Neuroscience Letters 442 (2008) 96–99 Contents lists available at ScienceDirect Neuroscience Letters journal homepage: www.elsevier.com/locate/neulet Bcl-x L inhibits Bax-induced alterations in mitochondrial respiration and calcium release A.V.F. Teles a , R.P. Ureshino a , D.J. Dorta a , G.S. Lopes a , Y.-T. Hsu b , S.S. Smaili a,∗ a Departamento de Farmacologia, Universidade Federal de São Paulo (Department of Pharmacology, Federal University of São Paulo), Rua Tres de Maio-100, São Paulo 04044-020, Brazil b Department of Biochemistry and Molecular Biology, Medical University of South Carolina, Charleston, SC 29425, USA article info Article history: Received 26 April 2008 Received in revised form 20 June 2008 Accepted 24 June 2008 Keywords: Bcl-xL Bax Calcium Apoptosis Mitochondria Respiratory chain ATP ADP Cell death abstract Apoptosis is a natural cell elimination process involved in a number of physiological and pathological events. This process can be regulated by members of the Bcl-2 family. Bax, a pro-apoptotic member of this family, accelerates cell death, while the pro-survival member, Bcl-x L , can antagonize the pro-apoptotic function of Bax to promote cell survival. In the present study, we have evaluated the effect of Bcl-x L on Bax- induced alterations in mitochondrial respiration and calcium release. We found that in primary cultured astrocytes, recombinant Bcl-x L is able to antagonize Bax-induced decrease in mitochondrial respiration and increase in mitochondrial calcium release. In addition, we found that Bcl-x L can lower the calcium store in the endoplasmic reticulum, thus limiting potential calcium flux induced by apoptosis. This regulation of calcium flux by Bcl-x L may represent an important mechanism by which this protein promotes cell survival. © 2008 Elsevier Ireland Ltd. All rights reserved. Apoptosis is a highly regulated process of selective cell deletion involved in development, normal cellular turnover, cell-mediated immunity, pathological disorders, and tumor regression [15]. Under such conditions, the expression of anti-apoptotic Bcl-2 family members, such as Bcl-x L , can attenuate the effect of an apoptotic response, maintain the survival, and promote the recovery of the cell. In contrast, the pro-apoptotic family members, such as Bax, promotes cell death in response to cytotoxic insults [15]. Bax exists as a soluble monomer, in an inactive conformation, in the cytoplasm of healthy cells [13]. In response to apopto- sis, it undergoes a conformational change and translocates to the outer mitochondrial membrane [10,12,13,28]. The mitochondrial bound Bax participates in the execution of mitochondrial dys- function, which is characterized by the release of cytochrome c and other apoptogenic factors from the mitochondrial intermem- brane space [15]. In general, this release is accompanied by a dissipation of the mitochondrial membrane potential ( m ), with permeabilization of mitochondria membranes [16]. It has been shown that Bax can cause the permeabilization of either the outer mitochondrial membrane or both outer and inner mitochondrial ∗ Corresponding author. Tel.: +55 11 5576 4449. E-mail address: ssmaili@farm.epm.br (S.S. Smaili). membranes, depending on the stimuli, conditions, and concentra- tion of Bax [15,20]. We have previously shown that Bax causes a reduction of mitochondrial respiratory rates and  m , which might be related to a deficiency in mitochondrial electron trans- port and proton pumping [3]. This contrasts with other studies which showed that a functional electron transport chain is nec- essary to enable Bax-induced cytotoxicity and the progression of the cell death process [11,17]. In addition, some evidence has shown that Bax and other pro-apoptotic members of the Bcl-2 family could modulate Ca 2+ stores within the endoplasmic retic- ulum (ER) and mitochondria (Ca 2+ m ) [18]. Thus, Bax not only causes a decrease in  m and the release of apoptogenic proteins from mitochondria, but it may also induce the release of Ca 2+ m which might be important for the amplicafication of apoptotic signals [3]. The pro-apoptotic effects of Bax can be antagonized by Bcl-x L ,a protein constitutively expressed and distributed in the cytoplasm and outer mitochondrial membranes [9,12]. Overexpression of Bcl- x L preserves Bax in an inactive conformation [4] and prevents the translocation of Bax from the cytoplasm to mitochondria [7]. How- ever, its effect on Bax-induced Ca 2+ m release and its relation with the electron transport chain and oxygen consumption is not known. Studies have suggested that Ca 2+ metabolism and homeostasis may modulate the signaling pathways of apoptosis. Since mitochondria 0304-3940/$ – see front matter © 2008 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.neulet.2008.06.073