Glycation-mediated inter-protein cross-linking is promoted by chaperone–client complexes of α-crystallin: Implications for lens aging and presbyopia

Abstract

Lens proteins become increasingly cross-linked through nondisulfide linkages during aging and cataract formation. One mechanism that has been implicated in this cross-linking is glycation through formation of advanced glycation end products (AGEs). Here, we found an age-associated increase in stiffness in human lenses that was directly correlated with levels of protein–cross-linking AGEs. α-Crystallin in the lens binds to other proteins and prevents their denaturation and aggregation through its chaperone-like activity. Using a FRET-based assay, we examined the stability of the αA-crystallin–γD-crystallin complex for up to 12 days and observed that this complex is stable in PBS and upon incubation with human lens–epithelial cell lysate or lens homogenate. Addition of 2 mm ATP to the lysate or homogenate did not decrease the stability of the complex. We also generated complexes of human αA-crystallin or αB-crystallin with alcohol dehydrogenase or citrate synthase by applying thermal stress. Upon glycation under physiological conditions, the chaperone–client complexes underwent greater extents of cross-linking than did uncomplexed protein mixtures. LC-MS/MS analyses revealed that the levels of cross-linking AGEs were significantly higher in the glycated chaperone–client complexes than in glycated but uncomplexed protein mixtures. Mouse lenses subjected to thermal stress followed by glycation lost resilience more extensively than lenses subjected to thermal stress or glycation alone, and this loss was accompanied by higher protein cross-linking and higher cross-linking AGE levels. These results uncover a protein cross-linking mechanism in the lens and suggest that AGE-mediated cross-linking of α-crystallin–client complexes could contribute to lens aging and presbyopia.

Oral administration of resveratrol or lactic acid bacterium improves lens elasticity

“…The homeostasis of lens proteins is associated with modifications including oxidation, deamidation, glycation, and the formation of disulfide bonds 36 . Indeed, in previous research, advanced glycation end-products mediated crosslinking and disulfide exchange among the proteins in the crystalline lens that are increased during aging 11 , 37 .…”

Microstructural determinants of lens stiffness in rat versus guinea pig lenses

“…Crystallin aggregation and protein cross-linking play a role in lens biomechanics and may be a target against presbyopia (Garner and Garner, 2016;Heys et al, 2007;Nandi et al, 2020;Randall and Vaughan, 1982;Soergel et al, 1999). However, crystallins can also interact with Factin and intermediate filament networks of the lens (Andley, 2009;Clark et al, 1999;Wang and Spector, 1996).…”

“…However, the proportion of alpha-crystallins in the nucleus decreases with age resulting in aggregation of other crystallins, nuclear dehydration and increased lens nuclear stiffness (Heys et al, 2004; Heys et al, 2007; McFall-Ngai et al, 1985; Ozaki and Mizuno, 1992; Roy and Spector, 1976). Crystallin aggregation and protein cross-linking play a role in lens biomechanics and may be a target against presbyopia (Garner and Garner, 2016; Heys et al, 2007; Nandi et al, 2020; Randall and Vaughan, 1982; Soergel et al, 1999). However, crystallins can also interact with F-actin and intermediate filament networks of the lens (Andley, 2009; Clark et al, 1999; Wang and Spector, 1996).…”

Proteinaceous Transformers: Structural and Functional Variability of Human sHsps

“…Furthermore, the transparent characteristic of the lens and the associated absence of any cell compartments implicate a drastic reduction in protein turnover, forcing its proteome to extend its lifetime. Thus, posttranslational and environmental modifications, like glycation of the proteins [43], might accumulate over time and change the behavior of many proteins. Due to limited protein turnover, damaged and aggregation-prone proteins accumulate over a lifetime and cataracts can be developed in an age-related fashion or by malfunction of specific members of the crystallin protein family.…”

“…In order to maintain lens transparency, the most common current model envisions sHsps as general aggregation suppressors via their characteristic chaperone function [46,47]. To date, it is not clear if a release mechanism from these sHsp-substrate complexes by ATP-dependent chaperones exists in the metabolically inactive lens [43]. However as described above, besides their chaperone function, α-crystallins additionally contribute to the crystalline interaction network of the lens.…”