MiPsummer Programme pdf - Mitochondrial Physiology Society

55
Abstract # 26
Myocardial Fatty Acid
Oxidation
is Regulated by CD36-Mediated FA F Signalingg
TA Pietka, D Samovski, J Sun, K Yang, B Aldridge, RW Gross, PD Stahl, NA Abumrad
Washingtonn University School of Medicine, St. Louis, Missouri, USA
Background: The multifunctional scavenger s receptor CD36
facilitates cellular long chain fatty acid (FA)
uptake and mediates FA-related intracellular signaling. The CD36-defici
ent (CD36KO) heart, fed
or fasted
utilizes less palmitate and more glucose indicating impaired fuel flexibility (1, 2) andd we recently
showed
that CD36KO mice subjected to an overnight fast develop electrical abnormalities and altered lipid
metabolismm (3).
Objectives:
We hypothesized that FA-signaling
g via CD36 at
the plasma membrane plays a key role in
regulating fatty acid oxidation and investigated the impact of
altered acylcarnitine production in the t CD36
deficient heart.
Methods: Acylcarnitine
content was determinedd in fasted wild-type (WT) and CD36KO hearts using
multidimensional shotgun lipidomics. OXPHOSS capacity and protein content of respiratory complex
subunits were measured
in isolated mitochondria
a from WT and CD36KOO hearts. Palmitate induced
activation of AMP kinase (AMPK, p-T172) protein was measured in control and CD36 knockdown C2C12
myotubes and fasted WT
and CD36KO mouse hearts by western blotting. Finally, palmitate induced
oxidation was measured
in intact and saponin-permeabilized
soleus muscle fibers from wild-type
mice.
Results: Consistent with
the known impairment of FA oxidation in the fasted CD36KO heart (1, 2), we
found that the fasted CD36KO heartt is deficient in the ability
to increase acylcarnitine production.
Additionally, there were no defects in mitochondrial oxidative
capacityy or respiratory chain protein subunits in myocardial
mitochondria from the CD36KOO mouse compared to wild-type.
Interestingly, despite the lack off increased FA oxidation or
acylcarnitine production, CD36 deficiency increased basal levels
and activation of AMPK in the heart. h Similar results were found
with CD36 knockdown C2C12 cells, which had a higher basal
activation of AMPK
that was unresponsive to the palmitate induced
activation of AMPK
observed inn control C2C12 cells. Thus, the lack
of FA oxidation in the fasted CD36 deficient heart likely
reflects a
limiting role
of plasma membrane-mediated FA supply and deficient FA-induced signaling and iss not due to
insufficient AMPK activation. To test this theory, O2 consumption induced by palmitate oxidation
was
measured in
intact and saponin-permeabilized wild-type mouse soleus muscle m fibers. We found that
permeabilization resulted in a ~50%
decrease in respiration (Figure), indicating that FA induced
uptake/signaling at the plasma membrane drivess FA oxidation.
Conclusion: Fatty acid binding to CD36 triggerss intracellular signaling events e that ultimately lead to
activation of AMPK and
results in enhanced fatty acid oxidation.
References:
1. Coburn, C.T., Knapp, F.F., Jr., Febbraio, M., Beets, A.L., Silverstein, R.L., and Abumrad, N.A. 2000. Defective
uptake and utilization of long chain fatty
acids in muscle and adipose tissues of CD36 knockout mice. J Biol Chem
275:32523-32529.
2. Nahle, Z., Hsieh, M., Pietka, T., Coburn, C.T., Grimaldi, P.A., Zhang, M.Q., Das, D D., and Abumrad, N.A. 2008.
CD36-dependent regulation of muscle FoxO1 and PDK4 in the PPAR delta/beta-mediated adaptation to metabolic
stress. J Biol
Chem 283:14317-14326.
3. Pietka, T.A., Sulkin, M. .S., Kuda, O., Wang, W., Zhou, D., Yamada, K.A., Yang, K., Su, X., Gross, R.W., Nerbonne,
J.M., et al. 2012. CD36 protein influences myocardial Ca2+ homeostasis and phospholipid metabolism: conduction
anomalies in CD36-deficient mice during fasting. J Biol Chem 287:38901-38912.