Article

Developmentally Regulated Ceramide Synthase 6 Increases Mitochondrial Ca2+ Loading Capacity and Promotes Apoptosis

Ralph H Johnson Veterans Affairs Medical Center, Charleston, South Carolina 29401, USA.
Journal of Biological Chemistry (Impact Factor: 4.57). 02/2011; 286(6):4644-58. DOI: 10.1074/jbc.M110.164392
Source: PubMed

ABSTRACT

Ceramides, which are membrane sphingolipids and key mediators of cell-stress responses, are generated by a family of (dihydro) ceramide synthases (Lass1-6/CerS1-6). Here, we report that brain development features significant increases in sphingomyelin, sphingosine, and most ceramide species. In contrast, C(16:0)-ceramide was gradually reduced and CerS6 was down-regulated in mitochondria, thereby implicating CerS6 as a primary ceramide synthase generating C(16:0)-ceramide. Investigations into the role of CerS6 in mitochondria revealed that ceramide synthase down-regulation is associated with dramatically decreased mitochondrial Ca(2+)-loading capacity, which could be rescued by addition of ceramide. Selective CerS6 complexing with the inner membrane component of the mitochondrial permeability transition pore was detected by immunoprecipitation. This suggests that CerS6-generated ceramide could prevent mitochondrial permeability transition pore opening, leading to increased Ca(2+) accumulation in the mitochondrial matrix. We examined the effect of high CerS6 expression on cell survival in primary oligodendrocyte (OL) precursor cells, which undergo apoptotic cell death during early postnatal brain development. Exposure of OLs to glutamate resulted in apoptosis that was prevented by inhibitors of de novo ceramide biosynthesis, myriocin and fumonisin B1. Knockdown of CerS6 with siRNA reduced glutamate-triggered OL apoptosis, whereas knockdown of CerS5 had no effect: the pro-apoptotic role of CerS6 was not stimulus-specific. Knockdown of CerS6 with siRNA improved cell survival in response to nerve growth factor-induced OL apoptosis. Also, blocking mitochondrial Ca(2+) uptake or decreasing Ca(2+)-dependent protease calpain activity with specific inhibitors prevented OL apoptosis. Finally, knocking down CerS6 decreased calpain activation. Thus, our data suggest a novel role for CerS6 in the regulation of both mitochondrial Ca(2+) homeostasis and calpain, which appears to be important in OL apoptosis during brain development.

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Available from: Tatyana I Gudz, Dec 03, 2014
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    • "In the final step of this pathway DHCer desaturase (DES) facilitates the formation of ceramide inserting a double bond between C4 and C5 of the sphingoid base. A variety of evidence suggests that this pathway occurs in the endoplasmic reticulum (Hirschberg et al., 1993) however, some enzymes were localized in mitochondria of some cell types (Yu et al., 2007; Novgorodov et al., 2011) but not others (Stiban et al., 2008; Mesicek et al., 2010), indicating that this localization might be cell-type specific. Even though under normal conditions liver mitochondria were shown to be devoid of DES activity (Stiban et al., 2008), N-myristoylation targeted the Figure 1 The basic structure of sphingolipids. "
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    ABSTRACT: Sphingolipid research has surged in the past two decades and has produced a wide variety of evidence supporting the role of this class of molecules in mediating cellular growth, differentiation, senescence, and apoptosis. Ceramides are a subgroup of sphingolipids (SLs) that are directly involved in the process of initiation of apoptosis. We, and others, have recently shown that ceramides are capable of the formation of protein-permeable channels in mitochondrial outer membranes under physiological conditions. These pores are indeed good candidates for the pathway of release of pro-apoptotic proteins from the mitochondrial intermembrane space (IMS) into the cytosol to initiate intrinsic apoptosis. Here, we review recent findings on the regulation of ceramide channel formation and disassembly, highlighting possible implications on the initiation of the intrinsic apoptotic pathway.
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    • "Activity measurements indicated activation of CerS6 in ischemic mitochondria apparently via post-translational mechanisms; IR did not affect the CerS6 protein expression (Yu et al., 2007). It appears that CerS6 is developmentally regulated and primarily generates C 16:0 -ceramide in brain mitochondria (Novgorodov et al., 2011a). An investigation into the role of CerS6 in mitochondria revealed that ceramide synthase down-regulation during brain development is associated with dramatically decreased mitochondrial Ca 2+ -loading capacity (CLC) which could be rescued by addition of ceramide. "

    Full-text · Dataset · Dec 2014
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    • "Activity measurements indicated activation of CerS6 in ischemic mitochondria apparently via post-translational mechanisms; IR did not affect the CerS6 protein expression (Yu et al., 2007). It appears that CerS6 is developmentally regulated and primarily generates C 16:0 -ceramide in brain mitochondria (Novgorodov et al., 2011a). An investigation into the role of CerS6 in mitochondria revealed that ceramide synthase down-regulation during brain development is associated with dramatically decreased mitochondrial Ca 2+ -loading capacity (CLC) which could be rescued by addition of ceramide. "

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