Mitochondria-Ros Crosstalk in the Control of Cell Death and Aging

Reactive oxygen species (ROS) are highly reactive molecules, mainly generated inside mitochondria that can oxidize DNA, proteins, and lipids. At physiological levels, ROS function as “redox messengers” in intracellular signalling and regulation, whereas excess ROS induce cell death by promoting the intrinsic apoptotic pathway. Recent work has pointed to a further role of ROS in activation of autophagy and their importance in the regulation of aging. This review will focus on mitochondria as producers and targets of ROS and will summarize different proteins that modulate the redox state of the cell. Moreover, the involvement of ROS and mitochondria in different molecular pathways controlling lifespan will be reported, pointing out the role of ROS as a “balance of power,” directing the cell towards life or death

p66Shc Aging Protein in Control of Fibroblasts Cell Fate

Reactive oxygen species (ROS) are wieldy accepted as one of the main factors of the aging process. These highly reactive compounds modify nucleic acids, proteins and lipids and affect the functionality of mitochondria in the first case and ultimately of the cell. Any agent or genetic modification that affects ROS production and detoxification can be expected to influence longevity. On the other hand, genetic manipulations leading to increased longevity can be expected to involve cellular changes that affect ROS metabolism. The 66-kDa isoform of the growth factor adaptor Shc (p66Shc) has been recognized as a relevant factor to the oxygen radical theory of aging. The most recent data indicate that p66Shc protein regulates life span in mammals and its phosphorylation on serine 36 is important for the initiation of cell death upon oxidative stress. Moreover, there is strong evidence that apart from aging, p66Shc may be implicated in many oxidative stress-associated pathologies, such as diabetes, mitochondrial and neurodegenerative disorders and tumorigenesis. This article summarizes recent knowledge about the role of p66Shc in aging and senescence and how this protein can influence ROS production and detoxification, focusing on studies performed on skin and skin fibroblasts

p53 at the endoplasmic reticulum regulates apoptosis in a Ca2+-dependent manner

The tumor suppressor p53 is a key protein in preventing cell transformation and tumor progression. Activated by a variety of stimuli, p53 regulates cell-cycle arrest and apoptosis. Along with its well-documented transcriptional control over cell-death programs within the nucleus, p53 exerts crucial although still poorly understood functions in the cytoplasm, directly modulating the apoptotic response at the mitochondrial level. Calcium (Ca(2+)) transfer between the endoplasmic reticulum (ER) and mitochondria represents a critical signal in the induction of apoptosis. However, the mechanism controlling this flux in response to stress stimuli remains largely unknown. Here we show that, in the cytoplasm, WT p53 localizes at the ER and at specialized contact domains between the ER and mitochondria (mitochondria-associated membranes). We demonstrate that, upon stress stimuli, WT p53 accumulates at these sites and modulates Ca(2+) homeostasis. Mechanistically, upon activation, WT p53 directly binds to the sarco/ER Ca(2+)-ATPase (SERCA) pump at the ER, changing its oxidative state and thus leading to an increased Ca(2+) load, followed by an enhanced transfer to mitochondria. The consequent mitochondrial Ca(2+) overload causes in turn alterations in the morphology of this organelle and induction of apoptosis. Pharmacological inactivation of WT p53 or naturally occurring p53 missense mutants inhibits SERCA pump activity at the ER, leading to a reduction of the Ca(2+) signaling from the ER to mitochondria. These findings define a critical nonnuclear function of p53 in regulating Ca(2+) signal-dependent apoptosis

Mitochondrial Ca2+and apoptosis

none12noneGiorgi, Carlotta; Baldassari, Federica; Bononi, Angela; Bonora, Massimo; De Marchi, Elena; Marchi, Saverio; Missiroli, Sonia; Patergnani, Simone; Rimessi, Alessandro; Suski, Jan M.; Wieckowski, Mariusz R.; Pinton, Paolo*Giorgi, Carlotta; Baldassari, Federica; Bononi, Angela; Bonora, Massimo; De Marchi, Elena; Marchi, Saverio; Missiroli, Sonia; Patergnani, Simone; Rimessi, Alessandro; Suski, Jan M.; Wieckowski, Mariusz R.; Pinton, Paol

Mitochondria-associated membranes (MAMs) as hotspot Ca 2+ signaling units

none13noneBononi, Angela; Missiroli, Sonia; Poletti, Federica; Suski, Jan M.; Agnoletto, Chiara; Bonora, Massimo; De Marchi, Elena; Giorgi, Carlotta; Marchi, Saverio; Patergnani, Simone; Rimessi, Alessandro; Wieckowski, Mariusz R.; Pinton, Paolo*Bononi, Angela; Missiroli, Sonia; Poletti, Federica; Suski, Jan M.; Agnoletto, Chiara; Bonora, Massimo; De Marchi, Elena; Giorgi, Carlotta; Marchi, Saverio; Patergnani, Simone; Rimessi, Alessandro; Wieckowski, Mariusz R.; Pinton, Paol

Mitochondria-Associated Membranes (MAMs) as Hotspot Ca(2+) Signaling Units.

The tight interplay between endoplasmic reticulum (ER) and mitochondria is a key determinant of cell function and survival through the control of intracellular calcium (Ca(2+)) signaling. The specific sites of physical association between ER and mitochondria are known as mitochondria-associated membranes (MAMs). It has recently become clear that MAMs are crucial for highly efficient transmission of Ca(2+) from the ER to mitochondria, thus controlling fundamental processes involved in energy production and also determining cell fate by triggering or preventing apoptosis. In this contribution, we summarize the main features of the Ca(2+)-signaling toolkit, covering also the latest breakthroughs in the field, such as the identification of novel candidate proteins implicated in mitochondrial Ca(2+) transport and the recent direct characterization of the high-Ca(2+) microdomains between ER and mitochondria. We review the main functions of these two organelles, with special emphasis on Ca(2+) handling and on the structural and molecular foundations of the signaling contacts between them. Additionally, we provide important examples of the physiopathological role of this cross-talk, briefly describing the key role played by MAMs proteins in many diseases, and shedding light on the essential role of mitochondria-ER interactions in the maintenance of cellular homeostasis and the determination of cell fate

Role of the c subunit of the FO ATP synthase in mitochondrial permeability transition

The term “mitochondrial permeability transition” (MPT) refers to an abrupt increase in the permeability of the inner mitochondrial membrane to low molecular weight solutes. Due to osmotic forces, MPT is paralleled by a massive influx of water into the mitochondrial matrix, eventually leading to the structural collapse of the organelle. Thus, MPT can initiate mitochondrial outer membrane permeabilization (MOMP), promoting the activation of the apoptotic caspase cascade as well as of caspase-independent cell death mechanisms. MPT appears to be mediated by the opening of the so-called “permeability transition pore complex” (PTPC), a poorly characterized and versatile supramolecular entity assembled at the junctions between the inner and outer mitochondrial membranes. In spite of considerable experimental efforts, the precise molecular composition of the PTPC remains obscure and only one of its constituents, cyclophilin D (CYPD), has been ascribed with a crucial role in the regulation of cell death. Conversely, the results of genetic experiments indicate that other major components of the PTPC, such as voltage-dependent anion channel (VDAC) and adenine nucleotide translocase (ANT), are dispensable for MPT-driven MOMP. Here, we demonstrate that the c subunit of the F(O) ATP synthase is required for MPT, mitochondrial fragmentation and cell death as induced by cytosolic calcium overload and oxidative stress in both glycolytic and respiratory cell models. Our results strongly suggest that, similar to CYPD, the c subunit of the F(O) ATP synthase constitutes a critical component of the PTPC

p53 at the endoplasmic reticulum regulates apoptosis in a Ca2+-dependent manner

The tumor suppressor p53 is a key protein in preventing cell transformation and tumor progression. Activated by a variety of stimuli, p53 regulates cell-cycle arrest and apoptosis. Along with its well-documented transcriptional control over cell-death programs within the nucleus, p53 exerts crucial although still poorly understood functions in the cytoplasm, directly modulating the apoptotic response at the mitochondrial level. Calcium (Ca2+) transfer between the endoplasmic reticulum (ER) and mitochondria represents a critical signal in the induction of apoptosis. However, the mechanism controlling this flux in response to stress stimuli remains largely unknown. Here we show that, in the cytoplasm, WT p53 localizes at the ER and at specialized contact domains between the ER and mitochondria (mitochondria-associated membranes). We demonstrate that, upon stress stimuli, WT p53 accumulates at these sites and modulates Ca2+ homeostasis. Mechanistically, upon activation, WT p53 directly binds to the sarco/ER Ca2+-ATPase (SERCA) pump at the ER, changing its oxidative state and thus leading to an increased Ca2+ load, followed by an enhanced transfer to mitochondria. The consequent mitochondrial Ca2+ overload causes in turn alterations in the morphology of this organelle and induction of apoptosis. Pharmacological inactivation of WT p53 or naturally occurring p53 missense mutants inhibits SERCA pump activity at the ER, leading to a reduction of the Ca2+ signaling from the ER to mitochondria. These findings define a critical nonnuclear function of p53 in regulating Ca2+ signal-dependent apoptosis