Enhanced Autophagy Contributes to Protective Effects of GM1 Ganglioside Against Aβ1-42-Induced Neurotoxicity and Cognitive Deficits

Interactions Between Extracellular Vesicles and Autophagy in Neuroimmune Disorders

Neuroimmune disorders, such as multiple sclerosis, neuromyelitis optica spectrum disorder, myasthenia gravis, and Guillain-Barré syndrome, are characterized by the dysfunction of both the immune system and the nervous system. Increasing evidence suggests that extracellular vesicles and autophagy are closely associated with the pathogenesis of these disorders. In this review, we summarize the current understanding of the interactions between extracellular vesicles and autophagy in neuroimmune disorders and discuss their potential diagnostic and therapeutic applications. Here we highlight the need for further research to fully understand the mechanisms underlying these disorders, and to develop new diagnostic and therapeutic strategies.

Molecular and cellular evidence of a direct interaction between the TRAF2 C-terminal domain and ganglioside GM1

TNF receptor-associated factor 2 (TRAF2) is involved in different cellular processes including signal transduction and transcription regulation. We here provide evidence of a direct interaction between the TRAF domain of TRAF2 and the monosialotetrahexosylganglioside (GM1). Previously, we showed that the TRAF domain occurs mainly in a trimeric form in solution, but it can also exist as a stable monomer when in the nanomolar concentration range. Here, we report that the quaternary structure of the TRAF domain is also affected by pH changes, since a weakly acidic pH (5.5) favors the dissociation of the trimeric TRAF domain into stable monomers, as previously observed at neutral pH (7.6) with the diluted protein. The TRAF domain-GM1 binding was similar at pH 5.5 and 7.6, suggesting that GM1 interacts with both the trimeric and monomeric forms of the protein. However, only the monomeric protein appeared to cause membrane deformation and inward vesiculation in GM1-containing giant unilamellar vesicles (GUVs). The formation of complexes between GM1 and TRAF2, or its TRAF domain, was also observed in cultured human leukemic HAP1 cells expressing either the truncated TRAF domain or the endogenous full length TRAF2. The GM1-protein complexes were observed after treatment with tunicamycin and were more concentrated in cells undergoing apoptosis, a condition which is known to cause cytoplasm acidification. These findings open the avenue for future studies aimed at deciphering the physiopathological relevance of the TRAF domain-GM1 interaction.

Obatoclax Rescues FUS-ALS Phenotypes in iPSC-Derived Neurons by Inducing Autophagy

Aging is associated with the disruption of protein homeostasis and causally contributes to multiple diseases, including amyotrophic lateral sclerosis (ALS). One strategy for restoring protein homeostasis and protecting neurons against age-dependent diseases such as ALS is to de-repress autophagy. BECN1 is a master regulator of autophagy; however, is repressed by BCL2 via a BH3 domain-mediated interaction. We used an induced pluripotent stem cell model of ALS caused by mutant FUS to identify a small molecule BH3 mimetic that disrupts the BECN1-BCL2 interaction. We identified obatoclax as a brain-penetrant drug candidate that rescued neurons at nanomolar concentrations by reducing cytoplasmic FUS levels, restoring protein homeostasis, and reducing degeneration. Proteomics data suggest that obatoclax protects neurons via multiple mechanisms. Thus, obatoclax is a candidate for repurposing as a possible ALS therapeutic and, potentially, for other age-associated disorders linked to defects in protein homeostasis.

GM1 Ganglioside as a Disease-Modifying Therapeutic for Parkinson's Disease: A Multi-Functional Glycosphingolipid That Targets Multiple Parkinson's Disease-Relevant Pathogenic Mechanisms

Parkinson's disease (PD) is a progressive neurodegenerative disorder affecting millions of patients worldwide. Many therapeutics are available for treating PD symptoms but there is no disease-modifying therapeutic that has been unequivocally shown to slow or stop the progression of the disease. There are several factors contributing to the failure of many putative disease-modifying agents in clinical trials and these include the choice of patients and clinical trial designs for disease modification trials. Perhaps more important, however, is the choice of therapeutic, which for the most part, has not taken into account the multiple and complex pathogenic mechanisms and processes involved in PD. This paper discusses some of the factors contributing to the lack of success in PD disease-modification trials, which have mostly investigated therapeutics with a singular mechanism of action directed at one of the many PD pathogenic processes, and suggests that an alternative strategy for success may be to employ multi-functional therapeutics that target multiple PD-relevant pathogenic mechanisms. Evidence is presented that the multi-functional glycosphingolipid GM1 ganglioside may be just such a therapeutic.

Dapagliflozin as an autophagic enhancer via LKB1/AMPK/SIRT1 pathway in ovariectomized/D-galactose Alzheimer's rat model

Autophagy and mitochondrial deficits are characteristics of early phase of Alzheimer's disease (AD). Sodium-glucose cotransporter-2 inhibitors have been nominated as a promising class against AD hallmarks. However, there are no available data yet to discuss the impact of gliflozins on autophagic pathways in AD. Peripherally, dapagliflozin's (DAPA) effect is mostly owed to autophagic signals. Thus, the goal of this study is to screen the power of DAPA centrally on LKB1/AMPK/SIRT1/mTOR signaling in the ovariectomized/D-galactose (OVX/D-Gal) rat model. Animals were arbitrarily distributed between 5 groups; the first group undergone sham operation, while remaining groups undergone OVX followed by D-Gal (150 mg/kg/day; i.p.) for 70 days. After 6 weeks, the third, fourth, and fifth groups received DAPA (1 mg/kg/day; p.o.); concomitantly with the AMPK inhibitor dorsomorphin (DORSO, 25 µg/rat, i.v.) in the fourth group and the SIRT1 inhibitor EX-527 (10 µg/rat, i.v.) in the fifth group. DAPA mitigated cognitive deficits of OVX/D-Gal rats, as mirrored in neurobehavioral task with hippocampal histopathological examination and immunohistochemical aggregates of p-Tau. The neuroprotective effect of DAPA was manifested by elevation of energy sensors; AMP/ATP ratio and LKB1/AMPK protein expressions along with autophagic markers; SIRT1, Beclin1, and LC3B expressions. Downstream the latter, DAPA boosted mTOR and mitochondrial function; TFAM, in contrary lessened BACE1. Herein, DORSO or EX-527 co-administration prohibited DAPA's actions where DORSO elucidated DAPA's direct effect on LKB1 while EX-527 mirrored its indirect effect on SIRT1. Therefore, DAPA implied its anti-AD effect, at least in part, via boosting hippocampal LKB1/AMPK/SIRT1/mTOR signaling in OVX/D-Gal rat model.

Glucosylceramide synthase inhibition reduces ganglioside GM3 accumulation, alleviates amyloid neuropathology, and stabilizes remote contextual memory in a mouse model of Alzheimer’s disease

Background

Gangliosides are highly enriched in the brain and are critical for its normal development and function. However, in some rare neurometabolic diseases, a deficiency in lysosomal ganglioside hydrolysis is pathogenic and leads to early-onset neurodegeneration, neuroinflammation, demyelination, and dementia. Increasing evidence also suggests that more subtle ganglioside accumulation contributes to the pathogenesis of more common neurological disorders including Alzheimer’s disease (AD). Notably, ganglioside GM3 levels are elevated in the brains of AD patients and in several mouse models of AD, and plasma GM3 levels positively correlate with disease severity in AD patients.

Methods

Tg2576 AD model mice were fed chow formulated with a small molecule inhibitor of glucosylceramide synthase (GCSi) to determine whether reducing glycosphingolipid synthesis affected aberrant GM3 accumulation, amyloid burden, and disease manifestations in cognitive impairment. GM3 was measured with LC-MS, amyloid burden with ELISA and amyloid red staining, and memory was assessed using the contextual fear chamber test.

Results

GCSi mitigated soluble Aβ42 accumulation in the brains of AD model mice when treatment was started prophylactically. Remarkably, GCSi treatment also reduced soluble Aβ42 levels and amyloid plaque burden in aged (i.e., 70 weeks old) AD mice with preexisting neuropathology. Our analysis of contextual memory in Tg2576 mice showed that impairments in remote (cortical-dependent) memory consolidation preceded deficits in short-term (hippocampal-dependent) contextual memory, which was consistent with soluble Aβ42 accumulation occurring more rapidly in the cortex of AD mice compared to the hippocampus. Notably, GCSi treatment significantly stabilized remote memory consolidation in AD mice—especially in mice with enhanced cognitive training. This finding was consistent with GCSi treatment lowering aberrant GM3 accumulation in the cortex of AD mice.

Conclusions

Collectively, our results indicate that glycosphingolipids regulated by GCS are important modulators of Aβ neuropathology and that glycosphingolipid homeostasis plays a critical role in the consolidation of remote memories.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13195-022-00966-0.

Pharmacological modulation of autophagy for Alzheimer’s disease therapy: Opportunities and obstacles

Alzheimer's disease (AD) is a prevalent and deleterious neurodegenerative disorder characterized by an irreversible and progressive impairment of cognitive abilities as well as the formation of amyloid β (Aβ) plaques and neurofibrillary tangles (NFTs) in the brain. By far, the precise mechanisms of AD are not fully understood and no interventions are available to effectively slow down progression of the disease. Autophagy is a conserved degradation pathway that is crucial to maintain cellular homeostasis by targeting damaged organelles, pathogens, and disease-prone protein aggregates to lysosome for degradation. Emerging evidence suggests dysfunctional autophagy clearance pathway as a potential cellular mechanism underlying the pathogenesis of AD in affected neurons. Here we summarize the current evidence for autophagy dysfunction in the pathophysiology of AD and discuss the role of autophagy in the regulation of AD-related protein degradation and neuroinflammation in neurons and glial cells. Finally, we review the autophagy modulators reported in the treatment of AD models and discuss the obstacles and opportunities for potential clinical application of the novel autophagy activators for AD therapy.

Rifampicin Suppresses Amyloid-β Accumulation Through Enhancing Autophagy in the Hippocampus of a Lipopolysaccharide-Induced Mouse Model of Cognitive Decline

BACKGROUND

Alzheimer's disease (AD) is characterized by amyloid-β (Aβ) deposition. The metabolism of Aβ is critically affected by autophagy. Although rifampicin is known to mediate neuroinflammation, the underlying mechanism by which rifampicin regulates the cognitive sequelae remains unknown.

OBJECTIVE

Based on our previous findings that rifampicin possesses neuroprotective effects on improving cognitive function after neuroinflammation, we aimed to examine in this study whether rifampicin can inhibit Aβ accumulation by enhancing autophagy in a mouse model of lipopolysaccharide (LPS)-induced cognitive impairment.

METHODS

Adult C57BL/6 mice were intraperitoneally injected with rifampicin, chloroquine, and/or LPS every day for 7 days. Pathological and biochemical assays and behavioral tests were performed to determine the therapeutic effect and mechanism of rifampicin on the hippocampus of LPS-induced mice.

RESULTS

We found that rifampicin ameliorated cognitive impairments in the LPS-induced mice. In addition, rifampicin attenuated the inhibition of autophagosome formation, suppressed the accumulation of Aβ1-42, and protected the hippocampal neurons against LPS-induced damage. Our results further demonstrated that rifampicin improved the neurological function by promoting autophagy through the inhibition of Akt/mTOR/p70S6K signaling pathway in the hippocampus of LPS-induced mice.

CONCLUSION

Rifampicin ameliorates cognitive impairment by suppression of Aβ1-42 accumulation through inhibition of Akt/mTOR/p70S6K signaling and enhancement of autophagy in the hippocampus of LPS-induced mice.

The significance of sialylation on the pathogenesis of Alzheimer's disease

Sialylation, one of the most common and complex modes of glycosylation, corresponds with the development of the infant brain and nervous system. The most prevalent neurodegenerative disease is Alzheimer's disease (AD), which is mainly characterized by cognitive decline and behavioral disorders. However, the relationship between sialylation and AD occurrence is poorly understood. In this article, we reviewed the role of sialylation on the occurrence and development of AD, then discussed the value of sialylation modification for AD diagnosis and treatment.

Autophagy-dependent removal of α-synuclein: a novel mechanism of GM1 ganglioside neuroprotection against Parkinson's disease

GM1 ganglioside is particularly abundant in the mammalian central nervous system and has shown beneficial effects on neurodegenerative diseases. In this study, we investigated the therapeutic effect of GM1 ganglioside in experimental models of Parkinson's disease (PD) in vivo and in vitro. Mice were injected with MPTP (30 mg·kg-1·d-1, i.p.) for 5 days, resulting in a subacute model of PD. PD mice were treated with GM1 ganglioside (25, 50 mg·kg-1·d-1, i.p.) for 2 weeks. We showed that GM1 ganglioside administration substantially improved the MPTP-induced behavioral disturbance and increased the levels of dopamine and its metabolites in the striatal tissues. In the MPP+-treated SH-SY5Y cells and α-synuclein (α-Syn) A53T-overexpressing PC12 (PC12α-Syn A53T) cells, treatment with GM1 ganglioside (40 μM) significantly decreased α-Syn accumulation and alleviated mitochondrial dysfunction and oxidative stress. We further revealed that treatment with GM1 ganglioside promoted autophagy, evidenced by the autophagosomes that appeared in the substantia nigra of PD mice as well as the changes of autophagy-related proteins (LC3-II and p62) in the MPP+-treated SH-SY5Y cells. Cotreatment with the autophagy inhibitor 3-MA or bafilomycin A1 abrogated the in vivo and in vitro neuroprotective effects of GM1 ganglioside. Using GM1 ganglioside labeled with FITC fluorescent, we observed apparent colocalization of GM1-FITC and α-Syn as well as GM1-FITC and LC3 in PC12α-Syn A53T cells. GM1 ganglioside significantly increased the phosphorylation of autophagy regulatory proteins ATG13 and ULK1 in doxycycline-treated PC12α-Syn A53T cells and the MPP+-treated SH-SY5Y cells, which was inhibited by 3-MA. Taken together, this study demonstrates that the anti-PD role of GM1 ganglioside resulted from activation of autophagy-dependent α-Syn clearance.

Implications of Glycosylation in Alzheimer's Disease

Alzheimer's disease (AD) is the most common cause of dementia, affecting millions of people worldwide, and no cure is currently available. The major pathological hallmarks of AD are considered to be amyloid beta plaques and neurofibrillary tangles, generated by respectively APP processing and Tau phosphorylation. Recent evidence imply that glycosylation of these proteins, and a number of other AD-related molecules is altered in AD, suggesting a potential implication of this process in disease pathology. In this review we summarize the understanding of glycans in AD pathogenesis, and discuss how glycobiology can contribute to early diagnosis and treatment of AD, serving as potential biomarkers and therapeutic targets. Furthermore, we look into the potential link between the emerging topic neuroinflammation and glycosylation, combining two interesting, and until recent years, understudied topics in the scope of AD. Lastly, we discuss how new model platforms such as induced pluripotent stem cells can be exploited and contribute to a better understanding of a rather unexplored area in AD.

Glycosphingolipids

Glycosphingolipids are amphiphilic plasma membrane components formed by a glycan linked to a specific lipid moiety. In this chapter we report on these compounds, on their role played in our cells to maintain the correct cell biology.In detail, we report on their structure, on their metabolic processes, on their interaction with proteins and from this, their property to modulate positively in health and negatively in disease, the cell signaling and cell biology.

Gangliosides in the Brain: Physiology, Pathophysiology and Therapeutic Applications

Gangliosides are glycosphingolipids highly abundant in the nervous system, and carry most of the sialic acid residues in the brain. Gangliosides are enriched in cell membrane microdomains ("lipid rafts") and play important roles in the modulation of membrane proteins and ion channels, in cell signaling and in the communication among cells. The importance of gangliosides in the brain is highlighted by the fact that loss of function mutations in ganglioside biosynthetic enzymes result in severe neurodegenerative disorders, often characterized by very early or childhood onset. In addition, changes in the ganglioside profile (i.e., in the relative abundance of specific gangliosides) were reported in healthy aging and in common neurological conditions, including Huntington's disease (HD), Alzheimer's disease (AD), Parkinson's disease (PD), amyotrophic lateral sclerosis (ALS), stroke, multiple sclerosis and epilepsy. At least in HD, PD and in some forms of epilepsy, experimental evidence strongly suggests a potential role of gangliosides in disease pathogenesis and potential treatment. In this review, we will summarize ganglioside functions that are crucial to maintain brain health, we will review changes in ganglioside levels that occur in major neurological conditions and we will discuss their contribution to cellular dysfunctions and disease pathogenesis. Finally, we will review evidence of the beneficial roles exerted by gangliosides, GM1 in particular, in disease models and in clinical trials.

Icaritin Improves Memory and Learning Ability by Decreasing BACE-1 Expression and the Bax/Bcl-2 Ratio in Senescence-Accelerated Mouse Prone 8 (SAMP8) Mice

Icaritin (ICT) is the main component in the traditional Chinese herb Epimedium, and it has been shown to have anti-Alzheimer's disease (AD) effects, but its neuroprotective effects and the pharmacological mechanisms are unclear. In the present study, senescence-accelerated mouse prone 8 (SAMP8) mice were randomly divided into a model group and an ICT-treated group. Learning and memory abilities were detected by the Morris water maze assay, and the expression of amyloid beta protein (Aβ) and β-site APP cleavage enzyme 1 (BACE1) was determined by Western blotting and polymerase chain reaction (PCR). Histological changes in CA1 and CA3 were detected by hematoxylin-eosin staining (H&E staining), and the immunohistochemical analysis was used to detect the expression and localization of Bax and Bcl-2. The results showed that compared with the SAMP8 mice, the ICT-treated SAMP8 mice showed improvements in spatial learning and memory retention. In addition, the number of necrotic cells and the morphological changes in CA1 and CA3 areas were significantly alleviated in the group of ICT-treated SAMP8 mice, and the expression of BACE1, Aβ_1-42 levels, and the Bax/Bcl-2 ratio in the hippocampus was obviously decreased in the ICT-treated group compared with the control group. The results demonstrated that ICT reduced BACE-1 levels, the contents of Aβ_1-42, and the Bax/Bcl-2 ratio, suggesting that ICT might have potential therapeutic benefits by delaying or modifying the progression of AD.

GM1 Oligosaccharide Crosses the Human Blood-Brain Barrier In Vitro by a Paracellular Route

Ganglioside GM1 (GM1) has been reported to functionally recover degenerated nervous system in vitro and in vivo, but the possibility to translate GM1′s potential in clinical settings is counteracted by its low ability to overcome the blood–brain barrier (BBB) due to its amphiphilic nature. Interestingly, the soluble and hydrophilic GM1-oligosaccharide (OligoGM1) is able to punctually replace GM1 neurotrophic functions alone, both in vitro and in vivo. In order to take advantage of OligoGM1 properties, which overcome GM1′s pharmacological limitations, here we characterize the OligoGM1 brain transport by using a human in vitro BBB model. OligoGM1 showed a 20-fold higher crossing rate than GM1 and time–concentration-dependent transport. Additionally, OligoGM1 crossed the barrier at 4 °C and in inverse transport experiments, allowing consideration of the passive paracellular route. This was confirmed by the exclusion of a direct interaction with the active ATP-binding cassette (ABC) transporters using the “pump out” system. Finally, after barrier crossing, OligoGM1 remained intact and able to induce Neuro2a cell neuritogenesis by activating the TrkA pathway. Importantly, these in vitro data demonstrated that OligoGM1, lacking the hydrophobic ceramide, can advantageously cross the BBB in comparison with GM1, while maintaining its neuroproperties. This study has improved the knowledge about OligoGM1′s pharmacological potential, offering a tangible therapeutic strategy.

On the role of sphingolipids in cell survival and death

Sphingolipids, universal components of biological membranes of all eukaryotic organisms, from yeasts to mammals, in addition of playing a structural role, also play an important part of signal transduction pathways. They participate or, also, ignite several fundamental subcellular signaling processes but, more in general, they directly contribute to key biological activities such as cell motility, growth, senescence, differentiation as well as cell fate, i.e., survival or death. The sphingolipid metabolic pathway displays an intricate network of reactions that result in the formation of multiple sphingolipids, including ceramide, and sphingosine-1-phosphate. Different sphingolipids, that have key roles in determining cell fate, can induce opposite effects: as a general rule, sphingosine-1-phosphate promotes cell survival and differentiation, whereas ceramide is known to induce apoptosis. Furthermore, together with cholesterol, sphingolipids also represent the basic lipid component of lipid rafts, cholesterol- and sphingolipid-enriched membrane microdomains directly involved in cell death and survival processes. In this review, we briefly describe the characteristics of sphingolipids and lipid membrane microdomains. In particular, we will consider the involvement of various sphingolipids per se and of lipid rafts in apoptotic pathway, both intrinsic and extrinsic, in nonapoptotic cell death, in autophagy, and in cell differentiation. In addition, their roles in the most common physiological and pathological contexts either as pathogenetic elements or as biomarkers of diseases will be considered. We would also hint how the manipulation of sphingolipid metabolism could represent a potential therapeutic target to be investigated and functionally validated especially for those diseases for which therapeutic options are limited or ineffective.

Neuroprotective effect of CPCGI on Alzheimer's disease and its mechanism

Alzheimer's disease (AD) is a multifactorial neurodegenerative disorder causing progressive memory loss and cognitive impairment. The aberrant accumulation of amyloid‑β (Aβ) and neuroinflammation are two major events in AD. Aβ‑induced neurotoxicity and oxidative stress are also involved in the pathogenesis of AD. The purpose of the current study was to investigate the effect of compound porcine cerebroside and ganglioside injection (CPCGI) on the progression of AD, and to explore the molecular mechanism. In vivo and in vitro models of AD were established and treated with CPCGI. Aβ40 and Aβ42 protein levels were detected using western blotting. Production of pro‑inflammatory factors [tumor necrosis factor (TNF)‑α and interleukin (IL)‑1β] and oxidative stress markers [malondialdehyde (MDA), superoxide dismutase (SOD)] and reactive oxygen species (ROS) production were determined. Cell viability and apoptosis were detected using 3‑(4,5‑dimethyl‑2‑thiazolyl)‑2,5‑​diphenyl‑2‑H‑tetrazolium bromide assay and flow cytometry analysis respectively. Results demonstrated that CPCGI administration reduced Aβ40 and Aβ42 accumulation, and inhibited inflammatory response and oxidative stress in the in vivo rat model of AD, evidenced by decreased Aβ40 and Aβ42 protein expression, reduced levels of TNF‑α and IL‑1β, reduced MDA content, enhanced SOD activity, and reduced ROS level. It was found that CPCGI enhanced cell viability and reduced cell apoptosis of Aβ25‑35 induced PC12 cells. In addition, the mitogen‑activated protein kinase/NF‑κB pathway was involved in the protective effect of CPCGI on AD. Taken together, the data demonstrated that CPCGI exerted a protective effect on AD by reducing Aβ accumulation, inhibiting inflammatory response and oxidative stress, In addition to preventing neuronal apoptosis.

Ligustilide protects PC12 cells from oxygen-glucose deprivation/reoxygenation-induced apoptosis via the LKB1-AMPK-mTOR signaling pathway

Autophagy has been shown to have a protective effect against brain damage. Ligustilide (LIG) is a bioactive substance isolated from Ligusticum chuanxiong, a traditional Chinese medicine. LIG has a neuroprotective effect; however, it is unclear whether this neuroprotective effect involves autophagy. In this study, PC12 cells were treated with 1 × 10^–5–1 × 10^–9 M LIG for 0, 3, 12 or 24 hours, and cell proliferation was evaluated using the 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium (MTS) assay. Treatment with 1 × 10^–6 M LIG for 3 hours had the greatest effect on cell proliferation, and was therefore used for subsequent experiments. PC12 cells were pre-treated with 1 × 10^–6 M LIG for 3 hours, cultured in 95% N₂/5% CO₂ in Dulbecco’s modified Eagle’s medium without glucose or serum for 4 hours, and then cultured normally for 16 hours, to simulate oxygen-glucose deprivation/reoxygenation (OGD/R). Cell proliferation was assessed with the MTS assay. Apoptosis was detected by flow cytometry. The expression levels of apoptosis-related proteins, Bcl-2 and Bax, autophagy-related proteins, Beclin 1 and microtubule-associated protein l light chain 3B (LC3-II), and liver kinase B1 (LKB1)-5′-adenosine monophosphate-activated protein kinase (AMPK)-mammalian target of rapamycin (mTOR) signaling pathway-related proteins were assessed by western blot assay. Immunofluorescence staining was used to detect LC3-II expression. Autophagosome formation was observed by electron microscopy. LIG significantly decreased apoptosis, increased Bcl-2, Beclin 1 and LC3-II expression, decreased Bax expression, increased LC3-II immunoreactivity and the number of autophagosomes, and activated the LKB1-AMPK-mTOR signaling pathway in PC12 cells exposed to OGD/R. The addition of the autophagy inhibitor 3-methyladenine or dorsomorphin before OGD/R attenuated the activation of the LKB1-AMPK-mTOR signaling pathway in cells treated with LIG. Taken together, our findings show that LIG promotes autophagy and protects PC12 cells from apoptosis induced by OGD/R via the LKB1-AMPK-mTOR signaling pathway.

Gangliosides: Treatment Avenues in Neurodegenerative Disease

Gangliosides are cell membrane components, most abundantly in the central nervous system (CNS) where they exert among others neuro-protective and -restorative functions. Clinical development of ganglioside replacement therapy for several neurodegenerative diseases was impeded by the BSE crisis in Europe during the 1990s. Nowadays, gangliosides are produced bovine-free and new pre-clinical and clinical data justify a reevaluation of their therapeutic potential in neurodegenerative diseases. Clinical experience is greatest with monosialo-tetrahexosyl-ganglioside (GM1) in the treatment of stroke. Fourteen randomized controlled trials (RCTs) in overall >2,000 patients revealed no difference in survival, but consistently superior neurological outcomes vs. placebo. GM1 was shown to attenuate ischemic neuronal injuries in diabetes patients by suppression of ERK1/2 phosphorylation and reduction of stress to the endoplasmic reticulum. There is level-I evidence from 5 RCTs of a significantly faster recovery with GM1 vs. placebo in patients with acute and chronic spinal cord injury (SCI), disturbance of consciousness after subarachnoid hemorrhage, or craniocerebral injuries due to closed head trauma. In Parkinson's disease (PD), two RCTs provided evidence of GM1 to be superior to placebo in improving motor symptoms and long-term to result in a slower than expected symptom progression, suggesting disease-modifying potential. In Alzheimer's disease (AD), the role of gangliosides has been controversial, with some studies suggesting a “seeding” role for GM1 in amyloid β polymerization into toxic forms, and others more recently suggesting a rather protective role in vivo. In Huntington's disease (HD), no clinical trials have been conducted yet. However, low GM1 levels observed in HD cells were shown to increase cell susceptibility to apoptosis. Accordingly, treatment with GM1 increased survival of HD cells in vitro and consistently ameliorated pathological phenotypes in several murine HD models, with effects seen at molecular, cellular, and behavioral level. Given that in none of the clinical trials using GM1 any clinically relevant safety issues have occurred to date, current data supports expanding GM1 clinical research, particularly to conditions with high, unmet medical need.

AMPKα1 overexpression improves postoperative cognitive dysfunction in aged rats through AMPK-Sirt1 and autophagy signaling

Postoperative cognitive dysfunction (POCD) is a common complication in elderly patients who undergo surgery involving anesthesia. Its underlying mechanisms remain unclear. Autophagy plays an important role in the damage and repair of the nervous system and is associated with the development of POCD. Using a rat model, adenosine monophosphate-activated protein kinase α1 (AMPKα1), an important autophagy regulator, was found to be significantly downregulated in rats with POCD that was induced by sevoflurane anesthesia or by appendectomy. Overexpression of AMPKα1-ameliorated POCD, as indicated by decreased escape latencies and increased target quadrant swimming times, swimming distances, and platform crossing times during Morris water maze tests. AMPKα1 overexpression activated autophagy signals by increasing the expression of light chain 3 II (LC3-II) and Beclin1 and decreasing the expression of p62 in the hippocampus of rats with POCD. Moreover, blocking autophagy by 3-methyladenine partly attenuated AMPKα1-mediated POCD improvement. Furthermore, overexpression of AMPKα1 could upregulate the expression of p-AMPK and Sirt1 in the hippocampus of rats with POCD. Intriguingly, inhibiting AMPK signals via Compound C effectively attenuated AMPKα1-mediated POCD improvement, concomitant with the downregulation of p-AMPK, Sirt1, LC3-II, and Beclin1 and the upregulation of p62. We thus concluded that overexpression of AMPKα1 can improve POCD via the AMPK-Sirt1 and autophagy signaling pathway.

GM1 Ganglioside Modifies α-Synuclein Toxicity and is Neuroprotective in a Rat α-Synuclein Model of Parkinson's Disease

While GM1 may interact with α-synuclein in vitro to inhibit aggregation, the ability of GM1 to protect against α-synuclein toxicity in vivo has not been investigated. We used targeted adeno-associated viral vector (AAV) overexpression of human mutant α-synuclein (A53T) in the rat substantia nigra (SN) to produce degeneration of SN dopamine neurons, loss of striatal dopamine levels, and behavioral impairment. Some animals received daily GM1 ganglioside administration for 6 weeks, beginning 24 hours after AAV-A53T administration or delayed start GM1 administration for 5 weeks beginning 3 weeks after AAV-A53T administration. Both types of GM1 administration protected against loss of SN dopamine neurons and striatal dopamine levels, reduced α-synuclein aggregation, and delayed start administration of GM1 reversed early appearing behavioral deficits. These results extend prior positive results in MPTP models, are consistent with the results of a small clinical study of GM1 in PD patients that showed slowing of symptom progression with chronic use, and argue for the continued refinement and development of GM1 as a potential disease modifying therapy for PD.

Sphingolipid metabolism - an ambiguous regulator of autophagy in the brain

In mammals, the brain exhibits the highest lipid content in the body next to adipose tissue. Complex sphingolipids are characteristic compounds of neuronal membranes. Vital neural functions including information flux and transduction occur along these membranes. It is therefore not surprising that neuronal function and survival is dependent on the metabolism of these lipids. Autophagy is a critical factor for the survival of post-mitotic neurons. On the one hand, it fulfils homeostatic and waste-recycling functions and on the other hand, it constitutes an effective strategy to eliminate harmful proteins that cause neuronal death. A growing number of experimental data indicate that several sphingolipids as well as enzymes catalyzing their metabolic transformations efficiently but very differently affect neuronal autophagy and hence survival. This review attempts to elucidate the roles and mechanisms of sphingolipid metabolism with regard to the regulation of autophagy and its consequences for brain physiology and pathology.

Monosialoganglioside protects against bupivacaine-induced neurotoxicity caused by endoplasmic reticulum stress in rats

Background

Local anesthetics in spinal anesthesia have neurotoxic effects, resulting in severe neurological complications. Intrathecal monosialoganglioside (GM1) administration has a therapeutic effect on bupivacaine-induced neurotoxicity. The aim of this study was to determine the underlying mechanisms of bupivacaine-induced neurotoxicity and the potential neuroprotective role of GM1.

Materials and methods

A rat spinal cord neurotoxicity model was established by injecting bupivacaine (5%, 0.12 μL/g) intrathecally. The protective effect of GM1 (30 mg/kg) was evaluated by pretreating the animals with it prior to the bupivacaine regimen. The neurological and locomotor functions were assessed using standard tests. The histomorphological changes, neuron degeneration and apoptosis, and endoplasmic reticulum stress (ERS) relevant markers were analyzed using immunofluorescence, quantitative real-time PCR, and Western blotting.

Results

Bupivacaine resulted in significant neurotoxicity in the form of aberrant neurolocomoter functions and spinal cord histomorphology and neuronal apoptosis. Furthermore, the ERS specific markers were significantly upregulated during bupivacaine-induced neurotoxicity. These neurotoxic effects were ameliorated by GM1.

Conclusion

Pretreatment with GM1 protects against bupivacaine-induced neurotoxicity via the inhibition of the GRP78/PERK/eIF2α/ATF4-mediated ERS.

HIF-1α/Beclin1-Mediated Autophagy Is Involved in Neuroprotection Induced by Hypoxic Preconditioning

Hypoxic preconditioning (HPC) exerts a protective effect against hypoxic/ischemic brain injury, and one mechanism explaining this effect may involve the upregulation of hypoxia-inducible factor-1 (HIF-1). Autophagy, an endogenous protective mechanism against hypoxic/ischemic injury, is correlated with the activation of the HIF-1α/Beclin1 signaling pathway. Based on previous studies, we hypothesize that the protective role of HPC may involve autophagy occurring via activation of the HIF-1α/Beclin1 signaling pathway. To test this hypothesis, we evaluated the effects of HPC on oxygen-glucose deprivation/reperfusion (OGD/R)-induced apoptosis and autophagy in SH-SY5Y cells. HPC significantly attenuated OGD/R-induced apoptosis, and this effect was suppressed by the autophagy inhibitor 3-methyladenine and mimicked by the autophagy agonist rapamycin. In control SH-SY5Y cells, HPC upregulated the expression of HIF-1α and downstream molecules such as BNIP3 and Beclin1. Additionally, HPC increased the LC3-II/LC3-I ratio and decreased p62 levels. The increase in the LC3-II/LC3-I ratio was inhibited by the HIF-1α inhibitor YC-1 or by Beclin1-short hairpin RNA (shRNA). In OGD/R-treated SH-SY5Y cells, HPC also upregulated the expression levels of HIF-1α, BNIP3, and Beclin1, as well as the LC3-II/LC3-I ratio. Furthermore, YC-1 or Beclin1-shRNA attenuated the HPC-mediated cell viability in OGD/R-treated cells. Taken together, our results demonstrate that HPC protects SH-SY5Y cells against OGD/R via HIF-1α/Beclin1-regulated autophagy.

MicroRNA-21 promotes the proliferation, migration and invasion of non-small cell lung cancer A549 cells by regulating autophagy activity via AMPK/ULK1 signaling pathway

The present study investigated the expression of microRNA (miR)-21 in non-small cell lung cancer (NSCLC) tissues, its biological functions and mechanism of autophagy regulation. A total of 46 patients with NSCLC were enrolled in the present study. To measure the expression of miR-21, reverse transcription-quantitative polymerase chain reaction (RT-qPCR) was employed. NSCLC A549 cells were transfected with miR-negative control (NC), miR-21 mimics or inhibitor. The CCK-8 assay was used to investigate the proliferation of A549 cells. To study migration and invasion abilities of A549 cells, The Transwell assay was performed. In addition, to determine the expression levels of ULK1, LC3B, AMPKα, p-AMPKα and p62 proteins, western blotting was conducted and laser confocal microscopy was performed to observe the formation of autophagosomes in A549 cells. To explore whether miR-21 regulates the biological functions of A549 cells via autophagy, an autophagy inhibitor, 3-MA, or agonist, rapamycin, were used in a rescue assay. Results indicated that miR-21 expression in NSCLC tissues was enhanced, and closely correlated with the occurrence and development of NSCLC. In vitro experiments showed that miR-21 mimics promoted the proliferation, migration and invasion of A549 cells, while miR-21 inhibitor inhibited these biological functions. Western blotting indicated that miR-21 upregulated autophagy marker LC3BII protein, but downregulated p62 protein. Laser confocal microscopy showed that miR-21 activated autophagy of A549. Rescue experiments indicated that autophagy reversed the effect of miR-21 on the proliferation, migration and invasion of A549 cells. Western blotting data suggested that autophagy-related AMPK/ULK1 signaling pathway was activated by miR-21, and interference or overexpression of ULK1 reversed the biological functions of miR-21. The present study demonstrated that miR-21 expression in NSCLC tissues was upregulated and positively correlated with lymphatic metastasis and clinical staging. In addition, miR-21 regulated autophagy activity of NSCLC A549 cells via AMPK/ULK1 signaling pathway, and promoted the proliferation, migration and invasion of NSCLC A549 cells.

Disease-modifying effects of ganglioside GM1 in Huntington's disease models

Huntington's disease (HD) is a progressive neurodegenerative disorder characterized by motor, cognitive and psychiatric problems. Previous studies indicated that levels of brain gangliosides are lower than normal in HD models and that administration of exogenous ganglioside GM1 corrects motor dysfunction in the YAC128 mouse model of HD In this study, we provide evidence that intraventricular administration of GM1 has profound disease-modifying effects across HD mouse models with different genetic background. GM1 administration results in decreased levels of mutant huntingtin, the protein that causes HD, and in a wide array of beneficial effects that include changes in levels of DARPP32, ferritin, Iba1 and GFAP, modulation of dopamine and serotonin metabolism, and restoration of normal levels of glutamate, GABA, L-Ser and D-Ser. Treatment with GM1 slows down neurodegeneration, white matter atrophy and body weight loss in R6/2 mice. Motor functions are significantly improved in R6/2 mice and restored to normal in Q140 mice, including gait abnormalities that are often resistant to treatments. Psychiatric-like and cognitive dysfunctions are also ameliorated by GM1 administration in Q140 and YAC128 mice. The widespread benefits of GM1 administration, at molecular, cellular and behavioural levels, indicate that this ganglioside has strong therapeutic and disease-modifying potential in HD.

Effects of thymosin β4 on oxygen‑glucose deprivation and reoxygenation‑induced injury

Cerebral ischemia causes severe brain injury and results in selective neuronal death through programmed cell death mechanisms, including apoptosis and autophagy. Minimizing neuronal injury has been considered a hot topic among clinicians. The present study elucidated the effect of thymosin β4 (Tβ4) on neuronal death induced by cerebral ischemia/reperfusion in PC12 cells that were subjected to oxygen‑glucose deprivation and reoxygenation (OGD/R). The survival, apoptotic and autophagy rates of PC12 cells were investigated. Tβ4 pre‑conditioning prior to OGD/R was performed to evaluate PC12‑cell viability and the protective mechanisms of Tβ4. Tβ4 significantly increased cell survival after OGD/R. Tβ4 inhibited the release of lactate dehydrogenase, downregulated malondialdehyde and upregulated the activities of glutathione peroxidase and superoxide dismutase. In addition, Tβ4 attenuated OGD/R‑associated decreases in the expression of P62 and the anti‑apoptotic protein B‑cell lymphoma‑2, as well as the upregulation of autophagy mediators, including autophagy‑related protein‑5 and the ratio of microtubule‑associated protein 1 light chain 3 (LC3) II vs. LC3 I. These results suggested that Tβ4 effectively inhibits cell apoptosis and autophagy induced by OGD/R. To the best of our knowledge, the present study was the first to report on the antioxidant, anti‑apoptotic and anti‑autophagic effects of Tβ4 in neuronal‑like PC12 cells. These results suggested that Tβ4 may be explored as a potential treatment for cerebral ischemia.

Overexpression of let-7a increases neurotoxicity in a PC12 cell model of Alzheimer's disease via regulating autophagy

Increased deposition of β-amyloid (Aβ) protein is one of the typical characteristics of Alzheimer's disease (AD). Recent evidence has demonstrated that the microRNA let-7 family, which is highly expressed in the central nervous system, participates in the regulation of pathologic processes of AD. In the present study, the effect of let-7a overexpression on Aβ1-40-induced neurotoxicity was evaluated in PC12 and SK-N-SH cells. The results indicated that overexpression of let-7a enhanced the neurotoxicity induced by Aβ1-40 in PC12 and SK-N-SH cells. In addition, the apoptosis induced by Aβ1-40 in PC12 and SK-N-SH cells was increased by let-7a overexpression. Furthermore, Aβ1-40 treatment increased the protein levels of microtubule-associated protein 1A/1B-light chain 3 (LC3) and beclin-1 and increased the LC3 II/I ratio. The mRNA expression levels of beclin-1, autophagy protein 5 (Atg-5) and Atg-7 were also increased by Aβ1-40 treatment in PC12 cells. Let-7a overexpression further upregulated the above autophagy-related markers. Furthermore, the protein level of p62 was increased by Aβ1-40 treatment, and this was further enhanced by let-7a overexpression. Finally, the present results demonstrated that the phosphoinositide-3-kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR) signaling pathway was involved in the autophagy regulation by let-7a. In conclusion, the present study demonstrates that the neurotoxicity induced by Aβ1-40 is augmented by let-7a overexpression via regulation of autophagy, and the PI3K/Akt/mTOR signaling pathway also serves a function in this process.