Mitochondria play a critical role in mediating both apoptotic and necrotic cell death. The mitochondrial permeability transition (mPT) leads to mitochondrial swelling, outer membrane rupture and the release of apoptotic mediators. The mPT pore is thought to consist of the adenine nucleotide translocator, a voltage-dependent anion channel, and cyclophilin D (the Ppif gene product), a prolyl isomerase located within the mitochondrial matrix. Here we generated mice lacking Ppif and mice overexpressing cyclophilin D in the heart. Ppif null mice are protected from ischaemia/reperfusion-induced cell death in vivo, whereas cyclophilin D-overexpressing mice show mitochondrial swelling and spontaneous cell death. Mitochondria isolated from the livers, hearts and brains of Ppif null mice are resistant to mitochondrial swelling and permeability transition in vitro. Moreover, primary hepatocytes and fibroblasts isolated from Ppif null mice are largely protected from Ca2+-overload and oxidative stress-induced cell death. However, Bcl-2 family member-induced cell death does not depend on cyclophilin D, and Ppif null fibroblasts are not protected from staurosporine or tumour-necrosis factor-alpha-induced death. Thus, cyclophilin D and the mitochondrial permeability transition are required for mediating Ca2+- and oxidative damage-induced cell death, but not Bcl-2 family member-regulated death.

Voltage-dependent anion channels (VDACs) have been implicated as essential mediators of mitochondrial-dependent cell death by functioning as a channel-forming unit within the mitochondrial permeability transition (MPT) pore and the target of Bcl-2 family members. Here we report the effects of deletion of the 3 mammalian Vdac genes on mitochondrial-dependent cell death. Mitochondria from Vdac1-, Vdac3-, and Vdac1/Vdac3-null mice exhibited a Ca 2+ and oxidative stress-induced MPT that was indistinguishable from wildtype mitochondria. Similarly, Ca 2+ and oxidative-stress-induced MPT and cell death was unaltered or even exacerbated in fibroblasts lacking VDAC1, VDAC2, VDAC3, VDAC1/3, and VDAC1/2/3. Wildtype and Vdac-deficient mitochondria and cells also exhibited equivalent cytochrome c release, caspase cleavage, and cell death in response to Bax and Bid activation. These results indicate that VDACs are dispensable for both MPT and Bcl-2 family member-driven cell death.Mitochondria are intracellular organelles that mediate high-energy phosphate production, fatty acid metabolism, porphyrin synthesis, ion homeostasis and apoptotic and necrotic cell death. Apoptotic cell death is mediated by both the "extrinsic" pathway; consisting of death receptor signaling constituents, as well as the "intrinsic" pathway; consisting of pro-death Bcl-2 family members functioning at the level of the mitochondria and endoplasmic reticulum (1). Mitochondria are also critically involved in necrotic cell death following Ca 2+ overload, hypoxia, and oxidative damage, leading to swollen or ruptured mitochondria. The MPT pore, a protein complex that spans both the outer and inner mitochondrial membranes, is considered the mediator of this event and has been hypothesized to minimally consist of the VDAC in the outer membrane, the adenine nucleotide translocase (ANT) in the inner membrane, and cyclophilin-D in the matrix (2-4).The VDAC is comprised of a family of evolutionarily conserved ion channels that are the most abundant proteins in the outer mitochondrial membrane. The physiologic function of VDACs is to control the movement of adenine nucleotides, NADH, and other metabolites across the outer membrane (5,6). However, VDACs have also been proposed to possess a pathological function as mediators of mitochondrial-dependent cell death through formation of the permeability pore (7,8). In addition, VDACs have been proposed to be essential binding partners for pro-apoptotic Bcl-2 family members (9-12), combining to form protein-permeable Here we assessed whether MPT was altered in Vdac1-, Vdac3-, and Vdac1/Vdac3-null mice. Western blotting of cardiac lysates from these mice showed the complete lack of the respective VDAC protein in each line without compensatory alterations in the other VDAC isoforms (Fig. 1a). There were also no significant changes in ANT and cyclophilin D, two other putative components of the MPT pore (Fig. 1a). Cardiac mitochondria isolated from wildtype, Vdac1-, Vdac3-, and Vdac1/Vdac3-null mice were assessed for...

Abstract-The cardiac extracellular matrix is a dynamic structural support network that is both influenced by, and a regulator of, pathological remodeling and hypertrophic growth. In response to pathologic insults, the adult heart reexpresses the secreted extracellular matrix protein periostin (Pn). Here we show that Pn is critically involved in regulating the cardiac hypertrophic response, interstitial fibrosis, and ventricular remodeling following long-term pressure overload stimulation and myocardial infarction. Mice lacking the gene encoding Pn (Postn) were more prone to ventricular rupture in the first 10 days after a myocardial infarction, but surviving mice showed less fibrosis and better ventricular performance. Pn Ϫ/Ϫ mice also showed less fibrosis and hypertrophy following long-term pressure overload, suggesting an intimate relationship between Pn and the regulation of cardiac remodeling. In contrast, inducible overexpression of Pn in the heart protected mice from rupture following myocardial infarction and induced spontaneous hypertrophy with aging. With respect to a mechanism underlying these alterations, Pn Ϫ/Ϫ hearts showed an altered molecular program in fibroblast function. Indeed, fibroblasts isolated from Pn Ϫ/Ϫ hearts were less effective in adherence to cardiac myocytes and were characterized by a dramatic alteration in global gene expression (7% of all genes). These are the first genetic data detailing the function of Pn in the adult heart as a regulator of cardiac remodeling and hypertrophy. (Circ Res. 2007;101:313-321.)