Calcium dysregulation potentiates wild-type myocilin misfolding: implications for glaucoma pathogenesis.
Emily G SaccuzzoMackenzie D MartinKamisha R HillMinh Thu MaYemo KuRaquel L LiebermanPublished in: Journal of biological inorganic chemistry : JBIC : a publication of the Society of Biological Inorganic Chemistry (2022)
Myocilin is secreted from trabecular meshwork cells to an eponymous extracellular matrix that is critical for maintaining intraocular pressure. Missense mutations found in the myocilin olfactomedin domain (OLF) lead to intracellular myocilin misfolding and are causative for the heritable form of early-onset glaucoma. The OLF domain contains a unique internal, hetero-dinuclear calcium site. Here, we tested the hypothesis that calcium dysregulation causes wild-type (WT) myocilin misfolding reminiscent of that observed for disease variants. Using two cellular models expressing WT myocilin, we show that the Ca<sup>2+</sup> ATPase channel blocker thapsigargin inhibits WT myocilin secretion. Intracellular WT myocilin is at least partly insoluble and aggregated in the endoplasmic reticulum (ER), and stains positively with an amyloid dye. By comparing the effect of thapsigargin on WT myocilin to that on a de novo secretion-competent Ca<sup>2+</sup>-free variant D478S, we discern that non-secretion of WT myocilin is due initially to calcium dysregulation, and is potentiated further by resultant ER stress. In E. coli, depletion of calcium leads to recombinant expression of misfolded isolated WT OLF but the D478S variant is still produced as a folded monomer. Treatment of cells expressing a double mutant composed of D478S and either disease variants P370L or Y437H with thapsigargin promotes its misfolding and aggregation, demonstrating the limits of D478S to correct secretion defects. Taken together, the heterodinuclear calcium site is a liability for proper folding of myocilin. Our study suggests a molecular mechanism by which WT myocilin misfolding may contribute broadly to glaucoma-associated ER stress. This study explores the effect of calcium depletion on myocilin olfactomedin domain folding.
Keyphrases
- wild type
- early onset
- endoplasmic reticulum
- extracellular matrix
- induced apoptosis
- late onset
- gene expression
- cell cycle arrest
- bone mineral density
- copy number
- mass spectrometry
- reactive oxygen species
- molecular dynamics simulations
- optic nerve
- autism spectrum disorder
- cell death
- smoking cessation
- cataract surgery
- body composition
- combination therapy
- tandem mass spectrometry
- angiotensin ii