Therapeutic activation of autophagy by combined treatment with rapamycin and trehalose in a mouse MPTP-induced model of Parkinson's disease

Mitophagy activation by rapamycin enhances mitochondrial function and cognition in 5×FAD mice

Alzheimer's disease (AD) is the most prevalent form of dementia, characterized by severe mitochondrial dysfunction, which is an intracellular process that is significantly compromised in the early stages of AD. Mitophagy, the selective removal of damaged mitochondria, is a potential therapeutic strategy for AD. Rapamycin, a mammalian target of rapamycin (mTOR) inhibitor, augmented autophagy and mitigated cognitive impairment. Our study revealed that rapamycin enhances cognitive function by activating mitophagy, alleviating neuronal loss, and improving mitochondrial dysfunction in 5 ×FAD mice. Interestingly, the neuroprotective effect of rapamycin in AD were negated by treatment with 3-MA, a mitophagy inhibitor. Overall, our findings suggest that rapamycin ameliorates cognitive impairment in 5 ×FAD mice via mitophagy activation and its downstream PINK1-Parkin pathway, which aids in the clearance of amyloid-β (Aβ) and damaged mitochondria. This study reveals a novel mechanism involving mitophagy regulation underlying the therapeutic effect of rapamycin in AD. This study provides new insights and therapeutic targets for rapamycin in the treatment of AD. However, there are still some shortcomings in this topic; if we can further knock out the PINK1/Parkin gene in animals or use siRNA technology, we can further confirm the experimental results.

Trehalose-Bearing Carriers to Target Impaired Autophagy and Protein Aggregation Diseases

In recent years, trehalose, a natural disaccharide, has attracted growing attention because of the discovery of its potential to induce autophagy. Trehalose has also been demonstrated to preserve the protein's structural integrity and to limit the aggregation of pathologically misfolded proteins. Both of these properties have made trehalose a promising therapeutic candidate to target autophagy-related disorders and protein aggregation diseases. Unfortunately, trehalose has poor bioavailability due to its hydrophilic nature and susceptibility to enzymatic degradation. Recently, trehalose-bearing carriers, in which trehalose is incorporated either by chemical conjugation or physical entrapment, have emerged as an alternative option to free trehalose to improve its efficacy, particularly for the treatment of neurodegenerative diseases, atherosclerosis, nonalcoholic fatty liver disease (NAFLD), and cancers. In the current Perspective, we discuss all existing literature in this emerging field and try to identify key challenges for researchers intending to develop trehalose-bearing carriers to stimulate autophagy or inhibit protein aggregation.

Lysosomes in senescence and aging

Dysfunction of lysosomes, the primary hydrolytic organelles in animal cells, is frequently associated with aging and age-related diseases. At the cellular level, lysosomal dysfunction is strongly linked to cellular senescence or the induction of cell death pathways. However, the precise mechanisms by which lysosomal dysfunction participates in these various cellular or organismal phenotypes have remained elusive. The ability of lysosomes to degrade diverse macromolecules including damaged proteins and organelles puts lysosomes at the center of multiple cellular stress responses. Lysosomal activity is tightly regulated by many coordinated cellular processes including pathways that function inside and outside of the organelle. Here, we collectively classify these coordinated pathways as the lysosomal processing and adaptation system (LYPAS). We review evidence that the LYPAS is upregulated by diverse cellular stresses, its adaptability regulates senescence and cell death decisions, and it can form the basis for therapeutic manipulation for a wide range of age-related diseases and potentially for aging itself.

Autophagy in Parkinson's Disease

Parkinson's disease (PD) is a devastating disease associated with accumulation of α-synuclein (α-Syn) within dopaminergic neurons, leading to neuronal death. PD is characterized by both motor and non-motor clinical symptoms. Several studies indicate that autophagy, an important intracellular degradation pathway, may be involved in different neurodegenerative diseases including PD. The autophagic process mediates the degradation of protein aggregates, damaged and unneeded proteins, and organelles, allowing their clearance, and thereby maintaining cell homeostasis. Impaired autophagy may cause the accumulation of abnormal proteins. Incomplete or impaired autophagy may explain the neurotoxic accumulation of protein aggregates in several neurodegenerative diseases including PD. Indeed, studies have suggested the contribution of impaired autophagy to α-Syn accumulation, the death of dopaminergic neurons, and neuroinflammation. In this review, we summarize the recent literature on the involvement of autophagy in PD pathogenesis.

Syringin Prevents 6-Hydroxydopamine Neurotoxicity by Mediating the MiR-34a/SIRT1/Beclin-1 Pathway and Activating Autophagy in SH-SY5Y Cells and the Caenorhabditis elegans Model

Defective autophagy is one of the cellular hallmarks of Parkinson's disease (PD). Therefore, a therapeutic strategy could be a modest enhancement of autophagic activity in dopamine (DA) neurons to deal with the clearance of damaged mitochondria and abnormal protein aggregates. Syringin (SRG) is a phenolic glycoside derived from the root of Acanthopanax senticosus. It has antioxidant, anti-apoptotic, and anti-inflammatory properties. However, whether it has a preventive effect on PD remains unclear. The present study found that SRG reversed the increase in intracellular ROS-caused apoptosis in SH-SY5Y cells induced by neurotoxin 6-OHDA exposure. Likewise, in C. elegans, degeneration of DA neurons, DA-related food-sensitive behaviors, longevity, and accumulation of α-synuclein were also improved. Studies of neuroprotective mechanisms have shown that SRG can reverse the suppressed expression of SIRT1, Beclin-1, and other autophagy markers in 6-OHDA-exposed cells. Thus, these enhanced the formation of autophagic vacuoles and autophagy activity. This protective effect can be blocked by pretreatment with wortmannin (an autophagosome formation blocker) and bafilomycin A1 (an autophagosome-lysosome fusion blocker). In addition, 6-OHDA increases the acetylation of Beclin-1, leading to its inactivation. SRG can induce the expression of SIRT1 and promote the deacetylation of Beclin-1. Finally, we found that SRG reduced the 6-OHDA-induced expression of miR-34a targeting SIRT1. The overexpression of miR-34a mimic abolishes the neuroprotective ability of SRG. In conclusion, SRG induces autophagy via partially regulating the miR-34a/SIRT1/Beclin-1 axis to prevent 6-OHDA-induced apoptosis and α-synuclein accumulation. SRG has the opportunity to be established as a candidate agent for the prevention and cure of PD.

Cogs in the autophagic machine-equipped to combat dementia-prone neurodegenerative diseases

Neurodegenerative diseases are often characterized by hydrophobic inclusion bodies, and it may be the case that the aggregate-prone proteins that comprise these inclusion bodies are in fact the cause of neurotoxicity. Indeed, the appearance of protein aggregates leads to a proteostatic imbalance that causes various interruptions in physiological cellular processes, including lysosomal and mitochondrial dysfunction, as well as break down in calcium homeostasis. Oftentimes the approach to counteract proteotoxicity is taken to merely upregulate autophagy, measured by an increase in autophagosomes, without a deeper assessment of contributors toward effective turnover through autophagy. There are various ways in which autophagy is regulated ranging from the mammalian target of rapamycin (mTOR) to acetylation status of proteins. Healthy mitochondria and the intracellular energetic charge they preserve are key for the acidification status of lysosomes and thus ensuring effective clearance of components through the autophagy pathway. Both mitochondria and lysosomes have been shown to bear functional protein complexes that aid in the regulation of autophagy. Indeed, it may be the case that minimizing the proteins associated with the respective neurodegenerative pathology may be of greater importance than addressing molecularly their resulting inclusion bodies. It is in this context that this review will dissect the autophagy signaling pathway, its control and the manner in which it is molecularly and functionally connected with the mitochondrial and lysosomal system, as well as provide a summary of the role of autophagy dysfunction in driving neurodegenerative disease as a means to better position the potential of rapamycin-mediated bioactivities to control autophagy favorably.

Inhibition of Protein Aggregation and Endoplasmic Reticulum Stress as a Targeted Therapy for α-Synucleinopathy

α-synuclein (α-syn) is an intrinsically disordered protein abundant in the central nervous system. Physiologically, the protein regulates vesicle trafficking and neurotransmitter release in the presynaptic terminals. Pathologies related to misfolding and aggregation of α-syn are referred to as α-synucleinopathies, and they constitute a frequent cause of neurodegeneration. The most common α-synucleinopathy, Parkinson's disease (PD), is caused by abnormal accumulation of α-syn in the dopaminergic neurons of the midbrain. This results in protein overload, activation of endoplasmic reticulum (ER) stress, and, ultimately, neural cell apoptosis and neurodegeneration. To date, the available treatment options for PD are only symptomatic and rely on dopamine replacement therapy or palliative surgery. As the prevalence of PD has skyrocketed in recent years, there is a pending issue for development of new disease-modifying strategies. These include anti-aggregative agents that target α-syn directly (gene therapy, small molecules and immunization), indirectly (modulators of ER stress, oxidative stress and clearance pathways) or combine both actions (natural compounds). Herein, we provide an overview on the characteristic features of the structure and pathogenic mechanisms of α-syn that could be targeted with novel molecular-based therapies.

Profiling neuroprotective potential of trehalose in animal models of neurodegenerative diseases: a systematic review

Trehalose, a unique nonreducing crystalline disaccharide, is a potential disease-modifying treatment for neurodegenerative diseases associated with protein misfolding and aggregation due to aging, intrinsic mutations, or autophagy dysregulation. This systematic review summarizes the effects of trehalose on its underlying mechanisms in animal models of selected neurodegenerative disorders (tau pathology, synucleinopathy, polyglutamine tract, and motor neuron diseases). All animal studies on neurodegenerative diseases treated with trehalose published in Medline (accessed via EBSCOhost) and Scopus were considered. Of the 2259 studies screened, 29 met the eligibility criteria. According to the SYstematic Review Center for Laboratory Animal Experiment (SYRCLE) risk of bias tool, we reported 22 out of 29 studies with a high risk of bias. The present findings support the purported role of trehalose in autophagic flux and protein refolding. This review identified several other lesser-known pathways, including modifying amyloid precursor protein processing, inhibition of reactive gliosis, the integrity of the blood-brain barrier, activation of growth factors, upregulation of the downstream antioxidant signaling pathway, and protection against mitochondrial defects. The absence of adverse events and improvements in the outcome parameters were observed in some studies, which supports the transition to human clinical trials. It is possible to conclude that trehalose exerts its neuroprotective effects through both direct and indirect pathways. However, heterogeneous methodologies and outcome measures across the studies rendered it impossible to derive a definitive conclusion. Translational studies on trehalose would need to clarify three important questions: 1) bioavailability with oral administration, 2) optimal time window to confer neuroprotective benefits, and 3) optimal dosage to confer neuroprotection.

Neuromelanin: Its role in the pathogenesis of idiopathic Parkinson's disease and potential as a therapeutic target

Parkinson's disease is an increasingly prevalent condition that involves the marked loss of dopaminergic neurons in the substantia nigra pars compacta. These neurons pigmented with neuromelanin along with other regions of the brain are almost exclusively victims of neurodegeneration in the disease. The link between neuromelanin and Parkinson's disease has been widely studied for decades. While many studies have outlined the pigment's neuroprotective function as a potent free radical scavenger, antioxidant, and ion-chelator, it has also been observed to play a role in cell death due to mitochondrial dysfunction and oxidative stress, especially in the parkinsonian disease state. This is due to the damaging effects of neuromelanin precursors, neuromelanin-related ion dysregulation and intra- and extraneuronal neuromelanin accumulation. Current and emerging therapeutic endeavours guided by these pathological processes may include antioxidant therapy, proteostasis enhancement, ion chelation and neuromelanin-targeted immunotherapy to prevent the accumulation, formation and effects of neuromelanin and oxidative neuromelanin precursors. Some of these therapeutic strategies are already in nascent stages, while others have produced mixed results in clinical trials. This review aims to provide an update on how neuromelanin and neuromelanin-related substances may be linked to the pathogenesis of Parkinson's disease and how future therapeutic strategies may be able to hamper or prevent neuromelanin-related pathological processes and ultimately modify disease progression in Parkinson's.

Vitamin A Promotes the Fusion of Autophagolysosomes and Prevents Excessive Inflammasome Activation in Dextran Sulfate Sodium-Induced Colitis

Vitamin A ensures intestinal homeostasis, impacting acquired immunity and epithelial barrier function; however, its role in innate immunity is mostly unknown. Here, we studied the impact of vitamin A in different dextran sulfate sodium (DSS)-induced colitis animal models. Interestingly, more severe DSS-induced colitis was observed in vitamin A-deficient (VAD) mice than in vitamin A-sufficient (VAS) mice; the same was observed in VAD severe combined immunodeficient mice lacking T/B cells. Remarkably, IL-1β production, LC3B-II expression, and inflammasome activity in the lamina propria were significantly elevated in VAD mice. Electron microscopy revealed numerous swollen mitochondria with severely disrupted cristae. In vitro, non-canonical inflammasome signaling-induced pyroptosis, LC3B-II and p62 expression, and mitochondrial superoxide levels were increased in murine macrophages (RAW 264.7) pretreated with retinoic acid receptor antagonist (Ro41-5253). These findings suggest that vitamin A plays a crucial role in the efficient fusion of autophagosomes with lysosomes in colitis.

Neurodegeneration, Mitochondria, and Antibiotics

Neurodegenerative diseases are characterized by the progressive loss of neurons, synapses, dendrites, and myelin in the central and/or peripheral nervous system. Actual therapeutic options for patients are scarce and merely palliative. Although they affect millions of patients worldwide, the molecular mechanisms underlying these conditions remain unclear. Mitochondrial dysfunction is generally found in neurodegenerative diseases and is believed to be involved in the pathomechanisms of these disorders. Therefore, therapies aiming to improve mitochondrial function are promising approaches for neurodegeneration. Although mitochondrial-targeted treatments are limited, new research findings have unraveled the therapeutic potential of several groups of antibiotics. These drugs possess pleiotropic effects beyond their anti-microbial activity, such as anti-inflammatory or mitochondrial enhancer function. In this review, we will discuss the controversial use of antibiotics as potential therapies in neurodegenerative diseases.

Effect of water-retention agents on Scomberomorus niphonius surimi after repeated freeze–thaw cycles: low-field NMR and MRI studies

Repeated freeze–thaw cycles can directly cause the changes in the water distribution, physicochemical characteristics, and microstructure of Scomberomorus niphonius surimi. To improve the quality of S. niphonius surimi, the effect of water retention agents (phosphate and trehalose) was investigated during freeze-thaw cycles. The results of low-field nuclear magnetic resonance (LF-NMR) combined with magnetic resonance imaging (MRI) analysis showed that the water retention agents could obviously decrease the water loss and water mobility during repeated freeze–thaw cycles. Water retention agent significantly reduced the cook loss and improved the surimi quality by decreasing the surimi protein denaturation. The scanning electron microscopy (SEM) characterization revealed that water retention agents could obviously ameliorate the protein structure damage. In addition, the principal component analysis combined with LF-NMR parameters showed clear discrimination between samples supplemented with different water retention agents. In a word, the LF-NMR and MRI might provide useful information in a non-invasive manner for monitoring the effects of water-retention agents on surimi after repeated freeze–thaw cycles.

Electroconvulsive Seizure Normalizes Motor Deficits and Induces Autophagy Signaling in the MPTP-Induced Parkinson Disease Mouse Model

OBJECTIVE

Electroconvulsive seizure (ECS) is a potent treatment modality for various neuropsychiatric diseases, including Parkinson disease (PD). Recent animal studies showed that repeated ECS activates autophagy signaling, the impairment of which is known to be involved in PD. However, the effectiveness of ECS on PD and its therapeutic mechanisms have not yet been investigated in detail.

METHODS

Systemic injection of a neurotoxin 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine hydrochloride (MPTP), which destroys dopaminergic neurons in the substantia nigra compacta (SNc), in mice was utilized to induce an animal model of PD. Mice were treated with ECS 3 times per week for 2 weeks. Behavioral changes were measured with a rotarod test. Molecular changes related to autophagy signaling in midbrain including SNc, striatum, and prefrontal cortex were analyzed with immunohistochemistry and immunoblot analyses.

RESULTS

Repeated ECS treatments normalized the motor deficits and the loss of dopamiergic neurons in SNc of the MPTP PD mouse model. In the mouse model, LC3-II, an autophagy marker, was increased in midbrain while decreased in prefrontal cortex, both of which were reversed by repeated ECS treatments. In the prefrontal cortex, ECS-induced LC3-II increase was accompanied with AMP-activated protein kinase (AMPK)-Unc-51-like kinase 1-Beclin1 pathway activation and inhibition of mamalian target of rapamycin signaling which promotes autophagy initiation.

CONCLUSION

The findings revealed the therapeutic effects of repeated ECS treatments on PD, which could be attributed to the neuroprotective effect of ECS mediated by AMPK-autophagy signaling.

The deficiency of Maged1 attenuates Parkinson's disease progression in mice

Melanoma-associated antigen D1 (Maged1) has critical functions in the central nervous system in both developmental and adult stages. Loss of Maged1 in mice has been linked to depression, cognitive disorder, and drug addiction. However, the role of Maged1 in Parkinson's disease (PD) remains unclear. In this study, we observed that Maged1 was expressed in the dopaminergic (DA) neurons of the substantia nigra in mice and humans, which could be upregulated by the in vivo or in vitro treatment with 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) or 1-Methyl-4-phenylpyridinium iodide (MPP+). Genetic ablation of Maged1 in mice attenuated motor deficits, the loss of DA neurons, and disease progression induced by MPTP. Moreover, Maged1 deficiency protected DA neurons against MPP+-induced toxicity in primary cultured cells. Mechanistically, loss of Maged1 upregulated the Akt signaling pathway and downregulated the mTOR signaling pathway in SH-SY5Y cells, which may in turn attenuate the cell apoptosis and impairment of autophagy. Consistent with it, the degeneration of midbrain and striatum among elderly Maged1 knockout mice was relatively mild compared to those in wild-type mice under physiological conditions. Taken together, this study suggested that Maged1 deficiency inhibited apoptosis and enhanced autophagy, which may provide a new potential target for the therapy of PD.

Molecular and therapeutic insights of rapamycin: a multi-faceted drug from Streptomyces hygroscopicus

The advancement in pharmaceutical research has led to the discovery and development of new combinatorial life-saving drugs. Rapamycin is a macrolide compound produced from Streptomyces hygroscopicus. Rapamycin and its derivatives are one of the promising sources of drug with broad spectrum applications in the medical field. In recent times, rapamycin has gained significant attention as of its activity against cytokine storm in COVID-19 patients. Rapamycin and its derivatives have more potency when compared to other prevailing drugs. Initially, it has been used exclusively as an anti-fungal drug. Currently rapamycin has been widely used as an immunosuppressant. Rapamycin is a multifaceted drug; it has anti-cancer, anti-viral and anti-aging potentials. Rapamycin has its specific action on mTOR signaling pathway. mTOR has been identified as a key regulator of different pathways. There will be an increased demand for rapamycin, because it has lesser adverse effects when compared to steroids. Currently researchers are focused on the production of effective rapamycin derivatives to combat the growing demand of this wonder drug. The main focus of the current review is to explore the origin, development, molecular mechanistic action, and the current therapeutic aspects of rapamycin. Also, this review article revealed the potential of rapamycin and the progress of rapamycin research. This helps in understanding the exact potency of the drug and could facilitate further studies that could fill in the existing knowledge gaps. The study also gathers significant data pertaining to the gene clusters and biosynthetic pathways involved in the synthesis and production of this multi-faceted drug. In addition, an insight into the mechanism of action of the drug and important derivatives of rapamycin has been expounded. The fillings of the current review, aids in understanding the underlying molecular mechanism, strain improvement, optimization and production of rapamycin derivatives.

The role of the endolysosomal pathway in α-synuclein pathogenesis in Parkinson's disease

Parkinson's disease (PD) is a chronic neurodegenerative disease that is characterized by a loss of dopaminergic neurons in the substantia nigra pars compacta of the midbrain (SNpc). Extensive studies into genetic and cellular models of PD implicate protein trafficking as a prominent contributor to the death of these dopaminergic neurons. Considerable evidence also suggests the involvement of α-synuclein as a central component of the characteristic cell death in PD and it is a major structural constituent of proteinaceous inclusion bodies (Lewy bodies; LB). α-synuclein research has been a vital part of PD research in recent years, with newly discovered evidence suggesting that α-synuclein can propagate through the brain via prion-like mechanisms. Healthy cells can internalize toxic α-synuclein species and seed endogenous α-synuclein to form large, pathogenic aggregates and form LBs. A better understanding of how α-synuclein can propagate, enter and be cleared from the cell is vital for therapeutic strategies.

Bi-Directional Relationship Between Autophagy and Inflammasomes in Neurodegenerative Disorders

The innate immune system, as the first line of cellular defense, triggers a protective response called inflammation when encountered with invading pathogens. Inflammasome is a multi-protein cytosolic signaling complex that induces inflammation and is critical for inflammation-induced pyroptotic cell death. Inflammasome activation has been found associated with neurodegenerative disorders (NDs), inflammatory diseases, and cancer. Autophagy is a crucial intracellular quality control and homeostasis process which removes the dysfunctional organelles, damaged proteins, and pathogens by sequestering the cytosolic components in a double-membrane vesicle, which eventually fuses with lysosome resulting in cargo degradation. Autophagy disruption has been observed in many NDs presented with persistent neuroinflammation and excessive inflammasome activation. An interplay between inflammation activation and the autophagy process has been realized over the last decade. In the case of NDs, autophagy regulates neuroinflammation load and cellular damage either by engulfing the misfolded protein deposits, dysfunctional mitochondria, or the inflammasome complex itself. A healthy two-way regulation between both cellular processes has been realized for cell survival and cell defense during inflammatory conditions. Therefore, clinical interest in the modulation of inflammasome activation by autophagy inducers is rapidly growing. In this review, we discuss the structural basis of inflammasome activation and the mechanistic ideas of the autophagy process in NDs. Along with comments on multiple ways of neuroinflammation regulation by microglial autophagy, we also present a perspective on pharmacological opportunities in this molecular interplay pertaining to NDs.

Dysregulated proteostasis network in neuronal diseases

Long-term maintenance of synaptic connections is important for brain function, which depends on varying proteostatic regulations to govern the functional integrity of neuronal proteomes. Proteostasis supports an interconnection of pathways that regulates the fate of proteins from synthesis to degradation. Defects in proteostatic signaling are associated with age-related functional decline and neurodegenerative diseases. Recent studies have advanced our knowledge of how cells have evolved distinct mechanisms to safely control protein homeostasis during synthesis, folding and degradation, and in different subcellular organelles and compartments. Neurodegeneration occurs when these protein quality controls are compromised by accumulated pathogenic proteins or aging to an irreversible state. Consequently, several therapeutic strategies, such as targeting the unfolded protein response and autophagy pathways, have been developed to reduce the burden of misfolded proteins and proved useful in animal models. Here, we present a brief overview of the molecular mechanisms involved in maintaining proteostatic networks, along with some examples linking dysregulated proteostasis to neuronal diseases.

Mitolysosome exocytosis: a novel mitochondrial quality control pathway linked with parkinsonism-like symptoms

Quality control of mitochondria is essential for their homeostasis and function. Light chain 3 (LC3) associated autophagosomes-mediated mitophagy represents a canonical mitochondrial quality control pathway. Alternative quality control processes, such as mitochondrial-derived vesicles (MDVs), have been discovered, but the intact mitochondrial quality control remains unknown. We recently discovered a novel mitolysosome exocytosis mechanism for mitochondrial quality control in flunarizine (FNZ)-induced mitochondria clearance, where autophagosomes are not required, but rather mitochondria are engulfed directly by lysosomes, mediating mitochondrial secretion. As FNZ results in parkinsonism, we propose that excessive mitolysosome exocytosis is the cause.

The contribution of altered neuronal autophagy to neurodegeneration

Defects in cellular functions related to altered protein homeostasis and associated progressive accumulation of pathological intracellular material is a critical process involved in the pathogenesis of many neurodegenerative disorders, including Alzheimer's disease and Parkinson's disease. Autophagy is an essential mechanism that ensures neuronal health by removing long-lived proteins or defective organelles and by doing so prevents cell toxicity and death within the central nervous system. Abundant evidence has shown that neuronal autophagy pathways are altered in Alzheimer's disease, Parkinson's disease and traumas of the central nervous system including Spinal Cord Injury and Traumatic Brain Injury. In this review, we aimed to summarize the latest studies on the role that altered neuronal autophagy plays in brain health and these pathological conditions, and how this knowledge can be leveraged for the development of novel therapeutics against them.

Autophagy mediates the clearance of oligodendroglial SNCA/alpha-synuclein and TPPP/p25A in multiple system atrophy models

Accumulation of the neuronal protein SNCA/alpha-synuclein and of the oligodendroglial phosphoprotein TPPP/p25A within the glial cytoplasmic inclusions (GCIs) represents the key histophathological hallmark of multiple system atrophy (MSA). Even though the levels/distribution of both oligodendroglial SNCA and TPPP/p25A proteins are critical for disease pathogenesis, the proteolytic mechanisms involved in their turnover in health and disease remain poorly understood. Herein, by pharmacological and molecular modulation of the autophagy-lysosome pathway (ALP) and the proteasome we demonstrate that the endogenous oligodendroglial SNCA and TPPP/p25A are degraded mainly by the ALP in murine primary oligodendrocytes and oligodendroglial cell lines under basal conditions. We also identify a KFERQ-like motif in the TPPP/p25A sequence that enables its effective degradation via chaperone-mediated autophagy (CMA) in an in vitro system of rat brain lysosomes. Furthermore, in a MSA-like setting established by addition of human recombinant SNCA pre-formed fibrils (PFFs) as seeds of pathological SNCA, we thoroughly characterize the contribution of CMA and macroautophagy in particular, in the removal of the exogenously added and the seeded oligodendroglial SNCA pathological assemblies. We also show that PFF treatment impairs autophagic flux and that TPPP/p25A exerts an inhibitory effect on macroautophagy, while at the same time CMA is upregulated to remove the pathological SNCA species formed within oligodendrocytes. Finally, augmentation of CMA or macroautophagy accelerates the removal of the engendered pathological SNCA conformations further suggesting that autophagy targeting may represent a successful approach for the clearance of pathological SNCA and/or TPPP/p25A in the context of MSA.Abbreviations: 3MA: 3-methyladenine; ACTB: actin, beta; ALP: autophagy-lysosome pathway; ATG5: autophagy related 5; AR7: atypical retinoid 7; CMA: chaperone-mediated autophagy; CMV: cytomegalovirus; CTSD: cathepsin D; DAPI: 4',6-diamidino-2-phenylindole; DMEM: Dulbecco's modified Eagle's medium; Epox: epoxomicin; GAPDH: glyceraldehyde-3-phosphate dehydrogenase; GCIs: glial cytoplasmic inclusions; GFP: green fluorescent protein; HMW: high molecular weight; h: hours; HSPA8/HSC70: heat shock protein 8; LAMP1: lysosomal-associated membrane protein 1; LAMP2A: lysosomal-associated membrane protein 2A; MAP1LC3/LC3: microtubule-associated protein 1 light chain 3; mcherry: monomeric cherry; MFI: mean fluorescence intensity; mRFP: monomeric red fluorescent protein; MSA: multiple system atrophy; OLN: oligodendrocytes; OPCs: oligodendroglial progenitor cells; PBS: phosphate-buffered saline; PC12: pheochromocytoma cell line; PD: Parkinson disease; PFFs: pre-formed fibrils; PIs: protease inhibitors; PSMB5: proteasome (prosome, macropain) subunit, beta type 5; Rap: rapamycin; RFP: red fluorescent protein; Scr: scrambled; SDS: sodium dodecyl sulfate; SE: standard error; siRNAs: small interfering RNAs; SNCA: synuclein, alpha; SQSTM1: sequestosome 1; TPPP: tubulin polymerization promoting protein; TUBA: tubulin, alpha; UPS: ubiquitin-proteasome system; WT: wild type.

Rotenone aggravates PD-like pathology in A53T mutant human α-synuclein transgenic mice in an age-dependent manner

Multiple factors such as genes, environment, and age are involved in developing Parkinson’s disease (PD) pathology. However, how various factors interact to cause PD remains unclear. Here, 3-month and 9-month-old hα-syn^+⁣/− mice were treated with low-dose rotenone for 2 months to explore the mechanisms that underline the environment–gene–age interaction in the occurrence of PD. We have examined the behavior of mice and the PD-like pathologies of the brain and gut. The present results showed that impairments of the motor function and olfactory function were more serious in old hα-syn^+/– mice with rotenone than that in young mice. The dopaminergic neuron loss in the SNc is more in old hα-syn^+/– mice with rotenone than in young mice. Expression of hα-syn^+/– is increased in the SNc of hα-syn^+/– mice following rotenone treatment for 2 months. Furthermore, the number of activated microglia cells increased in SNc and accompanied the high expression of inflammatory cytokines, namely, TNF-α and IL-18 in the midbrain of old hα-syn^+/– mice treated with rotenone. Meanwhile, we found that after treatment with rotenone, hα-syn positive particles deposited in the intestinal wall, intestinal microflora, and T lymphocyte subtypes of Peyer’s patches changed, and intestinal mucosal permeability increased. Moreover, these phenomena were age-dependent. These findings suggested that rotenone aggravated the PD-like pathologies and affected the brain and gut of human α-syn^+/– transgenic mice in an age-dependent manner.

Disaccharide Trehalose in Experimental Therapies for Neurodegenerative Disorders: Molecular Targets and Translational Potential

Induction of autophagy is a prospective approach to the treatment of neurodegeneration. In the recent decade, trehalose attracted special attention. It is an autophagy inducer with negligible adverse effects and is approved for use in humans according to FDA requirements. Trehalose has a therapeutic effect in various experimental models of diseases. This glucose disaccharide with a flexible α-1-1'-glycosidic bond has unique properties: induction of mTOR-independent autophagy (with kinase AMPK as the main target) and a chaperone-like effect on proteins imparting them natural spatial structure. Thus, it can reduce the accumulation of neurotoxic aberrant/misfolded proteins. Trehalose has an anti-inflammatory effect and inhibits detrimental oxidative stress partially owing to the enhancement of endogenous antioxidant defense represented by the Nrf2 protein. The disaccharide activates lysosome and autophagosome biogenesis pathways through the protein factors TFEB and FOXO1. Here we review various mechanisms of the neuroprotective action of trehalose and touch on the possibility of pleiotropic effects. Current knowledge about specific features of trehalose pharmacodynamics is discussed. The neuroprotective effects of trehalose in animal models of major neurodegenerative disorders such as Alzheimer's, Parkinson's, and Huntington's diseases are examined too. Attention is given to translational transition to clinical trials of this drug, especially oral and parenteral routes of administration. Besides, the possibility of enhancing the therapeutic benefit via a combination of mTOR-dependent and mTOR-independent autophagy inducers is analyzed. In general, trehalose appears to be a promising multitarget tool for the inhibition of experimental neurodegeneration and requires thorough investigation of its clinical capabilities.

Crosstalk of organelles in Parkinson's disease - MiT family transcription factors as central players in signaling pathways connecting mitochondria and lysosomes

Living organisms constantly need to adapt to their surrounding environment and have evolved sophisticated mechanisms to deal with stress. Mitochondria and lysosomes are central organelles in the response to energy and nutrient availability within a cell and act through interconnected mechanisms. However, when such processes become overwhelmed, it can lead to pathologies. Parkinson's disease (PD) is a common neurodegenerative disorder (NDD) characterized by proteinaceous intracellular inclusions and progressive loss of dopaminergic neurons, which causes motor and non-motor symptoms. Genetic and environmental factors may contribute to the disease etiology. Mitochondrial dysfunction has long been recognized as a hallmark of PD pathogenesis, and several aspects of mitochondrial biology are impaired in PD patients and models. In addition, defects of the autophagy-lysosomal pathway have extensively been observed in cell and animal models as well as PD patients' brains, where constitutive autophagy is indispensable for adaptation to stress and energy deficiency. Genetic and molecular studies have shown that the functions of mitochondria and lysosomal compartments are tightly linked and influence each other. Connections between these organelles are constituted among others by mitophagy, organellar dynamics and cellular signaling cascades, such as calcium (Ca²⁺) and mTOR (mammalian target of rapamycin) signaling and the activation of transcription factors. Members of the Microphthalmia-associated transcription factor family (MiT), including MITF, TFE3 and TFEB, play a central role in regulating cellular homeostasis in response to metabolic pressure and are considered master regulators of lysosomal biogenesis. As such, they are part of the interconnection between mitochondria and lysosome functions and therefore represent attractive targets for therapeutic approaches against NDD, including PD. The activation of MiT transcription factors through genetic and pharmacological approaches have shown encouraging results at ameliorating PD-related phenotypes in in vitro and in vivo models. In this review, we summarize the relationship between mitochondrial and autophagy-lysosomal functions in the context of PD etiology and focus on the role of the MiT pathway and its potential as pharmacological target against PD.

Trehalose-releasing nanogels: A step toward a trehalose delivery vehicle for autophagy stimulation

Trehalose has been widely studied as a treatment for a variety of human disorders due to its ability to stimulate autophagy. Trehalose, however, is poorly adsorbed and is hydrolyzed in the intestinal mucosa, and oral delivery requires relatively high doses to induce autophagy. The parenteral injection of trehalose-releasing nanogels proposed in this study offers an alternative mode of delivery. This study aimed to develop stable colloidal dispersions of trehalose-rich nanogels that could sustainably release trehalose under physiologically relevant conditions. The nanogel design was based on the covalent incorporation of 6-O-acryloyl-trehalose within a polymer network. A series of nine trehalose-rich nanogels with highly conjugated trehalose (up to 59 % w/w) were synthesized and shown to sustainably release trehalose at a rate that is not dose dependent. The nanogels were optimized to keep colloidal stability in serum-enriched cell culture media. The stable nanogels were not cytotoxic to primary HUVECs. Two selected nanogels with opposite surface charges were subjected to extended in vitro characterization that included a cellular uptake study and a hemocompatibility assay. Both nanogels were efficiently taken up by HUVECs during a short incubation. They also proved not to be hemolytic to human RBCs in concentrations up to 2.0 mg/mL. Finally, an in vivo autophagy stimulation study employing transgenic zebrafish and Drosophila larvae demonstrated that prolonged exposure to a cationic trehalose-releasing nanogel can induce autophagic activity in in vivo systems without any detectable toxicity.

Role of Ubiquitin-Proteasome and Autophagy-Lysosome Pathways in α-Synuclein Aggregate Clearance

Synuclein aggregation in neuronal cells is the primary underlying cause of synucleinopathies. Changes in gene expression patterns, structural modifications, and altered interactions with other cellular proteins often trigger aggregation of α-synuclein, which accumulates as oligomers or fibrils in Lewy bodies. Although fibrillar forms of α-synuclein are primarily considered pathological, recent studies have revealed that even the intermediate states of aggregates are neurotoxic, complicating the development of therapeutic interventions. Autophagy and ubiquitin-proteasome pathways play a significant role in maintaining the soluble levels of α-synuclein inside cells; however, the heterogeneous nature of the aggregates presents a significant bottleneck to its degradation by these cellular pathways. With studies focused on identifying the proteins that modulate synuclein aggregation and clearance, detailed mechanistic insights are emerging about the individual and synergistic effects of these degradation pathways in regulating soluble α-synuclein levels. In this article, we discuss the impact of α-synuclein aggregation on autophagy-lysosome and ubiquitin-proteasome pathways and the therapeutic strategies that target various aspects of synuclein aggregation or degradation via these pathways. Additionally, we also highlight the natural and synthetic compounds that have shown promise in alleviating the cellular damage caused due to synuclein aggregation.

Trehalose ameliorates prodromal non-motor deficits and aberrant protein accumulation in a rotenone-induced mouse model of Parkinson's disease

Trehalose has been recently revealed as an attractive candidate to prevent and modify Parkinson's disease (PD) progression by regulating autophagy; however, studies have only focused on the reduction of motor symptoms rather than the modulation of disease course from prodromal stage. This study aimed to evaluate whether trehalose has a disease-modifying effect at the prodromal stage before the onset of a motor deficit in 8-week-old male C57BL/6 mice exposed to rotenone. We found significant decrease in tyrosine hydroxylase immunoreactivity in the substantia nigra and motor dysfunction after 2 weeks rotenone treatment. Mice exposed to rotenone for a week showed an accumulation of protein aggregates in the brain and prodromal non-motor deficits, such as depression and olfactory dysfunction, prior to motor deficits. Trehalose significantly improved olfactory dysfunction and depressive-like behaviors and markedly reduced α-synuclein and p62 deposition in the brain. Trehalose further ameliorated motor impairment and loss of nigral tyrosine hydroxylase-positive cells in rotenone-treated mice. We demonstrated that prodromal non-motor signs in a rotenone-induced PD mouse model are associated with protein aggregate accumulation in the brain and that an autophagy inducer could be valuable to prevent PD progression from prodromal stage by regulating abnormal protein accumulation.

Alpha-Synuclein Targeting Therapeutics for Parkinson's Disease and Related Synucleinopathies

α-Synuclein (asyn) is a key pathogenetic factor in a group of neurodegenerative diseases generically known as synucleinopathies, including Parkinson's disease (PD), dementia with Lewy bodies (DLB) and multiple system atrophy (MSA). Although the initial triggers of pathology and progression are unclear, multiple lines of evidence support therapeutic targeting of asyn in order to limit its prion-like misfolding. Here, we review recent pre-clinical and clinical work that offers promising treatment strategies to sequester, degrade, or silence asyn expression as a means to reduce the levels of seed or substrate. These diverse approaches include removal of aggregated asyn with passive or active immunization or by expression of vectorized antibodies, modulating kinetics of misfolding with small molecule anti-aggregants, lowering asyn gene expression by antisense oligonucleotides or inhibitory RNA, and pharmacological activation of asyn degradation pathways. We also discuss recent technological advances in combining low intensity focused ultrasound with intravenous microbubbles to transiently increase blood-brain barrier permeability for improved brain delivery and target engagement of these large molecule anti-asyn biologics.

Trehalose Activates Hepatic and Myocardial Autophagy and Has Anti-Inflammatory Effects in db/db Diabetic Mice

Db/db mice (carrying a mutation in the gene encoding leptin receptor) show autophagy suppression. Our aim was to evaluate the effect of autophagy inducer trehalose on liver and heart autophagy in db/db mice and to study inflammation dysregulation and the suitability of chitinases’ expression levels as diabetes markers. Thirty-eight male db/db mice and C57/BL mice (control) were used. The db/db model manifested inflammation symptoms: overexpression of TNF-α in the spleen and underexpression of IL-10 in the liver and spleen (cytokine imbalance). Simultaneously, we revealed decreased expression of chitotriosidase (CHIT1) and acid mammalian chitinase (CHIA) in the liver of db/db mice. CHIA expression in db/db mice is significantly lower only in the spleen. Trehalose treatment significantly reduced blood glucose concentration and glycated hemoglobin. Treatment of db/db mice by trehalose was followed by increased autophagy induction in the heart and liver (increased autolysosomes volume density studied by morphometric electron-microscopic method). Trehalose exerted beneficial cardiac effects possibly via increased lipophagy (uptake of lipid droplets). The autophagy activation by trehalose had several positive effects on the heart and liver of db/db mice; therefore, lipophagy activation seems to be a promising therapy for diabetes.

Transcranial sonography depicts a larger substantia nigra echogenic area in renal transplant patients on calcineurin inhibitors than on rapamycin

BACKGROUND

After kidney transplantation neurologic manifestations may develop, including Parkinson's disease (PD). An enlarged substantia nigra (SN) by transcranial sonography has been recognized as a marker of PD.

METHODS

In renal transplant recipients (RTRs = 95) and controls (n = 20), measurement of mesencephalon, SN, third ventricle, spleen and carotid intima-media thickness (cIMT) and middle cerebral artery (MCA), kidney and spleen arteries Doppler resistive index (RI) were performed.

RESULTS

RTRs had larger SN, third ventricle and cIMT and higher renal RI than controls. The SN was larger in the CNIs group than in controls and rapamycin group, while the third ventricle was similar between patients but larger than in controls. In RTRs, SN showed a direct linear correlation with spleen and the third ventricle with age, cIMT and RI of the MCA, kidney and spleen. In CNIs group the SN correlated positively with age and cIMT, while the third ventricle reproduced RTRs correlations. Rapamycin group showed a direct linear relationship between the third ventricle and age and RI of the MCA, kidney and spleen; SN showed no correlations.

CONCLUSION

RTRs on CNIs present a larger SN area than on rapamycin, probably due to the antiproliferative effect of rapamycin. This finding might be relevant when interpreting TCS in RTRs.

TRPV4 contributes to ER stress and inflammation: implications for Parkinson’s disease

Background

Parkinson’s disease (PD) is a progressive neurodegenerative disorder. Its molecular mechanism is still unclear, and pharmacological treatments are unsatisfactory. Transient receptor potential vanilloid 4 (TRPV4) is a nonselective Ca²⁺ channel. It has recently emerged as a critical risk factor in the pathophysiology of neuronal injuries and cerebral diseases. Our previous study reported that TRPV4 contributed to endoplasmic reticulum (ER) stress in the MPP⁺-induced cell model of PD. In the present study, we detected the role and the mechanism of TRPV4 in 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced PD mice.

Methods

Intracerebral injection of an adeno-associated virus (AAV) into the substantia nigra (SN) of mice was used to knockdown or upregulate the expression of TRPV4 and intraperitoneal injection of MPTP. Rotarod and pole tests were used to evaluate the locomotor ability of mice. We used immunohistochemistry, Nissl staining and Western blot to detect the alterations in the number of tyrosine hydroxylase (TH)-positive neurons, Nissl-positive neurons, the levels of ER stress-associated molecules and proinflammatory cytokines in the SN.

Results

The SN was transfected with AAV for 3 weeks and expressed the target protein with green fluorescence. Knockdown of TRPV4 via injection of a constructed AAV-TRPV4 shRNAi into the SN alleviated the movement deficits of PD mice. Upregulation of TRPV4 via injection of a constructed AAV-TRPV4 aggravated the above movement disorders. The expression of TRPV4 was upregulated in the SN of MPTP-treated mice. Injection of AAV-TRPV4 shRNAi into the SN rescued the number of TH-positive and Nissl-positive neurons in the SN decreased by MPTP, while injection of AAV-TRPV4 induced the opposite effect. Moreover, MPTP-decreased Sarco/endoplasmic reticulum Ca²⁺-ATPase 2 (SERCA2) and pro-cysteinyl aspartate specific proteinase-12 (procaspase-12), MPTP-increased Glucose-regulated protein 78 (GRP78), Glucose-regulated protein 94 (GRP94) and C/EBP homologous protein (CHOP) were inhibited by AAV-TRPV4 shRNAi infection, and enhanced by AAV-TRPV4. In the same way, MPTP-decreased procaspase-1, MPTP-increased Interleukin-18 (IL-18), Cyclooxgenase-2 (COX-2) and 5-Lipoxygenase (5-LOX) were inhibited by AAV-TRPV4 shRNAi, or further exacerbated by AAV-TRPV4.

Conclusions

These results suggest that TRPV4 mediates ER stress and inflammation pathways, contributing to the loss of dopamine (DA) neurons in the SN and movement deficits in PD mice. Moreover, this study provides a new perspective on molecular targets and gene therapies for the treatment of PD in the future.

The Emerging Roles of Autophagy in Human Diseases

Autophagy, a process of cellular self-digestion, delivers intracellular components including superfluous and dysfunctional proteins and organelles to the lysosome for degradation and recycling and is important to maintain cellular homeostasis. In recent decades, autophagy has been found to help fight against a variety of human diseases, but, at the same time, autophagy can also promote the procession of certain pathologies, which makes the connection between autophagy and diseases complex but interesting. In this review, we summarize the advances in understanding the roles of autophagy in human diseases and the therapeutic methods targeting autophagy and discuss some of the remaining questions in this field, focusing on cancer, neurodegenerative diseases, infectious diseases and metabolic disorders.

Autophagy and Aging: Roles in Skeletal Muscle, Eye, Brain and Hepatic Tissue

Autophagy is an evolutionary conserved degradative process contributing to cytoplasm quality control, metabolic recycling and cell defense. Aging is a universal phenomenon characterized by the progressive accumulation of impaired molecular and reduced turnover of cellular components. Recent evidence suggests a unique role for autophagy in aging and age-related disease. Indeed, autophagic activity declines with age and enhanced autophagy may prevent the progression of many age-related diseases and prolong life span. All tissues experience changes during aging, while the role of autophagy in different tissues varies. This review summarizes the links between autophagy and aging in the whole organism and discusses the physiological and pathological roles of autophagy in the aging process in tissues such as skeletal muscle, eye, brain, and liver.

Treatment with Autophagy Inducer Trehalose Alleviates Memory and Behavioral Impairments and Neuroinflammatory Brain Processes in db/db Mice

Autophagy attenuation has been found in neurodegenerative diseases, aging, diabetes mellitus, and atherosclerosis. In experimental models of neurodegenerative diseases, the correction of autophagy in the brain reverses neuronal and behavioral deficits and hence seems to be a promising therapy for neuropathologies. Our aim was to study the effect of an autophagy inducer, trehalose, on brain autophagy and behavior in a genetic model of diabetes with signs of neuronal damage (db/db mice). A 2% trehalose solution was administered as drinking water during 24 days of the experiment. Expressions of markers of autophagy (LC3-II), neuroinflammation (IBA1), redox state (NOS), and neuronal density (NeuN) in the brain were assessed by immunohistochemical analysis. For behavioral phenotyping, the open field, elevated plus-maze, tail suspension, pre-pulse inhibition, and passive avoidance tests were used. Trehalose caused a slight reduction in increased blood glucose concentration, considerable autophagy activation, and a decrease in the neuroinflammatory response in the brain along with improvements of exploration, locomotor activity, anxiety, depressive-like behavior, and fear learning and memory in db/db mice. Trehalose exerted some beneficial peripheral and systemic effects and partially reversed behavioral alterations in db/db mice. Thus, trehalose as an inducer of mTOR-independent autophagy is effective at alleviating neuronal and behavioral disturbances accompanying experimental diabetes.

Restoration of Parkinson's Disease-Like Deficits by Activating Autophagy through mTOR-Dependent and mTOR-Independent Mechanisms in Pharmacological and Transgenic Models of Parkinson's Disease in Mice

We studied the possibilities of inhibition of neurodegeneration in MPTP-induced model of Parkinson's disease (PD) in C57Bl/6J mice and transgenic model of early PD stage (5-monthold B6.Cg-Tg(Prnp-SNCA*A53T)23Mkle/J mice) by autophagy activation through mTOR-dependent and mTOR-independent pathways with rapamycin and trehalose, respectively. Therapy with autophagy inducers in a "postponed" mode (7 days after MPTP intoxication) restored the expression of the dopaminergic neuron marker tyrosine hydroxylase and markedly improved cognitive function in the conditioned passive avoidance response (CPAR; fear memory). The transgenic model also showed an increase in the expression of tyrosine hydroxylase in the nigrostriatal system of the brain. An enhanced therapeutic effect of the combined treatment with the drugs was revealed on the expression of tyrosine hydroxylase, but not in the CPAR test. Thus, activation of both pathways of autophagy regulation in PD models with weakened neuroinflammation can restore the dopaminergic function of neurons and cognitive activity in mice.

Trehalose alleviates doxorubicin-induced cardiotoxicity in female Swiss albino mice by suppression of oxidative stress and autophagy

Clinically, the use of doxorubicin (DOX) is limited due to DOX-induced cardiotoxicity (DIC). The current study aimed to evaluate the cardioprotective effect of trehalose (TRE) against DIC in a female Swiss albino mouse model. Mice were divided into five experimental groups: Gp. I: saline control group (200 μl/mouse saline three times per week for 3 weeks day after day), Gp. II: DOX-treated group (2 mg/kg body weight three times per week for 3 weeks day after day), Gp. III: TRE group (200 μg/mouse three times per week for 3 weeks day after day), Gp. IV: DOX + TRE cotreatment group (animals were coadministered with DOX and TRE as in Gp. II and III, respectively), and Gp. V: DOX + TRE posttreatment group (animals were treated with DOX as in Gp. II followed by treatment with TRE as in Gp. III). DOX-treated mice showed significant elevation in cardiac injury biomarkers (lactate dehydrogenase, creatine kinase isoenzyme-MB, and cardiac troponin I), cardiac oxidative stress (OS) markers (malondialdehyde and myeloperoxidase), and cardiac levels of autophagy-related protein 5. Moreover, DOX significantly reduced the levels of total antioxidant capacity and activities of catalase and glutathione S-transferase. In contrast, TRE treatment of DOX-administered mice significantly improved almost all of the above-mentioned assessed parameters. Furthermore, histopathological changes of cardiac tissues observed in mice treated with TRE in combination with DOX were significantly improved as compared to DOX-treated animals. Taken together, the present study provides evidence that TRE has cardioprotective effects against DIC, which is likely mediated via suppression of OS and autophagy.

Targeting autophagy in disease: established and new strategies

Macroautophagy/autophagy is an evolutionarily conserved pathway responsible for clearing cytosolic aggregated proteins, damaged organelles or invading microorganisms. Dysfunctional autophagy leads to pathological accumulation of the cargo, which has been linked to a range of human diseases, including neurodegenerative diseases, infectious and autoimmune diseases and various forms of cancer. Cumulative work in animal models, application of genetic tools and pharmacologically active compounds, has suggested the potential therapeutic value of autophagy modulation in disease, as diverse as Huntington, Salmonella infection, or pancreatic cancer. Autophagy activation versus inhibition strategies are being explored, while the role of autophagy in pathophysiology is being studied in parallel. However, the progress of preclinical and clinical development of autophagy modulators has been greatly hampered by the paucity of selective pharmacological agents and biomarkers to dissect their precise impact on various forms of autophagy and cellular responses. Here, we summarize established and new strategies in autophagy-related drug discovery and indicate a path toward establishing a more efficient discovery of autophagy-selective pharmacological agents. With this knowledge at hand, modern concepts for therapeutic exploitation of autophagy might become more plausible.

Abbreviations: ALS: amyotrophic lateral sclerosis; AMPK: AMP-activated protein kinase; ATG: autophagy-related gene; AUTAC: autophagy-targeting chimera; CNS: central nervous system; CQ: chloroquine; GABARAP: gamma-aminobutyric acid type A receptor-associated protein; HCQ: hydroxychloroquine; LYTAC: lysosome targeting chimera; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; MTOR: mechanistic target of rapamycin kinase; NDD: neurodegenerative disease; PDAC: pancreatic ductal adenocarcinoma; PE: phosphatidylethanolamine; PIK3C3/VPS34: phosphatidylinositol 3-kinase catalytic subunit type 3; PtdIns3K: class III phosphatidylinositol 3-kinase; PtdIns3P: phosphatidylinositol 3-phosphate; PROTAC: proteolysis-targeting chimera; SARS-CoV-2: severe acute respiratory syndrome coronavirus 2; SQSTM1/p62: sequestosome 1; ULK1: unc-51 like autophagy activating kinase 1.

Mammalian/mechanistic target of rapamycin (mTOR) complexes in neurodegeneration

Novel targets to arrest neurodegeneration in several dementing conditions involving misfolded protein accumulations may be found in the diverse signaling pathways of the Mammalian/mechanistic target of rapamycin (mTOR). As a nutrient sensor, mTOR has important homeostatic functions to regulate energy metabolism and support neuronal growth and plasticity. However, in Alzheimer's disease (AD), mTOR alternately plays important pathogenic roles by inhibiting both insulin signaling and autophagic removal of β-amyloid (Aβ) and phospho-tau (ptau) aggregates. It also plays a role in the cerebrovascular dysfunction of AD. mTOR is a serine/threonine kinase residing at the core in either of two multiprotein complexes termed mTORC1 and mTORC2. Recent data suggest that their balanced actions also have implications for Parkinson's disease (PD) and Huntington's disease (HD), Frontotemporal dementia (FTD) and Amyotrophic Lateral Sclerosis (ALS). Beyond rapamycin; an mTOR inhibitor, there are rapalogs having greater tolerability and micro delivery modes, that hold promise in arresting these age dependent conditions.

circSAMD4A participates in the apoptosis and autophagy of dopaminergic neurons via the miR‑29c‑3p‑mediated AMPK/mTOR pathway in Parkinson's disease

Parkinson's disease (PD) can lead to movement injury and cognitive dysfunction. Although advances have been made in attenuating PD, the effect of inhibiting the development of PD remains disappointing. Therefore, the present study aimed at investigating the etiology of Parkinson's disease and developing an alternative therapeutic strategy for patients with PD. A PD mouse model was established using an intraperitoneal injection of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine hydrochloride (MPTP-HCl; 30 mg/kg/day for 5 days), and a PD cellular model was established by treating SH-SY5Y cells with different concentrations of 1-methyl-4-phenylpyridinium (MPP⁺) for 24 h. The expression levels of circular RNA sterile α motif domain containing 4A (circSAMD4A) and microRNA (miR)-29c-3p in both midbrain tissues and SH-SY5Y cells were detected via reverse transcription-quantitative PCR. The interaction between circSAMD4A and miR-29c-3p was verified using a dual-luciferase reporter experiment. Apoptosis-, autophagy- and 5′AMP-activated protein kinase (AMPK)/mTOR cascade-associated proteins in midbrain tissues and SH-SY5Y cells were detected using western blotting. Furthermore, TUNEL staining and flow cytometry were used to analyze cell apoptosis. It was found that circSAMD4A was upregulated, while miR-29c-3p was downregulated in both PD animal and cellular models. Moreover, circSAMD4A directly targeted and negatively regulated miR-29c-3p. Further studies identified that circSAMD4A knockdown inhibited MPTP- or MPP⁺-induced apoptosis and autophagy; however, these effects were abolished by an miR-29c-3p inhibitor. In addition, circSAMD4A knockdown repressed phosphorylated-AMPK expression and increased mTOR expression in MPTP- or MPP⁺-induced PD models, the effects of which were reversed by a miR-29c-3p inhibitor. Collectively, these results suggested that circSAMD4A participated in the apoptosis and autophagy of dopaminergic neurons by modulating the AMPK/mTOR cascade via miR-29c-3p in PD.

Autophagy-targeted therapy to modulate age-related diseases: Success, pitfalls, and new directions

Autophagy is a critical metabolic process that supports homeostasis at a basal level and is dynamically regulated in response to various physiological and pathological processes. Autophagy has some etiologic implications that support certain pathological processes due to alterations in the lysosomal-degradative pathway. Some of the conditions related to autophagy play key roles in highly relevant human diseases, e.g., cardiovascular diseases (15.5%), malignant and other neoplasms (9.4%), and neurodegenerative conditions (3.7%). Despite advances in the discovery of new strategies to treat these age-related diseases, autophagy has emerged as a therapeutic option after preclinical and clinical studies. Here, we discuss the pitfalls and success in regulating autophagy initiation and its lysosome-dependent pathway to restore its homeostatic role and mediate therapeutic effects for cancer, neurodegenerative, and cardiac diseases. The main challenge for the development of autophagy regulators for clinical application is the lack of specificity of the repurposed drugs, due to the low pharmacological uniqueness of their target, including those that target the PI3K/AKT/mTOR and AMPK pathway. Then, future efforts must be conducted to deal with this scenery, including the disclosure of key components in the autophagy machinery that may intervene in its therapeutic regulation. Among all efforts, those focusing on the development of novel allosteric inhibitors against autophagy inducers, as well as those targeting autolysosomal function, and their integration into therapeutic regimens should remain a priority for the field.

Rapamycin restores brain vasculature, metabolism, and blood-brain barrier in an inflammaging model

Rapamycin (RAPA) is found to have neuro-protective properties in various neuroinflammatory pathologies, including brain aging. With magnetic resonance imaging (MRI) techniques, we investigated the effect of RAPA in a lipopolysaccharide (LPS)-induced inflammaging model in rat brains. Rats were exposed to saline (control), or LPS alone or LPS combined with RAPA treatment (via food over 6 weeks). Arterial spin labeling (ASL) perfusion imaging was used to measure relative cerebral blood flow (rCBF). MR spectroscopy (MRS) was used to measure brain metabolite levels. Contrast-enhanced MRI (CE-MRI) was used to assess blood-brain barrier (BBB) permeability. Immunohistochemistry (IHC) was used to confirm neuroinflammation. RAPA restored NF-κB and HIF-1α to normal levels. RAPA was able to significantly restore rCBF in the cerebral cortex post-LPS exposure (p < 0.05), but not in the hippocampus. In the hippocampus, RAPA was able to restore total creatine (Cr) acutely, and N-acetyl aspartate (NAA) at 6 weeks, post-LPS. Myo-inositol (Myo-Ins) levels were found to decrease with RAPA treatment acutely post-LPS. RAPA was also able to significantly restore the BBB acutely post-LPS in both the cortex and hippocampus (p < 0.05 for both). RAPA was found to increase the percent change in BOLD signal in the cortex at 3 weeks, and in the hippocampus at 6 weeks post-LPS, compared to LPS alone. RAPA treatment also restored the neuronal and macro-vascular marker, EphB2, back to normal levels. These results indicate that RAPA may play an important therapeutic role in inhibiting neuroinflammation by normalizing brain vascularity, BBB, and some brain metabolites, and has a high translational capability.

Exosomes derived from miR-188-3p-modified adipose-derived mesenchymal stem cells protect Parkinson's disease

Parkinson’s disease (PD) is the second-most common neurodegenerative disease after Alzheimer’s disease. The most important pathological feature of PD is the irreversible damage of dopamine neurons, which is related to autophagy and neuroinflammation in the substantia nigra. Previous studies found that the activation of NAcht Leucine-rich repeat Protein 3 (NLRP3) inflammasome/pyroptosis and cell division protein kinase 5 (CDK5)-mediated autophagy played an important role in PD. Bioinformatics analyses further predicted that microRNA (miR)-188-3p potentially targets NLRP3 and CDK5. Adipose-derived stem cell (ADSC)-derived exosomes were found to be excellent vectors for genetic therapy. We assessed the levels of injury, autophagy, and inflammasomes in 1-methyl-4-phenyl-1,2,4,5-tetrahydropyridine (MPTP)-induced PD mice models and neurotoxin 1-methyl-4-phenylpyridinium (MPP+)-induced cell models after treating them with miR-188-3p-enriched exosomes. miR-188-3p-enriched exosome treatment suppressed autophagy and pyroptosis, whereas increased proliferation via targeting CDK5 and NLRP3 in mice and MN9D cells. It was revealed that mir-188-3p could be a new therapeutic target for curing PD patients.

Evaluating the Effects of Grain of Isogenic Wheat Lines Differing in the Content of Anthocyanins in Mouse Models of Neurodegenerative Disorders

Functional foods enriched with plant polyphenols and anthocyanins in particular attract special attention due to multiple beneficial bioactive properties of the latter. We evaluated the effects of a grain diet rich in anthocyanins in a mouse model of Alzheimer’s disease induced by amyloid-beta (Aβ) and a transgenic mouse model of Parkinson’s disease (PD) with overexpression of human alpha-synuclein. The mice were kept at a diet that consisted of the wheat grain of near isogenic lines differing in anthocyanin content for five–six months. The anthocyanin-rich diet was safe and possessed positive effects on cognitive function. Anthocyanins prevented deficits in working memory induced by Aβ or a long-term grain mono-diet; they partially reversed episodic memory alterations. Both types of grain diets prolonged memory extinction and rescued its facilitation in the PD model. The dynamics of the extinction in the group fed with the anthocyanin-rich wheat was closer to that in a group of wild-type mice given standard chow. The anthocyanin-rich diet reduced alpha-synuclein accumulation and modulated microglial response in the brain of the transgenic mice including the elevated expression of arginase1 that marks M2 microglia. Thus, anthocyanin-rich wheat is suggested as a promising source of functional nutrition at the early stages of neurodegenerative disorders.

Effects of Grape Polyphenols on the Life Span and Neuroinflammatory Alterations Related to Neurodegenerative Parkinson Disease-Like Disturbances in Mice

Functional nutrition is a valuable supplementation to dietary therapy. Functional foods are enriched with biologically active substances. Plant polyphenols attract particular attention due to multiple beneficial properties attributed to their high antioxidant and other biological activities. We assessed the effect of grape polyphenols on the life span of C57BL/6 mice and on behavioral and neuroinflammatory alterations in a transgenic mouse model of Parkinson disease (PD) with overexpression of the A53T-mutant human α-synuclein. C57BL/6 mice were given a dietary supplement containing grape polyphenol concentrate (GPC—1.5 mL/kg/day) with drinking water from the age of 6–8 weeks for life. Transgenic PD mice received GPC beginning at the age of 10 weeks for four months. GPC significantly influenced the cumulative proportion of surviving and substantially augmented the average life span in mice. In the transgenic PD model, the grape polyphenol (GP) diet enhanced memory reconsolidation and diminished memory extinction in a passive avoidance test. Behavioral effects of GP treatment were accompanied by a decrease in α-synuclein accumulation in the frontal cortex and a reduction in the expression of neuroinflammatory markers (IBA1 and CD54) in the frontal cortex and hippocampus. Thus, a GP-rich diet is recommended as promising functional nutrition for aging people and patients with neurodegenerative disorders.

The use of geroprotectors to prevent multimorbidity: Opportunities and challenges

Over 60 % of people over the age of 65 will suffer from multiple diseases concomitantly but the common approach is to treat each disease separately. As age-associated diseases have common underlying mechanisms there is potential to tackle many diseases with the same pharmacological intervention. These are known as geroprotectors and could overcome the problems related to polypharmacy seen with the use of the single disease model. With some geroprotectors now reaching the end stage of preclinical studies and early clinical trials, there is a need to review the evidence and assess how they can be translated practically and effectively into routine practice. Despite promising evidence, there are many gaps and challenges in our understanding that must be addressed to make geroprotective medicine effective in the treatment of age-associated multimorbidity. Here we highlight the key barriers to clinical translation and discuss whether geroprotectors such as metformin, rapamycin and senolytics can tackle all age-associated diseases at the same dose, or whether a more nuanced approach is required. The evidence suggests that geroprotectors' mode of action may differ in different tissues or in response to different inducers of accelerating ageing, suggesting that a blunt 'one drug for many diseases' approach may not work. We make the case for the use of artificial intelligence to better understand multimorbidity, allowing identification of clusters and networks of diseases that are significantly associated beyond chance and the underpinning molecular pathway of ageing causal to each cluster. This will allow us to better understand the development of multimorbidity, select a more homogenous group of patients for intervention, match them with the appropriate geroprotector and identify biomarkers specific to the cluster.

Lysosomotropic Features and Autophagy Modulators among Medical Drugs: Evaluation of Their Role in Pathologies

The concept of lysosomotropic agents significantly changed numerous aspects of cellular biochemistry, biochemical pharmacology, and clinical medicine. In the present review, we focused on numerous low-molecular and high-molecular lipophilic basic compounds and on the role of lipophagy and autophagy in experimental and clinical medicine. Attention was primarily focused on the most promising agents acting as autophagy inducers, which offer a new window for treatment and/or prophylaxis of various diseases, including type 2 diabetes mellitus, Parkinson's disease, and atherosclerosis. The present review summarizes current knowledge on the lysosomotropic features of medical drugs, as well as autophagy inducers, and their role in pathological processes.