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Differential participation of phospholipase A2 isoforms during iron-induced retinal toxicity. Implications for
G Rodríguez Diez1, R M Uranga, M V Mateos
1Instituto de Investigaciones Bioquímicas de Bahía Blanca, Universidad Nacional del Sur and Consejo Nacional de Investigaciones Científicas y Técnicas, 8000 Bahía Blanca, Argentina.
Abstract:
Both elevated iron concentrations and the resulting oxidative stress condition are common signs in retinas of patients with age-related macular degeneration (AMD). The role of phospholipase A(2) (PLA(2)) during iron-induced retinal toxicity was investigated. To this end, isolated retinas were exposed to increasing Fe(2+) concentrations (25, 200 or 800 μM) or to the vehicle, and lipid peroxidation levels, mitochondrial function, and the activities of cytosolic PLA(2) (cPLA(2)) and calcium-independent PLA(2) (iPLA(2)) were studied. Incubation with Fe(2+) led to a time- and concentration-dependent increase in retinal lipid peroxidation levels whereas retinal cell viability was only affected after 60 min of oxidative injury. A differential release of arachidonic acid (AA) and palmitic acid (PAL) catalyzed by cPLA(2) and iPLA(2) activities, respectively, was also observed in microsomal and cytosolic fractions obtained from retinas incubated with iron. AA release diminished as the association of cyclooxygenase-2 increased in microsomes from retinas exposed to iron. Retinal lipid peroxidation and cell viability were also analyzed in the presence of cPLA(2) inhibitor, arachidonoyl trifluoromethyl ketone (ATK), and in the presence of iPLA(2) inhibitor, bromoenol lactone (BEL). ATK decreased lipid peroxidation levels and also ERK1/2 activation without affecting cell viability. BEL showed the opposite effect on lipid peroxidation. Our results demonstrate that iPLA(2) and cPLA(2) are differentially regulated and that they selectively participate in retinal signaling in an experimental model resembling AMD.
Insights
Iron overload in the retina causes oxidative stress, impacting cell viability. This study reveals that specific phospholipase A(2) (PLA(2)) enzymes, cytosolic PLA(2) (cPLA(2)) and calcium-independent PLA(2) (iPLA(2)), play distinct roles in iron-induced retinal damage.
Area of Science:
- Ophthalmology
- Neuroscience
- Biochemistry
Background:
- Elevated iron and oxidative stress are hallmarks of age-related macular degeneration (AMD).
- Phospholipase A(2) (PLA(2)) enzymes are implicated in cellular responses to injury.
Purpose of the Study:
- To investigate the role of cytosolic PLA(2) (cPLA(2)) and calcium-independent PLA(2) (iPLA(2)) in iron-induced retinal toxicity.
- To elucidate the specific mechanisms by which these enzymes contribute to oxidative stress in an AMD model.
Main Methods:
- Isolated retinas were exposed to varying concentrations of Fe(2+) to induce oxidative stress.
- Lipid peroxidation, mitochondrial function, and PLA(2) activities (cPLA(2), iPLA(2)) were measured.
- Specific inhibitors for cPLA(2) (ATK) and iPLA(2) (BEL) were used to assess their impact on retinal damage.
Main Results:
- Fe(2+) exposure increased lipid peroxidation and affected cell viability over time.
- cPLA(2) and iPLA(2) mediated differential release of arachidonic acid and palmitic acid, respectively.
- Inhibiting cPLA(2) reduced lipid peroxidation and ERK1/2 activation, while inhibiting iPLA(2) had opposing effects.
Conclusions:
- iPLA(2) and cPLA(2) are differentially regulated in response to iron-induced retinal stress.
- These enzymes play selective roles in retinal signaling pathways relevant to AMD pathogenesis.
