Primary congenital glaucoma (PCG) is a severe autosomal recessive ocular disorder associated with considerable clinical and genetic heterogeneity. Recently, rare heterozygous alleles in the angiopoietin receptor-encoding gene TEK were implicated in PCG. We undertook this study to ascertain the second mutant allele in a large cohort (n = 337) of autosomal recessive PCG cases that carried heterozygous TEK mutations. Our investigations revealed 12 rare heterozygous missense mutations in TEK by targeted sequencing. Interestingly, four of these TEK mutations (p.E103D, p.I148T, p.Q214P, and p.G743A) co-occurred with three heterozygous mutations in another major PCG gene CYP1B1 (p.A115P, p.E229K, and p.R368H) in five families. The parents of these probands harbored either of the heterozygous TEK or CYP1B1 alleles and were asymptomatic, indicating a potential digenic mode of inheritance. Furthermore, we ascertained the interactions of TEK and CYP1B1 by co-transfection and pull-down assays in HEK293 cells. Ligand responsiveness of the wild-type and mutant TEK proteins was assessed in HUVECs using immunofluorescence analysis. We observed that recombinant TEK and CYP1B1 proteins interact with each other, while the disease-associated allelic combinations of TEK (p.E103D)∷CYP1B1 (p.A115P), TEK (p.Q214P)∷CYP1B1 (p.E229K), and TEK (p.I148T)∷CYP1B1 (p.R368H) exhibit perturbed interaction. The mutations also diminished the ability of TEK to respond to ligand stimulation, indicating perturbed TEK signaling. Overall, our data suggest that interaction of TEK and CYP1B1 contributes to PCG pathogenesis and argue that TEK-CYP1B1 may perform overlapping as well as distinct functions in manifesting the disease etiology.

Glaucoma is a leading cause of blindness affecting up to million people worldwide. High intraocular pressure (IOP) is a major risk factor for glaucoma. Inefficient aqueous humor (AqH) outflow resulting from structural or functional alterations in ocular drainage tissues are well established to cause high IOP, but the genes and pathways involved are poorly understood. We previously demonstrated that mutations in the gene encoding the serine protease PRSS56 induces ocular angle-closure and high IOP in mice and identified reduced ocular axial length as a potential contributing factor. Here we show that Prss56-/mice also exhibits an abnormal iridocorneal angle configuration characterized by a posterior shift of ocular drainage structures relative to the ciliary body and iris. Notably, we show that retina-derived PRSS56 is required between postnatal days 13 and 18 for proper iridocorneal configuration and that abnormal positioning of the ocular drainage tissues is not dependent on ocular size reduction in Prss56-/mice. Furthermore, we demonstrate that the genetic context modulates the severity of IOP elevation in Prss56 mutant mice and describe a progressive degeneration of ocular drainage tissues that likely contributes to the exacerbation of the high IOP phenotype observed on the C3H/HeJ genetic background. Finally, we identified five rare PRSS56 variants associated with human primary congenital glaucoma, a condition characterized by abnormal development of the ocular drainage structures. Collectively, our findings point to a role for PRSS56 in the development and maintenance of ocular drainage tissues and IOP homeostasis, and provide new insights into glaucoma pathogenesis.

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