Corneal decompensation in a boy with Kearns-Sayre syndrome

Fuchs endothelial corneal dystrophy: The vicious cycle of Fuchs pathogenesis

Fuchs endothelial corneal dystrophy (FECD) is the most common primary corneal endothelial dystrophy and the leading indication for corneal transplantation worldwide. FECD is characterized by the progressive decline of corneal endothelial cells (CECs) and the formation of extracellular matrix (ECM) excrescences in Descemet's membrane (DM), called guttae, that lead to corneal edema and loss of vision. FECD typically manifests in the fifth decades of life and has a greater incidence in women. FECD is a complex and heterogeneous genetic disease where interaction between genetic and environmental factors results in cellular apoptosis and aberrant ECM deposition. In this review, we will discuss a complex interplay of genetic, epigenetic, and exogenous factors in inciting oxidative stress, auto(mito)phagy, unfolded protein response, and mitochondrial dysfunction during CEC degeneration. Specifically, we explore the factors that influence cellular fate to undergo apoptosis, senescence, and endothelial-to-mesenchymal transition. These findings will highlight the importance of abnormal CEC-DM interactions in triggering the vicious cycle of FECD pathogenesis. We will also review clinical characteristics, diagnostic tools, and current medical and surgical management options for FECD patients. These new paradigms in FECD pathogenesis present an opportunity to develop novel therapeutics for the treatment of FECD.

Corneal Abnormalities Are Novel Clinical Feature in Wolfram Syndrome

PURPOSE

To evaluate corneal morphology among patients with Wolfram syndrome (WFS).

DESIGN

Comparative observational longitudinal case series of WFS patients with a laboratory approach in the WFS1 gene knockout (Wfs1KO) mouse model.

METHODS

A group of 12 patients with biallelic mutations in the WFS1 gene recruited from the whole country and a control group composed of 30 individuals with type 1 diabetes (T1D) were evaluated in a national reference center for monogenic diabetes. All subjects (n = 42) underwent a complete ophthalmic examination, computer videokeratography, and corneal thickness and endothelial measurements. Additionally, WFS patients (n = 9) underwent longitudinal videokeratography and Pentacam evaluation. Corneal characteristics were assessed and compared between both groups. Human and mouse corneas were subjected to immunohistochemistry to detect wolframin expression and microscopic evaluation to study corneal morphology ex vivo.

RESULTS

Clinical and topographic abnormalities similar to keratoconus were observed in 14 eyes (58.3%) of 8 WFS patients (66.7%). Flat keratometry, inferior-superior dioptric asymmetry, skewed radial axis, logarithm of keratoconus percentage index, index of surface variance, index of vertical asymmetry, keratoconus index, central keratoconus index, index of height asymmetry, and index of height decentration differed between WFS and T1D patients. Immunohistochemistry demonstrated wolframin expression in human and mouse corneas. Compared with Wfs1WT mice, Wfs1KO mice also presented corneal abnormalities.

CONCLUSIONS

Patients with WFS present a high prevalence of changes in corneal morphology compatible with the diagnosis of early stages of keratoconus. Observations in a mouse model suggest that a mutation in the WFS1 gene may be responsible for corneal abnormalities similar to keratoconus.

Endothelial dysfunction in a child with Pearson marrow-pancreas syndrome managed with Descemet stripping automated endothelial keratoplasty using a suture pull-through technique

A 4-year-old girl with a history of Pearson marrow-pancreas syndrome presenting with severe, progressive photophobia was found to have bilateral, diffuse corneal thickening and peripheral pigmentary retinopathy. She underwent Descemet stripping automated endothelial keratoplasty (DSAEK) surgery in both eyes using a modified suture pull-through technique. Postoperatively there was no evidence of cataract formation or graft detachment; her corneas thinned, and her photophobia improved dramatically.

Acute corneal edema without epithelium compromise. A case report and literature review

El edema de córnea es una entidad que se produce por un gran número de causas y tiene diversas formas de presentación y diferentes grados de afección. En este artículo se reporta el caso de un hombre con edema de córnea agudo sin compromiso epitelial, en el que el cuadro clínico, el examen oftalmológico y los estudios de extensión no lograron establecer su etiología. Además, se hace una revisión de la literatura disponible respecto a todas las posibles causas de edema de córnea agudo, agrupándolas en aquellas que ocasionan el edema por lesión o inflamación epitelial o estromal, por disfunción endotelial o por un aumento en la presión intraocular.

Mitochondrial dysfunction and oxidative stress in corneal disease

The cornea is the anterior transparent surface and the main refracting structure of the eye. Mitochondrial dysfunction and oxidative stress are implicated in the pathogenesis of inherited (e.g. Kearns Sayre Syndrome) and acquired corneal diseases (e.g. keratoconus and Fuchs endothelial corneal dystrophy). Both antioxidants and reactive oxygen species are found in the healthy cornea. There is increasing evidence of imbalance in the oxidative balance and mitochondrial function in the cornea in disease states. The cornea is vulnerable to mitochondrial dysfunction and oxidative stress due to its highly exposed position to ultraviolet radiation and high oxygen tension. The corneal endothelium is vulnerable to accumulating mitochondrial DNA (mtDNA) damage due to the post- mitotic nature of endothelial cells, yet their mitochondrial genome is continually replicating and mtDNA mutations can develop and accumulate with age. The unique physiology of the cornea predisposes this structure to oxidative damage, and there is interplay between inherited and acquired mitochondrial dysfunction, oxidative damage and a number of corneal diseases. By targeting mitochondrial dysfunction in corneal disease, emerging treatments may prevent or reduce visual loss.

Glutaminolysis is Essential for Energy Production and Ion Transport in Human Corneal Endothelium

Corneal endothelium (CE) is among the most metabolically active tissues in the body. This elevated metabolic rate helps the CE maintain corneal transparency by its ion and fluid transport properties, which when disrupted, leads to visual impairment. Here we demonstrate that glutamine catabolism (glutaminolysis) through TCA cycle generates a large fraction of the ATP needed to maintain CE function, and this glutaminolysis is severely disrupted in cells deficient in NH₃:H⁺ cotransporter Solute Carrier Family 4 Member 11 (SLC4A11). Considering SLC4A11 mutations leads to corneal endothelial dystrophy and sensorineural deafness, our results indicate that SLC4A11-associated developmental and degenerative disorders result from altered glutamine catabolism. Overall, our results describe an important metabolic mechanism that provides CE cells with the energy required to maintain high level transport activity, reveal a direct link between glutamine metabolism and developmental and degenerative neuronal diseases, and suggest an approach for protecting the CE during ophthalmic surgeries.

•

Glutamine contributes half of TCA cycle intermediates in human corneal endothelium.

•

Glutamine catabolism supplies significant ATP that fuels the endothelial pump function.

•

SLC4A11 (NH₃:2H⁺ cotransporter) knockout shows ammonia related oxidative damage.

•

Loss of SLC4A11 transporter disrupts expression of glutaminolysis enzymes.

The corneal endothelium (CE) is responsible for maintaining corneal transparency through the action of active transport processes. We report that CE metabolizes the amino acid glutamine producing ATP in support of active transport. In the mouse model of CHED (Congenital Hereditary Endothelial Dystrophy), which manifests corneal edema and loss of transparency, glutamine metabolism is disrupted due to loss of SLC4A11, an NH₃:2H⁺ transporter. This work sheds light on potential clinical therapies to facilitate CE function, the pathogenesis of CHED and Fuchs' Endothelial Corneal Dystrophy, and suggests that the ammonia handling capacity of SLC4A11 is essential for efficient metabolism of glutamine.

Genetic background and climatic droplet keratopathy incidence in a Mapuche population from Argentina

Purpose

To determine whether the incidence of and susceptibility to climatic droplet keratopathy (CDK), an acquired, often bilateral degenerative corneal disease, is influenced by the genetic background of the individuals who exhibit the disorder.

Methods

To determine whether the disease expression was influenced by the genetic ancestry of CDK cases in native Mapuche of the northwest area of Patagonia in Argentina, we examined mitochondrial DNA and Y-chromosome variation in 53 unrelated individuals. Twenty-nine of them were part of the CDK (patient) population, while 24 were part of the control group. The analysis revealed the maternal and paternal lineages that were present in the two study groups.

Results

This analysis demonstrated that nearly all persons had a Native American mtDNA background, whereas 50% of the CDK group and 37% of the control group had Native American paternal ancestry, respectively. There was no significant difference in the frequencies of mtDNA haplogroups between the CDK patient and control groups. Although the Y-chromosome data revealed differences in specific haplogroup frequencies between these two groups, there was no statistically significant relationship between individual paternal genetic backgrounds and the incidence or stage of disease.

Conclusions

These results indicate a lack of correlation between genetic ancestry as represented by haploid genetic systems and the incidence of CDK in Mapuche populations. In addition, the mtDNA appears to play less of a role in CDK expression than for other complex diseases linked to bioenergetic processes. However, further analysis of the mtDNA genome sequence and other genes involved in corneal function may reveal the more precise role that mitochondria play in the expression of CDK.

Increased nuclear factor-κB and loss of p53 are key mechanisms in Myalgic Encephalomyelitis/chronic fatigue syndrome (ME/CFS)

Fukuda's criteria are adequate to make a distinction between Myalgic Encephalomyelitis/chronic fatigue syndrome (ME/CFS) and chronic fatigue (CF), but ME/CFS patients should be subdivided into those with (termed ME) and without (termed CFS) post exertional malaise [Maes et al. 2012]. ME/CFS is considered to be a neuro-immune disease. ME/CFS is characterized by activated immuno-inflammatory pathways, including increased levels of pro-inflammatory cytokines, nuclear factor κB (NF-κB) and aberrations in mitochondrial functions, including lowered ATP. These processes may explain typical symptoms of ME/CFS, e.g. fatigue, malaise, hyperalgesia, and neurologic and autonomic symptoms. Here we hypothesize that increased NF-κB together with a loss of p53 are key phenomena in ME/CFS that further explain ME/CFS symptoms, such as fatigue and neurocognitive dysfunction, and explain ME symptoms, such as post-exertional malaise following mental and physical activities. Inactivation of p53 impairs aerobic mitochondrial functions and causes greater dependence on anaerobic glycolysis, elevates lactate levels, reduces mitochondrial density in skeletal muscle and reduces endurance during physical exercise. Lowered p53 and increased NF-κB are associated with elevated reactive oxygen species. Increased NF-κB induces the production of pro-inflammatory cytokines, which increase glycolysis and further compromise mitochondrial functions. All these factors together may contribute to mitochondrial exhaustion and indicate that the demand for extra ATP upon the commencement of increased activity cannot be met. In conditions of chronic inflammation and oxidative stress, high NF-κB and low p53 may conspire to promote neuron and glial cell survival at a price of severely compromised metabolic brain function. Future research should examine p53 signaling in ME/CFS.

Corneal endothelial dysfunction in Pearson syndrome

Mitochondrial disorders are associated with well recognized ocular manifestations. Pearson syndrome is an often fatal, multisystem, mitochondrial disorder that causes variable bone marrow, hepatic, renal and pancreatic exocrine dysfunction. Phenotypic progression of ocular disease in a 12-year-old male with Pearson syndrome is described. This case illustrates phenotypic drift from Pearson syndrome to Kearns-Sayre syndrome given the patient's longevity. Persistent corneal endothelial failure was noted in addition to ptosis, chronic external ophthalmoplegia and mid-peripheral pigmentary retinopathy. We propose that corneal edema resulting from corneal endothelial metabolic pump failure occurs within a spectrum of mitochondrial disorders.

Mitochondrial disorders with significant ophthalmic manifestations

Mitochondrial diseases are a clinically hetyerogenous group of disorders. They can be caused by mutations of nuclear or mitochondrial DNA (mtDNA). Some affect a single organ, but many involve multiple organ systems and often present with prominent neurologic and myopathic features. The eye is frequently affected, along with muscles and brain, but multisystem disease is common. Ophthalmic manifestations include cataract, retinopathy, optic atrophy, cortical visual loss, ptosis and ophthalmoplegia. Kearns-Sayre Syndrome (KSS), Mitochondrial Encephalopathy, Lactic Acidosis Stroke (MELAS), Myoclonic Epilepsy and Ragged Red Fiber myopathy (MERRF) and Lebers Hereditary Optic Neuropathy (LHON) are well known clinical entities that are secondary to mtDNA abnormalities, which has ophthalmic manifestations. Mitochondrial Dysfunction should be considered in the differential diagnosis of progressive multisystem disorder and specifically if there is associated neuro-ophthalmic manifestations, which may be the presenting symptom of these disorders.