Ian Weidling

Mitochondria-Derived Damage-Associated Molecular Patterns in Neurodegeneration

Inflammation is increasingly implicated in neurodegenerative disease pathology. As no acquired pathogen appears to drive this inflammation, the question of what does remains. Recent advances indicate damage-associated molecular pattern (DAMP) molecules, which are released by injured and dying cells, can cause specific inflammatory cascades. Inflammation, therefore, can be endogenously induced. Mitochondrial components induce inflammatory responses in several pathological conditions. Due to evidence such as this, a number of mitochondrial components, including mitochondrial DNA, have been labeled as DAMP molecules. In this review, we consider the contributions of mitochondrial-derived DAMPs to inflammation observed in neurodegenerative diseases.

Oxaloacetate Enhances Neuronal Cell Bioenergetic Fluxes and Infrastructure

We tested how the addition of oxaloacetate (OAA) to SH‐SY5Y cells affected bioenergetic fluxes and infrastructure, and compared the effects of OAA to malate, pyruvate, and glucose deprivation. OAA displayed pro‐glycolysis and pro‐respiration effects. OAA pro‐glycolysis effects were not a consequence of decarboxylation to pyruvate because unlike OAA, pyruvate lowered the glycolysis flux. Malate did not alter glycolysis flux and reduced mitochondrial respiration. Glucose deprivation essentially eliminated glycolysis and increased mitochondrial respiration. OAA increased, while malate decreased, the cell NAD+/NADH ratio. Cytosolic malate dehydrogenase 1 protein increased with OAA treatment, but not with malate or glucose deprivation. Glucose deprivation increased protein levels of ATP citrate lyase, an enzyme which produces cytosolic OAA, whereas OAA altered neither ATP citrate lyase mRNA nor protein levels. OAA, but not glucose deprivation, increased cytochrome oxidase subunit 2, PGC1α, PGC1β, and PGC1 related co‐activator protein levels. OAA increased total and phosphorylated SIRT1 protein. We conclude that adding OAA to SH‐SY5Y cells can support or enhance both glycolysis and respiration fluxes. These effects appear to depend, at least partly, on OAA causing a shift in the cell redox balance to a more oxidized state, that it is not a glycolysis pathway intermediate, and possibly its ability to act in an anaplerotic fashion.

Extracellular Mitochondria and Mitochondrial Components Act as Damage-Associated Molecular Pattern Molecules in the Mouse Brain

Mitochondria and mitochondrial debris are found in the brain’s extracellular space, and extracellular mitochondrial components can act as damage associated molecular pattern (DAMP) molecules. To characterize the effects of potential mitochondrial DAMP molecules on neuroinflammation, we injected either isolated mitochondria or mitochondrial DNA (mtDNA) into hippocampi of C57BL/6 mice and seven days later measured markers of inflammation. Brains injected with whole mitochondria showed increased Tnfα and decreased Trem2 mRNA, increased GFAP protein, and increased NFκB phosphorylation. Some of these effects were also observed in brains injected with mtDNA (decreased Trem2 mRNA, increased GFAP protein, and increased NFκB phosphorylation), and mtDNA injection also caused several unique changes including increased CSF1R protein and AKT phosphorylation. To further establish the potential relevance of this response to Alzheimer’s disease (AD), a brain disorder characterized by neurodegeneration, mitochondrial dysfunction, and neuroinflammation we also measured App mRNA, APP protein, and Aβ1–42 levels. We found mitochondria (but not mtDNA) injections increased these parameters. Our data show that in the mouse brain extracellular mitochondria and its components can induce neuroinflammation, extracellular mtDNA or mtDNA-associated proteins can contribute to this effect, and mitochondria derived-DAMP molecules can influence AD-associated biomarkers.

A Bioenergetics Systems Evaluation of Ketogenic Diet Liver Effects

Ketogenic diets induce hepatocyte fatty acid oxidation and ketone body production. To further evaluate how ketogenic diets affect hepatocyte bioenergetic infrastructure, we analyzed livers from C57Bl/6J male mice maintained for 1 month on a ketogenic or standard chow diet. Compared with the standard diet, the ketogenic diet increased cytosolic and mitochondrial protein acetylation and also altered protein succinylation patterns. SIRT3 protein decreased while SIRT5 protein increased, and gluconeogenesis, oxidative phosphorylation, and mitochondrial biogenesis pathway proteins were variably and likely strategically altered. The pattern of changes observed can be used to inform a broader systems overview of how ketogenic diets affect liver bioenergetics.

Mitochondrial Function and Neurodegenerative Diseases

Abstract Many neurodegenerative diseases feature mitochondrial dysfunction. This includes both common sporadic and rare Mendelian disorders. In some cases, mitochondrial defects mediate disease pathology, and in others, the defects actually initiate and drive the disease. Understanding the causes and consequences of mitochondrial dysfunction provides insight into neurodegenerative diseases and reveals potential therapeutic targets that could lead to new treatments. This chapter provides an overview of mitochondrial function and its role in cell physiology, presents current perceptions about the relevance of mitochondrial and bioenergetic dysfunction to neurodegenerative diseases, and discusses targeting mitochondria for therapeutic purposes.

MITOCHONDRIAL MEMBRANE POTENTIAL INFLUENCE ON PROCESSING AND LOCALIZATION OF APP

neuroblastoma cells and cell homogenates, and reversed the Abinduced increases in superoxide formation. KU-32 increased the Vmax of mitochondrial Complex I without affecting levels of Complex I proteins, and blocked the Ab inhibition of Complex I. We determined that the effects on Complex I were the result of inhibition of pyruvate dehydrogenase kinase (PDHK), both in isolated brain mitochondria and in SH-SY5Y cells. PDHK inhibition by the classic enzyme inhibitor, dichloroacetate, led to neuroprotection from Ab-induced cell injury similarly to KU-32. Inhibition of PDHK would lead to activation of the PDH complex, increase acetyl-CoA generation, stimulate the tricarboxylic acid cycle and Complex I, and enhance oxidative phosphorylation. Bioenergetic measurements in SH-SY5Y showed increases in oxygen consumption rates in KU-32-treated cells. Conclusions:These studies point to the potential value of PDHK as a target in AD therapy.

The ABCD's of 5′‐adenosine monophosphate‐activated protein kinase and adrenoleukodystrophy

This Editorial highlights a study by Singh and coworkers in the current issue of Journal of Neurochemistry, in which the authors present additional evidence that AMPKα1 is reduced in X‐linked adrenoleukodystrophy (X‐ALD). They make a case for increasing AMPKα1 activity for therapeutic purposes in this disease, and indicate how this goal may be achieved.