title: Cleavage of protein kinase D after acute hypoinsulinemia prevents excessive lipoprotein lipase-mediated cardiac triglyceride accumulation.
abstract: 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.
authors.affiliation: Faculty of Pharmaceutical Sciences, University of British Columbia, Vancouver, British Columbia, Canada.
authors.forename: Min Suk
authors.initials: MS
authors.lastname: Kim
authors.forename: Fang
authors.initials: F
authors.lastname: Wang
authors.forename: Prasanth
authors.initials: P
authors.lastname: Puthanveetil
authors.forename: Girish
authors.initials: G
authors.lastname: Kewalramani
authors.forename: Sheila
authors.initials: S
authors.lastname: Innis
authors.forename: Lucy
authors.initials: L
authors.lastname: Marzban
authors.forename: Susan F
authors.initials: SF
authors.lastname: Steinberg
authors.forename: Travis D
authors.initials: TD
authors.lastname: Webber
authors.forename: Timothy J
authors.initials: TJ
authors.lastname: Kieffer
authors.forename: Ashraf
authors.initials: A
authors.lastname: Abrahani
authors.forename: Brian
authors.initials: B
authors.lastname: Rodrigues
mesh_terms: 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*
chemical_list: D014280:Triglycerides; D006493:Heparin; C089212:protein kinase D; D011493:Protein Kinase C; D008071:Lipoprotein Lipase; D053148:Caspase 3