Connexin50D47A Decreases Levels of Fiber Cell Connexins and Impairs Lens Fiber Cell Differentiation

Berthoud, Viviana M.; Minogue, Peter J.; Yu, Helena; Schroeder, Richard; Snabb, Joseph I.; Beyer, Eric C.

doi:10.1167/iovs.13-13188

Cited by 35 publications

(74 citation statements)

References 32 publications

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“…In the lens, Cx50 is expressed in both the epithelial and fiber cell compartments. Mutations in Gja8 result in lenses that are too small (Berthoud et al, 2013; Xia et al, 2012). Similarly, targeted disruption of Gja8 in the lens invariably affects growth, with knockout lenses weighing ≈40% less than wild types (Rong et al, 2002; White et al, 1998).…”

Section: Molecular Genetic Insights Into Lens Growth Regulationmentioning

confidence: 99%

The lens growth process

Bassnett

Šikić

2017

Progress in Retinal and Eye Research

104

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The factors that regulate the size of organs to ensure that they fit within an organism are not well understood. A simple organ, the ocular lens serves as a useful model with which to tackle this problem. In many systems, considerable variance in the organ growth process is tolerable. This is almost certainly not the case in the lens, which in addition to fitting comfortably within the eyeball, must also be of the correct size and shape to focus light sharply onto the retina. Furthermore, the lens does not perform its optical function in isolation. Its growth, which continues throughout life, must therefore be coordinated with that of other tissues in the optical train. Here, we review the lens growth process in detail, from pioneering clinical investigations in the late nineteenth century to insights gleaned more recently in the course of cell and molecular studies. During embryonic development, the lens forms from an invagination of surface ectoderm. Consequently, the progenitor cell population is located at the surface and differentiated cells are confined to the interior. The interactions that regulate cell fate thus occur within the obligate ellipsoidal geometry of the lens. In this context, mathematical models are particularly appropriate tools with which to examine the growth process. In addition to identifying key growth determinants, such models constitute a framework for integrating cell biological and optical data, helping clarify the relationship between gene expression in the lens and image quality at the retinal plane.

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Section: Molecular Genetic Insights Into Lens Growth Regulationmentioning

confidence: 99%

The lens growth process

Bassnett

Šikić

2017

Progress in Retinal and Eye Research

104

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“…Homozygous Cx50D47A lenses showed a significant increase in ATF4 levels associated with increases in Chop transcript and protein, suggesting activation of a UPR. These changes probably occurred in organellecontaining fiber cells that reach deeper into the lens in Cx50D47A mice (3).…”

Section: Discussionmentioning

confidence: 98%

“…When expressed in transfected cells, Cx50D47N and Cx50D47A localize mostly within the ER (1). Lenses from mice expressing Cx50D47A have nuclear cataracts, reduced sizes, and impaired denucleation (3). Some immunoreactive Cx50 localizes intracellularly in lens epithelial cells from these mice (3).…”

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confidence: 99%

“…Lenses from mice expressing Cx50D47A have nuclear cataracts, reduced sizes, and impaired denucleation (3). Some immunoreactive Cx50 localizes intracellularly in lens epithelial cells from these mice (3). Homozygous Cx50D47A lenses have increased levels of ␣B-crystallins (3), which are responsive to several types of stress in different cell types, including lens epithelial cells (4 -7).…”

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The Cataract-linked Mutant Connexin50D47A Causes Endoplasmic Reticulum Stress in Mouse Lenses

Berthoud¹,

Minogue²,

Lambert

et al. 2016

Journal of Biological Chemistry

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Mice expressing connexin50D47A (Cx50D47A) exhibit nuclear cataracts and impaired differentiation. Cx50D47A does not traffic properly, and homozygous mutant lenses show increased levels of the stress-responsive ␣B-crystallins. Therefore, we assessed whether expression of Cx50D47A led to endoplasmic reticulum (ER) stress in the lens in vivo. Although pharmacologic induction of ER stress can be transduced by three different pathways, we found no evidence for activation of the IRE1␣ or ATF6 pathways in Cx50D47A-expressing lenses. In contrast, heterozygous and homozygous Cx50D47A lenses showed an increase in phosphorylated PERK immunoreactivity and in the ratio of phosphorylated to total EIF2␣ (2.4-and 3.3-fold, respectively) compared with wild type. Levels of ATF4 were similar in wild type and heterozygous lenses but elevated in homozygotes (391%). In both heterozygotes and homozygotes, levels of calreticulin protein were increased (184 and 262%, respectively), as was Chop mRNA (1.9-and 12.4-fold, respectively). CHOP protein was increased in homozygotes (384%). TUNEL staining was increased in Cx50D47A lenses, especially in homozygous mice. Levels of two factors that may be pro-survival, Irs2 and Trib3, were greatly increased in homozygous lenses. These results suggest that expression of Cx50D47A induces ER stress, triggering activation of the PERK-ATF4 pathway, which potentially contributes to the lens pathology and leads to increased expression of anti-apoptotic factors, allowing cell survival.Proteins that do not traffic properly or are misfolded can cause endoplasmic reticulum (ER) 2 stress. To compensate for the disturbance of proteostasis, cells transduce ER stress through at least three different signaling pathways: (a) the inositol-requiring enzyme 1 (IRE1␣)-dependent, (b) the activating transcription factor 6 (ATF6)-dependent, and (c) the PRKR-like ER kinase (PERK)-dependent pathways. Prolonged and uncompensated ER stress triggers the unfolded protein response (UPR), which may ultimately target the cells for apoptosis.Many disease-linked connexin mutants show impaired cellular trafficking. One such mutant has a missense mutation in the lens gap junction protein, connexin50 (Cx50), affecting amino acid residue 47 (Cx50D47N in humans and Cx50D47A in mice) and is linked to congenital cataracts (1, 2). When expressed in transfected cells, Cx50D47N and Cx50D47A localize mostly within the ER (1). Lenses from mice expressing Cx50D47A have nuclear cataracts, reduced sizes, and impaired denucleation (3). Some immunoreactive Cx50 localizes intracellularly in lens epithelial cells from these mice (3). Homozygous Cx50D47A lenses have increased levels of ␣B-crystallins (3), which are responsive to several types of stress in different cell types, including lens epithelial cells (4 -7). These observations suggest that expression of a Cx50D47 mutant may cause ER stress in the lens and contribute to pathology in this organ.The current understanding of cellular responses to ER stress is based on many studies in cultured cells...

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“…Connexins were detected by immunofluorescence and immunoblotting as previously described using anti-Cx46, anti-Cx50 and three different anti-Cx23 antibodies (Berthoud et al, 2013). One anti-Cx23 antibody (Sigma-Aldrich) was raised against a peptide corresponding to 26 of the 36 amino acids in the second extracellular loop of the predicted human Cx23, which shares 65% sequence identity with the mouse Cx23 including a stretch of 8 consecutive identical amino acids.…”

Section: Methodsmentioning

confidence: 99%

Connexin23 deletion does not affect lens transparency

Berthoud

Minogue

Snabb

et al. 2016

Experimental Eye Research

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While connexin46 (Cx46) and connexin50 (Cx50) are crucial for maintaining lens transparency and growth, the contributions of a more recently identified lens fiber connexin, Cx23, are poorly understood. Therefore, we studied the consequences of absence of Cx23 in mouse lenses. Cx23-null mice were generated by homologous Cre recombination. Cx23 mRNA was abundantly expressed in wild type lenses, but not in Cx23-null lenses. The transparency and refractive properties of Cx23-null lenses were similar to wild type lenses when examined by darkfield microscopy. Neither the focusing ability nor the light scattering was altered in the Cx23-null lenses. While both Cx46 and Cx50 localized to appositional fiber cell membranes (as in wild type lenses), their levels were consistently (but not significantly) decreased in homozygous Cx23-null lenses. These results suggest that although Cx23 expression can influence the abundance of the co-expressed lens fiber connexins, heterozygous or homozygous expression of a Cx23-null allele does not alter lens transparency.

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Connexin50D47A Decreases Levels of Fiber Cell Connexins and Impairs Lens Fiber Cell Differentiation

Cited by 35 publications

References 32 publications

The lens growth process

The lens growth process

The Cataract-linked Mutant Connexin50D47A Causes Endoplasmic Reticulum Stress in Mouse Lenses

Connexin23 deletion does not affect lens transparency

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