Death and Rescue Regulation of cardiac myocyte cell death Lin GH

Death pathway there are two principal forms of cell death: Necrosis & apoptosis

Myocyte death as a contributing factor to cardiac pathology Ischemic Injury and Myocyte Death There is evidence that apoptosis precedes necrosis and constitutes the prevailing form of myocyte death. infarction

Caspases as the Effector Machinery of Apoptosis Initiator caspases Other caspases Effector caspases cysteine-dependent aspartate-directed proteases

Caspase cascades are highly ordered effector caspases positive feedback Initiator caspases

Target proteins for caspases nuclear proteins Cytoskeletal proteins Regulatory proteins

Apoptotic death pathway Receptor- dependent Mitochondrion- dependent Extrinsic pathway Intrinsic pathway

Mechanisms of Caspase Activation Activation of caspases may take place either within death receptor complexes of the cytoplasmic membrane or by a mitochondrion-dependent mechanism within the cytosol

Death Receptor Pathway death domain-mediated protein interactions

The extrinsic pathway through death receptors

Mitochondrial Pathway Schematic diagram showing the mechanism of cytochrome c– dependent caspase activation apoptosis-inducing factor (AIF ).

Intrinsic pathway through the mitochondria Intracellular stresses such as increased oxidative stress, which may derive from the mitochondria themselves, activate the mitochondrial death pathway. apoptosome

Apaf-1 and activation of caspase-9 cytochrome c interacts with an adapter protein, apoptosis-activating factor (Apaf)-1

Morphological changes in mitochondria during cytochrome c release

Cytochrome c and the mitochondrial permeability transition pore opening of the MPTP may also influence cell death by effecting the release of cyt c and other apoptotic factors from the mitochondrial intermembrane space Central role of mitochondria during ischemia and reperfusion

The mitochondrial permeability transition pore cyclophilin D (Cyp-D) VDAC, voltage-dependent anion channel ANT, adenine nucleotide translocase

Regulatory Proteins ----Bcl-2 Protein Family Mediate both proapoptotic and antiapoptotic regulation The Bcl-2 family of proteins are key regulators of the mitochondrial death pathway. Bcl-2 Bcl-xLBax BH1 (red), BH2 (orange), BH3 (green), and BH4 (yellow)

Mechanisms suggested to mediate the antiapoptotic effect of bcl-2

Model for the mechanism of action of Bcl-2 family proteins

X-linked IAP neuronal IAP c-IAP1 c-IAP2 survivin caspase activity Since the levels of expression of IAPs (and other inhibitory proteins) appear to be high in the heart, modulation of these proteins may be a significant aspect of cardiac myocyte apoptosis. caspase activation not only requires proteolytic cleavage of the enzymes themselves, but removal of inhibitory influences (IAPs) is also necessary. Inhibitor of Apoptosis Proteins -

Signal Transduction Signal transduction pathways implicated in the regulation of cell survival and apoptosis The commitment to apoptosis is influenced by protein kinase cascades that may be activated in the cell. whereas some protein kinases are implicated in cytoprotection, and others enhance cell death.

The pathway that is most clearly implicated in cytoprotection in all cell types is the PI3K pathway This pathway is potently activated by insulin or insulin-like growth factor-1 (IGF-1). Modulation of myocyte cell death Phosphatidylinositol 3’-kinase

Akt Signaling

There are three well-characterized MAPK subfamilies that have already been mentioned, the ERKs, JNKs, and p38-MAPKs, all of which influence cell survival Mitogen-activated protein kinases

Toward Antiapoptosis as a New Treatment Modality Targets for Intervention Initiation, regulation, and effector mechanisms offer potential molecular targets for antiapoptotic intervention.

Antiapoptotic strategies FasL: Fas ligand; cyt. C: cytochrome c; ARC: apoptosis repressor with a caspase recruitment domain; AIF:apoptosis-inducing factor. Decoy receptor ARC IAPs BcL-2 family proteins Inhibitors of stress-activated protein kinases PI3K, ERK signaling pathway

Targeting the Proapoptotic Stimulus Acting on the Myocyte B-blocking agents, carvedilo,angiotensin-converting enzyme inhibitors, reducing oxidative stress,inhibition of death receptor stimulation Bcl-2 protein family (eg, Bcl-2 or Bcl-xL), apoptosis repressor with a caspase recruitment domain, decoy receptors,growth factors ( insulin-like growth factor-1, cardiotrophin-1, neuregulins), Promotion of Antiapoptotic Signaling proapoptotic members of the Bcl-2 protein family such as Bax, Bad, and Bid, synthetic drugs interfere with the proapoptotic activity of adaptor protein, inhibition of MPTP and intracellular signaling pathways in promoting apoptosis Targeting Proapoptotic Signaling Antiapoptotic strategies Targeting the Downstream Execution Phase of Apoptosis Inhibition of downstream caspases (caspase-3, -6, or -7)

Thank you ! Lin GH 2004/0924