rs9621532 with P = 3.71e-09. We observed weaker associations with other HDL loci (ABCA1, P = 9.73e-04; cholesterylester transfer protein, P = 1.41e-03; FADS1-3, P = 2.69e-02). Based on a lack of consistent association between HDL increasing alleles and AMD risk, the LIPC association may not be the result of an effect on HDL levels, but it could represent a pleiotropic effect of the same functional component. Results implicate different biologic pathways than previously reported and provide new avenues for prevention and treatment of AMD.

The tissue inhibitors of metalloproteinases (TIMPs): an ancient family with structural and functional diversity

Tissue inhibitors of metalloproteinases (TIMPs) are widely distributed in the animal kingdom and the human genome contains four paralogous genes encoding TIMPs 1 to 4. TIMPs were originally characterized as inhibitors of matrix metalloproteinases (MMPs), but their range of activities has now been found to be broader as it includes the inhibition of several of the disintegrin-metalloproteinases, ADAMs and ADAMTSs. TIMPs are therefore key regulators of the metalloproteinases that degrade the extracellular matrix and shed cell surface molecules. Structural studies of TIMP-MMP complexes have elucidated the inhibition mechanism of TIMPs and the multiple sites through which they interact with target enzymes, allowing the generation of TIMP variants that selectively inhibit different groups of metalloproteinases. Engineering such variants is complicated by the fact that TIMPs can undergo changes in molecular dynamics induced by their interactions with proteases. TIMPs also have biological activities that are independent of metalloproteinases; these include effects on cell growth and differentiation, cell migration, anti-angiogenesis, anti- and pro-apoptosis, and synaptic plasticity. Receptors responsible for some of these activities have been identified and their signaling pathways have been investigated. A series of studies using mice with specific TIMP gene deletions has illuminated the importance of these molecules in biology and pathology.

The role of angiogenesis in solid tumours: an overview

Angiogenesis is the physiological process of the formation of new blood vessels from pre-existing ones. Multiple molecules regulate angiogenesis, such as the vascular endothelial growth factor, angiopoietins, the fibroblast growth factor, the platelet-derived growth factor and the transforming growth factor-beta. Angiogenesis plays an important role in the growth, progression and metastasis of a tumour. Inhibiting the angiogenic process or targeting existing tumour vessels can be used for treatment of tumours as an alternative or in parallel with conventional chemotherapy. Many anti-angiogenic factors are under investigation and some are already being used in clinical practice with various results.

Effects of human recombinant PEDF protein and PEDF-derived peptide 34-mer on choroidal neovascularization

PURPOSE

Pigment epithelium-derived factor (PEDF) is a serpin with antiangiogenic properties. Previously, the authors showed that PEDF injected into the subconjunctiva reaches the choroid. Here, they examined the effects of PEDF polypeptide fragments on vessel sprouting and on choroidal neovascularization (CNV) after subconjunctival administration.

METHODS

Recombinant human PEDF (rhuPEDF) was cleaved at its serpin-exposed loop by limited chymotrypsin proteolysis. Synthetic PEDF peptides 34-mer (Asp(44)-Asn(77)) and 44-mer (Val(78)-Thr(121)) were used. Ex vivo chick aortic vessel sprouting assays were performed. CNV was induced in rats by laser injury of Bruch's membrane. Daily subconjunctival injections (0.01-10 pmol/d protein) were performed for 5 days starting at day of injury or at the seventh day after injury. New vessel volumes were quantified using optical sections of choroid/RPE flat-mounts labeled with isolectin-Ib4. PEDF distribution was evaluated by immunofluorescence of choroid/RPE/retina cross-sections.

RESULTS

Full-length rhuPEDF, cleaved rhuPEDF, or peptide 34-mer exhibited ex vivo antiangiogenic activity, but peptide 44-mer was inefficient. PEDF immunostaining around CNV lesions diminished after laser injury. Subconjunctival administration of rhuPEDF or 34-mer at 0.1 pmol/d decreased CNV lesion volumes by 52% and 47%, respectively, whereas those of 44-mer were similar to vehicle injections. Doses of 0.1 and 1 pmol/d rhuPEDF decreased fully developed CNV complex volumes by 45% and 50%, respectively, compared with vehicle injections.

CONCLUSIONS

A functional region for the inhibition of vessel sprouting and CNV resides within the 34-mer region of PEDF. Furthermore, subconjunctival administration of optimal range dosages of rhuPEDF or 34-mer can suppress and regress rat CNV lesions, demonstrating that these agents reach the choroid/RPE complex as functionally active molecules.