Cleavage of protein kinase D after acute hypoinsulinemia prevents excessive lipoprotein lipase-mediated cardiac triglyceride accumulation.
OBJECTIVE
During hypoinsulinemia, when cardiac glucose utilization is impaired, the heart rapidly adapts to using more fatty acids. One means by which this is achieved is through lipoprotein lipase (LPL). We determined the mechanisms by which the heart regulates LPL after acute hypoinsulinemia.


METHODS
We used two different doses of streptozocin (55 [D-55] and 100 [D-100] mg/kg) to induce moderate and severe hypoinsulinemia, respectively, in rats. Isolated cardiomyocytes were also used for transfection or silencing of protein kinase D (PKD) and caspase-3.


RESULTS
There was substantial increase in LPL in D-55 hearts, an effect that was absent in severely hypoinsulinemic D-100 animals. Measurement of PKD, a key element involved in increasing LPL, revealed that only D-100 hearts showed an increase in proteolysis of PKD, an effect that required activation of caspase-3 together with loss of 14-3-3zeta, a binding protein that protects enzymes against degradation. In vitro, phosphomimetic PKD colocalized with LPL in the trans-golgi. PKD, when mutated to prevent its cleavage by caspase-3 and silencing of caspase-3, was able to increase LPL activity. Using a caspase inhibitor (Z-DEVD) in D-100 animals, we effectively lowered caspase-3 activity, prevented PKD cleavage, and increased LPL vesicle formation and translocation to the vascular lumen. This increase in cardiac luminal LPL was associated with a striking accumulation of cardiac triglyceride in Z-DEVD-treated D-100 rats. CONCLUSIONS After severe hypoinsulinemia, activation of caspase-3 can restrict LPL translocation to the vascular lumen. When caspase-3 is inhibited, this compensatory response is lost, leading to lipid accumulation in the heart.
Kim
Min Suk
MS
Faculty of Pharmaceutical Sciences, University of British Columbia, Vancouver, British Columbia, Canada.
Wang
Fang
F
Puthanveetil
Prasanth
P
Kewalramani
Girish
G
Innis
Sheila
S
Marzban
Lucy
L
Steinberg
Susan F
SF
Webber
Travis D
TD
Kieffer
Timothy J
TJ
Abrahani
Ashraf
A
Rodrigues
Brian
B
D000818:Animals; D053148:Caspase 3 / Q000378:metabolism; D003921:Diabetes Mellitus, Experimental / Q000378:metabolism*; D006493:Heparin / Q000494:pharmacology; D006946:Hyperinsulinism / Q000201:enzymology / Q000378:metabolism*; D007700:Kinetics; D008071:Lipoprotein Lipase / Q000378:metabolism*; D032383:Myocytes, Cardiac / Q000201:enzymology / Q000378:metabolism*; D011493:Protein Kinase C / Q000378:metabolism*; D051381:Rats; D012016:Reference Values; D014280:Triglycerides / Q000378:metabolism*
D014280:Triglycerides; D006493:Heparin; C089212:protein kinase D; D011493:Protein Kinase C; D008071:Lipoprotein Lipase; D053148:Caspase 3