||<p>Polycyclic aromatic hydrocarbons (PAHs) such as benzo(a)pyrene (BaP) are ubiquitous
environmental contaminants. PAHs are toxicologically important for both humans and
wildlife in large part due to their mutagenic, carcinogenic, and teratogenic properties.
While the effects of adult and developmental exposures to PAHs are relatively well
characterized, the potential for PAHs to have effects across generations is an emerging
concern in the field of environmental health. In epidemiological studies, prenatal
exposure to PAHs is associated with adverse birth outcomes as well as later life metabolic,
neurological, and reproductive disorders— which have become global human health epidemics.
These findings have been validated in animal models, with reduced survivorship, increased
morphological deformities, and alterations in behavior, physiology, and disease risk
in multiple subsequent generations. However, the mechanisms underlying the multigenerational
effects of PAHs are poorly understood. This dissertation focuses on mitochondrial
contributions to the maternal and cross-generational toxicity of PAHs. </p><p>Mitochondria
are essential to the development, health, survival, and reproduction of all aerobic
organisms. The importance of maintaining mitochondrial function for health is supported
by the prevalence of mitochondrial diseases, which clinically manifest in at least
1 in 4,300 people. Mitochondrial diseases often present with metabolic, neurological,
and reproductive consequences, similar to those associated with prenatal PAH exposures.
Mitochondrial DNA (mtDNA) is maternally inherited and undergoes bottlenecks (i.e.
reductions in mtDNA copy number per cell) during oogenesis and early embryonic development,
creating potential for maternal and cross-generational inheritance of mitochondrial
diseases. Inheritance of mitochondrial dysfunction across generations has been established
for genetic, pharmacological, and dietary etiologies. Notably, mitochondria are important
targets of environmental contaminants such as PAHs, which affect bioenergetics at
multiple levels of biological organization. However, the potential for environmental
toxicant-induced mitochondrial dysfunction to have persistent effects across multiple
generations is still largely uncharacterized. This is the knowledge gap we address
in this dissertation.</p><p>To this end, we evaluate the persistent bioenergetic effects
of BaP – a model PAH and known mitochondrial toxicant – in F1 (maternally exposed)
and F2 (cross-generationally exposed or germline exposed) generations following a
chronic maternal (F0) dietary exposure using the model teleost Danio rerio. Maternally
exposed F1 embryos exhibit reduced mitochondrial DNA integrity, reduced mitochondrial
function and efficiency, and impaired antioxidant defense systems during development,
largely in the absence of effects in exposed F0 females. Metabolic shifts during development
create potential for disease pathologies and reduced organismal fitness later in life.
In F1 adults, mitochondrial dysfunction presents in cardiac tissue with reductions
in mitochondrial reserve capacity. Cardiac function and plasticity are key determinants
of fitness in the environment, and impaired function confers disease risk in humans.
Maternally BaP exposed F1 fish also exhibit altered locomotor activity throughout
life and reduced fear/anxiety behaviors as adults. </p><p>PAH-induced changes in mitochondrial
function and metabolic plasticity persist in the F2 embryos, two generations removed
from the original BaP exposure, suggesting cross-generational reductions in fitness
may follow a single exposure event. Metabolic consequences occur in F2 embryos at
F0 exposure levels that do not cause significant dysfunction in the F1 generation,
with important implications for evaluating the risk associated with the persistent
effects of pollution (e.g. lasting impacts of oil spill events) in the environment.</p><p>The
ability to adjust metabolism is crucial for organisms to effectively respond to a
variety of natural and anthropogenic stressors, suggesting that organisms with alterations
in fundamental bioenergetic processes may be more sensitive to secondary stressors.
Herein we demonstrate that F2 organisms with a cross-generational history of exposure
exhibit altered metabolic response to thermal stress, reduced thermal tolerance, and
fitness tradeoffs. Cross-generational exposure to BaP potentiates metabolic effects
under thermal stress even in the absence of effects at baseline temperature. Taken
together, these data suggest that exposure to PAHs such as BaP affects mitochondrial
function, organismal physiology, behavior, and secondary stress response capacity
across generations, creating potential for downstream population and ecosystem level