Caspase-dependent protein phosphatase 2A activation contributes to endotoxin-induced cardiomyocyte contractile dysfunction.
OBJECTIVE
Several studies report calcium mishandling, sarcomere disarray, and caspase activation during heart failure. Although active caspases have been shown to cleave myofibrillar proteins, little is known regarding their effects on calcium handling proteins. Therefore, we aimed to explore how endotoxin-induced caspase activation disrupts intracellular calcium regulation.


METHODS
Randomized controlled trial.


METHODS
Small animal research laboratory.


METHODS
Adult male Sprague-Dawley rats.


METHODS
Sepsis was induced by injection of endotoxin (10 mg/kg, intravenously). Caspase inhibition was achieved by coinjection with zVAD.fmk (3 mg/kg, intravenously). We first isolated adult rat ventricular myocytes from control, endotoxin, and (endotoxin + zVAD)-treated rats to characterize contractile parameters and cellular calcium homeostasis. Underlying molecular mechanisms responsible for calcium mishandling were explored on sarcoplasmic reticulum vesicles and mitochondria prepared from treated animals. All experiments were performed 4 hrs postendotoxin treatment.


RESULTS
zVAD normalized reductions in fractional cell shortening and relaxation rate triggered by endotoxin treatment. Both sarco-/endoplasmic reticulum Ca-ATPase and mitochondria-dependent calcium uptakes were impaired after endotoxin treatment and prevented when myocytes were isolated from zVAD-treated endotoxinic rat hearts. zVAD blocked endotoxin-induced phospholamban dephosphorylation, protein phosphatase 2A activation, and mitochondrial calcium retention capacity reduction. To strengthen these results, control sarcoplasmic reticulum vesicles and mitochondria were incubated with active recombinant caspase-3. Although no effects were observed on mitochondria, caspase-3 directly exerts detrimental effects on sarcoplasmic reticulum calcium uptake capacity by activating protein phosphatase 2A, leading to phospholamban dephosphorylation.


CONCLUSIONS
Caspase inhibition protects from endotoxin-induced sarcoplasmic reticulum calcium uptake capacity reduction and mitochondrial dysfunction.
Neviere
Remi
R
EA4484, Département de Physiologie, Université Lille2, Lille, France.
Hassoun
Sidi Mohamed
SM
Decoster
Brigitte
B
Bouazza
Youcef
Y
Montaigne
David
D
Maréchal
Xavier
X
Marciniak
Camille
C
Marchetti
Philippe
P
Lancel
Steve
S
D000818:Animals; D015153:Blotting, Western; D002118:Calcium / Q000032:analysis / Q000378:metabolism / Q000502:physiology; D020169:Caspases / Q000378:metabolism* / Q000502:physiology; D004731:Endotoxins / Q000494:pharmacology*; D004789:Enzyme Activation / Q000502:physiology; D006333:Heart Failure / Q000201:enzymology / Q000503:physiopathology; D008297:Male; D053078:Membrane Potential, Mitochondrial / Q000187:drug effects / Q000502:physiology; D008929:Mitochondria, Heart / Q000737:chemistry / Q000187:drug effects / Q000502:physiology; D009200:Myocardial Contraction / Q000187:drug effects / Q000502:physiology; D032383:Myocytes, Cardiac / Q000737:chemistry / Q000187:drug effects / Q000201:enzymology / Q000502:physiology*; D054648:Protein Phosphatase 2 / Q000378:metabolism* / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley
D004731:Endotoxins; D054648:Protein Phosphatase 2; D020169:Caspases; D002118:Calcium