PURPOSE: Lysyl oxidases, a family comprising lysyl oxidase (LOX) and four LOX-like enzymes (LOXL1-4), catalyse the cross-linking of elastin and collagen fibrils. Keratoconus (KC) is characterized by progressive thinning leading to irregular astigmatism, resulting in significant visual impairment. Although the pathogenesis of KC remains unclear, one of the current hypotheses is based on alterations in the organization and structure of collagen fibrils. To extend existing general knowledge about cross-linking enzymes in the human cornea, in the present study we have focused on the detection of LOXL enzymes. METHOD: The localization and distribution of LOXL1-4 were assessed in cryosections of 7 control donors (three males and three females; 25-68 years; mean age 46±17.6 years) and 8 KC corneas (5 males and 3 females; 25-46 years; mean age 31.3±7.5 years) using indirect fluorescent immunohistochemistry (IHC). The specimens were examined using an Olympus BX51 microscope (Olympus Co., Tokyo, Japan) at a magnification of 200-1000x. Western blot analysis of 4 control and 4 KC corneas was performed for all tested enzymes. RESULTS: All four LOX-like enzymes were present in all layers of control corneas as well as in the limbus and conjunctiva. Almost no differences between control and pathological specimens were found for LOXL1. A lower staining intensity of LOXL2 was found using IHC and Western blot analysis in KC specimens. Decreases of the signal and small irregularities in the staining were found in the epithelium, keratocytes and extracellular matrix, where a gradual anterior-posterior weakening of the signal was observed. LOXL3 IHC staining was lower in the corneal stromal extracellular matrix and keratocytes of KC samples. No prominent differences were detected using IHC for LOXL4, but a slight decrease was observed in KC corneas using Western blot analysis. CONCLUSION: We presume that the decrease of LOXL2 in KC corneas is more likely a consequence of the associated pathological processes (activation of stromal cells due to tissue weakening and consequent structural changes) than a direct cause leading to KC development. At this time, we are unable to provide a coherent explanation for the observed decrease of LOXL3 and LOXL4 in KC corneas.

• MeSH
• dospělí MeSH
• imunohistochemie MeSH
• izoenzymy metabolismus   MeSH
• keratinocyty enzymologie   patologie   ultrastruktura   MeSH
• keratokonus enzymologie   patologie   MeSH
• kolagen metabolismus   ultrastruktura   MeSH
• konjunktiva enzymologie   patologie   MeSH
• kontaktní čočky MeSH
• lidé středního věku MeSH
• lidé MeSH
• limbus corneae enzymologie   patologie   MeSH
• lysyloxidasa metabolismus   MeSH
• rohovka enzymologie   patologie   MeSH
• rohovkový endotel enzymologie   patologie   ultrastruktura   MeSH
• senioři MeSH
• stroma rohovky enzymologie   patologie   ultrastruktura   MeSH
• Check Tag
• dospělí MeSH
• lidé středního věku MeSH
• lidé MeSH
• mužské pohlaví MeSH
• senioři MeSH
• ženské pohlaví MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH

Keratoconus (KC) is an eye disease characterized by the progressive thinning and protrusion of the cornea, which results in the loss of visual acuity. This disorder remains poorly understood, although recent studies indicate the involvement of genetic and environmental factors. Recently, we have found that the distribution of the cross-linking enzyme lysyl oxidase (LOX) is markedly decreased in about 63 % of keratoconic specimens. Similarly, LOX activity is significantly reduced by 38 % compared to control tissue. Nearly 70 systemic disorders have been reported in association with KC, most of them affecting the extracellular matrix. In this review we attempted to ascertain whether any KC-associated diseases exhibit signs that may reflect LOX impairment. We hypothesized that very similar changes in the extracellular matrix, particularly at the level of collagen metabolism, including LOX impairment in mitral leaflets, may reflect an association between KC and mitral valve prolapse. Moreover, this putative association is supported by the high frequency of Down syndrome in both diseases. Among other disorders that have been found to coincide with KC, we did not find any in which the LOX enzyme may be directly or indirectly impaired. On the other hand, in cases where KC is present along with other connective tissue disorders (Marfan syndrome, Ehlers-Danlos syndrome and others), KC may not arise as a localized manifestation, but rather may be induced as the result of a more complex connective tissue disorder.

• MeSH
• keratokonus komplikace   enzymologie   MeSH
• lidé MeSH
• lysyloxidasa metabolismus   MeSH
• nemoci pojiva komplikace   MeSH
• Check Tag
• lidé MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• přehledy MeSH

Inadequate cross-linking between collagen lamellae is a characteristic feature of keratoconus corneas. The formation of covalent bonds between collagen and elastin fibrils, which maintain the biomechanical properties of the cornea, is mediated by the cuproenzyme lysyl oxidase and four lysyl oxidase-like enzymes. The aim of this study was to determine the distribution of lysyl oxidase and the total lysyl oxidase activity (lysyl oxidase and the four lysyl oxidase-like enzymes) in control and keratoconic corneas. Seven control and eight keratoconic corneas were used for the imunohistochemical detection of lysyl oxidase in corneal cryosections using two different antibodies. The total lysyl oxidase activity in the culture medium of corneal fibroblasts from six explanted keratoconic and four control corneas was measured using a fluorometric assay in the presence and absence of the lysyl oxidase inhibitor beta-aminopropionitrile and determined as the production of H(2)O(2) in nM per μg of total protein. In the control tissue, the most intense signal for lysyl oxidase was present in the corneal epithelium, in which perinuclear dots brightly projecting from more or less homogenous cytoplasmic staining may represent the lysyl oxidase propeptide. Less intense staining was present in keratocytes, the extracellular matrix and in the corneal endothelium. The epithelium of the limbus and the perilimbal conjunctiva showed intense to very intense staining. The distribution of lysyl oxidase was clearly decreased in at least five of the eight keratoconic specimens. The most marked signal reduction was observed in the stromal matrix and in keratocytes. Moreover, the signal in pathological specimens revealed a more irregular pattern, including the presence of intra- and extracellular clumps in the epithelium. Interestingly, endothelial cells showed no or very weak staining in areas just beneath negative stromal tissue. The mean activity of total lysyl oxidase in the keratoconic samples (2.60 ± 2.23 nM H(2)O(2)/μg of total protein) was more than 2.5-fold lower than in control tissue (6.83 ± 2.53 nM H(2)O(2)/μg of total protein), and the decrease was statistically significant (p = 0.0178). The location of lysyl oxidase in the healthy cornea, limbus and perilimbal conjunctiva was described. We hypothesize that the restricted lysyl oxidase distribution in keratoconic corneas, and particularly the decrease of total lysyl oxidase activity in cultured keratoconic fibroblasts, is one potential reason for the inadequate collagen cross-linking that is a hallmark of this disease.

• MeSH
• dospělí MeSH
• fluorescenční protilátková technika nepřímá MeSH
• keratokonus enzymologie   patologie   chirurgie   MeSH
• konjunktiva enzymologie   MeSH
• kultivované buňky MeSH
• lidé středního věku MeSH
• lidé MeSH
• limbus corneae enzymologie   MeSH
• lysyloxidasa metabolismus   MeSH
• mladiství MeSH
• mladý dospělý MeSH
• oxidoreduktasy aminokyselin metabolismus   MeSH
• rohovka enzymologie   MeSH
• rohovkové keratocyty enzymologie   MeSH
• senioři MeSH
• Check Tag
• dospělí MeSH
• lidé středního věku MeSH
• lidé MeSH
• mladiství MeSH
• mladý dospělý MeSH
• mužské pohlaví MeSH
• senioři MeSH
• ženské pohlaví MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH