Mitochondrial control of autophagic lysosomal pathway in Alzheimer's disease

Molecular mechanisms of mitochondrial homeostasis regulation in neurons and possible therapeutic approaches for Alzheimer's disease

Alzheimer's disease (AD) is a neurological disease with memory loss and cognitive decline, which affects a large proportion of the aging population. Regrettably, there are no drug to reverse or cure AD and drug development for the primary theory of amyloid beta deposition has mostly failed. Therefore, there is an urgent need to investigate novel strategies for preventing AD. Recent studies demonstrate that imbalance of mitochondrial homeostasis is a driver in Aβ accumulation, which can lead to the occurrence and deterioration of cognitive impairment in AD patients. This suggests that regulating neuronal mitochondrial homeostasis may be a new strategy for AD. We summarize the importance of mitochondrial homeostasis in AD neuron and its regulatory mechanisms in this review. In addition, we summarize the results of studies indicating mitochondrial dysfunction in AD subjects, including impaired mitochondrial energy production, oxidative stress, imbalance of mitochondrial protein homeostasis, imbalance of fusion and fission, imbalance of neuronal mitochondrial biogenesis and autophagy, and altered mitochondrial motility, in hope of providing possible therapeutic approaches for AD.

Application of Pt@ZIF-8 nanocomposite-based electrochemical biosensor for sensitive diagnosis of tau protein in Alzheimer's disease patients

Alzheimer's disease (AD) is a progressive brain disorder characterized by the ongoing decline of brain functions. Studies have revealed the detrimental effects of hyperphosphorylated tau (p-tau) protein fibrils in AD pathogenesis, highlighting the importance of this factor in the early-stage detection of AD conditions. We designed an electrochemical immunosensor for quantitative detection of the cis conformation of the p-tau protein (cis-p-tau) employing platinum nanoparticles (Pt NPs) supported on zeolitic imidazolate frameworks (ZIF) for modifying the glassy carbon electrode (GCE) surface. Under optimum conditions, the immunosensor selectively and sensitively detected cis-p-tau within the broad linear range of 1 fg mL-1 to 10 ng mL-1 and the low limit of detection (LOD) of 1 fg mL-1 with desired reproducibility and stability. Furthermore, the fabricated immunosensor's performance was examined for the cis-p-tau analysis in the serum of AD patients, indicating its accuracy and feasibility for real-sample analysis. Notably, this is the first application of Pt@ZIF-8 nanocomposite in fabricating a valid immunosensor for selective cis-p-tau detection, even in the presence of trans-p-tau. It is worth mentioning that the enzyme-linked immunosorbent assay (ELISA) reference technique is not able to evaluate pico- or femtomolar concentrations of cis-p-tau, making the fabricated immunosensor superior for early-stage measurement and screening of AD.

Piceatannol Protects PC-12 Cells against Oxidative Damage and Mitochondrial Dysfunction by Inhibiting Autophagy via SIRT3 Pathway

Oxidative stress has been identified as a major cause of cellular injury in a variety of neurodegenerative disorders. This study aimed to investigate the cytoprotective effects of piceatannol on hydrogen peroxide (H₂O₂)-induced pheochromocytoma-12 (PC-12) cell damage and explore the underlying mechanisms. Our findings indicated that piceatannol pre-treatment significantly attenuated H₂O₂-induced PC-12 cell death. Furthermore, piceatannol effectively improved mitochondrial content and mitochondrial function, including enhancing mitochondrial reactive oxygen species (ROS) elimination capacity and increasing mitochondrial transcription factor (TFAM), peroxisome-proliferator-activated receptor-γ coactivator-1α (PGC-1α) and mitochondria Complex IV expression. Meanwhile, piceatannol treatment inhibited mitochondria-mediated autophagy as demonstrated by restoring mitochondrial membrane potential, reducing autophagosome formation and light chain 3B II/I (LC3B II/I) and autophagy-related protein 5 (ATG5) expression level. The protein expression level of SIRT3 was significantly increased by piceatannol in a concentration-dependent manner. However, the cytoprotective effect of piceatannol was dramatically abolished by sirtuin 3 (SIRT3) inhibitor, 3-(1H-1,2,3-Triazol-4-yl) pyridine (3-TYP), which led to an exacerbated mitochondrial dysfunction and autophagy in PC-12 cells under oxidative stress. In addition, the autophagy activator (rapamycin) abrogated the protective effects of piceatannol on PC-12 cell death. These findings demonstrated that piceatannol could alleviate PC-12 cell oxidative damage and mitochondrial dysfunction by inhibiting autophagy via the SIRT3 pathway.

Role of mitochondrial dysfunction, oxidative stress and autophagy in progression of Alzheimer's disease

Alzheimer's disease (AD) is the most common form of dementia. The pathological hallmarks of AD are amyloid plaques [aggregates of amyloid beta (A)] and neurofibrillary tangles (aggregates of tau protein). Growing evidence suggests that tau accumulation is pathologically more relevant to the development of neurodegeneration and cognitive decline in AD patients than A plaques. Mitochondrial damage plays an important role in AD. Mitochondrial damage has been related to amyloid-beta or tau pathology or to the presence of specific presenilin-1 mutations. Elevate reactive oxygen species/reactive nitrogen species production and defective mitochondrial dynamic balance has been suggested to be the reason as well as the consequence of AD related pathology. Oxidative stress is a prominent early event in the pathogenesis of AD and is therefore believed to contribute to tau hyperphosphorylation. Several studies have shown that the autophagy pathway in neurons is important under physiological and pathological conditions. Therefore, this pathway plays a crucial role for the degradation of endogenous soluble tau. However, the relationship between mitochondrial dysfunctioning, oxidative stress, autophagy dysregulation, and neuronal cell death in AD remains unclear. Here, we review the latest progress in AD, with a special emphasis on mitochondrial dysfunctioning, oxidative stress, and autophagy. We also discuss the interlink mechanism of these three factors in AD.

Boosting the autophagy-lysosomal pathway by phytochemicals: A potential therapeutic strategy against Alzheimer's disease

The lysosome is a membrane-enclosed organelle in eukaryotic cells, which has basic pattern recognition for nutrient-dependent signal transduction. In Alzheimer's disease, the already declining autophagy-lysosomal function is exacerbated by an increased need for clearance of damaged proteins and organelles in aged cells. Recent evidence suggests that numerous diseases are linked to impaired autophagy upstream of lysosomes. In this way, a comprehensive survey on the pathophysiology of the disease seems necessary. Hence, in the first section of this review, we will discuss the ultimate findings in lysosomal signaling functions and how they affect cellular metabolism and trafficking under neurodegenerative conditions, specifically Alzheimer's disease. In the second section, we focus on how natural products and their derivatives are involved in the regulation of inflammation and lysosomal dysfunction pathways, including how these should be considered a crucial target for Alzheimer's disease therapeutics.

Chondroitin sulfate from sturgeon bone protects rat chondrocytes from hydrogen peroxide-induced damage by maintaining cellular homeostasis through enhanced autophagy

We previously reported that treatment with chondroitin sulfate from sturgeon bone (CSSB) promoted anti-apoptotic activity in hydrogen peroxide (H₂O₂)-treated chondrocytes and had a protective effect on mitochondria. It is known that cells can repair damaged mitochondria through autophagy, thus inhibiting the development of apoptosis. Therefore, it is reasonable to speculate that CSSB treatment may inhibit chondrocyte apoptosis via regulation of autophagy. We observed the mitochondrial morphology of chondrocytes treated with different doses of CSSB, and confirmed that CSSB did not affect cell activity or cause damage to mitochondria. When compared with H₂O₂ treatment alone, CSSB treatment increased the clearance and repair of damaged mitochondria and promoted fusion of damaged mitochondria and lysosomes. CSSB treatment also increased the number of autolysosomes. However, these events could be blocked in chondrocytes pretreated with the autophagy inhibitor chloroquine, resulting in a decreased level of autophagy and increased apoptosis. These results suggest that CSSB treatment helps maintain intracellular homeostasis and prevent injury in chondrocytes treated with H₂O₂ by increasing autophagy.

Copper-induced apoptosis and autophagy through oxidative stress-mediated mitochondrial dysfunction in male germ cells

Excess copper reduces sperm number and motility but the causes are unclear. We investigated the toxic effects of copper exposure on the immortalized male germ cell line GC-1. Copper addition to cells altered viability and morphology in a dose-dependent manner. Copper addition resulted in increased levels of reactive oxygen species (ROS), malonaldehyde (MDA) and lactate dehydrogenase (LDH) while catalase (CAT) activity and glutathione (GSH) declined. The mitochondrial transmembrane potential and ATP levels decreased in response to copper as did mitochondria fission that led to mitochondrial dysfunction. The apoptosis rate was also proportional to the level of copper in the growth medium. Copper also down-regulated Bcl2 and up-regulated Bax, Casp8 and Casp3 linking the effects of copper to increased apoptosis. The levels of mRNA for the autophagy-related genes (Atg3, Atg5, p62, Lc3b/Lc3a) and proteins (Lc3b/Lc3a, BECN1, Atg5, p62) all increased in copper-treated cells as were levels Lc3 determined by fluorescence microscopy. These results indicated that copper induces apoptosis and autophagy through oxidative stress-mediated mitochondrial dysfunction.

Oxidative Stress, Synaptic Dysfunction, and Alzheimer's Disease

Alzheimer's disease (AD) is a devastating neurodegenerative disorder without a cure. Most AD cases are sporadic where age represents the greatest risk factor. Lack of understanding of the disease mechanism hinders the development of efficacious therapeutic approaches. The loss of synapses in the affected brain regions correlates best with cognitive impairment in AD patients and has been considered as the early mechanism that precedes neuronal loss. Oxidative stress has been recognized as a contributing factor in aging and in the progression of multiple neurodegenerative diseases including AD. Increased production of reactive oxygen species (ROS) associated with age- and disease-dependent loss of mitochondrial function, altered metal homeostasis, and reduced antioxidant defense directly affect synaptic activity and neurotransmission in neurons leading to cognitive dysfunction. In addition, molecular targets affected by ROS include nuclear and mitochondrial DNA, lipids, proteins, calcium homeostasis, mitochondrial dynamics and function, cellular architecture, receptor trafficking and endocytosis, and energy homeostasis. Abnormal cellular metabolism in turn could affect the production and accumulation of amyloid-β (Aβ) and hyperphosphorylated Tau protein, which independently could exacerbate mitochondrial dysfunction and ROS production, thereby contributing to a vicious cycle. While mounting evidence implicates ROS in the AD etiology, clinical trials with antioxidant therapies have not produced consistent results. In this review, we will discuss the role of oxidative stress in synaptic dysfunction in AD, innovative therapeutic strategies evolved based on a better understanding of the complexity of molecular mechanisms of AD, and the dual role ROS play in health and disease.

General Anesthetics Regulate Autophagy via Modulating the Inositol 1,4,5-Trisphosphate Receptor: Implications for Dual Effects of Cytoprotection and Cytotoxicity

General anesthetics are both neuroprotective and neurotoxic with unclear mechanisms. General anesthetics may control cell survival via their effects on autophagy by activation of type 1 inositol triphosphate receptor (InsP₃R-1). DT40 or SH-SY5Y cells with only or over 99% expression of InsP₃R-1 were treated with isoflurane or propofol. Cell viability was determined by MTT reduction or LDH release assays. Apoptosis was determined by measuring Caspase-3 or by TUNEL assay. Autophagy activity was determined by measuring LC3 II and P62. We evaluated mitochondrial integrity using MitoTracker Green and cytosolic ATP levels. Fura2-AM was used to measure the concentrations of cytosolic calcium ([Ca²⁺]_c). Propofol significantly increased peak and integrated calcium response (P < 0.001) in cells with InsP₃R-1 but not in cells with triple knockout of InsP₃R. Both propofol and isoflurane increased autophagy induction (P < 0.05) in an mTOR- and InsP₃R- activity dependent manner. Short exposure to propofol adequately activated InsP₃-1 to provide sufficient autophagy for cytoprotection, while prolonged exposure to propofol induced cell apoptosis via impairment of autophagy flux through over activation of InsP₃-1. Propofol damaged mitochondria and decreased cytosolic ATP. The effects of general anesthetics on apoptosis and autophagy are closely integrated; both are caused by differential activation of the type 1 InsP₃R.

Evidence for Mitochondrial UPR Gene Activation in Familial and Sporadic Alzheimer's Disease

Mitochondrial perturbations such as oxidative stress, increased fission/fusion dysfunction, and mitophagy are consistent features of Alzheimer's disease (AD), yet the mechanisms that initiate these perturbations are unclear. One potential source for mitochondrial defects could be an imbalance in mitochondrial proteostasis. In this regard, studies indicate that a specialized mitochondrial unfolded protein response (mtUPR) is activated upon the aberrant accumulation of damaged or unfolded proteins in the mitochondrial matrix, resulting in the up-regulation of key genes involved in mitochondrial stabilization. To test whether mtUPR activation occurs in AD, we performed real-time quantitative PCR on postmortem frontal cortex samples from subjects classified as sporadic AD, familial AD linked to presenilin-1 mutations, or cognitively intact controls. Compared to controls, sporadic AD subjects exhibited a significant ~40-60% increase in expression levels of select genes activated by the mtUPR, including mitochondrial chaperones dnaja3, hspd1, and hspe1, mitochondrial proteases clpp and yme1l1, and txn2, a mitochondrial-specific oxidoreductase. Furthermore, levels of all six mtUPR genes were significantly up-regulated by ~70-90% in familial AD compared to controls, and these expression levels were significantly higher compared to sporadic AD. The increase in hspd1 (Hsp60) was validated by western blotting. These data support the concept that both sporadic and familial AD are characterized by mtUPR gene activation. Understanding the physiological consequences of this response may provide subcellular mechanistic clues to selective neuronal vulnerability or endogenous compensatory mechanisms during the progression of AD.

Moderate activation of autophagy regulates the intracellular calcium ion concentration and mitochondrial membrane potential in beta-amyloid-treated PC12 cells

Alzheimer's disease (AD) is an age-related and progressive neurodegenerative disease. Aggregated beta-amyloid (Aβ) disturbs Ca(2+) homeostasis and causes mitochondrial dysfunction and finally underlies AD. Recent evidence suggests that autophagy initiation by Beclin-1 protein might be involved in the pathogenesis of AD. However, the effects of Beclin-1 dependent autophagy on intracellular calcium ion concentration ([Ca(2+)]i) and mitochondrial membrane potential (MMP) is unclear. The effects of Beclin-1 dependent autophagy that were activated by a gradient concentration of autophagy activator rapamycin or inhibited by autophagy inhibitor 3-methyladenine (3-MA) on cell viability and cell morphology were examined. Pretreatment with rapamycin significantly up-regulated the expression of Beclin-1 in response to Aβ1-42 application, but after pretreatment with 3-MA it was significantly down-regulated. Moderate activation of Beclin-1 dependent autophagy had an up regulation effect on cell viability and could maintain the original morphology of cells. Furthermore, rapamycin or 3-MA on [Ca(2+)]i and MMP in Aβ1-42 treatment of PC12 cells were evaluated. We also report that PC12 cells treated with Aβ1-42 showed an increase in [Ca(2+)]i but a decrease in MMP when compared to the normal control. However the application of rapamycin prior to this prevented the increase in [Ca(2+)]i and the decrease in MMP in response to Aβ1-42. When 3-MA was applied this exacerbated the effect of Aβ1-42 on the [Ca(2+)]i and the MMP. This shows that moderate activation of Beclin-1 dependent autophagy by rapamycin can modulate Ca(2+) homeostasis and maintain MMP in response to Aβ1-42 induced cytotoxicity and so may have a preventive function in AD.

Cadmium induced inhibition of autophagy is associated with microtubule disruption and mitochondrial dysfunction in primary rat cerebral cortical neurons

Recent studies have reported that mitochondria serve as direct targets for cadmium- (Cd-) induced neuronal toxicity, which can be attenuated by autophagy. The molecular mechanisms' underlying Cd-induced mitochondrial dysfunction and autophagy in neurons are not known. In this study, we studied the upstream signaling pathways induced by Cd-mediated mitochondrial metabolism alterations using primary rat neuron as a model. We found that Cd induced the destruction of microtubules (MTs), and resulted in tau hyper-phosphorylation and decreased acetylated tubulin levels, which were related to a decrease in mitochondrial membrane potential (MMP) and adenosine triphosphate (ATP) levels. As a result of taxol disruption, alterations in macroautophagy, like altered cellular distribution of the autophagy-related protein light chain 3 beta (LC3B) and the expression of Atg5 were found compared with Cd group. We found for the first time that MT disruption induced by Cd reduced the levels of autophagy, leading to mitochondrial dysfunction. These observations suggest new therapeutic strategies aimed to activate or ameliorate pro-survival macroautophagy.

Early-onset Alzheimer's disease in two Iranian families: a genetic study

BACKGROUND

Early-onset Alzheimer's disease (EOAD) represents less than 5% of all AD cases. Autosomal dominant EOAD has been defined as the occurrence of at least three cases in three generations. Mutations in the amyloid precursor protein (APP), presenilin-1 and presenilin-2 genes have been recognized to be the cause of EOAD.

OBJECTIVE

We investigated the genotype of EOAD in two generations of two families with EOAD living in an Iranian village.

METHODS

The polymerase chain reaction method was used to study the presenilin-1 and APP genes in 25 subjects of these generations.

RESULTS

A guanine-to-adenine transition in exon 17 of the APP gene resulting in a valine-to-isoleucine substitution at codon 717 was detected in 14 subjects including 6 patients with EOAD.

CONCLUSION

This mutation demonstrates the importance of γ-secretase, the necessity of early detection of patients with memory decline in the susceptible population and raising public awareness of consanguinity marriages.

The Ambiguous Relationship of Oxidative Stress, Tau Hyperphosphorylation, and Autophagy Dysfunction in Alzheimer's Disease

Alzheimer's disease (AD) is the most common form of dementia. The pathological hallmarks of AD are amyloid plaques [aggregates of amyloid-beta (Aβ)] and neurofibrillary tangles (aggregates of tau). Growing evidence suggests that tau accumulation is pathologically more relevant to the development of neurodegeneration and cognitive decline in AD patients than Aβ plaques. Oxidative stress is a prominent early event in the pathogenesis of AD and is therefore believed to contribute to tau hyperphosphorylation. Several studies have shown that the autophagic pathway in neurons is important under physiological and pathological conditions. Therefore, this pathway plays a crucial role for the degradation of endogenous soluble tau. However, the relationship between oxidative stress, tau protein hyperphosphorylation, autophagy dysregulation, and neuronal cell death in AD remains unclear. Here, we review the latest progress in AD, with a special emphasis on oxidative stress, tau hyperphosphorylation, and autophagy. We also discuss the relationship of these three factors in AD.

Aβ1-42 monomers or oligomers have different effects on autophagy and apoptosis

The role of autophagy and its relationship with apoptosis in Alzheimer disease (AD) pathogenesis is poorly understood. Disruption of autophagy leads to buildup of incompletely digested substrates, amyloid-β (Aβ) peptide accumulation in vacuoles and cell death. Aβ, in turn, has been found to affect autophagy. Thus, Aβ might be part of a loop in which it is both the substrate of altered autophagy and its cause. Given the relevance of different soluble forms of Aβ1-42 in AD, we have investigated whether monomers and oligomers of the peptide have a differential role in causing altered autophagy and cell death. Using differentiated SK-N-BE neuroblastoma cells, we found that monomers hamper the formation of the autophagic BCL2-BECN1/Beclin 1 complex and activate the MAPK8/JNK1-MAPK9/JNK2 pathway phosphorylating BCL2. Monomers also inhibit apoptosis and allow autophagy with intracellular accumulation of autophagosomes and elevation of levels of BECN1 and LC3-II, resulting in an inhibition of substrate degradation due to an inhibitory action on lysosomal activity. Oligomers, in turn, favor the formation of the BCL2-BECN1 complex favoring apoptosis. In addition, they cause a less profound increase in BECN1 and LC3-II levels than monomers without affecting the autophagic flux. Thus, data presented in this work show a link for autophagy and apoptosis with monomers and oligomers, respectively. These studies are likely to help the design of novel disease modifying therapies.

Mitochondrial toxic effects of Aβ through mitofusins in the early pathogenesis of Alzheimer's disease

Mitochondrial dysfunction has been implicated in the pathogenesis of Alzheimer's disease (AD). However, it is obscure how amyloid-beta (Aβ) can impair mitochondria in the early stage of AD pathology. Using PrP-hAPP/hPS1 double-transgenic AD mouse model, we find that abnormal mitochondrial morphology and damaged mitochondrial structure in hippocampal neurons appear in the early stage of AD-like disease development. We also find consistent mitochondrial abnormalities in the SH-SY5Y cells, which express amyloid precursor protein (APP) Swedish mutation (APPsw) and have been used as a cell model of the early-onset AD. Significant changes of mitofusin GTPases (Mfn1 and Mfn2) were detected both in the PrP-hAPP/hPS1 brains and SH-SY5Y cells. Moreover, our results show that Aβ accumulation in neurons of PrP-hAPP/hPS1 mice can affect the neurogenesis prior to plaque formation. These findings suggest that mitochondrial impairment is a very early event in AD pathogenesis and abnormal expression of Mfn1 and Mfn2 caused by excessive intracellular Aβ is the possible molecular mechanism. Interestingly, L-theanine has significant effects on regulating mitochondrial fusion proteins in SH-SY5Y (APPsw) cells. Overall, our results not only suggest a new early mechanism of AD pathogenesis but also propose a preventive candidate, L-theanine, for the treatment of AD.

Gaucher disease: transcriptome analyses using microarray or mRNA sequencing in a Gba1 mutant mouse model treated with velaglucerase alfa or imiglucerase

Gaucher disease type 1, an inherited lysosomal storage disorder, is caused by mutations in GBA1 leading to defective glucocerebrosidase (GCase) function and consequent excess accumulation of glucosylceramide/glucosylsphingosine in visceral organs. Enzyme replacement therapy (ERT) with the biosimilars, imiglucerase (imig) or velaglucerase alfa (vela) improves/reverses the visceral disease. Comparative transcriptomic effects (microarray and mRNA-Seq) of no ERT and ERT (imig or vela) were done with liver, lung, and spleen from mice having Gba1 mutant alleles, termed D409V/null. Disease-related molecular effects, dynamic ranges, and sensitivities were compared between mRNA-Seq and microarrays and their respective analytic tools, i.e. Mixed Model ANOVA (microarray), and DESeq and edgeR (mRNA-Seq). While similar gene expression patterns were observed with both platforms, mRNA-Seq identified more differentially expressed genes (DEGs) (∼3-fold) than the microarrays. Among the three analytic tools, DESeq identified the maximum number of DEGs for all tissues and treatments. DESeq and edgeR comparisons revealed differences in DEGs identified. In 9V/null liver, spleen and lung, post-therapy transcriptomes approximated WT, were partially reverted, and had little change, respectively, and were concordant with the corresponding histological and biochemical findings. DEG overlaps were only 8–20% between mRNA-Seq and microarray, but the biological pathways were similar. Cell growth and proliferation, cell cycle, heme metabolism, and mitochondrial dysfunction were most altered with the Gaucher disease process. Imig and vela differentially affected specific disease pathways. Differential molecular responses were observed in direct transcriptome comparisons from imig- and vela-treated tissues. These results provide cross-validation for the mRNA-Seq and microarray platforms, and show differences between the molecular effects of two highly structurally similar ERT biopharmaceuticals.

Reconsider Alzheimer's disease by the 'calpain-cathepsin hypothesis'--a perspective review

Alzheimer's disease (AD) is characterized by slowly progressive neuronal death, but its molecular cascade remains elusive for over 100 years. Since accumulation of autophagic vacuoles (also called granulo-vacuolar degenerations) represents one of the pathologic hallmarks of degenerating neurons in AD, a causative connection between autophagy failure and neuronal death should be present. The aim of this perspective review is at considering such underlying mechanism of AD that age-dependent oxidative stresses may affect the autophagic-lysosomal system via carbonylation and cleavage of heat-shock protein 70.1 (Hsp70.1). AD brains exhibit gradual but continual ischemic insults that cause perturbed Ca(2+) homeostasis, calpain activation, amyloid β deposition, and oxidative stresses. Membrane lipids such as linoleic and arachidonic acids are vulnerable to the cumulative oxidative stresses, generating a toxic peroxidation product 'hydroxynonenal' that can carbonylate Hsp70.1. Recent data advocate for dual roles of Hsp70.1 as a molecular chaperone for damaged proteins and a guardian of lysosomal integrity. Accordingly, impairments of lysosomal autophagy and stabilization may be driven by the calpain-mediated cleavage of carbonylated Hsp70.1, and this causes lysosomal permeabilization and/or rupture with the resultant release of the cell degradation enzyme, cathepsins (calpain-cathepsin hypothesis). Here, the author discusses three topics; (1) how age-related decrease in lysosomal and autophagic activities has a causal connection to programmed neuronal necrosis in sporadic AD, (2) how genetic factors such as apolipoprotein E and presenilin 1 can facilitate lysosomal destabilization in the sequential molecular events, and (3) whether a single cascade can simultaneously account for implications of all players previously reported. In conclusion, Alzheimer neuronal death conceivably occurs by the similar 'calpain-hydroxynonenal-Hsp70.1-cathepsin cascade' with ischemic neuronal death. Blockade of calpain and/or extra-lysosomal cathepsins as well as scavenging of hydroxynonenal would become effective AD therapeutic approaches.

Aβ1-42-mediated down-regulation of Uch-L1 is dependent on NF-κB activation and impaired BACE1 lysosomal degradation

Amyloid-β 1-42 accumulation is the major pathogenetic event in Alzheimer's disease (AD), believed to be responsible for synaptic dysfunction and neuronal cell death. However, the physiologic activity of Aβ peptides remains elusive: Aβ might not only play a toxic role, but also act as a functional signaling intermediate. We recently reported that Aβ1-42 promotes BACE1 transcription through the activation of the JNK-c-jun pathway. Here, we show that the Aβ1-42-mediated increase in BACE1 expression is accompanied by a decrease in ubiquitin C-terminal hydrolase L1 (Uch-L1) expression and activity in different cellular models such as neuroblastoma SH-SY5Y as well as NT(2) neuronal cells. We also found that the increase in BACE1 and the decrease in Uch-L1 are related events and depend on NF-κB pathway; thus, Aβ1-42 is able to activate NF-κB pathway and the pretreatment with a pharmacological inhibitor, able to block the nuclear translocation of the transactivating unit p65, almost completely prevents both the decrease in Uch-L1 and the increase in BACE1 expression. In addition, the decrease in Uch-L1 activity interferes with the lysosomal degradation of BACE1, as demonstrated by the decrease in Cathepsin D activity and the partial accumulation of BACE1 in lysosomes after Aβ1-42 treatment as well after Uch-L1 inhibition. In support of the in vitro data, we observed low protein levels of Uch-L1 associated with high protein levels of BACE1 in sporadic AD brains. Our data suggest that Uch-L1 could be an attractive target for the development of new therapeutic approaches for AD.

Mitochondrial dysfunction and oxidative stress activate inflammasomes: impact on the aging process and age-related diseases

Oxidative stress and low-grade inflammation are the hallmarks of the aging process and are even more enhanced in many age-related degenerative diseases. Mitochondrial dysfunction and oxidative stress can provoke and potentiate inflammatory responses, but the mechanism has remained elusive. Recent studies indicate that oxidative stress can induce the assembly of multiprotein inflammatory complexes called the inflammasomes. Nod-like receptor protein 3 (NLRP3) is the major immune sensor for cellular stress signals, e.g., reactive oxygen species, ceramides, and cathepsin B. NLRP3 activation triggers the caspase-1-mediated maturation of the precursors of IL-1β and IL-18 cytokines. During aging, the autophagic clearance of mitochondria declines and dysfunctional mitochondria provoke chronic oxidative stress, which disturbs the cellular redox balance. Moreover, increased NF-κB signaling observed during aging could potentiate the expression of NLRP3 and cytokine proforms enhancing the priming of NLRP3 inflammasomes. Recent studies have demonstrated that NLRP3 activation is associated with several age-related diseases, e.g., the metabolic syndrome. We will review here the emerging field of inflammasomes in the appearance of the proinflammatory phenotype during the aging process and in age-related diseases.

A mitochondrial etiology of Alzheimer and Parkinson disease

BACKGROUND

The genetics and pathophysiology of Alzheimer Disease (AD) and Parkinson Disease (PD) appears complex. However, mitochondrial dysfunction is a common observation in these and other neurodegenerative diseases.

SCOPE OF REVIEW

We argue that the available data on AD and PD can be incorporated into a single integrated paradigm based on mitochondrial genetics and pathophysiology.

MAJOR CONCLUSIONS

Rare chromosomal cases of AD and PD can be interpreted as affecting mitochondrial function, quality control, and mitochondrial DNA (mtDNA) integrity. mtDNA lineages, haplogroups, such haplogroup H5a which harbors the mtDNA tRNA(Gln) A8336G variant, are important risk factors for AD and PD. Somatic mtDNA mutations are elevated in AD, PD, and Down Syndrome and Dementia (DSAD) both in brains and also systemically. AD, DS, and DSAD brains also have reduced mtDNA ND6 mRNA levels, altered mtDNA copy number, and perturbed Aβ metabolism. Classical AD genetic changes incorporated into the 3XTg-AD (APP, Tau, PS1) mouse result in reduced forebrain size, life-long reduced mitochondrial respiration in 3XTg-AD males, and initially elevated respiration and complex I and IV activities in 3XTg-AD females which markedly declines with age.

GENERAL SIGNIFICANCE

Therefore, mitochondrial dysfunction provides a unifying genetic and pathophysiology explanation for AD, PD, and other neurodegenerative diseases. This article is part of a Special Issue entitled Biochemistry of Mitochondria.

Mitochondrial abnormalities in Alzheimer's disease: possible targets for therapeutic intervention

Mitochondria from persons with Alzheimer's disease (AD) differ from those of age-matched control subjects. Differences in mitochondrial morphology and function are well documented, and are not brain-limited. Some of these differences are present during all stages of AD, and are even seen in individuals who are without AD symptoms and signs but who have an increased risk of developing AD. This chapter considers the status of mitochondria in AD subjects, the potential basis for AD subject mitochondrial perturbations, and the implications of these perturbations. Data from multiple lines of investigation, including epidemiologic, biochemical, molecular, and cytoplasmic hybrid studies, are reviewed. The possibility that mitochondria could potentially constitute a reasonable AD therapeutic target is discussed, as are several potential mitochondrial medicine treatment strategies.

Calcium channel blocking as a therapeutic strategy for Alzheimer's disease: the case for isradipine

Alzheimer's disease is the most devastating neurodegenerative disorder in the elderly, yet treatment options are severely limited. The drug development effort to modify Alzheimer's disease pathology by intervention at beta amyloid production sites has been largely ineffective or inconclusive. The greatest challenge has been to identify and define downstream mechanisms reliably predictive of clinical symptoms. Beta amyloid accumulation leads to dysregulation of intracellular calcium by plasma membrane L-type calcium channels located on neuronal somatodendrites and axons in the hippocampus and cortex. Paradoxically, L-type calcium channel subtype Ca(v)1.2 also promotes synaptic plasticity and spatial memory. Increased intracellular calcium modulates amyloid precursor protein processing and affects multiple downstream pathways including increased hyperphosphorylated tau and suppression of autophagy. Isradipine is a Federal Drug Administration-approved dihydropyridine calcium channel blocker that binds selectively to Ca(v)1.2 in the hippocampus. Our studies have shown that isradipine in vitro attenuates beta amyloid oligomer toxicity by suppressing calcium influx into cytoplasm and by suppressing Ca(v)1.2 expression. We have previously shown that administration of isradipine to triple transgenic animal model for Alzheimer's disease was well-tolerated. Our results further suggest that isradipine became bioavailable, lowered tau burden, and improved autophagy function in the brain. A better understanding of brain pharmacokinetics of calcium channel blockers will be critical for designing new experiments with appropriate drug doses in any future clinical trials for Alzheimer's disease. This review highlights the importance of Ca(v)1.2 channel overexpression, the accumulation of hyperphosphorylated tau and suppression of autophagy in Alzheimer's disease and modulation of this pathway by isradipine.

Phytic acid as a potential treatment for alzheimer's pathology: evidence from animal and in vitro models

Alzheimer's disease (AD) causes progressive, age-dependent cortical and hippocampal dysfunction leading to abnormal intellectual capacity and memory. We propose a novel protective treatment for AD pathology with phytic acid (inositol hexakisphosphate), a phytochemical found in food grains and a key signaling molecule in mammalian cells. We evaluated the protective and beneficial effects of phytic acid against amyloid-β (Aβ) pathology in MC65 cells and the Tg2576 mouse model. In MC65 cells, 48-72-hour treatment with phytic acid provided complete protection against amyloid precursor protein-C-terminal fragment-induced cytotoxicity by attenuating levels of increased intracellular calcium, hydrogen peroxide, superoxide, Aβ oligomers, and moderately upregulated the expression of autophagy (beclin-1) protein. In a tolerance paradigm, wild type mice were treated with 2% phytic acid in drinking water for 70 days. Phytic acid was well tolerated. Ceruloplasmin activity, brain copper and iron levels, and brain superoxide dismutase and ATP levels were unaffected by the treatment. There was a significant increase in brain levels of cytochrome oxidase and a decrease in lipid peroxidation with phytic acid administration. In a treatment paradigm, 12-month old Tg2576 and wild type mice were treated with 2% phytic acid or vehicle for 6 months. Brain levels of copper, iron, and zinc were unaffected. The effects of phytic acid were modest on the expression of AβPP trafficking-associated protein AP180, autophagy-associated proteins (beclin-1, LC3B), sirtuin 1, the ratio of phosphorylated AMP-activated protein kinase (PAMPK) to AMPK, soluble Aβ1-40, and insoluble Aβ1-42. These results suggest that phytic acid may provide a viable treatment option for AD.

Differential effects of rapamycin on rods and cones during light-induced stress in albino mice

PURPOSE

Autophagy is a lysosomal machinery-dependent process that catabolizes cellular components/organelles and proteins in an autophagic vacuole (AV)-dependent and -independent manner, respectively. Short-term exposure of the retina to bright light results in shortening of the outer segments, concomitant with AV formation. Autophagy is also induced by continuous long-term light damage, leading to photoreceptor cell death. Here the authors examined two questions: is autophagy induced during light damage proapoptotic or antiapoptotic, and are rods and cones affected differently? To this end, Balb/c mice exposed to light damage were treated with rapamycin to increase autophagy.

METHODS

Balb/c and GFP-LC3 mice were treated with rapamycin/vehicle. Photoreceptor degeneration was induced by 10-day light damage. Autophagy was documented by histologic, biochemical, and molecular tools; rod and cone survival was assessed by histology and electroretinography.

RESULTS

Light damage resulted in rod, but not cone, cell loss. Autophagy and AV formation was elicited in response to light damage, which was amplified by rapamycin. Rapamycin treatment significantly improved rod survival and function, reduced apoptosis, and normalized cytokine production that was increased in light damage. However, AV formation in GFP-LC3 mice revealed that light damage or rapamycin treatment induced AVs in cones, concomitant with reduced cone-mediated electroretinograms.

CONCLUSIONS

Systemic rapamycin treatment provided rod protection; however, AV formation was induced only in cones. Thus, rapamycin may act differentially in stressed photoreceptors; rapamycin might protect rods by normalizing cytokine production, removing damaged proteins by AV-independent autophagy, or both, whereas cones might be protected by AV-dependent autophagy, possibly involving reduced photon capture.

Mitochondria regulate autophagy by conserved signalling pathways

Autophagy is a conserved degradative process that is crucial for cellular homeostasis and cellular quality control via the selective removal of subcellular structures such as mitochondria. We demonstrate that a regulatory link exists between mitochondrial function and autophagy in Saccharomyces cerevisiae. During amino-acid starvation, the autophagic response consists of two independent regulatory arms-autophagy gene induction and autophagic flux-and our analysis indicates that mitochondrial respiratory deficiency severely compromises both. We show that the evolutionarily conserved protein kinases Atg1, target of rapamycin kinase complex I, and protein kinase A (PKA) regulate autophagic flux, whereas autophagy gene induction depends solely on PKA. Within this regulatory network, mitochondrial respiratory deficiency suppresses autophagic flux, autophagy gene induction, and recruitment of the Atg1-Atg13 kinase complex to the pre-autophagosomal structure by stimulating PKA activity. Our findings indicate an interrelation of two common risk factors-mitochondrial dysfunction and autophagy inhibition-for ageing, cancerogenesis, and neurodegeneration.