Differential production of superoxide by neuronal mitochondria

Transcriptome combined with Mendelian randomization to screen key genes associated with mitochondrial and programmed cell death causally associated with diabetic retinopathy

Background

Mitochondrial dysfunction in the retina can induce apoptosis of retinal capillary cells, leading to diabetic retinopathy (DR). This study aimed to explore key genes related to programmed cell death (PCD) and mitochondria in DR via bioinformatic analysis.

Methods

A differential analysis was performed to identify differentially expressed genes (DEGs) between DR and control samples using the GSE94019 dataset from the Gene Expression Omnibus (GEO) database. Pearson correlation analysis was then utilized to select genes linked to mitochondrial function and PCD (M-PCD). Candidate genes were identified by overlapping DR-DEGs and M-PCD genes, followed by functional annotation. Mendelian randomization (MR) analysis was employed to identify genes with causal relationships to DR. Key genes were identified through protein-protein interaction (PPI) analysis using six algorithms (DEgree, DMNC, EPC, MCC, Genes are BottleNeck, and MNC) within Cytoscape software. The expression patterns of these genes were validated using GSE94019 and GSE60436 datasets, as well as RT-qPCR. Enrichment analysis provided insights into the function and pathways of these key genes in DR. Differential immune cell profiles were determined via immune infiltration analysis, followed by exploring the relationships between immune cells, cytokines, and the identified genes. Correlations between key genes and apoptosis genes were also examined. In vivo experiments using RT-PCR, immunohistochemistry (IHC), and western blot analysis confirmed that MYC and SLC7A11 expression was significantly elevated in DR rat retinal tissues.

Results

From 658 candidate genes, 12 showed significant causal associations with DR. MYC and SLC7A11 were particularly notable, showing upregulated expression in DR samples and involvement in apoptosis and diabetes-related pathways. These genes were significantly associated with apoptotic genes and correlated positively with altered immune cell types and cytokines, suggesting a link between immune response and DR pathogenesis. In vivo findings confirmed that MYC and SLC7A11 expression was elevated in DR rat retinal tissues.

Conclusion

Key genes (MYC and SLC7A11) associated with mitochondrial function and PCD in DR were identified, offering insights into DR's pathological mechanisms and potential targets for diagnostic and therapeutic strategies.

Maculopapillary Bundle Degeneration in Optic Neuropathies

PURPOSE OF REVIEW

Degeneration of the maculopapillary bundle (MPB) is a prominent feature in a spectrum of optic neuropathies. MPB-selective degeneration is seen in specific conditions, such as nutritional and toxic optic neuropathies, Leber hereditary optic neuropathy (LHON), and dominant optic atrophy (DOA). Despite their distinct etiologies and clinical presentations, which encompass variations in age of incidence and monocular or binocular onset, these disorders share a core molecular mechanism: compromised mitochondrial homeostasis. This disruption is characterized by dysfunctions in mitochondrial metabolism, biogenesis, and protein synthesis. This article provides a comprehensive understanding of the MPB's role in optic neuropathies, emphasizing the importance of mitochondrial mechanisms in the pathogenesis of these conditions.

RECENT FINDINGS

Optical coherence tomography studies have characterized the retinal nerve fiber layer changes accompanying mitochondrial-affiliated optic neuropathies. Selective thinning of the temporal optic nerve head is preceded by thickening in early stages of these disorders which correlates with reductions in macular ganglion cell layer thinning and vascular atrophy. A recently proposed mechanism underpinning the selective atrophy of the MPB involves the positive feedback of reactive oxygen species generation as a common consequence of mitochondrial dysfunction. Additionally, new research has revealed that the MPB can undergo degeneration in the early stages of glaucoma, challenging the historically held belief that this area was not involved in this common optic neuropathy. A variety of anatomical risk factors influence the propensity of glaucomatous MPB degeneration, and cases present distinct patterns of ganglion cell degeneration that are distinct from those observed in mitochondria-associated diseases. This review synthesizes clinical and molecular research on primary MPB disorders, highlighting the commonalities and differences in their pathogenesis.

KEY POINTS (BOX)

1. Temporal degeneration of optic nerve fibers accompanied by cecocentral scotoma is a hallmark of maculopapillary bundle (MPB) degeneration. 2. Mechanisms of MPB degeneration commonly implicate mitochondrial dysfunction. 3. Recent research challenges the traditional belief that the MPB is uninvolved in glaucoma by showing degeneration in the early stages of this common optic neuropathy, yet with features distinct from other MPB-selective neuropathies. 4. Reactive oxygen species generation is a mechanism linking mitochondrial mechanisms of MPB-selective optic neuropathies, but in-vivo and in-vitro studies are needed to validate this hypothesis.

Neuron-specific mitochondrial oxidative stress results in epilepsy, glucose dysregulation and a striking astrocyte response

Mitochondrial superoxide (O₂^-) production is implicated in aging, neurodegenerative disease, and most recently epilepsy. Yet the specific contribution of neuronal O₂^- to these phenomena is unclear. Here, we selectively deleted superoxide dismutase-2 (SOD2) in neuronal basic helix-loop-helix transcription factor (NEX)-expressing cells restricting deletion to a subset of excitatory principle neurons primarily in the forebrain (cortex and hippocampus). This resulted in nSOD2 KO mice that lived into adulthood (2-3 months) with epilepsy, selective loss of neurons, metabolic rewiring and a marked mitohormetic gene response. Surprisingly, expression of an astrocytic gene, glial fibrillary acidic protein (GFAP) was significantly increased relative to WT. Further studies in rat primary neuron-glial cultures showed that increased mitochondrial O₂^-, specifically in neurons, was sufficient to upregulate GFAP. These results suggest that neuron-specific mitochondrial O₂^- is sufficient to drive a complex and catastrophic epileptic phenotype and highlights the ability of SOD2 to act in a cell-nonautonomous manner to influence an astrocytic response.

Activation of toll like receptor 4 (TLR4) promotes cardiomyocyte apoptosis through SIRT2 dependent p53 deacetylation

Cardiomyocyte inflammation followed by apoptosis and fibrosis is an important mediator for development and progression of heart failure. Activation of toll-like receptor 4 (TLR4), an important regulator of inflammation, causes the progression of cardiac hypertrophy and injury. However, the precise mechanism of TLR4-mediated adverse cardiac outcomes is still elusive. The present study was designed to find the role of TLR4 in cardiac fibrosis and apoptosis, and molecular mechanism thereof. Rats were treated with TLR4 agonist (LPS 12.5 μg/kg/day) through osmotic pump for 14 days. To simulate the condition in vitro, H9c2 cells were treated with LPS (1 μg/ml). Similarly, H9c2 cells were transfected with TLR4 and SIRT2 c-DNA clone for overexpression. Myocardial oxidative stress, inflammation, fibrosis and mitochondrial parameters were evaluated both in vitro and in vivo. Cardiac inflammation after LPS treatment was confirmed by increased TNF-α and IL-6 expression in rat heart. There was a marked increase in oxidative stress as observed by increased TBARS and decreased endogenous antioxidants (GSH and catalase), along with mitochondrial dysfunction as measured by mitochondrial complex activity in LPS-treated rat hearts. Histopathological examination showed the presence of cardiac fibrosis after LPS treatment. Protein expression of nuclear p53 and cleaved caspase-7/caspase-9 was significantly increased in LPS treated heart. Similar to in vivo study, nuclear translocation of p53, mitochondrial dysfunction and cellular apoptosis were observed in H9c2 cells treated with LPS. Our data also indicate that decreased expression of SIRT2 was associated with increased acetylation of p53 after LPS treatment. In conclusion, TLR4 activation in rats promotes cardiac inflammation, mitochondrial dysfunction, apoptosis and fibrosis. p53 and caspase 7/caspase 9 were found to play an important role in TLR4-mediated apoptosis. Our data suggest that, reducing TLR4 mediated fibrosis and apoptosis could be a novel approach in the treatment of heart failure, keeping in the view the major role played by TLR4 in cardiac inflammation.

Diabetic Retinopathy: The Role of Mitochondria in the Neural Retina and Microvascular Disease

Diabetic retinopathy (DR), a common chronic complication of diabetes mellitus and the leading cause of vision loss in the working-age population, is clinically defined as a microvascular disease that involves damage of the retinal capillaries with secondary visual impairment. While its clinical diagnosis is based on vascular pathology, DR is associated with early abnormalities in the electroretinogram, indicating alterations of the neural retina and impaired visual signaling. The pathogenesis of DR is complex and likely involves the simultaneous dysregulation of multiple metabolic and signaling pathways through the retinal neurovascular unit. There is evidence that microvascular disease in DR is caused in part by altered energetic metabolism in the neural retina and specifically from signals originating in the photoreceptors. In this review, we discuss the main pathogenic mechanisms that link alterations in neural retina bioenergetics with vascular regression in DR. We focus specifically on the recent developments related to alterations in mitochondrial metabolism including energetic substrate selection, mitochondrial function, oxidation-reduction (redox) imbalance, and oxidative stress, and critically discuss the mechanisms of these changes and their consequences on retinal function. We also acknowledge implications for emerging therapeutic approaches and future research directions to find novel mitochondria-targeted therapeutic strategies to correct bioenergetics in diabetes. We conclude that retinal bioenergetics is affected in the early stages of diabetes with consequences beyond changes in ATP content, and that maintaining mitochondrial integrity may alleviate retinal disease.

Pregnancy-associated plasma protein-aa supports hair cell survival by regulating mitochondrial function

To support cell survival, mitochondria must balance energy production with oxidative stress. Inner ear hair cells are particularly vulnerable to oxidative stress; thus require tight mitochondrial regulation. We identified a novel molecular regulator of the hair cells’ mitochondria and survival: Pregnancy-associated plasma protein-aa (Pappaa). Hair cells in zebrafish pappaa mutants exhibit mitochondrial defects, including elevated mitochondrial calcium, transmembrane potential, and reactive oxygen species (ROS) production and reduced antioxidant expression. In pappaa mutants, hair cell death is enhanced by stimulation of mitochondrial calcium or ROS production and suppressed by a mitochondrial ROS scavenger. As a secreted metalloprotease, Pappaa stimulates extracellular insulin-like growth factor 1 (IGF1) bioavailability. We found that the pappaa mutants’ enhanced hair cell loss can be suppressed by stimulation of IGF1 availability and that Pappaa-IGF1 signaling acts post-developmentally to support hair cell survival. These results reveal Pappaa as an extracellular regulator of hair cell survival and essential mitochondrial function.

Propagation and Selectivity of Axonal Loss in Leber Hereditary Optic Neuropathy

Leber hereditary optic neuropathy (LHON) is a syndrome of subacute loss of central vision associated with mutations in mitochondrial DNA coding for components of complex I. LHON preferentially involves small axons in the temporal optic nerve, but the reason is unclear. We performed a Monte Carlo simulation of the spread of injury in LHON axons to better understand the predilection for small axons. Optic nerve slices were modeled as grids containing axons with sizes from reported regional distributions. The propagation of injury from a localized concentration of superoxide was simulated as the spread via passive diffusion from one axon to adjacent axons, with basal production and scavenging rate proportional to axonal area and volume, respectively. Axonal degeneration occurred when intra-axonal concentrations reached a toxic threshold. Simulations demonstrated that almost all small and medium axons degenerated by the time steady-state was reached, but about 50% of large axons were preserved. The location of initial injury affected time to steady state, with nasal injuries reaching steady state faster than temporal injuries. The pattern of axonal degeneration in the simulations mirrored both visual fields and optic nerve histology from patients with LHON. These results provide insight into the nature of axonal loss in LHON.

Toll-Like Receptor 4 Inhibition Improves Oxidative Stress and Mitochondrial Health in Isoproterenol-Induced Cardiac Hypertrophy in Rats

BACKGROUND

Inflammation remains a crucial factor for progression of cardiac diseases and cardiac hypertrophy remains an important cause of cardiac failure over all age groups. As a key regulator of inflammation, toll-like receptor 4 (TLR4) plays an important role in pathogenesis of cardiac diseases. Being an important regulator of innate immunity, the precise pathway of TLR4-mediated cardiac complications is yet to be established. Therefore, the primary objective of the present study was to find the role of TLR4 in cardiac hypertrophy and the molecular mechanism thereof.

METHODS

Cardiac hypertrophy was induced with administration of isoproterenol (5 mg/kg/day, sc). TLR4 receptor inhibitor RS-LPS (lipopolysaccharide from the photosynthetic bacterium Rhodobacter sphaeroides; 5 μg/day) and agonist lipopolysaccharide (LPS) (from Escherichia coli; 3.12 μg/day) were administered through osmotic pump along with isoproterenol. Cardiac hypertrophy as well as oxidative stress and mitochondrial parameters were evaluated.

RESULTS

Cardiac hypertrophy was confirmed with increased heart weight/body weight ratio as well as assessment of hypertrophic markers in heart. There was a marked increase in the TLR4 expression and oxidative stress along with mitochondrial dysfunction in ISO group. TLR4 inhibition significantly decreased heart weight/body weight ratio and ANP, collagen, and β-MHC expression and restored the disturbed cellular antioxidant flux. The mitochondrial perturbations that were observed in hypertrophy heart was normalized after administration of TLR4 inhibitor but not with the agonist. TLR4 agonism further exaggerated the oxidative stress in heart and hence accelerated the disease development and progression.

CONCLUSION

Our data show that increased TLR4 ligand pool in cardiac hypertrophy may exaggerate the disease progression. However, inhibition of TLR4 attenuated cardiac hypertrophy through reduced cardiac redox imbalance and mitochondrial dysfunction.

Reactive oxygen species production in cardiac mitochondria after complex I inhibition: Modulation by substrate-dependent regulation of the NADH/NAD(+) ratio

Reactive oxygen species (ROS) production by isolated complex I is steeply dependent on the NADH/NAD(+) ratio. We used alamethicin-permeabilized mitochondria to study the substrate-dependence of matrix NADH and ROS production when complex I is inhibited by piericidin or rotenone. When complex I was inhibited in the presence of malate/glutamate, membrane permeabilization accelerated O2 consumption and ROS production due to a rapid increase in NADH generation that was not limited by matrix NAD(H) efflux. In the presence of inhibitor, both malate and glutamate were required to generate a high enough NADH/NAD(+) ratio to support ROS production through the coordinated activity of malate dehydrogenase (MDH) and aspartate aminotransferase (AST). With malate and glutamate present, the rate of ROS production was closely related to local NADH generation, whereas in the absence of substrates, ROS production was accelerated by increase in added [NADH]. With malate alone, oxaloacetate accumulation limited NADH production by MDH unless glutamate was also added to promote oxaloacetate removal via AST. α-ketoglutarate (KG) as well as AST inhibition also reversed NADH generation and inhibited ROS production. If malate and glutamate were provided before rather than after piericidin or rotenone, ROS generation was markedly reduced due to time-dependent efflux of CoA. CoA depletion decreased KG oxidation by α-ketoglutarate dehydrogenase (KGDH), such that the resulting increase in [KG] inhibited oxaloacetate removal by AST and NADH generation by MDH. These findings were largely obscured in intact mitochondria due to robust H2O2 scavenging and limited ability to control substrate concentrations in the matrix. We conclude that in mitochondria with inhibited complex I, malate/glutamate-stimulated ROS generation depends strongly on oxaloacetate removal and on the ability of KGDH to oxidize KG generated by AST.

The Role of the Reactive Oxygen Species and Oxidative Stress in the Pathomechanism of the Age-Related Ocular Diseases and Other Pathologies of the Anterior and Posterior Eye Segments in Adults

The reactive oxygen species (ROS) form under normal physiological conditions and may have both beneficial and harmful role. We search the literature and current knowledge in the aspect of ROS participation in the pathogenesis of anterior and posterior eye segment diseases in adults. ROS take part in the pathogenesis of keratoconus, Fuchs endothelial corneal dystrophy, and granular corneal dystrophy type 2, stimulating apoptosis of corneal cells. ROS play a role in the pathogenesis of glaucoma stimulating apoptotic and inflammatory pathways on the level of the trabecular meshwork and promoting retinal ganglion cells apoptosis and glial dysfunction in the posterior eye segment. ROS play a role in the pathogenesis of Leber's hereditary optic neuropathy and traumatic optic neuropathy. ROS induce apoptosis of human lens epithelial cells. ROS promote apoptosis of vascular and neuronal cells and stimulate inflammation and pathological angiogenesis in the course of diabetic retinopathy. ROS are associated with the pathophysiological parainflammation and autophagy process in the course of the age-related macular degeneration.

Energy metabolism in neuroblastoma and Wilms tumor

To support high proliferation, the majority of cancer cells undergo fundamental metabolic changes such as increasing their glucose uptake and shifting to glycolysis for ATP production at the expense of far more efficient mitochondrial energy production by oxidative phosphorylation (OXPHOS), which at first glance is a paradox. This phenomenon is known as the Warburg effect. However, enhanced glycolysis is necessary to provide building blocks for anabolic growth. Apart from the generation of ATP, intermediates of glycolysis serve as precursors for a variety of biosynthetic pathways essential for cell proliferation. In the last 10-15 years the field of tumor metabolism has experienced an enormous boom in interest. It is now well established that tumor suppressor genes and oncogenes often play a central role in the regulation of cellular metabolism. Therefore, they significantly contribute to the manifestation of the Warburg effect. While much attention has focused on adult solid tumors, so far there has been comparatively little effort directed at elucidation of the mechanism responsible for the Warburg effect in childhood cancers. In this review we focus on metabolic pathways in neuroblastoma (NB) and Wilms tumor (WT), the two most frequent solid tumors in children. Both tumor types show alterations of the OXPHOS system and glycolytic features. Chromosomal alterations and activation of oncogenes like MYC or inactivation of tumor suppressor genes like TP53 can in part explain the changes of energy metabolism in these cancers. The strict dependence of cancer cells on glucose metabolism is a fairly common feature among otherwise biologically diverse types of cancer. Therefore, inhibition of glycolysis or starvation of cancer cells through glucose deprivation via a high-fat low-carbohydrate diet may be a promising avenue for future adjuvant therapeutic strategies.

Conceptualizing how group singing may enhance quality of life with Parkinson's disease

Abstract Purpose: Group singing could be a promising component of neurorehabilitative care. This article aims to conceptualize how group singing may enable people with Parkinson's disease (PD) to synchronize their movement patterns to musical rhythm and enhance quality of life.

METHOD

Spanning the medical and social sciences, the article draws conceptually on literature on PD, group singing and rhythm in music; personal experience; and reasoning.

RESULTS

Conceptualizing PD in terms of disruptions to social and biological rhythms, we hypothesize how group singing may produce two socio-psychological states - connectedness and flow - that may entrain rhythm in people with PD. The states connect during group singing to elicit and enhance motor processes but may also reawaken after the group singing, through the recall and reactivation of the musical rhythms encoded during group singing.

CONCLUSIONS

In people with PD, this continuity of flow is hypothesized to be conducive to rhythmic entrainment during and after group singing and in turn to reduced deficits in motor timing and emotional processing, and improvements in quality of life. Empirical studies are needed to test this hypothesis in people with movement disorders such as PD. Implications for Rehabilitation Musical rhythm in group singing may enhance quality of life, and rehabilitation, in people with PD. Use group singing to produce two socio-psychological states - connectedness and flow - that may yield these health benefits. Include people with PD in singing groups to facilitate perceptual exposure to familiar music with melodic distinctiveness and a regular beat.

Mitochondrial activation in the growth-restricted fetus of monochorionic twins

OBJECTIVE

To study the regulatory mechanisms of selective intrauterine growth restriction (sIUGR) independent of confounding genetic factors, monochorionic (MC) twins are the ideal model, because they have identical genomic DNA. We hypothesize that the intrauterine growth restriction fetus has mitochondrial activation compared with its larger counterpart, and sought to demonstrate this using the MC twin model.

DESIGN

Fetal cord blood and amniotic fluid of MC twins were prospectively collected during delivery. Mitochondrial DNA of cord blood was measured using real-time quantitative polymerase chain reaction (PCR), and mitochondria in amniotic fluid mesenchymal stem cells (AFMSCs) were analyzed with MitoTracker staining.

SETTING

Tertiary referring center.

PATIENT(S)

Forty-three pairs of MC twins, including 24 pairs with sIUGR and 19 pairs without.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Mitochondrial DNA contents were measured and presented as fold difference between the small and large fetuses. After staining with MitoTracker, mitochondrial intensity in AFMSCs was analyzed with the Image J program.

RESULT(S)

The fold differences of the cord blood mitochondrial DNA content between the small and large twins were significantly higher in the MC twins with sIGUR (2.5 ± 1.2, n = 24 pairs) than in those without sIUGR (1.2 ± 0.3, n = 19 pairs). In addition, mitochondrial staining intensities were significantly higher in the AFMSCs derived from growth-restricted fetuses than from control fetuses.

CONCLUSION(S)

Mitochondrial activation in the sIUGR fetus of MC twins was likely regulated by locally adverse placental and blood flow conditions, instead of genetic factors.

Mitochondrial disorders and the eye

The clinical significance of disturbed mitochondrial function in the eye has emerged since mitochondrial DNA (mtDNA) mutation was described in Leber's hereditary optic neuropathy. The spectrum of mitochondrial dysfunction has become apparent through increased understanding of the contribution of nuclear and somatic mtDNA mutations to mitochondrial dynamics and function. Common ophthalmic manifestations of mitochondrial dysfunction include optic atrophy, pigmentary retinopathy, and ophthalmoplegia. The majority of patients with ocular manifestations of mitochondrial disease also have variable central and peripheral nervous system involvement. Mitochondrial dysfunction has recently been associated with age-related retinal disease including macular degeneration and glaucoma. Therefore, therapeutic targets directed at promoting mitochondrial biogenesis and function offer a potential to both preserve retinal function and attenuate neurodegenerative processes.

Mitochondrial H2O2 generated from electron transport chain complex I stimulates muscle differentiation

Mitochondrial reactive oxygen species (mROS) have been considered detrimental to cells. However, their physiological roles as signaling mediators have not been thoroughly explored. Here, we investigated whether mROS generated from mitochondrial electron transport chain (mETC) complex I stimulated muscle differentiation. Our results showed that the quantity of mROS was increased and that manganese superoxide dismutase (MnSOD) was induced via NF-κB activation during muscle differentiation. Mitochondria-targeted antioxidants (MitoQ and MitoTEMPOL) and mitochondria-targeted catalase decreased mROS quantity and suppressed muscle differentiation without affecting the amount of ATP. Mitochondrial alterations, including the induction of mitochondrial transcription factor A and an increase in the number and size of mitochondria, and functional activations were observed during muscle differentiation. In particular, increased expression levels of mETC complex I subunits and a higher activity of complex I than other complexes were observed. Rotenone, an inhibitor of mETC complex I, decreased the mitochondrial NADH/NAD(+) ratio and mROS levels during muscle differentiation. The inhibition of complex I using small interfering RNAs and rotenone reduced mROS levels, suppressed muscle differentiation, and depleted ATP levels with a concomitant increase in glycolysis. From these results, we conclude that complex I-derived O(2)·(-), produced through reverse electron transport due to enhanced metabolism and a high activity of complex I, was dismutated into H(2)O(2) by MnSOD induced via NF-κB activation and that the dismutated mH(2)O(2) stimulated muscle differentiation as a signaling messenger.

Superoxide is an associated signal for apoptosis in axonal injury

Optic neuropathy is the leading cause of irreversible blindness, and a paradigm for central nervous system axonal disease. The primary event is damage to retinal ganglion cell axons, with subsequent death of the cell body by apoptosis. Trials of neuroprotection for these and other neuronal diseases have mostly failed, primarily because mechanisms of neuroprotection in animals do not necessarily translate to humans. We developed a methodology for imaging an intracellular transduction pathway that signals neuronal death in the living animal. Using longitudinal confocal scanning multilaser ophthalmoscopy, we identified the production of superoxide within retrograde-labelled rat retinal ganglion cells after optic nerve transection. Superoxide was visualized by real-time imaging of its reaction product with intravitreally administered hydroethidine and confirmed by differential spectroscopy of the specific product 2-hydroxyethidium. Retinal ganglion cell superoxide increased within 24 h after axotomy, peaking at 4 days, and was not observed in contralateral untransected eyes. The superoxide signal preceded phosphatidylserine externalization, indicating that superoxide generation was an early event and preceded apoptosis. Intravitreal pegylated superoxide dismutase blocked superoxide generation after axotomy and delayed retinal ganglion cell death. Together, these results are consistent with superoxide being an upstream signal for retinal ganglion cell apoptosis after optic nerve injury. Early detection of axonal injury with superoxide could serve as a predictive biomarker for patients with optic neuropathy.

Mitochondrial optic neuropathy: In vivo model of neurodegeneration and neuroprotective strategies

This review summarizes the characteristics of a rodent toxicologic model of optic neuropathy induced by the mitochondrial complex I inhibitor rotenone. This model has been developed to fulfill the demand for a drug-screening tool providing a sound mechanistic context to address the role of mitochondrial dysfunction in the pathogenesis of neurodegenerative disorders. It features biochemical, structural, and functional retinal deficits that resemble those of patients with Leber's hereditary optic neuropathy, a mitochondrial disease characterized by selective degeneration of retinal ganglion cells, and for which an environmental component is believed to play a major triggering role. The available data support the efficiency, sensitivity, and versatility of the model for providing insights into the mechanisms of neurodegeneration, including mitochondrial dysfunction, oxidative stress and excitotoxicity. Screening work with this model has provided proof-of-principle that interventions targeting the electron transport chain, such as USP methylene blue and near-infrared light therapy, are effective at preventing neurodegeneration induced by mitochondrial dysfunction in vivo. Prospective developments of this model include the use of neuronal reporter genes for in vivo non-invasive assessment of retinal degeneration at different time points, and its combination with genetic approaches to elucidate the synergism of environmental and genetic factors in neurodegeneration.

Effectiveness of Novel Borane-Phosphine Complexes In Inhibiting Cell Death Depends on the Source of Superoxide Production Induced by Blockade of Mitochondrial Electron Transport

Central neurons undergo cell death after axotomy. One of the signaling pathways for this process is oxidative modification of one or more critical sulfhydryls in association with superoxide generation within mitochondria. Agents that reduce oxidized sulfhydryls are neuroprotective of axotomized retinal ganglion cells, and we hypothesized that this occurs via reversal of the effects of mitochondrial-produced superoxide. To study this, we measured the ability of the novel borane-phosphine complex drugs bis(3-propionic acid methyl ester)phenylphosphine borane complex (PB1) and (3-propionic acid methyl ester)diphenylphosphine borane complex (PB2) to inhibit the death of neuron-like RGC-5 cells induced by perturbation of the mitochondrial electron transport chain. We found that borane-phosphine complexes prevent neuronal cell death from superoxide produced by the redox-cycling agent menadione and the complex III inhibitor antimycin A, which produce superoxide towards the cytoplasm and matrix, but not the complex I inhibitor rotenone, which produces superoxide in the matrix alone. The ability of these disulfide reductants to prevent cell death may be predicted by the topology of superoxide production with respect to the mitochondrial matrix and extramitochondrial space.

N-acetylcysteine inhibits post-impact chondrocyte death in osteochondral explants

BACKGROUND

Chondrocyte death has been linked to injury-induced oxidative damage, suggesting that antioxidants could substantially improve viability. However, since reactive oxygen species play roles in normal physiology, there are concerns that antioxidants may have deleterious side effects. To address these issues, we studied the effects of N-acetylcysteine, a potent free radical scavenger, on chondrocyte viability and cartilage proteoglycan content in an in vitro cartilage injury model. We hypothesized that treatment with N-acetylcysteine soon after an impact injury would have significant chondrocyte-sparing effects and would prevent injury-induced proteoglycan losses.

METHODS

Bovine osteochondral explants were subjected to a single impact load with use of a drop-tower device. Chondrocyte viability was measured at multiple time points post-impact with use of fluorescent probes and confocal microscopy. Forty-eight hours after impact, the effects on viability of immediate post-impact treatment with N-acetylcysteine were compared with the effects of the caspase inhibitor N-CBZ-Val-Ala-Asp(O-Me) fluoromethyl ketone and those of the cell-membrane-stabilizing surfactant poloxamer 188. The effect of N-acetylcysteine on proteoglycan content was determined at seven and fourteen days post-impact.

RESULTS

Chondrocyte viability declined sharply within an hour and reached a steady state within six to twelve hours after impact. Immediate treatment with N-acetylcysteine doubled the number of viable chondrocytes assayed forty-eight hours after impact, and this effect was significantly greater than that of N-CBZ-Val-Ala-Asp(O-Me) fluoromethyl ketone. Even when N-acetylcysteine treatment was delayed for up to four hours after injury, it still had significant positive effects on cell viability at forty-eight hours. Moreover, N-acetylcysteine treatment significantly improved proteoglycan content at the impact sites at both seven and fourteen days after injury.

CONCLUSIONS

Treatment with N-acetylcysteine soon after a blunt impact injury can reduce chondrocyte death and proteoglycan loss measured seven to fourteen days after injury.

Diabetic retinal neurodegeneration is associated with mitochondrial oxidative stress and is improved by an angiotensin receptor blocker in a model combining hypertension and diabetes

OBJECTIVE

Diabetic retinopathy displays the features of a neurodegenerative disease. Oxidative stress is involved in the pathogenesis of diabetic retinopathy. This investigation sought to determine whether hypertension exacerbates the oxidative stress, neurodegeneration, and mitochondrial dysfunction that exists in diabetic retinopathy and whether these changes could be minimized by the angiotensin II type 1 (AT(1)) receptor blocker (ARB) losartan.

RESEARCH DESIGN AND METHODS

Diabetes was induced in spontaneously hypertensive rats (SHRs) and normotensive Wistar-Kyoto (WKY) rats. The diabetic SHRs were assigned to receive or not receive losartan.

RESULTS

The level of apoptosis in the retina was higher in diabetic WKY rats than in the control group, and higher levels were found in diabetic SHRs. The apoptotic cells expressed neural and glial markers. The retinal glial reaction was more evident in diabetic WKY rats and was markedly accentuated in diabetic SHRs. Superoxide production in retinal tissue increased in diabetic WKY rats, and a greater increase occurred in diabetic SHRs. Glutathione levels decreased only in diabetic SHRs. As a consequence, the levels of nitrotyrosine and 8-hydroxy 2'-deoxyguanosine, markers of oxidative stress, were elevated in diabetic groups, mainly in diabetic SHRs. Mitochondrial integrity was dramatically affected in the diabetic groups. The ARB treatment reestablished all of the above-mentioned parameters.

CONCLUSIONS

These findings suggest that concomitance of hypertension and diabetes exacerbates oxidative stress, neurodegeneration, and mitochondrial dysfunction in the retinal cells. These data provide the first evidence of AT(1)blockage as a neuroprotective treatment of diabetic retinopathy by reestablishing oxidative redox and the mitochondrial function.

Mitochondrial dysfunction and glaucoma

Glaucoma is increasingly recognized as a neurodegenerative disorder, characterized by the accelerated loss of retinal ganglion cells (RGCs) and their axons. Open angle glaucoma prevalence and incidence increase exponentially with increasing age, yet the pathophysiology underlying increasing age as a risk factor for glaucoma is not well understood. Accumulating evidence points to age-related mitochondrial dysfunction playing a key role in the etiology of other neurodegenerative disorders including amyotrophic lateral sclerosis, Alzheimer and Parkinson disease. The 2 major functions of mitochondria are the generation of ATP through oxidative phosphorylation and the regulation of cell death by apoptosis. This review details evidence to support our hypothesis that age-associated mitochondrial dysfunction renders RGCs susceptible to glaucomatous injury by reducing the energy available for repair processes and predisposing RGCs to apoptosis. Eliciting the role of mitochondria in glaucoma pathogenesis may uncover novel therapeutic targets for protecting the optic nerve and preventing vision loss in glaucoma.

Oxidative stress in Chinese patients with Leber's hereditary optic neuropathy

The cellular mechanisms of Leber's hereditary optic neuropathy (LHON) are poorly understood and there is little information on the onset of blindness and neurological degeneration. Here we define the relationship between oxidative stress and LHON pathogenicity at the cellular level. Venous blood was obtained from 14 patients with LHON, 21 asymptomatic maternal relatives and 30 normal individuals (controls). The level of free radicals in blood was assessed as luminol luminescence immediately and at 10 min after addition of phytohaemagglutinin. In LHON patients and their asymptomatic relatives, free radicals increased significantly immediately after adding phytohaemagglutinin compared with baseline and normal controls. After 10 min, however, there were no significant differences between and within the groups. These results suggest that the antioxidant capacity is reduced in the blood of patients with LHON and in asymptomatic relatives, and that oxidative stress plays a significant role in the pathogenesis of LHON.