Byproducts of normal mitochondrial metabolism and homeostasis include the buildup of potentially damaging levels of reactive oxygen species (ROS), Ca(2+), etc., which must be normalized. Evidence ...suggests that brief mitochondrial permeability transition pore (mPTP) openings play an important physiological role maintaining healthy mitochondria homeostasis. Adaptive and maladaptive responses to redox stress may involve mitochondrial channels such as mPTP and inner membrane anion channel (IMAC). Their activation causes intra- and intermitochondrial redox-environment changes leading to ROS release. This regenerative cycle of mitochondrial ROS formation and release was named ROS-induced ROS release (RIRR). Brief, reversible mPTP opening-associated ROS release apparently constitutes an adaptive housekeeping function by the timely release from mitochondria of accumulated potentially toxic levels of ROS (and Ca(2+)). At higher ROS levels, longer mPTP openings may release a ROS burst leading to destruction of mitochondria, and if propagated from mitochondrion to mitochondrion, of the cell itself. The destructive function of RIRR may serve a physiological role by removal of unwanted cells or damaged mitochondria, or cause the pathological elimination of vital and essential mitochondria and cells. The adaptive release of sufficient ROS into the vicinity of mitochondria may also activate local pools of redox-sensitive enzymes involved in protective signaling pathways that limit ischemic damage to mitochondria and cells in that area. Maladaptive mPTP- or IMAC-related RIRR may also be playing a role in aging. Because the mechanism of mitochondrial RIRR highlights the central role of mitochondria-formed ROS, we discuss all of the known ROS-producing sites (shown in vitro) and their relevance to the mitochondrial ROS production in vivo.
Heart failure (HF) is a progressive, debilitating condition characterized, in part, by altered ionic equilibria, increased ROS production and impaired cellular energy metabolism, contributing to ...variable profiles of systolic and diastolic dysfunction with significant functional limitations and risk of premature death. We summarize current knowledge concerning changes of intracellular Na+ and Ca2+ control mechanisms during the disease progression and their consequences on mitochondrial Ca2+ homeostasis and the shift in redox balance. Absent existing biological data, our computational modeling studies advance a new ‘in silico’ analysis to reconcile existing opposing views, based on different experimental HF models, regarding variations in mitochondrial Ca2+ concentration that participate in triggering and perpetuating oxidative stress in the failing heart and their impact on cardiac energetics. In agreement with our hypothesis and the literature, model simulations demonstrate the possibility that the heart’s redox status together with cytoplasmic Na+ concentrations act as regulators of mitochondrial Ca2+ levels in HF and of the bioenergetics response that will ultimately drive ATP supply and oxidative stress. The resulting model predictions propose future directions to study the evolution of HF as well as other types of heart disease, and to develop novel testable mechanistic hypotheses that may lead to improved therapeutics.
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•Heart failure exhibits altered cytoplasmic and mitochondrial Na+, Ca2+ and redox.•Modeling shows how redox and Na+ shape matrix Ca2+ and oxidative stress in HF.•Redox and Na+ govern divergent Ca2+ impacts on oxidative stress, energetics in HF.•Different redox scenarios may reconcile conflicting results in distinct HF animal models.
Food nutrients and metabolic supply-demand dynamics constitute environmental factors that interact with our genome influencing health and disease states. These gene-environment interactions converge ...at the metabolic-epigenome-genome axis to regulate gene expression and phenotypic outcomes. Mounting evidence indicates that nutrients and lifestyle strongly influence genome-metabolic functional interactions determining disease via altered epigenetic regulation. The mitochondrial network is a central player of the metabolic-epigenome-genome axis, regulating the level of key metabolites NAD(+), AcCoA (acetyl CoA), ATP acting as substrates/cofactors for acetyl transferases, kinases (e.g. protein kinase A) and deacetylases (e.g. sirtuins, SIRTs). The chromatin, an assembly of DNA and nucleoproteins, regulates the transcriptional process, acting at the epigenomic interface between metabolism and the genome. Within this framework, we review existing evidence showing that preservation of mitochondrial network function is directly involved in decreasing the rate of damage accumulation thus slowing aging and improving healthspan.
Glucagon-like peptide-1 (GLP-1), released from gut endocrine L cells in response to glucose, regulates appetite, insulin secretion, and gut motility. How glucose given orally, but not systemically, ...induces GLP-1 secretion is unknown. We show that human duodenal L cells express sweet taste receptors, the taste G protein gustducin, and several other taste transduction elements. Mouse intestinal L cells also express α-gustducin. Ingestion of glucose by α-gustducin null mice revealed deficiencies in secretion of GLP-1 and the regulation of plasma insulin and glucose. Isolated small bowel and intestinal villi from α-gustducin null mice showed markedly defective GLP-1 secretion in response to glucose. The human L cell line NCI-H716 expresses α-gustducin, taste receptors, and several other taste signaling elements. GLP-1 release from NCI-H716 cells was promoted by sugars and the noncaloric sweetener sucralose, and blocked by the sweet receptor antagonist lactisole or siRNA for α-gustducin. We conclude that L cells of the gut "taste" glucose through the same mechanisms used by taste cells of the tongue. Modulating GLP-1 secretion in gut "taste cells" may provide an important treatment for obesity, diabetes and abnormal gut motility.
Highlights • Age-related changes in cardiac energetics are discussed. • It is controversial if ATP production, delivery, or utilization change during aging. • Results from isolated mitochondria ...frequently differ from those obtained in tissue. • Unresolved and controversial questions requiring further studies are highlighted.
This study sought to identify subcellular Ca2+ signals within and among cells comprising the sinoatrial node (SAN) tissue.
The current paradigm of SAN impulse generation: 1) is that full-scale action ...potentials (APs) of a common frequency are initiated at 1 site and are conducted within the SAN along smooth isochrones; and 2) does not feature fine details of Ca2+ signaling present in isolated SAN cells, in which small subcellular, subthreshold local Ca2+ releases (LCRs) self-organize to generate cell-wide APs.
Immunolabeling was combined with a novel technique to detect the occurrence of LCRs and AP-induced Ca2+ transients (APCTs) in individual pixels (chronopix) across the entire mouse SAN images.
At high magnification, Ca2+ signals appeared markedly heterogeneous in space, amplitude, frequency, and phase among cells comprising an HCN4+/CX43− cell meshwork. The signaling exhibited several distinguishable patterns of LCR/APCT interactions within and among cells. Rhythmic APCTs that were apparently conducted within the meshwork were transferred to a truly conducting HCN4−/CX43+ network of striated cells via narrow functional interfaces where different cell types intertwine, that is, the SAN anatomic/functional unit. At low magnification, the earliest APCT of each cycle occurred within a small area of the HCN4 meshwork, and subsequent APCT appearance throughout SAN pixels was discontinuous and asynchronous.
The study has discovered a novel, microscopic Ca2+ signaling paradigm of SAN operation that has escaped detection using low-resolution, macroscopic tissue isochrones employed in prior studies: synchronized APs emerge from heterogeneous subcellular subthreshold Ca2+ signals, resembling multiscale complex processes of impulse generation within clusters of neurons in neuronal networks.
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Type II hexokinase is overexpressed in most neoplastic cells, and it mainly localizes on the outer mitochondrial membrane. Hexokinase II dissociation from mitochondria triggers apoptosis. The ...prevailing model postulates that hexokinase II release from its mitochondrial interactor, the voltage-dependent anion channel, prompts outer mitochondrial membrane permeabilization and the ensuing release of apoptogenic proteins, and that these events are inhibited by growth factor signalling. Here we show that a hexokinase II N-terminal peptide selectively detaches hexokinase II from mitochondria and activates apoptosis. These events are abrogated by inhibiting two established permeability transition pore modulators, the adenine nucleotide translocator or cyclophilin D, or in cyclophilin D knock-out cells. Conversely, insulin stimulation or genetic ablation of the voltage-dependent anion channel do not affect cell death induction by the hexokinase II peptide. Therefore, hexokinase II detachment from mitochondria transduces a permeability transition pore opening signal that results in cell death and does not require the voltage-dependent anion channel. These findings have profound implications for our understanding of the pathways of outer mitochondrial membrane permeabilization and their inactivation in tumors.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
1 Diabetes Section, Laboratory of Clinical Investigation and 3 Research Resources Branch, National Institute on Aging, National Institutes of Health, Baltimore, Maryland; 2 Department of Clinical ...Therapeutics, University of Athens School of Medicine, Alexandra Hospital; and 4 Hippokration Hospital, Athens, Greece
Submitted 23 July 2004
; accepted in final form 3 October 2005
Among the products of enteroendocrine cells are the incretins glucagon-like peptide-1 (GLP-1, secreted by L cells) and glucose-dependent insulinotropic peptide (GIP, secreted by K cells). These are key modulators of insulin secretion, glucose homeostasis, and gastric emptying. Because of the rapid early rise of GLP-1 in plasma after oral glucose, we wished to definitively establish the absence or presence of L cells, as well as the relative distribution of the incretin cell types in human duodenum. We confirmed the presence of proglucagon and pro-GIP genes, their products, and glucosensory molecules by tissue immunohistochemistry and RT-PCR of laser-captured, single duodenal cells. We also assayed plasma glucose, incretin, and insulin levels in subjects with normal glucose tolerance and type 2 diabetes for 120 min after they ingested 75 g of glucose. Subjects with normal glucose tolerance ( n = 14) had as many L cells (15 ± 1), expressed per 1,000 gut epithelial cells, as K cells (13 ± 1), with some containing both hormones (L/K cells, 5 ± 1). In type 2 diabetes, the number of L and L/K cells was increased (26 ± 2; P < 0.001 and 9 ± 1; P < 0.001, respectively). Both L and K cells contained glucokinase and glucose transporter-1, -2, and -3. Newly diagnosed type 2 diabetic subjects had increased plasma GLP-1 levels between 20 and 80 min, concurrently with rising plasma insulin levels. Significant coexpression of the main incretin peptides occurs in human duodenum. L and K cells are present in equal numbers. New onset type 2 diabetes is associated with a shift to the L phenotype.
duodenum; euglycemia; type 2 diabetes; glucagon-like peptide-1; gastric inhibitory polypeptide
Address for reprint requests and other correspondence: M. J. Theodorakis, M.D., Diabetes Section, NIA/NIH, 5600 Nathan Shock Dr., Baltimore, MD 21224
A reduced sinoatrial node (SAN) functional reserve underlies the age-associated decline in heart rate acceleration in response to stress. SAN cell function involves an oscillatory coupled-clock ...system: the sarcoplasmic reticulum (SR), a Ca
2+
clock, and the electrogenic-sarcolemmal membrane clock. Ca
2+
-activated-calmodulin-adenylyl cyclase/CaMKII-cAMP/PKA-Ca
2+
signaling regulated by phosphodiesterase activity drives SAN cells automaticity. SR-generated local calcium releases (LCRs) activate Na
+
/Ca
2+
exchanger in the membrane clock, which initiates the action potential (AP). We hypothesize that SAN cell dysfunctions accumulate with age. We found a reduction in single SAN cell AP firing in aged (20–24 mo) vs. adult (3–4 mo) mice. The sensitivity of the SAN beating rate responses to both muscarinic and adrenergic receptor activation becomes decreased in advanced age. Additionally, age-associated coincident dysfunctions occur stemming from compromised clock functions, including a reduced SR Ca
2+
load and a reduced size, number, and duration of spontaneous LCRs. Moreover, the sensitivity of SAN beating rate to a cAMP stress induced by phosphodiesterase inhibitor is reduced, as are the LCR size, amplitude, and number in SAN cells from aged vs. adult mice. These functional changes coincide with decreased expression of crucial SR Ca
2+
-cycling proteins, including SR Ca
2+
-ATPase pump, ryanodine receptors, and Na
+
/Ca
2+
exchanger. Thus a deterioration in intrinsic Ca
2+
clock kinetics in aged SAN cells, due to deficits in intrinsic SR Ca
2+
cycling and its response to a cAMP-dependent pathway activation, is involved in the age-associated reduction in intrinsic resting AP firing rate, and in the reduction in the acceleration of heart rate during exercise.
Constitutive Ca2+/calmodulin (CaM)-activation of adenylyl cyclases (ACs) types 1 and 8 in sinoatrial nodal cells (SANC) generates cAMP within lipid-raft-rich microdomains to initiate cAMP–protein ...kinase A (PKA) signaling, that regulates basal state rhythmic action potential firing of these cells. Mounting evidence in other cell types points to a balance between Ca2+-activated counteracting enzymes, ACs and phosphodiesterases (PDEs) within these cells. We hypothesized that the expression and activity of Ca2+/CaM-activated PDE Type 1A is higher in SANC than in other cardiac cell types.
We found that PDE1A protein expression was 5-fold higher in sinoatrial nodal tissue than in left ventricle, and its mRNA expression was 12-fold greater in the corresponding isolated cells. PDE1 activity (nimodipine-sensitive) accounted for 39% of the total PDE activity in SANC lysates, compared to only 4% in left ventricular cardiomyocytes (LVC). Additionally, total PDE activity in SANC lysates was lowest (10%) in lipid-raft-rich and highest (76%) in lipid-raft-poor fractions (equilibrium sedimentation on a sucrose density gradient). In intact cells PDE1A immunolabeling was not localized to the cell surface membrane (structured illumination microscopy imaging), but located approximately within about 150nm inside of immunolabeling of hyperpolarization-activated cyclic nucleotide-gated potassium channels (HCN4), which reside within lipid-raft-rich microenvironments. In permeabilized SANC, in which surface membrane ion channels are not functional, nimodipine increased spontaneous SR Ca2+ cycling. PDE1A mRNA silencing in HL-1 cells increased the spontaneous beating rate, reduced the cAMP, and increased cGMP levels in response to IBMX, a broad spectrum PDE inhibitor (detected via fluorescence resonance energy transfer microscopy).
We conclude that signaling via cAMP generated by Ca2+/CaM-activated AC in SANC lipid raft domains is limited by cAMP degradation by Ca2+/CaM-activated PDE1A in non-lipid raft domains. This suggests that local gradients of Ca2+–CaM or different AC and PDE1A affinity regulate both cAMP production and its degradation, and this balance determines the intensity of Ca2+-AC-cAMP-PKA signaling that drives SANC pacemaker function.
•PDE1A expression and activity are higher in sinoatrial node than in left ventricle.•PDE1A immunolabeling is localized close to the cell surface membrane of SANC.•PDE1A cAMP regulation modulates basal SANC pacemaker function.
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