Amelioration of Mitochondrial Quality Control and Proteostasis by Natural Compounds in Parkinson's Disease Models

The Interplay of Mitochondrial Bioenergetics and Dopamine Agonists as an Effective Disease-Modifying Therapy for Parkinson's Disease

Parkinson's disease (PD) is a progressive neurological ailment with a slower rate of advancement that is more common in older adults. The biggest risk factor for PD is getting older, and those over 60 have an exponentially higher incidence of this condition. The failure of the mitochondrial electron chain, changes in the dynamics of the mitochondria, and abnormalities in calcium and ion homeostasis are all symptoms of Parkinson's disease (PD). Increased mitochondrial reactive oxygen species (mROS) and an energy deficit are linked to these alterations. Levodopa (L-DOPA) is a medication that is typically used to treat most PD patients, but because of its negative effects, additional medications have been created utilizing L-DOPA as the parent molecule. Ergot and non-ergot derivatives make up most PD medications. PD is successfully managed with the use of dopamine agonists (DA). To get around the motor issues produced by L-DOPA, these dopamine derivatives can directly excite DA receptors in the postsynaptic membrane. In the past 10 years, two non-ergoline DA with strong binding properties for the dopamine D2 receptor (D2R) and a preference for the dopamine D3 receptor (D3R) subtype, ropinirole, and pramipexole (PPx) have been developed for the treatment of PD. This review covers the most recent research on the efficacy and safety of non-ergot drugs like ropinirole and PPx as supplementary therapy to DOPA for the treatment of PD.

Dietary Natural Flavonoids: Intervention for MAO-B Against Parkinson's Disease

Parkinson's disease (PD) stands as the second most common neurological disorder after Alzheimer's disease, primarily affecting the elderly population and significantly compromising their quality of life. The precise etiology of PD remains elusive, but recent research has shed light on potential factors, including the formation of α-synuclein aggregates, oxidative stress, neurotransmitter imbalances, and dopaminergic neurodegeneration in the substantia nigra pars compacta (SNpc) region of the brain, culminating in motor symptoms such as bradykinesia, akinesia, tremors, and rigidity. Monoamine oxidase (MAO) is an essential enzyme, comprising two isoforms, MAO-A and MAO-B, responsible for the oxidation of monoamines such as dopamine. Increased MAO-B activity is responsible for decreased dopamine levels in the SNpc region of mid brain which is remarkably associated with the pathogenesis of PD-like manifestations. Inhibitors of MAO-B enhance striatal neuronal responses to dopamine, making them valuable in treating PD, which involves dopamine deficiency. Clinically approved MAO-B inhibitors such as selegiline, L-deprenyl, pargyline, and rasagiline are employed in the management of neurodegenerative conditions associated with PD. Current therapeutic interventions including MAO-B inhibitors for PD predominantly aim to alleviate these motor symptoms but often come with a host of side effects that can be particularly challenging for the patients. While effective, they have limitations, prompting a search for alternative treatments, there is a growing interest in exploring natural products notably flavonoids as potential sources of novel MAO-B inhibitors. In line with that, the present review focuses on natural flavonoids of plant origin that hold promise as potential candidates for the development of novel MAO-B inhibitors. The discussion encompasses both in vitro and in vivo studies, shedding light on their potential therapeutic applications. Furthermore, this review underscores the significance of exploring natural products as valuable reservoirs of MAO-B inhibitors, offering new avenues for drug development and addressing the pressing need for improved treatments in PD-like pathological conditions. The authors of this review majorly explore the neuroprotective potential of natural flavonoids exhibiting notable MAO-B inhibitory activity and additionally multi-targeted approaches in the treatment of PD with clinical evidence and challenges faced in current therapeutic approaches.

Novel Insights into Parkin-Mediated Mitochondrial Dysfunction and "Mito-Inflammation" in α-Synuclein Toxicity. The Role of the cGAS-STING Signalling Pathway

The prevalence of age-related neurodegenerative diseases, such as Parkinson's disease (PD) and related disorders continues to grow worldwide. Increasing evidence links intracellular inclusions of misfolded alpha-synuclein (α-syn) aggregates, so-called Lewy bodies (LB) and Lewy neuritis, to the progressive pathology of PD and other synucleinopathies. Our previous findings established that α-syn oligomers induce S-nitrosylation and deregulation of the E3-ubiquitin ligase Parkin, leading to mitochondrial disturbances in neuronal cells. The accumulation of damaged mitochondria as a consequence, together with the release of mitochondrial-derived damage-associated molecular patterns (mtDAMPs) could activate the innate immune response and induce neuroinflammation ("mito-inflammation"), eventually accelerating neurodegeneration. However, the molecular pathways that transmit pro-inflammatory signals from damaged mitochondria are not well understood. One of the proposed pathways could be the cyclic GMP-AMP synthase (cGAS) - stimulator of interferon genes (STING) (cGAS-STING) pathway, which plays a pivotal role in modulating the innate immune response. It has recently been suggested that cGAS-STING deregulation may contribute to the development of various pathological conditions. Especially, its excessive engagement may lead to neuroinflammation and appear to be essential for the development of neurodegenerative brain diseases, including PD. However, the precise molecular mechanisms underlying cGAS-STING pathway activation in PD and other synucleinopathies are not fully understood. This review focuses on linking mitochondrial dysfunction to neuroinflammation in these disorders, particularly emphasizing the role of the cGAS-STING signaling. We propose the cGAS-STING pathway as a critical driver of inflammation in α-syn-dependent neurodegeneration and hypothesize that cGAS-STING-driven "mito-inflammation" may be one of the key mechanisms promoting the neurodegeneration in PD. Understanding the molecular mechanisms of α-syn-induced cGAS-STING-associated "mito-inflammation" in PD and related synucleinopathies may contribute to the identification of new targets for the treatment of these disorders.

J24335 exerts neuroprotective effects against 6-hydroxydopamine-induced lesions in PC12 cells and mice

Parkinson's disease is the second most prevalent age-related neurodegenerative disease and disrupts the lives of people aged >60 years. Meanwhile, single-target drugs becoming inapplicable as PD pathogenesis diversifies. Mitochondrial dysfunction and neurotoxicity have been shown to be relevant to the pathogenesis of PD. The novel synthetic compound J24335 (11-Hydroxy-1-(8-methoxy-5-(trifluoromethyl)quinolin-2-yl)undecan-1-one oxime), which has been researched similarly to J2326, has the potential to be a multi-targeted drug and alleviate these lesions. Therefore, we investigated the mechanism of action and potential neuroprotective function of J24335 against 6-OHDA-induced neurotoxicity in mice, and in PC12 cell models. The key target of action of J24335 was also screened. MTT assay, LDH assay, flow cytometry, RT-PCR, LC-MS, OCR and ECAR detection, and Western Blot analysis were performed to characterize the neuroprotective effects of J24335 on PC12 cells and its potential mechanism. Behavioral tests and immunohistochemistry were used to evaluate behavioral changes and brain lesions in mice. Moreover, bioinformatics was employed to assess the drug-likeness of J24335 and screen its potential targets. J24335 attenuated the degradation of mitochondrial membrane potential and enhanced glucose metabolism and mitochondrial biosynthesis to ameliorate 6-OHDA-induced mitochondrial dysfunction. Animal behavioral tests demonstrated that J24335 markedly improved motor function and loss of TH-positive neurons and dopaminergic nerve fibers, and contributed to an increase in the levels of dopamine and its metabolites in brain tissue. The activation of both the CREB/PGC-1α/NRF-1/TFAM and PKA/Akt/GSK-3β pathways was a major contributor to the neuroprotective effects of J24335. Furthermore, bioinformatics predictions revealed that J24335 is a low toxicity and highly BBB permeable compound targeting 8 key genes (SRC, EGFR, ERBB2, SYK, MAPK14, LYN, NTRK1 and PTPN1). Molecular docking suggested a strong and stable binding between J24335 and the 8 core targets. Taken together, our results indicated that J24335, as a multi-targeted neuroprotective agent with promising therapeutic potential for PD, could protect against 6-OHDA-induced neurotoxicity via two potential pathways in mice and PC12 cells.

The Zebrafish Model as a New Discovery Path for Medicinal Plants in the Treatment of Parkinson's Disease

Parkinson's disease (PD) is one of the most frequent degenerative central nervous system disorders affecting older adults. Dopaminergic neuron failure in the substantia nigra is a pathological sign connected with the motor shortfall of PD. Due to their low teratogenic and adverse effect potential, medicinal herbs have emerged as a promising therapy option for preventing and curing PD and other neurodegenerative disorders. However, the mechanism through which natural compounds provide neuroprotection against PD remains unknown. While testing compounds in vertebrates such as mice is prohibitively expensive and time-consuming, zebrafish (Danio rerio) may offer an appealing alternative because they are vertebrates and share many of the same characteristics as humans. Zebrafish are commonly used as animal models for studying many human diseases, and their molecular history and bioimaging properties are appropriate for the study of PD. However, a literature review indicated that only six plants, including Alpinia oxyhylla, Bacopa monnieri, Canavalia gladiate, Centella asiatica, Paeonia suffruticosa, and Stachytarpheta indica had been investigated as potential PD treatments using the zebrafish model. Only C. asiatica and B. monnieri were found to have potential anti-PD activity. In addition to reviewing the current state of research in this field, these plants' putative mechanisms of action against PD are explored, and accessible assays for investigation are made.

Emerging Role of Plant-Based Bioactive Compounds as Therapeutics in Parkinson's Disease

Neurological ailments, including stroke, Alzheimer's disease (AD), epilepsy, Parkinson's disease (PD), and other related diseases, have affected around 1 billion people globally to date. PD stands second among the common neurodegenerative diseases caused as a result of dopaminergic neuron loss in the midbrain's substantia nigra regions. It affects cognitive and motor activities, resulting in tremors during rest, slow movement, and muscle stiffness. There are various traditional approaches for the management of PD, but they provide only symptomatic relief. Thus, a survey for finding new biomolecules or substances exhibiting the therapeutic potential to patients with PD is the main focus of present-day research. Medicinal plants, herbal formulations, and natural bioactive molecules have been gaining much more attention in recent years as synthetic molecules orchestrate a number of undesired effects. Several in vitro, in vivo, and in silico studies in the recent past have demonstrated the therapeutic potential of medicinal plants, herbal formulations, and plant-based bioactives. Among the plant-based bioactives, polyphenols, terpenes, and alkaloids are of particular interest due to their potent anti-inflammatory, antioxidant, and brain-health-promoting properties. Further, there are no concise, elaborated articles comprising updated mechanism-of-action-based reviews of the published literature on potent, recently investigated (2019-2023) medicinal plants, herbal formulations, and plant based-bioactive molecules, including polyphenols, terpenes, and alkaloids, as a method for the management of PD. Therefore, we designed the current review to provide an illustration of the efficacious role of various medicinal plants, herbal formulations, and bioactives (polyphenols, terpenes, and alkaloids) that can become potential therapeutics against PD with greater specificity, target approachability, bioavailability, and safety to the host. This information can be further utilized in the future to develop several value-added formulations and nutraceutical products to achieve the desired safety and efficacy for the management of PD.

Neuroprotective effect of chlorogenic acid on Parkinson's disease like symptoms through boosting the autophagy in zebrafish

Parkinson's disease (PD) is characterized by both motor and non-motor symptoms, including hypokinesia, postural instability, dopaminergic (DA) neurons loss, and α-synuclein (α-syn) accumulation. A growing number of patients show negative responses towards the current therapies. Thus, preventative or disease-modifying treatment agents are worth to further research. In recent years, compounds extracted from natural sources become promising candidates to treat PD. Chlorogenic acid (CGA) is a phenolic compound appearing in coffee, honeysuckle, and eucommia that showed their potential as antioxidants and neuroprotectors. In this study, we investigated the anti-PD activity of CGA by testing its effect on 1-methyl-4-phenyl-1-1,2,3,6-tetrahydropyridine (MPTP) zebrafish model of PD. It was shown that CGA relieved MPTP-induced PD-like symptoms including DA neurons and blood vessel loss, locomotion reduction, and apoptosis events in brain. Moreover, CGA modulated the expression of PD- and autophagy-related genes (α-syn, lc3b, p62, atg5, atg7, and ulk1b), showing its ability to promote the autophagy which was interrupted in the PD pathology. The unblocked effect of CGA on autophagy was further verified in 6-hydroxydopamine (6-OHDA)-modeled SHSY5Y cells. Our findings indicated that CGA might relieve PD by boosting the autophagy in neuronal cells that makes CGA a potential candidate for anti-PD treatment.

4-Phenylbutyrate Mitigates the Motor Impairment and Dopaminergic Neuronal Death During Parkinson's Disease Pathology via Targeting VDAC1 Mediated Mitochondrial Function and Astrocytes Activation

Parkinson's disease (PD) is a progressive motor neurodegenerative disorder significantly associated with protein aggregation related neurodegenerative mechanisms. In view of no disease modifying drugs, the present study was targeted to investigate the therapeutic effects of pharmacological agent 4-phenylbutyric acid (4PBA) in PD pathology. 4PBA is an FDA approved monocarboxylic acid with inhibitory activity towards histone deacetylase and clinically treats urea cycle disorder. First, we observed the significant protective effects of 4PBA on PD specific neuromuscular coordination, level of tyrosine hydroxylase, α-synuclein level and neurotransmitter dopamine in both substantia nigra and striatal regions of the experimental rat model of PD. Further results revealed that treatment with 4PBA drug exhibited significant protection against disease related oxidative stress and augmented nitrite levels. The disease pathology-related depletion in mitochondrial membrane potential and augmented level of calcium as well as mitochondrion membrane located VDAC1 protein level and cytochrome-c translocation were also significantly attenuated with 4PBA administration. Inhibited neuronal apoptosis and restored neuronal morphology were also observed with 4PBA treatment as measured by level of pro-apoptotic proteins t-Bid, Bax and cleaved caspase-3 along with cresyl violet staining in both substantia nigra and striatal regions. Lastly, PD-linked astrocyte activation was significantly inhibited with 4PBA treatment. Altogether, our findings suggest that 4PBA exerts broad-spectrum neuroprotective effects in PD animal model.

Potential anti-Parkinsonian's effect of S-(+)-linalool from Cinnamomum osmophloeum ct. linalool leaves are associated with mitochondrial regulation via gas-1, nuo-1, and mev-1 in Caenorhabditis elegans

Parkinson's disease (PD) is one of the prevalent neurodegenerative diseases, and developing new treatments from natural products is of particular interest. Essential oils from Cinnamomum osmophloeum ct. linalool leaves contain high levels (~95%) of S-(+)-linalool. The neuroprotective effects of linalool have been previously described, yet the underlying molecular mechanisms remain largely unknown. This study aimed to investigate the potential anti-Parkinsonian's effect of S-(+)-linalool on mitochondrial regulation and decipher the underlying molecular mechanisms in Caenorhabditis elegans PD model. Essential oils at 20 mg/L and 20 mg/L S-(+)-linalool each significantly attenuated the damaging effects of 6-hydroxydopamine (6-OHDA) on dopaminergic (DA) neurons and decreased the mitochondrial unfolded protein response (UPR^mt ) to antimycin. RNAi knockdown of mitochondrial complex I (gas-1, nuo-1), and complex II (mev-1) genes prevented the improvement of mitochondrial activity by S-(+)-linalool. The protective effects of S-(+)-linalool on 6-OHDA-induced behavior changes were absent in a DA-specific strain of C. elegans produced by gas-1, nuo-1, and mev-1 RNAi knockdown. These results suggest the potential anti-Parkinsonian's effect of S-(+)-linalool is associated with mitochondrial activity and regulated by gas-1, nuo-1, and mev-1 in C. elegans. Our findings suggest that S-(+)-linalool might be a promising candidate for therapeutic application to inhibit the progression of PD.

The Common Cellular Events in the Neurodegenerative Diseases and the Associated Role of Endoplasmic Reticulum Stress

Neurodegenerative diseases are inseparably linked with aging and increase as life expectancy extends. There are common dysfunctions in various cellular events shared among neurogenerative diseases, such as calcium dyshomeostasis, neuroinflammation, and age-associated decline in the autophagy-lysosome system. However, most of all, the prominent pathological feature of neurodegenerative diseases is the toxic buildup of misfolded protein aggregates and inclusion bodies accompanied by an impairment in proteostasis. Recent studies have suggested a close association between endoplasmic reticulum (ER) stress and neurodegenerative pathology in cellular and animal models as well as in human patients. The contribution of mutant or misfolded protein-triggered ER stress and its associated signaling events, such as unfolded protein response (UPR), to the pathophysiology of various neurodegenerative disorders, including Alzheimer's, Parkinson's, and Huntington's disease, amyotrophic lateral sclerosis, and prion disease, is described here. Impaired UPR action is commonly attributed to exacerbated ER stress, pathogenic protein aggregate accumulation, and deteriorating neurodegenerative pathologies. Thus, activating certain UPR components has been shown to alleviate ER stress and its associated neurodegeneration. However, uncontrolled activation of some UPR factors has also been demonstrated to worsen neurodegenerative phenotypes, suggesting that detailed molecular mechanisms around ER stress and its related neurodegenerations should be understood to develop effective therapeutics against aging-associated neurological syndromes. We also discuss current therapeutic endeavors, such as the development of small molecules that selectively target individual UPR components and address ER stress in general.

Neuroprotective effect of YIAEDAER peptide against Parkinson's disease like pathology in zebrafish

Parkinson's disease (PD) is characterized by the loss of dopaminergic (DA) neurons in the substantia nigra (SN) and aggregation of α-synuclein (α-syn). Current PD therapies merely provide symptomatic relief, lacking the disease-modifying therapeutic strategies against that could reverse the ongoing neurodegeneration. In the quest of exploring novel disease modifying therapeutic strategies, compounds from natural sources have gained much attention in recent days. YIAEDAER (Tyr-Ile-Ala-Glu-Asp-Ala-Glu-Arg) peptide is a multi-functional peptide isolated and purified from the visceral mass extract of Neptunea arthritica cumingii (NAC) with plethora of pharmacological activities, however its neuroprotective effect against MPTP induced PD model is not yet reported. We found YIAEDAER peptide co-treatment could suppressed the MPTP-induced locomotor impairment in zebrafish, ameliorates the MPTP induced degeneration of DA neurons, inhibited the loss of vasculature and loss of cerebral vessels, suppressed α-syn levels. Moreover, YIAEDAER peptide modulates several genes related to autophagy (α-syn, pink1, parkin, atg5, atg7, beclin1, ulk1b, ulk2, and ambra1a), and oxidative stress (sod1, sod2, gss, gpx4a, gsto2, and cat). Hence, our finding suggests that YIAEDAER peptide might be a potential therapeutic candidate against MPTP-induced PD like condition.

Search for safer and potent natural inhibitors of Parkinson's disease

After Alzheimer's disease, Parkinson's disease (PD) has taken second place in becoming one of the most commonly occurring neurological diseases being responsible for a number of disabling motor symptoms ranging from bradykinesia, akinesia, tremors to rigidity, that mostly targets the elderly population and severely disrupts their quality of life. The true underlying pathology of PD yet remains a mystery, however, recent advances in the field have pointed towards the production of α-synuclein aggregates, oxidative stress, and an imbalance between levels of acetylcholine and dopamine neurotransmitters in the brain that have been shown to result in loss of coordinated movement. Current treatments of PD include the gold standard dopamine precursor L-dopa, dopamine agonists pergolide and bromocriptine, catechol-o-methyl transferases inhibitors, entacapone and tolcapone and monoamine oxidase inhibitors such as Selegine and Rasagiline amongst several other drugs. While these drugs are successful in treating motor symptoms of the disease, they do so with a plethora of side effects that are especially debilitating to the elderly. In the recent years, a considerable amount of attention has been shifted towards phytocompounds such as flavonoids and green tea catechins due to promising experimental results. In this review, we have compiled phytocompounds that have shown potent activity against some of the most important targets for antiparkinsonian therapy. These compounds have exhibited activities that transcend the limits of simply attenuating mitochondrial oxidative stress and have opened doors to the discovery of novel lead compounds for newer, efficacious antiparkinsonian therapies with wider therapeutic windows.

The Renin-Angiotensin System Modulates Dopaminergic Neurotransmission: A New Player on the Scene

Parkinson's disease (PD) is an extrapyramidal disorder characterized by neuronal degeneration in several regions of the peripheral and central nervous systems. It is the second most frequent neurodegenerative disease after Alzheimer's. It has become a major health problem, affecting 1% of the world population over 60 years old and 3% of people beyond 80 years. The main histological findings are intracellular Lewy bodies composed of misfolded α-synuclein protein aggregates and loss of dopaminergic neurons in the central nervous system. Neuroinflammation, apoptosis, mitochondrial dysfunction, altered calcium homeostasis, abnormal protein degradation, and synaptic pathobiology have been put forward as mechanisms leading to cell death, α-synuclein deposition, or both. A progressive loss of dopaminergic neurons in the substantia nigra late in the neurodegeneration leads to developing motor symptoms like bradykinesia, tremor, and rigidity. The renin-angiotensin system (RAS), which is involved in regulating blood pressure and body fluid balance, also plays other important functions in the brain. The RAS is involved in the autocrine and paracrine regulation of the nigrostriatal dopaminergic synapses. Dopamine depletion, as in PD, increases angiotensin II expression, which stimulates or inhibits dopamine synthesis and is released via AT1 or AT2 receptors. Furthermore, angiotensin II AT1 receptors inhibit D1 receptor activation allosterically. Therefore, the RAS may have an important modulating role in the flow of information from the brain cortex to the basal ganglia. High angiotensin II levels might even aggravate neurodegeneration, activating the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase complex, which leads to increased reactive oxygen species production.

Extracellular Vesicles and Damage-Associated Molecular Patterns: A Pandora's Box in Health and Disease

Sterile inflammation develops as part of an innate immunity response to molecules released upon tissue injury and collectively indicated as damage-associated molecular patterns (DAMPs). While coordinating the clearance of potential harmful stimuli, promotion of tissue repair, and restoration of tissue homeostasis, a hyper-activation of such an inflammatory response may be detrimental. The complex regulatory pathways modulating DAMPs generation and trafficking are actively investigated for their potential to provide relevant insights into physiological and pathological conditions. Abnormal circulating extracellular vesicles (EVs) stemming from altered endosomal-lysosomal system have also been reported in several age-related conditions, including cancer and neurodegeneration, and indicated as a promising route for therapeutic purposes. Along this pathway, mitochondria may dispose altered components to preserve organelle homeostasis. However, whether a common thread exists between DAMPs and EVs generation is yet to be clarified. A deeper understanding of the highly complex, dynamic, and variable intracellular and extracellular trafficking of DAMPs and EVs, including those of mitochondrial origin, is needed to unveil relevant pathogenic pathways and novel targets for drug development. Herein, we describe the mechanisms of generation of EVs and mitochondrial-derived vesicles along the endocytic pathway and discuss the involvement of the endosomal-lysosomal in cancer and neurodegeneration (i.e., Alzheimer's and Parkinson's disease).

leaf extract protects against H2O2-induced oxidative stress by increasing autophagy in PC12 cells

The effect of Apocynum venetum leaf extract (AVLE) on the nervous system has been widely studied, but its effect on injured neurons is not fully understood. In the present study, the protective effect of AVLE on injured neurons was determined. H2O2 was used to induce oxidative stress in PC12 cells and cell viability assays were used to determine the optimum concentration range of AVLE and its protective effects against oxidative stress. A live-dead assay was performed to confirm the effects of AVLE on oxidative stress. Subsequently, expression of apoptotic proteins including Bax and cleaved-caspase-3 were evaluated to determine whether AVLE affected apoptosis, and reactive oxygen species (ROS) levels were detected to determine the role of AVLE in H2O2 exposure. Furthermore, expression of autophagic proteins including LC3-II and p62 were detected to evaluate the effects of AVLE on autophagic activity, and cells were treated with 3-methyladenine (3-MA), an autophagic inhibitor, to identify the underlying protective mechanism of AVLE. The results showed that the optimum conditions to induce oxidative stress were treatment with 40 µM H2O2 for 2 h, and the suitable range of AVLE concentrations was shown to be 1-100 µg/ml. AVLE improved cell viability in PC12 cells following treatment with H2O2. AVLE reduced the expression of Bax and cleaved-caspase-3, and decreased ROS production. Furthermore, AVLE upregulated LC3-II expression and downregulated p62 expression, whereas treatment with 3-MA increased the levels of ROS and apoptotic proteins. These results suggest that AVLE may protect injured neurons against oxidative stress-induced apoptosis, and this effect may be associated with the reduction of ROS by increasing autophagy.

Mitochondrial Dysfunction, Oxidative Stress, and Neuroinflammation: Intertwined Roads to Neurodegeneration

Oxidative stress develops as a response to injury and reflects a breach in the cell’s antioxidant capacity. Therefore, the fine-tuning of reactive oxygen species (ROS) generation is crucial for preserving cell’s homeostasis. Mitochondria are a major source and an immediate target of ROS. Under different stimuli, including oxidative stress and impaired quality control, mitochondrial constituents (e.g., mitochondrial DNA, mtDNA) are displaced toward intra- or extracellular compartments. However, the mechanisms responsible for mtDNA unloading remain largely unclear. While shuttling freely within the cell, mtDNA can be delivered into the extracellular compartment via either extrusion of entire nucleoids or the generation and release of extracellular vesicles. Once discarded, mtDNA may act as a damage-associated molecular pattern (DAMP) and trigger an innate immune inflammatory response by binding to danger-signal receptors. Neuroinflammation is associated with a large array of neurological disorders for which mitochondrial DAMPs could represent a common thread supporting disease progression. The exploration of non-canonical pathways involved in mitochondrial quality control and neurodegeneration may unveil novel targets for the development of therapeutic agents. Here, we discuss these processes in the setting of two common neurodegenerative diseases (Alzheimer’s and Parkinson’s disease) and Down syndrome, the most frequent progeroid syndrome.

Generation and Release of Mitochondrial-Derived Vesicles in Health, Aging and Disease

Mitochondria are intracellular organelles involved in a myriad of activities. To safeguard their vital functions, mitochondrial quality control (MQC) systems are in place to support organelle plasticity as well as physical and functional connections with other cellular compartments. In particular, mitochondrial interactions with the endosomal compartment support the shuttle of ions and metabolites across organelles, while those with lysosomes ensure the recycling of obsolete materials. The extrusion of mitochondrial components via the generation and release of mitochondrial-derived vesicles (MDVs) has recently been described. MDV trafficking is now included among MQC pathways, possibly operating via mitochondrial-lysosomal contacts. Since mitochondrial dysfunction is acknowledged as a hallmark of aging and a major pathogenic factor of multiple age-associated conditions, the analysis of MDVs and, more generally, of extracellular vesicles (EVs) is recognized as a valuable research tool. The dissection of EV trafficking may help unravel new pathophysiological pathways of aging and diseases as well as novel biomarkers to be used in research and clinical settings. Here, we discuss (1) MQC pathways with a focus on mitophagy and MDV generation; (2) changes of MQC pathways during aging and their contribution to inflamm-aging and progeroid conditions; and (3) the relevance of MQC failure to several disorders, including neurodegenerative conditions (i.e., Parkinson's disease, Alzheimer's disease) and cardiovascular disease.

Inter-Organelle Membrane Contact Sites and Mitochondrial Quality Control during Aging: A Geroscience View

Mitochondrial dysfunction and failing mitochondrial quality control (MQC) are major determinants of aging. Far from being standalone organelles, mitochondria are intricately related with cellular other compartments, including lysosomes. The intimate relationship between mitochondria and lysosomes is reflected by the fact that lysosomal degradation of dysfunctional mitochondria is the final step of mitophagy. Inter-organelle membrane contact sites also allow bidirectional communication between mitochondria and lysosomes as part of nondegradative pathways. This interaction establishes a functional unit that regulates metabolic signaling, mitochondrial dynamics, and, hence, MQC. Contacts of mitochondria with the endoplasmic reticulum (ER) have also been described. ER-mitochondrial interactions are relevant to Ca²⁺ homeostasis, transfer of phospholipid precursors to mitochondria, and integration of apoptotic signaling. Many proteins involved in mitochondrial contact sites with other organelles also participate to degradative MQC pathways. Hence, a comprehensive assessment of mitochondrial dysfunction during aging requires a thorough evaluation of degradative and nondegradative inter-organelle pathways. Here, we present a geroscience overview on (1) degradative MQC pathways, (2) nondegradative processes involving inter-organelle tethering, (3) age-related changes in inter-organelle degradative and nondegradative pathways, and (4) relevance of MQC failure to inflammaging and age-related conditions, with a focus on Parkinson’s disease as a prototypical geroscience condition.

Mitochondrial Signatures in Circulating Extracellular Vesicles of Older Adults with Parkinson's Disease: Results from the EXosomes in PArkiNson's Disease (EXPAND) Study

Systemic inflammation and mitochondrial dysfunction are involved in neurodegeneration in Parkinson’s disease (PD). Extracellular vesicle (EV) trafficking may link inflammation and mitochondrial dysfunction. In the present study, circulating small EVs (sEVs) from 16 older adults with PD and 12 non-PD controls were purified and characterized. A panel of serum inflammatory biomolecules was measured by multiplex immunoassay. Protein levels of three tetraspanins (CD9, CD63, and CD81) and selected mitochondrial markers (adenosine triphosphate 5A (ATP5A), mitochondrial cytochrome C oxidase subunit I (MTCOI), nicotinamide adenine dinucleotide reduced form (NADH):ubiquinone oxidoreductase subunit B8 (NDUFB8), NADH:ubiquinone oxidoreductase subunit S3 (NDUFS3), succinate dehydrogenase complex iron sulfur subunit B (SDHB), and ubiquinol-cytochrome C reductase core protein 2 (UQCRC2)) were quantified in purified sEVs by immunoblotting. Relative to controls, PD participants showed a greater amount of circulating sEVs. Levels of CD9 and CD63 were lower in the sEV fraction of PD participants, whereas those of CD81 were similar between groups. Lower levels of ATP5A, NDUFS3, and SDHB were detected in sEVs from PD participants. No signal was retrieved for UQCRC2, MTCOI, or NDUFB8 in either participant group. To identify a molecular signature in circulating sEVs in relationship to systemic inflammation, a low level-fused (multi-platform) partial least squares discriminant analysis was applied. The model correctly classified 94.2% ± 6.1% PD participants and 66.7% ± 5.4% controls, and identified seven biomolecules as relevant (CD9, NDUFS3, C-reactive protein, fibroblast growth factor 21, interleukin 9, macrophage inflammatory protein 1β, and tumor necrosis factor alpha). In conclusion, a mitochondrial signature was identified in circulating sEVs from older adults with PD, in association with a specific inflammatory profile. In-depth characterization of sEV trafficking may allow identifying new biomarkers for PD and possible targets for personalized interventions.

Cellular Stress-Modulating Drugs Can Potentially Be Identified by in Silico Screening with Connectivity Map (CMap)

Accompanied by increased life span, aging-associated diseases, such as metabolic diseases and cancers, have become serious health threats. Recent studies have documented that aging-associated diseases are caused by prolonged cellular stresses such as endoplasmic reticulum (ER) stress, mitochondrial stress, and oxidative stress. Thus, ameliorating cellular stresses could be an effective approach to treat aging-associated diseases and, more importantly, to prevent such diseases from happening. However, cellular stresses and their molecular responses within the cell are typically mediated by a variety of factors encompassing different signaling pathways. Therefore, a target-based drug discovery method currently being used widely (reverse pharmacology) may not be adequate to uncover novel drugs targeting cellular stresses and related diseases. The connectivity map (CMap) is an online pharmacogenomic database cataloging gene expression data from cultured cells treated individually with various chemicals, including a variety of phytochemicals. Moreover, by querying through CMap, researchers may screen registered chemicals in silico and obtain the likelihood of drugs showing a similar gene expression profile with desired and chemopreventive conditions. Thus, CMap is an effective genome-based tool to discover novel chemopreventive drugs.