The Mitochondrial Ca(2+) Uniporter: Structure, Function, and Pharmacology.

Mitochondrial Ca(2+) uptake is crucial for an array of cellular functions while an imbalance can elicit cell death. In this chapter, we briefly reviewed the various modes of mitochondrial Ca(2+) uptake and our current understanding of mitochondrial Ca(2+) homeostasis in regards to cell physiology and pathophysiology. Further, this chapter focuses on the molecular identities, intracellular regulators as well as the pharmacology of mitochondrial Ca(2+) uniporter complex

The Effect of OPA1 on Mitochondrial Ca2+ Signaling

The dynamin-related GTPase protein OPA1, localized in the intermembrane space and tethered to the inner membrane of mitochondria, participates in the fusion of these organelles. Its mutation is the most prevalent cause of Autosomal Dominant Optic Atrophy. OPA1 controls the diameter of the junctions between the boundary part of the inner membrane and the membrane of cristae and reduces the diffusibility of cytochrome c through these junctions. We postulated that if significant Ca2+ uptake into the matrix occurs from the lumen of the cristae, reduced expression of OPA1 would increase the access of Ca2+ to the transporters in the crista membrane and thus would enhance Ca2+ uptake. In intact H295R adrenocortical and HeLa cells cytosolic Ca2+ signals evoked with K+ and histamine, respectively, were transferred into the mitochondria. The rate and amplitude of mitochondrial [Ca2+] rise (followed with confocal laser scanning microscopy and FRET measurements with fluorescent wide-field microscopy) were increased after knockdown of OPA1, as compared with cells transfected with control RNA or mitofusin1 siRNA. Ca2+ uptake was enhanced despite reduced mitochondrial membrane potential. In permeabilized cells the rate of Ca2+ uptake by depolarized mitochondria was also increased in OPA1-silenced cells. The participation of Na+/Ca2+ and Ca2+/H+ antiporters in this transport process is indicated by pharmacological data. Altogether, our observations reveal the significance of OPA1 in the control of mitochondrial Ca2+ metabolism

Developmental Role of Macrophage Cannabinoid-1 Receptor Signaling in Type-2 Diabetes

Islet inflammation promotes beta-cell loss and type-2 diabetes (T2D), a process replicated in Zucker Diabetic Fatty (ZDF) rats in which beta-cell loss has been linked to cannabinoid-1 receptor (CB1R)-induced pro-inflammatory signaling in macrophages infiltrating pancreatic islets. Here, we analyzed CB1R signaling in macrophages and its developmental role in T2Dalpha. ZDF rats with global deletion of CB1R are protected from beta-cell loss, hyperglycemia and nephropathy present in ZDF littermates. Adoptive transfer of CB1R-/- bone marrow to ZDF rats also prevents beta-cell loss and hyperglycemia, but not nephropathy. ZDF islets contain elevated levels of CB1R, IL-1beta, TNF-alpha, the chemokine CCL2 and interferon regulatory factor-5 (IRF5), a marker of M1 inflammatory macrophage polarization. In primary cultured rodent and human macrophages, CB1R activation increased Irf5 expression, whereas knockdown of Irf5 blunted CB1R-induced secretion of inflammatory cytokines without affecting CCL2 expression, which was p38MAPKalpha-dependent. Macrophage-specific in vivo knockdown of Irf5 protected ZDF rats from beta-cell loss and hyperglycemia. Thus, IRF5 is a crucial downstream mediator of diabetogenic CB1R signaling in macrophages and a potential therapeutic target

Cannabinoid CB1\mathrm{CB_1} receptor overactivity contributes to the pathogenesis of idiopathic pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is a life-threatening disease without effective treatment, highlighting the need for identifying new targets and treatment modalities. The pathogenesis of IPF is complex, and engaging multiple targets simultaneously might improve therapeutic efficacy. To assess the role of the endocannabinoid/cannabinoid receptor 1 (endocannabinoid/CB$_1$R) system in IPF and its interaction with inducible nitric oxide synthase (iNOS) as dual therapeutic targets, we analyzed lung fibrosis and the status of the endocannabinoid/CB$_1$R system and iNOS in mice with bleomycin-induced pulmonary fibrosis (PF) and in lung tissue and bronchoalveolar lavage fluid (BALF) from patients with IPF, as well as controls. In addition, we investigated the antifibrotic efficacy in the mouse PF model of an orally bioavailable and peripherally restricted CB$_1$R/iNOS hybrid inhibitor. We report that increased activity of the endocannabinoid/CB$_1$R system parallels disease progression in the lungs of patients with idiopathic PF and in mice with bleomycin-induced PF and is associated with increased tissue levels of interferon regulatory factor-5. Furthermore, we demonstrate that simultaneous engagement of the secondary target iNOS by the hybrid CB$_1$R/iNOS inhibitor has greater antifibrotic efficacy than inhibition of CB$_1$R alone. This hybrid antagonist also arrests the progression of established fibrosis in mice, thus making it a viable candidate for future translational studies in IPF

Mitochondrial cAMP and Ca(2+) metabolism in adrenocortical cells.

The biological effects of physiological stimuli of adrenocortical glomerulosa cells are predominantly mediated by the Ca(2+) and the cAMP signal transduction pathways. The complex interplay between these signalling systems fine-tunes aldosterone secretion. In addition to the well-known cytosolic interactions, a novel intramitochondrial Ca(2+)-cAMP interplay has been recently recognised. The cytosolic Ca(2+) signal is rapidly transferred into the mitochondrial matrix where it activates Ca(2+)-sensitive dehydrogenases, thus enhancing the formation of NADPH, a cofactor of steroid synthesis. Quite a few cell types, including H295R adrenocortical cells, express the soluble adenylyl cyclase within the mitochondria and the elevation of mitochondrial [Ca(2+)] activates the enzyme, thus resulting in the Ca(2+)-dependent formation of cAMP within the mitochondrial matrix. On the other hand, mitochondrial cAMP (mt-cAMP) potentiates the transfer of cytosolic Ca(2+) into the mitochondrial matrix. This cAMP-mediated positive feedback control of mitochondrial Ca(2+) uptake may facilitate the rapid hormonal response to emergency situations since knockdown of soluble adenylyl cyclase attenuates aldosterone production whereas overexpression of the enzyme facilitates steroidogenesis in vitro. Moreover, the mitochondrial Ca(2+)-mt-cAMP-Ca(2+) uptake feedback loop is not a unique feature of adrenocortical cells; a similar signalling system has been described in HeLa cells as well

The motivations and methodology for high-throughput PET imaging of small animals in cancer research.

Item does not contain fulltextOver the last decade, small-animal PET imaging has become a vital platform technology in cancer research. With the development of molecularly targeted therapies and drug combinations requiring evaluation of different schedules, the number of animals to be imaged within a PET experiment has increased. This paper describes experimental design requirements to reach statistical significance, based on the expected change in tracer uptake in treated animals as compared to the control group, the number of groups that will be imaged, and the expected intra-animal variability for a given tracer. We also review how high-throughput studies can be performed in dedicated small-animal PET, high-resolution clinical PET systems and planar positron imaging systems by imaging more than one animal simultaneously. Customized beds designed to image more than one animal in large-bore small-animal PET scanners are described. Physics issues related to the presence of several rodents within the field of view (i.e. deterioration of spatial resolution and sensitivity as the radial and the axial offsets increase, respectively, as well as a larger effect of attenuation and the number of scatter events), which can be assessed by using the NEMA NU 4 image quality phantom, are detailed.1 september 201