Synthesis of lens capsule and plasma membrane glycoproteins by lens epithelial cells and fibers in the rat

A multifunction murine Col4a1 allele reveals potential gene therapy parameters for Gould syndrome

Basement membranes (BMs) are specialized extracellular matrix (ECM) structures essential for organ morphogenesis, architecture, and function. BM composition and properties vary between tissues, developmental stages, and disease states, and there is only a rudimentary understanding of BM dynamics. Here, we introduce a versatile mouse model carrying a multifunctional dual-color fluorescence tagged allele with knockout potential for the fundamental BM component type IV collagen alpha 1 (COL4A1). This allele enables the characterization of cell type- and time-specific contributions to BMs and the generation of a conditional Col4a1 null allele. We demonstrate the utility of this unique genetic resource in providing clinically relevant insights for individuals with Gould syndrome - a multisystem disorder caused by COL4A1 and COL4A2 mutations. We show active COL4A1 turnover in postnatal cerebrovascular BMs, identifying a potential interventional window for cerebrovascular manifestations associated with Gould syndrome. We also demonstrate that heterozygous Col4a1 deletion is significantly less pathogenic than dominant Col4a1 missense mutations, which has important implications for gene therapy.

Lysyl hydroxylase 3 is required for normal lens capsule formation and maintenance of lens epithelium integrity and fate

Lens abnormalities are a major cause of reduced vision and blindness. One mechanism that can lead to reduced lens transparency, i.e. cataract, is abnormal behavior of lens epithelial cells (LECs), the precursors of the transparent lens fiber cells. Here we describe a zebrafish mutation causing the embryonic lens epithelium to generate cellular masses comprising partially differentiated lens fiber cells. We identify the mutant gene as plod3, which encodes for Lysyl hydroxylase 3 (Lh3), an enzyme essential for modification of collagens, including Collagen IV, a main component of the lens capsule. We show that plod3-deficient lenses have abnormal lens epithelium from an early developmental stage, as well as abnormal lens capsules. Subsequently, upregulation of TGFβ signaling takes place, which drives the formation of lens epithelial cellular masses. We identify a similar phenotype in Collagen IVα5-deficient embryos, suggesting a key role for the defective lens capsule in the pathogenesis. We propose that plod3 and col4a5 mutant zebrafish can serve as useful models for better understanding the biology of LECs during embryonic development and in formation of lens epithelium-derived cataract.

Eye organogenesis: A hierarchical view of ocular development

This chapter provides an overview of the early developmental origins of six ocular tissues: the cornea, lens, ciliary body, iris, neural retina, and retina pigment epithelium. Many of these tissue types are concurrently specified and undergo a complex set of morphogenetic movements that facilitate their structural interconnection. Within the context of vertebrate eye organogenesis, we also discuss the genetic hierarchies of transcription factors and signaling pathways that regulate growth, patterning, cell type specification and differentiation.

The lens capsule

The lens capsule is a modified basement membrane that completely surrounds the ocular lens. It is known that this extracellular matrix is important for both the structure and biomechanics of the lens in addition to providing informational cues to maintain lens cell phenotype. This review covers the development and structure of the lens capsule, lens diseases associated with mutations in extracellular matrix genes and the role of the capsule in lens function including those proposed for visual accommodation, selective permeability to infectious agents, and cell signaling.

Thickening of the amnion basement membrane and its relationship to placental inflammatory lesions and fetal and maternal disorders

OBJECTIVE

The aim of this study is the morphological and morphometric analysis of the basement membrane amniotic epithelium of the chorionic plate to establish possible correlation between the basement membrane amniotic epithelium thickening and maternal and fetal disorders.

STUDY DESIGN

Ninety-one placentas of infants delivered in Medical Hospital School were studied with hematoxylin-eosin (H&E) and Periodic Acid Schiff (PAS) methods, morphometric and ultrastructural analysis.

RESULTS

Of the 91 placentas analyzed, 17 (18.6%) were normal with regard to placental morphology, fetal and maternal history. Basement membrane amniotic epithelium thickening was significantly greater in the cases associated with chorioamnionitis (P=0.013), villitis (P=0.040), maternal hypertension syndromes during pregnancy (P=0.027) and stillborn (P=0.040) babies. The electron microscopic examination of the basement membrane amniotic epithelium identified a structural alteration and edema of the dense lamina.

CONCLUSION

Thickening of the basement membrane amniotic epithelium was associated with morphologic placental abnormalities and/or fetal or maternal disorders. Thickening of the basement membrane amniotic epithelium was identified away from the site of placental inflammation, possibly being a consequence of cytokines, supporting more than a local effect. This could be a new insight into the pathogenesis of fetal and maternal complications associated with inflammatory placental lesions.

Mechanical properties of the human lens capsule

The human lens capsule has recently been the subject of much attention in an attempt to understand its physiological function in relation to the accommodative function, its functional reserve in the elderly population, and its potential in relation to cataract surgery. This overview presents our current knowledge of the mechanical properties of the human lens capsule, discussed on basis of its structure and its role in accommodation and cataract surgery.

Vocal cord basement membrane in non-sudden infant death syndrome cases

Vocal cord basement membrane thickening (VCBMT) has been observed in children with sudden infant death syndrome (SIDS). It has been proposed that this lesion could be used as a positive indicator of this syndrome in autopsies of children who have died unexpectedly. The present investigation aimed to analyze vocal cord basement membranes from autopsies of children 0 to 365 days old. A total of 134 larynges were analyzed. Histological sections of paraffin-embedded larynges stained with H&E and submitted to histochemical staining with periodic acid-Schiff (PAS), Masson's trichrome, syrius red, and Carstairs were used for light microscopy analysis. Immunohistochemistry with monoclonal anti-collagen IV antibody was used to determine the nature of VCBMT. The study was completed with morphometry of H&E- and PAS-stained sections and revision of the clinical information contained in the hospital files. VCBMT was found in 25 cases (18.7%) and showed characteristics of normal basement membrane, including immunoreactivity to collagen IV. Our data support the conclusions that VCBMT is frequently seen in pediatric autopsies, is seen in children in all age-groups studied whose deaths were due to causes other than SIDS, and is commonly associated with infectious diseases. Like SIDS, VCBMT occurs in the first year of life.

Glycosaminoglycans in components of the rabbit eye: synthesis and characterization

PURPOSE

To trace the eye components involved in proteoglycan synthesis and to characterize the sulfated glycosaminoglycans which are associated to these macromolecules.

METHODS

Sodium [(35)S]-sulfate was injected intravitreally and the rabbits were killed at different time intervals after the injection. The glycosaminoglycans of choroid, ciliary body, cornea, iris, lens capsule, retina and sclera were extracted and processed for estimations of their specific activities, and for electrophoresis plus autoradiography with or without previous treatment with specific enzymes. In addition, methacrylate sections of the eyes were analysed by autoradiography.

RESULTS

The peak of specific activities of the glycosaminoglycans of all eye components occurred at 2 days after the intravitreal injection of [( 35)S]-sulfate. The autoradiography of the agarose gels revealed three types of glycosaminoglycans, namely, heparan-, chondroitin- and dermatan sulfate, only in the retina. The other eye components contained heparan sulfate and either chondroitin or dermatan sulfate. Tissue autoradiography together with the biochemical techniques contributed to unravel the origin of the glycosaminoglycans in the eye components.

CONCLUSIONS

The results of the present investigation have shown that heparan sulfate, contrasting to chondroitin sulfate and dermatan sulfate, is synthesized in all eye components studied and that the glycosaminoglycan composition differs according to the tissue of origin.

TGF-beta elicits fibronectin secretion and proliferation in cultured chick lens epithelial cells

PURPOSE

To determine if the cataract forming influence of TGF-beta on lens cells is due to its effects on the ECM.

METHODS

Primary cultures of chick lens annular pad cells were exposed to TGF-beta and various exogenously supplied components of the lens capsule. Proliferative response were measured through tritiated thymidine incorporation into DNA. Cell spreading accompanying increased matrix interactions and growth was monitored with phase contrast microscopy. ECM proteins were detected in culture media and as deposited matrices with Western blotting and silver staining. TGF-beta receptors were identified with Western blotting.

RESULTS

Chick lens cells were shown to express type I and II TGF-beta receptors. TGF-beta stimulated cell growth and ECM production particularly with regard to fibronectin. Fibronectin was secreted into the culture medium and deposited onto plastic substrates. Plating cells on ECM components found in the lens capsule further increased their growth in response to TGF-beta.

CONCLUSIONS

These results indicate that TGF-beta may have a normal function in the lens regulating capsular protein production. The potent stimulation of lens cell growth by TGF-beta may be due to mis-regulated production of lens capsular proteins not normally found in great abundance.

Radioactive fucose as a tool for studying glycoprotein secretion

The efficiency and reliability of radioactive fucose as a specific label for newly synthesized glycoproteins were investigated. Young adult male rabbits were injected intravitreally with [3H]-fucose, [3H]-galactose. [3H]-mannose, N-acetyl-[3H]-glucosamine or N-acetyl-[3H]-mannosamine, and killed 40 h after injection. In another series of experiments rabbits were injected with either [3H]-fucose or several tritiated amino acids and the specific activity of the vitreous proteins was determined. Vitreous samples were also processed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and histological sections of retina, ciliary body and lens (the eye components around the vitreous body) were processed for radioautography. The specific activity (counts per minute per microgram of protein) of the glycoproteins labeled with [3H]-fucose was always much higher than that of the proteins labeled with any of the other monosaccharides or any of the amino acids. There was a good correlation between the specific activity of the proteins labeled by any of the above precursors and the density of the vitreous protein bands detected by fluorography. This was also true for the silver grain density on the radioautographs of the histological sections of retina, ciliary body and lens. The contribution of radioautography (after [3H]-fucose administration) to the elucidation of the biogenesis of lysosomal and membrane glycoproteins and to the determination of the intracellular process of protein secretion was reviewed. Radioactive fucose is the precursor of choice for studying glycoprotein secretion because it is specific, efficient and practical for this purpose.

Spatio-temporal distribution of acidic and basic FGF indicates a role for FGF in rat lens morphogenesis

As part of an investigation into the role of FGF in lens development, we have studied the distribution of both aFGF and bFGF during eye morphogenesis from embryonic days 10 to 18 (E10-E18) in the rat. For aFGF, reactivity was found only in ectoderm at E10, prior to contact between the optic vesicle and presumptive lens ectoderm. During lens placode formation (E11) there was a transient, diffuse reactivity for aFGF in anterior optic vesicle cells directly apposed to the labelled ectoderm of the lens placode. At E12 the diffuse reactivity of the lens placode had changed to a discrete localisation along the basolateral surfaces of differentiating cells in the lens pit. Similar reactivity was associated with neuroblasts along the inner margin of the optic cup. At the early lens vesicle stage (E13) the baso-lateral aFGF-like reactivity associated with elongating lens cells was more intense and extensive. From the late lens vesicle stage (E14) to E18, reactivity in the lens was increasingly restricted to the equatorial regions which incorporate the germinative and transitional zones. From E16 to E18, aFGF-like reactivity in the retina was predominantly localised in the peripheral regions corresponding to the developing ciliary body and iris and in the central retina associated with ganglion cell axons. For bFGF, weak reactivity was detectable as early as E13 in the developing lens capsule and increased in intensity during lens development with the posterior capsule reacting more intensely than the anterior capsule. Retinal bFGF-like reactivity was first detected at E14, associated with differentiating ganglion cells in the central retina. From E16 to E18 the retinal ganglion cells showed increasing reactivity and the pattern of reactivity followed the centro-peripheral pattern of retinal development. Thus reactivity for aFGF is first detected in presumptive lens ectoderm and subsequently in optic vesicle cells which are closely associated with lens ectoderm. This raises the possibility that aFGF may be involved in inductive interactions between presumptive lens ectoderm and optic vesicle. Furthermore the localisation patterns established for both aFGF and bFGF during lens and retina morphogenesis suggest an important role for FGF in regulating their morphogenesis and growth.

Acidic and basic FGF in ocular media and lens: implications for lens polarity and growth patterns

We have shown previously that FGF induces lens epithelial cells in explant culture to proliferate, migrate and differentiate into fibre cells in a progressive concentration-dependent manner. In situ, these processes occur in a distinct anterior-posterior pattern in clearly defined regions of the lens. Thus anterior-posterior differences in the bio-availability of FGF in the lens environment may play a role in determining lens polarity and growth patterns. In this study, using heparin chromatography and western blotting (or ELISA), we established that both acidic and basic FGF are present in the aqueous and vitreous (the ocular media that bathe the anterior and posterior compartments of the lens, respectively). In addition, substantially more FGF was recovered from vitreous than from aqueous. Both forms of FGF were also detected in lens fibre cells and capsule. A truncated form of basic FGF (less than 20 × 10(3) M(r)) predominated in every case with traces of higher M(r) forms in lens cells. For acidic FGF, the classical full-length form (about 20 × 10(3) M(r)) predominated in lens cells and a truncated form was found in vitreous. The capsule contained a higher M(r) form. Using our explant system, we also tested the biological activity of ocular media and FGF fractions obtained from vitreous and lens cells. Vitreous but not aqueous contained fibre-differentiating activity. Furthermore, virtually all the fibre-differentiating activity of vitreous was shown to be FGF-associated, as follows: (a) this activity remained associated with FGF during fractionation of vitreous by heparin and Mono-S chromatography and (b) the activity of the major FGF-containing fraction was blocked by antibodies to acidic and basic FGF. Posterior, but not anterior, capsule was shown to have mitogenic activity, which was neutralised by FGF antibodies and associated only with the cellular surface. These results support our hypothesis that FGF is involved in determining the behaviour of lens cells in situ. In particular, a key role for FGF in determining lens polarity and growth patterns is suggested by the anterior-posterior differences in the bio-availability of FGF in the ocular media and capsule.

The roles of laminin and fibronectin in the development of the lens capsule

This study examines the distribution of laminin and fibronectin in the rat lens capsule during development. Both these extracellular matrix glycoproteins are localised in the interspace between presumptive lens and presumptive retina as well as in their basal laminae. The lens capsule arises from multilayering of the basal lamina of the lens cells. Immunofluorescence localises both laminin and fibronectin in the capsule at 16 days of embryonic development, although reactivity for fibronectin is much weaker than for laminin. In the 19 day embryo only laminin is detected. This indicates that during embryonic development fibronectin becomes a minor component of lens cell ECM and is not accumulated in the developing capsule. The roles of laminin and fibronectin in promoting cell migration during development were analysed in explant cultures. Lens epithelial explants from 16, 17 and 19 day old embryos and neonatal rats were grown on a laminin or fibronectin substratum. Lens cells from all ages of rats migrated on the laminin substratum, whereas lens cells progressively lost the ability to migrate on a fibronectin substratum as the age of the donor increased. This developmental loss of ability to migrate on fibronectin in vitro coincides with the developmental loss of fibronectin from the lens capsule in vivo. Therefore, we propose that whilst both laminin and fibronectin may be important for promoting migration of lens cells on their substratum at early stages of lens morphogenesis, during development laminin takes over as the key molecule that promotes migration on the capsule.

Traffic through the Golgi apparatus as studied by radioautography

The ability to radiolabel biological molecules, in conjunction with radioautographic or cell fractionation techniques, has brought about a revolution in our knowledge of dynamic cellular processes. This has been particularly true since the 1940's, when isotopes such as 35S and 14C became available, since these isotopes could be incorporated into a great variety of biologically important compounds. The first dynamic evidence for Golgi apparatus involvement in biosynthesis came from light microscope radioautographic studies by Jennings and Florey in the 1950's, in which label was localized to the supranuclear Golgi region of goblet cells soon after injection of 35S-sulfate. When the low energy isotope tritium became available, and when radioautography could be extended to the electron microscope level, a great improvement in spatial resolution was achieved. Studies using 3H-amino acids revealed that proteins were synthesized in the rough endoplasmic reticulum, migrated to the Golgi apparatus, and thence to secretion granules, lysosomes, or the plasma membrane. The work of Neutra and Leblond in the 1960's using 3H-glucose provided dramatic evidence that the Golgi apparatus was involved in glycosylation. Work with 3H-mannose (a core sugar in N-linked side chains), showed that this sugar was incorporated into glycoproteins in the rough endoplasmic reticulum, providing the first radioautographic evidence that glycosylation of proteins did not occur solely in the Golgi apparatus. Studies with the tritiated precursors of fucose, galactose, and sialic acid, on the other hand, showed that these terminal sugars are mainly added in the Golgi apparatus. With its limited spatial resolution, radioautography cannot discriminate between label in adjacent Golgi saccules. Nonetheless, in some cell types, radioautographic evidence (along with cytochemical and cell fractionation data) has indicated that the Golgi is subcompartmentalized in terms of glycosylation, with galactose and sialic acid being added to glycoproteins only within the trans-Golgi compartment. In the last ten years, radioautographic tracing of radioiodinated plasma membrane molecules has indicated a substantial recycling of such molecules to the Golgi apparatus.

Partial characterization, origin and turnover of glycoproteins of the rabbit vitreous body

L-[3H]fucose was injected intravitreally into rabbits that were killed from 1 hr to 28 days after injection. The vitreous bodies were processed for radiometric techniques, and electrophoresis followed by fluorography. Unbound [3H]fucose remained at a high level up to 1 day, whereas the peak of [3H]fucose bound to glycoproteins was observed at 3 days after injection with a continuous decrease afterwards. The turnover rate of vitreous glycoproteins was estimated at 4.37% per day and their turnover time at 22.85 days. Electrophoresis and fluorography combined revealed about 14 bands of glycoproteins with fucose residues and there were strong indications of differences in turnover rate among individual glycoproteins. The most prominent band in the Coomassie blue-stained gels was the one having a molecular weight of 69 kDa and it was not labeled with [3H]fucose. This band was tentatively identified as serum albumin. On the other hand, the 14 bands labeled with [3H]fucose were glycoproteins originating from within the eye, that is, they are intrinsic constituents of the vitreous body.

The origin of the intrinsic glycoproteins of the rabbit vitreous body: an immunohistochemical and autoradiographic study

A cartilage matrix glycoprotein (CMGP), previously identified in human and bovine vitreous, now has been found in the vitreous body of rabbits aged 1-22 months by immunohistochemical techniques. Epithelial cells of the inner layer of the ciliary epithelium contain material that has immunologic cross-reactivity with a specific antibody to CMGP. These cells also secrete glycoproteins, as determined by autoradiography after intravitreal injection of [3H]fucose. Approximately 14 bands, representing intrinsic glycoproteins containing fucose residues, can be identified in fluorograms of SDS-polyacrylamide gels of vitreous bodies from 6- and 22-month-old rabbits. Fluorograms of gels of samples of vitreous and ciliary bodies from several time points after intravitreal injection of [3H]fucose reveal at least seven comigrating protein bands and also demonstrate turnover of the labeled ciliary body glycoproteins. These results suggest that the inner layer of the ciliary epithelium is the source of the glycoproteins of the vitreous body and that these glycoproteins undergo turnover, probably throughout the entire life of the animals.

A morphometric analysis of the development of the rat lens capsule

This study analysed patterns of growth of the lens capsule by measuring capsule thickness at 13, 16 and 19 days of embryonic development and 2, 21, 140 and 600 days of post-natal development. The major findings were that, at early stages of embryonic development, the posterior capsule was thicker than the anterior capsule. However, at later stages, the posterior capsule did not increase in thickness whereas the anterior capsule continued to thicken so that, by 2 days of post-natal development, the situation was reversed and the anterior capsule was significantly thicker than the posterior capsule. This trend continued and by 600 days post-natal development, the anterior capsule was 7.5 times thicker than the posterior capsule. In these older lenses the capsule tapered sharply in thickness from the anterior to the posterior equatorial region. These regional differences in thickness of the lens capsule, and the changes reported during development, may reflect changes in capsule production by epithelial and fibre cells as they differentiate.