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Reduced Apaf-1 levels in cardiomyocytes engage strict regulation of apoptosis by endogenous XIAP.

Potts MB, Vaughn AE, McDonough H, Patterson C, Deshmukh M - J. Cell Biol. (2005)

Bottom Line: The cardiomyocyte resistance to cytochrome c is mediated by endogenous XIAP, as XIAP-deficient cardiomyocytes die rapidly with cytosolic cytochrome c alone.Importantly, we found that cardiomyocytes, like neurons, have markedly reduced Apaf-1 levels and that this decrease in Apaf-1 is directly linked to the tight regulation of caspase activation by XIAP.These data identify an important function of XIAP in cardiomyocytes and point to a striking similarity in the regulation of apoptosis in postmitotic cells.

View Article: PubMed Central - PubMed

Affiliation: Neuroscience Center, Department of Cell and Developmental Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA.

ABSTRACT
Overexpression studies have identified X-linked inhibitor of apoptosis protein (XIAP) as a potent inhibitor of caspases. However, the exact function of endogenous XIAP in regulating mammalian apoptosis is less clear. Endogenous XIAP strictly regulates cytochrome c-dependent caspase activation in sympathetic neurons but not in many mitotic cells. We report that postmitotic cardiomyocytes, unlike fibroblasts, are remarkably resistant to cytosolic microinjection of cytochrome c. The cardiomyocyte resistance to cytochrome c is mediated by endogenous XIAP, as XIAP-deficient cardiomyocytes die rapidly with cytosolic cytochrome c alone. Importantly, we found that cardiomyocytes, like neurons, have markedly reduced Apaf-1 levels and that this decrease in Apaf-1 is directly linked to the tight regulation of caspase activation by XIAP. These data identify an important function of XIAP in cardiomyocytes and point to a striking similarity in the regulation of apoptosis in postmitotic cells.

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Cytosolic microinjection of cytochrome c induces death in fibroblasts but not cardiomyocytes. Neonatal rat cardiomyocytes and dermal fibroblasts were microinjected with 25 μg/μl of bovine or yeast cytochrome c, and cell survival (using morphological criteria) was assessed at multiple times after the injections. (A) Phase-contrast and fluorescence photographs of the cells 3 h after the injections of cytochrome c. The injected cells (arrows) were identified by the presence of rhodamine dextran coinjected with the cytochrome c. (B) Quantitation of cell survival. Data shown are the mean ± SEM of three independent experiments.
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fig1: Cytosolic microinjection of cytochrome c induces death in fibroblasts but not cardiomyocytes. Neonatal rat cardiomyocytes and dermal fibroblasts were microinjected with 25 μg/μl of bovine or yeast cytochrome c, and cell survival (using morphological criteria) was assessed at multiple times after the injections. (A) Phase-contrast and fluorescence photographs of the cells 3 h after the injections of cytochrome c. The injected cells (arrows) were identified by the presence of rhodamine dextran coinjected with the cytochrome c. (B) Quantitation of cell survival. Data shown are the mean ± SEM of three independent experiments.

Mentions: Sympathetic neurons, unlike many mitotic cells, are remarkably resistant to cytosolic cytochrome c. To determine whether terminally differentiated cardiomyocytes display the same resistance, we microinjected primary mouse neonatal cardiomyocytes with cytochrome c. As a control, we also microinjected fibroblasts isolated from the same animals. Bovine cytosolic cytochrome c alone was sufficient to induce rapid cell death in fibroblasts, with 90% of fibroblasts dying within 30 min of the injections (Fig. 1). In contrast, bovine cytochrome c alone was incapable of inducing cell death in cardiomyocytes, as >90% of cardiomyocytes remained viable even 10 h after the cytochrome c injections (Fig. 1). Control injections with yeast cytochrome c, which is incapable of activating caspases (Ellerby et al., 1997), did not induce death in either fibroblasts or cardiomyocytes. Thus, neonatal cardiomyocytes, just like sympathetic neurons, were markedly resistant to cytosolic injection of cytochrome c.


Reduced Apaf-1 levels in cardiomyocytes engage strict regulation of apoptosis by endogenous XIAP.

Potts MB, Vaughn AE, McDonough H, Patterson C, Deshmukh M - J. Cell Biol. (2005)

Cytosolic microinjection of cytochrome c induces death in fibroblasts but not cardiomyocytes. Neonatal rat cardiomyocytes and dermal fibroblasts were microinjected with 25 μg/μl of bovine or yeast cytochrome c, and cell survival (using morphological criteria) was assessed at multiple times after the injections. (A) Phase-contrast and fluorescence photographs of the cells 3 h after the injections of cytochrome c. The injected cells (arrows) were identified by the presence of rhodamine dextran coinjected with the cytochrome c. (B) Quantitation of cell survival. Data shown are the mean ± SEM of three independent experiments.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2171313&req=5

fig1: Cytosolic microinjection of cytochrome c induces death in fibroblasts but not cardiomyocytes. Neonatal rat cardiomyocytes and dermal fibroblasts were microinjected with 25 μg/μl of bovine or yeast cytochrome c, and cell survival (using morphological criteria) was assessed at multiple times after the injections. (A) Phase-contrast and fluorescence photographs of the cells 3 h after the injections of cytochrome c. The injected cells (arrows) were identified by the presence of rhodamine dextran coinjected with the cytochrome c. (B) Quantitation of cell survival. Data shown are the mean ± SEM of three independent experiments.
Mentions: Sympathetic neurons, unlike many mitotic cells, are remarkably resistant to cytosolic cytochrome c. To determine whether terminally differentiated cardiomyocytes display the same resistance, we microinjected primary mouse neonatal cardiomyocytes with cytochrome c. As a control, we also microinjected fibroblasts isolated from the same animals. Bovine cytosolic cytochrome c alone was sufficient to induce rapid cell death in fibroblasts, with 90% of fibroblasts dying within 30 min of the injections (Fig. 1). In contrast, bovine cytochrome c alone was incapable of inducing cell death in cardiomyocytes, as >90% of cardiomyocytes remained viable even 10 h after the cytochrome c injections (Fig. 1). Control injections with yeast cytochrome c, which is incapable of activating caspases (Ellerby et al., 1997), did not induce death in either fibroblasts or cardiomyocytes. Thus, neonatal cardiomyocytes, just like sympathetic neurons, were markedly resistant to cytosolic injection of cytochrome c.

Bottom Line: The cardiomyocyte resistance to cytochrome c is mediated by endogenous XIAP, as XIAP-deficient cardiomyocytes die rapidly with cytosolic cytochrome c alone.Importantly, we found that cardiomyocytes, like neurons, have markedly reduced Apaf-1 levels and that this decrease in Apaf-1 is directly linked to the tight regulation of caspase activation by XIAP.These data identify an important function of XIAP in cardiomyocytes and point to a striking similarity in the regulation of apoptosis in postmitotic cells.

View Article: PubMed Central - PubMed

Affiliation: Neuroscience Center, Department of Cell and Developmental Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA.

ABSTRACT
Overexpression studies have identified X-linked inhibitor of apoptosis protein (XIAP) as a potent inhibitor of caspases. However, the exact function of endogenous XIAP in regulating mammalian apoptosis is less clear. Endogenous XIAP strictly regulates cytochrome c-dependent caspase activation in sympathetic neurons but not in many mitotic cells. We report that postmitotic cardiomyocytes, unlike fibroblasts, are remarkably resistant to cytosolic microinjection of cytochrome c. The cardiomyocyte resistance to cytochrome c is mediated by endogenous XIAP, as XIAP-deficient cardiomyocytes die rapidly with cytosolic cytochrome c alone. Importantly, we found that cardiomyocytes, like neurons, have markedly reduced Apaf-1 levels and that this decrease in Apaf-1 is directly linked to the tight regulation of caspase activation by XIAP. These data identify an important function of XIAP in cardiomyocytes and point to a striking similarity in the regulation of apoptosis in postmitotic cells.

Show MeSH
Related in: MedlinePlus