Analysis of nuclear fiber cell compaction in transparent and cataractous diabetic human lenses by scanning electron microscopy

BACKGROUND: Compaction of human ocular lens fiber cells as a function of both aging and cataractogenesis has been demonstrated previously using scanning electron microscopy. The purpose of this investigation is to quantify morphological differences in the inner nuclear regions of cataractous and non-cataractous human lenses from individuals with diabetes. The hypothesis is that, even in the presence of the osmotic stress caused by diabetes, compaction rather than swelling occurs in the nucleus of diabetic lenses. METHODS: Transparent and nuclear cataractous lenses from diabetic patients were examined by scanning electron microscopy (SEM). Measurements of the fetal nuclear (FN) elliptical angles (anterior and posterior), embryonic nuclear (EN) anterior-posterior (A-P) axial thickness, and the number of EN fiber cell membrane folds over 20 μm were compared. RESULTS: Diabetic lenses with nuclear cataract exhibited smaller FN elliptical angles, smaller EN axial thicknesses, and larger numbers of EN compaction folds than their non-cataractous diabetic counterparts. CONCLUSION: As in non-diabetic lenses, the inner nuclei of cataractous lenses from diabetics were significantly more compacted than those of non-cataractous diabetics. Little difference between diabetic and non-diabetic compaction levels was found, suggesting that diabetes does not affect the degree of compaction. However, consistent with previous proposals, diabetes does appear to accelerate the formation of cataracts that are similar to age-related nuclear cataracts in non-diabetics. We conclude that as scattering increases in the diabetic lens with cataract formation, fiber cell compaction is significant

Analysis of nuclear fiber cell compaction in transparent and cataractous diabetic human lenses by scanning electron microscopy

BACKGROUND: Compaction of human ocular lens fiber cells as a function of both aging and cataractogenesis has been demonstrated previously using scanning electron microscopy. The purpose of this investigation is to quantify morphological differences in the inner nuclear regions of cataractous and non-cataractous human lenses from individuals with diabetes. The hypothesis is that, even in the presence of the osmotic stress caused by diabetes, compaction rather than swelling occurs in the nucleus of diabetic lenses. METHODS: Transparent and nuclear cataractous lenses from diabetic patients were examined by scanning electron microscopy (SEM). Measurements of the fetal nuclear (FN) elliptical angles (anterior and posterior), embryonic nuclear (EN) anterior-posterior (A-P) axial thickness, and the number of EN fiber cell membrane folds over 20 μm were compared. RESULTS: Diabetic lenses with nuclear cataract exhibited smaller FN elliptical angles, smaller EN axial thicknesses, and larger numbers of EN compaction folds than their non-cataractous diabetic counterparts. CONCLUSION: As in non-diabetic lenses, the inner nuclei of cataractous lenses from diabetics were significantly more compacted than those of non-cataractous diabetics. Little difference between diabetic and non-diabetic compaction levels was found, suggesting that diabetes does not affect the degree of compaction. However, consistent with previous proposals, diabetes does appear to accelerate the formation of cataracts that are similar to age-related nuclear cataracts in non-diabetics. We conclude that as scattering increases in the diabetic lens with cataract formation, fiber cell compaction is significant

Perturbing the Ubiquitin Pathway Reveals How Mitosis Is Hijacked to Denucleate and Regulate Cell Proliferation and Differentiation In Vivo

The eye lens presents a unique opportunity to explore roles for specific molecules in cell proliferation, differentiation and development because cells remain in place throughout life and, like red blood cells and keratinocytes, they go through the most extreme differentiation, including removal of nuclei and cessation of protein synthesis. Ubiquitination controls many critical cellular processes, most of which require specific lysines on ubiquitin (Ub). Of the 7 lysines (K) least is known about effects of modification of K6.We replaced K6 with tryptophan (W) because K6 is the most readily modified K and W is the most structurally similar residue to biotin. The backbone of K6W-Ub is indistinguishable from that of Wt-Ub. K6W-Ub is effectively conjugated and deconjugated but the conjugates are not degraded via the ubiquitin proteasome pathways (UPP). Expression of K6W-ubiquitin in the lens and lens cells results in accumulation of intracellular aggregates and also slows cell proliferation and the differentiation program, including expression of lens specific proteins, differentiation of epithelial cells into fibers, achieving proper fiber cell morphology, and removal of nuclei. The latter is critical for transparency, but the mechanism by which cell nuclei are removed has remained an age old enigma. This was also solved by expressing K6W-Ub. p27(kip), a UPP substrate accumulates in lenses which express K6W-Ub. This precludes phosphorylation of nuclear lamin by the mitotic kinase, a prerequisite for disassembly of the nuclear membrane. Thus the nucleus remains intact and DNAseIIβ neither gains entry to the nucleus nor degrades the DNA. These results could not be obtained using chemical proteasome inhibitors that cannot be directed to specific tissues.K6W-Ub provides a novel, genetic means to study functions of the UPP because it can be targeted to specific cells and tissues. A fully functional UPP is required to execute most stages of lens differentiation, specifically removal of cell nuclei. In the absence of a functional UPP, small aggregate prone, cataractous lenses are formed

Alzheimer's Disease Amyloid-β Links Lens and Brain Pathology in Down Syndrome

Down syndrome (DS, trisomy 21) is the most common chromosomal disorder and the leading genetic cause of intellectual disability in humans. In DS, triplication of chromosome 21 invariably includes the APP gene (21q21) encoding the Alzheimer's disease (AD) amyloid precursor protein (APP). Triplication of the APP gene accelerates APP expression leading to cerebral accumulation of APP-derived amyloid-β peptides (Aβ), early-onset AD neuropathology, and age-dependent cognitive sequelae. The DS phenotype complex also includes distinctive early-onset cerulean cataracts of unknown etiology. Previously, we reported increased Aβ accumulation, co-localizing amyloid pathology, and disease-linked supranuclear cataracts in the ocular lenses of subjects with AD. Here, we investigate the hypothesis that related AD-linked Aβ pathology underlies the distinctive lens phenotype associated with DS. Ophthalmological examinations of DS subjects were correlated with phenotypic, histochemical, and biochemical analyses of lenses obtained from DS, AD, and normal control subjects. Evaluation of DS lenses revealed a characteristic pattern of supranuclear opacification accompanied by accelerated supranuclear Aβ accumulation, co-localizing amyloid pathology, and fiber cell cytoplasmic Aβ aggregates (∼5 to 50 nm) identical to the lens pathology identified in AD. Peptide sequencing, immunoblot analysis, and ELISA confirmed the identity and increased accumulation of Aβ in DS lenses. Incubation of synthetic Aβ with human lens protein promoted protein aggregation, amyloid formation, and light scattering that recapitulated the molecular pathology and clinical features observed in DS lenses. These results establish the genetic etiology of the distinctive lens phenotype in DS and identify the molecular origin and pathogenic mechanism by which lens pathology is expressed in this common chromosomal disorder. Moreover, these findings confirm increased Aβ accumulation as a key pathogenic determinant linking lens and brain pathology in both DS and AD