Woods, A.K.
and Storey, K.B. 2007. Cytoplasmic phospholipase
A2 regulation in the hibernating thirteen-lined ground squirrels. Cell Mol Biol Lett. 12: 621-632.
DOI: 10.2478/s11658-007-0036-8
Cytoplasmic phospholipase
A2 regulation in the hibernating thirteen-lined ground squirrels.
Ashley
K. Woods and Kenneth B. Storey
Abstract
Cytosolic
calcium-dependent phospholipase A2 (cPLA2) has
multiple roles including production of arachidonic
acid (a key player in cellular signaling pathways) and membrane remodeling.
Additionally, since catabolism of arachidonic acid
generates free radicals, the enzyme is also implicated in ischemic injury to
mammalian organs. Regulation of cPLA2 could be important in the suppression and
prioritization of cellular pathways in animals that undergo reversible
transitions into hypometabolic states. The present study examines the responses
and regulation of cPLA2 in skeletal muscle and liver of hibernating thirteen-lined
ground squirrels, Spermophilus tridecemlineatus. cPLA2
activity decreased significantly by 43% in liver during hibernation, compared
with euthermic controls, and Km values for arachidonoyl
thio-PC substrate fell in both organs during
hibernation to 61% in liver and 28% in muscle of the corresponding euthermic
value. To determine whether these responses were due to a change in the
phosphorylation state of the enzyme, Western blotting was employed using
antibodies recognizing phospho-Ser505 on α-cPLA2. The amount of
phosphorylated α-cPLA2 in hibernator liver was just 38% of the value in euthermic
liver. Furthermore, incubation of liver extracts under conditions that enhanced
protein phosphatase action caused a greater reduction in the detectable amount
of phospho-Ser505 enzyme content in euthermic, versus hibernator, extracts. The
data are consistent with a suppression of cPLA2 function during torpor via
enzyme dephosphorylation, an action that may contribute to the well developed ischemia
tolerance and lack of oxidative damage found in hibernating species over cycles
of torpor and arousal.