Ursula Schlötzer-Schrehardt

Collagen IV is essential for basement membrane stability but dispensable for initiation of its assembly during early development

Basement membranes are specialized extracellular matrices consisting of tissue-specific organizations of multiple matrix molecules and serve as structural barriers as well as substrates for cellular interactions. The network of collagen IV is thought to define the scaffold integrating other components such as, laminins, nidogens or perlecan, into highly organized supramolecular architectures. To analyze the functional roles of the major collagen IV isoform α1(IV)2α2(IV) for basement membrane assembly and embryonic development, we generated a null allele of the Col4a1/2 locus in mice, thereby ablating both α-chains. Unexpectedly, embryos developed up to E9.5 at the expected Mendelian ratio and showed a variable degree of growth retardation. Basement membrane proteins were deposited and assembled at expected sites in mutant embryos, indicating that this isoform is dispensable for matrix deposition and assembly during early development. However, lethality occurred between E10.5-E11.5, because of structural deficiencies in the basement membranes and finally by failure of the integrity of Reicherts membrane. These data demonstrate for the first time that collagen IV is fundamental for the maintenance of integrity and function of basement membranes under conditions of increasing mechanical demands, but dispensable for deposition and initial assembly of components. Taken together with other basement membrane protein knockouts, these data suggest that laminin is sufficient for basement membrane-like matrices during early development, but at later stages the specific composition of components including collagen IV defines integrity, stability and functionality.

Pseudoexfoliation syndrome for the comprehensive ophthalmologist. Intraocular and systemic manifestations.

BACKGROUND Renewed interest in pseudoexfoliation syndrome (PEX) may be attributed to an increased awareness of many clinical risks not only for open-angle glaucoma and its recent recognition as a generalized disorder. This review summarizes the range of intraocular and extraocular manifestations. Involvement of all tissues of the anterior segment of the eye results in a spectrum of intraocular complications that have management implication for all practicing ophthalmologists. DESIGN The study design was a review. METHODS Clinical diagnosis depends on biomicroscopy, biocytology, and laser-tyndallometry. Laboratory research methods range from light and electron microscopy, to immunohistochemical and molecular biologic approaches. OBSERVATIONS Clinical-histopathologic correlations focus on the involvement of lens (PEX-phacopathy), zonular apparatus (zonulopathy), ciliary body (cyclopathy), iris (iridopathy), trabecular meshwork (trabeculopathy), and cornea (corneal endotheliopathy) leading to the following complications: (1) open-angle glaucoma as well as angle-closure glaucoma due to pupillary and ciliary block; (2) phacodonesis, lens dislocation, and increased incidence of vitreous loss in extracapsular cataract surgery caused by alterations of the zonular apparatus and its insertion into the ciliary body and lens; (3) blood-aqueous barrier breakdown (pseudouveitis), anterior chamber hypoxia, iris stromal hemorrhage, pigment epithelial melanin dispersion, poor or asymmetric pupillary dilatation, and formation of posterior synechiae due to involvement of all cell populations of the iris; and (4) early diffuse corneal endothelial decompensation explained by a damaged and numerically reduced endothelium. CONCLUSIONS In view of the multitude of clinical complications, PEX is of relevance to comprehensive ophthalmologists, including specialists in glaucoma, cataract, cornea, neuro-ophthalmology, and retina. Special attention to the risks associated with PEX is advised before, during, and after surgery.

Factor H related protein 1 (CFHR-1) inhibits complement C5 convertase activity and terminal complex formation

Homozygous deletion of a 84-kb genomic fragment in human chromosome 1 that encompasses the CFHR1 and CFHR3 genes represents a risk factor for hemolytic uremic syndrome (HUS) but has a protective effect in age-related macular degeneration (AMD). Here we identify CFHR1 as a novel inhibitor of the complement pathway that blocks C5 convertase activity and interferes with C5b surface deposition and MAC formation. This activity is distinct from complement factor H, and apparently factor H and CFHR1 control complement activation in a sequential manner. As both proteins bind to the same or similar sites at the cellular surfaces, the gain of CFHR1 activity presumably is at the expense of CFH-mediated function (inhibition of the C3 convertase). In HUS, the absence of CFHR1 may result in reduced inhibition of terminal complex formation and in reduced protection of endothelial cells upon complement attack. These findings provide new insights into complement regulation on the cell surface and biosurfaces and likely define the role of CFHR1 in human diseases.

A stepwise approach to donor preparation and insertion increases safety and outcome of Descemet membrane endothelial keratoplasty.

Purpose: Lamellar techniques for selective replacement of diseased corneal structures have recently been improved. Descemet membrane endothelial keratoplasty (DMEK) allows the sole replacement of the endothelium-Descemet membrane layer (EDM). However, widespread use of DMEK is currently limited because of problems with donor preparation namely the tearing of the Descemet membrane and the difficulty to unfold the EDM graft in the anterior chamber (AC). Methods: A standardized DMEK procedure that allows safe preparation of EDM, atraumatic introduction of EDM into the AC, reliable orientation of EDM during surgery, and stepwise unfolding within the AC is described in 80 patients. Visual acuity and corneal endothelial cell density were assessed. Results: A stepwise approach using a novel bimanual underwater technique to harvest EDM from donor corneal buttons allows reproducible generation of grafts without tearing the Descemet membrane. Injection of the EDM roll into the AC is achieved by use of a standard injector cartridge, whereas the depth of AC is maintained by an irrigation handpiece. Marks at the margin of EDM allow orientation. Finally, unfolding EDM in the AC is achieved by sequential use of water jets and air bubbles. In the early phase of the learning curve, 4 patients were regrafted because of graft failure. Endothelial cell density decreased from 2600 ± 252 to 1526 ± 341 cells per square millimeter 1 month after DMEK. Conclusions: A novel technique for graft preparation and EDM injection results in improved safety with a high rate of successful DMEKs.

PSEUDOEXFOLIATION SYNDROME AND ANEURYSMS OF THE ABDOMINAL AORTA

We assessed the association between pseudoexfoliation syndrome, a common age-related fibrillopathy of unknown cause, and vascular diseases, especially aneurysms of the abdominal aorta. In a prospective single-blind study we ophthalmoscopically examined 55 patients with aneurysms of the abdominal aorta and 41 controls with carotic-artery occlusion. 24 of 55 patients with aortic aneurysm showed signs of manifest (17 of 55 patients) or early-stage (seven of 55) pseudoexfoliation syndrome. Eight of 41 control patients showed manifest (seven of 41 patients) and early (one of 41) ocular pseudoexfoliation (p=0.016). These findings, including histopathological examinations, suggest an association between aneurysms of the abdominal aorta and pseudoexfoliation syndrome.

Kindlin-1 is a phosphoprotein involved in regulation of polarity, proliferation, and motility of epidermal keratinocytes.

A novel family of focal adhesion proteins, the kindlins, is involved in attachment of the actin cytoskeleton to the plasma membrane and in integrin-mediated cellular processes. Deficiency of kindlin-1, as a result of loss-of-function mutations in the KIND1 gene, causes Kindler syndrome, an autosomal recessive genodermatosis characterized by skin blistering, progressive skin atrophy, photosensitivity and, occasionally, carcinogenesis. Here we characterized authentic and recombinantly expressed kindlin-1 and show that it is localized in basal epidermal keratinocytes in a polar fashion, close to the cell surface facing the basement membrane, in the areas between the hemidesmosomes. We identified two forms of kindlin-1 in keratinocytes, with apparent molecular masses of 78 and 74 kDa, corresponding to phosphorylated and desphosphorylated forms of the protein. In kindlin-1-deficient skin, basal keratinocytes show multiple abnormalities: cell polarity is lost, proliferation is strongly reduced, and several cells undergo apoptosis. In vitro, deficiency of kindlin-1 in keratinocytes leads to strongly reduced cell proliferation, decreased adhesion, undirected motility, and intense protrusion activity of the plasma membrane. Taken together, these results show that kindlin-1 plays a role in keratinocyte adhesion, polarization, proliferation, and migration. It is involved in organization and anchorage of the actin cytoskeleton to integrin-associated signaling platforms.

Why is glaucoma associated with exfoliation syndrome

Exfoliation syndrome (XFS) is an age-related, generalized disorder of the extracellular matrix characterized by production and progressive accumulation of a fibrillar material in tissues throughout the anterior segment and also in connective tissue portions of various visceral organs. Mature exfoliation fibrils are composed of 8-10 nm microfibrils resembling elastic microfibrils. The exact chemical composition of exfoliation material (XFM) remains unknown. It appears to consist of a complex glycoprotein/ proteoglycan structure composed of a protein core surrounded by abundant glycoconjugates. The protein components include both non-collagenous basement membrane components and epitopes of the elastic fiber system, particularly components of elastic microfibrils. Overall, XFS is the most common identifiable cause of glaucoma, accounting for the majority of cases in some countries, and causing both open-angle glaucoma and angle-closure glaucoma. Iridolenticular friction leads to loss of XFM from the anterior lens surface and disruption of the iris pigment epithelium, resulting in pigment deposition in the trabecular meshwork, which also produces XFM locally. The primary cause of chronic pressure elevation appears to be the active involvement of trabecular cells and Schlemms canal cells in particular, in the generalized pathologic matrix process with subsequent degenerative changes of Schlemms canal and adjacent tissues. Narrow angles and angle-closure are common in XFS. Pupillary block may be caused by a combination of posterior synechiae, increased iris thickness or rigidity, or anterior lens movement secondary to zonular weakness or dialysis. Enlargement of the lens due to cataract formation and relative pupillary constriction are additional factors.

Corneal Limbal Microenvironment Can Induce Transdifferentiation of Hair Follicle Stem Cells into Corneal Epithelial‐like Cells

The aim of this study was to investigate the transdifferentiation potential of murine vibrissa hair follicle (HF) stem cells into corneal epithelial‐like cells through modulation by corneal‐ or limbus‐specific microenvironmental factors. Adult epithelial stem cells were isolated from the HF bulge region by mechanical dissection or fluorescence‐activated cell sorting using antibodies to α6 integrin, enriched by clonal expansion, and subcultivated on various extracellular matrices (type IV collagen, laminin‐1, laminin‐5, fibronectin) and in different conditioned media derived from central and peripheral corneal fibroblasts, limbal stromal fibroblasts, and 3T3 fibroblasts. Cellular phenotype and differentiation were evaluated by light and electron microscopy, real‐time reverse transcription‐polymerase chain reaction, immunocytochemistry, and Western blotting, using antibodies against putative stem cell markers (K15, α6 integrin) and differentiation markers characteristic for corneal epithelium (K12, Pax6) or epidermis (K10). Using laminin‐5, a major component of the corneo‐limbal basement membrane zone, and conditioned medium from limbal stromal fibroblasts, clonally enriched HF stem and progenitor cells adhered rapidly and formed regularly arranged stratified cell sheets. Conditioned medium derived from limbal fibroblasts markedly upregulated expression of cornea‐specific K12 and Pax6 on the mRNA and protein level, whereas expression of the epidermal keratinocyte marker K10 was strongly downregulated. These findings suggest that adult HF epithelial stem cells are capable of differentiating into corneal epithelial‐like cells in vitro when exposed to a limbus‐specific microenvironment. Therefore, the HF may be an easily accessible alternative therapeutic source of autologous adult stem cells for replacement of the corneal epithelium and restoration of visual function in patients with ocular surface disorders. STEM CELLS 2009;27:642–652

A Histopathologic Study of Zonular Instability in Pseudoexfoliation Syndrome

A weak zonular apparatus has been postulated to account for the high incidence of phacodonesis, lens dislocation, and vitreous complications during extracapsular cataract surgery in eyes with pseudoexfoliation syndrome. To clarify and localize the cause of zonular weakness, we examined 11 eyes with pseudoexfoliation syndrome by using scanning and transmission electron microscopy. The production of pseudoexfoliation material by both the nonpigmented ciliary epithelium and the pre-equatorial lens epithelium resulted in typical alterations of the zonules at three levels. (1) At their origin and anchorage in the ciliary body, the zonular bundles were separated from the disrupted basement membrane of the nonpigmented epithelium by intercalating pseudoexfoliation fibers. (2) In the pars plicata of the ciliary body, pseudoexfoliation material infiltrated the zonular bundles passing alongside the ciliary processes leading to zonular rupture. (3) At their attachment to the anterior lens capsule, the zonular lamella was focally lifted and subsequently ruptured by pseudoexfoliation masses erupting through the capsular surface. The immunohistochemical demonstration of lysosomal enzymes within pseudoexfoliation aggregates indicates that proteolytic mechanisms facilitate zonular disintegration. Ophthalmologists treating eyes with pseudoexfoliation syndrome should be aware of these alterations.

Association of LOXL1 Common Sequence Variants in German and Italian Patients with Pseudoexfoliation Syndrome and Pseudoexfoliation Glaucoma

PURPOSE Three common sequence variants in the lysyl oxidase-like 1 (LOXL1) gene were recently associated with both pseudoexfoliation (PEX) and pseudoexfoliation glaucoma (PEXG) in populations from Iceland and Sweden. In this study, the genetic association of these variants was investigated in patients with PEX or PEXG of German and Italian descent. METHODS The three LOXL1 single-nucleotide polymorphisms (SNPs), one intronic (rs2165241) and two nonsynonymous coding SNPs (rs1048661: R141L and rs3825942: G153D) were genotyped in a total of 726 unrelated patients with PEX or PEXG (517 Germans and 209 Italians) and 418 healthy subjects who had normal findings in repeated ophthalmic examinations, and a genetic association study was performed. RESULTS Strong association with the three LOXL1 common sequence variants was seen in both the PEX and PEXG patient groups independent of their geographic origin (rs2165241, combined OR = 3.42, P = 1.28 x 10(-40); rs1048661, OR = 2.43, P = 2.90 x 10(-19); and rs3825942, OR = 4.87, P = 8.22 x 10(-23)). Similarly, the common frequent haplotype (G-G) composed of the two coding SNPs (rs1048661 and rs3825942) was strongly associated in PEX and PEXG cohorts of both populations with the disease (combined OR = 3.58, P = 5.21x 10(-43)). CONCLUSIONS Genetic variants in LOXL1 confer risk to PEX in German and Italian populations, independent of the presence of secondary glaucoma, confirming findings in patients from Northern Europe.