Post-translationally Abnormal Collagens of Prolyl 3-Hydroxylase-2 Null Mice Offer a Pathobiological Mechanism for the High Myopia Linked to Human LEPREL1 Mutations

• Published in: The Journal of biological chemistry Vol. 290; no. 13; pp. 8613 - 8622
• Main Authors: Hudson, David M., Joeng, Kyu Sang, Werther, Rachel, Rajagopal, Abbhirami, Weis, MaryAnn, Lee, Brendan H., Eyre, David R.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 27.03.2015; American Society for Biochemistry and Molecular Biology
• Subjects: 3-Hydroxyproline; Amino Acid Sequence; Animal Model; Animals; Collagen; Collagen Type I - metabolism; Collagen Type IV - metabolism; Cornea - metabolism; Extracellular Matrix; Genetic Predisposition to Disease; Humans; Hydroxylation; Lens Capsule, Crystalline - metabolism; Mass Spectrometry (MS); Mice, Inbred C57BL; Mice, Knockout; Molecular Bases of Disease; Molecular Sequence Data; Mutation; Myopia - genetics; Organ Specificity; Phenotype; Post-translational Modification (PTM); Procollagen-Proline Dioxygenase - genetics; Procollagen-Proline Dioxygenase - metabolism; Prolyl 3-Hydroxylase; Protein Processing, Post-Translational; Sclera; Sclera - enzymology; Sclera - pathology; Animal Model; Extracellular Matrix; Collagen; Mass Spectrometry (MS); Post-translational Modification (PTM); Prolyl 3-Hydroxylase; 3-Hydroxyproline; Sclera
• DOI: 10.1074/jbc.M114.634915
• ISSN: 0021-9258

Myopia, the leading cause of visual impairment worldwide, results from an increase in the axial length of the eyeball. Mutations in LEPREL1, the gene encoding prolyl 3-hydroxylase-2 (P3H2), have recently been identified in individuals with recessively inherited nonsyndromic severe myopia. P3H2 is a member of a family of genes that includes three isoenzymes of prolyl 3-hydroxylase (P3H), P3H1, P3H2, and P3H3. Fundamentally, it is understood that P3H1 is responsible for converting proline to 3-hydroxyproline. This limited additional knowledge also suggests that each isoenzyme has evolved different collagen sequence-preferred substrate specificities. In this study, differences in prolyl 3-hydroxylation were screened in eye tissues from P3h2-null (P3h2n/n) and wild-type mice to seek tissue-specific effects due the lack of P3H2 activity on post-translational collagen chemistry that could explain myopia. The mice were viable and had no gross musculoskeletal phenotypes. Tissues from sclera and cornea (type I collagen) and lens capsule (type IV collagen) were dissected from mouse eyes, and multiple sites of prolyl 3-hydroxylation were identified by mass spectrometry. The level of prolyl 3-hydroxylation at multiple substrate sites from type I collagen chains was high in sclera, similar to tendon. Almost every known site of prolyl 3-hydroxylation in types I and IV collagen from P3h2n/n mouse eye tissues was significantly under-hydroxylated compared with their wild-type littermates. We conclude that altered collagen prolyl 3-hydroxylation is caused by loss of P3H2. We hypothesize that this leads to structural abnormalities in multiple eye tissues, but particularly sclera, causing progressive myopia. Background: Mutations in LEPREL1, the gene encoding prolyl 3-hydroxylase-2 (P3H2), cause severe nonsyndromic myopia. Results: Collagens I and IV from P3h2-null mouse eye tissues were significantly reduced in 3-hydroxylation compared with wild-type littermates. Conclusion: Loss of P3h2 causes altered collagen prolyl 3-hydroxylation from multiple tissues. Significance: Improved understanding of molecular mechanisms of myopia could aid in early diagnosis and treatment of irreversible vision loss.