A leading cause of blindness worldwide, glaucoma is a devastating disease with no cure. Elevated intraocular pressure (IOP) caused by defects in the aqueous humor outflow (AHO) pathway is the most important risk factor for disease progression and vision loss (Coleman and Miglior, 2008; Becker, 1961). Indeed, IOP reduction is currently the only therapeutic intervention proven to slow glaucoma progression in patients. In both humans and mice, the majority of AHO occurs through the conventional route (Johnson et al., 2017; Toris et al., 1999; Toris et al., 2000; Millar et al., 2011; Millar et al., 2015), comprised of the trabecular meshwork (TM) and the large, lymphatic-like Schlemm’s canal (SC) located in the iridocorneal angle (Johnson et al., 2017; Park et al., 2014; Aspelund et al., 2014; Kizhatil et al., 2014). Aqueous humor from the anterior chamber enters SC through the TM and is drained through a series of collector channels into the episcleral veins and systemic circulation. Recent studies have identified the importance of endothelial signaling molecules in development and maintenance of SC and the conventional outflow pathway, and critical roles have been described for the endothelial transcription factor PROX1 (Park et al., 2014) as well as the VEGFR2/3 (Kizhatil et al., 2014; Aspelund et al., 2014) and TEK (Thomson et al., 2014; Kim et al., 2017; Souma et al., 2016; Thomson et al., 2017) receptor tyrosine kinase signaling pathways.

TEK (Tunica interna endothelial cell kinase, also known as TIE2) is the tyrosine kinase receptor for the angiopoietin (Angpt) ligands ANGPT1, ANGPT2 and ANGPT4 (Saharinen et al., 2017). The Angpt-TEK pathway is essential for SC development and maintenance, and loss of function mutations in TEK or the gene encoding its primary ligand ANGPT1 have been identified in patients with primary congenital glaucoma, a severe form of glaucoma characterized by early/childhood onset, buphthalmos and optic neuropathy (Souma et al., 2016; Thomson et al., 2017; Kabra et al., 2017). Furthermore, recent genome-wide association studies have identified risk variants linked to the TEK signaling pathway in adults with elevated IOP and open angle glaucoma, the most common form of glaucoma worldwide (Khawaja et al., 2018; Gao et al., 2018; MacGregor et al., 2018).

In mice, post-natal Tek deletion leads to complete failure of SC development and rapidly progressing glaucoma (Thomson et al., 2014; Kim et al., 2017; Souma et al., 2016). A similar disease is observed in mice lacking the TEK ligand ANGPT1, confirming that ANGPT-TEK signaling is essential for canal development (Thomson et al., 2017). Importantly, while Tek knockout mice exhibit complete loss of SC, a hypomorphic canal characterized by focal narrowing and convolutions is observed in haploinsufficient animals (Tek^+/- mice) (Souma et al., 2016). This hypomorphic SC is associated with moderate IOP elevation, indicating a clear dose-dependent effect of TEK signaling in development and function of the aqueous outflow pathway and suggesting that TEK activation using genetic or pharmacological approaches might provide novel treatments for patients with high-pressure glaucoma. Indeed, the clear dose-dependent relationship between ANGPT-TEK signaling and severity of disease presentation in rodent models supports the argument that therapeutic modulation of this pathway will be efficacious in patients (Plenge et al., 2013).

Activation of the TEK receptor has been achieved in vitro and in vivo either by increasing activity of endogenous ANGPT ligands, providing ANGPT recombinant proteins (Kim et al., 2005; Souma et al., 2018), or by suppression of the phosphatase PTPRB (also known as the Vascular Endothelial Protein Tyrosine Phosphatase, VE-PTP) (Winderlich et al., 2009; Shen et al., 2014; Carota et al., 2019), which strongly dephosphorylates TEK (Souma et al., 2018; Fachinger et al., 1999). PTPRB inhibition results in ligand-independent increased TEK phosphorylation at all phosphorylated tyrosine residues, and leads to a dramatic increase in downstream signaling (Souma et al., 2018; Carota et al., 2019). Here, we show that developmental deletion of a single Ptprb allele in mice is sufficient to reduce PTPRB expression and leads to increased TEK activation in vivo. Furthermore, in Tek^+/- haploinsufficient mice, this increased TEK activation is sufficient for normal SC development, preventing both ocular hypertension and retinal ganglion cell (RGC) loss.

To increase the level of TEK phosphorylation in vivo, we utilized a Ptprb^NLS-LacZ knock-in reporter allele (Bäumer et al., 2006) to delete a single allele of the Ptprb gene. This construct incorporates a β-Galactosidase cDNA tagged with a nuclear localization signal in place of the first exon of Ptprb, preventing production of PTPRB protein. As previously described, heterozygous Ptprb^NLS-LacZ/WT mice are born normally (Bäumer et al., 2006), although expression of PTPRB was reduced by approximately 50% (Figure 1A, uncropped images presented as Figure 1—figure supplement 1). Likewise, Tek heterozygosity resulted in approximately 50% reduction in TEK protein detected in lung lysate (Figure 1A). Reductions in phosphatase abundance had a direct effect on TEK activation and Ptprb^NLS-LacZ/WT mice showed approximately a 118% increase in phosphorylated TEK when measured in lung tissue using an immunoprecipitation assay (Figure 1B, uncropped images presented as Figure 1—figure supplement 2), confirming our hypothesis that changes in PTPRB expression would have a direct impact on TEK phosphorylation.

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The finding that Ptprb^NLS-LacZ/WT haploinsufficient mice exhibited markedly increased TEK phosphorylation suggested that these animals would provide a powerful tool to study the effect of PTPRB blockade on SC development in the context of reduced TEK signaling. Therefore, we crossed mice carrying the Ptprb^NLS-LacZ allele with a previously-described mouse model of Tek heterozygosity, creating a constitutive model of Tek^+/-;Ptprb^NLS-LacZ/WT double haploinsufficency. Adult Tek haploinsufficient mice have been reported to exhibit a hypomorphic SC insufficient for normal AHO, leading to moderate IOP elevation (Souma et al., 2016). To test our hypothesis that ~50% reduction of PTPRB activity might prevent the glaucoma phenotype in Tek^+/- mice without the need to increase ligand availability, Tek^+/-;Ptprb^NLS-LacZ/WT double heterozygous mice were generated, and enucleated eyes were collected. After fixation, eyes were prepared for whole-mount immunostaining and visualized using confocal microscopy. Consistent with previous findings (Souma et al., 2016), analysis of CD31-positive SC area revealed a hypomorphic canal phenotype in adult Tek heterozygous mice when compared to littermate controls (Control: 29,974 ± 2145, Tek^+/-: 17,457 ± 1040 μm²/20x field; Figure 2A). This phenotype was abrogated by deletion of a single Ptprb allele in Tek^+/-;Ptprb^NLS-LacZ/WT animals, which exhibited normal SC area (Tek^+/-;Ptprb^NLS-LacZ/WT: 23,848 ± 1574 μm²/20x field). Importantly, despite elevated TEK activation, Ptprb^NLS-LacZ/WT animals displayed a normal SC (Ptprb^NLS-LacZ/WT: 28,175 ± 1668 μm²/20x field), suggesting reduction of PTPRB function is well tolerated during SC development in the absence of other mutations.

Figure 2

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Developmental haploinsufficency of Tek and Ptprb had clear effects on adult SC area in our model. To determine if this phenotype was due to altered proliferation of SC endothelial cells (ECs), we next analyzed eyes collected at P5 when SC development is underway. In Tek^+/- eyes, we observed a marked reduction in the proportion of PROX1+ SC ECs which were also positive for Ki-67 (Control: 0.302 ± 0.022, Tek^+/-: 0.214 ± 0.016), suggesting that the hypomorphic canal phenotype in these animals may be due to reduced proliferation during canal development (Figure 2B, quantified in C). Strikingly, normal proliferation of PROX1+ SC cells was observed in Tek^+/-;Ptprb^NLS-LacZ/WT mice (Tek^+/-;Ptprb^NLS-LacZ/WT: 0.345 ± 0.039), providing a potential mechanism for the observed effects on canal area in adulthood. A similar effect was observed on PROX1 expression, which was dramatically decreased in the SC of Tek^+/- eyes at P5 and appeared normal in the eyes of Tek^+/-;Ptprb^NLS-LacZ/WT littermates (Norm. AFU: Control: 1.0 ± 0.12, Tek^+/-: 0.49 ± 0.07, Tek^+/-;Ptprb^NLS-LacZ/WT: 0.82 ± 0.065, Figure 2D).

In addition to decreased area, Tek^+/- SCs are characterized by focal thinning and convolutions which are not present in WT littermates (Souma et al., 2016) (Figure 2E). Interestingly, although Ptprb haploinsufficency resulted in increased proliferation and expanded canal area in Tek^+/-;Ptprb^NLS-LacZ/WT animals, these focal defects were still observed—suggesting that directional signaling may play a role in proper canal formation which cannot be recapitulated by nonspecific TEK activation.

We next examined the effect of altered SC area in Tek^+/- and Tek^+/-;Ptprb^NLS-LacZ/WT mice on aqueous humor homeostasis. Tek heterozygous mice on an outbred background were found to have elevated IOP at 30 weeks of age (Figure 3A, Control: 13.7 ± 0.23, Tek^+/- 18.15±0.33 mmHg). Consistent with observations of SC morphology, while Ptprb^NLS-LacZ/WT mice had normal IOP (13.81 ± 0.82 mmHg), incorporation of this allele into the Tek^+/- model was beneficial and blunted the ocular hypertension associated with Tek haploinsufficiency, despite the presence of focal morphological defects (Tek^+/-;Ptprb^NLS-LacZ/WT IOP: 14.92 ± 0.31 mmHg). To confirm the impact of the Ptprb^NLS-LacZ-induced IOP reduction on the retina, we counted BRN3B positive ganglion cells in an additional cohort of mice at 19 weeks of age (Figure 3B). While Tek heterozygous mice showed a marked reduction in RGCs, this loss did not occur in Tek^+/;Ptprb^NLS-LacZ/WT mice.

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TEK signaling is critical for retinal angiogenesis, and to exclude the possibility that vascular defects and subsequent ischemia were responsible for RGC loss in Tek^+/- mice, we examined vascular morphology in our animals. We first examined retinas collected at P5, when development of the superficial vasculature is ongoing. At this timepoint, CD31 staining revealed normal progress of the angiogenic sprouting front in Tek^+/-, Ptprb^NLS-LacZ/WT, and Tek^+/;Ptprb^NLS-LacZ/WT mice when compared to littermate controls (Figure 3—figure supplement 1A). At P20, when development of the mature retinal vasculature is complete, we observed normal patterning in all three retinal vascular layers in mice of all genotypes (Figure 3—figure supplement 1B). By this timepoint, hyaloid vessels were not observed in animals of any genotype. Taken together, these data suggest that blunted IOP elevation in Tek^+/;Ptprb^NLS-LacZ/WT animals likely had a direct impact on glaucoma pathogenesis in our model and that retinal ischemia is unlikely to account for the RGC loss observed in Tek haploinsufficient mice.

Ocular hypertension is the single most important risk factor for glaucoma in patients, and reducing IOP is the only therapeutic intervention proven to slow disease progression. Although aqueous humor flow through the conventional (trabecular) outflow pathway represents the majority of AHO, drugs targeting this outflow pathway were not available until the recent introduction of the Rho kinase inhibitors ripasudil and netarsudil. However, while these molecules provide exciting new treatment options, clinical trials have not shown them to be superior to current standard of care therapies for lowering IOP (Tanna and Johnson, 2018), underscoring the need for additional drug targets and treatment options.

Angpt-TEK signaling is essential for development (Thomson et al., 2014; Souma et al., 2016; Thomson et al., 2017) and maintenance (Kim et al., 2017) of SC, an essential component of the conventional AHO pathway. Dysregulation of Angpt-TEK signaling results in hypomorphic or failed SC formation, elevated IOP and glaucoma in mice and humans. Intriguingly, recent GWAS studies of subjects with ocular hypertension have identified common variants in members of the Angpt-TEK signaling pathway (Khawaja et al., 2018; Gao et al., 2018; MacGregor et al., 2018). These GWAS findings suggest that in addition to the complete loss-of-function variants previously described in PCG, less impactful variants may play a role in more common forms of adult-onset glaucoma. These reports, combined with the strong dose dependent response of SC development and function to TEK signaling observed in the mouse, suggest that the Angpt-TEK signaling axis is a sensitive and important regulator of SC and AHO and may provide a valuable IOP-lowering therapeutic target for treatment of glaucoma patients. Indeed, a recent study has demonstrated the effectiveness of targeting the Angpt-TEK signaling pathway in a mouse model of glaucoma using an antibody which increases the signaling ability of the context-dependent, weak TEK agonist ANGPT2 by clustering it into higher-order multimers (Kim et al., 2017; Park et al., 2016). ANGPT2-clustering antibody treatment was found to increase TEK phosphorylation in aged mice and lower IOP in an injury-induced model of ocular hypertension (Kim et al., 2017).

Here, we demonstrate an alternative approach targeting the endothelial phosphatase PTPRB, which acts on TEK (Souma et al., 2018; Winderlich et al., 2009; Bäumer et al., 2006) as well as VE-Cadherin, VEGFR2 and FGD5 (Nawroth et al., 2002; Broermann et al., 2011; Mellberg et al., 2009; Hayashi et al., 2013; Braun et al., 2019). Using a genetic approach to PTPRB ablation allowed us to achieve consistent reduction in protein levels, with deletion of a single Ptprb allele leading to approximately 50% reduction in protein expression. In Tek-WT lung tissue, this was sufficient to cause a marked elevation in TEK phosphorylation. PTPRB inhibition has been previously studied as a potential therapeutic intervention in vascular disease (Shen et al., 2014), and the PTPRB inhibitor AKB-9778 is currently undergoing clinical trials for treatment of diabetic macular edema, where it is well-tolerated by patients (Campochiaro et al., 2016). While mid-term results for the AKB-9778 TIME-2 trial failed to achieve the primary endpoint in diabetic macular edema, two important observations were reported from this clinical trial: the drug was well tolerated and safe in patients and IOP was lower in the treatment arm (Aerpio Pharmaceuticals Inc, 2019).

We have previously reported that defects in Angpt-TEK signaling cause a range of SC and IOP phenotypes corresponding to the degree of pathway dysfunction, ranging from complete absence of SC (Tek knockout or Angpt1;Angpt2 double knockout mice) to less severely hypomorphic canal morphology (Tek haploinsufficency) (Thomson et al., 2014; Kim et al., 2017; Souma et al., 2016; Thomson et al., 2017). Although the phenotype of Tek haploinsufficient mice is milder than that observed in PCG patients with heterozygous TEK loss-of-function mutations (Souma et al., 2016), we selected this model as Tek heterozygous mice are viable, fertile and exhibit a consistent SC phenotype without the need for Cre recombinase-mediated gene deletion. Furthermore, this mouse model has many features of glaucoma including ocular hypertension and loss of retinal ganglion cells which more faithfully recapitulate disease seen in patients with common forms of open angle glaucoma then the more severe model of total Tek deletion. Consistent with our previous findings, adult Tek^+/- mice in this study displayed a hypomorphic SC phenotype due to decreased EC proliferation which was associated with elevated IOP and loss of BRN3B+ retinal ganglion cells. These defects were blunted by developmental Ptprb haploinsufficency in Tek^+/-;Ptprb^NLS-LacZ/WT mice, likely due to increased basal TEK phosphorylation and resulting EC proliferation in Ptprb^NLS-LacZ/WT animals. In addition, expression of PROX1, a key marker of mature SC endothelial cells, was dramatically reduced in Tek^+/- SCs at P5. Expression was normal in Tek^+/-;Ptprb^NLS-LacZ/WT eyes, consistent with previous reports from our lab and elsewhere suggesting that Angpt1-TEK signaling may be critical for maintenance of this crucial transcription factor in the SC endothelium (Park et al., 2014; Kim et al., 2017; Thomson et al., 2017; Truong et al., 2014). However, our data do not indicate whether PROX1 expression is directly downstream of TEK activation or is otherwise dependent on a mature SC endothelial phenotype.

While these results highlight the potential of PTPRB as a therapeutic target for patients with TEK-associated PCG, the recent association of Angpt-TEK variants with ocular hypertension and the findings of Kim et al using an ANGPT2 clustering antibody suggest that this pathway may also provide a valuable therapeutic target for adult patients with primary open angle glaucoma, a significantly larger group then TEK-associated PCG. Future studies using targeted gene deletion or therapies that inhibit PTPRB such as siRNA, antibodies or small molecule inhibitors will provide additional insights and pave the way for translation of these findings into the clinic.

All data described have been included in the manuscript. No data sets were generated during the course of this study.

1. Website

   1. Aerpio Pharmaceuticals Inc

   (2019) Aerpio pharmaceuticals announces results from time-2b study of akb-9778 in diabetic retinopathy [Press release]

   Accessed March 18, 2019.

   http://ir.aerpio.com/phoenix.zhtml?c=254540&p=irol-newsArticle&ID=2391547
2. 1. Aspelund A
   2. Tammela T
   3. Antila S
   4. Nurmi H
   5. Leppänen VM
   6. Zarkada G
   7. Stanczuk L
   8. Francois M
   9. Mäkinen T
   10. Saharinen P
   11. Immonen I
   12. Alitalo K

   (2014) The schlemm's canal is a VEGF-C/VEGFR-3-responsive lymphatic-like vessel

   Journal of Clinical Investigation 124:3975–3986.

   https://doi.org/10.1172/JCI75395

   • PubMed
   • Google Scholar
3. 1. Bäumer S
   2. Keller L
   3. Holtmann A
   4. Funke R
   5. August B
   6. Gamp A
   7. Wolburg H
   8. Wolburg-Buchholz K
   9. Deutsch U
   10. Vestweber D

   (2006) Vascular endothelial cell-specific phosphotyrosine phosphatase (VE-PTP) activity is required for blood vessel development

   Blood 107:4754–4762.

   https://doi.org/10.1182/blood-2006-01-0141

   • PubMed
   • Google Scholar
4. 1. Becker B

   (1961)

   Tonography in the diagnosis of simple (open angle) glaucoma

   Transactions - American Academy of Ophthalmology and Otolaryngology 65:156–162.

   • PubMed
   • Google Scholar
5. 1. Belteki G
   2. Haigh J
   3. Kabacs N
   4. Haigh K
   5. Sison K
   6. Costantini F
   7. Whitsett J
   8. Quaggin SE
   9. Nagy A

   (2005) Conditional and inducible transgene expression in mice through the combinatorial use of Cre-mediated recombination and tetracycline induction

   Nucleic Acids Research 33:e51.

   https://doi.org/10.1093/nar/gni051

   • Google Scholar
6. 1. Braun LJ
   2. Zinnhardt M
   3. Vockel M
   4. Drexler HC
   5. Peters K
   6. Vestweber D

   (2019) VE-PTP inhibition stabilizes endothelial junctions by activating FGD5

   EMBO Reports 20:e47046.

   https://doi.org/10.15252/embr.201847046

   • PubMed
   • Google Scholar
7. 1. Broermann A
   2. Winderlich M
   3. Block H
   4. Frye M
   5. Rossaint J
   6. Zarbock A
   7. Cagna G
   8. Linnepe R
   9. Schulte D
   10. Nottebaum AF
   11. Vestweber D

   (2011) Dissociation of VE-PTP from VE-cadherin is required for leukocyte extravasation and for VEGF-induced vascular permeability in vivo

   The Journal of Experimental Medicine 208:2393–2401.

   https://doi.org/10.1084/jem.20110525

   • PubMed
   • Google Scholar
8. 1. Campochiaro PA
   2. Khanani A
   3. Singer M
   4. Patel S
   5. Boyer D
   6. Dugel P
   7. Kherani S
   8. Withers B
   9. Gambino L
   10. Peters K
   11. Brigell M
   12. TIME-2 Study Group

   (2016) Enhanced benefit in diabetic macular edema from AKB-9778 Tie2 activation combined with vascular endothelial growth factor suppression

   Ophthalmology 123:1722–1730.

   https://doi.org/10.1016/j.ophtha.2016.04.025

   • PubMed
   • Google Scholar
9. 1. Carota IA
   2. Kenig-Kozlovsky Y
   3. Onay T
   4. Scott R
   5. Thomson BR
   6. Souma T
   7. Bartlett CS
   8. Li Y
   9. Procissi D
   10. Ramirez V
   11. Yamaguchi S
   12. Tarjus A
   13. Tanna CE
   14. Li C
   15. Eremina V
   16. Vestweber D
   17. Oladipupo SS
   18. Breyer MD
   19. Quaggin SE

   (2019) Targeting VE-PTP phosphatase protects the kidney from diabetic injury

   The Journal of Experimental Medicine 216:936–949.

   https://doi.org/10.1084/jem.20180009

   • PubMed
   • Google Scholar
10. 1. Coleman AL
    2. Miglior S

    (2008) Risk factors for Glaucoma onset and progression

    Survey of Ophthalmology 53 Suppl1:S3–S10.

    https://doi.org/10.1016/j.survophthal.2008.08.006

    • PubMed
    • Google Scholar
11. 1. Economides AN
    2. Frendewey D
    3. Yang P
    4. Dominguez MG
    5. Dore AT
    6. Lobov IB
    7. Persaud T
    8. Rojas J
    9. McClain J
    10. Lengyel P
    11. Droguett G
    12. Chernomorsky R
    13. Stevens S
    14. Auerbach W
    15. Dechiara TM
    16. Pouyemirou W
    17. Cruz JM
    18. Feeley K
    19. Mellis IA
    20. Yasenchack J
    21. Hatsell SJ
    22. Xie L
    23. Latres E
    24. Huang L
    25. Zhang Y
    26. Pefanis E
    27. Skokos D
    28. Deckelbaum RA
    29. Croll SD
    30. Davis S
    31. Valenzuela DM
    32. Gale NW
    33. Murphy AJ
    34. Yancopoulos GD

    (2013) Conditionals by inversion provide a universal method for the generation of conditional alleles

    PNAS 110:E3179–E3188.

    https://doi.org/10.1073/pnas.1217812110

    • PubMed
    • Google Scholar
12. 1. Fachinger G
    2. Deutsch U
    3. Risau W

    (1999) Functional interaction of vascular endothelial-protein-tyrosine phosphatase with the angiopoietin receptor Tie-2

    Oncogene 18:5948–5953.

    https://doi.org/10.1038/sj.onc.1202992

    • PubMed
    • Google Scholar
13. 1. Gao XR
    2. Huang H
    3. Nannini DR
    4. Fan F
    5. Kim H

    (2018) Genome-wide association analyses identify new loci influencing intraocular pressure

    Human Molecular Genetics 27:2205–2213.

    https://doi.org/10.1093/hmg/ddy111

    • PubMed
    • Google Scholar
14. 1. Hayashi M
    2. Majumdar A
    3. Li X
    4. Adler J
    5. Sun Z
    6. Vertuani S
    7. Hellberg C
    8. Mellberg S
    9. Koch S
    10. Dimberg A
    11. Koh GY
    12. Dejana E
    13. Belting HG
    14. Affolter M
    15. Thurston G
    16. Holmgren L
    17. Vestweber D
    18. Claesson-Welsh L

    (2013) VE-PTP regulates VEGFR2 activity in stalk cells to establish endothelial cell polarity and lumen formation

    Nature Communications 4:1672.

    https://doi.org/10.1038/ncomms2683

    • PubMed
    • Google Scholar
15. 1. John SW
    2. Hagaman JR
    3. MacTaggart TE
    4. Peng L
    5. Smithes O

    (1997)

    Intraocular pressure in inbred mouse strains

    Investigative Ophthalmology & Visual Science 38:249–253.

    • PubMed
    • Google Scholar
16. 1. Johnson M
    2. McLaren JW
    3. Overby DR

    (2017) Unconventional aqueous humor outflow: a review

    Experimental Eye Research 158:94–111.

    https://doi.org/10.1016/j.exer.2016.01.017

    • PubMed
    • Google Scholar
17. 1. Kabra M
    2. Zhang W
    3. Rathi S
    4. Mandal AK
    5. Senthil S
    6. Pyatla G
    7. Ramappa M
    8. Banerjee S
    9. Shekhar K
    10. Marmamula S
    11. Mettla AL
    12. Kaur I
    13. Khanna RC
    14. Khanna H
    15. Chakrabarti S

    (2017) Angiopoietin receptor TEK interacts with CYP1B1 in primary congenital Glaucoma

    Human Genetics 136:941–949.

    https://doi.org/10.1007/s00439-017-1823-6

    • PubMed
    • Google Scholar
18. 1. Khawaja AP
    2. Cooke Bailey JN
    3. Wareham NJ
    4. Scott RA
    5. Simcoe M
    6. Igo RP
    7. Song YE
    8. Wojciechowski R
    9. Cheng CY
    10. Khaw PT
    11. Pasquale LR
    12. Haines JL
    13. Foster PJ
    14. Wiggs JL
    15. Hammond CJ
    16. Hysi PG
    17. UK Biobank Eye and Vision Consortium, NEIGHBORHOOD Consortium

    (2018) Genome-wide analyses identify 68 new loci associated with intraocular pressure and improve risk prediction for primary open-angle Glaucoma

    Nature Genetics 50:778–782.

    https://doi.org/10.1038/s41588-018-0126-8

    • PubMed
    • Google Scholar
19. 1. Kim KT
    2. Choi HH
    3. Steinmetz MO
    4. Maco B
    5. Kammerer RA
    6. Ahn SY
    7. Kim HZ
    8. Lee GM
    9. Koh GY

    (2005) Oligomerization and multimerization are critical for angiopoietin-1 to bind and phosphorylate Tie2

    Journal of Biological Chemistry 280:20126–20131.

    https://doi.org/10.1074/jbc.M500292200

    • PubMed
    • Google Scholar
20. 1. Kim J
    2. Park DY
    3. Bae H
    4. Park DY
    5. Kim D
    6. Lee CK
    7. Song S
    8. Chung TY
    9. Lim DH
    10. Kubota Y
    11. Hong YK
    12. He Y
    13. Augustin HG
    14. Oliver G
    15. Koh GY

    (2017) Impaired angiopoietin/Tie2 signaling compromises schlemm's canal integrity and induces glaucoma

    Journal of Clinical Investigation 127:3877–3896.

    https://doi.org/10.1172/JCI94668

    • PubMed
    • Google Scholar
21. 1. Kizhatil K
    2. Ryan M
    3. Marchant JK
    4. Henrich S
    5. John SW

    (2014) Schlemm's canal is a unique vessel with a combination of blood vascular and lymphatic phenotypes that forms by a novel developmental process

    PLOS Biology 12:e1001912.

    https://doi.org/10.1371/journal.pbio.1001912

    • PubMed
    • Google Scholar
22. 1. MacGregor S
    2. Ong JS
    3. An J
    4. Han X
    5. Zhou T
    6. Siggs OM
    7. Law MH
    8. Souzeau E
    9. Sharma S
    10. Lynn DJ
    11. Beesley J
    12. Sheldrick B
    13. Mills RA
    14. Landers J
    15. Ruddle JB
    16. Graham SL
    17. Healey PR
    18. White AJR
    19. Casson RJ
    20. Best S
    21. Grigg JR
    22. Goldberg I
    23. Powell JE
    24. Whiteman DC
    25. Radford-Smith GL
    26. Martin NG
    27. Montgomery GW
    28. Burdon KP
    29. Mackey DA
    30. Gharahkhani P
    31. Craig JE
    32. Hewitt AW

    (2018) Genome-wide association study of intraocular pressure uncovers new pathways to Glaucoma

    Nature Genetics 50:1067–1071.

    https://doi.org/10.1038/s41588-018-0176-y

    • PubMed
    • Google Scholar
23. 1. Mellberg S
    2. Dimberg A
    3. Bahram F
    4. Hayashi M
    5. Rennel E
    6. Ameur A
    7. Westholm JO
    8. Larsson E
    9. Lindahl P
    10. Cross MJ
    11. Claesson-Welsh L

    (2009) Transcriptional profiling reveals a critical role for tyrosine phosphatase VE-PTP in regulation of VEGFR2 activity and endothelial cell morphogenesis

    The FASEB Journal 23:1490–1502.

    https://doi.org/10.1096/fj.08-123810

    • PubMed
    • Google Scholar
24. 1. Millar JC
    2. Clark AF
    3. Pang I-H

    (2011) Assessment of aqueous humor dynamics in the mouse by a novel method of Constant-Flow infusion

    Investigative Opthalmology & Visual Science 52:685–694.

    https://doi.org/10.1167/iovs.10-6069

    • Google Scholar
25. 1. Millar JC
    2. Phan TN
    3. Pang I-H
    4. Clark AF

    (2015) Strain and age effects on aqueous humor dynamics in the mouse

    Investigative Opthalmology & Visual Science 56:5764–5776.

    https://doi.org/10.1167/iovs.15-16720

    • Google Scholar
26. 1. Nawroth R
    2. Poell G
    3. Ranft A
    4. Kloep S
    5. Samulowitz U
    6. Fachinger G
    7. Golding M
    8. Shima DT
    9. Deutsch U
    10. Vestweber D

    (2002) VE-PTP and VE-cadherin ectodomains interact to facilitate regulation of phosphorylation and cell contacts

    The EMBO Journal 21:4885–4895.

    https://doi.org/10.1093/emboj/cdf497

    • Google Scholar
27. 1. Park DY
    2. Lee J
    3. Park I
    4. Choi D
    5. Lee S
    6. Song S
    7. Hwang Y
    8. Hong KY
    9. Nakaoka Y
    10. Makinen T
    11. Kim P
    12. Alitalo K
    13. Hong YK
    14. Koh GY

    (2014) Lymphatic regulator PROX1 determines schlemm's canal integrity and identity

    Journal of Clinical Investigation 124:3960–3974.

    https://doi.org/10.1172/JCI75392

    • PubMed
    • Google Scholar
28. 1. Park JS
    2. Kim IK
    3. Han S
    4. Park I
    5. Kim C
    6. Bae J
    7. Oh SJ
    8. Lee S
    9. Kim JH
    10. Woo DC
    11. He Y
    12. Augustin HG
    13. Kim I
    14. Lee D
    15. Koh GY

    (2016) Normalization of tumor vessels by Tie2 activation and Ang2 inhibition enhances drug delivery and produces a favorable tumor microenvironment

    Cancer Cell 30:953–967.

    https://doi.org/10.1016/j.ccell.2016.10.018

    • PubMed
    • Google Scholar
29. 1. Plenge RM
    2. Scolnick EM
    3. Altshuler D

    (2013) Validating therapeutic targets through human genetics

    Nature Reviews Drug Discovery 12:581–594.

    https://doi.org/10.1038/nrd4051

    • PubMed
    • Google Scholar
30. 1. Saharinen P
    2. Eklund L
    3. Alitalo K

    (2017) Therapeutic targeting of the angiopoietin-TIE pathway

    Nature Reviews Drug Discovery 16:635–661.

    https://doi.org/10.1038/nrd.2016.278

    • PubMed
    • Google Scholar
31. 1. Schindelin J
    2. Arganda-Carreras I
    3. Frise E
    4. Kaynig V
    5. Longair M
    6. Pietzsch T
    7. Preibisch S
    8. Rueden C
    9. Saalfeld S
    10. Schmid B
    11. Tinevez J-Y
    12. White DJ
    13. Hartenstein V
    14. Eliceiri K
    15. Tomancak P
    16. Cardona A

    (2012) Fiji: an open-source platform for biological-image analysis

    Nature Methods 9:676–682.

    https://doi.org/10.1038/nmeth.2019

    • Google Scholar
32. 1. Shen J
    2. Frye M
    3. Lee BL
    4. Reinardy JL
    5. McClung JM
    6. Ding K
    7. Kojima M
    8. Xia H
    9. Seidel C
    10. Lima e Silva R
    11. Dong A
    12. Hackett SF
    13. Wang J
    14. Howard BW
    15. Vestweber D
    16. Kontos CD
    17. Peters KG
    18. Campochiaro PA

    (2014) Targeting VE-PTP activates TIE2 and stabilizes the ocular vasculature

    Journal of Clinical Investigation 124:4564–4576.

    https://doi.org/10.1172/JCI74527

    • PubMed
    • Google Scholar
33. 1. Souma T
    2. Tompson SW
    3. Thomson BR
    4. Siggs OM
    5. Kizhatil K
    6. Yamaguchi S
    7. Feng L
    8. Limviphuvadh V
    9. Whisenhunt KN
    10. Maurer-Stroh S
    11. Yanovitch TL
    12. Kalaydjieva L
    13. Azmanov DN
    14. Finzi S
    15. Mauri L
    16. Javadiyan S
    17. Souzeau E
    18. Zhou T
    19. Hewitt AW
    20. Kloss B
    21. Burdon KP
    22. Mackey DA
    23. Allen KF
    24. Ruddle JB
    25. Lim SH
    26. Rozen S
    27. Tran-Viet KN
    28. Liu X
    29. John S
    30. Wiggs JL
    31. Pasutto F
    32. Craig JE
    33. Jin J
    34. Quaggin SE
    35. Young TL

    (2016) Angiopoietin receptor TEK mutations underlie primary congenital Glaucoma with variable expressivity

    Journal of Clinical Investigation 126:2575–2587.

    https://doi.org/10.1172/JCI85830

    • PubMed
    • Google Scholar
34. 1. Souma T
    2. Thomson BR
    3. Heinen S
    4. Carota IA
    5. Yamaguchi S
    6. Onay T
    7. Liu P
    8. Ghosh AK
    9. Li C
    10. Eremina V
    11. Hong YK
    12. Economides AN
    13. Vestweber D
    14. Peters KG
    15. Jin J
    16. Quaggin SE

    (2018) Context-dependent functions of angiopoietin 2 are determined by the endothelial phosphatase VEPTP

    PNAS 115:1298–1303.

    https://doi.org/10.1073/pnas.1714446115

    • PubMed
    • Google Scholar
35. 1. Tanna AP
    2. Johnson M

    (2018) Rho kinase inhibitors as a novel treatment for Glaucoma and ocular hypertension

    Ophthalmology 125:1741–1756.

    https://doi.org/10.1016/j.ophtha.2018.04.040

    • PubMed
    • Google Scholar
36. 1. Thomson BR
    2. Heinen S
    3. Jeansson M
    4. Ghosh AK
    5. Fatima A
    6. Sung HK
    7. Onay T
    8. Chen H
    9. Yamaguchi S
    10. Economides AN
    11. Flenniken A
    12. Gale NW
    13. Hong YK
    14. Fawzi A
    15. Liu X
    16. Kume T
    17. Quaggin SE

    (2014) A lymphatic defect causes ocular hypertension and Glaucoma in mice

    Journal of Clinical Investigation 124:4320–4324.

    https://doi.org/10.1172/JCI77162

    • PubMed
    • Google Scholar
37. 1. Thomson BR
    2. Souma T
    3. Tompson SW
    4. Onay T
    5. Kizhatil K
    6. Siggs OM
    7. Feng L
    8. Whisenhunt KN
    9. Yanovitch TL
    10. Kalaydjieva L
    11. Azmanov DN
    12. Finzi S
    13. Tanna CE
    14. Hewitt AW
    15. Mackey DA
    16. Bradfield YS
    17. Souzeau E
    18. Javadiyan S
    19. Wiggs JL
    20. Pasutto F
    21. Liu X
    22. John SW
    23. Craig JE
    24. Jin J
    25. Young TL
    26. Quaggin SE

    (2017) Angiopoietin-1 is required for Schlemm's canal development in mice and humans

    Journal of Clinical Investigation 127:4421–4436.

    https://doi.org/10.1172/JCI95545

    • PubMed
    • Google Scholar
38. Book

    1. Thomson BR
    2. Quaggin SE

    (2018) Morphological Analysis of Schlemm’s Canal in Mice

    In: Oliver G, Kahn M. L, editors. Lymphangiogenesis: Methods and Protocols. New York: Springer. pp. 153–160.

    https://doi.org/10.1007/978-1-4939-8712-2_10

    • Google Scholar
39. 1. Toris CB
    2. Yablonski ME
    3. Wang Y-L
    4. Camras CB

    (1999) Aqueous humor dynamics in the aging human eye

    American Journal of Ophthalmology 127:407–412.

    https://doi.org/10.1016/S0002-9394(98)00436-X

    • Google Scholar
40. 1. Toris CB
    2. Zhan GL
    3. Wang YL
    4. Zhao J
    5. McLaughlin MA
    6. Camras CB
    7. Yablonski ME

    (2000) Aqueous humor dynamics in monkeys with laser-induced Glaucoma

    Journal of Ocular Pharmacology and Therapeutics 16:19–27.

    https://doi.org/10.1089/jop.2000.16.19

    • PubMed
    • Google Scholar
41. 1. Truong TN
    2. Li H
    3. Hong YK
    4. Chen L

    (2014) Novel characterization and live imaging of schlemm's canal expressing Prox-1

    PLOS ONE 9:e98245.

    https://doi.org/10.1371/journal.pone.0098245

    • PubMed
    • Google Scholar
42. 1. Winderlich M
    2. Keller L
    3. Cagna G
    4. Broermann A
    5. Kamenyeva O
    6. Kiefer F
    7. Deutsch U
    8. Nottebaum AF
    9. Vestweber D

    (2009) VE-PTP controls blood vessel development by balancing Tie-2 activity

    The Journal of Cell Biology 185:657–671.

    https://doi.org/10.1083/jcb.200811159

    • PubMed
    • Google Scholar

Author details

1. Benjamin R Thomson

   1. Feinberg Cardiovascular and Renal Research Institute, Northwestern University Feinberg School of Medicine, Chicago, United States
   2. Division of Nephrology and Hypertension, Northwestern University Feinberg School of Medicine, Chicago, United States

   Contribution

   Conceptualization, Data curation, Formal analysis, Validation, Investigation, Visualization, Methodology, Writing—original draft, Project administration, Writing—review and editing

   Competing interests

   No competing interests declared

   "This ORCID iD identifies the author of this article:" 0000-0001-6565-5866

2. Isabel A Carota

   1. Feinberg Cardiovascular and Renal Research Institute, Northwestern University Feinberg School of Medicine, Chicago, United States
   2. Division of Nephrology and Hypertension, Northwestern University Feinberg School of Medicine, Chicago, United States

   Contribution

   Conceptualization, Investigation, Methodology

   Competing interests

   was employed by Eli Lilly and Company during the time of study completion and manuscript preparation

   "This ORCID iD identifies the author of this article:" 0000-0002-7980-2377

3. Tomokazu Souma

   1. Feinberg Cardiovascular and Renal Research Institute, Northwestern University Feinberg School of Medicine, Chicago, United States
   2. Division of Nephrology and Hypertension, Northwestern University Feinberg School of Medicine, Chicago, United States

   Present address

   Division of Nephrology, Duke University School of Medicine, Durham, United States

   Contribution

   Conceptualization, Writing—review and editing

   Competing interests

   No competing interests declared

   "This ORCID iD identifies the author of this article:" 0000-0002-3285-8613

4. Saily Soman

   1. Feinberg Cardiovascular and Renal Research Institute, Northwestern University Feinberg School of Medicine, Chicago, United States
   2. Division of Nephrology and Hypertension, Northwestern University Feinberg School of Medicine, Chicago, United States

   Contribution

   Formal analysis, Investigation, Writing—review and editing

   Competing interests

   No competing interests declared

5. Dietmar Vestweber

   Max Planck Institute for Molecular Biomedicine, Münster, Germany

   Contribution

   Resources, Writing—review and editing

   Competing interests

   is a scientific advisory board member of Aerpio Pharmaceuticals

   "This ORCID iD identifies the author of this article:" 0000-0002-3517-732X

6. Susan E Quaggin

   1. Feinberg Cardiovascular and Renal Research Institute, Northwestern University Feinberg School of Medicine, Chicago, United States
   2. Division of Nephrology and Hypertension, Northwestern University Feinberg School of Medicine, Chicago, United States

   Contribution

   Conceptualization, Formal analysis, Supervision, Funding acquisition, Validation, Project administration, Writing—review and editing

   For correspondence

   quaggin@northwestern.edu

   Competing interests

   has applied for patents related to therapeutic targeting of the ANGPT-TEK pathway in ocular hypertension and glaucoma and receives research support, owns stock in and is a director of Mannin Research

   "This ORCID iD identifies the author of this article:" 0000-0002-3706-5727

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