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Caspase-8 inactivation in T cells increases necroptosis and suppresses autoimmunity in Bim-/- mice.

Bohgaki T, Mozo J, Salmena L, Matysiak-Zablocki E, Bohgaki M, Sanchez O, Strasser A, Hakem A, Hakem R - J. Cell Biol. (2011)

Bottom Line: Dysregulation of either the extrinsic or intrinsic apoptotic pathway can lead to various diseases including immune disorders and cancer.In addition to its role in the extrinsic apoptotic pathway, caspase-8 plays nonapoptotic functions and is essential for T cell homeostasis.We show that, similar to caspase-8(-/-) T cells, Bim(-/-) T cells that also lack caspase-8 displayed elevated levels of necroptosis and that inhibition of this cell death process fully rescued the survival and proliferation of these cells.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Medical Biophysics, University of Toronto, Toronto, Ontario M5G 2M9, Canada.

ABSTRACT
Dysregulation of either the extrinsic or intrinsic apoptotic pathway can lead to various diseases including immune disorders and cancer. In addition to its role in the extrinsic apoptotic pathway, caspase-8 plays nonapoptotic functions and is essential for T cell homeostasis. The pro-apoptotic BH3-only Bcl-2 family member Bim is important for the intrinsic apoptotic pathway and its inactivation leads to autoimmunity that is further exacerbated by loss of function of the death receptor Fas. We report that inactivation of caspase-8 in T cells of Bim(-/-) mice restrained their autoimmunity and extended their life span. We show that, similar to caspase-8(-/-) T cells, Bim(-/-) T cells that also lack caspase-8 displayed elevated levels of necroptosis and that inhibition of this cell death process fully rescued the survival and proliferation of these cells. Collectively, our data demonstrate that inactivation of caspase-8 suppresses the survival and proliferative capacity of Bim(-/-) T cells and restrains autoimmunity in Bim(-/-) mice.

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Additional loss of caspase-8 does not rescue impaired intrathymic T cell development in Bim-deficient mice. (A) Representative flow cytometric analysis of thymocytes from tcasp8−/−Bim−/− and control (WT, tcasp8−/−, and Bim−/−) mice (left). Numbers in the quadrants indicate the percentages of the different thymocyte subpopulations. Histograms show the mean percentages of thymocyte subpopulations from 10 young mice of each genotype (right). (B) Representative expression levels of TCR-β on thymocytes of the mice indicated in A are shown (left). Histograms show the mean percentages of thymocytes with high TCR-β expression levels from 10 young mice for each genotype (right). Data represent the mean ± SEM (error bars). *, P < 0.05 as compared with WT; •, P < 0.05 as compared with the tcasp8−/−.
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fig1: Additional loss of caspase-8 does not rescue impaired intrathymic T cell development in Bim-deficient mice. (A) Representative flow cytometric analysis of thymocytes from tcasp8−/−Bim−/− and control (WT, tcasp8−/−, and Bim−/−) mice (left). Numbers in the quadrants indicate the percentages of the different thymocyte subpopulations. Histograms show the mean percentages of thymocyte subpopulations from 10 young mice of each genotype (right). (B) Representative expression levels of TCR-β on thymocytes of the mice indicated in A are shown (left). Histograms show the mean percentages of thymocytes with high TCR-β expression levels from 10 young mice for each genotype (right). Data represent the mean ± SEM (error bars). *, P < 0.05 as compared with WT; •, P < 0.05 as compared with the tcasp8−/−.

Mentions: Although caspase-8 is dispensable for intrathymic T cell development (Salmena et al., 2003), Bim is essential for the deletion of autoreactive thymocytes (Bouillet et al., 2002). To investigate the effects of combined inactivation of caspase-8 and Bim, we generated tcasp8−/−Bim−/− mice that harbor homozygous germline mutations of Bim and deficiency of caspase-8 restricted to T cell lineage. All mice examined were on C57BL/6 × 129/J mixed genetic background, as on a mixed background, Bim−/− mice develop autoimmunity (Bouillet et al., 1999). We examined intrathymic T cell development in both young (6–8 wk old) and old (>6 mo) tcasp8−/−Bim−/− mice and their controls. Total thymocyte numbers of tcasp8−/−Bim−/− mice were comparable to tcasp8−/−, Bim−/−, and WT mice at both ages (Fig. S1, A and B). FACS analysis demonstrated that there are no significant differences in the percentages (and numbers) of the four major thymocyte subpopulations (CD4−CD8−, CD4+CD8+, CD4+CD8−, and CD4−CD8+) between tcasp8−/− mice and their WT littermates at all ages, whereas, as reported (Bouillet et al., 1999), a significantly decreased proportion of the immature CD4+CD8+ and increased representation of CD4−CD8−, as well as the mature CD4+CD8− and CD4−CD8+ thymocytes, were observed in Bim−/− mice compared with WT controls (Figs. 1 A and S1 C). Similar to the Bim−/− mice, tcasp8−/−Bim−/− mice contained reduced numbers of CD4+CD8+ thymocytes, whereas the numbers of CD4−CD8− as well as the mature CD4+CD8− and CD4−CD8+ thymocytes were increased to a similar extent as in Bim−/− mice (Figs. 1 A and S1 C). Consistent with the increased representation of mature T cells in thymi from Bim−/− and tcasp8−/−Bim−/− mice, the proportions and numbers of thymocytes expressing high levels of TCR-β were increased in Bim−/− and tcasp8−/−Bim−/− mice compared with tcasp8−/− and WT controls (Figs. 1 B and S1 D). These data indicate that caspase-8 deficiency does not further perturb intrathymic T cell development in Bim-deficient mice.


Caspase-8 inactivation in T cells increases necroptosis and suppresses autoimmunity in Bim-/- mice.

Bohgaki T, Mozo J, Salmena L, Matysiak-Zablocki E, Bohgaki M, Sanchez O, Strasser A, Hakem A, Hakem R - J. Cell Biol. (2011)

Additional loss of caspase-8 does not rescue impaired intrathymic T cell development in Bim-deficient mice. (A) Representative flow cytometric analysis of thymocytes from tcasp8−/−Bim−/− and control (WT, tcasp8−/−, and Bim−/−) mice (left). Numbers in the quadrants indicate the percentages of the different thymocyte subpopulations. Histograms show the mean percentages of thymocyte subpopulations from 10 young mice of each genotype (right). (B) Representative expression levels of TCR-β on thymocytes of the mice indicated in A are shown (left). Histograms show the mean percentages of thymocytes with high TCR-β expression levels from 10 young mice for each genotype (right). Data represent the mean ± SEM (error bars). *, P < 0.05 as compared with WT; •, P < 0.05 as compared with the tcasp8−/−.
© Copyright Policy - openaccess
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC3198166&req=5

fig1: Additional loss of caspase-8 does not rescue impaired intrathymic T cell development in Bim-deficient mice. (A) Representative flow cytometric analysis of thymocytes from tcasp8−/−Bim−/− and control (WT, tcasp8−/−, and Bim−/−) mice (left). Numbers in the quadrants indicate the percentages of the different thymocyte subpopulations. Histograms show the mean percentages of thymocyte subpopulations from 10 young mice of each genotype (right). (B) Representative expression levels of TCR-β on thymocytes of the mice indicated in A are shown (left). Histograms show the mean percentages of thymocytes with high TCR-β expression levels from 10 young mice for each genotype (right). Data represent the mean ± SEM (error bars). *, P < 0.05 as compared with WT; •, P < 0.05 as compared with the tcasp8−/−.
Mentions: Although caspase-8 is dispensable for intrathymic T cell development (Salmena et al., 2003), Bim is essential for the deletion of autoreactive thymocytes (Bouillet et al., 2002). To investigate the effects of combined inactivation of caspase-8 and Bim, we generated tcasp8−/−Bim−/− mice that harbor homozygous germline mutations of Bim and deficiency of caspase-8 restricted to T cell lineage. All mice examined were on C57BL/6 × 129/J mixed genetic background, as on a mixed background, Bim−/− mice develop autoimmunity (Bouillet et al., 1999). We examined intrathymic T cell development in both young (6–8 wk old) and old (>6 mo) tcasp8−/−Bim−/− mice and their controls. Total thymocyte numbers of tcasp8−/−Bim−/− mice were comparable to tcasp8−/−, Bim−/−, and WT mice at both ages (Fig. S1, A and B). FACS analysis demonstrated that there are no significant differences in the percentages (and numbers) of the four major thymocyte subpopulations (CD4−CD8−, CD4+CD8+, CD4+CD8−, and CD4−CD8+) between tcasp8−/− mice and their WT littermates at all ages, whereas, as reported (Bouillet et al., 1999), a significantly decreased proportion of the immature CD4+CD8+ and increased representation of CD4−CD8−, as well as the mature CD4+CD8− and CD4−CD8+ thymocytes, were observed in Bim−/− mice compared with WT controls (Figs. 1 A and S1 C). Similar to the Bim−/− mice, tcasp8−/−Bim−/− mice contained reduced numbers of CD4+CD8+ thymocytes, whereas the numbers of CD4−CD8− as well as the mature CD4+CD8− and CD4−CD8+ thymocytes were increased to a similar extent as in Bim−/− mice (Figs. 1 A and S1 C). Consistent with the increased representation of mature T cells in thymi from Bim−/− and tcasp8−/−Bim−/− mice, the proportions and numbers of thymocytes expressing high levels of TCR-β were increased in Bim−/− and tcasp8−/−Bim−/− mice compared with tcasp8−/− and WT controls (Figs. 1 B and S1 D). These data indicate that caspase-8 deficiency does not further perturb intrathymic T cell development in Bim-deficient mice.

Bottom Line: Dysregulation of either the extrinsic or intrinsic apoptotic pathway can lead to various diseases including immune disorders and cancer.In addition to its role in the extrinsic apoptotic pathway, caspase-8 plays nonapoptotic functions and is essential for T cell homeostasis.We show that, similar to caspase-8(-/-) T cells, Bim(-/-) T cells that also lack caspase-8 displayed elevated levels of necroptosis and that inhibition of this cell death process fully rescued the survival and proliferation of these cells.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Medical Biophysics, University of Toronto, Toronto, Ontario M5G 2M9, Canada.

ABSTRACT
Dysregulation of either the extrinsic or intrinsic apoptotic pathway can lead to various diseases including immune disorders and cancer. In addition to its role in the extrinsic apoptotic pathway, caspase-8 plays nonapoptotic functions and is essential for T cell homeostasis. The pro-apoptotic BH3-only Bcl-2 family member Bim is important for the intrinsic apoptotic pathway and its inactivation leads to autoimmunity that is further exacerbated by loss of function of the death receptor Fas. We report that inactivation of caspase-8 in T cells of Bim(-/-) mice restrained their autoimmunity and extended their life span. We show that, similar to caspase-8(-/-) T cells, Bim(-/-) T cells that also lack caspase-8 displayed elevated levels of necroptosis and that inhibition of this cell death process fully rescued the survival and proliferation of these cells. Collectively, our data demonstrate that inactivation of caspase-8 suppresses the survival and proliferative capacity of Bim(-/-) T cells and restrains autoimmunity in Bim(-/-) mice.

Show MeSH
Related in: MedlinePlus