S U M M A R YThis study localized malondialdehyde (MDA, a toxic byproduct of lipid peroxidation), nitrotyrosine [NT, a cytotoxic byproduct of nitric oxide (NO)], and nitric oxide synthase isomers (NOS) in normal and diseased human corneas. Normal corneas ( n ϭ 11) and those with clinical and histopathological diagnoses of keratoconus ( n ϭ 26), bullous keratopathy ( n ϭ 17), and Fuchs' endothelial dystrophy ( n ϭ 12) were examined with antibodies specific for MDA, NT, eNOS (constitutive NOS), and iNOS (inducible NOS). Normal corneas showed little or no staining for MDA, NT, or iNOS, whereas eNOS was detected in the epithelium and endothelium. MDA was present in all disease groups, with each group displaying a distinct pattern of staining. NT was detected in all keratoconus and approximately one half of Fuchs' dystrophy corneas. iNOS and eNOS were evident in all the diseased corneas. Keratoconus corneas showed evidence of oxidative damage from cytotoxic byproducts generated by lipid peroxidation and the NO pathway. Bullous keratopathy corneas displayed byproducts of lipid peroxidation but not peroxynitrite (MDA but not NT). Conversely, Fuchs' dystrophy corneas displayed byproducts of peroxynitrite with little lipid peroxidation (NT ϾϾ MDA). These data suggest that oxidative damage occurs within each group of diseased corneas. However, each disease exhibits a distinctive profile, with only keratoconus showing prominent staining for both nitrotyrosine and MDA. These results suggest that keratoconus corneas do not process reactive oxygen species in a normal manner, which may play a major role in the pathogenesis of this disease.

Keratoconus corneas have elevated levels of cathepsins V/L2, -B, and -G, which can stimulate hydrogen peroxide production, which, in turn, can upregulate catalase, an antioxidant enzyme. In addition, decreased TIMP-1 and increased cathepsin V/L2 levels may play a role in the matrix degradation that is a hallmark of keratoconus corneas. The findings support the hypothesis that keratoconus corneas undergo oxidative stress and tissue degradation.

PURPOSE.To determine whether keratoconus (KC) corneal fibroblast cultures have increased reactive oxygen species (ROS) production and are more susceptible to stress-related challenges. METHODS. Normal (n ϭ 9) and KC (n ϭ 10) stromal fibroblast cultures were incubated in either neutral-or low-pH conditions, with or without hydrogen peroxide. Catalase activities were measured with a fluorescent substrate assay. Superoxide and ROS/reactive nitrogen species (RNS) productions were determined with an amine-reactive green-dye assay and 2Ј,7Ј-dichlorodihydrofluorescein diacetate (H 2 DCFDA) dye assay, respectively. Cell viability was analyzed by a dye-exclusion assay. Caspase 3 activity was measured by a fluorochrome inhibitor of caspase (FLICA) assay. A cationic (green) dye was used to measure the mitochondrial membrane potential (⌬⌿m). RESULTS. KC fibroblasts had increased superoxide and ROS/RNS production (6.2-fold, P Ͻ 0.001 and 1.8-fold, P Ͻ 0.001, respectively) and catalase activity (P Ͻ 0.01) with higher concentrations of H 2 O 2 compared with normal cultures (P ϭ 0.16). After a low-pH stress challenge, KC fibroblasts maintained higher ROS/RNS levels (3.3-fold, P Ͻ 0.02), showed higher caspase-3 activity (7.5-fold, P Ͻ 0.02) and decreased ⌬⌿m (2.6-fold, P Ͻ 0.04), and had decreased cell viability (37%, P Ͻ 0.005 vs. 20%, P Ͻ 0.27) compared with normal fibroblasts. CONCLUSIONS. Under identical conditions, KC fibroblasts had increased basal generation of ROS/RNS and were more susceptible to stressful challenges (low-pH and/or H 2 O 2 conditions) than were normal fibroblasts. In addition, the stressed KC fibroblasts possessed characteristics similar to those found in the intact KC corneas (increased catalase activity, ROS production, and apoptosis). These properties may play a role in the pathogenesis of KC. (Invest Ophthalmol Vis Sci.

The geographic origins of populations can be identified by their maternally inherited mitochondrial DNA (mtDNA) haplogroups. This study compared human cybrids (cytoplasmic hybrids), which are cell lines with identical nuclei but mitochondria from different individuals with mtDNA from either the H haplogroup or L haplogroup backgrounds. The most common European haplogroup is H while individuals of maternal African origin are of the L haplogroup. Despite lower mtDNA copy numbers, L cybrids had higher expression levels for nine mtDNA-encoded respiratory complex genes, decreased ATP turnover rates and lower levels of ROS production, parameters which are consistent with more efficient oxidative phosphorylation. Surprisingly, GeneChip arrays showed that the L and H cybrids had major differences in expression of genes of the canonical complement system (5 genes), dermatan/chondroitin sulfate biosynthesis (5 genes) and CCR3 signaling (9 genes). Quantitative nuclear gene expression studies confirmed that L cybrids had (a) lower expression levels of complement pathway and innate immunity genes and (b) increased levels of inflammation-related signaling genes, which are critical in human diseases. Our data support the hypothesis that mtDNA haplogroups representing populations from different geographic origins may play a role in differential susceptibilities to diseases.

BackgroundMitochondrial dysfunction is associated with the development and progression of age-related macular degeneration (AMD). Recent studies using populations from the United States and Australia have demonstrated that AMD is associated with mitochondrial (mt) DNA haplogroups (as defined by combinations of mtDNA polymorphisms) that represent Northern European Caucasians. The aim of this study was to use the cytoplasmic hybrid (cybrid) model to investigate the molecular and biological functional consequences that occur when comparing the mtDNA H haplogroup (protective for AMD) versus J haplogroup (high risk for AMD).Methodology/Principal FindingsCybrids were created by introducing mitochondria from individuals with either H or J haplogroups into a human retinal epithelial cell line (ARPE-19) that was devoid of mitochondrial DNA (Rho0). In cybrid lines, all of the cells carry the same nuclear genes but vary in mtDNA content. The J cybrids had significantly lower levels of ATP and reactive oxygen/nitrogen species production, but increased lactate levels and rates of growth. Q-PCR analyses showed J cybrids had decreased expressions for CFH, C3, and EFEMP1 genes, high risk genes for AMD, and higher expression for MYO7A, a gene associated with retinal degeneration in Usher type IB syndrome. The H and J cybrids also have comparatively altered expression of nuclear genes involved in pathways for cell signaling, inflammation, and metabolism.Conclusion/SignificanceOur findings demonstrate that mtDNA haplogroup variants mediate not only energy production and cell growth, but also cell signaling for major molecular pathways. These data support the hypothesis that mtDNA variants play important roles in numerous cellular functions and disease processes, including AMD.

A unique genomic deletion within intron 2 close to the 5' splice junction of the SOD1 gene was identified in three patients with KC. Moreover, mRNA from one affected individual also had two transcript splice variants (LE2 and LE2E3) that others have shown to code for proteins lacking the active site of the SOD1 enzyme. Further studies should be conducted to determine whether a causal relationship exists between these two events that may increase oxidative stress and be associated with KC.

KC corneas exhibit more mtDNA damage than do normal corneas. The previously reported increased oxidative stress and altered integrity of mtDNA may be related to each other and may be important in KC pathogenesis.

Age-related macular degeneration (AMD) is the leading cause of vision loss in developed countries. While linked to genetic polymorphisms in the complement pathway, there are many individuals with high risk alleles that do not develop AMD, suggesting that other 'modifiers' may be involved. Mitochondrial (mt) haplogroups, defined by accumulations of specific mtDNA single nucleotide polymorphisms (SNPs) which represent population origins, may be one such modifier. J haplogroup has been associated with high risk for AMD while the H haplogroup is protective. It has been difficult to assign biological consequences for haplogroups so we created human ARPE-19 cybrids (cytoplasmic hybrids), which have identical nuclei but mitochondria of either J or H haplogroups, to investigate their effects upon bioenergetics and molecular pathways. J cybrids have altered bioenergetic profiles compared with H cybrids. Q-PCR analyses show significantly lower expression levels for seven respiratory complex genes encoded by mtDNA. J and H cybrids have significantly altered expression of eight nuclear genes of the alternative complement, inflammation and apoptosis pathways. Sequencing of the entire mtDNA was carried out for all the cybrids to identify haplogroup and non-haplogroup defining SNPs. mtDNA can mediate cellular bioenergetics and expression levels of nuclear genes related to complement, inflammation and apoptosis. Sequencing data suggest that observed effects are not due to rare mtDNA variants but rather the combination of SNPs representing the J versus H haplogroups. These findings represent a paradigm shift in our concepts of mt-nuclear interactions.