Knockout of the intermediate filament protein CP49 destabilises the lens fibre cell cytoskeleton and decreases lens optical quality, but does not induce cataract

Kirk

Journal of Biological Chemistry

2004

The purpose of this study was to characterize covalent multimers with molecular mass of >90 kDa in the waterinsoluble (WI) proteins of aging human lenses. The experimental approach was to first separate the multimers (molecular mass >90 kDa) as individual spots by two-dimensional gel electrophoresis and next analyze compositions of each multimers by matrix-assisted laser desorption ionization-time of flight and electrospray ionization-tandem mass spectrometric (ES-MS/MS) methods. The WI proteins from lenses of 25-and 41-yearold subjects showed distinct 5-and 16-multimer spots on two-dimensional gels, respectively, but the spots from 52-and 72-year-old lenses were non-descript and diffused. ES-MS/MS analyses showed two types of covalent multimers in 25-and 41-year-old lenses, i.e. the first type composed of fragments of eight different crystallins (i.e. ␣A, ␣B, ␤A3, ␤A4, ␤B1, ␤B2, ␥S, and ␥D), and the second type of ␣-, ␤-, and ␥-crystallins (possibly fragments) and two beaded filament proteins (phakinin and filensin). The most commonly identified species in the complexes of 41-year-old lenses were: ␣A-fragment (C-terminally truncated, residues 1-157), ␣B-fragment (residues 83-90), ␤B1-crystallin (residues 60 -71), ␤A3 (residues 33-44), ␤A4 (residues 106 -117), filensin (residues 78 -90), and phakinin (residues 77-89). Three post-translational modifications (i.e. oxidation of Met and Trp, conversion of Ser to dehydroalanine, and formylation of His) were observed in ␣A-crystallin fragment, and the first two modifications could cross-link proteins. Together, the results suggested that covalent multimers appeared early in life (i.e. 25 years of age) and increased in number with aging, and the two beaded filament proteins form covalent complexes with crystallin fragments in vivo.Mammalian lens contains three major structural proteins that are known as ␣-, ␤-, and ␥-crystallins. Among these, the ␣-and ␤-crystallins exist as oligomers, whereas the ␥-crystallin as a monomer. The ␣A-and ␣B-crystallins, the two subunits and primary gene products of ␣-crystallin, aggregate to form 800,000-Da oligomers, whereas ␤-and ␥-crystallins originated via gene duplication and form a superfamily. These structural proteins, by virtue of their special structural interactions and high concentrations, contribute to the transparency of the lens and provide refractive index to focus light on to the retina. With aging, crystallins show aggregation, cross-linking, and water insolubilization. Together, these processes contribute to the development of age-related lens opacity. Presently, the sequence of events that lead to development of opacity is not well understood. However, evidence suggests that a variety of posttranslational modifications in crystallins lead to their aggregation, cross-linking, and eventually water insolubilization. Because of several of the post-translational modifications simultaneously occur during aging in the native, aggregated, and water-insoluble crystallins, the identification of a single or combination of potenti...

Section: Discussionmentioning

confidence: 99%

Characterization of Covalent Multimers of Crystallins in Aging Human Lenses

Kirk

Journal of Biological Chemistry

2004

“…The discovery of the first cataract-causing mutations in BFSP2 (48,49) and the observation that targeted deletion of Bfsp2 from the mouse genome resulted in loss of optical properties and the eventual appearance of cataract established that beaded filaments are critical to the optical properties of the eye lens (50). When the lens phenotypes of the different mouse knockouts (46,(50)(51)(52) and the clinical descriptions for the six pedigrees (48,49,(53)(54)(55)(56) covering mutations in BFSP1 and BFSP2 (Table 2) are considered, three key messages emerge: first, beaded filaments are essential to the optical properties of the eye lens; second, beaded filaments are critical to lens transparency, and mutations in BFSP1 and BFSP2 can cause cataract; and third, beaded filaments temper the aging of the eye lens.…”

Section: Role Of Beaded Filaments In the Eye Lens: Cataractcausing Mumentioning

confidence: 99%

“…When the lens phenotypes of the different mouse knockouts (46,(50)(51)(52) and the clinical descriptions for the six pedigrees (48,49,(53)(54)(55)(56) covering mutations in BFSP1 and BFSP2 (Table 2) are considered, three key messages emerge: first, beaded filaments are essential to the optical properties of the eye lens; second, beaded filaments are critical to lens transparency, and mutations in BFSP1 and BFSP2 can cause cataract; and third, beaded filaments temper the aging of the eye lens. These messages are developed in the next two sections.…”

Section: Role Of Beaded Filaments In the Eye Lens: Cataractcausing Mumentioning

confidence: 99%

Functions of the intermediate filament cytoskeleton in the eye lens

Song¹,

Landsbury²,

Dahm³

et al. 2009

J. Clin. Invest.

160

107

Intermediate filaments (IFs) are a key component of the cytoskeleton in virtually all vertebrate cells, including those of the lens of the eye. IFs help integrate individual cells into their respective tissues. This Review focuses on the lens-specific IF proteins beaded filament structural proteins 1 and 2 (BFSP1 and BFSP2) and their role in lens physiology and disease. Evidence generated in studies in both mice and humans suggests a critical role for these proteins and their filamentous polymers in establishing the optical properties of the eye lens and in maintaining its transparency. For instance, mutations in both BFSP1 and BFSP2 cause cataract in humans. We also explore the potential role of BFSP1 and BFSP2 in aging processes in the lens.

“…In the mouse, the knockout of the corresponding gene does not lead to cataracts, even if the absence of CP49 causes a subtle loss of optical clarity in the lens (Alizadeh et al, 2002;Sandilands et al, 2003). Moreover, a deletion of the splice-acceptor site in exon 2 of the mouse Bfsp2 results in a splicing of exon 1 to exon 3 and causes a frameshift in the reading frame as well as the introduction of a stop codon at position 2 of exon 3 in the Bfsp2 transcript.…”

Section: Cytoskeletal Proteinsmentioning

confidence: 99%

Congenital hereditary cataracts

Graw¹

2004

Int. J. Dev. Biol.

127

Congenital cataracts are rare and occur in developed countries with a frequency of 30 cases among 100,000 births with a further 10 cases being diagnosed during childhood. They reflect mainly genetically caused developmental alterations in the lens and surrounding ocular tissues. Even if modern Human Genetics has made large steps forward in the characterization of human hereditary disorders, the underlying developmental processes can only be investigated in model organisms. The mouse is such a good model because of its similarity (as a mammal) and its genetic characterization. This review brings together our genetic and developmental knowledge of congenital, human cataracts with the corresponding mouse models. First, early events will be influenced by genes coding for transcription factors like Pax6, Pitx3, Maf or Sox. If the lens is maturing, mutations affecting the lens membranes (aquaporins/Mip, Lim-2 or connexins) or the structural proteins of the cytosol of the lens fiber cells (the crystallins) become more important. From a genetic point of view it becomes obvious that cataract-causing mutations are not distributed randomly. The discovery of a broad variety of genes important for eye and lens development made much progress in the recent years. Nevertheless, there still remains a long list of mutations to be characterized and functionally investigated both in mouse and man indicating a broad genetic heterogeneity in that which clinicians simply refer to as a "cataract".