Pathogenesis of retinal ganglion cell death in Leber hereditary optic neuropathy (LHON): possible involvement of mitochondria, light and glutamate

The primary vascular dysregulation syndrome: implications for eye diseases

Vascular dysregulation refers to the regulation of blood flow that is not adapted to the needs of the respective tissue. We distinguish primary vascular dysregulation (PVD, formerly called vasospastic syndrome) and secondary vascular dysregulation (SVD). Subjects with PVD tend to have cold extremities, low blood pressure, reduced feeling of thirst, altered drug sensitivity, increased pain sensitivity, prolonged sleep onset time, altered gene expression in the lymphocytes, signs of oxidative stress, slightly increased endothelin-1 plasma level, low body mass index and often diffuse and fluctuating visual field defects. Coldness, emotional or mechanical stress and starving can provoke symptoms. Virtually all organs, particularly the eye, can be involved. In subjects with PVD, retinal vessels are stiffer and more irregular, and both neurovascular coupling and autoregulation capacity are reduced while retinal venous pressure is often increased. Subjects with PVD have increased risk for normal-tension glaucoma, optic nerve compartment syndrome, central serous choroidopathy, Susac syndrome, retinal artery and vein occlusions and anterior ischaemic neuropathy without atherosclerosis. Further characteristics are their weaker blood–brain and blood-retinal barriers and the higher prevalence of optic disc haemorrhages and activated astrocytes. Subjects with PVD tend to suffer more often from tinnitus, muscle cramps, migraine with aura and silent myocardial ischaemic and are at greater risk for altitude sickness. While the main cause of vascular dysregulation is vascular endotheliopathy, dysfunction of the autonomic nervous system is also involved. In contrast, SVD occurs in the context of other diseases such as multiple sclerosis, retrobulbar neuritis, rheumatoid arthritis, fibromyalgia and giant cell arteritis. Taking into consideration the high prevalence of PVD in the population and potentially linked pathologies, in the current article, the authors provide recommendations on how to effectively promote the field in order to create innovative diagnostic tools to predict the pathology and develop more efficient treatment approaches tailored to the person.

Genotype-phenotype correlations in Leber hereditary optic neuropathy

Leber hereditary optic neuropathy (LHON), acute or subacute vision loss due to retinal ganglion cell death which in the long run leads to optic nerve atrophy is one of the most widely studied maternally inherited diseases caused by mutations in mitochondrial DNA. Although three common mutations, 11778G>A, 14484T>C or 3460G>A are responsible for over 90% of cases and affect genes encoding complex I subunits of the respiratory chain, their influence on bioenergetic properties of the cell is marginal and cannot fully explain the pathology of the disease. The following chain of events was proposed, based on biochemical and anatomical properties of retinal ganglion cells whose axons form the optic nerve: mitochondrial DNA mutations increase reactive oxygen species production in these sensitive cells, leading to caspase-independent apoptosis. As LHON is characterized by low penetrance and sex bias (men are affected about 5 times more frequently than women) the participation of the other factors-genetic and environmental-beside mtDNA mutations was studied. Mitochondrial haplogroups and smoking are some of the factors involved in the complex etiology of this disease.

Transgenic mice expressing cyan fluorescent protein as a reporter strain to detect the effects of rotenone toxicity on retinal ganglion cells

This is the first study using a reporter transgenic model to investigate the effects of an environmental toxin on the retina. Rotenone is a widely used pesticide that inhibits mitochondrial complex I and produces neurotoxicity. Previous studies demonstrated the time course and dose response of rotenone toxicity on retinal ganglion cells (RGC). However, previous analyses of rotenone-induced retinotoxicity provided little detail of the optic nerve axons and cellular pathology. These limitations were successfully surmounted by using a transgenic mouse line shown to express cyan fluorescent protein (CFP) in neurons, including RGC, under regulatory elements of the human the thy1.1 promoter (thy-CFP). Data showed that CFP expression is limited to RGC and their processes in the retina of thy-CFP mice. Eyes exposed to the pesticide rotenone displayed marked alterations in RGC morphology, inner plexiform layer, optic disc, and optic nerves. After 24 h, the number of CFP-labeled RGC was reduced 50%. Correlated with a loss of RGC bodies was an approximate 50% reduction in CFP fluorescence intensity at the optic disc. The findings showed that rotenone-induced degeneration of RGC and their processes can be visualized with exquisite detail in thy-CFP mice, and that this approach may provide a novel and effective way to monitor the association between environmental toxins and neurodegeneration in living animals.