Batten disease and the control of the Fo subunit c pore by cGMP and calcium

Integrative human and murine multi-omics: Highlighting shared biomarkers in the neuronal ceroid lipofuscinoses

Neuronal ceroid lipofuscinosis (NCL) is a group of neurodegenerative disorders whose molecular mechanisms remain largely unknown. Omics approaches are among the methods that generate new information on modifying factors and molecular signatures. Moreover, omics data integration can address the need to progressively expand knowledge around the disease and pinpoint specific proteins to promote as candidate biomarkers. In this work, we integrated a total of 62 proteomic and transcriptomic datasets originating from humans and mice, employing a new approach able to define dysregulated processes across species, stages and NCL forms. Moreover, we selected a pool of differentially expressed proteins and genes as species- and form-related biomarkers of disease status/progression and evaluated local and spatial differences in most affected brain regions. Our results offer promising targets for potential new therapeutic strategies and reinforce the hypothesis of a connection between NCLs and other forms of dementia, particularly Alzheimer's disease.

Neuronal Ceroid Lipofuscinoses: Connecting Calcium Signalling through Calmodulin

Despite the increased focus on the role of calcium in the neuronal ceroid lipofuscinoses (NCLs, also known as Batten disease), links between calcium signalling and the proteins associated with the disease remain to be identified. A central protein in calcium signalling is calmodulin (CaM), which regulates many of the same cellular processes affected in the NCLs. In this study, we show that 11 of the 13 NCL proteins contain putative CaM-binding domains (CaMBDs). Many of the missense mutations documented from NCL patients overlap with the predicted CaMBDs and are often key residues of those domains. The two NCL proteins lacking such domains, CLN7 and CLN11, share a commonality in undergoing proteolytic processing by cathepsin L, which contains a putative CaMBD. Since CaM appears to have both direct and indirect roles in the NCLs, targeting it may be a valid therapeutic approach for treating the disease.

Calcium and regulation of the mitochondrial permeability transition

Recent years have seen renewed interest in the permeability transition pore, a high conductance channel responsible for permeabilization of the inner mitochondrial membrane, a process that leads to depolarization and Ca²⁺ release. Transient openings may be involved in physiological Ca²⁺ homeostasis while long-lasting openings may trigger and/or execute cell death. In this review we specifically focus (i) on the hypothesis that the PTP forms from the F-ATP synthase and (ii) on the mechanisms through which Ca²⁺ can reversibly switch this energy-conserving nanomachine into an energy-dissipating device.

The Mitochondrial Permeability Transition Pore: Channel Formation by F-ATP Synthase, Integration in Signal Transduction, and Role in Pathophysiology

The mitochondrial permeability transition (PT) is a permeability increase of the inner mitochondrial membrane mediated by a channel, the permeability transition pore (PTP). After a brief historical introduction, we cover the key regulatory features of the PTP and provide a critical assessment of putative protein components that have been tested by genetic analysis. The discovery that under conditions of oxidative stress the F-ATP synthases of mammals, yeast, and Drosophila can be turned into Ca(2+)-dependent channels, whose electrophysiological properties match those of the corresponding PTPs, opens new perspectives to the field. We discuss structural and functional features of F-ATP synthases that may provide clues to its transition from an energy-conserving into an energy-dissipating device as well as recent advances on signal transduction to the PTP and on its role in cellular pathophysiology.

Reprint of "The mitochondrial permeability transition pore and its adaptive responses in tumor cells"

This review covers recent progress on the nature of the mitochondrial permeability transition pore (PTP) – a key effector in the mitochondrial pathways to cell death – and on the adaptive responses of tumor cells that desensitize the PTP to Ca(2+) and reactive oxygen species (ROS), thereby playing an important role in the resistance of tumors to cell death. The discovery that the PTP forms from dimers of F-ATP synthase; and the definition of the Ca(2+)- and ROS-dependent signaling pathways affecting the transition of the F-ATP synthase from an energy-conserving to an energy-dissipating device open new perspectives for therapeutic intervention in cancer cells.

The mitochondrial permeability transition pore: molecular nature and role as a target in cardioprotection

The mitochondrial permeability transition (PT) - an abrupt increase permeability of the inner membrane to solutes - is a causative event in ischemia-reperfusion injury of the heart, and the focus of intense research in cardioprotection. The PT is due to opening of the PT pore (PTP), a high conductance channel that is critically regulated by a variety of pathophysiological effectors. Very recent work indicates that the PTP forms from the F-ATP synthase, which would switch from an energy-conserving to an energy-dissipating device. This review provides an update on the current debate on how this transition is achieved, and on the PTP as a target for therapeutic intervention. This article is part of a Special Issue entitled "Mitochondria: from basic mitochondrial biology to cardiovascular disease".

F-ATPase of Drosophila melanogaster forms 53-picosiemen (53-pS) channels responsible for mitochondrial Ca2+-induced Ca2+ release

Mitochondria of Drosophila melanogaster undergo Ca(2+)-induced Ca(2+) release through a putative channel (mCrC) that has several regulatory features of the permeability transition pore (PTP). The PTP is an inner membrane channel that forms from F-ATPase, possessing a conductance of 500 picosiemens (pS) in mammals and of 300 pS in yeast. In contrast to the PTP, the mCrC of Drosophila is not permeable to sucrose and appears to be selective for Ca(2+) and H(+). We show (i) that like the PTP, the mCrC is affected by the sense of rotation of F-ATPase, by Bz-423, and by Mg(2+)/ADP; (ii) that expression of human cyclophilin D in mitochondria of Drosophila S2R(+) cells sensitizes the mCrC to Ca(2+) but does not increase its apparent size; and (iii) that purified dimers of D. melanogaster F-ATPase reconstituted into lipid bilayers form 53-pS channels activated by Ca(2+) and thiol oxidants and inhibited by Mg(2+)/γ-imino ATP. These findings indicate that the mCrC is the PTP of D. melanogaster and that the signature conductance of F-ATPase channels depends on unique structural features that may underscore specific roles in different species.

The mitochondrial permeability transition pore and its adaptive responses in tumor cells

This review covers recent progress on the nature of the mitochondrial permeability transition pore (PTP) - a key effector in the mitochondrial pathways to cell death - and on the adaptive responses of tumor cells that desensitize the PTP to Ca(2+) and reactive oxygen species (ROS), thereby playing an important role in the resistance of tumors to cell death. The discovery that the PTP forms from dimers of F-ATP synthase; and the definition of the Ca(2+)- and ROS-dependent signaling pathways affecting the transition of the F-ATP synthase from an energy-conserving to an energy-dissipating device open new perspectives for therapeutic intervention in cancer cells.

The intracellular location and function of proteins of neuronal ceroid lipofuscinoses

Neuronal ceroid lipofuscinoses are a group of diseases characterized by accumulation of hydrophobic proteins in lysosomes of neurons and other types of cells. NCLs are caused by at least 8 mutant genes (CLN1-CLN8), though CLN4 and CLN7 have not yet been identified. Except for Cln1p, the protein encoded by CLN1, the defective proteins are associated with lysosomal accumulation of mitochondrial ATP synthase subunit c. Cln1p and Cln2p are soluble lysosomal enzymes, targeted to lysosomes in a mannose 6-phosphate dependent manner. Mutations in the lysosomal protease cathepsin D cause another NCL. Cln3p, Cln5p, Cln6p and Cln8p are thought to be transmembrane proteins. Cln3p and Cln5p are localized in the endosome-lysosomal compartment. Deficiency of endosomal membrane protein CLC-3, a member of the chloride channel family, causes NCL-like phenotype and lysosomal storage of subunit c. Herein, we review the features of NCL and NCL-related proteins and discuss the involvement of the proteins in lysosomal degradation of subunit c.

Guanylyl cyclase is an ATP sensor coupling nitric oxide signaling to cell metabolism

Defending cellular integrity against disturbances in intracellular concentrations of ATP ([ATP](i)) is predicated on coordinating the selection of substrates and their flux through metabolic pathways (metabolic signaling), ATP transfer from sites of production to utilization (energetic signaling), and the regulation of processes consuming energy (cell signaling). Whereas NO and its receptor, soluble guanylyl cyclase (sGC), are emerging as key mediators coordinating ATP supply and demand, mechanisms coupling this pathway with metabolic and energetic signaling remain undefined. Here, we demonstrate that sGC is a nucleotide sensor whose responsiveness to NO is regulated by [ATP](i). Indeed, ATP inhibits purified sGC with a K(i) predicting >60% inhibition of NO signaling in cells maintaining physiological [nucleotide](i). ATP inhibits sGC by interacting with a regulatory site that prefers ATP > GTP. Moreover, alterations in [ATP](i), by permeabilization and nucleotide clamping or inhibition of mitochondrial ATP synthase, regulate NO signaling by sGC. Thus, [ATP](i) serves as a "gain control" for NO signaling by sGC. At homeostatic [ATP](i), NO activation of sGC is repressed, whereas insults that reduce [ATP](i,) derepress sGC and amplify responses to NO. Hence, sGC forms a key synapse integrating metabolic, energetic, and cell signaling, wherein ATP is the transmitter, allosteric inhibition the coupling mechanism, and regulated accumulation of cGMP the response.

Pharmacological strategies to block rod photoreceptor apoptosis caused by calcium overload: a mechanistic target-site approach to neuroprotection

PURPOSE

Photoreceptor apoptosis and resultant visual deficits occur in humans and animals with inherited, and disease-, injury- and chemical-induced retinal degeneration. Our aims were three-fold: 1) to determine the kinetics of rod apoptosis and Ca2+ overload in Pde6b9rd1) mice and developmentally lead-exposed rats, 2) to establish a pathophysiologically-relevant model of Ca2+ overload/rod-selective apoptosis in isolated rat retina and 3) to examine different mechanistic based neuroprotective strategies that would abrogate or mollify rod Ca2+ overload/apoptosis.

METHODS

Retinal morphometry and elemental calcium content ([Ca]) determined the kinetics of rod apoptosis and Ca2+ overload. A multiparametric analysis of apoptosis including rod [Ca], a live/dead assay, rod oxygen consumption, cytochrome c immunoblots and caspase assays was combined with pharmacological studies of an isolated rat retinal model of rod-selective Ca2+ overload/apoptosis.

RESULTS

Ca2+ overload preceded rod apoptosis in mice and rats, although the extent and kinetics in each differed significantly. The isolated rat model of rod Ca2+ overload/apoptosis showed that blockade of Ca2+ entry through rod cGMP-activated channels with L-cis diltiazem was partially neuroprotective, whereas blockade of Ca2+ entry into rods through L-type Ca2+ channels with D-cis diltiazem or verapamil provided no protection. Inhibition of the mitochondrial Na+/Ca2+ exchanger with D-cis diltiazem provided no protection. CsA and NIM811, mitochondrial permeability transition pore (mPTP) inhibitors, blocked all Ca(2+)-induced apoptosis, whereas the caspase-3 inhibitor DEVD-fmk only blocked the downstream cytochrome c-induced apoptosis.

CONCLUSIONS

The successful pharmacological neuroprotective strategies for rod Ca2+ overload/apoptosis targeted the rod cGMP-activated channels or mPTP, but not the rod L-type Ca2+ channels.