Ischemia-induced alterations of mitochondrial structure and function in brain, liver, and heart muscle of young and senescent rats

Aging aggravates hepatic ischemia-reperfusion injury in mice by impairing mitophagy with the involvement of the EIF2α-parkin pathway

Hepatic ischemia-reperfusion (I/R) injury fundamentally influences the performance of aged liver grafts. The significance of mitophagy in the age dependence of sensitivity to I/R injury remains poorly understood. Here, we show that aging aggravated hepatic I/R injury with decreased mitophagy in mice. The enhancement of mitophagy resulted in significant protection against hepatic I/R injury. Parkin, an E3 ubiquitin ligase, was found depleted by I/R in aged livers. In oxygen-glucose deprivation reperfusion (OGD-Rep.)-treated L02 cells, parkin silencing impaired mitophagy and aggravated cell damage through a relative large mitochondrial membrane potential transition. The phosphorylation of the endoplasmic reticulum stress response protein EIF2α, which was also reduced in the aged liver, induced parkin expression both in vivo and vitro. Forty-six hepatic biopsy specimens from liver graft were collected 2 hours after complete revascularization, followed by immunohistochemical analyses. Parkin expression was negatively correlated to donor age and the peak level of aspartate aminotransferase within first week after liver transplantation. Our translational study demonstrates that aging aggravated hepatic I/R injury by impairing the age-dependent mitophagy function via an insufficient parkin expression and identifies a new strategy to evaluate the capacity of an aged liver graft in the process of I/R through the parkin expression.

Mitophagy and Oxidative Stress in Cancer and Aging: Focus on Sirtuins and Nanomaterials

Mitochondria are the cellular center of energy production and of several important metabolic processes. Mitochondrion health is maintained with a substantial intervention of mitophagy, a process of macroautophagy that degrades selectively dysfunctional and irreversibly damaged organelles. Because of its crucial duty, alteration in mitophagy can cause functional and structural adjustment in the mitochondria, changes in energy production, loss of cellular adaptation, and cell death. In this review, we discuss the dual role that mitophagy plays in cancer and age-related pathologies, as a consequence of oxidative stress, evidencing the triggering stimuli and mechanisms and suggesting the molecular targets for its therapeutic control. Finally, a section has been dedicated to the interplay between mitophagy and therapies using nanoparticles that are the new frontier for a direct and less invasive strategy.

Autophagy suppresses age-dependent ischemia and reperfusion injury in livers of mice

BACKGROUND & AIMS

As life expectancy increases, there are greater numbers of patients with liver diseases who require surgery or transplantation. Livers of older patients have significantly less reparative capacity following ischemia and reperfusion (I/R) injury, which occurs during these operations. There are no strategies to reduce the age-dependent I/R injury. We investigated the role of autophagy in the age dependence of sensitivity to I/R injury.

METHODS

Hepatocytes and livers from 3- and 26-month-old mice were subjected to in vitro and in vivo I/R, respectively. We analyzed changes in autophagy-related proteins (Atg). Mitochondrial dysfunction was visualized using confocal and intravital multi-photon microscopy of isolated hepatocytes and livers from anesthetized mice, respectively.

RESULTS

Immunoblot, autophagic flux, genetic, and imaging analyses all associated the increase in sensitivity to I/R injury with age with decreased autophagy and subsequent mitochondrial dysfunction due to calpain-mediated loss of Atg4B. Overexpression of either Atg4B or Beclin-1 recovered Atg4B, increased autophagy, blocked the onset of the mitochondrial permeability transition, and suppressed cell death after I/R in old hepatocytes. Coimmunoprecipitation analysis of hepatocytes and Atg3-knockout cells showed an interaction between Beclin-1 and Atg3, a protein required for autophagosome formation. Intravital multi-photon imaging revealed that overexpression of Beclin-1 or Atg4B attenuated autophagic defects and mitochondrial dysfunction in livers of older mice after I/R.

CONCLUSIONS

Loss of Atg4B in livers of old mice increases their sensitivity to I/R injury. Increasing autophagy might ameliorate liver damage and restore mitochondrial function after I/R.

Structural and functional damage sustained by mitochondria after traumatic brain injury in the rat: evidence for differentially sensitive populations in the cortex and hippocampus

The cellular and molecular pathways initiated by traumatic brain injury (TBI) may compromise the function and structural integrity of mitochondria, thereby contributing to cerebral metabolic dysfunction and cell death. The extent to which TBI affects regional mitochondrial populations with respect to structure, function, and swelling was assessed 3 hours and 24 hours after lateral fluid-percussion brain injury in the rat. Significantly less mitochondrial protein was isolated from the injured compared with uninjured parietotemporal cortex, whereas comparable yields were obtained from the hippocampus. After injury, cortical and hippocampal tissue ATP concentrations declined significantly to 60% and 40% of control, respectively, in the absence of respiratory deficits in isolated mitochondria. Mitochondria with ultrastructural morphologic damage comprised a significantly greater percent of the population isolated from injured than uninjured brain. As determined by photon correlation spectroscopy, the mean mitochondrial radius decreased significantly in injured cortical populations (361 +/- 40 nm at 24 hours) and increased significantly in injured hippocampal populations (442 +/- 36 at 3 hours) compared with uninjured populations (Ctx: 418 +/- 44; Hipp: 393 +/- 24). Calcium-induced deenergized swelling rates of isolated mitochondrial populations were significantly slower in injured compared with uninjured samples, suggesting that injury alters the kinetics of mitochondrial permeability transition (MPT) pore activation. Cyclosporin A (CsA)-insensitive swelling was reduced in the cortex, and CsA-sensitive and CsA-insensitive swelling both were reduced in the hippocampus, demonstrating that regulated MPT pores remain in mitochondria isolated from injured brain. A proposed mitochondrial population model synthesizes these data and suggests that cortical mitochondria may be depleted after TBI, with a physically smaller, MPT-regulated population remaining. Hippocampal mitochondria may sustain damage associated with ballooned membranes and reduced MPT pore calcium sensitivity. The heterogeneous mitochondrial response to TBI may underlie posttraumatic metabolic dysfunction and contribute to the pathophysiology of TBI.

Creatine and creatinine metabolism

The goal of this review is to present a comprehensive survey of the many intriguing facets of creatine (Cr) and creatinine metabolism, encompassing the pathways and regulation of Cr biosynthesis and degradation, species and tissue distribution of the enzymes and metabolites involved, and of the inherent implications for physiology and human pathology. Very recently, a series of new discoveries have been made that are bound to have distinguished implications for bioenergetics, physiology, human pathology, and clinical diagnosis and that suggest that deregulation of the creatine kinase (CK) system is associated with a variety of diseases. Disturbances of the CK system have been observed in muscle, brain, cardiac, and renal diseases as well as in cancer. On the other hand, Cr and Cr analogs such as cyclocreatine were found to have antitumor, antiviral, and antidiabetic effects and to protect tissues from hypoxic, ischemic, neurodegenerative, or muscle damage. Oral Cr ingestion is used in sports as an ergogenic aid, and some data suggest that Cr and creatinine may be precursors of food mutagens and uremic toxins. These findings are discussed in depth, the interrelationships are outlined, and all is put into a broader context to provide a more detailed understanding of the biological functions of Cr and of the CK system.

Roles of nitric oxide in brain hypoxia-ischemia

A large body of evidence has appeared over the last 6 years suggesting that nitric oxide biosynthesis is a key factor in the pathophysiological response of the brain to hypoxia-ischemia. Whilst studies on the influence of nitric oxide in this phenomenon initially offered conflicting conclusions, the use of better biochemical tools, such as selective inhibition of nitric oxide synthase (NOS) isoforms or transgenic animals, is progressively clarifying the precise role of nitric oxide in brain ischemia. Brain ischemia triggers a cascade of events, possibly mediated by excitatory amino acids, yielding the activation of the Ca2+-dependent NOS isoforms, i.e. neuronal NOS (nNOS) and endothelial NOS (eNOS). However, whereas the selective inhibition of nNOS is neuroprotective, selective inhibition of eNOS is neurotoxic. Furthermore, mainly in glial cells, delayed ischemia or reperfusion after an ischemic episode induces the expression of Ca2+-independent inducible NOS (iNOS), and its selective inhibition is neuroprotective. In conclusion, it appears that activation of nNOS or induction of iNOS mediates ischemic brain damage, possibly by mitochondrial dysfunction and energy depletion. However, there is a simultaneous compensatory response through eNOS activation within the endothelium of blood vessels, which mediates vasodilation and hence increases blood flow to the damaged brain area.

Heightened resistance of the neonatal brain to ischemia-reperfusion involves a lack of mitochondrial damage in the nerve terminal

Mitochondria are known targets of ischemia-reperfusion injury in adult brain. Although neonates are more resistant to ischemic episodes, the mechanisms accounting for this are not yet fully understood. The aim of this study therefore was to determine whether a difference in post-ischemic mitochondrial function may play a role in the heightened recovery of the neonatal brain following ischemia-reperfusion. We have therefore compared the effects of an in vitro model of ischemia on the enzymes of the mitochondrial respiratory chain in isolated nerve terminals (synaptosomes) from neonatal and adult rats. Ischemia caused a significant, reversible decrease in mitochondrial Complex I activity in both adult and neonatal preparations. In neonatal preparations alone, ischemia also led to a significant decrease in mitochondrial Complexes II-III activity. Following 30 min of reperfusion mitochondrial Complexes II-III and IV exhibited decreased activity in synaptosomes from adult, but not neonatal rats. These data suggest a difference in the susceptibility of adult as compared to neonatal nerve terminal mitochondria to ischemia-reperfusion. These data show for the first time that nerve terminal mitochondria from immature animals remain undamaged following a period of ischemia and reperfusion, in contrast to nerve terminal mitochondria from the adult brain. This adds to the growing body of evidence that mitochondrial function plays a key role in neuronal death following cerebral ischemia reperfusion.

Interrelationships between astrocyte function, oxidative stress and antioxidant status within the central nervous system

Astrocytes have, until recently, been thought of as the passive supporting elements of the central nervous system. However, recent developments suggest that these cells actually play a crucial and vital role in the overall physiology of the brain. Astrocytes selectively express a host of cell membrane and nuclear receptors that are responsive to various neuroactive compounds. In addition, the cell membrane has a number of important transporters for these compounds. Direct evidence for the selective co-expression of neurotransmitters, transporters on both neurons and astrocytes, provides additional evidence for metabolic compartmentation within the central nervous system. Oxidative stress as defined by the excessive production of free radicals can alter dramatically the function of the cell. The free radical nitric oxide has attracted a considerable amount of attention recently, due to its role as a physiological second messenger but also because of its neurotoxic potential when produced in excess. We provide, therefore, an in-depth discussion on how this free radical and its metabolites affect the intra and intercellular physiology of the astrocyte(s) and surrounding neurons. Finally, we look at the ways in which astrocytes can counteract the production of free radicals in general by using their antioxidant pathways. The glutathione antioxidant system will be the focus of attention, since astrocytes have an enormous capacity for, and efficiency built into this particular system.

The "anti-pyrimidine effect" of hypoxia and brequinar sodium (NSC 368390) is of consequence for tumor cell growth

The rationale of the present study was to investigate the simultaneous effect of hypoxia and drugs with an "anti-pyrimidine effect" on tumor cell proliferation to evaluate putative changes in the sensitivity of cells to these kinds of chemotherapeutic treatment on reduced O2 tension. Pyrimidine de novo biosynthesis, at the stage of respiratory chain-dependent dihydroorotate dehydrogenase, was found to be a biochemical target site for oxygen deficiency as well as for Brequinar Sodium (6-fluoro-2-(2'-fluoro-1,1'-biphenyl-4-yl)-3-methyl-4-quinoline carboxylic acid sodium salt) (Brequinar). Increasing drug concentrations (0.1-50 microM) reduced the proliferation rate of in vitro cultured Ehrlich ascites tumor cells (IC50 = 0.25 microM). Decreasing concentrations of O2 reduced the proliferation rate (50% at approximately 3.5% O2). Brequinar at 2.5 microM stimulated the incorporation of exogenous [14C]uridine into RNA to 140 and 190% of controls, respectively, as a result of active salvage pathways, whereas it decreased the incorporation of [14C]NaHCO3 by the de novo pathway (to 20 and 5% of controls, respectively). Cells routinely grown in glucose-free, uridine-supplemented medium were resistant to 12.5 microM of the drug. The complete growth pattern of the tumor cells (increase in cell number and protein, RNA and DNA content of cultures during a 24-hr culture period) was examined (i) on reducing the O2 tension of the atmosphere stepwise from 20 to 1% O2; (ii) on addition of 0.125 microM Brequinar; and (iii) under both conditions. The combination was found to give an additive inhibitory effect under moderate hypoxia (5-20% O2) and a greater than additive effect if the oxygen tension was further reduced (1-5%).

Ischemic injury to rat forebrain mitochondria and cellular calcium homeostasis

The three-vessel occlusion model of Kameyama et al. (Kameyama, M., Suzuki, J., Shirane, R. and Ogawa, A. (1985) Stroke 16, 489-493) was adapted with modifications to induce complete reversible rat forebrain ischemia. A fast and simple procedure for the isolation and purification of rat brain mitochondria, which provides high yield, is described. Mitochondria isolated from ischemic brain (12-30 min ischemia) exhibited decreases in State 3 respiratory rates of approx. 70% with NAD-linked respiratory substrates. Less effect was observed with succinate and rotenone. The State 4 respiratory activity remained near control levels except at 15 min of ischemia (25% increase) with NAD-linked substrates. Similarly, with succinate and rotenone, an approx. 30% increase in State 4 activity was observed at 20 min of ischemia. Consequently, the respiratory control indices (RCIs) were decreased. Both the respiratory rates and RCIs could be restored to near control levels upon the addition of EGTA(EDTA) or ruthenium red to the assay mixture. Analysis employing fura-2 as a Ca2+ probe, indicated a great decrease in the first order rate constant for Ca2+ uptake of ischemic mitochondria and a significant increase in Ca2+ homeostasis with an increase in the cytosolic Ca2+ concentration which results in excessive association of Ca2+ on the mitochondrial membrane and an inhibition of the respiratory chain-linked oxidative phosphorylation and Ca(2+)-transport activity of forebrain mitochondria. These deficits are proportional to the duration of ischemia.