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Metabolic Disorders
Project:
PKU
Phil
Laipis,
Ph.D.
Description
in development.
Project: Disorders
of Fatty Acid
oxidation
Terry
Flotte,
M.D.
Beta-oxidation
of fatty
acids within
the mitochondria
represents
a key
component of
energy metabolism
in the
fasting state
and during
times of physiologic
stress.
A complex multi-organ
pathway
is responsible
for the
mobilization
of free
fatty acids
from peripheral
adipocytes,
import
of fatty acids
into the mitochondrial
matrix
of hepatocytes,
myocytes,
and other cells
via the
carnitine cycle
and oxidation
of fatty
acids via the
beta-oxidation
spiral
to acetyl-CoA.
The acetyl
CoA produced
is then
ready to either
enter the tri-carboxylic
acid
cycle or exit
the cell as
ketone bodies,
while reducing
equivalents
in the
form of NADH+
and FADH2 are
channeled directly
to the electron
transport
chain. Disorders
of mitochondrial
fatty
acid oxidation
(FAO) as a
group represent
a relatively
common
class of metabolic
disorders,
the most
common of which
typically present
with either
Sudden Infant
Death Syndrome
(SIDS) or with
a combined
cardiac and
skeletal
myopathy. Treatment
of these disorders
has consisted
primarily
of dietary
manipulation
and has
been far less
than optimal
to this point.
The recent
development
of recombinant
adeno-associated
virus
(rAAV) vectors
for highly
efficient transduction
of hepatocytes
and myofibers
presents
new tools for
the study of
FAO disorders.
Specifically,
our laboratory
has produced
rAAV
vectors expressing
FAO enzymes
whose
deficiency
results in
myopathy, such
as short-chain
acyl
CoA dehydrogenase
(SCAD)
and long-chain
acyl
CoA dehydrogenase
(LCAD).
Human cell
lines from
patients deficient
in these enzymes
are available,
and mutant
mouse
models exist
for both of
these disorders.
We propose
to utilize
rAAV
vectors expressing
FAO enzymes
in an
attempt to
unravel the
pathobiology
of FAO
disorders and
to better define
endpoints for
molecular or
cell-based
therapies of
these
disorders.
This will be
accomplished
in three
specific aims:
(1) To assess
the extent
to which genetic
correction
of a limited
percentage
of SCAD
deficient or
LCAD deficient
cells
within a cell
population
or organ can
effect
biochemical
correction
of fatty
acid oxidation.
(2) To
determine whether
receptor binding
and entry are
the limiting
steps for stable
transduction
by rAAV
in an intact
mammalian liver
or muscle bundle.
(3) To test
the hypothesis
that
the liver pathology
observed in
LCAD and VLCAD
deficiencies
are secondary
to the
accumulation
of toxic
metabolites
as opposed
to primary
energy
failure within
hepatocytes.
(4) To
determine whether
global phenotypic
correction
of FAO
deficiency
in mice is
more effective
after
widespread
vector delivery
after
intrauterine
or neonatal
IV injection.
The information
gained
from these
studies could
also be used
to guide the
feasibility
of other
organ-directed
therapies,
potentially
including
stem cell transplantation.
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