Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 100, Issue 3, Pages 1022-1027Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.0333594100
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Funding
- NCRR NIH HHS [RR04050, P41 RR004050] Funding Source: Medline
- NEI NIH HHS [EY06891, EY09213, F32 EY006891, R01 EY006891, T35EY07088, T35 EY007088] Funding Source: Medline
- NIEHS NIH HHS [P42 ES010337, ES10337, ES03183] Funding Source: Medline
- NINDS NIH HHS [NS14718, R01 NS014718] Funding Source: Medline
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Photoreceptor apoptosis and resultant visual deficits occur in humans and animals with inherited and disease-, injury-, and chemical-induced retinal degeneration. A clinically relevant mouse model of progressive rod photoreceptor-selective apoptosis was produced by low-level developmental lead exposure and studied in combination with transgenic mice overexpressing Bcl-x(L) only in the photoreceptors. A multiparametric analysis of rod apoptosis and mitochondrial structure-function was performed. Mitochondrial cristae topography and connectivity, matrix volume, and contact sites were examined by using 3D electron tomography. Lead-induced rod-selective apoptosis was accompanied by rod Ca2+ overload, rhodopsin loss, translocation of Bax from the cytosol to the mitochondria, decreased rod mitochondrial respiration and membrane potential, mitochondrial cytochrome c release, caspase-3 activation, and an increase in the number of mitochondrial contact sites. These effects occurred without mitochondrial matrix swelling, outer membrane rupture, caspase-8 activation, or Bid cleavage. Bcl-x(L) overexpression completely blocked all apoptotic events, except Ca2+ overload, and maintained normal rod mitochondrial function throughout adulthood. This study presents images of mitochondrial contact sites in an in vivo apoptosis model and shows that Bcl-x(L) overexpression blocks increased contact sites and apoptosis. These findings extend our in vitro retinal studies with Pb2+ and Ca2+ and suggest that developmental lead exposure produced rod-selective apoptosis without mitochondrial swelling by translocating cytosolic Bax to the mitochondria, which likely sensitized the Pb2+ and Ca2+ overloaded rod mitochondria to release cytochrome c. These results have relevance for therapies in a wide variety of progressive retinal and neuronal degenerations where Ca2+ overload, lead exposure, and/or mitochondrial dysfunction occur.
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