Loss of ciliary zonule protein hydroxylation and lens stability as a predicted consequence of biallelic ASPH variation

Purpose: Stability of the crystalline lens requires formation of microfibril bundles and their higher-order structures of ciliary zonules. Trauma, malformation, or degeneration of the ciliary zonules can lead to dislocation or displacement of the lens, which in turn can cause transient or permanent loss of visual acuity. The purpose of this study was to identify the predicted substrates of aspartyl/asparaginyl hydroxylase (ASPH), a 2-oxoglutarate- and Fe2+-dependent hydroxylase, which may account for the lens instability phenotype of ASPH-associated syndromes.

Methods: A single proband of European ancestry with spherophakia and high myopia was subjected to exome sequencing. Proteins containing the ASPH hydroxylation motif were identified within the SwissProt protein database.

Results: We identified 105 putative substrates of ASPH-mediated hydroxylation in the human proteome, of which two (fibrillin-1 and latent transforming growth factor beta binding protein-2) are associated with inherited ectopia lentis syndromes, and are essential for microfibril and ciliary zonule development.

Conclusion: Our results implicate ASPH-mediated hydroxylation in the formation of FBN1/LTBP2 microfibril bundles and competent ciliary zonules.